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Re-foaming speaker surrounds

Discussion in 'The DIY Workshop' started by Rudy, May 2, 2016.

  1. Rudy

    Rudy ♪♫♪♫♫♪♪♫♪♪ Staff Member

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    On some speakers the foam on the woofer decomposes over time. No need to replace the driver--you can either have it repaired, or do the job yourself. There are kits on eBay and Amazon for most popular speakers with foam surrounds. The kit contains the foam surround needed to repair the speaker, adhesive, and instructions.

    I lucked into a pair of Dahlquist DQM-9 speakers, nearly free. They were not an inexpensive speaker back in the day, but also were not top of the line either. The speaker uses Magnat drivers from Germany; rumor has it that Magnat may have made the entire system for Dahlquist. The Dahlquist company became popular for their model DQ-10 time-aligned loudspeaker array, and are still a collectible to this day.

    The DQM-9 is your basic three-way system, with two ports facing rearward for cabinet tuning.

    The foam was of course half rotted away. Clockwise from top left are the four steps I took for the project. The first was the original condition--the rubber was there, but the lightest touch makes it fall apart. Second, the basket and cone after the old surround was removed, and the gluing surfaces cleaned up. Third is with the foam glued to the cone, and the fourth is the completed driver. The foam may look a bit wavy here, but that flattens out as the adhesive cures.

    PhotoGrid_1462237591202.jpg

    I lucked out--Simply Speakers provided the foam surround, and it is a perfect, exact fit. (Some had complained they needed to trim the foam to fit. Because it was a perfect fit, I did not need to worry about aligning the loose cone--I matched to the existing circumference on the woofer (where the old surround was glued).

    The cabinets are not in the greatest shape--they cleaned up OK. The grille on one side was cracked on the diagonal corners--I need to reglue it and add reinforcements to fix. The aluminum trim is also a bit pitted in places--I wanted to see the outcome of the project before doing any heavy cleaning or restoration. The front baffle of the speaker is a black velvet material to cut sonic reflections.

    PhotoGrid_1462237735594-01.jpeg

    Back when I heard the DQM series in the mid 1980s, I remember the vocals had a chesty character to them. I figured the cabinet needed an internal brace. When I had the woofer off, I noticed that the bottom half of the cabinet had no stuffing in it at all. I added some polyester batting to the cavity before reassembling.

    The results came out well! Surprisingly strong bass in these cabinets. They image wonderfully. I need to tweak placement in the room. A future improvement (aside from cosmetics) will be to replace the capacitors in the crossovers, as they are 30+ years old (with a lifespan of maybe 20 years--they drift away from their original value over time, due to breakdown inside the capacitor). I might also add a felt circle around the outside of the tweeter, as I've seen on some systems.

    So, aside from the other issues, it's easy to re-foam a speaker which has a rotted foam surround. Some speakers use a rubber surround, but many used foam. If you can visually see the foam is starting to rot (it'll develop a crack, or a chunk may be missing), or if you feel the bass is weaker than you remember it and you hear a rattling noise, then your foam is likely shot. It's around $25 for the kit, or a repair shop that specializes in this can refoam them for an affordable fee.
     
    Last edited: May 11, 2016
    darkmatter likes this.
  2. Rudy

    Rudy ♪♫♪♫♫♪♪♫♪♪ Staff Member

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    A little more information on these.

    The DQM-9 is pictured above. There is also a slightly smaller model, the DQM-9C (aka DQM-9 Compact) which uses a smaller 9" driver, as opposed to the nearly 11" driver here. The 9" used a butyl rubber surround which did not deteriorate, where the 11" used the foam. The midrange and tweeter were the same.

    The crossovers use higher grade film capacitors, so they are not prone to breakdown like common electrolytics. Upgrading them will not serve much purpose. The crossovers for each driver were mounted on separate boards, on separate sides of the cabinet, so that there was no electromagnetic interference between the coils.

    The list price of the DQM-9 in 1982 was ~$1200, rising to ~$1400 a couple of years later. The Grafyx speakers I have were listed at $320/pair around 1982, to put things into perspective. (In 1979, they were $280/pair, with the Polk Monitor 7 at $260/pair and Monitor 10 at $320/pair, the two models I directly compared them with.) The price point of the Dahlquists put them in a different tier entirely.

    Finally, I am inclined to believe these were built for Dahlquist by Magnat, as I have seen similar cabinetry in Magnat's systems from the same time period, using the same electrostatically-aligned felt on the front baffle. It would not be a stretch of the imagination to consider Magnat producing these to Dahlquist's specifications. Here is the Magnat All Ribbon II--notice the same felt:


    upload_2016-5-11_22-39-49.png
     
  3. Shipwreck

    Shipwreck Member

    I have a basement full of speakers I need to re-foam. Someday, someday.
     
  4. Rudy

    Rudy ♪♫♪♫♫♪♪♫♪♪ Staff Member

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    @Shipwreck I remember buying some 6.5", 8" and 10" surrounds in bulk for maybe an average of $1.50 each. Thing is, I haven't seen them in a few years, and they were generic "roll" sizes. These online suppliers have to get them from somewhere. It's just a matter of finding out where.

    The last kit I bought (for the Dahlquists above) was from a place called Simply Speakers, and they use a different adhesive than the glorified Elmer's glue that some of the others offer. That and their foam kit (the FSK-10i) fit this set perfectly, to where I didn't even have to worry about centering the foam onto the cone properly. Easiest set I've ever done, in fact.
     
  5. Shipwreck

    Shipwreck Member

    There's a seller of the kits here in Portland, it's called Jay-mac.
     
    Rudy likes this.
  6. darkmatter

    darkmatter Maitre d' Forums Staff Member

    Location:
    East Anglia UK
    I have to get some JBL 2245 bass units refoamed though it would affect the parameters somewhat I may get a firm local to me to put in rubber surrounds as replacements treat the cones to drop the resonance from 20 Hz to 18 Hz
     
    Rudy likes this.
  7. Rudy

    Rudy ♪♫♪♫♫♪♪♫♪♪ Staff Member

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    I bought my generic foam surrounds here (it took someone's mention of it at AudioKarma before I remembered):

    https://www.matelectronics.com/speaker-edges/

    It will work good in some, but not all, speakers. The 6.5" worked fine on my Boston A40s. The 10" had roll that was smaller than the original on the Boston A150s I refoamed, but to be honest, they still sounded quite good when I was done.
     

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