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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
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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eldartford
4,262 posts
 
Sean...A speaker (driver) is most like a PM DC motor. Except for static friction, (if any) which causes a "deadband" for plus/minus a small voltage, the torque constant (KT) of such a DC motor is completely constant over its useful range. We used a servo motor with more than 400 inch oz of torque capability to measure gimbal bearing friction of about two inch oz, and gimbal unbalance to an accuracy of better than a tenth of an inch oz. Perhaps you are thinking of AC motors, which do not develop much torque at low rpm. And, BTW, the DC motors in the PWM gimbal servos that I worked with "changed direction" (when commanded) at 300Hz...not exactly tweeters, but certainly comparable to woofers.

Apart from broadband sensitivity, frequency response might vary with SPL. I can do that test too!
kenl
131 posts
 
I've followed this thread with great interest, as I'm now trying to decide on one Velo DD-18 or two DD-12's. My room houses 2 separate systems, 2-ch & HT. Due to furnishings and construction, I can place one DD-18 in the right rear corner, next to the 2nd row sofa; or 2 DD-12's in the front of the room flanking the center channel speaker under the front projection screen.

My question for those familiar with the Velodyne DD series is:

When adjusting the built-in equalization using 2 subs, how does the 2nd sub take the effects of the 1st sub into consideration? Is the entire system playing when these calculations are made, or just the subwoofer that's being equalized?

And now back to the original question. If 2 subs are better than one, specifically concerning the Velo DD series, would two DD-12's be as good as one DD-18 for both 2-ch & HT? I'm particularly concerned with HT, since I'm sure 2 DD-12's would be great stereo subs for 2-ch.

Thanks for your opinions and advice.
no_slouch OP
48 posts
 
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..
kenl
131 posts
 
No slouch,

Thanks for your input. I'm assuming step #2 as was described by Velodyne makes gross adjustments to the 2nd sub, while step #3 fine-tunes the combined subs. Just my guess.

I'm surprised that a Velodyne rep would disparage their smaller subs by calling them toys. Aerial's sub is in the 12" category, and it's anything but a toy. Some think it may be the best under $8k sub.

I'm very much interested in your impression of the DD-18. Let us know your impressions. If possible, try and listen to the DD-12 & DD-15 if they are also available. I'd be curious as to how they compare.

Thanks.
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