# I need help finding 80hz on my amp



## Oo_ben_oO (Oct 20, 2009)

Hi guys i have got a Legacy LA978 1200watt 2 channel amp running a 2000w legacy steel sub. link to amp if helps LA978 - 1200 Watt 2 Channel Bridgeable MOSFET Amplifier @ LegacyCarAudio.com -

Now im trying to get my sub nice clean bass that hits you. I do have a power cap installed to.

Now i have got a JVC kd-lhx551 hu that has a built in subwoofer frequency e.g 55hz, 85hz, 115hz i have got it set to 85hz as it seems to have more bass power that hits you. But some songs sound not exactly true and sounds abit to boomy or muddey if that how to explain it. 

Now i have my amp set to LPF to about 1/3 way around my lp filter goes from 35 to 400 hz and there's no markings to tell me where 80hz is exactly so its just a guess.

So does anyone have a suggestion or a picture of where abouts 80hz will be on my lpf.

I did have someone say to me once that if i set the x over to full my hu will do the work to sort frequency's out. what do you guys think about that. 

Can anyone help me please


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## Oo_ben_oO (Oct 20, 2009)

bump


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## blazeplacid (May 19, 2008)

just adjust it what you think is about right

I wouldnt go more than half way. 

Maybe between 1/4 and 1/2
3/8???


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## TREETOP (Feb 11, 2009)

You have a crossover in your head unit- set your amp crossover to flat, full, off, or whatever setting defeats it.

Boominess or muddiness is more likely caused by your enclosure (or your subwoofer itself) than by your crossover point.


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## Mooble (Oct 21, 2007)

Play an 80Hz test tone. Turn the knob until you hear it.


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## Oo_ben_oO (Oct 20, 2009)

TREETOP said:


> You have a crossover in your head unit- set your amp crossover to flat, full, off, or whatever setting defeats it.
> 
> Boominess or muddiness is more likely caused by your enclosure (or your subwoofer itself) than by your crossover point.


On my hu i have a setting for subwoofer to set it to 55hz 85hz and 112hz option at the mo i got it on 85hz and i got my lpf over 1/2 my lpf goes from 35hz all the way upto 400hz. is it best to keep my hu on 85hz and then as someone said get a 80hz test cd if i can find one


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## TREETOP (Feb 11, 2009)

No off the shelf crossover in any head unit, amplifier, or processor cuts off like a brick wall. Simply playing an 80hz tone won't do it and here's why. 
Common crossover slopes are 6, 12, 18, and 24db/octave, with a few having an even steeper slope option (800PRS has 30 and 36db/octave for sub I believe). 
What this means in easy terms: I'm not familiar with the head unit you have but let's assume it has a 2nd order lowpass crossover which is 12db/octave (the most common).
If you select 85hz as your lowpass point, because of the slope it still plays plenty of information beyond 85hz, just at a diminishing amount- The next octave above 85 is 170, at a 12db/octave slope the 170hz signal will still be coming through- just 12db quieter than your "cutoff" point of 85hz. At 340hz it will be 24db quieter, at 680hz it'll be 36db quieter than 85hz, etc. Eventually there's a frequency that's not reproduced at all, because of the signal being cut to the point it doesn't overcome the volume of the speakers.
So, playing an 80hz sine wave, you could set your crossover anywhere above 80 and still hear it, but setting it below 80 will still allow the signal through as well. 
For example, you could play an 80hz sine wave, with your crossover set to 55hz at 12db/octave, and the 80hz tone will sound almost as loud as at the 85hz setting.

I think you're focusing on the crossover when the real issue is likely elsewhere. I'm able to refrain from insulting your choice in equipment because I'm well aware that proper setup, planning and tuning can often have more weight on how something sounds than the equipment itself. What I'm guessing though is that your enclosure isn't built for the type of sound you're looking for.
What can you tell us about your sub enclosure?


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## Oo_ben_oO (Oct 20, 2009)

TREETOP said:


> No off the shelf crossover in any head unit, amplifier, or processor cuts off like a brick wall. Simply playing an 80hz tone won't do it and here's why.
> Common crossover slopes are 6, 12, 18, and 24db/octave, with a few having an even steeper slope option (800PRS has 30 and 36db/octave for sub I believe).
> What this means in easy terms: I'm not familiar with the head unit you have but let's assume it has a 2nd order lowpass crossover which is 12db/octave (the most common).
> If you select 85hz as your lowpass point, because of the slope it still plays plenty of information beyond 85hz, just at a diminishing amount- The next octave above 85 is 170, at a 12db/octave slope the 170hz signal will still be coming through- just 12db quieter than your "cutoff" point of 85hz. At 340hz it will be 24db quieter, at 680hz it'll be 36db quieter than 85hz, etc. Eventually there's a frequency that's not reproduced at all, because of the signal being cut to the point it doesn't overcome the volume of the speakers.
> ...


this is a link to the sub i got

LSW127 - 12” 2000 Watt Legacy Steel Series Woofer @ LegacyCarAudio.com -

im running it with a legacy 1200w amp and the sub box is ported with sound proofing inside to make it more punchy and clean.

I tried the sub out on my house hifi and it sounded amazing but as i got it in the car it sounds brilliant dont get me wrong but still abit boomy.

Hence the reason why im trying to locate the 80hz mark on the lpf.

Another question if i was to set my amp on full xover and left the hu on 85hz will that make a difference or would it be pointless.

Thanks for the help so far btw

oh if this help for my hu info here's a instruction manual for it http://safemanuals.com/user-guide-instructions-owner-manual/JVC/KD-LHX501-_E


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## TREETOP (Feb 11, 2009)

The size of the enclosure, and the area and length of the port, are what tunes a ported enclosure. Tuning too high can make the sub sound boomy, tuning too low can lose output or make the sub sound floppy and uncontrolled. There are SO many variables in tuning a ported enclosure to a particular sub, to the particular vehicle, to the particular sound you're seeking. There's a lot more to a properly designed system than putting a sub in a prefabricated enclosure and adjusting the crossover frequency. 
There are no T/S parameters listed on the page you linked so I don't have any input on exactly what your sub needs for an enclosure for a certain response.

Your other question has already been answered.


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## gijoe (Mar 25, 2008)

TREETOP said:


> The size of the enclosure, and the area and length of the port, are what tunes a ported enclosure. Tuning too high can make the sub sound boomy, tuning too low can lose output or make the sub sound floppy and uncontrolled. There are SO many variables in tuning a ported enclosure to a particular sub, to the particular vehicle, to the particular sound you're seeking. There's a lot more to a properly designed system than putting a sub in a prefabricated enclosure and adjusting the crossover frequency.
> There are no T/S parameters listed on the page you linked so I don't have any input on exactly what your sub needs for an enclosure for a certain response.
> 
> Your other question has already been answered.


What Treetop is saying is that the problem you have with your sub being boomy isn't going to go away by changing the crossover point. I'll bet a different box will fix your problems.

On to your question about the crossover. Like treetop said, set it to anything higher than 85, you can turn it all the way to the right, which you said is 400hz. Set the crossover on the hu and the signal will already be set to 85hz at whatever slope. As long as your amp is set above 85hz it really doesn't matter.


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## Oo_ben_oO (Oct 20, 2009)

thanks guys you all helped me to solve it. I turned the amps LPF all the way upto 400hz and then kept the hu to 85hz and level 5 out of 8 and my EQ settings to flat apart from treble for my tops and it sounds alot better. thanks very much guys it sounds alot better now its seems to be hitting the low more as well as the high thanks very much again. cheers


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