Midbass Diameter - How to Decide?

[J.R.Freeman]

Good morning all,

With the myriad of midbass drivers available, deciding upon one can be difficult. One critical decision (perhaps the first in the search-refining process) concerns driver diameter. What are some of the pros and cons to the various sizes? Are some diameters regarded as ideal for midbasses? Please feel free to jump in with opinions!

I'm something of a novice but I understand that application dictates to some extent hardware choice. So our theoretical driver pick needs some constraints. Let's say I want to build a 2 way system, we'll say with an F3 of about 55 Hz. It could be either sealed or vented (to make things more complicated)! The system will see a mid-sized living room at most, and will need to play at moderate volumes. So we don't need 120 dB @ 55 Hz or anything crazy like that. So just a good all around system with an emphasis on accuracy.

Now, from what I can tell, a smaller midbass of say 5 inches, would have an easier time reaching the upper end, allowing for a higher crossover point. So if we can cross over at say 3 KHz or higher, the crossover point is less audible. Also, would not the lower Mms of the smaller driver help with transient response? Unfortunately our F3 of 55 would be harder to hit, and would likely need a vented alignment.

Comparatively, a 8 inch driver would have much less trouble with that F3, and might be able to do it with a sealed enclosure. But added Mms I should think would mean worse transient response, even though sealed enclosures tend to favor transients. We wouldn't be able to cross over as high either. On the plus I have found mid range often sounds more natural through a wider driver, with less beaming.

Who can offer some factual insight to supplement my ramblings? :P I used to think the best bet was a larger midbass, but now I'm not so sure. I wanted to stay away from vented enclosures for the transient response of a sealed, but if a smaller driver can react more quickly, it stands to have a superior transient character even with the vent, which would also allow it to hit a lower F3 than it otherwise would be able to. With so many diameters, how does one pick?

Jim

[bzfcocon]

On the plus I have found mid range often sounds more natural through a wider driver, with less beaming.

I'm not sure what you mean with the statement above: a wider driver (I assume you mean a larger diameter) will have MORE beaming than a smaller one - it's one of the reasons you would want to cross over lower.

Overall, the choice depends of the tweeter or whatever you plan to use with that woofer: lower crossover points means you need capable(and more expensive) tweeters. It's a trade-off you should pick.

[Bill Fuss]

A good source of reference material would be Mr Krutke's zaphaudio website. Tons of info, read it all.

Bill

[J.R.Freeman]

Originally posted by bzfcocon
I'm not sure what you mean with the statement above: a wider driver (I assume you mean a larger diameter) will have MORE beaming than a smaller one - it's one of the reasons you would want to cross over lower.

Ahh, perhaps I am using the term incorrectly. This is all subjective, of course, but I have found that smaller drivers to 'squawk' in the upper mid-range, and are noticeably directional (is that not 'beaming'?).

And to Bill Fuss - thanks for the reference. I will give it a read!

[Conrad Hoffman]

There are many ways to skin a cat. I've had little success with larger drivers, and very much success with the Dynaudio 17W75 (been a while- I think that's the right number), the 5" mid-bass, combined with a 1" dome tweeter like the Morels. That combination still likes a 4th order crossover for best results. It also needs bass cabinets or a sub to sound really good. I've had a few two way systems, but they never really satisfied me. The old Genesis went with a reduced size mid-bass, combined with a large passive radiator. That worked quite well. There are also the KEF "Q" speakers for home theater that use a 4 or 5" driver and perform well. IMO, the days of 2-way systems with large drivers have pretty much ended, and for good reason. BTW, I've also drifted to open back enclosures and think they have a much more natural sound quality.

[myhrrhleine]

Use the smallest diameter possible.
This is dictated by the lowest frequency sound desired and the loudest volume desired.

[tinitus]

6" i a good size that does it all, but I am not saying that any 6" will do

[BHTX]

I just received my 3 factory buyout "SoundTech" Eminence Delta Pro-12A's for $66 each (usually like $110+ or something).

http://www.partsexpress.com/pe/showd...number=299-500
http://www.partsexpress.com/pe/showd...number=290-510

..12" midbass for the win.
Planning on using them in a 3-way, probably with the DDS waveguide and BMS CD, with a 15" pro woofer highpassed 2nd order (for 4th order roll off) at 40Hz, at which point a few massive 18" TL's will take over. Crossover points will probably be about 40Hz, 200Hz, and 1500Hz, 4th order acoustic.

edit:
J.R.Freeman, I completely understand what you're referring to when you mention smaller mid drivers tending to "squawk".
I'm hoping that won't be a problem with my new project.

[J.R.Freeman]

Wow BHTX, that will be quite the system! Those look like nice 12's for sure.

Regarding the diameter debate, there are still a lot of questions. myhrrhleine said to use the smallest possible constrained by Fs and max SPL. But what advantage would a smaller driver have? Higher crossover point?

Mr. Hoffman I agree with your statement that they are many ways to get things done, and certainly there are a few answers to the midbass application. 5" seems small to me, but I bet what it can cover of the low range is nice and tight.

Does anyone know of, or have a link to, information regarding this dilemma?

Jim

[BlueWizard]

I would take the opposite approach to what Myhrrhleine said, though the difference in our approaches is more philosophical than literal.

I would go for the largest speaker I could find that would still give me the high range I needed. Of course, this assume that it would also cover the bass range as well.

Also, I take some exception to the general use of the term 'midbass', though I think it is being used correctly here. To me, and I could be wrong, 'midbass' means Midrange and Bass. I recently read a thread where someone wanted 'midbass' speakers that were large, went exceptionally low, and were loud. I thought to myself, he doesn't want midbass, he wants bass speakers. Sorry, just rambling.

I think, and again -generally, speakers 8" or smaller are the only speakers capable of midbass. There are probably rare exceptions, but anything 10" and above, is pretty much a straight bass speaker.

That said, I would also agree with Tinitus, that speakers in the 5" to ~6" range probably give the best results. There are many commercial speakers in this range that have clear clean mids and solid bass. So, I think this puts you in the sweet spot; large enough for good bass, small enough for good midrange.

But, as others have hinted, there are so many variables that it is almost impossible to nail down to a perfect range or size of speaker. But, I still stick to my philosophy of picking the biggest speaker that will do the job within a user's selected design parameters.

Yes, I know ...rambling...rambling.

Steve/bluewizard