Calling Dr. Spec!

steveinaz

Will the SVS 25-31 PC Plus that I'm considering work well for 2-channel only system? I'm still stressing because I like my music reproduced very accurately and still wonder if a sub may over-bloat my sound? It would be used with a pair of Athena AS-F2 towers (35-20kHz, +/-3dB)...

Your opinions are most welcome and appreciated...

VR3

No.....

I havnt found a frequency or volume that makes my SVS stand out in any way and its the bottum of the line.

They are very accurate and move everything in the house. And my neighbors house, and I cant exactly sit there and tell ya where its at, well actually I can.....its this gigantic 16 in wide, 31 in tall cylinder. lol...

They are awesome, go for it!

tryrrthg

If you're looking for the flattest in room response for music you may want to look at the 16-46. The 16-46 will gradually roll off slower than the 25-31, and when you factor in room gain, that gradual roll off will most likely be brought back "up" giving you a flatter in room response.

Where as the 25-31 and room gain may actually give you a hump in response around the tune point and then drop off quickly after that.

Also "theoretically" the transient response on the lower tuned sub will be better, but I doubt you'll be able to hear it. In all cases I'm sure you'll be more than happy. If it were me I'd go for the 20-39 and get the best of both worlds (SPL and extention).

steveinaz

Cool, thanks for the tips fellas. I will keep the 20-39 in mind...

Dr. Spec

Great responses. (thumbs up)

"Bloat" is usually a function of emphasis in the 40-60 Hz region.

Depending on the size of your room, room gain can vary from nothing to quite significant. Room gain and boundary gain are two different things. Boundary gain is an overall (uniform) increase in total SPL going from anechoic to a room with six boundaries.

Room gain is a phenomenon where the lowest frequencies are boosted. The smaller the room, the more room gain you will see, and the earlier in the spectrum it will occur.

Regardless of the model you select, they will all exhibit similar room gain, since it is a function of the room more than the sub.

While the tune points and rated extension of the enclosures clearly differ, SVS goes to great extents to ensure they all exhibit a nearly identical FR curve down to about 22 Hz.

Below that, the 25-31 will begin to trail off, and below 17 Hz the 20-39 will trail off. The monstrous 16-46 will not start to trail off until about 13 Hz.

If you plug a port on a variable tune model, then you DO lose some output above the tune point, and this must be compensated for by upping the calibration level about 1.5 dB.

I agree, the 20-39 enclosure is a nice blend of extension and output, but all three subs will exhibit nearly identical group delay and impulse response characteristics (collectively known as transient response) down to the tune point. GD always skyrockets at the tune point, but if the sub is tuned low enough, the human ear cannot reliably detect GD shifts in the 25 Hz or lower region.

The 25-31 is the best choice for aggressive HT applications in larger rooms. It still has good extension to 20-21 Hz and the tune point is 25 Hz (where woofer excursion is limited and tightly controlled), so it is very difficult to bottom out due to overexcursion. It will also exhibit the lowest THD of the three models in the 23-30 Hz bandwidth for the same reason; less cone excursion = less distortion.

The 16-46 is easier to bottom out in comparison since it is tuned to 16 Hz and the woofer gets no help from the resonators in the more common bass regions of 20-30 Hz, and cone excursion is considerably higher to achieve the same output level.

Overall, any of them will do a fine job with most popular music. The 16-46 is really only needed for full bore 32 foot organ with true 16-17 Hz notes. Any of them would excel with rock, pop, fusion, jazz.

Doc

steveinaz

Thanks Doc, I appreciate you taking the time. You ARE the "bass authority" as far as I can see. :cool:

Dr. Spec

Thanks, and tryrrthg's post was excellent too.

Based on what I have seen from both 20 Hz and 25 Hz models in my room, he may be right about the 25 Hz model have a "slight" emphasis in the 27-22 Hz region as compared to the 20 or 16 Hz models, but it probably won't be more than about 2 dB in that region.

All the models will pretty much react the same way in the same room/location down to about 22 Hz and then you'll see significant differences in extension below that point.

In a small to moderate size room, I would definitely count on room gain with any model.

Here's an example for the PB1-ISD vs. the STF-3 both near field and in-room. Note the significant room gain for both models starting below 30 Hz on the in-room screen shot. You won't hear/notice room gain on anything but the deepest music passages; on 99% of popular music, you would have no idea it was even present.

You can expect the 25-31PC+ to behave similarly in room to the PB1-ISD. Naturally, the Plus can be tuned even deeper, if you desire - at the expense of some output loss in the higher registers.

Doc

tryrrthg

Originally posted by Dr. Spec
Thanks, and tryrrthg's post was excellent too.

Thanks Doc!

Steve, if it makes you feel any better. I just finished a DIY sonosub with the original SVS driver (now replaced with the ISD). It is tuned just a tad over 20hz. When I finished it, I pretty much just put it in my room, set it up by ear in about 5 minutes and then ran a frequency response curve. It is ugly! I had over a 15dB hump between 55 and 25hz and another small hump between 85 and 65. Granted I've still got some adjusting to do to placement, etc, but my sub still never sounds bloaty. even with that hump it sounds tight and punchy. And this is from the lowliest driver that SVS has ever produced. Granted it's no slouch but it sounds great. I can't wait to upgrade, if it's not with an infinite baffle or another DIY (because they're so fun) it will be an SVS.

Good luck!

steveinaz

Thanks all for the excellent input. I think I have a good listening room, rectangular, about 14' wide by about 26' deep. The ceiling is vaulted and ranges from 8' (left wall) to about 12' at the center. My system is against the 14' wall, with my couch about 10' from the speakers, which are about 8' apart. My thought is to place the SVS cylinder in the corner by the left speaker, as there is about 26" of space from the back side of the left speaker.

Ceruleance

If you want really accurate bass you should consider an SVS with a parametric equalizer. I have a nice room gain hump in my HT at about 55hz, once I equalized it the realism of the bass improved. Explosions sound more like explosions and outdoor rock concerts sound more like outdoor rock concerts, in neither case does it sound like the "subwoofer is playing a tone now".

tryrrthg

Originally posted by Ceruleance
If you want really accurate bass you should consider an SVS with a parametric equalizer.

I agree, the more I read about subs the more I realize that unless you get REALLY lucky with your room, you'll need to EQ a sub to get the BEST results.

I hope to get a Behringer Feedback Destroyer in the future. From what I've read this thing is worth it's weight in gold to the bass-head. Obviously there are better EQ's out there but this thing does a great job for the money, from what I've read...

gatemplin

The BFD 1124 is excellent. I had a huge 15-20 dB hump around 40 Hz in my room. I easily tamed it and it was like having a whole new sub. I also added some boost in the teens and twenties.

If you want to learn more about the BFD check out http://www.snapbug.ws/bfd.htm

It is not as hard to use as it may first appear. If you get stuck there are many experts over at HTF.

kberg

Hey Doc,

Interested to hear your thoughts on the BFD 1124...Thx, KB

Dr. Spec

Originally posted by kberg
Hey Doc,

Interested to hear your thoughts on the BFD 1124...Thx, KB

Never used it. If my room needed one, I'd probably have one by now.

The snapbug guidance document is apparently a God send for new users. The BFD seems to do a very good job for very little $$ once use of it is mastered.

Clearly, accurate FR measurements are needed to properly correct/compensate for room modes. I think the minimum should be 1/12 octave test tones and the RS meter with correction factors. It's not perfect, but it will reveal large peaks/nulls.

Finally, boosting nulls is a bad idea which is usually met with limited or no success. Placement and phase should be the first tools used, and then peaks should be cut only after that.

gatemplin

Originally posted by Dr. Spec
Finally, boosting nulls is a bad idea which is usually met with limited or no success. Placement and phase should be the first tools used, and then peaks should be cut only after that. [/B]

Yep, the BFD wont help much with nulls. I tried boosting but it makes little difference and there is only +16dB boost. I have found that changing phase can make a big difference in response.

Another advantage to the BFD is that you can make a house curve in the frequency response which is what I did.

kberg

Thanks, Doc. I have yet to do the FR sweeps and curve creation. Not that I haven't had the time - rather, I still only have a DVD player that will not read burned discs!

Btw, can you (once again) post a link to your thread(s) on how to perform the FR sweep and plot the curve? I may just borrow a buddy's player to get the job done. Perhaps the player could affect the results, but I just want a general idea of where I'm at. Thx!

Dr. Spec

http://beyond_gomer.tripod.com/

Go here for the test tones.

Ask Paul for the spreadsheet; his has already been modified for the RS meter. I don't use that method anymore, but regardless, my version has CFs for the B&K meter and won't give proper results for the RS meter.

tryrrthg

here are some more test tones. they go in 1hz increments. I've also made an excel spreadsheet with the corrected values for the RS meter. These work well.

http://www.snapbug.ws/sinewaves/

kberg

Thanks, guys.