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How to Choose an Amplifier.

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URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=75836
Printed Date: February 27, 2021 at 10:34 AM


Topic: How to Choose an Amplifier.

Posted By: haemphyst
Subject: How to Choose an Amplifier.
Date Posted: April 07, 2006 at 11:16 AM

I have seen several (ok, MANY) posts here lately, asking about how to choose an amplifier, with all sorts of "Is this good...?" types of questions.

Here is what I look at when choosing an amplifier, and in their order of preference:

1. Power. I know, this is where MOST people look first, but it's the very reason you are buying an amp, right? Also knowing Ohm's Law, and knowing that I will almost always load an amplifier with the maximum specified impedance (impedance - 4 ohms or higher, NOT load - 4 ohms or lower), I need to know exactly how much power I am looking at to start with. When loading an amp with a higher impedance, the amp will make less power, so I have to keep this spec in mind the whole time. My speakers are almost always chosen before I decide to start looking for an amplifier, I know the impedance and efficiency numbers when I start. This will help me decide how much power I need or want for that particular driver compliment. I will NEVER look at "Max Ratings". They are often worthless, generally overinflated, selling tools, designed by old-school, low-end amplifier companies, originally made to sell product. (You remember how it went (and still goes today)... This 800 watt amplifier is only 200 dollars, but the Nakamichi 160 watt monoblock is 1300 bux for the pair. Which were (are) YOU going to buy?) Ahhhh, the power of advertising... Classic Nakamichi, Alpine, Linear Power, Orion, Eclipse, etc., THEY never posted "Maximum Power" numbers, did they? Unfortunately, even the good products of today will state maximum power output, I just disregard the numbers posted.

2. Signal to noise ratio. This one I place a bit more weight on, especially when the amplifier is going to be used in a mid-bass (important), mid-range (more important) or highs (MOST important) application. The higher the better, and there is no exception to this rule for me. Amps with tube stages are typically less capable than their solid state stablemates in this area, but I do make exceptions for tube amps. It is NOT a terribly important spec for a bass amp, so when shopping for a bass amp, don't bother with this number. Dedicated bass amps, BTW, usually offer awful SNR numbers.

3. Efficiency. Here's where you will be able to tell a decent manufacturer from the crap. Let's say you are looking at an 250 watt (RMS) amplifier. The first physical thing I look at, is how big a fuse do they recommend (or what size fuse is in the end of the amp)? I know right now that 250 watts OUT will demand (and I use 50% efficiency to keep it simple) 500 watts in. 500 watts in, divided by the (car running) battery voltage (14.4v) is about 35A. If I look at the end of the amp, and see a 20A fuse, I'm walking away, as there is no way that amp can make 250 REAL watts, continuously. 14.4v times 20A, equals 280 watts in. 250 watts out, divided by 280 watts in, translates to an 89% efficiency. In a class A/B amp, this is an impossible number, and it even stretches the imagination for digital amps, as well. The theoretical MAXIMUM efficiency for class A/B is 66%, (95% for digital) so someone is lying. I don't care WHO the manufacturer is, if these numbers don't add up, I will start looking elsewhere... Now, if all the other specification look good, AND I can get in the vicinity of the RMS power I am looking for, I will buy an amp that's efficiency number might be stretching the truth a bit. My old Nak 160 watt monoblocks had 40A (that's 480 watts in - a 33% efficiency, people!) fuses in each one, and they ran hotter than a firecracker, even loaded at over 8 ohms. I liked that. posted_image

4. Terminals. A frequently overlooked part of an amp, this is a very important part of an amp to me. A car is a place frought with vibrations. A cheap or cheezy feeling connector in power or speaker terminals and most ESPECIALLY in the RCA inputs, will often cause problems in the future. Setscrews for power, quality terminal blocks for speaker outputs, and Tiffany style RCA connections (the type attached to the chassis, rather than a block of plastic soldered to the PC board.) The quality of the I/Os can be a direct indicator of the attention to detail paid to the rest of the piece. Translation? Overall Quality.

5. Heat sink. This one is simple. How does it look? I eventually chose Eclipse gear, because it looked like jewelry. Fine finish and appearance. Also, heatsink size and quality can be another indicator of quality of the amplifier as whole. A heavy heatsink will also provide better thermal stability, a nice thing in an amp.

6. Damping Factor. I used to place more emphasis on this spec, but my research recently (over the last few years, really) has, while not proven to me it is a useless spec, has not proven to me it is an extremely important spec. This is why this particular spec is a little further down the list. While I place a bit more emphasis on it for a bass or mid-bass amp, I, admittedly, place less weight here than I used to...

7. Price. Money rarely means much to me in an amp, (much like my computers - "Life's too short to build slow computers." - David Draper) it's something I am going to be keeping for a long time usually, so I will save if necessary to get EXACTLY (or close to) what I am looking for.

These are the things I look for when trying to decide on an amp. OBVIOUSLY, there are going to be VERY few amps on the market that will make me happy across the board, but then some of the physical characteristics listed above can be made to fit me and my desires with a little time, a couple extra bux, and some careful use of a soldering iron. All of the above things will cost more, but it will ADD more to the finished product as well... posted_image

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."



Replies:

Posted By: jcollin
Date Posted: April 07, 2006 at 2:28 PM
Some of this stuff is a little over my head, I have one Kicker Comp VR sub, 10 in, with 2 ohm dual voice coils, im wiring it in series so it will have a 4 ohm load, what would be a good type of amp for me to run, Mono or 2 channel???




Posted By: haemphyst
Date Posted: April 07, 2006 at 3:30 PM
Any stereo amp stable to 2 ohms per channel will work in this configuration. A stero amp wired one voice coil per channel, or, a stero amp bridged, to the two coils wired in series (as you have stated) will still be "seeing" two ohms per channel. You could also (and while I wouldn't do it...) buy a mono amp capable of running a one ohm load, and wire the two voice coils in parallel. Several options here.

Use my suggestions from above, and look around for an amplifier that will suit your needs:

1) a stereo amp stable to 2 ohms per channel

or

2) a mono amp stable to 1 ohm per channel

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: jcollin
Date Posted: April 07, 2006 at 3:47 PM
That was exactly the reply I was hoping to get, thanks for your time.




Posted By: stevdart
Date Posted: April 07, 2006 at 7:50 PM

haemphyst, valuable info there.  I have a couple of questions.

What's your opinion of this scenario, regarding #3 Efficiency:  I have a USacoustics 4 channel amplifier that I bought last year as a discontinued model through one of the online houses.  It's a USC4065 rated at 4 X 65 watts.  The brand is "engineered in the USA" and the manufacturing was outsourced to China.  The amp came with a nicely presented, well-written manual that specified 2 X 20 amp fuses.

(On the contrary, the manual that came with the USacoustics mono amp that I got the year before was very poorly written / presented...and the build was in Taiwan.  But both amps perform extremely well.)

Using the guidelines you wrote of with an estimation of 50% efficiency, the fuses as described in the manual are right on.  2 X 65 watts out = 130 X 2 (50% efficiency) = 260 watts in;  260 / 14.4 volts = 18 amps.)  

However, the amplifier arrived with two 30 amp fuses installed!  Not getting anywhere by trying to email them for the proper fuse value to use, I just left the 30's in there and chalked it up as "too many cooks spoil the broth" with all the outsourcing to this location and that one to finally arrive with a finished product.  My guess was that the workers in the Chinese assembly plant decided to borrow fuses meant for a higher line of amp when they ran out of 20's for this one.

We all know how the industry has turned in the last few years with the outsourcing issue, and my guess is that this type of thing is more commonplace than we might care to think.  Can we actually look at the fuse value on a new amp nowadays and use that as criteria for acceptance?  Have you seen anything of the like with borrowed or rearranged parts?

And the second thing I want to ask:  you said "I liked that" re: the "hotter than a firecracker" Nak...does the heat value on the outside of the amp relate to the heat transfer through the case, and so you like that because the heat sink was working well?  Or was it because the efficiency was low and therefore more apt to be a better amplifier?  ...Or neither?



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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: haemphyst
Date Posted: April 08, 2006 at 12:25 AM
stevdart wrote:

haemphyst, valuable info there. I have a couple of questions.

What's your opinion of this scenario, regarding #3 Efficiency: I have a USacoustics 4 channel amplifier that I bought last year as a discontinued model through one of the online houses. It's a USC4065 rated at 4 X 65 watts. The brand is "engineered in the USA" and the manufacturing was outsourced to China. The amp came with a nicely presented, well-written manual that specified 2 X 20 amp fuses.

(On the contrary, the manual that came with the USacoustics mono amp that I got the year before was very poorly written / presented...and the build was in Taiwan. But both amps perform extremely well.)

Using the guidelines you wrote of with an estimation of 50% efficiency, the fuses as described in the manual are right on. 2 X 65 watts out = 130 X 2 (50% efficiency) = 260 watts in; 260 / 14.4 volts = 18 amps.)

However, the amplifier arrived with two 30 amp fuses installed! Not getting anywhere by trying to email them for the proper fuse value to use, I just left the 30's in there and chalked it up as "too many cooks spoil the broth" with all the outsourcing to this location and that one to finally arrive with a finished product. My guess was that the workers in the Chinese assembly plant decided to borrow fuses meant for a higher line of amp when they ran out of 20's for this one.



If I had seen something like that issue, I would have likely jumped to the same conclusion. (Sadly, "Made In USA" means little, if anything anymore...) If not the borrowed fuse from the wrong amp, I might have even gone to something as simple as a typo in the manual. 20 and 30 are pretty close to one another on the keyboard, so that also is a possibility. How many times have we been reading a manual or something of that ilk, and wondered if this is what is REALLY trying to be said, or is this a literal translation. I don't know any Chinese or Japanese or Korean numbers or glyphs, and if the manual was actually presented in one of those languages to distribution channels, a simple language barrier could explain this issue.

4ch X 65w X 2 = 520W in.
14.4v X 40A = 576W in. (reasonable, and would fit MY critera well...)
12.6v X 60A = 756W in. (This would also be a reasonable safety margin, IF the power supply were regulated i.e. it maintained the SAME output power, regardless of the input voltage. Lower input voltage would demand more current.) Two 25A fuses would have been a better choice, but 30's were possibly more available? or less expensive?

stevdart wrote:

We all know how the industry has turned in the last few years with the outsourcing issue, and my guess is that this type of thing is more commonplace than we might care to think. Can we actually look at the fuse value on a new amp nowadays and use that as criteria for acceptance? Have you seen anything of the like with borrowed or rearranged parts?



I suppose it IS possible, but I think that the US Government powers that be try to make certain that electronics sold here are safe... An (intentional or otherwise) overfuse situation would cerainly not meet the definition of "safe".

stevdart wrote:

And the second thing I want to ask: you said "I liked that" re: the "hotter than a firecracker" Nak...does the heat value on the outside of the amp relate to the heat transfer through the case, and so you like that because the heat sink was working well? Or was it because the efficiency was low and therefore more apt to be a better amplifier? ...Or neither?



I was afraid somebody would call me on that statement. posted_image Neither. And both. The mass of the heatsink on those amps was (sorry...) massive. Their thermal stability was astounding. The fins were probably smaller than they SHOULD have been, for effective transfer of energy to the atmosphere, and they stayed hot for a long time. The latent heat and the time it lasted, was to me, an indicator of the quality of the heatsink. The sheer amount of heat GENERATED, was to me, an indicator of the very Class "A" biasing... this was just for me, and nobody else ever wondered about the biasing, but they were ready to complain about the heat... Class "A" is a very inefficient amplifier class, and these amps were simply examples of such. As good as my present system sounds, it pales compared to that setup... (I should see if that guy wants to sell 'em back to me...)

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: Velocity Motors
Date Posted: April 09, 2006 at 9:27 AM
Very well written haemphyst, you've got my vote.

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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA




Posted By: beehasmytshirt
Date Posted: April 14, 2006 at 12:20 AM

good info





Posted By: j0ne
Date Posted: April 14, 2006 at 2:23 AM

Very good info, its odd, i see alot of crappy amps being sold for way too much, nothing new, however, Profile seems to make good quality stuff for as cheap as it gets. I run the CL800 for my sub. $100.01 shipped. Signal / Noise Ratio- >105db      Total Harmonic Distortion->0.05% Bridged RMS at 4 ohms- 600 watts    and 2 30 amp Fuses.     Any one see anything really wrong with theese amps? I am really impressed with them, and am about to recomend them in my next amature install.





Posted By: russ lund
Date Posted: April 15, 2006 at 2:04 PM

Nice article,not biased towards any specific company,just personal experience.Good Job!!! Russ



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BigDog




Posted By: weedfan
Date Posted: April 16, 2006 at 1:08 AM
so if i got a 4 channel 2000watt amp  and i had 2 800 watt subs , would that work? can i use more subs?




Posted By: haemphyst
Date Posted: April 16, 2006 at 4:04 AM
j0ne] wrote:

Very good info, its odd, i see alot of crappy amps being sold for way too much, nothing new, however, Profile seems to make good quality stuff for as cheap as it gets. I run the CL800 for my sub. $100.01 shipped. Signal / Noise Ratio- >105db      Total Harmonic Distortion->0.05% Bridged RMS at 4 ohms- 600 watts    and 2 30 amp Fuses.     Any one see anything really wrong with theese amps? I am really impressed with them, and am about to recomend them in my next amature install.



No, I have seen decent results using Profile amps as well. Their efficiency is a bit optimistic on that amp. I get 69.4% efficiency. I would say a little bit of derating is in order, say closer to 500 to 520 watts on an RMS basis.

weedfan wrote:

so if i got a 4 channel 2000watt amp and i had 2 800 watt subs , would that work? can i use more subs?

It would really depend on the hardware... What amp? What woofers? Sealed, vented, bandpass, TL? We'll need TONS more info than that.

Generally speaking though, you can run ANY amplifier on ANY (number of) woofer(s), so long as power handling is not exceeded (read: PROPER level matchings), and the amp is not overloaded.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: weedfan
Date Posted: April 16, 2006 at 5:01 AM
uhh... let me see . pyle driver 4 channel ,2000watt plad413 amp,  two 10" 800watt pioneer ts-w256c subs. sealed i guess..thats all i know right now . im knew 2 all this stuff.




Posted By: duoproductionx
Date Posted: April 24, 2006 at 10:46 PM
always remember the peak power means nothing i went to a large sale advertising "1000w amplifiers for 100 bucks!"
they were pyramid giant ass looking things, no RMS or any actual specs arround the thing, had to get a guy to open the box to find out that this "1000w amp" was pushing 20w RMS on 2 channels, funny consittering my 'lesser amp' from walmart to push my 5.25s and 6x9s is a 4 channel amp with 50rms on EACH channel. so remember children, RMS, love peak power!

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97 Monte Carlo
CDA-9885, PZI Crunch 5 channel,12in MB Quart Premium.




Posted By: weedfan
Date Posted: April 26, 2006 at 6:47 AM
so u sayin that amp aint 2000watts?




Posted By: Master Asylum
Date Posted: April 28, 2006 at 12:44 PM

Hae, you know I love you... Wow, its been many months and I come back to see this wickedly nice read. Thanks for making time at work actually informative! Anyways... Very wonderful read and you certainly deserve the certification thing under your name(cool as heck idea).

And he was saying simply that your amp may not be capable of its listed power. Just try and find a RMS rating number for it. If there isn't one of those available than one of the guys can explain a better way to try and figure it out. I just wouldn't rely on it, my personal opinion though.



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1998 Monte Carlo w/
Eclipse CD8454
2xRockford 5.25" Power 2-way T152C
2xRockford 6"x9" Punch 3-way FRC4369
1xMemphis 16-MCH1300 5-channel
2xKicker 12" L5 Solobaric-2 Ohm




Posted By: DYohn
Date Posted: April 28, 2006 at 1:01 PM

weedfan wrote:

so u sayin that amp aint 2000watts?

Yes, that's exactly what he's saying.  What kind of fuses are in that amp?

Master Asylum wrote:

Hae, you know I love you... Wow, its been many months and I come back to see this wickedly nice read

Welcome back!



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Support the12volt.com




Posted By: weedfan
Date Posted: April 28, 2006 at 10:52 PM
dont know ... it dont say.




Posted By: DYohn
Date Posted: April 29, 2006 at 12:36 AM
FYI, the rating on the Pyle PLAD413 is 200 watts X 4 channels @ 4-ohms.  It appears to have 2 20-amp fuses, so the actual usable capability is probably more like to 50 watts per channel.  There is no way in the world that amp can produce 2000 watts, period.

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Support the12volt.com




Posted By: weedfan
Date Posted: April 29, 2006 at 3:48 AM
dam. that sux. thats what i wanted to get for sure. so what would u suggest i should get to power 2 10" subs pioneer ts-w256c 800watts?




Posted By: weedfan
Date Posted: April 29, 2006 at 1:42 PM

i guess thats y its cheap.... $100.00





Posted By: hang time mazda
Date Posted: May 03, 2006 at 11:16 PM

i just read the info posted and it was very interesting. i have been out of car audio for many years and i am getting ready to do an install in one of my trucks. i just bought 4 pioneer ts-1041d's and was wondering if the amp i have would work and how well and how i should wire the subs to it. the amp i have is an old orion concept 97 3 special edition.

any help would be great, thanks





Posted By: blk04civiclx
Date Posted: May 05, 2006 at 4:00 PM
Hello guys, this was an interesting read. But I still am unclear on how to do the calculations..  posted_image  Lets see, I have a Kenwood 9152d amp which is equipped with 2X30amp fuses and it is said to put out 500rms@4ohms and 900rms@2ohms&1ohm.  Is this possible?  Or are they just overrating the amp..  It does push my cvr12's at a 4ohm load pretty well.. but i want it louder..

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M.




Posted By: et3rnal
Date Posted: May 07, 2006 at 6:21 PM

hey i just learned alot from reading this lol.. so im just goin to ask.... I just recently bought 2 audiobahn 1206t flame Q's.. and i need an amp around $200 that will put  ( what u think will be ) more then enough power to make these sound good. i was thinkin about goin with a cheap high wattage amp.. but then relized i was a nub and should be lookin at other things then just straight power.. so can someone help me find an amp for a good price that has good quality and power for these subs?





Posted By: pyro_527
Date Posted: May 07, 2006 at 11:52 PM
I read through all 3 pages of this thread and I have a question.  Why would you run an amp at 8 ohms or greater impedence when you can get so much more out of it running at 4,2 or 1 ohm (provided amp is capable of running 1 ohm stable).  Higher impedence = less power out...

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Dopeler effect: The tendency of stupid ideas to seem smarter when they come to you quicker....




Posted By: gamfreak
Date Posted: May 08, 2006 at 3:29 AM
Ok i new here wat is the bes t signal to noise ratio for a mid range ,mid bass , high frequency amplifier



O and Just to let you guys know Awesome job on the site you guys are the best posted_image




Posted By: haemphyst
Date Posted: May 13, 2006 at 7:38 PM
pyro_527 wrote:



I read through all 3 pages of this thread and I have a question.  Why would you run an amp at 8 ohms or greater impedence when you can get so much more out of it running at 4,2 or 1 ohm (provided amp is capable of running 1 ohm stable).  Higher impedence = less power out...

Distortion is lower, efficiency is higher, damping is higher, less heat... All good things in life.

Why would anyone insist on running an amplifier at it's rated load or even above?

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: epcenter5hz
Date Posted: May 21, 2006 at 11:25 PM
This question is mainly to “Haemphyst”

Ignore this post if this sound like a rhetorical question… just wanted to know your options on this amp. I have a Hifonics Gen XI colossus & the maximum rms rangs is about 3,000 watts 2ohms mono or 1500x2 @ 1 ohm stereo. How credible do u this amp is since it’s a maxxsonics version… I got a chance to get an reply from “Stephen Mantz” himself… & he more or less said that it’s not as good as the Gen XIII or lower colossus
. specs state it will draw about 420 amps @ 3000watts rms???




Posted By: DYohn
Date Posted: May 22, 2006 at 10:57 AM

gamfreak wrote:

Ok i new here wat is the bes t signal to noise ratio for a mid range ,mid bass , high frequency amplifier

The higher the better.  The best I've seen is 114db S/N.



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Support the12volt.com




Posted By: haemphyst
Date Posted: May 22, 2006 at 11:40 AM
IMO, the HiFonics stuff was only ever medium range gear, and always overrated a bit, and I would agree, that their "ratings" have become a bit more... "optimistic"... as the company aged and re-organized. The fuses say yes, but I'd still be a bit wary of that spec...

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: bmann_420
Date Posted: May 22, 2006 at 4:06 PM
Great Thread Guys   :D  Had to let you know, so many people dont know the difference between max and RMS.... whatsoever  posted_image




Posted By: bmann_420
Date Posted: May 22, 2006 at 4:08 PM
Cant edit your posts?  Blah,  I was gonna say the funner question is, do they know what RMS means?  I know what it means, but not why or the definition of the meaning.




Posted By: weedfan
Date Posted: May 22, 2006 at 7:52 PM
huh?




Posted By: epcenter5hz
Date Posted: May 23, 2006 at 3:55 AM
To find AVERAGE power you multiply peak voltage times .707. That gives RMS
voltage. Then multiply peak current by .707. That gives RMS current. Now RMS
voltage times RMS current gives AVERAGE power.
NOTE that .707 times .707 = .499 or rounded to .5. So AVERAGE power is 1/2 of
peak power




Posted By: russ lund
Date Posted: May 23, 2006 at 4:35 PM
I still have a Gen XI Colossus in our display.I keep it to show up those guys that come in with that cheap junk they bought somewhere else.That amp is 600 watts RMS per channel into a 4 ohm load.It has 1800 watts bridged into a 4 ohm load and 2400 watts into 2 ohm load.That is a rock solid unit,I had a series 7 that I had to have repaired twice.I sold 2 series 8 w/o any problem.We also sold 2 XI's w/o incident.We had taken ours and bridged it down to 1 ohm(Don't do it except for 30 sec bursts) it drew between 220 and 230 amps.Use that amp you'll love it.Just feed it plenty of power and a damn good ground !!!!!!!!!!!!!!!   Russ

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BigDog




Posted By: bmann_420
Date Posted: May 23, 2006 at 7:29 PM

epcenter5hz wrote:

To find AVERAGE power you multiply peak voltage times .707. That gives RMS
voltage. Then multiply peak current by .707. That gives RMS current. Now RMS
voltage times RMS current gives AVERAGE power.
NOTE that .707 times .707 = .499 or rounded to .5. So AVERAGE power is 1/2 of
peak power

Thanks bud, always good to know that one.  Just gatta remember it thats all.





Posted By: epcenter5hz
Date Posted: May 24, 2006 at 5:56 AM
russ lund wrote:

I still have a Gen XI Colossus in our display.I keep it to show up those guys that come in with that cheap junk they bought somewhere else.That amp is 600 watts RMS per channel into a 4 ohm load.It has 1800 watts bridged into a 4 ohm load and 2400 watts into 2 ohm load.That is a rock solid unit,I had a series 7 that I had to have repaired twice.I sold 2 series 8 w/o any problem.We also sold 2 XI's w/o incident.We had taken ours and bridged it down to 1 ohm(Don't do it except for 30 sec bursts) it drew between 220 and 230 amps.Use that amp you'll love it.Just feed it plenty of power and a damn good ground !!!!!!!!!!!!!!!   Russ


Thanks for the input… I’m from the old school too (been into car audio since 1989 & got completely involved in 1993). It’s hard to find any documented credible specs on the XI colossus’s… but I tell you what… I’ve seen one of these old school colossus in actions in 1996… a guy had 2 very long colossus in a mini van (I’m not sure what series it was) but he had it on 4 18” original “Hart” subs on an epicenter… & it sounded almost as loud as a train wreck coming down your block… this dude was sick because he hade a DB drag power levels & SPL as his daily driver with 2 colossus, but was tuned better for listening & not competing…




Posted By: perkster
Date Posted: May 27, 2006 at 12:16 PM
soooo if i have an 2 channel amp with an RMS of 200W x 2 and bridge it, how much juice should i be able to get out of it?




Posted By: bmann_420
Date Posted: May 27, 2006 at 1:33 PM
The RMS Rating.  If you did one channel, you would get 100 watts rms if the ohm load is right also.  And if you bridge it, you will get the true 200 watts.  If it is to 2 speakerrs it will be 100 each if its wired right, or 200 to one.




Posted By: perkster
Date Posted: May 27, 2006 at 1:57 PM
thank you, i never understood bridging really

i've got two 12" DVC subs at 600 watt rms and 4 ohms
if i buy a 4 ohm mono amp to run both of them, how many watts do i need? is it 1200 or 600




Posted By: bmann_420
Date Posted: May 28, 2006 at 4:17 PM
If you got 2 DVC's that are 4 ohms, you want a 2 channel 1000 watt amp, or an amp like Say JL that can run at 1 ohm.  Cause thte way you wire up your subs is going to be either a 4 ohm load or a 1ohm load.  So a 2 channel will bridge it, or a 1 ohm stable amp will just work regular.  But if you have 2 600 watt subs, you need a min of 1000 amps. (its is good to have 1200 also, but 1000 will d, especially if its actually more, like with Rockford Fosgate's "Birth Certificates".  They are always rated lower than what you get.   You almost need aut gage cable (0 gauge) and a cap and a seperate battery.  An upgraaded alternator would help also, so you dont wind up on the side of the road with a burnt out alternator.




Posted By: adrian12
Date Posted: July 07, 2006 at 3:21 AM
good1

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you can learn something new everyday




Posted By: dakkh
Date Posted: July 10, 2006 at 11:20 PM
I got a Alpine Type R 10" woofer in a sealed box. I run it with a Pioneer GMT-510 Amp, the model number may be not right as its different in walmart in canada. Anyways, it moves this dam speaker pretty good. Sometimes it cuts out when i got the bass turned high, but then i just turn it down. So far so good. BTW it has a whoppin 760 watts printed on the outside of it, its got two 20 amp fuse in it, total of 40 amps there. Its putting approximately 380 watts to my sub if i am running 14 + volts which is pretty good but may not be true watts, that type r in case you dont know is rated for up to 500 watts, so the amp is less than the speaker but it still holds its own. CIAO DUDE

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DKH




Posted By: Tnilli
Date Posted: July 17, 2006 at 6:53 PM
Ok i didnt want to start a new thread cause i figure someone in here can help. My friend just bought a KAPPA PERFECT10DVQ
10" Die-cast subwoofer

And i'm tryign to help him find an amp to run it. I really am still confused between all the 2 ohm and 4 ohm stuff. He listens to rock music, (korn, slipknot, metallica, etc.) and i cant figure out what amp he'll need for that sub. Its specs are...

Specifications
Power Handling, RMS:400 Watts
Power Handling, Peak:1600 Watts
Sensitivity: 90dB
Frequency Response (±3dB): 25Hz - 400Hz
Mounting Depth: 6-1/2"
Impedance: 2 or 8 Ohms depending on wiring

So i found 3 amps that i think might work...but i dont know depending on 2 ohms or 4 ohms. InfinityREF611A, Alpine MRP-M650, and Alpine MRP-M450. It's not for sound competitions or anything to that nature, and its only 1 10''. Its just for that tight bass needed in rock music. Thanks for your help!




Posted By: anmclark23
Date Posted: July 25, 2006 at 6:14 PM

I think you should always consider budget first in this situation. This is definitely a category worth putting money into. A high quality amplifier will definitely make a statement when combined with a reasonable set of speakers. However, the longevity of the system must be considered in most cases where budget is an issue.

Otherwise, we're talking amplifiers. This means that a variety of other considerations for your scenario must be made.





Posted By: cva me
Date Posted: September 08, 2006 at 2:22 PM
haemphyst,

Thank you for your post it had a lot of valuable info. Unfortunatly im one of those "old school's" trying to get back into it. There have been many changes since my time. I learned alot from your article but still have a question. I have two 4ohm 8" fosgate p2 subs 2oowatts rms each, with a fosgate punch p325.2 amp @ 325watts rms bridged at 4ohms. I am not looking to win any competitions or anything, sound is good. Is my amp too small at this wattage for these subs?
Thank you




Posted By: haemphyst
Date Posted: September 10, 2006 at 11:55 AM
Well, since with (2) 4 ohm woofers, there is no way for you to get 4 ohms, you may be a bit "underpowered"... You can run 4 ohms per channel, or bridged into 8 ohms (which, as far as the amp is concerned, is the same as 4 ohms per channel). If you're worried about giving them all they are rated for, then you have two options: You can get a larger stereo amp (200-250 watts per channel at 4 ohms), to run in stereo mode at 4 ohms, or a 400-500 watt monoblock, stable at 2 ohms... Either of these are viable options for you, but that 325 bridged at 4 ohms will give you less than 100 watts per woofer, either bridged into 8 ohms, or stereo at 4 ohms.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: cva me
Date Posted: September 10, 2006 at 10:34 PM
haemphyst,

Wow things have changed since the 80's. I had a punch45 with two punch 10's, bridge the amp and it would flip a cassette tape on the roof, back in the day. Now its so confusing. So you recommend me gettin a bigger amp? (Im partial to fosgate so ill stick to them) I'll need at least 400 to 500 watts to get what im looking for right? I have 30 days to return my p325.2 amp to upgrade, would a mono amp be more advisable. Let me ask you this then...as a rule of thumb i need to get an amp at least the same rms wattage of all my subs added together? I am considering upgrading to two 10's with rms of 200rms each also, so get nothing less than a 400 watt amp right? What ohm subs is advisable then?
Thanks




Posted By: haemphyst
Date Posted: September 10, 2006 at 10:56 PM
I'd recommend a mono amp, around 400 to 500 watts. If you can return that amp, do so... It's not gonna be big enough.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: cva me
Date Posted: September 11, 2006 at 9:17 AM
Does it matter what ohm subs i get then when i do get 10's? Is 4 or 8 better than the other?
Thanks




Posted By: haemphyst
Date Posted: September 11, 2006 at 9:35 AM
Yes. There is no "better", necessarily.

OK, so you already HAVE the woofers, right? There are two, 4 ohm drivers. Keep those, exchange just the amp. Parallel them, (or most mono amps have two sets of terminals, run one woofer to each set) and you'll be done. This will present a 2 ohm load to the amplifier, perfectly safe.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: cva me
Date Posted: September 11, 2006 at 3:04 PM
I currently have 4ohm 8", gonna upgrade to 10" in the near future, now Amp is going to be a 5oowatt mono...Question was does it really matter what ohm sub to buy, or is it all preference. Im sorry for any confusion i've caused.
Thank you for all your advice you've helped me tremendously.




Posted By: haemphyst
Date Posted: September 11, 2006 at 3:42 PM
Yes, the impedance DOES matter... this is what you have to know to make certain you load the amp correctly, without overloading it. See the home page on the12volt.com, and there is a subwoofer wiring configurator.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: cva me
Date Posted: September 11, 2006 at 5:13 PM
Copy, thanks again. Sorry im so remedial on this topic. Do amps work at a varity of ohms or ohm specific like the subs?




Posted By: haemphyst
Date Posted: September 11, 2006 at 11:28 PM
Every amplifier will have a minimum safe operating load. While you do not have to load to this minimum, it is an important number to be aware of. The minimum impedance (maximum load) should never be exceeded, you'll destroy your amp in short order, however you can always load it with a higher impedance (less load) with no ill effects, with the exception of reducing the power avaialable. I, however, don't see this as a real negative, as the amp will run cooler, with lower distortion, and improved damping factor...

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: grunge311
Date Posted: September 13, 2006 at 10:37 AM
I have a question regarding the power/fuse rating section of this thread..

I have an amp that is rated 4x50@4ohm with a 30a fuse. 4x50=200 30x14.4=432 200/432 = 46% This works out to 46% efficiency, which is in the respectable area.

But this amp is also rated at 2x200@4ohm, but the fuse remains 30a, does the math stay the same? if so then 200x2 =400 30x14.4=432 400/432= 92%

I guess I just want to know is do you always use the lowest rating? what about dropping ohms and such?




Posted By: cva me
Date Posted: September 13, 2006 at 10:19 PM
haemphyst,
You have been a wealth of knowledge thank you again. If could just ask you just one more piece of advice...Due to new budget, I have to stay with the Punch p325.2 I am however upgrading to p1 10"s. @ 150 watts rms each, my amp states 2 or 4ohm stable. Specs

state 325 wattsx1 rms @ 4ohms bridged,

16o wattsx2 rms @ 2ohms,
which ohm subs do you advise to get in order to get the max power?




Posted By: pmendoza408
Date Posted: September 16, 2006 at 7:32 PM
thanks for the support




Posted By: haemphyst
Date Posted: September 16, 2006 at 7:50 PM
Get the two 8 ohm woofers, parallel them, and bridge the amp to that load, that will give you the maximum power available - 325 watts, around 160 watts per woofer.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: lessismorespl
Date Posted: September 18, 2006 at 11:43 AM
Personally, I look at 3 factors when buying any car audio product.

1. what kind of sound I'm looking for.

2. how well the components match up.

3. what is my budget.

Too many people base their decisions on what other's have, how much it cost, how powerful it is(which w/ some manufacturers can be very misleading), etc....

Basically no amplifier is junk, some are made better than others, some have more features, some have better cosmetics, etc... The installation is probably 80%-90% of how well a system operates, even high end equipment can sound weak and have the worse SQ.

How long it last is up to the user, I have seen high end amplifier live a short life due to abuse and lack of knowledge. Just b/c an amplifier cost $1K-$2K does not mean it has everlasting life.

I have built systems for under $500(4 ch. & 2ch. amps, 2 subs, and a lower end H/U) that has sounded as good as system 3 times the price.

Too many people look at the amplifier as the heart and soul of a system. Although they do compliment a system, it all comes down to the installation.

Just my opinion, I have been a member here for awhile now, just seldom post b/c I'm often busy. I participate off & on in several forums.   





Posted By: larzzzz
Date Posted: December 19, 2006 at 3:12 PM
With regards to amp ratings I assume that max power is generated with transient signals.... a hard crash of the cymbals or a hard bass note etc. The amp is not designed to reproduce such signal levels continuously but can sustain brief periods without distorting the signal or clipping. So I basically cut the max power rating in half to give me a continous power rating of what I think that the amp is capable of running all day at. Just adding another $0.02




Posted By: i_know_nothing
Date Posted: February 11, 2007 at 10:55 PM
first, im not real new to car audio, i just really know about the installing aspect of it, and have minimal Knowledge of the component aspect.

I have two Eclipse 88120DVC (year 2000 model) and i have been looking for an amp to push them.
specs: 500W RMS
1,000W Peak.
The FS - 27Hz,
Qts - 0.30,
DCR - 3.0ohm/coil,

originally i had 2 Alpine MRP-M450 pushing them and they just seamed like they where not doing the job.

the first thing i was looking at was 2 Alpine MRD-M1005.
second was the Audiobahn A12001DT
third was the Orion HCCA-D2400

but please help me...im not even shure if im heading in the right direction.




Posted By: sethat
Date Posted: March 14, 2007 at 9:11 PM
anthony71 wrote:

Here's a good site that discusses some more features necessary when purchasing a car amplifier: guide to car amplifiers. It has very good info. Helped me a lot.


First sentence from the above link: "Car amplifiers convert low-power signals received by car speakers to high-powered signals, improving their volume and sound quality."

Here's something to think about. Theoretically, I have never known of any amplifier in existence that actually improves the sound quality of a signal. This is why every amplifier has a certain percentage of THD. After a signal leaves a head unit, it's all downhill from there.   Every piece of conductor and electronics (even baffles and enclosures) that interfaces with the signal before it reaches your ear is going to cause an incremental decrease in quality.

Another factor that I consider when selecting equipment is distortion.    Start with a good high volt signal and use the least invasive equipment, pertaining to THD, that your budget will allow.

The signal is never cleaner than the moment it passes through the DAC and out of your head unit.

Hey, this post was probably overkill, but it motivated me to finally register.




Posted By: stop82lp
Date Posted: March 24, 2007 at 10:11 PM
haemphyst wrote:

I have seen several (ok, MANY) posts here lately, asking about how to choose an amplifier, with all sorts of "Is this good...?" types of questions.

Here is what I look at when choosing an amplifier, and in their order of preference:

1. Power. I know, this is where MOST people look first, but it's the very reason you are buying an amp, right? Also knowing Ohm's Law, and knowing that I will almost always load an amplifier with the maximum specified impedance (impedance - 4 ohms or higher, NOT load - 4 ohms or lower), I need to know exactly how much power I am looking at to start with. When loading an amp with a higher impedance, the amp will make less power, so I have to keep this spec in mind the whole time. My speakers are almost always chosen before I decide to start looking for an amplifier, I know the impedance and efficiency numbers when I start. This will help me decide how much power I need or want for that particular driver compliment. I will NEVER look at "Max Ratings". They are often worthless, generally overinflated, selling tools, designed by old-school, low-end amplifier companies, originally made to sell product. (You remember how it went (and still goes today)... This 800 watt amplifier is only 200 dollars, but the Nakamichi 160 watt monoblock is 1300 bux for the pair. Which were (are) YOU going to buy?) Ahhhh, the power of advertising... Classic Nakamichi, Alpine, Linear Power, Orion, Eclipse, etc., THEY never posted "Maximum Power" numbers, did they? Unfortunately, even the good products of today will state maximum power output, I just disregard the numbers posted.

2. Signal to noise ratio. This one I place a bit more weight on, especially when the amplifier is going to be used in a mid-bass (important), mid-range (more important) or highs (MOST important) application. The higher the better, and there is no exception to this rule for me. Amps with tube stages are typically less capable than their solid state stablemates in this area, but I do make exceptions for tube amps. It is NOT a terribly important spec for a bass amp, so when shopping for a bass amp, don't bother with this number. Dedicated bass amps, BTW, usually offer awful SNR numbers.

3. Efficiency. Here's where you will be able to tell a decent manufacturer from the crap. Let's say you are looking at an 250 watt (RMS) amplifier. The first physical thing I look at, is how big a fuse do they recommend (or what size fuse is in the end of the amp)? I know right now that 250 watts OUT will demand (and I use 50% efficiency to keep it simple) 500 watts in. 500 watts in, divided by the (car running) battery voltage (14.4v) is about 35A. If I look at the end of the amp, and see a 20A fuse, I'm walking away, as there is no way that amp can make 250 REAL watts, continuously. 14.4v times 20A, equals 280 watts in. 250 watts out, divided by 280 watts in, translates to an 89% efficiency. In a class A/B amp, this is an impossible number, and it even stretches the imagination for digital amps, as well. The theoretical MAXIMUM efficiency for class A/B is 66%, (95% for digital) so someone is lying. I don't care WHO the manufacturer is, if these numbers don't add up, I will start looking elsewhere... Now, if all the other specification look good, AND I can get in the vicinity of the RMS power I am looking for, I will buy an amp that's efficiency number might be stretching the truth a bit. My old Nak 160 watt monoblocks had 40A (that's 480 watts in - a 33% efficiency, people!) fuses in each one, and they ran hotter than a firecracker, even loaded at over 8 ohms. I liked that. posted_image

4. Terminals. A frequently overlooked part of an amp, this is a very important part of an amp to me. A car is a place frought with vibrations. A cheap or cheezy feeling connector in power or speaker terminals and most ESPECIALLY in the RCA inputs, will often cause problems in the future. Setscrews for power, quality terminal blocks for speaker outputs, and Tiffany style RCA connections (the type attached to the chassis, rather than a block of plastic soldered to the PC board.) The quality of the I/Os can be a direct indicator of the attention to detail paid to the rest of the piece. Translation? Overall Quality.

5. Heat sink. This one is simple. How does it look? I eventually chose Eclipse gear, because it looked like jewelry. Fine finish and appearance. Also, heatsink size and quality can be another indicator of quality of the amplifier as whole. A heavy heatsink will also provide better thermal stability, a nice thing in an amp.

6. Damping Factor. I used to place more emphasis on this spec, but my research recently (over the last few years, really) has, while not proven to me it is a useless spec, has not proven to me it is an extremely important spec. This is why this particular spec is a little further down the list. While I place a bit more emphasis on it for a bass or mid-bass amp, I, admittedly, place less weight here than I used to...

7. Price. Money rarely means much to me in an amp, (much like my computers - "Life's too short to build slow computers." - David Draper) it's something I am going to be keeping for a long time usually, so I will save if necessary to get EXACTLY (or close to) what I am looking for.

These are the things I look for when trying to decide on an amp. OBVIOUSLY, there are going to be VERY few amps on the market that will make me happy across the board, but then some of the physical characteristics listed above can be made to fit me and my desires with a little time, a couple extra bux, and some careful use of a soldering iron. All of the above things will cost more, but it will ADD more to the finished product as well... posted_image




Posted By: stop82lp
Date Posted: March 24, 2007 at 10:12 PM
i have a volfenahg 200 watt amplifier , i also have two 10in cerwib nega v max subwoofers. the amp isnt stable at 1 ohm. but i just want to know the best way to wire themn without blowing anything? please hep a rookie out : )




Posted By: stop82lp
Date Posted: March 24, 2007 at 10:15 PM
i forget they are 600 rms and 1200 watt peak per sub.




Posted By: ender6456
Date Posted: March 25, 2007 at 8:50 PM
Haemphyst, you offered some great information on choosing the right amplifier, but I being a lamen...ended up confusing myself with all that information.  I recently purchased two Audiobahn (yes...i know most people dont like Audiobahn, but they offered the best wattage versus mounting depth that I could find) ALUM10N Subs.  The subs are dual 6 ohms (someone already told me to buy a third one, but the box I have is specific for my vehicle and it only holds two 10's) and are rated at 800w RMS.  I plan on running these in parallel which means they would end up at 1.5 ohms, i think.  Now the difficult part, the amp I had planned on getting was an Audiobahn A2300HCT which is rated at 2400w rms @ 1 ohm.  If I can do math correctly, that means that I will get 1800w @ 1.5 ohms, plenty for my two 800w 10's.  After I found this thread, I tried to do the math and the calculations I got were not good, which made me think that either the amp was really bad or I screwed up the numbers.  FYI: the amp comes with four 40amp fuses.  Any help you can offer would be greatly appreciated, thank you.




Posted By: haemphyst
Date Posted: March 26, 2007 at 5:08 PM
That amp won't do 2400 watts. It only get 2300 watts in, at 14.4 volts. That amp is probably 1100 to 1200 watts on a good day. I wouldn't run it at 1 ohm, either... 1.5? Close, but I think you'll survive with that.

But, yes, you'll have either 1.5, 6, or 24 ohms to play with...

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."




Posted By: kno88y
Date Posted: June 30, 2009 at 3:39 PM
after reading this im alittle better on bits and bobs but still lacking the whole ohm bit lol, im gussing if an amp doesn't advertise rms/ohms per chanel its not worth buying ??

so if i buy a 1200w amp (600w,rms) and run 4 450w 6x9's (200w,rms) of each channel

this wouldnt work i would need a 2000w (1000w,rms), like i say they dont advertise these details ??




Posted By: mightylight
Date Posted: October 18, 2009 at 7:43 AM
SO whats the difference of Load and Impeadance? I have a 3 OHM Subwoofer, would a 4 OHM stable amp work?

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cj Lancaster




Posted By: danjarus1975
Date Posted: November 25, 2009 at 12:09 PM
How do I find a amp that has the exact RMS of my subs, I have four 2000w subs (1000w rms @ 4 ohm). When I shop for amps, I only see amp with an lesser RMS like 3200w never 4000w exactly. I want to run them altogether to make them 2 ohm stable! I see mono amps that are 4500w max (1500w RMS x 1 @ 2) will that power each sub to it's normal RMS? Or, where can I find an amp that will work for me?

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Laron "Danja" Williams




Posted By: laoz3
Date Posted: November 26, 2009 at 5:21 AM

hmm that is a good one but from my past experiece is that you would  not find the numbers to match up exactly. Either the rms on the amp is too low or too high and really i would perfer the amp to be lower. The reason for that would be just is that you dont over push the sub woofer.Most subwoofers have a green zone so to speak that a speaker can handle the constant power going through it and if your pushin it right at the max that ova time that subwoofer would blow.





Posted By: laoz3
Date Posted: November 26, 2009 at 5:34 AM

sorry didnt see your other Q's r the subs single or dual. If there single voice coil then i would go 2 subs runin parallel basically + to + and - to - then to your amp if they r dual voice coil i would buy an amp that can handle a 1ohm load and run them in parallel again and so you would need 2 amps that can handle a 1 ohm load and then just basically connect 2 subs to each amp in parallel mode.

Also im not a pro at installing a system I picked it up from alot of trial and error and BELIEVE me I did alot of errors if any of this info is incorrect im sorry and if im right then im glad i can help u





Posted By: danjarus1975
Date Posted: December 01, 2009 at 6:57 PM

thay all are DVC!



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Laron "Danja" Williams




Posted By: danjarus1975
Date Posted: December 01, 2009 at 6:58 PM

Sorry, I mean they are DVC!



-------------
Laron "Danja" Williams




Posted By: briankmizell
Date Posted: December 07, 2009 at 7:49 AM

I would like to thank you for such and informative post you have made. I have several questions for you about my set up.

I have two JL audio amplifiers, a 300/2 and a 250/1

The 300/2 calls for a 40 amp fuse, doing the math I think that equals out to 52% efficiency.

The 250/1 calls for a 30 amp fuse, doing the math this one should be 57.8% efficient.

1st question is, do these numbers sound right?

Now, my truck came equiped with a 55 amp alternator.

I have added two 12" electric fans that have a 50 amp relay on them. 

I have a electric fuel pump that pulls about 7 amps.

The max draw of all my compents would be approximately 180 amps (thats my guess)

I will be running a 2/0 gauge power wire from the battery to a distribution block and then from there two 4 gauge wires will be run, one  to each amp with a 30 amp fuse on one, and a 40 amp fuse on the other.

I will also add a 4 gauge wire running from the battery to the positive output post on the alternator.

2nd question is, would I need a 200 amp alternator, or would 140 amps be sufficient?

3rd question is, what size of fuse would I need to put in the 2/0 gauge power wire next to the battery?

4th question is, do I need a fuse on the 4 gauge wire between the battery and the alternator, if so what size?

5th and final question, will I need to upgrade anything else on the truck since I will be running such a high out put alternator?

If you need more info such as speakers and resistence of each one etc, let me know and I will get them for you.

Thanks in advance for your reply,

Brian Mizell





Posted By: briankmizell
Date Posted: December 12, 2009 at 10:55 PM
Bump




Posted By: oldspark
Date Posted: December 13, 2009 at 12:18 AM
briankmizell wrote:

The max draw of all my compents would be approximately 180 amps (thats my guess)

... would I need a 200 amp alternator, or would 140 amps be sufficient?



You have answered your own question - 140A is not enough for 180A.
That's unless you run the 2nd alternator as a separate system for your audio (you can share a common ground, but not their power outputs).

Be aware that just because fans have a 50 amp relay doesn't mean they draw 50A. 10 Amps each is more common (ie, typically 80-100W each.)


Fusing between the battery and alternator is an interesting question. Older vehicles never had them.
Alternators are generally self-limiting in terms of their output current.   
The main reason for adding a fuse was for "normal protection" against battery discharge in case of shorted cables.
Some argue the fuse is also to protect the alternator diodes in case of a reverse connected battery, but I find they rarely do.

From the alternator's point of view, except as above, there is little reason for the fuse except where a short from a high-output alternator may become a safety issue.
The fuse sizing will be to protect the cable (ie, not above the cable rating), else whatever battery or alternator maximum or short-circuit current limit is desired. (Many vehicles have fuses less than the alternator rated current, but they will usually have loads taken off the alternator - eg - headlight power.)


The above are not answers per se, but are considerations only.

If the above change your implementation, then some trivial dribble follows...

Where 2 alternators are possible, many keep the existing system intact and add a second alternator with its own battery to power the audio system (or whatever), and add sufficient ground straps (that's something that is often overlooked - hence resulting in a "electronic fry" situation! posted_image ).

If only one alternator is possible, a new alternator that covers standard plus additional "average" load is substituted.
Although a bigger battery may be used, usually a second sealed battery is added as close as possible to the heavy current system - eg, an AGM battery next to the audio amps - with the 2nd battery connected to the alternator ONLY whilst the alternator is charging.
This means localised heavy wiring only with few voltage-sag problems (ie, no caps needed).
The alternator to 2nd battery cable need not be as heavy as the normal audio amp cabling - it only carries the charge & load current to the second battery, hence should be rated to the alternator's max current output.
But the latter alternator to 2nd battery current will be limited by the size of the relay used. (Typically 60A or larger with a circuit breaker; could be fused if the cable & relay matches or exceeds the alternator output.) (This is separate to the 2nd battery's own fuse/protection.)




Posted By: 08canyon
Date Posted: December 15, 2009 at 2:21 PM
OK... For some reason this is confusing me. I have an RE Audio XT-800.2 amp, 100W RMS x 2 Channel @ 4Ohms, unit has a 25 amp fuse in it. Is the advertised RMS for real?




Posted By: oldspark
Date Posted: December 15, 2009 at 4:51 PM
Why the confusion?

25A x 12V = 300W   (based on a literal "12V" system)

25A x 13.8V = 345W ("normal" rating voltage)

25A x 14.4V = 360W   (common max system voltage for lead-acid batteries)

All exceed the claimed 2x100W = 200W rating.
(All figures above are RMS - I rarely quote anything else unless denoted!)


If you are still confused - do NOT continue reading.....

FYI - a common electrical practice is to run fuses at no more than 70% capacity - ie, 200W/.7 = 285W minimum "fuse rating" (divide by whatever voltage is applicable).

But, some devices may run fuses higher than that if the device doesn't tolerate a 42% overload etc (ie 70% x 142% = 100%).

And the amplifier's inefficiency must be added to the above 200W.




Posted By: briankmizell
Date Posted: December 16, 2009 at 11:55 PM
oldspark wrote:

briankmizell wrote:

The max draw of all my compents would be approximately 180 amps (thats my guess)

... would I need a 200 amp alternator, or would 140 amps be sufficient?



You have answered your own question - 140A is not enough for 180A.
That's unless you run the 2nd alternator as a separate system for your audio (you can share a common ground, but not their power outputs).

Be aware that just because fans have a 50 amp relay doesn't mean they draw 50A. 10 Amps each is more common (ie, typically 80-100W each.)

Fusing between the battery and alternator is an interesting question. Older vehicles never had them.
Alternators are generally self-limiting in terms of their output current.   
The main reason for adding a fuse was for "normal protection" against battery discharge in case of shorted cables.
Some argue the fuse is also to protect the alternator diodes in case of a reverse connected battery, but I find they rarely do.

From the alternator's point of view, except as above, there is little reason for the fuse except where a short from a high-output alternator may become a safety issue.
The fuse sizing will be to protect the cable (ie, not above the cable rating), else whatever battery or alternator maximum or short-circuit current limit is desired. (Many vehicles have fuses less than the alternator rated current, but they will usually have loads taken off the alternator - eg - headlight power.)

The above are not answers per se, but are considerations only.

If the above change your implementation, then some trivial dribble follows...

Where 2 alternators are possible, many keep the existing system intact and add a second alternator with its own battery to power the audio system (or whatever), and add sufficient ground straps (that's something that is often overlooked - hence resulting in a "electronic fry" situation! posted_image ).

If only one alternator is possible, a new alternator that covers standard plus additional "average" load is substituted.
Although a bigger battery may be used, usually a second sealed battery is added as close as possible to the heavy current system - eg, an AGM battery next to the audio amps - with the 2nd battery connected to the alternator ONLY whilst the alternator is charging.
This means localised heavy wiring only with few voltage-sag problems (ie, no caps needed).
The alternator to 2nd battery cable need not be as heavy as the normal audio amp cabling - it only carries the charge & load current to the second battery, hence should be rated to the alternator's max current output.
But the latter alternator to 2nd battery current will be limited by the size of the relay used. (Typically 60A or larger with a circuit breaker; could be fused if the cable & relay matches or exceeds the alternator output.) (This is separate to the 2nd battery's own fuse/protection.)

Thank you for your reply, some of that info I had to read a couple of times for it to soak in........lol but I got it.





Posted By: 93_civic
Date Posted: January 27, 2010 at 10:07 AM

great post haemphyst thanks!

but i had a question, when trying to find the "Efficiency" on an amp, you dont say what rms to calculate? for example im looking into buying an amp that says its 400w rms @ 4ohm's and 600w rms @ 2ohm's. i added up the calculations for 2ohm's first as i plan on running the amp at 2ohm's, but the numbers didnt add up. so i decided to retry using the 4ohm's settings and everything seems to add up nicely. what i dont understand is, will i only get efficient power if i run the amp @ 4ohm's?

so just to make sure, i was wondering if you could give me your input on if this amp is good for me or not. im planning on running a 600w rms sub in a single vented box @ 2ohm's. thanks in advance!  posted_image

800 Watts Total Output Power

600 Watts RMS x 1 Channel @ 2 Ohm

400 Watts RMS x 1 Channel @ 4 Ohm

Full MOSFET Circuitry

60dB Channel Separation

90dB Signal to Noise Ratio

22K Ohm Input Impedance

200mV - 4V Input Sensitivity

Frequency Response: 20Hz - 20kHz

THD <0.05%

Fuse Rating: 2 x 25A






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