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15" vs 18" subwoofer - which to buy?

If price and room space/aesthetics were not a big issue, is there any reason to get a 15" subwoofer over an 18" one? My main issue is not disturbing the neighbors too much. I'm confused about the difference between a 15" and 18" subwoofer. I want to get the best sound quality possible for low-to-medium volume use.

I've heard that an 18" subwoofer can be played at low decibels and provide good bass resolution and fullness of sound, while to achieve the same volume with a 15" subwoofer, the power has to be much higher. So for any given sound volume, the main difference is in distortion- and higher distortion sound may be more obtrusive. Is this true? it seems counterintuitive that an 18" subwoofer could be better for neighbors than a 15" subwoofer.

However, I compared a B&W800 (12") vs B&W850 (15"). I listened from the other side of the store wall (not as thick as my apt), and at minimum levels which I found satisfying for HT, I found the 12" more obvious and 'boomy' sounding while the 18" produced a more subtle (though actually more powerful), lower frequency vibration, like a very low-level rumbling background earthquake. The 15" subwoofer did seem more of a disturbance because of it's 'obvious' sound. However, I worry that an 18" won't even start producing quality sound until a certain volume that was much higher than a 15", and consequently potentially more disruptive for neighbors. Is this true? What is the relationship between subwoofer size, low sound volume, and subjective listening experience?

Unfortunately, it will be difficult to get an opportunity to hear both the DD-15 and DD-18 which I am considering, so I hope someone can help out here.
no_slouch
no_slouch OP
48 posts
 
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.
flemke
596 posts
 
http://www.velodyne.com/velodyne/products/specs/DigitalDrive.html
Look at the specs.
rives
953 posts
 
Your question is now much more difficult. Since cost is not an issue, go with 2 subs. Now which sub is not so easy. It depends on the volume of the room, the size of the cone, and the subwoofer design itself. The first two are pretty easy. Suffice to say, if your room is 22 x 30 with 9 foot ceilings (big volume) you should go with the 18 inch. If you have a small room, you may actually be better off with the smaller cone, particularly since you've already indicated that you want to play at low volumes. Some drivers need enough power into them to really break the inertia of the voice coil. I have not demoed, nor do I know about the low level performance of the Velodyne's. This might be a case that Velodyne may be no good at all for low level playing, or they may be great--I have no idea there.

Why not call Velodyne? That might sound crazy, but they want you to be happy too, and you are talking about buying multiples of their subs. Most people would say--of course they will try to sell you the big sub. But I'm not so sure, someone in corporate will want you to walk away as a happy customer and tell other people you are happy. If you explain your situation, it would be in their best interest to tell you which one would work best for you.
eldartford
4,262 posts
 
Rives...I don't understand your comment about "inertia". The effect of cone mass does not have any threshold to be "broken". If the parameter were "friction" what you say would make sense, but a cone driver has no friction, just mass.

If sensitivity diminishes at low power level something other than inertia is at work. I, like every other audiophile, have the impression that this occurs, but I am of the opinion that it is the human ear sensitivity that is diminishing rather than the speaker output.

Because it is servo controlled, I would expect a Velodyne to perform well at low volume. If there were any nonlinearity of the driver at low SPL the servo would counteract it. As you suggest, Velodyne should have something to say about this.
no_slouch OP
48 posts
 
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.
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