AVA250 Subwoofer Plate Amplifier (1 Viewer)

[Brian Dobbs]

I don't understand the power specs of this amp. I am not familiar with plate amplifiers so can someone please explain to me why it can run 250w at 4 ohms, and only 180w at 8 ohms? For those of you who know my situation, I'm thinking of substituting my stereo receiver for this amplifier. Also, how many 4 ohm speakers could I run off of this amplifier? thanks
AVA250 Specifications
POWER 8 ohms, 180W - 4 ohms, 250W
Crossover Frequency 40 Hz to 160 Hz, second order Butterworth
Frequency Reponse 14 Hz to 160 Hz, +1/-3 dB
Phase Rotation 0 to 180 degrees
Gain Range 30 dB
EQ Filter Q 0.96
EQ Filter Frequency 18 Hz
THD Less than 0.1% THD at rated power
S/N Greater than 103 dB at rated power
Weight 12 pounds
Overall Size 10.5" wide by 10.5" high
Mounting Cutout 9.25" wide by 9.25" high
Mounting/Front Depth 3.5"/1"
Input Voltage 115/230V switchable, 50/60 Hz
High pass outputs First order Butterworth, 125 Hz
(on speaker level outputs only)
PRICE $179 each

 

[Dustin B]

That is what an amp is supposed to do. It is supposed to output more power as the ohm load goes down. This is another way of judging how good an amp is. The closer it comes to doubling its output power when the ohm load is halved the better the amp is. Go take a look at the specs on Krell amps. Their power output exactly doubles with every halving of the ohm load. This is also why cheap receivers (low end Kenwood, Pioneer, JVC, RCA) don't sound as good as the better units (mid to high end Denon, Yamaha, Onkyo etc). When the ohm load goes down on the cheap ones their power output barely increases.

 

[Brian Dobbs]

So this amp isn't specific about impedance? My stereo receiver requires an 8 ohm speaker, so hooking up two 4 ohm speakers in series would solve that problem. The stereo is also 100 watts per channel. Let's just say I had the volume turned up all the way so all 100 watts were being used. Wouldn't that mean that each speaker would receive 50 watts? I know I'm missing something here, but is this concept totally different than the plate amplifier/ohm relationship? What I'm asking is, if I had the plate amplifier cranked all the way up, wouldn't 125 watts go to one speaker and the other 125 go to the other speaker, assuming they were in series?

 

[Dustin B]

The AVA250 is rated at 8 ohms and 4 ohms and can drive both loads. Driving a load that is higher than what an amp is rated at is not a problem. It's driving a load that is lower than the amp is rated at that can cause a problem. The driver wants too much current and the amp over heats and shuts down if it can't provide it.
The ohm ratings of drivers are also a nominal value, not an absolute value. Depending on frequency, volume and probably several other factors the load a driver presents to an amp can fluctuate.
I can't answer your question about how the power gets split up between drivers in series, I don't have enough electrical engineering knowledge, hopefully someone else who does can explain it. I can point out though that with your logic and the AVA250 specs it would be 90 watts per driver (since two 4 ohm drivers in series is a 8 ohm load and the AVA250 only outputs 180 watts into 8 ohms). But my gut tells me drivers in series don't quite work like that.

 

[Chris Eriksen]

Brian,
For a basic audio reference, I would highly recommend reading through the following web site: http://www.eatel.net/~amptech/elecdisc/caraudio.htm

 

[Jason Pannell]

If you hook up two 4 Ohm speakers in series, the power dissapated by both will be half of the total power output of the amp. However 2 4 Ohm speakers in series has a total resistance of 8 Ohms, therefore with that amplifier each speaker will get approx. 90W, because the amp puts out 180W into an 8 Ohm load. Hope that this makes sense.
Thanks,
Jason Pannell