# How to set subsonic filter properly?



## SQ Monte (Sep 12, 2009)

I just finished up with the rebuild of my system (see sig) last weekend and when I was setting the dials on my sub amp before powering it up I set my subsonic filter to what I thought was around 20Hz. After listening to a few songs I realized that it wasn't getting as low as it should considering my box is tuned to 30Hz and my xover is set to 100Hz so I turned down the SS filter a little more and it sounded alot better.

This got me thinking, isn't there a more precise way to set the subsonic filter other than eyeballing it? If anybody knows can you please share it with me? I'm probably going to leave it as is until my new wiring arrives (hopefully by next weekend) but once I have my wiring i'm going to rewire my amps so it all looks neat back there and I'll want to set the SS properly while i'm at it.

Thanks in advance


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## Austin (Mar 12, 2009)

I usually just try to play the lowest hitting song i can find or some sine waves and turn it up as loud as i would have it then adjust it so it doesn't bottom out.


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## alachua (Jun 30, 2008)

The best way is to do exactly what you are doing. Set it and listen. Keep an eye on the subs to make sure they aren't bottoming out and just keep playing with it until you find a setting you like best.


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## 60ndown (Feb 8, 2007)

http://www.realmofexcursion.com/downloads.htm

use these


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## MarkZ (Dec 5, 2005)

alachua said:


> The beat way is to do exactly what you are doing. Set it and listen. Keep an eye on the subs to make sure they aren't bottoming out a d just keep playing with it until you find a setting you like best.


x2

What kind of subs and enclosure?


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## TREETOP (Feb 11, 2009)

As a very general rule of thumb, I usually set an infrasonic filter 1/3 octave below tuning frequency.


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## sqshoestring (Jun 19, 2007)

TREETOP said:


> As a very general rule of thumb, I usually set an infrasonic filter 1/3 octave below tuning frequency.


Right, or play tones lower and lower and when it unloads excursion will go up you will see it. Play that tone and turn the subsonic up until it settles down, so you can play tones back down and it does not have more excursion with the lower tones under your tuning. If you beat it hard then set it a little higher so you are not wasting any power on the unloaded tones, but right it will eat into your bottom response.


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## SQ Monte (Sep 12, 2009)

Thanks for the responses, I guess I'll continue doing it by ear then. 

A buddy came by yesterday and we drove around town pounding so he could check out the new setup and he came away from it with this take, "it kills on songs in the mid 30's and up but can't hang on the lows." I want to change that! I'm not expecting my setup to murder 20Hz tones but mid to high 20's would be nice. Right now my subs are in a box that's 4 cubes and tuned to 30Hz...suggested enclosure size is 1.75 per sub, tuned to 30Hz. Think my box is the culprit or will my setup just not play that low no matter what I do?


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## 60ndown (Feb 8, 2007)

make the port 6% longer should tune it a little lower.(are you certain the box is tuned to 30 hz?)

pita tho. 

or 

seal the port and you have a big ass sealed box which will play very low with reduced power handling. 

id start with setting the ssf @ 23 hz and take it easy on the volume until i was sure, then drop it to 22, 21, you might find you dont need it at all, any ssf setting will deny you the low lows, but it protects your sub from over excursion and damage.

if your smart, and USE YOUR EARS AND YOUR BRAIN you will hear if your sub is doing something it shouldnt and can turn it down a notch. 

you have strong subs i dont think you will have any problems turning the ssf off, 

as long as you listen to how they are performing, any noise that sounds off, turn em down a notch.


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## SQ Monte (Sep 12, 2009)

60ndown said:


> make the port 6% longer should tune it a little lower.(are you certain the box is tuned to 30 hz?)
> 
> pita tho. or seal the port and you have a big ass sealed box which will play very low with reduced power handling.
> 
> ...


Yep, i'm certain it's tuned to 30Hz. If i'm going to do anything, I'd build a new box built to exactly 3.5 cubes and tuned to 30Hz.

The song we're basing our assessment off of is "Demons" by Tech N9ne, that song has a low note in it that's pretty sick and I've heard what it should sound like both in my HT and on my boys setup 2 15's, 6k watts....I know, I know, alot more cone area and way more power but i'm not expecting the loudness of his but I do think my setup should be able to kill that low note though especially tuned at 30Hz.

Do you think my expectations are too high?


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## MarkZ (Dec 5, 2005)

What vehicle is this? And what's your buddy's vehicle? That could help explain the disparity.


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## SQ Monte (Sep 12, 2009)

MarkZ said:


> What vehicle is this? And what's your buddy's vehicle? That could help explain the disparity.


My car is a 04 Monte Carlo, he's got a 04 F150


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## sqshoestring (Jun 19, 2007)

With my IB subs I run 15Hz SS, it hits 20 just fine but I do have to EQ it up with these subs. My new ones should be better. Right you will have to port it lower, watch the excursion on low notes. It will unload under tuning and xmax.


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## RENAULT10 (May 24, 2010)

HI SQ MONTE.

The port works as a bandpass filter, so the first thing you must to do is verify the frecuency response of your sistem, you can use a decibelimeter or a rta begining with the lower tone you can use, you must to draw a chart. with the values of your response, with this you will find the peak frecuency of your enclosure, once done this you can determinate de frecuency -3 dB of the port, 

From this value to the lower frecuencies, your enclosure works as a infinite bafle, thus there is no damping to the cone, the excursion increases, and the control is minimum. decreasing the amount of sound.

for example: if you detect that the -3dB point is set at the 26 Hz in your chart, you have to use this frecuency with a tone generator, and do the next, identify in your chart the peak value for your port and take that value. we can say 90 dB. 

use your 26 Hz tone and calibrate your sistem to get the same 90 dB measured with your dBmeter or RTA, now begin to adjust your subsonic filter up to the position where the amplitud gets 3 dB below your initial value, that is 87 dB. whith this action you have adjusted your subsonic filter to the exact frecuency where the information begins to waste power with no benefits. 

I hope my poor english and my coments can help you.


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## tinctorus (Oct 5, 2009)

60ndown said:


> make the port 6% longer should tune it a little lower.(are you certain the box is tuned to 30 hz?)
> 
> pita tho.
> 
> ...


Wouldnt a sealed box INCREASE the power handling???
I have always been told that sealed boxes require more power as they are not as efficient


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## Austin (Mar 12, 2009)

tinctorus said:


> Wouldnt a sealed box INCREASE the power handling???
> I have always been told that sealed boxes require more power as they are not as efficient


Yes but as you get to bigger boxes the cone control of the small box goes down and you approach a situation like IB where it can bottom out easier.


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