AR11B mid-range driver failure

[pilot]

Hi Everyone,

I am new to The Classic Speaker Pages. Great web site! Really interesting and a huge resource of so much great information!   

I have a question regarding my AR11Bs.  I just finished recapping (replaced the 8 uF caps) and rebuilding the crossovers on a pair of KLH Model 6s, circa 1959-1960? (S/Ns 14xx and 24xx range) I found on Craig's List. The speakers sound wonderful. I decided to connect them to my Pioneer VSX DS1 A/V receiver (130 W/channel RMS) along with the pair of AR11Bs. After about 15 mins. of listening, 10 o'clock on the volume control, one of the ARs developed a problem. The volume of the right channel dropped off and I suddenly heard lots of distortion. I determined the distortion was coming from the mid-range driver. Disassembled the AR11B (removed all drivers) and tested the tweeter and  mid-range (woofer is OK). The tweeter DC resistance measurement is 4.2 ohms (OK) and the mid-range is testing at 18.7 ohms. Obviously a problem. Quick test on both drivers with a low level signal from the DS1 indicates the mid-range is very distorted and turns on and off. 
I am looking for an AR OEM replacement mid-range driver, P/N 200010-1.  If anyone has one for sale I would be interested in buying it. Vintage-AR, as everyone here already knows, repairs mid-range drivers for ARs but they suggest the possibility of failures in the future unrelated to the repair, which concerns me.  Thanks to everyone in advance for your help and any suggestions.

[Aadams]

1 hour ago, pilot said:

RMS) along with the pair of AR11Bs

The description implies you were using all four speakers simultaneously which could be what led to failure. Your Receiver is rated for a 4 to 16 ohm load but you must use the impedance selector to limit the output at 4ohms.  If you run both pair simultaneously your nominal impedance is below 4 ohms which could have caused the amp to distort and damage the mid driver. 

Edit:  Maybe I am wrong but, assuming you were running all 4 at once the nominal load would be about 2.6 ohms.

Broken mids are a RoyC specialty area. If he doesn't drop in pretty soon send him a PM.  We are lucky to have him as a resource.

Adams.

 

[pilot]

1 hour ago, Aadams said:

The description implies you were using all four speakers simultaneously which could be what led to failure. Your Receiver is rated for a 4 to 16 ohm load but you must use the impedance selector to limit the output at 4ohms.  If you run both pair simultaneously your nominal impedance is below 4 ohms which could have caused the amp to distort and damage the mid driver. 

Edit:  Maybe I am wrong but, assuming you were running all 4 at once the nominal load would be about 2.6 ohms.

Broken mids are a RoyC specialty area. If he doesn't drop in pretty soon send him a PM.  We are lucky to have him as a resource.

Adams.

Hi Adams,

Thank you for your reply. I agree that I am presenting 2.6 ohms to the amp but I would have thought the Pioneer could handle that load if I didn't push the volume up too much. Apparently not. I also agree with you that this load could cause the mids to fail. Thought I was safe, guess not. Thank you also for the suggestion to contact RoyC if he doesn't drop in. I'd like his advice on the KLH Model 6s also regarding the cloth surround sealant he offers.

 

 

[pilot]

Hi Adams,

Thank you for your reply. I agree that I am presenting 2.6 ohms to the amp but I would have thought the Pioneer could handle that load if I didn't push the volume up too much. Apparently not. I also agree with you that this load could cause the mids to fail. Thought I was safe, guess not. Thank you also for the suggestion to contact RoyC if he doesn't drop in. I'd like his advice on the KLH Model 6s also regarding the cloth surround sealant he offers.

[Aadams]

54 minutes ago, pilot said:

Apparently not.

Experience is the best teacher but unfortunately it does a lot of killing.  When comes to 12 inch ARs I wouldn't trust any amp not explicitly rated at 2 ohms to carry a nominal load of less than 4 ohms, especially one that has a 4 ohm switch that reduces power output.  I have one by the way and it is an AV receiver.

Adams

[pilot]

Do you know if RoyC offers a repair service or does he have an inventory of spare parts?

[Aadams]

16 minutes ago, pilot said:

o you know if RoyC offers a repair service or does he have an inventory of spare parts?

Check your messages.

[RoyC]

4 hours ago, pilot said:

Do you know if RoyC offers a repair service or does he have an inventory of spare parts?

Hi guys,

The only relatively repairable AR dome mids are the AR-3 mids (the first two versions), not the later AR-3a (AR-11, etc) type. I do many repairs for Vintage AR and the success rate for the later mid is near zero. Occasionally a lead is broken just under the metal screen, which can be repaired, but most often there is a non-repairable break at the dome. The dome's suspension, which cannot adequately be repaired or replaced, would have to be cut to reach the break. The OP's high resistance reading is typical when one of the dome's voice coil leads is about ready to fall off. See photo below...

pilot, is your AR-11 mid the later version with the pink fiberglass pad and silver colored screen? If so, I have exactly one of them. Send me a PM if interested.

Roy