Originally Posted by commsysman
It's the VOLUME of the room that counts; not the floor area. It is 4800 CUBIC FEET.
You need a 12-inch subwoofer with at least 350 watts of RMS Power (about 600 watts Peak). an 8 or 10 inch sub is totally inadequate.
Let;'s put it this way, my audio system has a listening distance of about 12 feet but it is in a room that is in a home with a fairly open plan so the joint open area is maybe 25 x 20 with a 9 1/2 foot ceiling. I have 2 12" subwoofers and the 2 15" subwoofer drivers on hand to complete the project.
Your receiver can put out 90 watts to ONLY TWO channels, when driving a resistor test load; read the specs.
Agreed. but with a significant difference in interpretation that is based on strong engineering principles and experience both on the test bench and in actual use.
It won't deliver that much without distortion to two real speaker systems.
Well taking a narrow reading I have to agree, the AVR "...won't deliver that much without distortion to two real speaker systems", it will deliver far more!
Here's some reasons why:
The impedance of speakers may go below their rated impedance over part of their range, but on the average they tend to go higher. Here's an example that I picked to be a reasonable worst case:
Notice that there are some dips below 4 ohms, but there are more peaks that go well up to 6, 8 ohms and beyond. I picked this speaker for my example because just about every other speaker I know of would illustrate my claims even better.
This argument is even made stronger because speakers have a property called reactance that is far more than that of the resistors used to bench test and rate AVRs. A reactive load does not dissipate energy like a resistor, it just stores energy and shortly later "gives it back" to the receiver during other parts of the output wave cycle. Basically what happens is that while you are playing music with the AVR some of its power is taken from the positive voltage power supply, momentarily stored in the loudspeaker's reactive components and then absorbed back into the AVR's negative power supply, and vice versa.
Secondly, music differs from the pure sine waves used in the tests referenced above in that it has a significantly higher values of a property called crest factor. High crest factor means far less strain on parts like power transformers, output transistors and heat sinks. The crest factor of music is so much higher than that of the pure sine waves used to bench test and estimate power ratings of AVRs, that the 2-channel tests mentioned above could be achieved for 6-8 channels with real music and real speakers.
Old school receivers and amplifiers had far heavier power transformers and heat sinks, but what they brought to the table mostly went unused.