Eytan Gidron wrote on Sat, 08 March 2008 11:08 |
I am spec'ing a background music system with Turbosound speakers and Crest amps. The are two zones:
1) A large outdoor open area which I want to cover with 4 x Turbo TCS-121C 12" speakers at four corners. The cable length from the amp room is about 100M (330 ft). These speakers can be ordered with a 70/100V transformer option (the maximum tap is 120W).
2) A smaller space for which I want to use 8 x Turbo Impact-65T speakers. This area is about 50M (165 ft) from the amps. These speakers also have a 70/100V transformer (the maximum tap is 60W).
I have no experience with 70/100V lines, but it seems to me that because of the cable length I should go this route. My questions are:
- The speakers can work with both 70V and 100V lines. Crest has amplifiers for both 70V and 100V. Which should I use? Are there any advantages for using one type of system over the other?
- Which amplifier power ratings should I use? I would like to have the speakers operate at full bandwidth (without high-passing).
- Which cable gauge should I use?
Any advice would be helpful.
Thanks,
|
As others have offered constant voltage systems often have compromised LF response because of the step up/ step down transformers.
For perspective imagine the size and weight of your amplifier's power transformer. That is sized to pass power at 50 Hz, now to pass that same power at 25 Hz, it would have to be twice as big and heavy. If you could find one rated to go that low. Most constant voltage designs don't even try to hit 20 Hz on low end at full power.
As has already been mentioned, you can get around the limitation of the step up transformer end by using direct drive. A 100V line is the same voltage as a conventional amp that delivers 1250W into 8 ohms. Your only LF limitation in that case will be the stepdown transformers on the turbosound speakers which hopefully will be of similar performance to the speakers (but check the specifications).
If you are driving 8x60W taps and 4x120W taps from a single line that's almost a kW, so a
1250W@8 ohm amp is not overkill. However for background music you may not want to run at full volume, especially in the smaller space.
A stereo amp gives you two zones, so roughly 500W on each side of a
2x1250W@8 ohm amp.
JR