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In Reply to: high end wide range bass drivers posted by rick57 on September 24, 2002 at 00:57:08:
If I understand correctly, the target is "95 dB efficient, flat to 18 Hz, in a 3-4 cubic foot box".I don't think that's possible.
A 95-dB efficient woofer with parameters that would will give you -6 dB at 18 Hz (which, assuming a bit of room gain would be essentially "flat" to 18 Hz) would require a box of about 30 cubic feet internal volume.
If you go with a 90 dB efficient woofer, you can hit the same low bass cut-off in a 10 cubic foot box.
If you relax the bass extension requirement by an octave to 36 Hz in-room, with a 95-dB woofer you can get away with a 4 cubic foot box. If you go with a 90 dB efficient woofer, you can get about 24 Hz in the same size box.
If you really want -6 dB at 18 Hz in a 4 cubic foot box, you can get it with an 86 dB efficient woofer. But, you'd need a vent 6" in diameter and 54" long.
Note that these figures may shift around a bit with different modeling programs - but the basic trends are valid.
Now, you're probably inclined to trade off efficiency for bandwidth and go with the lower efficiency woofer. In my experience, that would be a mistake. You see, an 86 db or even a 90 dB efficient woofer will compress significantly more than a 95 dB efficient woofer. Even if you bi-amplify to match the relative loudness levels, you will still have two major problems: First, the bass will not be as dynamic-sounding as the rest of the system. Second, you can only voice the system to sound exactly right at one volume level. Any louder and the midrange and tweeter will be too loud; any softer and they will be to quiet. Incidentally, this efficiency non-linearity problem plagues many loudspeaker systems.
If you want lifelike dynamics (which, based on your midrange and tweeter choices, it sounds like you do), then you're going to have to either relax your deep bass extension requirments, or relax your box size requirements.
In my opinion, good dynamics is worth trading off extension for. Building a speaker that can shake your room is no great feat; it can be done rather easily with a low-efficiency woofer and lots of amplifier power, and maybe a little EQ. But buildng a system that is coherent and dynamic down to an honest, tight, solid 40 Hz or so - ah, that is rare and delicious.
By the way, if someone knows how to get an honest (no EQ) -6 dB point at 18 Hz (before room gain) in a 4 cubic foot box at 95 dB efficiency, I'd love to be proven wrong!!
Follow Ups:
Thanks to all who've responded so farAs you may have guessed I'm a newbie. I starting reading my first DIY book (Dickason's Loudspeaker Design Cookbook, 5th ed., and waiting on the 6th ed) just a week ago.
Duke, I'd like to know why a lower efficiency driver gets the same extension in a smaller box - I thought it would be the other way around??
(I did say) I'd consider EQ, as long as it didn't diminish the dynamics too much.
I agree good dynamics is worth trading off extension for.
The 3-4 cubic foot is just a target, but a look
www.jblpro.com/pages/components/2235h.htm
showed the JBL 2235H 15's may be able to do it or come close, perhaps in a larger box (to be further investigated). I'll have to find out their price too.
The Lambda 15 TDX (I think $390) may also come close. John at Lambda is coming up with his ideas, I'll let y'all know. I was aiming to get about 4 octaves - 18 - 300 Hz.The point of my post was to identify what driver (up to say $400-500) will come nearest, then see if I am better with Plan B: a main down to say 40 Hz, and separate sub(s) more for home theatre.
It sounds like you think 'Plan B'. Can you recommend a moderate priced bass driver then better than the PHLs; or more importantly a sub driver/ design approach to cover 18-40 Hz??
Since my post, I've had a quick look at transmission line subs. According to Dickason, TLs have the slowest rolloff, and other things being equal the best transient response. There are a number of designs on the web, some using the good value Shiva sub. Some look very unusual, have modest footprints. So (subject to further investigation) this looks most promising.
Tthylantyr, at the treble end, the Stage Accompany SA8535 isodynamic tweeter sounds great but too dear. But good to hear another glowing report on PHL!
If anyone can comment or suggest some good (not overly expensive) options -
Muchos thankos
Richard
Richard -You wrote: "I'd like to know why a lower efficiency driver gets the same extension in a smaller box - I thought it would be the other way around??"
Three major driver parameters influence the efficiency of a driver (and of course each of these parameters are in turn established by other parameters):
1. Efficiency goes up linearly as Vas goes up.
2. Efficiency goes down linearly as Qes goes down.
3. Efficiency goes up with the CUBE (third power!) of the driver's resonant frequency.
All of these things work against the low bass response in a given box size. If Vas goes up, then the in-box system resonance goes up. If Qes goes down, then the alignment is shifted to one with less bass response. And of course if the driver's resonant frequency goes up, it produces less low bass.
I have an idea for a woofer that I think would come as close as possible to filling your requirements and be within your budget. Please e-mail me at audiokinesis@cox.net and I'll discuss it with you.
Best of luck to you!
Duke
Can I hear an AMEN!Thanks, Duke, informative as ever.
I gave at the office!
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