400 WATTS into a 5.25" 45W RMS Speaker ?

[johnviera]

Can you guys help me figure this out?

I have an old reliable QSC RMX 1450 AMP that I use to use for DJing parties . It use to crank these 2 two-way 15" woofer and a horn tweeter cabs.

The other day I adopted these 2 high-end 6" bookshelf speakers. I hooked up the QSC amp and I could easily push them to 9/10 volume levels with no problem. I was scratching my head. This amp puts out 250W@ 8 ohms STEREO and 450W@ 4 ohms STEREO. I use to drive those 15"s at 7/10 or maybe 8/10. So I figured ok..ok.. those high end monitors must have a weird large impedance x-over or some weird high current amp necessity thing.

So today I get a pair of brand new POLK Audio db521 coaxial car speakers. They are 5.25 inches and are rated 45W RMS 100W MAX 4 OHMS and 93 db. I hook them up to the QSC amp and they are asking for some at 8/10 volume. What ?!?! @ 450 WATTS !!!

What is up? Is my amp messed up? It sounds fine, looks fine, I know how to hook up this stuff. I am confused.

Thanks,
JV

[stratus46]

How long did you run at that level and more importantly, how long do you _think_ you can run at that level?

G²

[johnviera]

Ran it for a whole song with the car speakers. Amp never even got hot. Plus the amp use to get hot with the big DJ speakers. Now with the bookshelfs for hours or the car audio it is blowing cold air.

Is there an easy way for me to test the output watts?

I read some FAQ online and tried it. It only went up to 8 volts. Iused a test tone sweep of Youtube. I know.. i know. high tech stuff.

[EWorkshop1708]

Speakers take more power when not being fed distortion.

[soltari_knight]

JV,

You might want to start with your source. Amps require certain input voltage to attain full power. For example, if your amp requires 1V input for full power output and your source only provides 200mV, then your amp is only doing 1/5 power.

A quick check with your manuals maybe helpful on this case without getting any tools.

Ps: if you are getting only 8V @ 8ohms, then your speaker is only dissipating at 8W.

[gray5596]

If you are measuring 8 volts at the speakers, you are pumping out about 16 watts.
(P=E2 / R) Perhaps your CD/MP3 player has a low output level, so try another input source.

[gray5596]

Sorry, I was typing and didn't notice Soltari's post. He figured the power on 8 ohms and I figured it on 4 ohms.

[stratus46]

Originally Posted by soltari_knight

JV,

You might want to start with your source. Amps require certain input voltage to attain full power. For example, if your amp requires 1V input for full power output and your source only provides 200mV, then your amp is only doing 1/5 power.

Nope. Not even close. 1/5 the Voltage reduces the power to 1/25. Remember power is E²/R.

G²

[wg_ski]

Unless your clip lights are flashing wildly, the amp will be putting out less than 10% rated power on average. An amp rated at "400 watts RMS" is really only good for 400 watts peak, unless you want every cycle of a constantly-changing waveform to be clipped. If you did push that amp to full power continuously, it would get blazing hot within a few minutes, the speakers would be toast, and before that, the distortion would be so bad you can't tell what song is playing. And you'll probably trip your 20 amp mains breaker.

[Original Burnedfingers]

I think this has been covered but to recap don't pay any attention to where the input control is set. If its set a say a 9 it doesn't necessarily mean the amplifier is putting out almost full power. It all depends on the signal being fed into the amplifier. More signal = more power at the same number setting.

Fixed an amplifier for a guy once and his comment to me was I only had it set a 5 on the input control. Well a source like the 1812 overture with cannon blasts being fed into a preamp that was turned up 3/4 or more output was enough to do the deed. Like I said I fixed the amp checked it out let it run on a load and pronounced it good. The guy took it home and did the same thing.
I repaired it again explained the situation to him once more and the amp still lives yet today.

A small speaker will and usually survives when being fed by a large amplifier as long as the person doesn't do something stupid like asking the speaker to put out extra low end or drive to very loud levels. I am of the opinion that most speaker specifications are 100% bs. I look for spec that rates the speaker with pink noise at a specific wattage. Example is a pair of Altec model 9 speakers rated at 60 watts pink noise. The same speaker are rated for amplifiers I believe in the 30-250 watt range. Took out a low freq and a midrange in my younger years by driving the speakers with a 60 watt amplifier. They have had 400 watts per channel on them since without problems.