Using two dissimilar midrange drivers?

terpodion

terpodion

Active Member
I'm thinking of using two midrange drivers per side in the ever changing main speakers in the big, scary system that lives in my garage / workshop.

An Eminence Alpha 6A (6") and a Selenium 8PW-2 (8"). Why? first and foremost because I have them laying around and because my theory is to make that band more linear. The Alpha is hot in the 1.5 to 5kHz range and the 8PW-2 is hot below that. When I had the Alpha in the system by itself, it sounded very nasal, but I was using a cheap MCM Electronics passive crossover.

This is now a tri-amp system with a BGW 250D driving the midrange. An Ashley active crossover will allow me to experiment. The drivers will be time aligned as closely as humanly as possible, stacked vertically and spaced as closely as possible.

I can't find a lot of information on using dissimilar drivers in the same range in the same speaker. What little I can find says it's a bad idea. I'm skeptical. In any case, I bought a bunch of toggle switches from a Radio Shak going toes up so I'll be able to do comparisons by switching various drivers on and off.
 
Register to hide this ad
Shouldn't be a problem long as you match the positions and drivers side to side for proper imaging ...

Wondering how you're planning to compensate for ohms load as you switch drivers in and out? Both parallel and serial have their potential issues ...
 
Side to side? I would think just the opposite given that our ears are mounted horizontally - I have always heard that drivers are best mounted vertically as we cannot tell vertical differences. It's one of the oft-stated flaws in a d'Appolito arrangement. Still, each set of drivers will be in a sub-enclosure so I can try it both ways. The BGW power amp can easily handle a 4 Ohm load so that's no problem. BTW, all the amps in this system are BGW. The crossover is an Ashley.
 
Stuffed mid1.jpg Stuffed mid1.jpg Stuffed mid 2.jpg Stuffed mid 3.jpg This is what they are looking like so far. Yes, progress is slow. That's fiberglass batting I'm stuffing them with. It's rigid and comes in sheets. It's leftover from some organ project in the past. There will be no back. With all those glass fibers in there very little comes out the back. I did some preliminary testing with an ancient tube tone generator and they are very effective from 120Hz. Believe it or not, audible output starts at 40 Hz. I'm going to cover the front of the baffles with thick felt to kill diffraction. Also, I do not care what these look like. They are designed for 0.00 WAF. I may glue hunks of rubber to the sides to kill any resonance in the plywood sides. I "tap tested" them and they are fairly non resonant. It's surprising how much the cross brace did in that regard. It is also damped with a felt strip glued on with a generous amount of RTV.
 
terpodion said:
The Alpha is hot in the 1.5 to 5kHz range and the 8PW-2 is hot below that.
Click to expand...
Let me give you a little food for thought.

The frequency response graphs that you are quoting data from were extracted under specific, controlled conditions. Your application of these drivers differs significantly from the test conditions, and their frequency response in your room and acoustic alignment will differ accordingly.

That said, and back to the cruxt of your question, since these drivers have very similar sensitivity and power handling you shouldn't encounter any fundamental issues using them together, and they might actually pair up pretty well.

My biggest concern would be if and what kind of crazy response anomalies there might be when you start to get several degrees off axis since the two drivers will have very different polar responses. The reverberant and reflective environment of a garage might do much to negate any audible artifacts.

terpodion said:
With all those glass fibers in there very little comes out the back.
Click to expand...
Once they(the speakers) are in place and you have stopped fiddling with them, a light shot of the wife's hairspray is mighty effective at making loose glass fibers stay put, and your speakers will smell nice.
 
I would toss both mids you have chosen, and look elsewhere. Altec made a great 10 in folks like to use as a mid and JBL made some fantastic 8" drivers. I would rather have a vertical row of 4 JBL 8" mids than what you are playing with. I ve installed systems where we needed vertical pattern control that we couldn't achieve with 15 inch drivers where LF horns lost control. So we made the systems 3 way using as many as six 8 inch JBLs mounted in a vertical column as low midrange drivers crossing at 200 on the bottom and 1200 to the Large format HF horns. They required a lot of power as compared to the horns, but did the job. Altec made a special enclosure for double 15's called the 815 that had a high degree of low mid control, but rolled off the bass at 80 hz for high level voice reproduction. But we just didn't have the space. Again the JBL 8 inch solved the problem. Ev made some nice drivers, too, though they couldn't handle the power the JBL's could.
 
"I would toss both mids you have chosen, and look elsewhere." I'll take that into consideration. However, this is a garage and I could buy a lot of gasoline, fuel oil and other necessities for what I would spend on JBL / EV / Altec drivers. This is what I have and what I'm going to use. But thanks so much for reading my post and responding to it.

"Hairspray is a PVA solution. You may mimic hairspray using a solution of white glue and solvent with an airbrush." Hairspray is PVA!?!? Glad I'm not a girl! Again, this is a garage. I'm not concerned about a few stray glass fibers floating around. If you knew what goes on in there, you would be more concerned by what could damage the cones. I should probably make protective grilles. I don't have an airbrush anyway. But I do have two paint sprayers and an industrial insecticide sprayer which I suppose would work. And again, thanks for your response.

Given the above, what I am doing out there might be described as Redneck / Bohemian Audiophilia. I use what I got or what I can get on the cheap; curb finds, dumpster diving, thrift shops and stuff I have had for decades. This is one reason why I use BGW amplifiers. They are clean and go for fairly cheap on the auction sites. They are built like a tank and wide open to modification. I make no pretensions that I'm building a super-high-end system but it produces clean sound and can get ungodly loud. It is always a work in progress.
 
Last edited:
I have always had an interest in different voicing of speakers. Nothing more crazy than my current boiler room setup with a pair of AR 18 matched with a pair of NHT sub zero(or something like that.) small speakers. I also have them in series and found that is the best sound overall. My JBL 10" sub rounds out the whole setup.
 
Speakerlab did the same thing with dissimilar woofers sharing the same cabinet space. Afaik the key to making it work was a dissimilar Qts for the drivers, one high and one low.

Cheers,
James
 
I have an old book on loudspeaker design (I think it was sold by Radio Shack) where there are plans for a double enclosure / single woofer design. I don't even want top think about crunching the T/S numbers for a double dissimilar woofer, single enclosure design.
 
pdm4606 said:
I have always had an interest in different voicing of speakers. Nothing more crazy than my current boiler room setup with a pair of AR 18 matched with a pair of NHT sub zero(or something like that.) small speakers. I also have them in series and found that is the best sound overall. My JBL 10" sub rounds out the whole setup.
Click to expand...
I use the 18S in my bedroom system. They were a curb find. I replaced the trashed woofers with Peerless models. It worked well. I guess you could call that voicing BTW, part of my craft is as a voicer of organ pipes. Few, if any, of the principals involved with pipes applies to speakers in terms of voicing.
 
terpodion said:
Few, if any, of the principals involved with pipes applies to speakers in terms of voicing.
Click to expand...
Probably not until you get down to the root laws of physics.

There's a fundamental disparity between the organ pipe and the speaker. One has the design goal of being a producer of sound, with specific tone and timbre, attack and decay(think of a pipe voiced with a pronounced "chiff"}, and probably a few more descriptors.

The other has the design goal of converting an electrical signal to a reproduction of sound, the most faithful of which will impart no "voice" of their own.

I would opine that what you are actually doing with these midrange drivers is much more akin to tuning than voicing. More specifically, tuning to your application.
 
bowtie427ss said:
Probably not until you get down to the root laws of physics.

There's a fundamental disparity between the organ pipe and the speaker. One has the design goal of being a producer of sound, with specific tone and timbre, attack and decay(think of a pipe voiced with a pronounced "chiff"}, and probably a few more descriptors.

The other has the design goal of converting an electrical signal to a reproduction of sound, the most faithful of which will impart no "voice" of their own.

I would opine that what you are actually doing with these midrange drivers is much more akin to tuning than voicing. More specifically, tuning to your application.
Click to expand...
The only analogies I can think of off hand are stopped pipe / open pipe - sealed enclosure / vented enclosure. Even that is a bit of a stretch.

You might think that being an audiophile I'd be building "hybrid organs" with electronic voices in addition to pipes. But it is just the opposite. I never mix the two.
 
Electronic voices are too 2 dimensional. It may be possible to electronically simulate the effects of the elasticity of air, and the effect that vortices created by the motion of air over the lips and mouth of a typical pipe have on the propagation of sound waves. But, i don't think the technology exists in a "package" that is both affordable and practical...................... yet.

Thankfully, for those with a decent level of hearing acuity there probably won't be anything that replaces the sound of a pipe organ in our lifetime.

I applaud your willingness to step outside the box with your experimentation. This is where true innovation comes from.
 
I can't believe that it has been a year and a half since I started this thread. I have, more or less, completed the system. Honestly, it makes me question my sanity.

The midrange drivers in question, sound quite excellent. Most of the time, I leave both of them on. They seem the most linear, smoothest that way. I experiment though. The Doors sound best with the Eminence on and the Selenium off. The opposite with Glenn Gould.

The tweeters are Morel CAT 378, two each side, angled. Powered by a BGW Model 85. Efficient, accurate and with two of them, no perceptible power compression.

The mids in question are powered by a BGW 250D. Yes, we are BGW fans here.

The woofers are Dayton Series II 15" in enclosures that I made out of good, old fashioned 3/4" particle board that some theater group threw out after the show closed. There was a lot of it so I doubled it up for 1 1/2" thick walls heavily braced with hardwood scraps from the various pipe organ projects. They are flat to 50Hz, vented via Boxplot. A BGW 8500T powers them. A real beast of an amp. With these speakers, it will kick you in the chest like a Doc Martin boot.

The subwoofers bear some description. Eight 15 inch drivers. They are in two enclosures with two sets in isobaric, push-pull. They are stacked in a corner, on top of each other. The two are slightly different. One is a bit larger, with the low end approaching a Chebyshev alignment. I had the drivers custom made more than a decade ago by Eminence for an esoteric musical instrument amp I was developing. Um, well, that didn't work out so I was left with ten 15" subwoofers. The other two are in my office with an entirely different system. Gawd, I have so many speakers! In any case, I couldn't find BGW amps big enough to power these power hungry beasts so opted for two Crown CE 1000's. At 900 watts RMS bridged mono they come close to slake their thirst for power.

A three way, Ashley active crossover divides up the spectrum. I think that's one of the determining factors. There are no passive crossovers in this system at all. IMHO 2nd order, passive crossovers (the most common type) take away something fundamental - the "acoustical soul". I dunno. I'm just going by what my ears tell me.
 
You must log in or register to reply here.
Back
Top Bottom