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AR91 - Weak Tweeters?


seventy1

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Hello, I’m relatively new to world of AR but have been learning here and at AK. I found my AR91s at a Salvation Army this summer needing some TLC and woofer surrounds. After re-foaming and giving my first listen, they sounded lush and full on the bottom, but not much happening midrange on up. After recapping, things got much better. However, it still seems like I’m missing upper end output. Cymbals and other high frequency content generally sounds recessed. I haven’t done an A to B with other speakers, but hope to find time during the holiday.

The room setup is not ideal with a cabinet three inches away from the side of the LH speaker, the RH 2 ft from the side wall but usually obscured by a leather chair. The speakers are three inches off the back wall at normal height but with carpet spikes installed to the bases. I’m driving them with a Denon POA-2400A and a Luxman R115 preamp. With all resistor switches at “0”, the mids sound harsh, so I set those to “-3”. The tweeters measure 3.3 Ω and 3.2 Ω.

I ran some frequency sweeps with a remedial software tool and a mic that came with my Marantz 7.1 receiver. The results look like I’m not losing loudness at high frequency, curious drop out at 150 Hz, though.

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Here's what I used for the crossover caps:

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Now my questions, is what I’m hearing in line with the AR91 voicing possibly aggravated with less than ideal placement and fifty-something old ears? Would I notice a difference if I ran a high quality 0.1 mfd cap in parallel with the 3.9 to bring the tweeter crossover up to the original design? Should I consider replacing or repairing the tweeters? Old ferrofluid? Thanks for any suggestions.

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Welcome to this friendly forum.

I would not add 0,1 cap to make true 4 uf cap. But checking that cap values are within spec may be better idea... even I I have not found new off spec caps too often.

Try clean switches and double or triple check everything (including pahasing of drive units) before doing anything to drive units.

Merry Christmas and Happy New Year to you

Kimmo

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Hi seventy1,

Just curious....do you still have the foam inserts for the mids and tweeters?

Although I've never listened to my 91s with the inserts removed, I suspect that the mids and tweeter might sound a bit more harsh.

I don't have any thoughts regarding your judgement regarding the weakness of your tweeters.

Steve

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I restored a pair of 91s with Dayton PP caps. The tweeters sparkle with clarity and detail. I don't see anything wrong with the xover work. I really can't see how you made the connection to the switch on the 4uF cap. Do you think you might have a cold solder joint?

Did you test the new caps for actual value before installing?

What is the DCR of the entire speaker xover circuit?

I think kimmo (iso) might have meant for you to check the wiring at the drivers and make sure the yellow wire goes to the pos. terminal on the tweet and the orange wire to the pos. terminal on the mid. and red to pos. on the woofer.

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Welcome to the CSP!

Great find! 91s at the Sal!

I have a pair that I couldn't pass up but I don't really use them (I use 3a's). Hope some of our more knowledgeable members can help you out.

One suggestion: Use a toilet paper or paper towel tube as a stethoscope to listen to just the tweeter while playing and see if you are getting proper output from them.

-Kent

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Thanks for the input. The foam blankets were just crumbled goo when I found these, so I haven't heard them with vs. without. Some reading suggests that they don't make much difference. I may get some foam and make my own, but mostly for esthetics.

David, most of my cap solder joints were to the cut old cap wire since it was hard to de-solder and untwist the old wire from the terminals when working through the woofer hole. I was pretty careful with the soldering, but it's not impossible that there's a bad joint in there somewhere. But bad on both speakers? They do sound similar to each other, to my ears. I'll take a look when I open things up to check polarity. How can I tell which terminal is positive on the speakers? I recall doing a 9v battery check on the woofers and I think I marked the mids and tweeters before disconnecting wires... I did not check any capacitance values, my Fluke doesn't do such things. How do I check the DCR of the crossovers?

I have put my ear to the tweeters and I've played them solo, so I know they work, just weak to my ears. Thanks again for the help, guys.

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Each driver should have a part number label on the backside by the wire terminals. The red dot on the label is located nearest the positive terminal.

To check the speaker DCR set your fluke to ohms and put one lead to the positive speaker binding post and the other to the negative.

I suppose its possible the ferrofluid has dried but I have no idea what that would do to the sound.

It's also possible you have bad caps. I've had issues with one Erse Pulse-X, some mylar and NPE caps.

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There is not too much in the tweeter portion of crossover that will usually fail. If you do not find anything to suspicous, maybe you should try to solder wire across your preferred position of level switch to eliminate bad switch, that is otherwise a bit difficult to verify.

If all this fails, your suggestion aboud dried ferrofluid seems most obvious cause for low output. There are refill kits available, but Tom may have best knowledgo how refill should be done.

Best Regards

Kimmo

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  • 4 weeks later...

I took some time away from this project over the holidays, but got pulled back in when one of the speakers started sounding horribly distorted last night. It seems one of the woofer's voice coil is dragging now. I noticed that the spider was weak on this woofer when I re-foamed it, but it played ok until now. The resistance is high, 6.3 ohms, and it no longer moves freely.

As for the other checks, all of the phasing (+,-) connections checked ok. I measured resistance all around, see below, and with the exception of the bad woofer, I think all is good? I was a little surprised to see the good speaker measure 3.0 ohms, expected 4, but maybe that's dynamic?

Any advice on what to do about the woofer? Rebuild, new, used from the auction place? Until I get this sorted, these will go to the basement and I think I'll lug up the JBL L65s, even though placement will be impossible...

Sorry, I'm not sure why I can't link the jpeg image of the resistance table, says the image extension is not allowed?

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As far as the limited tweeter output, do you get much change in the sound when you toggle the adjustments for it?

I think so, but they're down in the basement with the woofer removed, so I can't experiment at the moment. I know I had a bigger change with the mid switch. Mids flat was too harsh on some material, -3 about right. The room is rather dead, so I don't think any speaker would sound too bright.

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Seems to me the most logical things that could be bad once you check Caps is the adjustment and the tweeter itself (ferrofluid). If you can figure out how to bypass the adjustment just temporarily to try it you can rule that in or out. Maybe someone else has a way to test those they can share.

As far as the tweeter itself, ferrofluid does age. Dries out and everything gets muted. Frankly, if someone like Roy knows how to service those, I would just send them to them and have it done either way. If they aren't going now, they will at some point and probably sooner rather than later.

I am sending my tweeters and mids from my ADS speakers out for that even though they sound pretty good right now.

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