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High Efficiency Speaker Asylum: Re: Mass Corner by BEARZ

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Re: Mass Corner

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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


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