Survey: Your deam bass/midbass driver specs?

[Bill F.]

What specs and/or performance characteristics would you like to see in a bass or midbass driver? Allow your imagination some leeway, but try to keep it real. This question is more than academic--future production may be a possibility. (No promises, though!)

I'm trying to see what niche markets might need servicing.

TIA for your help,

Bill

[DIY_newbie]

Ok you asked for it :

QTS = 0.707
Fs < 15hz
atleast 12" diamater
xmax 10mm peak-to-peak

Optimized to minimize IM and hormonic distortion
Sensativity as high as possible >93db would be nice

You did say we had some leeway

--Chris

[Bill F.]

Hi Chris,

Ah yes, the open baffle special! Believe it or not, I actually think those specs may be approachable--somewhat. It would call for a very special suspension, though, to keep the Fs low with a Mms low enough for some efficiency...

[DIY_newbie]

Originally posted by Bill F.
Hi Chris,

Ah yes, the open baffle special! Believe it or not, I actually think those specs may be approachable--somewhat. It would call for a very special suspension, though, to keep the Fs low with a Mms low enough for some efficiency...

You guessed it! I forgot to mention it would be nice to be able to play upto 250-300 hz as well

It would model pretty well in a sealed box as well, especially with an Fs that low

--Chris

[454Casull]

Since I wouldn't be buying anything, I would be doing you a disservice by posting my opinion.

[Bill F.]

[ScottG]

Rather than think of T/S params consider this:

1. dipole with a baffle no larger than 16 inches in width.
2. passband: 40Hz to 600 Hz with an attenuated high freq. response starting around 300 Hz. (that when considering the "eq" in #8 below provides something approaching a 1st order low pass around 300 Hz for easy transition to a midrange.)
3. 94 db (1 watt/1 meter) after eq. attenuation across the passband
4. >105 db (1watt/1 meter) for peaks.
5. IMD virtually non-existant in the passband.
6. THD <.5% in the passband for ANY harmonic and less than .05% for 4th or higher order harmonics at reference level of 94db.
7. No more than 4X the max distortion level at the peak spl operation - with distortion becomming progressive with excursion levels.
8. EQ. requiring only a 1st order filter at 20 Hz (obviously not an air-core inductor). In otherwords 6db of dipole compensation at 80Hz, 160Hz, 320Hz. Madisound should be able to custom make them for a reasonable cost.. OR a more costly (core with less hysterisis) solution could be from Mundorf or possibly from Dave at Inact Audio.
9. A nominal 8 ohms impeadance.
10. Low magnet hysterisis AND a smaller magnet size to reduce reflections and back-pressure.
11. Low total cost.

Basic design considerations based on whats above:

#1 - is self explanatory but it suggests a total driver (and basket) diameter that does not exeed 16 inches. I.E. a nominal 15 inch driver or 2 nominal 8 inch drivers side by side (horizontally).

#2 - to get the high freq. attenuation the driver should likely have a lossy dust cap, AND/OR the driver should have the back (magnet side) facing forward (a-la Wilson Bench/Goldmund).

#2,3,6,9 - to achieve this high an eff. at these freq.s with this low a distortion level the driver will need to be constructed something like a 7 inch lowther. Lowther's typically have a low fs but don't have a useable freq. response an octave "+" above their fs due to their construction.. This is good for both eff. and distortion levels in their OPERATING passband (which is usually 70-80 Hz and above). This passband is an octave above their mechancial resonance (36 Hz) and as such THD is considerably lower.

This suggests an fs for our driver to be less than 20 Hz, (likely 15 Hz), with a qts. of just under .2. Again - we specifically do NOT want a useable freq. response anywhere near the fs of the driver.

Furthermore to obtain higher effective levels of eff. the drivers should be either 2 "12" or "15" inch 16 ohm drivers run in parallel, OR 4 "8" inch 32 ohm drivers run in parallel (or better yet 8 "8" inch 64 ohm drivers in parallel). (..and either solution should meet the 16 inch baffle width spec.) Cosidering cost though, the likely solution is 2 "15" inch 16 ohm drivers.

#4, 7 - the suspension should be progessive and lite with VERY low resistance at low excursion levels. (Likely a pleated paper design similar to what Supravox uses.)

#8 - is self explanatory

#10 - This probably means the use of neo "wrapped" in some high iron content steel to increase field strength.

#11 - Total driver cost PER SPEAKER should not exceed $225 US with around $25 US additional for shipping. I.E. 2 "15" inch 16 ohm drivers should be at most $225 US.

[Bill F.]

Hi Scott,

Thanks for the in-depth shopping list! It helps me to be able to see what goals people would like to shoot at, since drivers can be designed for a wide variety of behaviors.

One thing about efficiency goals like yours with OBs--they're really hard to hit. For example, on a 16" wide open baffle, any driver will be ~18dB down from its 4pi efficiency @ 40Hz. So, to hit a 94dB/W target, the driver would have to be 112dB/W @ 40Hz!

Cheers,

Bill

[AuroraB]

Wouldn't 2 x 16" sidede wings + somee overhead at the top for mid/treble do some tricks....
obviously the "thing" must have some rear support to stannd upright..

Otherwise this sounds quite alot like my own wishful thinking theses days....maybe I'll have some luck after all...

[gzubeck]

Scott,

I'm assuming we are talking a three way system or a driver for a subwoofer enclosure...cause a 15" driver sounds awfully big when you could use some 7" revelators! I was looking at the sonus Faber speakers and I think in some of their designs they use the revelator with a first order crossover...couldn't you use these in a 2.5 way or MTM design? I appreciate your comments and suggestions...