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

Showing 3 responses by rives

I'm going to recommend something entirely different. Get 2 lesser subs rather than one big one. You can place them in such a way to cancel out certain room modes and get a much more even response throughout the listening room. I also think those with parametric eq built in is very useful, you can fine tune the one mode (floor to ceiling) that you usually can't do much about based on positioning. The Harmon Group wrote a great paper on number of subwoofers. There's a link to it on our resources page. There's also a paper we wrote on speaker placement, which includes subwoofer placement.
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: I probably didn't state things very clearly. You are correct, it's not really inertia in the classical sense, rather it's the amount of current needed in the voice coil to get the driver moving in the first place. You have to overcome that intial friction. I've been told by speaker manufacturers that this is an issue for larger drivers. To move them properly with good control you have big magnets and big voice coils and this can become an issue playing at low volumes. (A speaker manufacturer is probably better to comment on this than I am) You are also correct about the perceived loss of bass at low volumes, this is the work done by Feltcher and Munsen, that shows how our ear sensitivity drops off in the lower octaves and that it is a non-linear phenomenon and becomes a greater discrepency at lower volumes. Lastly, with regard to your comments about the servo. You are probably right too, though some servos are better than others (I've measured some that weren't too hot), my guess is that Velodyne has been doing this for so long that there's is probably pretty close to spot on--but having never measured it I don't know for sure. Keith Yates did a few articles on subwoofers and some very extensive measurements. I don't think they published the low level data, but he may have it. Now I'm curious and will likely ask him.