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I am preparing Altec A-7 cabinets by properly bracing and damping them, and am planning on putting JBL 2235 drivers in the boxes. I will be using Altec 803B multicell horns with Nippon Gakkei MS-1401A compression drivers for 300hz-20k. The 2235 drivers were the only ones that went down to 30hz. Someone said that these were not the proper drivers for the A-7 box. Wondering why not and what driver would be more appropriate.
Bill
Follow Ups:
"Wondering why not and what driver would be more appropriate."Poor mass corner on the 2235.
Other than the Altec choices, the JBL 2205 is a good choice, along with the E145. An E140 with a paper dustcap. Drivers like the 2220 will have less bass, more mids. 2227 looks like it may be OK.
Tom Danley likes the 2226 in the 825 with the vent retuned, I have a letter around somewhere that goes into it. Anyway Tom has done it and measured it and it does do somewhat lower bass.
My viewpoint digresses from the standard orthodoxy.The Altec A7 style speaker was intended for max intellegibility and output at a time when there were few if any high power amps or drivers, and loudness and loudness alone were the main design goals.
Using the A7 in a home playback system means that the goals are rather different. One thing for certain, you can throw away a whole lot of SPL requirements in favor of other possibilities.
The whole point of the partially horn loaded 15" driver in the A7 was to make it possible to meet the horn without resorting to high power amps (not available at the time) or EQ (again headroom was the problem in that day). As is, the original design meant that the 511 or worse, the 811 had to be padded down to match to the upper range of the horn on the A7 box.
My own view is that the 511 and the 811 are awful, horrid horn designs that should be avoided completely if possible. They were "cheap" to make in the day, and were "replacements" for the multi-cell designs. Imho, ur better off by far with the multi-cells or a tractrix. I prefer greatly getting the horn freq down to 300Hz. or less, and obviating as much of the A7's front loaded horn's contribution.
Obviously, this is somewhat at odds with the original design concept and application. But it has benefits - the main one being that imho any speaker system that has a xover point in the 500-1000Hz. range is at a great disadvantage sonically.
Now, skipping the front horn of a minute - the A7 is merely a large volume ported enclosure. If you forget for a moment about the "efficiency" issue and think only about actually getting bass below 50Hz. out of the box, it becomes quickly apparent what the T/S parameters are going to have to be. Clearly, you have to be prepared to sacrifice some "efficiency" to get <40Hz. response.
If ur hell bent on running with a small low power amp, then thinking about it this way isn't going to work at all. But, if you can stand the thought of using two amps (biamping) or even one larger amp (be it tubes or solid state) then getting some LF extension is possible, and at greater efficiency than the standard everyday "high-end" speaker too. Not at the mythic "100dB/1w" levels though. Few speakers really acheive that anyhow.
Any run through a T/S & box simulation program will show you quickly that a driver like the 2235 will actually produce bass down to about 30Hz in good style. There is a thread that talks about using a 2245 -
http://db.audioasylum.com/cgi/t.mpl?f=hug&m=117051 - but as a woofer in the bottom half of the A7 box that is iso'd from the midbass + horn. The 2245 is similar to the 2235, but with a greater VAS and higher sensitivity - although it does not tune without EQ as low as the 2235 in this box. (and they suggest EQ, which implies a larger amp, and the use of an EQ box...)If ur counting on the gain in the midbass horn to meet ur 500 or 800Hz. horn, then the 2235 is likely NOT the speaker for you. (Dunno yet really, haven't yet measured it in the A7 box!) Actually, that splitting of the cabinet idea is probably a better one overall IF ur counting on the midbass horn's contribution(s). But, Bill's situation does not require getting up that high at all, in fact for him, the silly midbass horn is something of a minor deficit... where he will be meeting it, the midbass horn will *just* be starting to rise in response, as it then gets lopped off at ~250Hz.!
Personally, I don't want a 15" driver running up to 500Hz. or 800Hz. And, I don't find this sort of arrangement to be a "strength" at all for these venerable old school boxes! The design was a major compromise from the very start, and remains so today, perhaps more so since there are other viable alternatives in terms of high efficiency designs.
So, you can see the requirements for Bill's proposed system are rather different than that of the typical A7 set up... otoh, all of the A7s will benefit greatly from additional stiffening & internal damping...
Oh btw, it looks like if you place the ports near the bottom or side walls, the boundary effect there may help to reduce the length required so that the requisite port area can still be achieved without excessive port length for tuning low enough with a driver like the 2235. (in situ test/tuning is required though...)
Recent tests using FFT and 3-4 various 416 type alnico drivers (varying Fs, fwiw) showed awful, choppy response curves and very very "bad" tuning in the stock cabinet. Significant midbass pass through was also measured out of the so-called port. Imho, internal damping and absorption ought to be employed to cut down or eliminate the midbass output from the "port" even in a stock A7 cabinet... fwiw.
As always, ymmv!
:_)
_-_-bearz
My 803/MS-1401 will go down to 300hz. Forgive my ignorance but what is the mass corner of the JBL 2235. Why is this a poor choice for the A-7 box. Would there be a better choice of cabinets/bass drivers for my application, such as eq and/or midbass/subwoofer combo?
I'm not sure but Nippon Gakki is another name used by Yamaha, and when I did a search on MS-1401A the picture I found looked a lot like Yamaha drivers that I have seen . . . although "they all look alike." There is a loudspeaker put out by Meyer Sound Laboratories that uses a driver of the same name, the UPA-1 and its derivatives. In case you weren't aware of this background, this might give you some insight into how to get best use out of the components you have to work with.
Bill---The Altec 416s and 515s are the proper woofers; 416 is A7 and 515 is A5.These drivers both make superb upper bass and lower midrange, the very best avilable IMO. It's precisely because of these qualities that one should use 825-828 (A7) box, if not why bother? It's BECAUSE of the 416 or 515 that people use the box, you don't use it because it makes good bass (the lower bass will be down in level regardless of the driver used because of the box'es shelved response) but because WITH THE RIGHT DRIVERS it does the upper bass-midrange so well.
Play to the box'es strengths not it's weaknesses. Don't put the cart before the horse.
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