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Not Enough Power? Or Knowledge?


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bpensak 
Member - Posts: 8
Member spacespace
Joined: January 01, 2004
Location: United States
Posted: July 02, 2005 at 11:21 PM / IP Logged  

Sorry for the probably obvious to most questions, but I have never experimented with speakers until now...

2001 Chevrolet Silverado 1500HD Crew Cab

- Just installed Alpine 6-1/2" Type R Components In The Front, 6-1/2" Type R Coaxials in the back. Wired directly off head unit (40w x 4 - Also Alpine Din & a Half) and I am disappointed with their output. I believe the obvious is that in order to have it louder and crisper, I need to step up to the plate and install a 4 channel amp. Looking to stay with Alpine, and considering the MRV-F345. I will eventually add another amp to run 2 10" Alpine Type R Subs, but for now looking to resolve the first part of my install.

Can anyone advise/help me with resolving my issue? I don't understand the full use of watts per channel in relation to ohms, and after reading the info on certain amps, I'm lost. I don't want to purchase another part and be unhappy with it again.

Also, I'm sure there are those out there that will criticize me for using all Alpine, but I just wanted to stay consistent in the whole vehicle. I'm not out for competition, just good clean sound (that can be played somewhat loud).

I appreciate any advice/help in advance.

NicP 
Member - Posts: 29
Member spacespace
Joined: March 26, 2005
Location: Australia
Posted: July 03, 2005 at 12:12 AM / IP Logged  
the problem you have is that your headunit is rated at its peak output power not its RMS output power, the headunit is probably something like 18wRMS x 4
The speakers you have are 4 ohms, you should be looking at a 4 channel amp that gives you approx the RMS power that your speakers are rated at when running at 4 ohms
boulderguy 
Silver - Posts: 510
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Joined: April 17, 2005
Location: United States
Posted: July 03, 2005 at 1:59 AM / IP Logged  

First off, keeping all the electronics "consistant" from a single company only helps you when it all gets fried & you have to send it all back - you can use the same box.  Nothing wrong with Alpine stuff, but why limit yourself?  anyway...

Ohms work like this - an ohm is a measure of resistance.  If you put a wire across your battery terminals, there's no resistance (& you'll melt things).  By putting resistance in there, you're metering the amount of current flow.  More ohms = more resistance = less current flow (or fewer watts per channel).  Speakers have resistance - usually 4 ohms each in cars.  Amps usually rate their output when using a 4 ohm resistance (IE one speaker), but frequently will also give ratings at 2, 1, even 1/2 & 1/4 ohms.  Anytime you cut the resistance in half, say from 4 ohms to 2, you'll effectively half the resistance "between the battery terminals" (in this description) and double the amount of current flowing.  But ignore those ratings for now, it just confuses your baseline of comparison. 

look for a 4-channel amp that has RMS (that's constant output) of about 50 wpc into 4 ohms.  Good place to start.  Go bigger if you want more.  Like NicP says, watch out for the "Peak" power rating, that's the RMS plus the headroom reserved for musical peaks - usually twice the RMS but not sustainable for more than a few millisecs.  Companies use this number as a marketing ploy to make you think you're getting more than you are - like your headunit did.

Invariably someone's going to try to sell you a 2-channel amp & tell you to run it at 2 ohms (meaning two speakers per channel output - - effectively doubling up).  What this does is in theory doubles your constant power output from those 2 amp channels by cutting the resistance (ohms) in half.  Don't ask how, that's another topic.  What you're doing here is tricking the amp into putting out twice the power, which is fine.  What they won't tell you is that the amp's ability to respond to musical peaks - the amp's headroom, or peak power - can't be doubled. 

So say you've got a 100w RMS amp with 100w of headroom, you trick it into doing 200w RMS by operating in 2 ohm, but still only have 100w headroom.  The amp can now only respond to peaks with 25w per speaker instead of 50w.  It makes the music louder, but much less dynamic.

So the take-home message is to stay with a four-channel amp w/1 channel per speaker for best results.  Do that & you can mostly ignore all the ohm ratings.

stevdart 
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Joined: January 24, 2004
Location: Pennsylvania, United States
Posted: July 03, 2005 at 9:14 AM / IP Logged  

Alpine amps are a little more confusing than some others.  They will produce a given amount of power no matter what the impedance of the speakers are.  Have a look at several different brands of ampifiers...look at the output ratings...and it will click as to how an impedance load (measured in ohms) causes an amplifier to produce output differently.

Without impedance, there is no power output.  Thus, when you install your amplifier the deck would then become the "preamp", and will not provide power.  It will perform at its best this way.

Don't feel like you have to understand Ohm's Law and all the variables associated with power, current and resistance right away.  It takes months of study to grasp it all.  Other than this forum, which in time will provide you with just about all the info you would need...another site to look at is http://www.BCAE1.com.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
bpensak 
Member - Posts: 8
Member spacespace
Joined: January 01, 2004
Location: United States
Posted: July 03, 2005 at 9:32 AM / IP Logged  

Thanks to everyone for the replies! (NicP, boulderguy, stevdart)

Looks like an amp will be the key to unlock the potential of what I just installed.

I will look at a few, I've read in other forums about pro's & con's of various brands, will be going out today and checking a few places out.

On the same subject, once I install the amp, should I run new wire to each speaker from the amp, or simply splice in at the door jambs inside the cab, or run wires back up to behind the head unit and tap the factory wires? I've already installed them in the factory wiring, soldered, but I want to do it right from here on out. Any help is again appreciated, I've never installed an amp either. Basic wiring no problem, hookup the right way, unknown by me.

oonikfraleyoo 
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Posted: July 03, 2005 at 12:16 PM / IP Logged  
I always run all new wire. It takes a little longer but better safe than sorry.
Nik
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boulderguy 
Silver - Posts: 510
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Joined: April 17, 2005
Location: United States
Posted: July 03, 2005 at 1:09 PM / IP Logged  
I agree - if you're doing the amp, might as well do new wire too.  Don't take a 2nd mortgage on it tho - a decent quality 16 guage is fine for 50wpc +/-.   And Stevdart's right, you don't need to grasp Ohm's law at this point, just know enough to be able to look at the same type of specs when comparing equipment (EG - power produced at 4 ohms RMS).  Apples to apples, you know.
bpensak 
Member - Posts: 8
Member spacespace
Joined: January 01, 2004
Location: United States
Posted: July 03, 2005 at 6:01 PM / IP Logged  

Great Info & Thanks!

I stopped at a few places this weekend and two different shops both refered me to the JL Audio 4 Channel Amps, either the e4300 or the Slash Series 300/4. Onces price conservative, the others alittle higher. Any recommendations or other brands to refer to ?

Thanks again for all the help! It's been a relief! Nothing like a holiday weekend project...

boulderguy 
Silver - Posts: 510
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Joined: April 17, 2005
Location: United States
Posted: July 03, 2005 at 7:05 PM / IP Logged  

I'd spend the extra $.  It sounds like the car audio bug has bitten you, and if so, you'll just wish you had gotten the better amp anyhow.  Regret's more expensive than credit card interest rates. 

The JL amps are excellent choices.  I hear the MB Quart amps are good, but I haven't listened to them (anyone have an opinion there?).  I'm partial to Soundstream.  There's plenty of higher end stuff, but you'll pay for it.  If you ain't afraid to Ebay you'll find some screaming deals.

bpensak 
Member - Posts: 8
Member spacespace
Joined: January 01, 2004
Location: United States
Posted: July 03, 2005 at 11:21 PM / IP Logged  

I've looked around eBay and found better deals than the shop (no overhead of course). I'm considering the JL 300/4 which states:

75 W RMS x 4 @ 1.5 ohm-4 ohm (11V-14.5V)

My 6-1/2" Components in the front say they are rated @ 70W RMS (4ohm) (Peak 350W). My rear 6-1/2" Coaxials say they're good for 50W RMS (4ohm) (Peak250W). If I use the amp, do I have a higher chance of blowing the rears since the amps gonna push 75w to them? Or is that only if I crank it hard?

It sounds like the amp will be plenty to run all 4 channels, but am I going overkill and risking damage to the rears? (Dang Audio Bug).

Now that I'm commited, I can't stop there. Subs & Amp. Considering 2 10" (Rated @ 300w RMS @ 4ohm) Alpine Type S with a JL Audio 500/1 (500 W RMS @ 1.5 ohm-4 ohm (11V-14.5V)). Obviously I'm not maxing the RMS power out to the subs since I'm running two, but would I be happy with this setup (thump for the buck) - also keeping in mind I'm not trying to blow out my windows. I looked at the type R 10", but they are rated for 500w RMS (two of those would only equal 250w RMS from the amp, so why not run a smaller rated sub right? (I think I'm catching on to this now - Man, I really hate this audio bug!)

Thanks in advance for the replies - hat's off to you boulderguy! Big help!

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