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AR-9 Lower midrange distortion issue. SOLVED !


lance G
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Thanks to everyone who contributed to my other posting regarding "AR-9 basic re-capping advice". This is on-going and I will be most happy to update as things progress.

This site has been of great interest to me and of great benefit, I have harboured the desire to repay the use of the facility in some way, should the opportunity arise.

The following may be obvious to many, but if it helps anyone I shall be gratified.

On to the subject matter. I have relatively recently been fortunate enough I feel to come into the possession af a pair of AR-9 speakers, I believe possibly a relatively rare thing here in the U.K. They were in a great basic condition, but as is the nature of these things, new broom sweeping clean as they say, I have been "going through them" thoroughly checking their integrity. obviously the matter of replacing the capacitors was/is being dealt with in my other posting.

I had when listening to music, at times, (higher volumes, certain frequencies/instruments) thought I noticed some distortion in perhaps one of the lower midrange drivers, upon removal and inspection I discovered the following as illustrated in the first picture (don't worry, it's a very blunt knife !). The dustcap had partially parted company with the cone. Source of the distortion problem discovered and rectified by re-glueing the offending dust cap.

However, and this is what may be of more general interest and perhaps help to others, is that upon further inspection the apparent cause of the dustcap detachment was discovered.

The flexible wire lead from the positive connector to the voice coil, when the cone was at rest, appeared to be too short with almost no surplus wire to allow movement of the cone. It seems this was done at the time of manufacture. I did compare with the other speakers LMR driver, and it was only this one wire which was apparently too short.

In practice, with the travel of the cone when playing, no doubt at higher volume levels, the wire was being pulled taught which resulted in the pulling away of the cone from the dustcap in precisely the location where the wire passes through the cone to the voice coil. Of further interest I believe, this in effect "strangled" the driver from reproducing sound as it should.

Thinking about this further, it would never be possible to quickly check for the possibility of a short wire by pressing the cone inwards, it would only be when the cone moves outwards when being driven that the wire/wires could possibly be put under tension either partly or fully.

I have rectified the situation by slightly swiveling and gently bending the input tabs on the driver, as in the second picture, to equalise the length of wire from both the positive and negative connectors to the cone, thereby leaving an equal amount of "slack" to allow full movement.

 

I am now pleased to report that there is no distortion, and that whilst I appreciate there is some psychology attached to these matters, the sound seems to be somewhat improved.

I do hope the above may be useful to others to bear in mind.

 

P.S. Whilst there is a picture posted, if anyone might notice, does the foam on the driver look to be original/the correct profile ? also what are the correct dimensions of the driver foams for the AR-9 ? For example what is the correct woofer roll profile/size ? What is the correct profile/size for the lower midrange ? Thanks, Lance.

 

 

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Hi Lance, congratulations for your AR9, they will give you great satisfactions and it seems right that besides replacing the capacitors of the crossovers (check if you can also all the other resiatenze values, coils and switches), also restores the 4 woofers and the two midwoofers.
Regarding the wire lead flexibile, in the last photo it seems to see that the welding is not flat and similar to that of the negative contact, perhaps it was an intervention performed by the previous owner or a technician (when you found the dustcap partially detached, probably you could have raised or detached it further to see if there was any repair on the top of the cone where the wires run!).
What you did: releasing the natural oscillation of the cone is right and if you have solved the problem as you reported, I think you should no longer intervene (just check that the wire braid is intact).
Regarding the foam, finding the original is no longer possible and I am sure that on CSP you will find many tips on the most suitable surround foam, furthermore due to the fact that this woofer is used in AR9 as a midwoofer, I think that even if the one currently in use does not were the most correct, this does not significantly affect the sound of the speaker correctly; however here there are several experts and happy owners of AR9 who will be able to help you!
I wish you good listening

Giorgio

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Hi Giorgio, thanks for the supportive reply and your further input.

I do think it may be worth anyone bearing in mind where appropriate the available length of the flexible wiring between the connectors and the cone. Especially if there is a perceived issue with sound quality.

The connectors are on a small insulated plate which can be subject to an element of rotation (perhaps by knocking accidentally ?) which results in a lengthening of one wire, unlikely to be an issue, but of more concern the shortening of the opposite wire which could cause the issues I have experienced.

This would tend to be proportionally more relevant to larger drivers where they experience a larger range of travel.

I do think that the problems I have had stem from when the driver was manufactured, as in my opinion the soldering looks to be original (I have had some experience of soldering for what is now approaching 40 years).

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9 hours ago, Kal87bmw said:

Someone re coned the lower mid ranges on the ones I just got and used double roll cloth surrounds & 200044 midranges. Has anyone heard off this I keep reading no one offers cloth surrounds. And is there any difference between 200028 midranges & 200028

Kal87bmw you might want to start a separate thread for this and provide photos.

Aadams

 

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