Any consensus on surround speaker format?

[David Gatti]

Dipoles, bipoles or monopoles?
Full range, coaxial, or MT?
Required low & high frequency extension?
The industry doesn't seem to have settled on a particular format.

Currently I 'm thinking an 8" woofer crossing over at 800Hz to a pair 3" fullranges (eg Tangband)in a horizontal TMT arrangement (fullranges on the left & right sides of the box, and the woofer on the front).
On the other hand, Seas coaxials or a simple MT are nice simple options.

[Timn8ter]

It seems that Dolby left the door wide open for surround speaker design. I think it may depend on how large you want the listening position to be. In SACD or DVD-A surround it generally comes down to a very small listening position with 5 identical speakers capable of the usual 20-20kHz response range. For a larger listening area, such as a home theater, dipoles will probably serve better. Typically, there is a LFE channel so low frequency extension from the satellites is not necessary. Somewhere between 80-100Hz should be adequate. High frequencies are found quite often in surround channels so a minimum of 15kHz extension would be advisable.

[Mr Evil]

I prefer having all the speakers identical. Otherwise, sounds panning around will change their character depending on their position, which doesn't sound so good. Of course whether that's a problem or not depends on the type of source material.

[GM]

Consensus? Well, there's Dolby's cinema/studio mixing room recommendations so to my way of thinking the closer a HT layout conforms to it, the better.

Assuming there's been no changes in recent years, the surrounds are mixed on what's called an 'x' curve, and there's more than one depending on the mixing room's size and the whim of the eng./producer/client/whoever. The original standard is flat from 63-2kHz, with both ends rolling off at 3dB/octave, so 20Hz is -5dB and 20kHz is -10dB, but according to Dolby, some mix the bottom flat to 20Hz and AFAIK there's nothing on the DVD to warn you, so caveat emptor. The modified curve is flat to 2kHz, but rolls off at 1.5dB/octave (-5dB/20kHz), though some prefer to keep it flat to 4kHz, then roll it off at 3dB/octave (-7dB/20kHz). If the surrounds are set to small, then everything below 100Hz is sent to the L/R mains, and of course if they're set to small, then all the channel's LF goes to the LFE.

Also, some mix the surrounds at 79dB Vs 85dB to improve dialog intelligibility in a home's typically higher ambient noise, so on movies where this is a problem try setting the surround's reference lower.

Nothing like having multiple 'standards', eh? Bottom line, best to design around a 'worst case' scenario.

Anyway, a cinema's/studio mixing room's surround system is based on the dictum that if you provide enough insignicant sources they combine to be as one, ~ the same as a 'finite' line array of many single drivers with the comb filtering between them providing the proper amount of diffusion. They should be mounted up high and angled down so they can cover/overlap as much of the listening area as possible. Consequently, a small sealed or aperiodically loaded co-ax, or MT is desired, ergo if a single speaker/channel is used then a multi driver version such as your TMT works well if the angles/driver polar responses suits the app.

If you choose to use multiple speakers/channel, then the HT rule-of-thumb is to position the first one ~1/3 of the room's depth back from the screen plane with the rear most one being the same distance from the rear wall, with similar spacing along the back wall. If the room is deep enough, then spacing additional ones ~the same as the center-to-mains distance worked well the one time I tried it. Obviously, for a small room, one speaker on the side and rear wall/channel is all that's required, though four sounds subjectively better to me. If you have surround EX, then of course the rear speakers will be separate channels.

WRT all drivers being the same, it's what I prefer/recommend, as does Dolby for HT/mixing rooms, but if enough speakers/channel are used it doesn't seem to matter. Witness a cinema's super large horn loaded LCR system Vs a bunch of ~small TM or TMW surrounds.

As always, YMMV.

GM

[Cyrus_s]

IIRC 'Correct' would be identical wideband driver setups all the way around with a sub for the LFE channel that is equally wideband. As much as a subwoofer can be that is.

Of course after this, taste and real world applications come into play.

hth,