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Where can i get an inline subsonic filter???

 

Anonymous
 
i am building a vented box for my sub and i have a JBL BP600.1 amp that i wanna use on it.

i wanna tune the box to 34hz and i need an inline subsonic filter because i dont have one on my amp....where can i get one that will be 34hz???

also do they make variable inline subsonic filters?

or should i just buy another 600 watt amp that is 1 ohm stable w/ a built-in filter???if so suggest an amp....
 

New member
Username: Tbone

Post Number: 7
Registered: 02-2004
The Inline "Subsonic" filter you are seeking is called an "F-mod" and I think they are available online at Crutchfield. However, I do not think that you need a "Subsonic" filter for 35 hz, natural rolloff below 34 hz will occur naturally, and you are really looking to cancel all higher frequencies (90+) from your subs. Actually, you tune a ported box by various Port Tube Lengths and Widths, not with a filter. I would suggest installing a Crossover to help you optimize the sound quality of your system.
 

Gold Member
Username: Glasswolf

Post Number: 1409
Registered: 12-2003
Tbone, the JBL amp has it's own low-pass filter built into the amp.
when using subs in a vented box, you do want a subsonic filter, otherwise the subs will try to reproduce frequencies below the ports' tuned frequency, which is often 35-45Hz, and well above the lowest frequency the subs can hit (particularly since boxes are usually tuned above the Fs of the sub) and if the subs do try to hit a frequency below the port tuning, the sub loses damping, and will easily over-excurse.
Then you get a fried sub.

Sealed boxes retain damping all the way down the line, and with cabin gain below the transfer point, combined with natural roll-off 'in a sealed box' you will get a flat response down to about 9Hz.

in a ported box, you want to cut off the amp with a high-pass SSF just below the tuned port frequency, then use a low-pass filter on the amp at around 80Hz, effectively making a notch filter, although the SSF is usually 24dB/octave, and the HPF is usually more like 18dB/octave.
 

Bronze Member
Username: Tbone

Post Number: 13
Registered: 02-2004
Do you think that Coils rolloff fast enough to accomplish this? This could be a cheap alternative, even though it would take away a little power.
 

Anonymous
 
where can I get the shiznit I need?
 

Bronze Member
Username: Tbone

Post Number: 17
Registered: 02-2004
Well, if the amp has its own low-Pass filter you could start by switching it to low-Pass, that should take care of the high Freqencies, as for the Sub-Sonic filter you could check online. Anyway, by switching on the Low Pass filter, you are halfway there.
 

Anonymous
 
All the JBL BP600.1 has is a Low-pass filter....i have the filter set at around 90-110hz now and i know i NEED a subsonic filter!!!

i can't find one!!! I've seen the ones that just plug into your RCA's and i think that is the kind i need!!!

Where can i find one that will work right on my amp and sub when i tune the box to 34hz???And the only ones i have ever seen had a set frequence for a cut off point...is there a variable inline subsonic filter out there that i could get??? Does anyone know a website or something that i can get either one??????
 

Bronze Member
Username: Tbone

Post Number: 21
Registered: 02-2004
I purchased my at crutchfield, but it has been quite awhile ago, and i am not sure if they still offer them, I will check though.
 

Bronze Member
Username: Tbone

Post Number: 22
Registered: 02-2004
Just check crutchfield, and they have the inline ones for $30.00, the only problem is that they start a 12 db rolloff at 50 hz, and you want to tune the box all the way down to 35 hz. They did have an active Kicker 3-way crossover for $149.00 that let you high pass the front and rears from 35 hz, sounds like what you need, run of the rear output, not the sub output, and set it for 35 hz. I would suggest going to local audio shop in your area and seeing if they had an active crossover with high-pass outputs vairable to 35 hz. They would also help with some questions since you will be purchasing it from them. Let me know.
 

helpmeplease
Unregistered guest
Well.....I found a 30hz subsonic filter but i dont have room in the box to tune it to 30hz

Can i tune the box to 34hz and still use the 30hz filter....or is this a no go....will i get enough roll off???.....

also i may have enough room in the box to tune as low as 32hz....no lower though.....

please please help....i need to have the box built in a week or so!!!!
 

Bronze Member
Username: Tbone

OK United States

Post Number: 93
Registered: Feb-04
Makes me wonder if you could add polyfill to make the subs think they have even more airspace, which usually works on sealed boxes. If they think they have more airspace then you could tune it to 30 hz. Don't know, I usually only use polyfill in small sealed boxes, and have never tried it in a vented box though.
 

Anonymous
 
the prot length is what is holding me back here....not air space

i think that the 30hz subsonic filter have a 12 db per octive roll off rate....and an octive lower than 30 hz is 15 hz...right???

if so then one octive lower than 34hz would be 17hz....would this be enough for my sub????or would i get too much over excursion and blow it like this????....i mean the roll off rate isnt that much of a difference....or is it enough to realy matter ????
 

Bronze Member
Username: Tbone

OK United States

Post Number: 97
Registered: Feb-04
Yeah, that would be fast enough roll off. If the port length is the only problem, use a bendable port.
 

Anonymous
 
So if i tune the box to 34hz and use the 30hz FMOD then it'll be just fine???right???
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