2 plus 2, Various, what to do with 2 sets of 2+2\'s?

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Marc Russo2004-02-23 22:21

What to do with 2 sets of 2+2\'s? Dear Andy, I am lucky to have 2 sets 2+2\'s. One medallion, one not. What are your thoughts on using 2 interfaces per speaker to drive 1 set better (how do I go about this?) or alternatively sticking 2 speakers side by side or constructing my own frame to make a \'Mode 8\". Which of these options is likely to give the best sound? Marc Russo Australia

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Andy Szabo2004-02-23 22:21

I don\'t see much advantage in using two interfaces per 2+2 speaker. The original MK-121 interface is plenty capable of driving four panels. Also, you would need another stereo amplifier for the extra interfaces, since paralleling two interfaces on a single amplifier channel is not recommended. You\'d still have the radiating surface of just four panels, with an awful lot of extra electronics.

The idea of combining both the interfaces and the panels to make a Model Eight does have some merit. You would still need a total of four channels of amplification, but now you would also have twice the radiating area. That makes a big difference! There are a few points to consider:

Low Frequency Transformer The low-frequency transformer in a stock Model Eight interface has a lower step-up ratio than the regular MK-121, because less bass boost is required due to the increased panel area. Using the low-frequency transformers in your existing MK-121\'s might provide a little too much bass. Your room characteristics and personal tastes will determine whether this is a problem.

Panel Size The stock Model Eight uses four 8-inch panels in the two center columns, and four 9-inch panels in the two outer columns. Since you\'ll be constructing these from 2+2 speakers, you will have all 9-inch panels. This is not a problem in itself, but be aware that the frame will be about 2-inches wider than a stock Model Eight.

Frames Because of the 8-degree angle between panels on the 2+2, you won\'t want to simply butt the two 2+2 frames together. That would yield a “W” shape to the layout of the panels, which would make for some strange-sounding interference patterns. You\'ll need to construct a new frame, with a 4-degree angle between each column of panels.

Wiring Configuration I don\'t remember if the stock Model Eight\'s panels were grouped four-above and four-below, or four-right and four-left. You can do it either way, but I would suggest a third scheme. I would wire them with the two center columns on one interface, and the two outer columns on the other interface. This will give you some additional flexibility, by being able to run the speakers as a full 8-panel system, or just a 2+2 “with wings”. You can also adjust the relative volume of the inner and outer sets independently (via the amplifiers if they have level controls), and be able to control the dispersion pattern and imaging somewhat. In your case, I would certainly put the Medallion models on the center columns.

Room Size The Model Eight is a big speaker, and deserves (some would say requires ) an appropriately large room. I wouldn\'t consider using them in a room with the shortest dimension any less than 15-feet.

Gains/Losses In comparing the Model 2+2 vs. the Model Eight, you will certainly gain in low bass response and overall dynamic capability. The Eights can fill even fairly large rooms with very impressive sound pressure levels. On the minus side, the imaging will be somewhat less precise, although you may be able to compensate some with the wiring scheme mentioned above. This was an inherent limitation of Acoustat\'s pre-Spectra speakers. Small, narrow models had the best imaging, but so-so bass response and dynamic output. The larger, wider models had much better bass and volume capacity, but they offered less precise imaging. This trade-off was solved with the Spectra series, where all the models have the same excellent imaging qualities, with more bass/volume capability as the speaker size increases.

Overall, I think this sounds like a neat project. My biggest concern would be the different low-frequency transformers, and their potential for too much bass boost. Again, the wiring scheme mentioned above could compensate for some of that. Good Luck, and let us know how you make out!

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