Info on the Yamaha JA-6681 compression driver

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#444
Tube Radio said:
What size driver is the JA6681B? Someone on another forum mentioned I'd need a 2" to 1" adapter then I saw a picture of the original yamaha adapter used to adapt that driver to a horn and it said for a 1.4" driver.
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About 1.4". But the driver has a long throat. Without the throat the opening right after the phase plug is about 1". Some recomments to remove the throat to get the angles right for your horn, but I managed to get the angles right using an IWATA horn. The throat is high quality and I believe it helps to start the horn with smooth aluminum walls.
 
#451
Optimal horn

Allo.
I just got me a pair of these Yamaha JA6681B 😉
So what to do with them now? I think I need some advice on the appropriate horn -- can you guys give me some tips?

So far, here is my plan, and I'm open to ideas or adjustments: I plan to use these in their optimal range and not to force them to play out of their comfort zone, as a part of a system that will have a 12-15" woofer and a tweeter.
1. I am thinking 600hz-8khz with 6db/octave active filtering. What range would you suggest? Keep in mind I am trying to NOT have a huge horn on these.
2. I'd like to use a flattened horn ( radial? )to minimize the spacing to woofer. I am also considering a waveguide like the SEOS 24. Please share your thoughts on the two points above with this Yamaha.
3. I would prefer to try a decent, affordable horn that is not too expensive, just to get idea of the sound of these, with good, even off axis response.

thank you,
Herman
 
#452
First, open them up and clean the diaphragm and magnetic gap from dust. Use a signal generator to test alignment when you reinsert it. Check for a large capacitor, the smaller Ja4281B had one. If so, remove it and replace with your own crossover. This driver is able to play down to 440 Hz very comfortably. You could try to use a larger horn. When testing you can use anything really. It is bette to invest in a quality horn. You can quite easily make one yourself. It will just take some time.
 
#453
noviygera said:
I plan to use these in their optimal range and not to force them to play out of their comfort zone, as a part of a system that will have a 12-15" woofer and a tweeter.
Click to expand...
Good idea.

1. I am thinking 600hz-8khz with 6db/octave active filtering. What range would you suggest?
Click to expand...
This range sound perfectly reasonable, BUT first order (6dB/octave) filtering is generally a VERY BAD idea with horns, for a number of reasons:
- it won't protect the driver from overexcursion (you need at least a 2nd order high-pass just to keep the excursion constant below cut-off);
- it will lead to increased distortion AND the infamous "horn honk";
- it will NOT lead to good phase tracking between the woofer and the mid, because of the intrinsic roll-off behaviour of both speaker units;
- etc. etc...

At the very minimum, if using an active filter, you can try to minimize the overlap and the ensuing mismatch problems by using steep (e.g. 24dB/oct) filters. An even better approach would be to use asymmetric slopes on the LP and HP and/or delay on the HP branch, but this requires that you can take good measurements and most of all that you really know what you're doing.

Keep in mind I am trying to NOT have a huge horn on these.
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If you plan to use the driver down to 600Hz, the horn will have to be fairly large. A good rule of thumb is for its cut-off frequency to be 1 octave lower than the minimum intended freq., i.e. 300Hz in this case. And then the equivalent mouth circumference needs to be at least = c/300 = 115cm.

To give you an idea, these drivers were originally intended by Yamaha to be used with the AD-3500 adapters + H-1230 horns, and I think something along those lines would be a good match for your intended application.

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2. I'd like to use a flattened horn ( radial? )to minimize the spacing to woofer.
Click to expand...
I think this is a good idea too.

3. I would prefer to try a decent, affordable horn that is not too expensive, just to get idea of the sound of these, with good, even off axis response.
Click to expand...
I wouldn't skimp on the quality of the horn, if I were you. The end result will depend MORE on the horn than on the compression driver.

Marco
 
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#456
Even more important at this point:
Please advice on the proper way to thoroughly test the JA-6681 to make sure they are performing properly (what should I look out for and what to measure / inspect).

Also, the foam in the back chamber is completely deteriorated. The felt still looks good though. Any advice replacing the foam?

thanks,
Herman
 
#457
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