Sunday, September 5, 2021

Who Knew I Could Repair Speakers?

Granted, it didn't involve any soldering. As noted in an earlier post about a new (used) pair of tweeters I bought on Ebay, the original tweeters on my 1980s Snell Jii speakers had gotten tired-sounding. If I had been smart, I would have done a Google search about that problem before buying the new tweeters, but when they arrived, they were a bit loud compared to the Snell's woofers. I had anticipate that they might, given that their sensitivity is 92dbs, compared to the woofers' 90dbs. So, either I was going to have to add a resistor to each of the new tweeters or try a different fix. That's when it finally occurred to me that there might be some way of repairing the old speakers.

I learned from some online audio discussions that the problem I was having with the original Snell tweeters could be fixed, and I found several recommendations on how to go about doing it. Apparently, the cause of the problem is that the sealant on the old tweeters had become dry and brittle, and that degraded the sound quality. So, the fix is to simply to replace the old sealant. Of course, I had no idea if that would be more easily said than done. What I did know is that it had to be done carefully, in order to avoid damaging the mesh or the electronics behind it. 

Instead of following suggestions to take the entire speaker apart, I followed the advice that appealed intuitively to me. Since the mesh sits at the front, sticking through the hole in the speaker cabinet, it should be possible to remove the old sealant from it without disturbing anything else. There was still the question of what to use to remove the old sealant. Various recommendations include mineral spirits, isopropyl alcohol, abrasives Q-tips and a toothbrush. I didn't have an mineral spirits, so I started with some alcohol and Q-tips. No success. So I started thinking about what else I had in the house, and I immediately thought about Goop-Off, which is a great adhesive remover. It worked like a charm, though it took a while until the entire mesh had changed color from brown to silver. 

After making sure it was dry, I started in on the next step, which involved applying new sealant to the mesh. Recommendations for what sealant to use ranged from shellac and watered-down wood glue to liquicized plastic. I may have some wood glue somewhere around here, but I had my doubts about how well it would work, assuming I didn't water it down too much or not enough. What I did find was a spray can containing outdoor furniture varnish. The same person who recommended against taking apart the entire speaker noted that he had used marine spar varnish, which is pretty close to what I had to hand. I didn't want to spray the varnish directly onto the mesh because I was worried it might go through the mesh and effect the electronics underneath. So, I got a paint brush and sprayed the varnish onto the brush. Anywhere between three and five coats were recommended. I decided to start with three, and then listen to the speakers before deciding whether or not to add additional coats. 

Without any sealant on the mesh, the tweeter is very bright and practically shouts. The sealant serves as a kind of equalizer, rounding off the (too) sharp edges of high-frequency sound. After applying the first three costs of varnish (each of which, fortunately, dries within a couple of hours), I listened to various tracks I know quite well. Immediately, I could tell that the old varnish had, indeed, been the culprit masking the sound form the tweeters. They were much louder and brighter than they had been. In fact, they sounded a bit too bright, so I decided to add another coat of varnish, and then a second, after again determining that the sound was still a bit too edgy. Interestingly, while everyone else had recommended three coats, the person who recommended not to take the speaker apart and to use varnish as new sealant said he had used five coats. It was the right number for me as well. 

The old tweeters on my Snell Jiis' sound nearly brand new at this point. I didn't need to buy the other tweeters after all, though I'm sure I'll eventually find some use for them. Whoever mounted them did a great job, and they're in great shape. I just need to keep my eyes out for a couple of solo-mounted woofers that match their impedance and sensitivity. In the meantime, I've reattached the Amphion super-tweeters I had been using because I still like how they extend the frequency range and add a bit more air to the Snells' tweeters. I find them especially valuable when listening at low volumes, when both high and low frequencies tend to be lacking. [I've still got an old NAD preamp with a "Volume Control," which one no longer finds on modern amplifiers, the purpose of which is to boost both low and high end frequencies when listening at low volumes.] 

All's well that end's well in the world of hifi audio.

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