+/- 3dB???

gregure

Ok, sorry guys. I know I've been here for awhile, and I really should know this, but it's just one of those things you think you know but never really were sure about.

When the specs for a sub reads lower limit +/- 3dB, what does that actually mean? I read it to mean that the sub is still going strong at that point, for example 20 Hz, and then begins to roll off, but is that correct? Does that mean it is still going strong at 20 Hz or not? For example, the Hsu VTF-3 says its lower limit is 20 Hz +/- 3dB in max. output, and 18 Hz in max extension, but most reviews I've read prefer the max output for the precision and impact. So, are you still getting decent output at 20Hz, or is it just able to reach those Hz, but not with power, at +/- 3dB? Thanks.

PS.
I know, I know, SVS is the best at lower frequencies, but I'm not sure my new place, or budget, will be big enough for an SVS at this point.

Dr. Spec

The -3 dB point (aka F3) is the point on the frequency response curve where the response falls 3 dB lower than the average level above.

That's only half of the equation.

How loudly it can play at that frequency with acceptably low distortion is the other half.

Taken together, they provide a good picture of the sub's low frequency capabilities.

http://www.hometheaterforum.com/htforum/showthread.php?s=&postid=2362682#post2362682

Go here for my review of the STF-2. Check the ground plane FR and THD numbers.

It's about -3 dB at 24 Hz and -9 dB at 20 Hz. But look at the differences in clean output. 75 dB @ 20 Hz and 92 dB @ 25 Hz - big difference.

In room (at the seat), the STF-2 hits 91 dB @ 20 Hz, and 100 dB at 25 Hz (10% THD). This is due to boundary effects and room gain, which helps boost the deepest frequencies.

So even though the in-room curve shows the STF-2 getting to 20 Hz, it can only put out 91 dB cleanly at that frequency. Damn good for a 40 lb, $400 sub, but it won't fluff your pants either.

EricH

I know, I know, SVS is the best at lower frequencies, but I'm not sure my new place, or budget, will be big enough for an SVS at this point. [/B][/QUOTE]


Well, their new 10" sub is only going to be $399, and their PB1-isd is $599. Their frequency response charts are pretty impressive for those price points:

PB10 95db @ 25hz
92db @ 20hz

PB1-isd 96db @ 25hz
95db @ 20hz
90db @ 18hz

bknauss

The +/-3dB points should be measured at 1W output. When you turn up the power to a real listening level, the freq response doesn't generally change all that much, so the spec'd numbers should be a decent guide.