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Dakotaman
Dodge Dakota
JOIN HERE
9/04/2005
01:46:59
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 Subject: Smelling the subs??
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I have a pair of L7 12's in my cab, they are each in a 3.12cu. Ft. slot ported box tuned to about 29hz. When i have the bass all the way up, mostly on songs with really low low bass, i can "smell" the subs, it is an electrical smell. But it only is noticeable when low bass is playing, i think this is because the subs are moving slower from max to max, and it moves more air out of the ports, i was just wondering how bad this is. heres a link to a pict of my set-up, btw, its not done quite yet, still got a little finishing work to be done,
Thanks for any input,
Steve
http://i16.photobucket.com/albums/b19/scuba__steve/DSC00588.jpg
http://i16.photobucket.com/albums/b19/scuba__steve/DSC00587.jpg
http://i16.photobucket.com/albums/b19/scuba__steve/DSC00585.jpg
p.s. it knocks pretty hard, dynamated the enitre rear cab, and both doors, no raddles at all!!
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Jim Z
GenI
9/04/2005
09:35:26
| RE: Smelling the subs??
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When i have the bass all the way up, mostly on songs with really low low bass, i can "smell" the subs, it is an electrical smell.
You're overheating the voice coils. Keep it up and you can kiss the speakers goodbye.
But it only is noticeable when low bass is playing, i think this is because the subs are moving slower from max to max, and it moves more air out of the ports, i was just wondering how bad this is.
It's very bad. Your speaker is "unloading" at those frequencies (below box resonance,) and the enclosure/port are doing nothing to control the speaker. Get a subsonic filter on there immediately.
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Dakotaman
Dodge Dakota
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9/04/2005
11:03:45
| RE: Smelling the subs??
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no no, when i said low low bass and it going from max to max, i didn't mean it was below the tuning freq. Its just that the bass is soo low that the subs move in and out slower and more air is being shot out the ports, the subs are still "in control". But as far as the smell goes, why would this be happening? My amps definatly are not over powering the subs, subs are 750RMS 1500MAX and my amp is 560RMS 980MAX running @ 4 ohms. The amps are not hot when this happens so i guess they aren't under any stress. Plenty of power is being provided to the amps, i have 200AMP alternator and all 1/0 guage wiring. Could the amps be clipping?, the gain is only 1/2 way up. Please help.
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Jim Z
GenI
9/04/2005
12:57:02
| RE: Smelling the subs??
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no no, when i said low low bass and it going from max to max, i didn't mean it was below the tuning freq. Its just that the bass is soo low that the subs move in and out slower and more air is being shot out the ports, the subs are still "in control".
I don't think you understand what's going on. if air is "blowing out" of the ports, then it isn't controlling the woofer. A vented box relies on the column of air in the port to resonate roughly in phase with the speaker. This is what helps re-inforce the SPL from the woofer, and extend the frequency response further down. Air blowing out of the ports is a sure sign that the box is unloaded.
What are the dimensions of your port?
But as far as the smell goes, why would this be happening?
here's the thing- a speaker is not a purely resistive load. It's only 4 ohms (or whatever its rated impedance is) at a few points in its frequency range. The reason this is is that it is a coil of wire moving through a magnetic field. around resonance, the impedance can rise to over 50 ohms. So most of the time, the amplifier is not delivering its power at rated impedance; for a given output voltage, the power to the speaker will be much greater at 4 ohms than at 50 ohms (Ohm's law, P=V2/R.)
Where am I going with this? one of the places where the speaker impedance is actually 4 ohms (or 2 or 8) is below resonance. So when you hammer it down that low, you are actually trying to make the voice coil dissipate that 500 watts or so, and it really can't do that. In essence, the woofer relies on the back-EMF generated in the coil to reduce the actual power being delivered.
So, since you're unloaded and below resonance, you're trying to make the voice coil dissipate far more heat than it's capable of, and it's starting to burn the insulation off.
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Jim Z
GenI
9/04/2005
13:09:20
| RE: Smelling the subs??
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This is a speaker's impedance curve. Let's pretend it's hooked up to your amp. Your amp, when it delivers 560 watts into 4 ohms, it's outputing about 47 volts RMS. So in the speaker represented by the curve above, pushing a 100 Hz tone at 47 volts will actually P=(472/26)=84 watts. Now a 20 Hz tone would deliver 472/6 = 368 watts. Running the speaker continuously at 2 Hz would most likely burn it up.
in your situation, the resonant peak will most likely be at 60 Hz or so, but the theory's the same.
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Dakotaman
Dodge Dakota
JOIN HERE
9/05/2005
22:33:25
| RE: Smelling the subs??
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thank you Jim Z, you seem to be very knowledgeable in this area and i apecreciate it. Hey, any chance you have any secrets about fixing alternator whine? I got it pretty good (pretty loud), brand new alternator (replaced for more power, not to fix noise), all grounds are as short as possible, about 8inches, i tryed a ground loop isolator in line with the RCA wires going to my 4 channel amp, didn't do anything. I've tryed grounding everything directly to the battery, all to one central point on the frame (including ground for CD player), all over the place. (Oh, and i'm suspecting the problem is being caused by a ground loop) and none of this has shown any signifcant improvements. Anymore advice i would love, thanks
Steve
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