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Old 5th March 2010, 03:01 PM   #1
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Default 1000w amp driving a 1 watt speaker

how do i drive a speaker with a over powered amp and not let the speaker explode?

i have a kicker L7 12 inch rated at 750wrms from kicker. i am driving this with a JBL BP1200.1 amp. i have blown 2 coils out of this thing and right now i have the amp at 50% gain.

i want over powered amps because i use this stereo all day long and i dont want the amps getting exceisvly hot. so i figured i would over shoot the amps by a little bit this way i could use 100% of the speakers capacity.

i would like to upgrade the speakers so they candle handle more of the amps power. but i think i would be in a similar situation. using 20% of the speakers capacity and 100% of the amps or vice versa.

i cant seem to get a consistant answer as to how to accuratly figure out the power handeling of a speaker the answers i get are grossly exaggerated conservitavly (so not to blow anything up ever) or aggresivly (to market and sell speakers with crazy power handeling capabilities)

i realize that the box determines a lot and the music also determines a lot but there must be a accurate way to figure out a best guess instead of just blowing up a voice coil then turning the amp down 10% and repeat... this is getting expensive and annoying
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Old 5th March 2010, 03:06 PM   #2
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You will always blow up coils...
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Old 5th March 2010, 03:16 PM   #3
el`Ol is offline el`Ol  Germany
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Get a Tripath class D amp. Never gets hot and won't ever blow up your speakers.
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Old 5th March 2010, 03:29 PM   #4
Glowbug is offline Glowbug  United States
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Quote:
Originally Posted by el`Ol View Post
Get a Tripath class D amp. Never gets hot and won't ever blow up your speakers.


If only it were that easy

Quote:
how do i drive a speaker with a over powered amp and not let the speaker explode?
Using an amp rated for X watts doesn't mean you have to use it like that. Learn to recognize the distortion from the onset of clipping, and know when your woofers are starting to get unhappy. Get someone locally who can help you, if you're having trouble hearing it for yourself at first. The other thing that might help is to get your amp on a 'scope at your typical listening levels - it'd be instantly apparent if you're clipping the amp.

The gain position really doesn't matter, you can toast subs at either end of the potentiometer - what's important here is the relationship of the preout voltage to the gain position. The amp is capable of full power regardless of where the knob is set.
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Old 5th March 2010, 03:39 PM   #5
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If you're not driving the amp to hard clipping, the sub is simply not capable of doing what you want it to do. If it could, you wouldn't need to drive it so hard. You need more subs. If you only have one, use two. If you don't have room for two, use one that's more efficient or one that can handle more power.
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Old 5th March 2010, 03:54 PM   #6
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Glowbug and Perry's answers are good. You are willing to spend for an oversized amp in the interest of increased reliability and reducing distortion, right? So it makes no sense to undersize the woofer in that interest. If you're having consistent problems with driver failure you're operating far into the red zone though for some reason the high distortion in that case isn't promting you to turn the volume down. It does get harder to hear around the port frequency (assuming ports) because of the filtering property of the resnonant system, but maybe the distortion isn't so much of a problem for you compared to demanded SPL. Most autosound drivers are moderate to very poor efficiency. They are designed for good extension in small boxes with the benifit of cabin gain. Unfortunately efficiency is tightly strapped to box volume in any case, so if you want a little woofer to play loud and low it is going to get hot. That's why there are so many extremely built car woofers on the market. In the end knowing exactly how hard you're pushing your drivers isn't why you run your system. You should probably seriously review what you want from your woofers and redesign for that with new woofers and possibly new enclosures to suit. It might hit you hard in money up front but there's a good chance it will be reliable for years and sound good all along. Ultimately you will find that the big money is in how far down the -3dB point lies. Physics says you can get any combination of higher efficiency, reduced size, and lower cost by raising the -3dB point. The reason you can't get a hard answer on this is that it's a matter of personal preference and goals. Anyone can lead you in the right direction if you know what you want but I don't think anyone can make the woofer you have do it.

Last edited by Andrew Eckhardt; 5th March 2010 at 03:58 PM.
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Old 5th March 2010, 03:59 PM   #7
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I would guess that you clipped that poor speaker to death.

You might think the amp had enough clean headroom because of advertised numbers, but reality is often much different.


I think some people will over-drive their systems and cause damage no matter what the situation is. For example; if the amp is underpowered they will drive it into clipping and fry the voice coil with DC, but if the amp has excess headroom they will over-drive the sub until it exceeds it's thermal rating or part of the suspension gets broken.

I think they key here is to learn when to turn the volume down.
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Last edited by theAnonymous1; 5th March 2010 at 04:06 PM.
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Old 5th March 2010, 04:25 PM   #8
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Scampo, I would start by assuming that you need at least 6dB more of safe continous power output, which means you're looking at four times the woofer you now have. Reducing woofer drive 3dB means that excursion is halved, the difference between 1000 and 500 watts. Don't get into trying to run woofers near Xmax to get your money's worth. The truth is linearity is much better far below that and suspension and coil life goes up fast. 3dB of power headroom sounds ridiculously expensive but that's the reality of long life, low distortion systems.
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Old 5th March 2010, 10:42 PM   #9
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so is this speaker for certain clipping? the way i understood clipping was that it is the amplifier running out of power. there is no way this amp is running out of power. the first voice coil i just put a pure sine wave into the speaker till the coil lit on fire. i would think the easiest way to hear for clipping would be with a a sine wave? no? and this sounded perfectly perfect, (till the fire, then not so perfect)

i will set up a scope if this helps me learn what to watch for but i just dont think it is clipping or distorting at all.

the reason i am building it this way is i dont want the amps getting ridiculously hot. the last 2 amps i had ran so hot that i used to squish my sandwiches in between them and use them as a panini press. aside from tasty lunches i figured this cant possibly be got for the longevity of these amps plus it heated up my cab in the summer. so i thought why not use bigger amps and just use less of the available power. both times i blew up this speaker the amp wasn't even warm so i figure i am on to something.

i have purchased new subs but i dont want to put them in and have the same problems im having now.

so in short,
-put a scope in and look for clipping
-listen to the speaker distort

is there anything else i can look for before it explodes again? because right now i am just running it with no dust cover and just jamming my finger in there to test for temperature (i know quite scientific).

im going back tmrw with a new coil installed, if nothing else im getting pretty good at changing the coils on these things LOL.
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Old 5th March 2010, 11:34 PM   #10
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The speaker simply can't do what you need it to do. If it could, you wouldn't be driving enough power into it to blow it.

Do you have the space for 2 woofers?

What about a better woofer (something from DD?)?

For most car audio subs that can handle significant power, the dust cap is part of the cooling system and is required to pull the air into the gap around the voice coil. Without it, the air flow will be significantly reduced.
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