075 dcr low but plays fine.

[kingjames]

I have an 075 that reads 2.7 dcr but plays fine. I had a guy sine wave it and it still checks out. Why would the ohm's be so low? Thanks in advance.

[scott fitlin]

2.7 ohm DCR? Thats just wrong, something is wrong with that VC. Is this one of your units, or did you buy it used off ebay or something?

I would change the fram, that DCR is just wrong.

[kingjames]

Actually Scott, these are part of that 030 system that I found and sold on Ebay back in July.I just got an email saying the dcr is low on both of them.When I had them I hooked them up to my L100's and they played fine.I don't believe I did a dcr test on them.I check them this way as I believe a dcr test doesn't tell you that much.

The guy I sold them to is now saying the ohm's are low and he was the one who had a guy sine wave them.He says they sound as good as another pair he has with no noise or anthing.I guess he's building a system for someone and doesn't really know what to tell the guy if he ask for a dcr test.

Are low ohms a sign of a bad diaphragm?If so why do they sound the same?I told him to come over here and join up for some really good info.

Are diaphram's still available for these? Thanks for the info.

[louped garouv]

the diaphragms are available still....

:)


i don't know nada about the dcr issue....

:o:

[kingjames]

I stand corrected they are reading 2.0 ohms and not 2.7 ohms as stated previous.They play fine and according to this guy he had them sine waved
and everything checks ok. I have asked him to use another meter and will let you know when he gets the new readings from another meter.

[kingjames]

Here is an email that I got from this guy. Sounds like a nice person.

" I hooked them up and they sounded just fine. I brought them to a JBL dealer and he put them on one of those sign waves for sound and he compared it to another 075 that I had to see if the volume would be lower in the 2 ohm ones but they sounded the same. They sounded fine going through the sound wave system too. They sound just like the other ones that I have. I just don't know what to tell this guy if he says anything about the ohms being low. Why are so many people concerned about the ohms any way. Is there a reason people are so concerned about ohms. This is the first time this has happened because I have never owned a 075 before. All my other horns the 175 jbl and the 85's all had higher ohms and I never had to worry. I just don't want to piss this guy off and I don't want to look like I don't know anything about the 075's. What do think. Any help would be appreciated from you. Do you know any one you could call and ask them why the ohms would be so low and does it mean the 075 is defective or something. thanks John
that's what I am really worried about that the 075 is defective some how.
thanks John"

[kingjames]

something's fishy...
current diaphragms should read ~6ohms.
aftermarket?



Not aftermarket,all wax seals are intact.

[louped garouv]

with the seals intact and apparently "functioning"

ouch...

maybe find another pair to substitute....

and Ebay the seals intact unit to a "collector" as a "rare and valuable item recently checked by JBL techs"


:rotfl: :rotfl: :rotfl: :rotfl:

[scott fitlin]

The only thing I can think of is the guys meter calibration is off, and isnt a correct reading.

[kingjames]

The only thing I can think of ois the guys meter calibration is off, and isnt a correct reading.
My feelings exactly Scott, I asked him to recheck with another meter.I'm waiting for the new readings.

[hjames]

The only thing I can think of is the guys meter calibration is off, and isnt a correct reading.

Yeah - have him pop a new battery in that meter!
That kind of reading must be some kinda fluke ...
:applaud:

[louped garouv]

I thought flukes were good meters

:rotfl:
:rotfl:
:rotfl:
:rotfl:

[scott fitlin]

Yeah - have him pop a new battery in that meter!
That kind of reading must be some kinda fluke ...
:applaud:OR, the guy isnt using a Fluke meter?

Fluke always gives me a good reading!

:)

[hjames]

OR, the guy isnt using a Fluke meter?

Fluke always gives me a good reading!

:)
Sure - I got my classic fluke at home too - but when the battery dies the meter brand doesn't matter any more - it might as well be from Mannny, Moe, and Jack!

[scott fitlin]

Yeah, its true, weak batteries give wrong readings!

[kingjames]

I thought flukes were good meters

:rotfl:
:rotfl:
:rotfl:
:rotfl:

You're really on a roll today.:D

[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!:blink:

[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 .

<> :)