swwdts

05-23-2006, 11:45 PM

Ok, if I had an amp/subwoofer w/ a 100 watts peak in 4 ohms load .Would it go down to 75watts peak in an 8 ohm load?

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swwdts

05-23-2006, 11:45 PM

Ok, if I had an amp/subwoofer w/ a 100 watts peak in 4 ohms load .Would it go down to 75watts peak in an 8 ohm load?

N. Abstentia

05-24-2006, 04:00 AM

It does not really matter, since the peak rating is useless. You need to look at the RMS rating which gives you the useable power. If it's 100 watt 'peak' it's probably actually 40-50 watts RMS.

swwdts

05-24-2006, 08:06 AM

My owners manual lists that the FTC rating is less than 1% THD @ 56w @ 100hz @ 4 ohms. So, 8 ohms would make it only a 28 watt @ 100 hz @ 8 ohms ? Is that right? If it is the amp is going in Mondays trash pick up...

N. Abstentia

05-24-2006, 09:35 AM

1% is a lot of distortion, and it should be rated at 20-20khz instead of just at 100hz so it's not rated very good. What kind of amp is this? Sounds like a Pyramid car audio amp :)

swwdts

05-24-2006, 02:39 PM

It is an amp built into my KLH subwoofer.The KLH subwoofer is on its way to the dump & I am keeping its box for the new subwoofer that I am replacing it with.The replacement sub will be from Parts Express on pg 287 there is a Dayton loudspeaker w/ a 5 year war. on it.For those of you who have the book it is the QT255-4 subwoofer.Item # 295550 . Anyway,I have never heard of that brand I hope they are good.I bought the KLH at H & H Gregg .The bass sounds like a boom from a 1980's SEGA console.No boom just bleepThey said that it was a good one.I'll never shop there again.

N. Abstentia

05-24-2006, 03:15 PM

Well it probably WAS a good sub for the price you paid. What was it? $89? What did you expect?

And, is this the same .6 cu.ft. box you asked about before? If so, don't expect much difference. You'll need 1.5-2.0 cu.ft to get deep response out of it. If you can go 2 cu.ft. I'd go with a 12"

And, is this the same .6 cu.ft. box you asked about before? If so, don't expect much difference. You'll need 1.5-2.0 cu.ft to get deep response out of it. If you can go 2 cu.ft. I'd go with a 12"

swwdts

05-24-2006, 05:35 PM

Yah it is still the down firing 10" sub box. w/ 0.67 cubic air space.I found a 10" MTX that would work but,it was over $ 150.00.Due to current cash flow I have to stay under 150....My 8" sony ( 100 watts RMS ) subwoofer hooked up to my pioneer 600watt amp set on - 20 can make my living room windows vibrate. In a room 20' L x 12' W anything over a 10" powered subwoofer would be over kill.

Smokey

05-24-2006, 06:24 PM

Ok, if I had an amp/subwoofer w/ a 100 watts peak in 4 ohms load .Would it go down to 75watts peak in an 8 ohm load?

A simple calculation will answer your question.

First we need to find the voltage..

Voltage (squared) / resistance = watt

voltage (squared) / 4 ohm = 100 watts

voltage (squared) = 4 ohm x 100

voltage (squared) = 400 volts

voltage = 20 volts

Now that we have voltage (assuming the Amp's rail voltage doesn't change when load is varied), we can plug in the 8 ohm to find watts. So....

20 (squared) / 8 ohm = watts

400 / 8 = 50 watts

So 8 ohm load will result in 50 watts output.

You can use the formula below to plug in any numbers :)

http://www.sengpielaudio.com/OhmschesGesetzA.gif

A simple calculation will answer your question.

First we need to find the voltage..

Voltage (squared) / resistance = watt

voltage (squared) / 4 ohm = 100 watts

voltage (squared) = 4 ohm x 100

voltage (squared) = 400 volts

voltage = 20 volts

Now that we have voltage (assuming the Amp's rail voltage doesn't change when load is varied), we can plug in the 8 ohm to find watts. So....

20 (squared) / 8 ohm = watts

400 / 8 = 50 watts

So 8 ohm load will result in 50 watts output.

You can use the formula below to plug in any numbers :)

http://www.sengpielaudio.com/OhmschesGesetzA.gif

N. Abstentia

05-24-2006, 07:14 PM

Problem is..there's no way of knowing how much of that 50 watts is wasted as heat and distortion.

paul_pci

05-24-2006, 08:28 PM

All calculations aside, the bottom line is that there is no need to keep the sub amp.

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