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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
eldartford
4,262 posts
 
Sean....I did not get to rerun the test last night when background noise was low. Maybe tonight. I am quite sure that the background noise is the reason that the plot becomes nonlinear at low level. By the way, the data looks too perfect over much of the range, and you might be suspicious, but that is exactly what I read from the instruments. It surprised me.

Per you suggestion I will run a test using only the dynamic cone subwoofer with a warble tone as a signal. This will cover the range 22.5 to 250. The warble will come from an Audio Control Richter Scale equalizer, and it is only as good as it is. One problem I anticipate here is that if I go to any loud SPL all the windows and doors are going to rattle, and screw up the measurements.
sean
6,231 posts
 
If you are going to test a sub, try to get the meter as close as possible to try and eliminate room nodes. Otherwise, the linearity that you measured last time will be thrown out the window. The room itself will have a "knee in the curve" in terms of the excitability of nodes, etc... Sean
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cytocycle
1,043 posts
 
I loved that Audio Control Richter Scale and the sweep it can do I use to use it to shake apartment rooms like 4-8 apartments away and no one could tell where the shaking was coming from.. College was great fun!
eldartford
4,262 posts
 
MORE DATA

Signal..SPL
..NONE...40 to 55 background noise
..-80....42
..-75....46
..-70....50
..-65....53
..-60....58
..-55....63
..-50....68
..-45....73
..-40....78
..-35....83
..-30....88
..-25....93
..-20....98
..-15....103
..-10....108

The signal was white noise, as before, but limited to frequencies below 400 Hz, and reproduced by my subwoofer system. (Easy to do. I just muted the HF and adjusted the X/O frequency up to 400 Hz). From prior experience I know that the warble tone would have rattled things. The mic was positioned about one foot from the 15 inch driver.

This time I set the signal level using the preamp volume control, and read the resulting SPL. When reading the SPL for the range below about 60 dB I took the lowest of rms indications over about 30 seconds, which corresponded to a lull in the traffic (background noise). For the higher SPL readings I took the average, as before.

Plot the data and you will see that there is almost no suggestion of decreased sensitivity at low SPL, which I attribute to the greater care that I took to minimize error due to background noise. And anyway, the SPL range where the data is not perfectly linear (for whatever reason) is so low as to be almost inaudible, so it wouldn't matter anyway. I am particularly happy to see no compression for high SPL, which would be a worse problem.

All of this is for my speakers :-). Maybe yours are different :-(
sean
6,231 posts
 
El: Thanks for taking the time to perform this second set of tests. I would only comment that a loudspeaker works much like an inductive electrical motor i.e. voltage is fed into a coil and the resultant fluctuations in magnetic field create motion of varying speeds.

Think about that aspect of operation and what is required to bring the motor up to a linear operating speed and you'll have a better idea of what happens to a speaker too. The fact that a speaker also has to deal with the mechanical / thermal losses of the suspension increases the variables involved and the linearity of operation. On top of that, motors typically don't change direction at a rapid rate of speed and / or change loading characteristics as signal is varied.

There's a lot going on here that may / may not show up on an SPL meter. Sean
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