Multiple small drivers for large output?

[diarav]

Hi,
I am complete newbie and had this strange thought.

Is it possible to combine a set of low power small drivers to build a speaker system having higher power? If I have drivers capable of 10W output, can I combine 5 of them to give me say 50W output or so?

If so, should they be in series/parallel?

Thanks
Din

[Cal Weldon]

Yes you can connect together but 5 won't be the number.

2,4,8,16 are the most common combinations. What drivers do you have and what is the nominal impedance rating?

[anatech]

Hi Din,
Think Bose 901. If your research this speaker it may give you some insights.

Did you just shudder Cal?

-Chris

[Curmudgeon]

It's been tried several times. The first I know of was the "Sweet 16" which appeared in Popular Mechanics, in the '60's I think. It was the first speaker design of a ham radio hobbyist, and was quite naive. Later Bose used the idea for their first speaker design.

The fundamental problem is the bass. You can't really get useful output below the drivers' low frequency resonance, which of course is fairly high for small, light cones.

Another problem for home use, is that you tend to get beaming because of the effective radiating area. Maximum dispersion is from a point source, and a multi-driver array takes you further from that ideal. (This can be useful for controlled pattern professional speakers, another issue entirely. )

Another problem can be power handling. Small, good drivers are not cheap; small cheap drivers tend to have very low power handling capabilities (with some exceptions), so the power handling for the array can be less than intuitively expected.

Inexpensive small drivers tend to have inexpensive cones and surrounds, as well as small magnetic assemblies, so high frequency performance is not outstanding.

The idea can be implemented successfully, but then it's not cheap; e.g. the Pipedreams. There are many reasons why the 3 way (and it's variations) has become the standard design; it's simply won out against the competition over time.

[anatech]

Hi Curmudgeon,
Don't forget about the terrible high frequency response!

I measured the Bose 901 eq (ghastly thing!) once. The high and low gain was +13 dB and + 15 dB as I recall. I can't remember which end was boosted more. The power supply was extremely simple (not good) and the components were less than great quality. I guess teh quality was in keeping with the loudspeaker.

-Chris

[Cal Weldon]

What?

Bose is no good?

[anatech]

Hi Cal,
I didn't say anything about the speaker, well I guess I kinda did. The EQ box is really poorly executed.

-Chris

[Curmudgeon]

Umm, I'm prone to occasional bouts of wry understatement:

"Inexpensive small drivers tend to have inexpensive cones and surrounds, as well as small magnetic assemblies, so high frequency performance is not outstanding."

Actually, the reason I'm so familiar with the Sweet 16 is that a non-technical friend of mine built a pair long ago, and still has the original article. I promised to build him a pair of rear speakers in payment for his building the boxes for the Great Project. He absolutely, resolutely, unshakeably had his heart set on modern Sweet 16's... it turned out that Madisound had a sale on small Fostex FE-E banana pulp "full ranges" (4"? 3"?), which, with a nice little Seas woofer does very well. Very well indeed. So actually, the highs are fine for ambience speakers; not terribly extended, but clean. I don't remember the sales price offhand, perhaps $16 each, so that puts them well out of the price range of most Sweeties. The enclosure is a wall mounted truncated diamond, central section for the woofer, and 4 Fostice/slanted side, for dispersion. Proto was nice, finals not done until he finishes the kitchen cabinets, a matter about which his wife has become quite resolute.

[anatech]

Hi Curmudgeon,

"Inexpensive small drivers tend to have inexpensive cones and surrounds, as well as small magnetic assemblies, so high frequency performance is not outstanding."

Ever read something quickly and not have it all register? I do.

I'm sure your speaker doesn't require an EQ in the audio path anywhere.

Anyone ever hear a 901 without the EQ? Yup, it sounds even worse. Don't try it, you may need counseling afterwards.

-Chris

[Curmudgeon]

No, no eq to speak of; the 3" (I'm pretty sure) Fostice are really quite nice.

I remember back when the original Bose came out, one of the local High Fidelity Shoppes carried it briefly. Their newsletter related that they felt something was wrong, had it measured, and found that there was quite a hole in the upper mid freq response. I don't remember, did they have a "super"-tweeter? If so, given the area that the multiple drivers were spread over, (and some rear-firing if I remember?) decent phase behavior at the crossover would have been tricky.