Full Version: How important is a subsonic filter?
How important is a subsonic filter in subwoofer amps? What does it do exactly? Block out all frequencies below what the sub can do? Does this help to not blow the sub? Does this help quality of output? Thanks.
subsonics are a HP filter that you set to a frequency below the audible spectrum. they are usually 'steep' (eg: 24dB/oct) and variable, allowing a setting around 10~40Hz.
they are more important with ported subbox enclosures. ported boxes will have a 'tuning frequency', where the sub/box combo will play down to ok then roll-off dramatically (ie: not reproduce very loudly). if you deliver the sub a frequency that's below this, then the sub is no longer damped by the port, so behaves as if it is 'free-air' to a degree. this means it can fairly easily over excurt and distort.
you have to determine if the tuning frequency is high enough that you would expect your music recordings to deliver frequencies below it. however, most ported boxes are tuned no higher than ~40Hz. it means you should avoid playing loudly frequencies below this; then again, few recordings offer much subbass down that low. but you could use a subsonic set to around 40Hz to help.
in sealed setups it is less important cos the box will always dampen the sub's excursion and limit overexcursion and distortion.
regardless, it can help the amp. by removing the sub-subbass, the amp won't have to struggle so hard to amplify it and make the subwoofer reproduce it. this will theorectically improve SQ.
not essential, worth having for ported; otherwise it's a bonus.
they are more important with ported subbox enclosures. ported boxes will have a 'tuning frequency', where the sub/box combo will play down to ok then roll-off dramatically (ie: not reproduce very loudly). if you deliver the sub a frequency that's below this, then the sub is no longer damped by the port, so behaves as if it is 'free-air' to a degree. this means it can fairly easily over excurt and distort.
you have to determine if the tuning frequency is high enough that you would expect your music recordings to deliver frequencies below it. however, most ported boxes are tuned no higher than ~40Hz. it means you should avoid playing loudly frequencies below this; then again, few recordings offer much subbass down that low. but you could use a subsonic set to around 40Hz to help.
in sealed setups it is less important cos the box will always dampen the sub's excursion and limit overexcursion and distortion.
regardless, it can help the amp. by removing the sub-subbass, the amp won't have to struggle so hard to amplify it and make the subwoofer reproduce it. this will theorectically improve SQ.
not essential, worth having for ported; otherwise it's a bonus.
Thanks! that pretty much covers it all... I was asking because I had a choice between the following sub amps for a 4ohm single coil sub (400w rms nominal, 800w max)...
Soundstream Tarantula 700.2 (2 channel amp bridgeable for 700w rms @ 4ohms)
12db crossover
heaps of features i dont understand
recommended by my installer (freeway car audio)
NO subsonic filter
looks REALLY nice
or
Phoenix Gold Ti 800.1 (mono that does 400w continuous RMS @ 4ohms)
has subsonic filter
24db crossover
heaps of features i dont understand
looks nice
Soundstream Tarantula 700.2 (2 channel amp bridgeable for 700w rms @ 4ohms)
12db crossover
heaps of features i dont understand
recommended by my installer (freeway car audio)
NO subsonic filter
looks REALLY nice
or
Phoenix Gold Ti 800.1 (mono that does 400w continuous RMS @ 4ohms)
has subsonic filter
24db crossover
heaps of features i dont understand
looks nice
so does that mean that the subsonic filter should be set to or higher than the frequency the box is tuned to?
so does that mean that the subsonic filter should be set to or higher than the frequency the box is tuned to?
Subsonic filters aren't really needed for sealed woofers, as the air spring offered by the box protects the woofer against over excursion in the bottom octave of music. Subsonic filter are, however, very handy for protecting woofers in ported systems and should be set just below the woofer's tuning frequency. This is because just half an octave below tuning frequency - say 22.5Hz for a 30Hz tuning - the woofer is 180% out of phase to the port and effectively has zero power handling.
Think of it like a rev limiter for your woofer!
Think of it like a rev limiter for your woofer!
if you have a sub that is designed for a ported box..then id use the ported box design
Once you port a sub i would definitely recommend a subsonic filter set at or just below tuning frequency of your sub.
we did some leap models of my sub a while ago and it basically stated without a subsonic filter the sub would try and move 53mm @10hz. In band it was estimated (by leap) that the sub would travel at 20mm@30hz. BAsically you want to move your sub towards xmax in-band you have to use a subsonic filter to control cone movement below the tuning port.
so to sum up. if you use a ported box a subsonic filter will reduce distortion.
Once you port a sub i would definitely recommend a subsonic filter set at or just below tuning frequency of your sub.
we did some leap models of my sub a while ago and it basically stated without a subsonic filter the sub would try and move 53mm @10hz. In band it was estimated (by leap) that the sub would travel at 20mm@30hz. BAsically you want to move your sub towards xmax in-band you have to use a subsonic filter to control cone movement below the tuning port.
so to sum up. if you use a ported box a subsonic filter will reduce distortion.
There is very little sub 40Hz info in 99% of music and I've never used a subsonic filter on any system I've owned or used. I have yet to blow a subwoofer through over excusrion below 40Hz in ten years and over what must now be 500 woofers used.
Again think of a subsonic like a rev limiter. It is nice insurance but unless you intentionally 'over rev' your woofer there's bugger all chance of hurting it through over excursion during normal music usage.
Again think of a subsonic like a rev limiter. It is nice insurance but unless you intentionally 'over rev' your woofer there's bugger all chance of hurting it through over excursion during normal music usage.
QUOTE (Damon)
There is very little sub 40Hz info in 99% of music and I've never used a subsonic filter on any system I've owned or used. I have yet to blow a subwoofer through over excusrion below 40Hz in ten years and over what must now be 500 woofers used.
Again think of a subsonic like a rev limiter. It is nice insurance but unless you intentionally 'over rev' your woofer there's bugger all chance of hurting it through over excursion during normal music usage.
Again think of a subsonic like a rev limiter. It is nice insurance but unless you intentionally 'over rev' your woofer there's bugger all chance of hurting it through over excursion during normal music usage.
But then again you are a bit of a softy when it comes to ported boxes woofers and heaps of power! :hehe:
Softy?
Well, if I was a thrasher who constantly pushed the redline all the time a rev limiter would be wise. For some reason, though, I seem to be able to play a system how I want with what music I want and have never needed a subsonic.
For thrashers they make more sense.
Well, if I was a thrasher who constantly pushed the redline all the time a rev limiter would be wise. For some reason, though, I seem to be able to play a system how I want with what music I want and have never needed a subsonic.
For thrashers they make more sense.
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