15" vs 18" subwoofer - which to buy?

Thanks for your responses so far. I will audition Bag End and Martin Logan, in addition to Velodyne. Up to now, I am inclined towards Velodyne because of the easy built-in room correction features. I'm not sure that Revel is available in Hong Kong, where I plan to make the purchase. I will also look into the Aurios and Auralex Gramma, recommended from a previous posting.

I guess I have a very basic question..before getting into differences in speaker design, if possible. That is, is it possible for a large subwoofer (or several smaller subwoofers in one enclosure) to be effectively played at an equally low volume as a small subwoofer? I'm really not concerned about large volume sound for the medium-term, and want to achieve the best possible sound, i.e. bass extension, resolution/clarity, and fullness, at extremeley low to low volumes. All other things being equal, should i just get the largest subwoofer (or largest total cone volume, for those who advocate using several smaller cones) possible? I guess I don't understand the physics involved..

my Velodyne dealer recommends the 18" over the 15", independent of room size (mine happens to be about 14 x 35 feet), placement issues and price. he said the main reasons people would go for the smaller subs is because of price and lack of physical space for the cabinet, and that inside this subwoofer line, volume/neighbor issues are a total non-factor, since i have control over the volume. is this true at low levels, or is there a "minimum" effective volume threshold for the 18" which is higher than for the 15"?

My dilemma at this point is not about 1 vs. 2 subs. Should I get two larger 18" subwoofers then? Would larger subs would hinder room placement in my case? The difference is about four hundred dollars from my dealer between the two sizes, and I can afford two 18" models - cost is not an issue in the case.

Flemke, I have no plans to crank my subwoofer(s) either, I will play at low volume at least during the next year in this apartment. My question is whether the DD-18 can be played at an equally low volume as the DD-15, and achieve better effect musically. Unfortunately, I won't have a chance to demo both in the showroom.

Rives...good idea. I called Velodyne and the guy told me that for a 4000 cubic foot room, he would recommend two DD-15s or one DD-18 (he said these are equivalent, as are four DD-15s and two DD-18s). When I mentioned cost wasn't an issue, he recommended DD-18s, and said that there was absolutely no downside to getting a larger subwoofer, as far as low-level playing and neighborly relations. The DD-18 can always be adjusted to a lower volume and match any low volume DD-15, and in fact at low volumes one would be hard-pressed to tell the difference between the two boxes.

To follow-up, I called Bag End and the sales guy told me that there was no difference in quality between the Infra 12" and 18" at low volumes (I said I heard a large difference at any volume between 12" and 15" with B&Ws, and he said, "well, not with ours"). This was also quite different from what the Velodyne guy told me, which was that anything 12" and below is basically a 'toy' and that the move to a 15" is a dramatic step up at any volume. The Martin Logan guy gave me the opposite advice- that the smaller Depth may have an edge in clarity and response over the Descent at lower volumes, because of its agility.
Three different manufacturers, three different basic responses...bigger is better, no difference, and smaller is better.....

Kenl,

Both of your questions were addressed by the Velodyne rep with whom I spoke.

1) He said that equalization with 2 subs is a 'bit tricky'. First you need to play subwoofer A by itself and do the equalization for that sub alone, then you need to play subwoofer B by itself and do the equalization for that sub alone. Finally, you play both subwoofers, and do the equalization for sub A. I didn't quite understand the logic of the second step....

2) The velodyne rep said that 2 DD-15s are equal to 1 DD-18, and 4 DD-15s are equal to 2 DD-18s. He said that the DD-12 is a 'toy', which seemed to implyt that no combination of DD-12s would match even a DD-15.

I listened to the Bag End Infra 18 subwoofer today, and I am certain that the 18" inch subwoofer is suitable for low-volume playing without disturbing the neighbors. It seems to sound subtler than the 15" B&W I demoed, although it does seem a bit slow, as Porschecab mentioned (but its the first time I heard an 18" subwoofer outside of a club, so I'm not sure it's a fair perception). I will listen to the DD-18 tomorrow, and make a decision then..

Thanks everyone for your comments.

I put in an order for a black DD-18 subwoofer. Originally I thought I wanted the maple, but I really liked the gloss finish on the black.

In total, I listened to the DD-12, DD-18, BagEnd Infra18, Rel Stadium III, B&W800 and 850. My impression was that an 18" subwoofer could be played well at low volume. I had never heard a home subwoofer before, and was amazed at what it added to movies and HT, hence I decided to get the biggest one I could. Although the Velodyne retail salesperson and various other people on this forum and elsewhere have assured me that the smaller 12" and 15" subwoofers should work about as well in smaller rooms (they said that room size should be my only consideration), I didn't have the chance to test this. In the small to mid-sized showrooms (250-400 sq feet?), and sitting at a close distance to the subwoofers, I found it hard to believe any number of 12" subwoofers could ever match an 18" subwoofer. The 12" ones didn't seem to have authoritative impact, and in fact I didn't really like the 'punchy' bass they put out- I see why someone might call them a toy, no offense intended to anybody. Is it a non-contested fact that multiple 12" subwoofers could match or best a single 18" subwoofer in terms of quality of low bass? It seemed so hard to believe in the store.

Also, a reviewer for a hifi magazine was in the store that afternoon, and I got to listen in for his review of the 1812 subwoofer for about 45 minutes of home theater, and I decided I wanted to get as close to what i heard there as possible

The DD-18 will arrive in about 2-3 weeks at my apartment, I'll try and post a follow-up around then.