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Old 26th August 2010, 12:37 AM   #1
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Default 0.8 ohm drivers

Has anyone ever heard of this before? I bought a few 10" sub woofers of very reputable name and proceeded to cook the 5th channel of my amp. I thought it was overheating due to lack of air space around it. come to find out, it was the 1.3 ohm impedance of the two subs wired in parallel that I thought was going to be 2 ohms. After I cooked my amp, I checked the impedance of all of the drivers that are not in enclosures to find each measuring 0.8 of an ohm. A check of the two in my truck resulted in the same reading. I only have an old Fluke model 77 for my testing needs, so, I can't do a whole lot. I am going to need some advise with the amp repair in the near future but, for now. 0.8 ohm drivers????
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Old 26th August 2010, 12:46 AM   #2
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1.3 ohm DCR is what you would expect of a nominal 2 ohm speaker. 0.8 for a 1 ohm speaker.

I've not run into woofers with this low an impedance.

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Old 26th August 2010, 12:48 AM   #3
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Old 26th August 2010, 03:59 AM   #4
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My only guess is custom drivers for competition, or botched repairs. A wall of 10" subs divided into sets of 3 and wired in series, driven by some 1 or 2 ohm stable amps would be feasible and not too unpractical. Any other thoughts?
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Old 26th August 2010, 04:24 AM   #5
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I have a general question. Normally a person would check a mid range speaker with an impedance meter using a 1Khz (or higher) tone, but because a sub woofer operates at lower frequencies, is there a standard tone used for sub woofers? 100 hz perhaps?
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Old 27th August 2010, 01:20 AM   #6
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Quote:
Originally Posted by xinstalr View Post
Has anyone ever heard of this before? I bought a few 10" sub woofers of very reputable name and proceeded to cook the 5th channel of my amp. I thought it was overheating due to lack of air space around it. come to find out, it was the 1.3 ohm impedance of the two subs wired in parallel that I thought was going to be 2 ohms. After I cooked my amp, I checked the impedance of all of the drivers that are not in enclosures to find each measuring 0.8 of an ohm. A check of the two in my truck resulted in the same reading. I only have an old Fluke model 77 for my testing needs, so, I can't do a whole lot. I am going to need some advise with the amp repair in the near future but, for now. 0.8 ohm drivers????
Try measuring just your test leads. Mine are 0.4 Ohm. You could have drivers with shorted VC. Can you provide the make / Model no.

Terry
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Old 27th August 2010, 01:34 AM   #7
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You almost certainly have a shorted coil. It's probably very borwn and flaky. Does it rub in the gap? I'm pretty sure you can zero the lead resistance on a 77.
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Old 28th August 2010, 03:50 AM   #8
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Originally Posted by pheonix358 View Post
Try measuring just your test leads. Mine are 0.4 Ohm. You could have drivers with shorted VC. Can you provide the make / Model no.

Terry
Just test leads measure 00.0 - 00.1. They were advertised as Rockford Fosgate P1 10". the voice coil count and impedence were not specified. They have the riveted ring around the cone which would indicate a P210S4 or P210S8. There is no plastic basket cover that should be on the P2. I assume that was for channeling air around the basket and magnet for cooling. They were sold as is and with no assumed warranty from the manufacturer or any other party.
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Old 28th August 2010, 04:40 AM   #9
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Originally Posted by Andrew Eckhardt View Post
You almost certainly have a shorted coil. It's probably very borwn and flaky. Does it rub in the gap? I'm pretty sure you can zero the lead resistance on a 77.

I would love to know how to zero the lead resistance. I do not have the manual.

No rubbing what so ever. The excursion is silky smooth throughout the travel on all 8 of them. And they sound great. They just under load most amplifiers on the market. Wouldn't a shorted VC cause some SQ issues not to mention rough (grindy) spots somewhere in the travel? Is it possible that part of the coil was removed as an attempted repair? Less wind less resistance? Remember I'm a completely uneducated DIY 'er here?
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Old 28th August 2010, 06:14 AM   #10
benb is offline benb  United States
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Quote:
Originally Posted by xinstalr View Post
Has anyone ever heard of this before? I bought a few 10" sub woofers of very reputable name and proceeded to cook the 5th channel of my amp. I thought it was overheating due to lack of air space around it. come to find out, it was the 1.3 ohm impedance of the two subs wired in parallel that I thought was going to be 2 ohms. After I cooked my amp, I checked the impedance of all of the drivers that are not in enclosures to find each measuring 0.8 of an ohm. A check of the two in my truck resulted in the same reading. I only have an old Fluke model 77 for my testing needs, so, I can't do a whole lot. I am going to need some advise with the amp repair in the near future but, for now. 0.8 ohm drivers????
That's a really low impedance - I would have put these in series. Does your amp say it can drive a 2 ohm load?
Quote:
Originally Posted by gray5596 View Post
I have a general question. Normally a person would check a mid range speaker with an impedance meter using a 1Khz (or higher) tone, but because a sub woofer operates at lower frequencies, is there a standard tone used for sub woofers? 100 hz perhaps?
That might be a reasonable frequency, but I'd want to see a curve of the impedance vs. frequency before giving a "number" for the impedance - maybe not THE lowest impedance of the graph, but maybe a sort-of average weighted towards the low side. You can go to manufacturer's sites and see the impedance curves for "8 ohm subwoofers" and see what they do.
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