My question to all of you guys is this,specially to GONK (since he just purchased a SV subwoofer)My main speakers are in my room +3db's at 30 hz,at 25 hz they are down by 6 db's.My question, is it worth going to the expenditure of a subwoofer for just the last octave?meaning from 20hz to 30hz,and is there alot of movies with information bellow the 30hz mark.(I am in the waiting list for the 950.and waiting...)I get a very good shake at 30hz in my room,and my spl's are at 110db's peak!

You would probably feel more with a sub. How much that's worth to you I don't know. I bought a used SVS sub cs20-39 for under $300, and they are frequently for sale by people upgrading to the latest and greatest.

If I had mains that went down to 30hz, I would probably turn the sub off for music and use it only for HT. You would get much more coherent sound that way, and most music doesn't go that low.

I'm not Gonk, but I play one on T.V.

I have an SV on order (20-39PC Plus).
It sounds like, if you're going to get a sub, it would have to be a pretty good one. If your fronts are that good at reproducing LFE, you would not want an inadequate sub.
Correct me if I'm wrong, but the human ear (generally) can hear down to 20hz. Information below that is felt more than heard. I also believe that good subwoofers supplement what your fronts are capable of achieving. I don't believe that you would set your sub, or internal crossover, to 30hz. It would be set higher so that there was a seamless integration between your fronts and sub. So actually, your sub would be playing more than just the last octave...and that's only the octave you can hear.
SV's website has recommended DVD's with lots of LFE. Further, they have waterfall charts to show how low and intense some of these tracks go. Also, taking some of that LFE "burden" off your fronts means that they can more capably and efficiently reproduce the upper frequencies.
You're right...gonk will say this alot better.

Good answer, EFSIII. I don't know that I can add much to it, as you covered the main technical reasons to get a sub.

I was very satisfied with the performance of my speakers for a year and a half without a sub. Since your mains look like they can reach a bit lower than mine, you are probably in a similar situation.

One thing that prompted me to take the plunge and add a sub was DVD-Audio -- without a sub or bass management to allow the LFE channel to be redirected to large mains, that channel is lost entirely. Several discs ended up sounding noticeably weaker as DVD-A than as DTS or DD (Blue Man Group, for example). Once I got a sub, though, I was glad I had it. Not only does it make all the difference with DVD-A, but it also does reveal the deep bass hiding in some DVD's. There have only been a few instances where I noticed some extra oomph in TV watching (a couple times on CSI reruns, as I recall). It is a little more noticeable on music, but it's on movies that it can really make its presence known.

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gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review

BTW, one octave down from 30 Hz would be 15 Hz.

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Matthew J. Hill
matt@idsi.net

Buy an SVS 16-46 PCi. You will not be disappointed.

How about the 25-31 PCi ?

Just to add a bit to the other comments - frequency response is not the only thing to consider. Many large floorstanding speakers have good bass extension but are not really adequate for generating the high SPL at low frequencies that HT may demand.

What the speaker can do at 1 watt and what it can do at 200 watts are generally quite different. Typically you will see distortion caused by excursion limiting way before you might expect it. In most cases if the driver is moving more than +- 0.25 inches (6mm) you are close to serious distortion. Some drivers can do more, but they are usually the type used in subs, not floorstanding speakers.

Thank you all,i think i am going to demo the 20-39 the price is SUPER low (looking into the Velodynes,M&K,)i hope is not a waste of time,every body talks very highly of SVsubwoofers.I guess it could turn into another super deal like the Outlaw 1050.....smile.

The 25-31 is 31 inches tall, and is tuned to 25hz. I believe you can have it tuned at the factory down to about 22hz. All the PCi's have the same power and features.
How low you want to go ends up being the question.
I think the 20-39 offers the best of both worlds. It appears capable of handling nearly anything that a movie soundtrack can dish out. Except for the lowest of the low pipe organ music, the 20-39 is more than enough for music.