Subwoofer calibration, for the 2-channel challenged..

steveinaz

Ok, Dr. Spec, other well informed folk's, etc....see if I got this right:

1. Download some freq sweeps (15Hz-100Hz, I guess would do it for a 25-31?)
2. get RS SPL meter
3. Turn-on both main/sub speakers
4. Run sweeps and take measurements at listening position of each freq's dB level (keeping master volume constant)
5. Plot and look at curve to see how response looks
6. Adjust XO freq and Phase as necessary to flatten response as much as possible, re-measure and check
7. Set level of sub to your hearts desire

tryrrthg

You may want to run a frequency sweep of your mains alone, just to see what they're doing alone, and see where you might want to set your low pass x-over. then add the sub to see what it does to the curve, then you might also want to see what the sub does alone. all doing this without changing the volume.

I've been trying to do this with my system but I'm moving next week so I didn't bother giving myself a headache trying to get it perfect quite yet.

steveinaz

Ok, I'll do that. Looking at my Athena's response curve in the Stereophile review, it shows about a 3dB drop at 35Hz, comes up to reference at about 42Hz. This being the case, I figured I'd start at 60Hz on the SV XO and work my way down...sound reasonable?

RuSsMaN

You can do all that, sure.

I say just sit down and listen to familiar material, and start twistin knobs. Your ears are the best instrument you have to get your 'blend' right.

Cheers,
Russ

tryrrthg

My "little" dyn's say -3db at 41hz, but I'm still getting HUGE amounts of bass in the low 30's without a sub (thank you very much room gain). So I've got my crossover as low as it will go (40hz). From there I just mess with the phase. I wish I could crossover a little lower. Other than that, that's all the farther I've gotten, the rest was by ear, like Russ said...

Dr. Spec

Great advice - all. Mains alone is critical; what they did in Sterephile and what they do in your room are two different things.

Make sure to check the mains at a realistic volume to see where they "really" trail off when they are asked to move some air. Don't scorch the VC's, though - sine waves are killer on woofers and only run it long enough to stablize the meter and grab a reading and then shut down and let the VCs cool off. Ditto for the SVS when you bring that into the loop.

Phase will be critical, and evaluating what the mains do alone, and also when the SVS is brought on line will be an important part of finding the right phase setting. The gain part will be pretty easy - adjust it until the transition from the mains to the sub is fairly stable and smooth in overall level.

Expect some room gain below 35 Hz and I wouldn't worry much about that; it's too low to affect the SQ (from a boom standpoint) on music. In fact room gain is generally considered a positive attribute by most since the human ear is less sensitive to the lowest frequencies and a boost in the 30-20 Hz region sounds and feels great to most people without adding a hint of boom or bloat.

steveinaz

Here's the Athena AS-F2 in-room measurements (stereophile), I know this doesn't do much good, but I was thinking it might show potential problem areas with crossover settings...

steveinaz

See...I told you I was ANAL. The damn thing isn't even here yet and I'm stressing...LOL!

Dr. Spec

Interesting. The Athena's actually start signing off at exactly 60 Hz.

Because of room gain, they are back to baseline at 40 Hz, but the important thing to realize is that the 40 Hz level is already down considerably from the 60 Hz level.

If you were to place them outside and run a ground plane sweep, they would start trailing off from baseline at exactly 60 Hz.

Maybe your guess at 60 Hz wasn't such a bad one, Steve. :-)

In comparison, when SVS does ground plane tuning, the subwoofer is tuned to maintain a flat output to the rated tune point before trailing off. That's OUTSIDE.

Due to room gain, in Steve's room, the 25-31PC+ will not reach baseline levels again until about 21 Hz. That's why this model is so popular with the music and HT crowd - it trolls very low despite its (very) conservatively rated tune point.

The 20-39 gets to 16-17 Hz in room, and the 16-46 gets to 12-13 Hz in room! Frankly its amazing the extension and air moving capability of these subs.

steveinaz

See! I knew posting that graph would shed a little more light on the situation...Thanks Doctor!

Given the "honest" nature of SVS, I figured their ratings would lean to the conservative--that, and the fact that I favor absolute output over "bone-grinding" bass led me to selecting the 25-31 over the 20-39.