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Author Topic: Surround speaker cable run length - same? Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 11-04-2009 09:03 PM                     The higher the frequency the more likely you are to see propegation delay. I still disagree with series parallel and except for cheap skate installations there is no real excuse for doing it. You will still see lots of phase related errors happenning by sending sound through one set of speakers. Usually the phase errors are caused more by the x-over then any other part of the speaker. Mark  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 11-04-2009 09:17 PM                        So, when did 70v lines become unpopular for surround speakers? Other than the cost of the transformers, is there any disadvantage to this arrangement?  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 11-04-2009 11:21 PM                        quote: Scott Norwood So, when did 70v lines become unpopular for surround speakers? Other than the cost of the transformers, is there any disadvantage to this arrangement? Offhand, I'd guess a couple of reasons. First, you can use the same amplifiers you're already using for your stage speakers. Of course, you could put a 70v transformer in the booth, but why bother? Installing an amp with a 70v output wouldn't make sense to today's highly efficient chains, because now you have 2 models of amp in your rack... 3, if you're running a different subwoofer amp. Easier to tie them all together, or series/parallel them and hope Mark doesn't show up to service the booth.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-05-2009 06:40 AM                     ANY amp can be made to run a 70V system so some of Jack's theory is gone. QSC even makes the OT300 and OT600 for their amps to run 70V. So Scott hit upon it, mostly. It is a money thing. You are going to need an output transformer large enough that will handle the output wattage of the amp (for surrounds, nowadays, it is going to be at least 400-watts for even small theatres). The typical surround speaker in a digital performance is going to need to be able to handle 100-watts or more...so the speaker transformer is going to need to be big enough to handle that. Note these transformers are going to need to be of high quality or frequency response will suffer. You add up the two transformers in the rack and the 8 to say 24 transformers in the theatre and you could have bought a lot more amplifier(s) and larger speaker wire. 70V systems work well when each speaker doesn't have to play REAL loud. Like in distributed music systems. The typical ceiling speaker is going to be tapped at 15W or less (often just 1-3 watts). Thus, you can cut up your amplifier's power to power a great many speakers. Furthermore, with the higher voltage, you have lower current so your speaker wire can be relatively small with no ill effects. Steve  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 11-05-2009 10:30 AM                        quote: Steve Guttag ANY amp can be made to run a 70V system so some of Jack's theory is gone. QSC even makes the OT300 and OT600 for their amps to run 70V. I thought I said that, Steve. You can easily put a transformer in the rack and convert your amp for 70v operation... unless you're talking about something else. A few drive-ins have matched indoor theatre amplifiers to their field systems this way, even though there are plenty of amps on the market with 70v outputs. Still, I doubt that many indoor operators will see enough advantage in this technique to use it.  |  IP: Logged

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