Optimal bass driver size for sound quality - is bigger really better?

[doug20]

Originally Posted by Antripodean

Thanks for everyone's input. It seems apparent that choosing the right size bass driver for the job at hand is still the key. However, it would have been nice if there was one optimal size

Definitely, If there were 8" high sensitivity drivers (>94 dB) that played from 50Hz to 1500Hz then without issues then I would love to have one!!

[jernejc]

that driver seems to be close:
http://www.jantzen-audio.com/downloa...Oct07_v1-f.pdf

unfortunately a bit too low Qms

[Brett]

Originally Posted by Antripodean

With the proliferation of large bass drivers (18" and greater), is there a point where sound quality is second to displacement? (I am talking about bass rather than subwoofers although they are of interest too). Are drivers just getting bigger for the sake of it? Is 12" the optimal bass driver size? (I am talking about sealed or ported boxes). Are there limitations with the conventional materials used to make cones that create a maximum driver size?

I would be interested to know the science behind optimal/largest bass driver size. If there are special circumstances where larger drivers are achieving better sound quality then I am interested. I am aware that not everyone wants a 2 foot wide baffle but that can be ignored for now.

'Optimum' cone size is going to depend on system design and performance goals and where and how well the performance tradeoffs are made. If you want to use a 21" to 1k, you are going to need to design a special driver, and it will still beam lower because of size, but using a more conventionally sized, say 15" to 500Hz is usually no issue at all for pro oriented drivers. Some of the dedicated sub drivers don't look like they'd be all that good that high, but there is a dearth of measurements on this as most applications have little use for FR data that high.

Originally Posted by TheSeekerr

The second issue is high frequency response - which is a whole different game, and in general, bigger cones don't do it very well. They also tend to come with bigger motors which tend to be more inductive, limiting HF response anyway (see the attached IB response of the aforementioned Maelstrom-X).

The inductance need not be all that high with good motor design; my AE TD 15's have 0.3mH and very good Le(x). There are plenty of other pro drivers with good Le and still have high sensitivity and power handling, due to good motor design and features such as shorting rings.

Originally Posted by TheSeekerr

So, in short: large drivers make good subs, but not particularly great woofers for 2 or 3 way speakers.

I could not agree less.

Originally Posted by Loren42

Baffle size is another issue. Strength is a concern and the baffle step response may be another issue. A 15" driver with a baffle width of 20" puts the baffle step at about 200 Hz, which is not a good point in the spectrum for a step response nor a crossover point.

Could you explain your logic behind this comment.

Originally Posted by doug20

Pro audio 12" 15" woofers (B&C, AESpeakers, Eminence, JBL) work very well up past 100Hz.

A lot higher than that Doug, as you well know. Maybe you meant 1k?

Originally Posted by StigErik

I've been using 21" woofers the last year or so. A bit surprising that those heavy monsters works really well up to 350 Hz in open baffle, and possibly even higher. For a three-way, I think you should go for a very large woofer without much compromise!

I haven't used 21's, mainly 15 and 18" but I would otherwise agree with good drivers 350Hz is no problem at all for an xover, and for some drivers, much higher is possible.

[doug20]

Originally Posted by Brett

A lot higher than that Doug, as you well know. Maybe you meant 1k?

Yep, typo!!

[doug20]

Originally Posted by Brett

The inductance need not be all that high with good motor design; my AE TD 15's have 0.3mH and very good Le(x). There are plenty of other pro drivers with good Le and still have high sensitivity and power handling, due to good motor design and features such as shorting rings.

John @ AESpeakers makes great drivers. Even the AV series have decent measurements up past 500Hz and those are high end subwoofer drivers that can play from 15Hz to 500Hz...that is sweet.

[Brett]

Originally Posted by jernejc

that driver seems to be close:
http://www.jantzen-audio.com/downloa...Oct07_v1-f.pdf

unfortunately a bit too low Qms

" Be aware that normal box- simulations do not apply to this kind of driver" Huh?

[bzfcocon]

Originally Posted by alspe

If using in main bass area, I would always look for driver which can handle 600 Hz without trouble. No XO in area where bass instruments are.

Can you please elaborate more on that ? AFAIK, there are speakers with crossover in the 100Hz region (Linkwitz' Orion), what would be the big NO-NO there ?

[mordante]

I am very very new to DIY speakers. But woudn't bass driver size also be dependant on room size? My living/audio room is about 4meter wide, 6 meter long on 3 meters high.

What I'm trying to say is that I think that bigger is better for a woofer when you play in a very large room or outdoors. Indoors or in smaller rooms there might be other issues as well.

[alspe]

Originally Posted by bzfcocon

Can you please elaborate more on that ? AFAIK, there are speakers with crossover in the 100Hz region (Linkwitz' Orion), what would be the big NO-NO there ?

Yes, there is always speakers with all kind of XO's and drivers. I do not criticize any speakers. To me, 100 Hz XO sounds like speakers and a subwoofer.

[jerome69]

Originally Posted by mordante

I am very very new to DIY speakers. But woudn't bass driver size also be dependant on room size? My living/audio room is about 4meter wide, 6 meter long on 3 meters high.

What I'm trying to say is that I think that bigger is better for a woofer when you play in a very large room or outdoors. Indoors or in smaller rooms there might be other issues as well.

Not necessary