How to find 80hz on my mono amp?

hi guys,

i'd like some advice or help with this as im lost as to how and where 80hz is on my amp.

firstly, here is the 12inch sub woofer enclosure im using and its specs:

JBL GTO-1260BR 300mm Bass-Reflex Subwoofer Box Subwoofer

GT4-12/300mm Enclosure: bass-reflex

Power handling, RMS: 250W

Power handling, Max: 1000W

Sensitivity (2.83V/1m):

92dB Frequency response: 35Hz – 200Hz

Impedance: 4 ohms

Dimensions (L x D x H):460mm x 437mm x 360mm

and here is my amp and spec's, its a pioneer gm-7200m mono :

mono subwoofer car amplifier

250 watts RMS x 1 at 4 ohms (360 watts RMS x 1 at 2 ohms)

variable low-pass filter (40-240 Hz, 12 dB per octave)

selectable bass boost (0, 6, 9, 12 dB at 50 Hz)

--------------------------------------------------------------------------------------------------------------------------------------------------------------------

ok guys,

the amp is installed, is getting plently of power ( i dont think its a demanding amp anyway ) and i can hear it playing along with the music.

only problem is that it doesnt sound right at all. its as almost as if it misses the timing of the beat by a fraction of a second, or im thinking

the problem is that its not tuned properly ( seems more likely as it sounds really flat and not impressive ).

i have a pioneer p80mp headunit with 3 pre-outs feeding it the music and each pre-out has 6.5v going to it and it matches my amps perfectly.

my thinking was to buy both amps from the same range/model line up from pioneer.

anyways, i have my hpf on the headunit set to 80hz, and the lpf is also set to 80hz.

however, my mono amp has a frequency knob and this goes from 40 - 240hz.

i have it currently set up like this : ( its a very simple amp with not much tweakability )

you can see from the photo where the knobs are currently set to by the green arrows. my thinking is that if the amp frequency starts out at 40hz,

well then all i need is another 40hz, so i just gave a guess at this and raised the knob to where i think 80hz would be.

am i correct in my method or completely off the mark altogether?

where exactly would 80hz on this amp be ?

if you know where it is, could you please save the above photo, open it up with paint, and mark where it is with a green arrow and repost.

thanks for your time guys ,

dave, ireland.

-------------
live by the ford,die by the ford.

well since the range of that LPF is 40 to 240, difference of 200hz between all the way down and all the way up. so if you had it directly in the middle i would assume it was at 140hz. so 80hz seems like it would be just under 1/4th. from the look of your picture it is as good as you can get since all anyone can do is make an educated guess

-------------

hi,

thanks for the reply :)

ya, that was my thinking also.

but i could be wrong too. if i have 80hz for my high pass and my low pass, should i be looking at setting the amp to 80hz too or do i need

to set it closer to the highest range of the subwoofer, which is 200hz?

i saw an article on this while googling earlier, where the guy said you should start off by upping the frequency on the amp to match the spec of the woofer.

i'll go look and repost it.

-------------
live by the ford,die by the ford.

hi again ,

i found the info i googled earlier :

https://answers.yahoo.com/question/index?qid=20081204131556AARPM0R

basically,  the guy looking for help is asking where he should set his frequency knobs to. kinda like me. here is the answer he got :

Set the LPF on the amp to just below the highest range in the frequency response of the subs. Example, if the subs are 20-200Hz, set the LPF to about 180 Hz.

If you have them in the wrong enclosure, that will be part of the issue too.

Be sure to set the gain or level right as well.

The purpose of the gain is to match the signal volts RMS coming from the source (CD player, etc.) to the input of the amp to prevent clipping (damage by over powering).

Here is a guide that will help you set the gain correctly < color=#006699>https://www.box.net/shaRED / uchv4dbk88

You'll need a multi-meter (AC voltmeter, $15 from Radio$hack), Microsoft Excel and a way to burn an audio CD from an MP3.

If you don't have Excel, use this link < color=#006699>https://www.box.net/shaRED / nkkw1dhk4g

See my site for more info < color=#006699>https://spkrbox1.spaces.live.com

Source(s):

-------------
live by the ford,die by the ford.

davemk7 wrote:

---

hi,

thanks for the reply :)

ya, that was my thinking also.

but i could be wrong too. if i have 80hz for my high pass and my low pass, should i be looking at setting the amp to 80hz too or do i need

to set it closer to the highest range of the subwoofer, which is 200hz?

i saw an article on this while googling earlier, where the guy said you should start off by upping the frequency on the amp to match the spec of the woofer.

i'll go look and repost it.

---

if you have the radio's lowpass set at 80hz then it doesn't matter what you set the amp to as long as it is not lower than what you have the radio set to. you can have the amp set to 240hz and it wont matter because it is receiving a signal that is already filtered.

-------------

this is the thing,

i dont trust pioneer headunits when it comes to setting the filters from the menu of the cd player.

i think once the signal is fed out from the cd player in the form of the 6.5v pre-out, i think its up to the amps to do the filtering.

because the 4 channel amp i have , which is also pioneer, has a 80hz hpf switch which automatically  cuts to 80hz.

if i turn this switch to normal, all the bass goes to the front door components, which tells me that the cd menu hpf doesnt affect the pre-out signal.

i think i should really contact pioneer in fairness.

its their fault anyways.

if they were any good, they would have a switch on the mono amp also, which is auto tuned to 80hz for simplicity.

but no, they have to be awkward in order for the customer to bring his/her car to the audio dealer and get " set - up " or " tuned " for an extra price. its like buying a tv and having to call the dealer to tune it in. except the fact that you know when youve got the right channel with tuning a tv. with car audio, its all guessing unless you know what your doing.

im sad now :(   lol.

-------------
live by the ford,die by the ford.

even if that were true, you can just set the amp to 80hz like you had it. it wont hurt anything to have 2 different filters. and besides 80hz is still in the range of bass frequencies and can still be dangerous to some speakers if you have enough power to them. this is why when you defeat the amps HPF it might sound like it is getting more bass because it is getting more bass. and the highpass is not an absolute cutoff point for frequencies below what it is set at, it is just the point at which it starts to gradually fade the output below the set frequency. so even though you have it set at 80hz you will still get frequencies down to about 55hz.

-------------

maybe i need a 10" sub then , which would have tighter bass .

its a possibility that the 12" i have just doesnt sound good. its ported so possibility goes too low and resonates the car. giving bad vibes.

it gets very boomy, sloppy boomy that is. nothing is tight or accurate.

you think a 10" would sound better?

-------------
live by the ford,die by the ford.

davemk7 wrote:

---

maybe i need a 10" sub then , which would have tighter bass .

its a possibility that the 12" i have just doesnt sound good. its ported so possibility goes too low and resonates the car. giving bad vibes.

it gets very boomy, sloppy boomy that is. nothing is tight or accurate.

you think a 10" would sound better?

---

its probly the ported box im guessing you mean the round ports every sub i have heard in a round hole ported box sound that way. try a vented box that has a long rectangle hole they seem to be right on and hit hard if built to the right specs.

-------------
87 ramcharger eclipse CD5000 2 15" memphis M3 kenwood 900rms mono amps

99 dodge cummins diesel eclipse CD4000 1 12" memphis Mclass 800rms audiobuhn amp

moparfan1234 wrote:

---

davemk7 wrote:

---

maybe i need a 10" sub then , which would have tighter bass .

its a possibility that the 12" i have just doesnt sound good. its ported so possibility goes too low and resonates the car. giving bad vibes.

it gets very boomy, sloppy boomy that is. nothing is tight or accurate.

you think a 10" would sound better?

---

its probly the ported box im guessing you mean the round ports every sub i have heard in a round hole ported box sound that way. try a vented box that has a long rectangle hole they seem to be right on and hit hard if built to the right specs.

---

round ports or square ports, it doesn't matter as long as they have the right surface area to avoid port noise and they are the right length, with respect to the boxs' internal volume, to give you a good tuning frequency to match the sub.

12 or 10, this isnt your problem. a 12 doesn't sound sloppy because it is a 12 and just switching to a 10 and keeping the same overall box design wont give you any better results. i have an 18 in my truck and it isn't boomy, bass is very tight and smooth. woofer size is not what causes boomyness it is poor box design. it could also be possible that the acoustics in that car are helping to give you a boomy sound too.

-------------

hey guys,

the box is a jbl enclosure and sub in one. its a special edition box and sub.

here is a link :

https://uk.shopping.com/-jbl+gto+1260br

the box is perfectly made for the sub as the manufacturer is a good one ( in my view ).

i think soundnsecure may be right when he says it doesnt matter about the size of the sub.

if he has an 18" woofer that gives tight bass well then i guess it has to be down to my car acoustics and amp set up.

i have a 5.1 system for my pc, its the logitech z5500 and the sub is ported on that also. it sounds amazing tbh.

but the thing is, it is a 10" woofer and ive been told that a 10" inch hits tighter and snappy than a 12 will.

a 12" will sound lower and get better deeper notes. and no, i cant try my pc sub in my car lol.

:)

-------------
live by the ford,die by the ford.

davemk7 wrote:

---

hey guys,

the box is perfectly made for the sub as the manufacturer is a good one ( in my view ).

unfortunately even prefab boxes from good manufacturers might not have your best interests in mind. they build a box that is most likely to make most people happy, which means they usually put higher output over sound quality. and it is impossible for one box design to work well in all situations, you just got unlucky with the acoustics of your car.

but the thing is, it is a 10" woofer and ive been told that a 10" inch hits tighter and snappy than a 12 will.

ive been told that too, but there is no truth to that. everybodys first instinct is to blame their subwoofers when it doesn't sound exactly like they want it, but most of the time its because of the box.

a 12" will sound lower and get better deeper notes. and no, i cant try my pc sub in my car lol.

:)

---

your PC subwoofer sounds a lot better because it is in a large open room with far better acoustics than your car. and sadly i've seen people try to pull off the old PC sub in the car trick and it never works out.

-------------

yes, i think your spot on with your synopsis tbh.

i have just spent an hour in my car playing back dynamic tracks with good mid bass and bass.

like this one : https://www.youtube.com/watch?v=xlkEw6jGem4

sound quality in the vid is crap , just giving an example of the tunes i play.

anyways,  i started from scratch.

headunit settings all at zero.

then i chaned the hpf to 80, the lpf to 80.

i let the song play.

the start of the song above sounded great through my components, with the mid bass giving good snap and attack and the tweeters joined in perfectly to blend into the overall rythmn.

once the bass kicked in, it sounded distorted , uneven, and basically out of control.

i tried from 40hz, all the way up to 200hz on the amp and it sounds the same no matter what setting. ( just got deeper bass further up the frequency range from 100hz on. it did not get clearer )

ok, as for me, i'd like to thank everyone who posted and commented on my question.

my plan of thinking/action at present is this :

both pioneer headunits i have sound exactly the same ( i have back up cd players in case one breaks. being pioneer, they break once a year due to the flip face )

i am going to try and borrow another headunit , preferably an alpine unit , to test and see if the music gets better by just switching cd players. 

( please note that my components rock big time and i love them, im just having probs with the sub , how it sounds, or the cd player is sending a crap signal to the sub )

i will go past my local car shop and ask to try a different sub, preferably one thats a 10" and in a sealed box. i may try a number of sub boxes as i know the owner of the store quite well.

something has to be the weak link here. its either the cd player signal, the amp or the sub.

it could even be a mixture of both. im going to get to the bottom of it and will give feedback .

i'll take the car to test other sub boxes tomorrow.

thursday i will try fitting an alpine unit and will fiddle with it for awhile.

-------------
live by the ford,die by the ford.

update :

well lads, i paid a visit to the guy i know and he has his own i.c.e shop.

he fiddled around with the set up and found what was wrong.

i shouldnt have my hpf and my lpf set at 80hz.

he set the components to 120hz hpf, and then he matched the sub to 120hz lpf.

he told me that at 80hz the sub didnt have much tones to produce, hence , my sub outputting weak ass tones

and the reason its distorted is because i didnt have the amp set up properly with regards to gain / lpf setting.

im playing music now and it sounds more wholesome, if that makes any sense. the guy said i was causing a hole in the music the way i had it set up with

the 80hz hpf/lpf. he also said that although my front components were handling the 80hz beautifully ( and they do, the snap and attack is mega ) he reccomended

that i use 120hpf to save the components from any future damage and to stop starving the sub of proper notes that it wants to play.

once he switched the system to 120hz, i swear, you shudda heard the difference.

anyways, he told me to go play more with the amp frequency setting and to play back music , preferably the same track over and over,

untill it blended well with the components up front.

well, im happy enough at this stage to find out that my gear does work , and that its a good tidy little system ( he said everything is set up properly and very neat ).

its just a matter now to find the right setting on the amp for the frequency, which shouldnt be hard, he just said to turn the knob up untill it sounded good to me.

result !!!!!!!!!!!!!!!!!!!!!    :)    

thanks for the help anyways guys, im just really glad i got it sorted and got the help i needed from all involved :)

thanks :)

-------------
live by the ford,die by the ford.