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Sub sonic filter

 

Silver Member
Username: Johnnylemoine

LaPlace, Louisiana United States

Post Number: 145
Registered: Aug-04
can some one explain exactly why you need a sub sonic filter on when you have a sub in a ported box. What exactly will happen to the sub if the filter is not on? why does it do this? Please explain the mechanics and stuff about it.
Thanks.
 

Silver Member
Username: Johnnylemoine

LaPlace, Louisiana United States

Post Number: 149
Registered: Aug-04
damn, nobody?
 

ppi art
Unregistered guest
the subsonic filter will free up some of you amplifiers power, and may be used to protect a smaller subwoofer incapible of producing hz below 30.
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 2104
Registered: May-04
Below tuning, the subwoofer "unloads" from the box, performing as if the box wasn't there b/c the air in the port can't control the cone. This equates to extreme excursion (possibly overexcursion) and if you don't run a subsonic filter, it could result in mechanical damage to the subwoofer.
 

Silver Member
Username: Audiobahn_man

Freakmont, MI

Post Number: 156
Registered: Aug-04
I have 2 V-Max's and a Sony 1200w amp, in a 4.3 cubic foot box with 1 inch of insulation on each sides tuned to 33 Hz, do i need a filter, my amp already has a low pass set on 110 Hz?
 

Juggalo Jeff
Unregistered guest
alright ya'll i have 2 10" alpine type r's in a q logic box which can be sealed or ported right now it is ported and the port tubes are to specification 12" inches each my amp has a subsonic filter on it but the level is all the way down are my subs being hurt at all and how do u kno what ur tuning is at
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 2128
Registered: May-04
Steven, a subsonic could probably help you, I'd go w/ about 25 hz.

Juggalo Jeff, depends on what the box is tuned at. 5-10 hz below the tuned frequency usually works well. Better safe than sorry, hard to say whether they're stressed mechanically or not (or ever will be) but as they say "an ounce of prevention is worth a pound of cure".
 

Silver Member
Username: Audiobahn_man

Freakmont, MI

Post Number: 158
Registered: Aug-04
will it make it sound better?
 

Silver Member
Username: Johnnylemoine

LaPlace, Louisiana United States

Post Number: 151
Registered: Aug-04
alright guys, thanks for your input.
 

Juggalo Jeff
Unregistered guest
how do i kno what my box is tuned at?
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 2149
Registered: May-04
Steven, it could possibly if you're having trouble at really low (below say 25 hz) bass tones and your sub is bottoming out at loud levels, but very little music gets that low, so w/ most songs you probably wouldn't notice a difference. The amp will have more power since it isn't having to produce those tones as loudly (subsonics take a LOT of power). But of course, that only applies when the music has that signal on it. Basically, it's more for prevention than it is for sound.

Juggalo, it depends on the size of the enclosure, surface area of the port and port length. Also depends on the subs displacement.
 

Juggalo Jeff
Unregistered guest
well i just have a q logic box with 2 10" alpine type r's(1041d) it is ported right now the tubes are both 12 inches right now which is what the sub calls for and the diameter is 3 inches maybe 4. I believe the box volume is 1.0 cu. ft for each sub
 

Silver Member
Username: Fishy

Tamarac, FL USA

Post Number: 392
Registered: Sep-04
If that's one cubic feet AFTER accounting for port and speaker displacement then your tuning frequency is

1) aprox. 47 Hz for a 4" round port

2) aprox. 36 Hz for a 3" round port

Gonna be a lil higher for both if the volume is somewhat less.

-Fishy
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 2155
Registered: May-04
I don't know if that 1.0 cu ft volume is net or gross, but you're best off giving me the internal dimensions of the box for each subwoofer. Also, make sure what diameter the port is, an inch diameter makes a huge difference in tuning frequency.
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 2156
Registered: May-04
Ok, found your box on Crutchfield. I trust Fishy, and the fact that most prefabs are in high 30s and 40s anyway. That box uses 3" ports, so your tuning is in the high 30s. Subsonic of about 30 hz will work.
 

Silver Member
Username: Fishy

Tamarac, FL USA

Post Number: 397
Registered: Sep-04
Oh crap. Trust.

Now I gotta double check.

-Fishy
 

Silver Member
Username: Fishy

Tamarac, FL USA

Post Number: 398
Registered: Sep-04
36.27 Hz with 12" long 3" i.d. port in 1.0 ft^3.

:-)

-Fishy
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 2161
Registered: May-04
I gave you a reasonable margin, high 30s was all I expected of you ;).
 

Juggalo Jeff
Unregistered guest
yea thats what it is i just have a power acoustik amp and it has the sub sonic filter on it just the dial it goes from 30 hz to 175 hz and i got it all the way down on 30 hz so this is fine right
 

Silver Member
Username: Fishy

Tamarac, FL USA

Post Number: 437
Registered: Sep-04
Yeah, thats probably fine.

I have my box tuned at 28.8 and I run mine about 20 Hz.

-Fishy
 

Juggalo Jeff
Unregistered guest
aight thanks jon and fishy for all that
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