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Old 04-15-2007, 05:31 PM   #1
BlitzSix
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Fosgate amp questions

I recently aquired a fosgate T4004 amp, and some alpine type S speakers, pictured below:




If one was to read the specs, they would see that this amp is rated at 25 RMS x 4 @ 4 ohm.

The alpines are rated at 2-50 RMS @ 4 ohm. So the amp would push them at 25 RMS, which is good (not underpowering or overpowering them).

Here are the specs:



As you can see, 25 RMS per channel on 4 ohm.

But, as you observe the birth sheet, it says 91 RMS x 4 at 4 ohm!



Can someone explain to me how this works? Why does it show that my amp is putting out almost 4 times teh power it's supposed to put out? Am I reading the wrong or something? Why would fosgate do this? Is this amp too powerful for my speaker now?

Please help

Also, why does it say 55.842% effieciency? What does this mean? Does it mean my amp sucks?

Thanks.
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Old 04-15-2007, 06:58 PM   #2
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no, not a chance. your amp is just underrated. consider this a good thing. most are overrated.
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Old 04-16-2007, 02:50 PM   #3
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haha, awesome.

91rms is a lot safer than 25rms. Enjoy the significantly better sound (if it was actually 25rms I wouldn't even want to run it).
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Old 04-16-2007, 03:02 PM   #4
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Its actually a good thing, jus dont turn ur gains all the way up.
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Old 04-16-2007, 05:19 PM   #5
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Thanks guys. I won't turn them all the way up

Jay... can you explain please? How is running the speakers at an RMS that's almost twice the maximum safer than running then them within their range?
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Old 04-16-2007, 05:58 PM   #6
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25rms is low. Extremely low.

Speakers sound better given more power (same other variables). It's actually 10x safer to run an amp with a lot more power than the speaker than vice versa (or even running just 25rms). This is because the speaker will distort audibly before the amp clips. And the vast majority of the time, it's amp clipping which damages drivers.
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Old 04-17-2007, 12:26 AM   #7
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That sounds logical, but why would the amp clip if its running within the required RMS.

Would you consider this amp good to push these speakers? Are these speakers good?

Is it okay if I use a Memphis amp which pushes out 1100 RMS to power 2 fosgate power 10s that are rated at 150-600 rms each ? So 550 to each sub?
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Old 04-17-2007, 12:34 PM   #8
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Quote:
Originally Posted by BlitzSix
That sounds logical, but why would the amp clip if its running within the required RMS.

Would you consider this amp good to push these speakers? Are these speakers good?

Is it okay if I use a Memphis amp which pushes out 1100 RMS to power 2 fosgate power 10s that are rated at 150-600 rms each ? So 550 to each sub?
The amp will clip if the volume is too high. And if the amp isn't as capable as the speakers, you won't have much audible warning; by the time you hear clipping it might be too late. On the contrary, if the amp is better than the speakers the drivers will just distort, which gives you a nice reminder to calm down on the volume.

That amp sounds good, and the speakers are decent too. As long as you have a good headunit and tune it all properly, that should be a great sounding system.

The Memphis amp, is it 1100rms into 2ohms? And what is the impedance of the subs?
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Old 04-17-2007, 05:19 PM   #9
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Quote:
Originally Posted by Mystikal
The amp will clip if the volume is too high. And if the amp isn't as capable as the speakers, you won't have much audible warning; by the time you hear clipping it might be too late. On the contrary, if the amp is better than the speakers the drivers will just distort, which gives you a nice reminder to calm down on the volume.

That amp sounds good, and the speakers are decent too. As long as you have a good headunit and tune it all properly, that should be a great sounding system.

The Memphis amp, is it 1100rms into 2ohms? And what is the impedance of the subs?
Uhh the Memphis amp is 1100 RMS at 1 ohm. And it's 1 ohm stable. And okay I found this part confusing but my audio guy assured me it makes sense: The subs are dual 4 ohm coils, which somehow makes each one run at 2 ohms which somehow makes them run together at 1 ohm when you connect them in parallel, thus being good for the amp. Does this make sense? He told me to go with the T110D4 isntead of the T110D2 because with the d4 i can run them at 1 ohm or something.



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Old 04-17-2007, 06:07 PM   #10
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he is right.

Two DVC 4ohms sub could be wired up to run at either a 4ohm or 1ohm load.
See below.

The reason the 1ohm load is X-out is bcus the amp i took this from isn't 1ohm stable, but urs is.
Attached Images
File Type: jpg dvc.jpg (68.1 KB, 42 views)
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Old 04-18-2007, 01:03 PM   #11
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Quote:
Originally Posted by Mystikal
The amp will clip if the volume is too high. And if the amp isn't as capable as the speakers, you won't have much audible warning; by the time you hear clipping it might be too late. On the contrary, if the amp is better than the speakers the drivers will just distort, which gives you a nice reminder to calm down on the volume.
Doesn't the protect mode turn on if too much load is on it?

PS THanks t dot.
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Old 04-17-2007, 09:35 AM   #12
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the amp clips when its driven past its specs. notice on the spec sheet its stated '91rms @ <1%THD' - this is the distortion spec. they didnt get that value by maxing the gains. any amp will distort if you push it too hard.

yes, the amp is perfect for those speakers. sounds pretty decent.

and yes, you can use that amp on the subs. i used a 1500wrms amp to power 2 subs rated at 350 apiece havent blown them up yet
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Old 04-17-2007, 10:33 AM   #13
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Just use your ears or have your system tuned properly.

Don't just turn everything up and expect it to sound good.
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Old 04-17-2007, 02:21 PM   #14
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Overpowering >> underpowering. You can always turn the gain down.
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