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????
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.
dave
I've not run into woofers with this low an impedance.
dave
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?
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?
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
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.
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.
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?
That's a really low impedance - I would have put these in series. Does your amp say it can drive a 2 ohm load?
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.
xinstalr,
as you are at the limit of measuring resistance why not connect the drivers in series and measure them. You could also get a resistor to check your meter, say 4.7 ohm.
sp
as you are at the limit of measuring resistance why not connect the drivers in series and measure them. You could also get a resistor to check your meter, say 4.7 ohm.
sp
Rockford Fosgate® - Article Detail
Hi, see P1 series specifications, 10" are 1.4 or 1.8 ohms nominal, rgds, sreten.
Simply rewire the pair as series that will give you your > 2ohms.
Hi, see P1 series specifications, 10" are 1.4 or 1.8 ohms nominal, rgds, sreten.
Simply rewire the pair as series that will give you your > 2ohms.
Last edited:
All the manuals for the 77 should be on the Fluke site. For permanent lead zeroing you will probably have to open up the case and refer to the service manual. I would say if you can get a 77 to occasionally read 0 then you are as close as practical with that meter.
If the Re is the same between multiple drivers you don't have a short, because shorts are fairly random deals on a voice coil and you're not going to get exactly the same number of turns left or same quality of short between the leads of any two drivers. If there's no rubbing then there's Usually no short. You have to destroy insulation to get a short one way or another. You can measure resonance Q but you have to do it with a test signal large enough to drive the coil end turns close to the gap to easily detect shorts on long coils. Shorts between full layers will drop Q like a rock, because there's always a short in the gap. You can find that just by tapping on the cone and listening for the ring. Winding inductance can be affected a lot. You can attempt to inspect the coil through the surround or vents. If you have a good eye and you can see the coil very well at all you can guess the wire gauge close enough to tell the difference within a whole wire gauge on big low impedance woofers. Try setting some calipers to the diameter you think the wire is, and use "micrometer eye" to figure whether they match. Attempt to determine winding wire length by noticing number of layers and the amount hanging over the top plate at rest. Double the overhang to account for what's on the other side, add top plate thickness, and you have coil length. Determine coil mean diameter. You should then be able to calculate good coil resistance from available wire gauge charts.
If the Re is the same between multiple drivers you don't have a short, because shorts are fairly random deals on a voice coil and you're not going to get exactly the same number of turns left or same quality of short between the leads of any two drivers. If there's no rubbing then there's Usually no short. You have to destroy insulation to get a short one way or another. You can measure resonance Q but you have to do it with a test signal large enough to drive the coil end turns close to the gap to easily detect shorts on long coils. Shorts between full layers will drop Q like a rock, because there's always a short in the gap. You can find that just by tapping on the cone and listening for the ring. Winding inductance can be affected a lot. You can attempt to inspect the coil through the surround or vents. If you have a good eye and you can see the coil very well at all you can guess the wire gauge close enough to tell the difference within a whole wire gauge on big low impedance woofers. Try setting some calipers to the diameter you think the wire is, and use "micrometer eye" to figure whether they match. Attempt to determine winding wire length by noticing number of layers and the amount hanging over the top plate at rest. Double the overhang to account for what's on the other side, add top plate thickness, and you have coil length. Determine coil mean diameter. You should then be able to calculate good coil resistance from available wire gauge charts.
Last edited:
You could always resort to a transformer. I believe there are some specifically made for autosound, but at subwoofer frequencies a 60 Hz power transformer will work. 2:1 voltage ratio = 4:1 impedance. I've been using a 1.5 kVA Hammond 120/120/120/120 transformer to drive a 1 ohm ContraBass servo motor. If you wanted the challenge of winding a transformer, a microwave oven transformer core should work.
This isn't a particularly great solution for car use. Apart from the drag on performance and economy of adding weight, it'll need to be very securely mounted in case of a crash.
This isn't a particularly great solution for car use. Apart from the drag on performance and economy of adding weight, it'll need to be very securely mounted in case of a crash.
Last edited:
Hi.
Maybe that can be useful.
Rockford Fosgate Punch 10" Stage 2 - P210S4 & P210S8 TECHNICAL SPECIFICATIONS
Maybe that can be useful.
Rockford Fosgate Punch 10" Stage 2 - P210S4 & P210S8 TECHNICAL SPECIFICATIONS
Actually, you should graph the impedance response (20-20k) in an infinite baffle and take the line that is not greater than 20% the minimum (including DCR) for "rated" impedance according to the IEC spec.
Yes, if you can arrange to do it, running two drivers in series has few sonic drawbacks aside from damping factor (which is a bigger shortcoming in theory than in practice).
It also seems to me, outside of commercial sound, there is a lot of latitude for mismatching amps and loads. Ordinarily you have to be pretty demanding or abusive to cook an amp although, I guess, if the speaker load (not just DC resistance) really was .8 Ohms, that would come close to abuse.
Funny, nobody has proposed getting information by just measuring the operating impedance (rather than the DC wire resistance) by what motorcyclists call "curbside" or "shade tree" amateur methods.
At the very simplest:
get a plain old resistor whose value you can be sure of in the 2-8 ohm range, wire it in series with the driver, and feed the pair with any kind of steady audio tone, but 100-400 Hz is best.
Then you figure out how much is being consumed by the resistor and how much by the driver and, after doing the math, their relative impedances.
I hope there is no need for anybody to demonstrate their intellectual superiority here by identifying all the 262 types of imprecisions in the method... but rather any practical improvements or simplifications, as shade-tree methods go.
It also seems to me, outside of commercial sound, there is a lot of latitude for mismatching amps and loads. Ordinarily you have to be pretty demanding or abusive to cook an amp although, I guess, if the speaker load (not just DC resistance) really was .8 Ohms, that would come close to abuse.
Funny, nobody has proposed getting information by just measuring the operating impedance (rather than the DC wire resistance) by what motorcyclists call "curbside" or "shade tree" amateur methods.
At the very simplest:
get a plain old resistor whose value you can be sure of in the 2-8 ohm range, wire it in series with the driver, and feed the pair with any kind of steady audio tone, but 100-400 Hz is best.
Then you figure out how much is being consumed by the resistor and how much by the driver and, after doing the math, their relative impedances.
I hope there is no need for anybody to demonstrate their intellectual superiority here by identifying all the 262 types of imprecisions in the method... but rather any practical improvements or simplifications, as shade-tree methods go.
Last edited:
- Status
- Not open for further replies.