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Midrange Driver Has No Sound But Measures 6.8 ohm

larry777

larry777

Active Member
I have a set of rare Sansui SP-L500 speakers that have already been recapped. I noticed that the midrange driver in my left speaker was no longer putting out sound so I switched the driver over to the right speaker and it still didn't work. The original right driver does work in the left speaker so I know that the crossovers are ok. I also measured both drivers using my multimeter and both these 8 ohm drivers measure exactly 6.8 ohms each. Any idea why I don't get any sound from this left midrange ? Thanks for your help.
 
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Can the midrange cone be pushed in? Compare it with the working one. The fact that you're getting a measurement from your MM means that the coil wire is intact, but the voice coil could be jammed in the magnet, or could have gotten detached from the cone. I assume this is a sealed back driver, so working on it will be difficult. If I'm wrong and it has a subenclosure, you'll want to remove that to take a closer look at the back of the cone.
 
If you are getting reading from the midrange driver, the only thing logical is the crossover unit.
 
The midrange driver seems stiffer than the working one when I try pushing in on the cone. I don't want to push too hard and damage the cone. I also noticed a bit of rust where the magnet attaches to the basket which is not present on the working driver. I can see where the coil attaches to the spider/cone and everything looks good there. The magnet also has a slight opening where it attaches to the basket where the rust is, so moisture could have gotten in there. Is their some type of spray that I can use in that area to maybe free up the voice coil ?
 
larry777 said:
The midrange driver seems stiffer than the working one when I try pushing in on the cone. I don't want to push too hard and damage the cone. I also noticed a bit of rust where the magnet attaches to the basket which is not present on the working driver. I can see where the coil attaches to the spider/cone and everything looks good there. The magnet also has a slight opening where it attaches to the basket where the rust is, so moisture could have gotten in there. Is their some type of spray that I can use in that area to maybe free up the voice coil ?
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Are you trying to run sound through it with just midrange only with the crossover of course?
 
No, with the midrange driver inside the three way speaker cabinets. When the two midrange drivers were tested with the multimeter they were removed from the cabinets and both measure 6.8 ohms.
 
All the drivers I’ve had that had stuck coils (whether from a shifted magnet, rust, foam in the gap etc) still made sound. It’s just the woofer had zero excursion.

I have a pair of horn drivers that have good DCRs, but very very low output. I can only guess that something is Fubr in the VC and it must be replaced.

Since you have nothing to lose you could pour some fast evaporating solvent in the VC gap. Cut the dust cap off first of course.
And if that doesn’t work look for a new (used) mid on eBay.
 
larry777 said:
The midrange driver seems stiffer than the working one when I try pushing in on the cone. I don't want to push too hard and damage the cone.
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As long as you don't exceed the excursion limits of the cone, you should be fine.

I think the next thing I'd try would be to connect the speaker wire directly from your amp to the questionable midrange. Don't do it for too loud or for too long, but this could provide some useful info depending on results.
 
I took the midrange driver out of the cabinet again and tried pushing in from around the aluminum cap and also where the cone meets the basket and it dosn't seem to move. So I think that the coil could be stuck. Since the speaker measures 6.8 ohms whould a speaker repair shop be able to fix it ? The speakers are very rare so getting a replacement would be very unlikely. The speakers sound superb when all the drivers work and still very good even with that midrange out of action. So getting it working again is top priority. Should I just ship it out for repair or is there other options ? And the big question....Is it repairable ?
 
Could a shop repair it? Most likely, assuming you can find somone willing to work on it. Many shops will only repair speakers when replacement parts are available. Almost definitely not the case here.
 
Since it’s a midrange and would be easy to ship, I would contact AKer GordonW to see if he might be able to fix it.
 
Thanks for all the help Guys. I may make contact with GordonW to see what he has to say. I live in Canada so that could be an issue shipping accross the border.
 
larry777 said:
Thanks for all the help Guys. I may make contact with GordonW to see what he has to say. I live in Canada so that could be an issue shipping accross the border.
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No real issue, just cost. And it won't be too bad. Talk to Gordon.

Biggles
 
Exercise the cone through its xmax. Manually and/or with a 1.5vdc battery.

The voice coil probably has a serious amount of rub, thus no output.

If you recone this mid, it will sound different from the other. Best to do both.
 
Tricky is what I’d say if it were mine. I tend to trust myself more than some tech unless I know him and I know he’s more meticulous than I am.

I’d “carefully” remove the dust cap to reveal just how bad the obstruction is. Take pics - post them here and let’s see if we can achieve a happy ending.
 
Larry, if you don’t mind, let’s go back to what is the history on the speakers how long have you had them? Where were they stored?

I did a search and see you recapped them in 2018. Have you been using them since? Did you buy them in 2018? If you’ve been using them since - are you sure the mid- range ever worked since you acquired them? Do you use them in your basement, garage, living room?

the answers to these questions may not help fixing, but it will help to understand what happened. I’m curious…
 
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Lux Man said:
Larry, if you don’t mind, let’s go back to what is the history on the speakers how long have you had them? Where were they stored?

I did a search and see you recapped them in 2018. Have you been using them since? Did you buy them in 2018? If you’ve been using them since - are you sure the mid- range ever worked since you acquired them? Do you use them in your basement, garage, living room?

the answers to these questions may not help fixing, but it will help to understand what happened. I’m curious…
Click to expand...

I bought these speakers new in 1978 when I picked up my Sansui AU-717 amplifier. They have been down stairs in a fully completed basement ( Split Entry Home ) for the last few years. I use a dehumidifier from time to time when moisture builds up but not all the time. When I play music I usually check the drivers to make sure they are working properly. I didn't use this system for a month or so until a few days ago and thats when I noticed the driver was not making any sound. As mentioned in an earlier post these speakers have already been recapped and is not the problem. The no sound issue followed to the other speaker cabinet when I switched the midrange drivers, so everything else about the speakers including the Mid & High frequency switches work ok. I recall the midrange working properly just before this last time. What do you think about removing the dustcap will tell us ?
 
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