Subwoofer measurements

Drumingman

OK , you own a big subwoofer that rattles the mantle. You claim it hits 20cps.
If you're playing a movie or music at 85 to 90 db, if you have a program playing that requires a 25Hz reproduction, which would probally be a pipe oragn or an explosion, how many watts would it take to do this with a 12 inch sub with a sensitivity of 90 dbs@ 1 FT. When playing notes this low through this single driver at this sound pressure, what is the distortion level of the sub?

ohskigod

I'm not an expert, but the power requirements depend on how big the box is. if its got alot of displacement, that usually means not as much relative power as trying to pull off big bass in a small cabinet.

infinite baffle subwoofers can have multiple drivers and still not require much power to get the drivers to Xmax.

for my DIY sub, (142.5l displacement, which is like 5 or so cubic feet), I use a 500 watt sub with the svs 12.1 driver I just swapped in (from a shiva driver) seems to be just about right, but I could probably get away with 250 watts as well.

RuSsMaN

Come on Lou, play along. This one BEGS to be f'd with.

PolkThug

1 watt. 0 distortion.

Drumingman

It is a serious question. When listening to music 10 or 15% distortion would probally not be acceptable through the mid range and high end, or would it?
I know some of the higher end speakers tell you about the distortion levels of their product. I find it hard to believe that a single 12 inch sub can reproduce very low frequencies at a decent listening level without introducing a significant amount of distortion, and this can be true in the 30 to 40 Hz range.
When buying a sub does your specs include these numbers?

unc2701

Usually these specs are not included... see:
http://www.polkaudio.com/homeaudio/specs/psw1000/

no distortion spec.

Now some drivers specs will include it, but that's pretty rare:
http://www.madisound.com/pdf/aurasound/NS18-992-4A.pdf

regardless, I fail to see where you're going with this...

PolkThug

Drumingman wrote:

I find it hard to believe that a single 12 inch sub can reproduce very low frequencies at a decent listening level without introducing a significant amount of distortion, and this can be true in the 30 to 40 Hz range.

Believe it. Good quality subs (ie SVS) won't distort at reasonable volumes. Of all the freq testing on my PB10's, I never saw any 1st or 2nd order harmonic distortions that were above the noise floor of the room.

Why did you bring this up? Maybe you are hearing other objects in the room resonating.

ohskigod

how do you find it hard to believe? and yet subwoofers exist. Mine plays low, it doesnt distort. I dont care what the stats are, I trust my ears.

Dennis Gardner

I've read that SVS considers 10% to be the human hearing threshold at sub frequencies.

univera

It seems that most built in sub amps aren't nearly as clean as amps specifically designed for mains because they don't have to be. I am sure there are plenty of exceptions.

Drumingman

Gee, you guys sure are on the defense today. I thought it was a legit Q considering the cost of a real good sub and the quality you like from your main drivers. Considering a 12 inch sub has to move 1&1/2 to 2 inches to reproduce a 20hz tone and then it pulling double duty by playing the channels from both sides, seems it would make it very hard for the driver to do. Now I know most folks on this forum have subs, and I even have a passive one. Because the lower notes are the the most difficult to reproduce and I was shopping around for a good sub I looked at some full range speakers that had very low distortion across the audio spectrum. but some of these speakers used multiple woofers per cabinet in order to acheive this low level. So this brought me back to the distortion levels in a Single High Powered Sub. Yes, I think most subs can reproduce a good bass signal down to 35 to 40 cycles but I also believe that when it gets much lower at reference levels the manufacturer will not publish these numbers because of the distortion levels. It's just something I've been pondering before investing in a sub with vague specs.

tryrrthg

Drumingman wrote:

Considering a 12 inch sub has to move 1&1/2 to 2 inches to reproduce a 20hz tone

Not true of most decent ported subs. When I say "decent" I mean subs that are actually tuned in the 20-25hz range. The driver is actually moving the LEAST around the tune point. At or near the tune point you are getting most of your output from the port and very little from the driver. The driver really has to work after the tune point, but the ported design rolls off so quickly after the tune point that it doesn't have a whole lot of output anyway.

Of course all of this is based on a ported sub. Because of the sealed design's roll off, a sealed sub will need a whole lot of excursion and a lot of EQ and or room gain to play 20hz.

Check out the secrets of HT reviews of subwoofers. They do a lot of disctortion and max output measurements. Club Polk's own Dr. Spec is now a reviewer there.