075 dcr low but plays fine.

[kingjames]

I thought flukes were good meters

You're really on a roll today.

[kingjames]

He just had them checked by another shop and the dcr's are 2.0 ohms per speaker. My question then is, can the ohm's be this low and still play fine? These have now been checked by 2 shops with one giving a sine wave test and they sound great.A,b tested them with another set and no difference in sound or volume level.

Dumbfounded to say the least!

[edgewound]

Either there is shorted turns in the voice coil, or a terminal lug is shorted to the top plate....maybe through some corrosion built up on the ancient structure.

Have your tech do a continuity test from both leads directly to the top plate. It should read open. if there is continuity to the top plate, there is something wrong.

I bet they don't sound fine for 075's. A sweep test with normal test voltage will kill small animals...and your ears.

2 ohms DCR is just wrong. It should range 5.7-6.7 to be within factory spec.

[Earl K]

- If these coils do prove to be partially shorted ( after following Edgewounds' advice on measuring the terminal lugs ) / then take the drivers back and resell them as "cores" in need of voice-coils .
- Chock this all up to experience.

<. Earl K

[kingjames]

- If these coils do prove to be partially shorted ( after following Edgewounds' advice on measuring the terminal lugs ) / then take the drivers back and resell them as "cores" in need of voice-coils .
- Chock this all up to experience.

<. Earl K

If I have learned anything from this is that a dcr test is crucial and not like most people who say it isin't. In this case the ears are not hearing it all. These were checked by 2 shops with both shops saying they sounded fine.

[edgewound]

...a dcr test is crucial and not like most people who say it isn't. In this case the ears are not hearing it all. These were checked by 2 shops with both shops saying they sounded fine.

They should have their hearing checked.

[kingjames]

They should have their hearing checked.

ken, these also played for me as well. They sounded good to me as well.

[mech986]

Hi,

Have been following the posts with interest. I'd agree with Edgewound about the possible modes that would have the DCR so low. I'd suggest pulling the diaphragm and take a good look at the voice coil windings to see if there are any bright spots (rubbing) or burnt spots (overheating or excess current) where the insulation may have failed. If there is continuity with the mounting plate, then you have a low ohmage path in parallel with the coil windings, so that would make sense too.

I would tend to believe the shorted turns because that would still allow the diaphragm to work, but at reduced output (less turns equals less magnetic field energy being produced IIRC) relative to normal. Being the O7x series is highly efficient, you might not miss 6-8 db of output compared to the rest of the midrange/bass system.

It seems to me if the tweeter was shorting to the faceplate, the faceplate should start getting warm due to current passing thorugh it. May not be much of a load change though to the amp since the amp sees the crossover components which set the overall impedence.

One key issue though is the DCR dictates to an extent the impedence that the crossover sees and is designed for. If the DCR is 1/2 or less than the OEM values, the crossover points, slopes, and Q will likely be affected. If the crossover point drops much lower than 7K, you will eventually have damage to the ring diaphragm. Something else to consider.

Hope the problem is the faceplate short - that should be easily remedied with careful inspection and reorientation of the lead contacts or judicious placement of insulating material. Shorted voice coil turns - don't know about repairing that one unless you can vacuum impregnate/bake the windings with new insulation/varnish, assuming it can seep inbetween the turns.

Let us know if you find anything on inspection.

Regards,

Bart

[Earl K]

ken, these also played for me as well. They sounded good to me as well.

- "Sounded Good" is such an elusive term that it's almost empty of meaning.

- "Measured & still up to Spec. " would offer a greater likelyhood that a used Lansing device is performing as either manufacturer designed them to.

- Of course,this more technical approach would entail that "Top-Shelf" eBay sellers buy some measurement gear ( such as, TrueRTA & WooferTester2, etc. ) and offer the resulting info as a "Value Added" feature within their sales.

<>

[Earl K]

I would tend to believe the shorted turns because that would still allow the diaphragm to work, but at reduced output (less turns equals less magnetic field energy being produced IIRC) relative to normal. Being the O7x series is highly efficient, you might not miss 6-8 db of output compared to the rest of the midrange/bass system.

Yes, that's correct .

- "Shorted Turns" means less "effective" turns in the gap. That would translate ( in this case ) into a significant reduction in the BL product. This lowering of the "force-factor", relative to the diaphragms' weight would mean less driving force per unit of weight and therefore less "output". ( Diaphragm weight is usually expressed as "mms", which is diaphragm weight plus with the weight of the air "pushed" by the diaphragm ) .
- (From a different perspective, loading a heavier diaphragm onto the original healthy 8 ohm coil, would yield somewhat similar results ) .
- So, in this case, efficiency goes down and the FR curve will change .

- The lowering of the effective impedance ( from 9 ohms to 2.5 ohms ) means the source amp will deliver more watts ( if it is able ) / somewhat offsetting the loss of "real" efficiency .

<>