Sunday 22 October 2023

Repairing a Boston Acoustics Micromedia subwoofer

19:35 Posted by G No comments

 I've had my 2.1 computer speakers system for a very long time (I knew this as I bought them when I was at my old company, and I've been at my current employer for 17 years.  But when I actually disassembled the subwoofer, it has 'May 1997' on it, so that's a good 26 years service, so not unreasonable for it to have it first problem

Over the last couple of weeks there has been a nasty vibration at lower frequencies, annoyingly just in the range of some peoples voices, so when spending the day on video calls it was getting a little grating.

So first point of call was internet research. I didn't actually find anything that useful, but there was this YouTube video, which isn't very illuminating, but there were other references to speaker surrounds that had perished over time.

This is the same system as I had. So I started taking it apart (4 crosshead screws, one in each corned - you can see them recessed).  This allows you to take off the whole front of the subwoofer.  However I couldn't work out how to give myself enough room to inspect the subwoofer closely enough.  I couldn't work out how to get the front off as it the video (I still don't know how it was done in the video) .  For me the sub cable had no slack and I couldn't stretch it from the back of the enclosure.  So as it wasn't working properly and I'd had it for 26 years, I thought I'd nothing to lose by cutting the cable. I reasoned that I could always extend the cable and connect it via some sort of cable connector.

Once I'd cut the cable this is what I found :

Left hand image is the rear of the front panel, you can see the cut speaker cable and the bass port which fits into the hole above the sub. You can see from the photo on the right that the subwoofer speaker surround has perished, and therefore this was the likely cause of vibration. 

The photo above shows the problem most clearly,  you can see the near side of the speaker surround has completely perished, but the actual cone (made of paper I think) is still in good condition.

So more internet searching suggested that either Ebay or a company called North Speaker parts could sort out replacement surrounds.  I went with North Speaker parts, as they were UK based, and seemed to be a specialist.  So for the princely sum of £8 I ordered a 5" foam speaker surround replacement kit. This included glue, brush, instructions and 2 new surrounds (even though I only needed one) - kit from here. They arrived neatly packed two days later, very happy with their service.

So as per the North Speakers instructions, with the careful use of a Stanley knife, and rubbing alcohol (we used nail varnish remover) we managed [I enlisted the help of my son, hence the we] to get the majority of the old surround off.  having done that helpful teenager then applied the glue to reattach the cone to the new surround.  Allow that to bond, then an hour later he glued the cone/new surround to the brass frame.  This is more difficult as there's much less space to work with, and it took a while for the glue to actually stick to the new surround. We let this set overnight.

In the morning we checked our work, and it looked pretty promising

So while son was working on the speaker I was working on the cabling. I had spoken a while ago to our plumber and he was raving about Wago connectors. This project looked like a good opportunity to try them out, so a quick trip to ScrewFix for a pack on 100 (not sure I'll ever get through even half of these). I went for these ones - link.  To be honest their blurb says halves the time to make connections, but I found them a real pain (could easily be user error), it could also be that they are designed for solid core mains cable, in which case I can see it would be much easier.  However I had stranded cable, and it probably took me about an hour to get the 4 connections working ! (again could be user error!).

However finally we got it all together, you can see in the photo below a couple of the wago connectors and the sub back in situ.  We tested it like this and there was still some vibration, so I was a bit worried that we hadn't succeeded, however when we screwed it all together it all sounded good ! It's not perfect - when I really turn up the bass there is still a bit of vibration, but at normal levels it sounds perfectly fine. 

I'm really happy how it worked, and my £100 investment (I can't actually remember what I paid), is still going strong. Slightly weird to think I bought this setup before I met my wife, before we got married, before either of the kids arrived, and it's still going strong !

Thank you Boston Acoustics for making such good kit ! and hope this article is useful !

Finally a well earned beer after the project...


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