Hey all. I plan on picking up an amp (Infinity Reference 7451A) with 139 watts RMS x4 channels @2ohms, and two pairs of speakers, one with 75 watts RMS power handling per speaker @2ohm, the other with 90 per speaker @2ohm.

If that confused you, basically, the amp is pushing too much power for the speakers to handle over time (75/90 needed, 139 provided). I'm wondering what i'd need to limit the power down to the speaker's individual power ratings. If I have to wire something in, would it increase resistance? I know nothing about wiring if I haven't displayed it already.
Thanks for any help!

P.S. No, I won't buy a different amp.

 

what speakers are you running?

 

There should be gain controls you can turn down to take care of that.

 

Amp
http://www.sonicelectronix.com/item_8014.html#

Speakers
http://www.sonicelectronix.com/item_5154.html
http://www.sonicelectronix.com/item_4295.html

 

Yeap... it's pretty much called a volume ****. :D

And actually, having more power than your speakers can handle isn't really a bad thing. Unless you run them to the max for extended periods. In actuality, the higher power amp will treat those woofs much better than an amp matched spec-for-spec. The thing is that amps driving subs are often driven into clipping, exceeding the amp's max output and sending the THD through the roof. What does this mean? It means that the woofs are no longer being properly controlled. Oh, and they start seeing heavy square wave content, which is almost as bad as DC.

So, in short, there are 2 ways to blow your speakers. Sending them dirty signal and sending them too much signal. A lesser amp is more likely to commit the former, and a bigger amp, the latter. I'd prefer the latter, as that kind of death is just caused by heat, and it doesn't happen instantaneously.

 

Duh duh duhhhhh.

 

Woo! Thank you so much. A question though, is there a good way to measure what would be considered too much? Or would that point of volume already be considered unbearable?

 

Man they are saying you only put out max wattage when its turned all the way up. If the gain on the amp is turned down a little you cut back on the actual output. You should be able to tell also if you are overdriving the speakers because it will sound like crap.

 

You can use an O-scope or digital multi meter. If you use one of those to set your gains then you should be fine.

 

Exactly. I just felt like being a know-it-all tonight.

And it takes VERY little change in volume to make a huge difference in the amount of juice sent to the voice coil. A drop of 3dB in volume cust the current to the speakers in HALF. So go ahead and show off your system to your buddies. As long as nothing SOUNDS distorted and you keep your runs to a few short minutes, you'll be fine.

 

The component set isn't worrying me as much now. It's the coaxials that I plan to put in the back. Their power handling is 75. 139 watts is pretty close to double what they can handle. Will turning the gain down affect sound quality? Or is gain simply the amount of power sent?

[/noob]

 

Gain control is just another way to say "volume ****". Typically (at least for reputable companies), RMS tests are accomplished over extended periods. We're talking tens of minutes.

And are you going to be running subs? If so, highpass the components (front AND rears) at 60-80hz. That right there will pretty much eliminate the possibility of your 140W amp smoking the woofers.

 

Oh yeah, that's right. Low frequencies take more power. I'm going to be installing a 13Ov.2 and a Nine.2x at the same time I do all the work. Thanks man, helped me out a lot!

 

One last thing, dude. The system you've outlined above is PLENTY to cause you permanent hearing loss in a VERY short period of time. Never forget that. Unless you're not worried about the stereo that's installed in the car you buy when you're 30... Check my posted age and then ask me how I know that. It sucks. Hard.

 

Which is why i'm stretching my teenage budget beyond belief to go for a SQ setup. Hell, I could have gotten a beast amplifier and a pre-packaged set of two Kicker Comps for around $500 and had the block hear me from a mile away, but i'm saving up almost $1200 to get the good stuff. Thanks for the consideration though. As a drummer and general music enthusiast, I know what my hearing will mean to me in the years to come.

 

A gain control is NOT a volume ****. Gains are used to match the signal strength from the source(ie head unit) to the amplifiers input section BEFORE the amp's output section.

Without making this a long Technical response, basically if you max out the gain of an amp you will only be able to turn your head unit about 1/4 of the way up and the amp will be pushing it's maximum clean output. Any further and the amps output will just be distorted. Distortion = heat = fried speakers. The idea is to set the gains of an amp to reach full undistorted power when the head unit is turned all the way up to it's full undistorted output. (with most head units that point is about 4/5 of the way up).

An other note, even the best speakers out there are, at best, 50% efficient. Yes, that means if your speakers are rated 50watts, then you should have a 100watt amp driving them.

So g3kko is correct in saying that it is better to have more amp then speaker. But never think of a gain control as a volume ****.

So, don't worry, your set-up is fine.

 

Thanks for the input all. I CANNOT wait to get the funds for all of this together. I plan on doing all of the install myself, from the Big Three 0-awg wiring to the Optima Yellow Top battery to pulling the interior out and deadening everything that vibrates.

 

Did you say 1/0 power wire, Optima yellow top and sound deadening everywhere?

 

another thing... the speakers you are getting are 4 ohm not 2 which means the amp will put out about half as much power at 4 ohms. i'm pretty sure the reference series from infinity is 4ohm.

 

The best measurement instrument for that is your own ears. If you crank it and can easily determine if the speakers are distorting by listening, turn it down before you damage them. If you listen, almost all speakers will warn you that they're not getting a healthy signal (outside their freq.range, too much power and/or distortion, etc), such that you can turn it down to avoid damage.