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Greg Mueller
Amateur Astronomer, Machinist, Filmnut http://www.muellersatomics.com/

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What Greg should really do is to buy more of a smaller type of surround speaker and an amp that can handle two ohm loads. This will give three benefits...
1. Improved coverage and less localization effect.

2. The surrounds can then be wired for either 4 ohms or 2 ohms, all in parallel which is the preferred way to wire them. There are way less phase problems that will occur at different frequencys than if the sound for the next speaker in line had already passed through another speaker. Also, good used power amps are a dime a dozen these days. Just check E-Bay.

Stay clear of transformers, they will just degrade performance. You should also be cautious when running speaker systems below 4 ohms unless you are familiar with the characteristics of the speakers and amplifier you are using. The rated impedance of a speaker is a "nominal" impedance - the actual impedance may vary considerably over the frequency range. Some speakers are worse in this respect than others and it is not unusual for a speaker rated at 4 ohms to have impedance dips well below 2 ohms at some frequencies. Unless the amplifer can handle this you can end up with amplifier overload in certain parts of the frequency spectrum.

That's not to say don't use 2 ohms, just be judicious in your choice of equipment.

Another tip, never use less than two pair of surround speakers, even in your home system. And if you can only manage two pair, make sure that one pair is mounted just in front of, and the other pair just behind, the main listening area. This will give the best dispersion of the surround sound field.

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Ray Derrick
President
Panalogic Corporation Pty Limited
44 Carrington Road
Castle Hill NSW 2154
Australia
Phone: 61 (0)2 9894 6655
Fax: 61 (0)2 9894 6935

Many of the amplifiers out there can now safely handle 2-Ohm nominal impedance loads (per/channel).

QSC has a marvelous amplifier the DCA-1222 that can run with 1.6-Ohm loads all day...in fact that was one of it's design criteria.

QSC also has a 4-channel amplifier that will handle down to 2-Ohms a channel. This not only has the obvious EX potential but allows one to break up the surround array so that one can run all speakers in parallel up to a 16-surround array.

As to the imedance curves...this really isn't too much of an issue in movie theatres and particularly on the surrounds. Most of the low-impedance part of the curve of most speakers is in the very low frequency. Most of the surround speakers in use today have an LF cutoff below 80Hz or 50Hz (depending on size and quality). Most cinema processors (and some amps, like QSC) offer the ability to high-pass the surround channel to either 50Hz and above. As such, one never will have the low part of the impedance curve come into play.

As a side note for the DTS users out there. DTS places their subwoofer track onto the Ls and Rs surround channels. It is REAL important to high-pass your surrounds at a frequency at or above where your surrounds can safely play. If you have ever used the emperical test disc and played the sweep section, you will hear when the subwoofer section comes...a distinct "flapping" sound at first when the sweep first starts....that isn't your subwoofer but the poor hapless surround cones flapping about.

Another reason to high-pass is it simply wastes amplifier power and potentially will damage the speaker to have a surround speaker play below it's cutoff frequency.

Steve