Most of you that know me personally realize I’m an audiophile nut job. During the colder months I tend to stay inside and do less photography to concentrate on other hobbies. I’m also a sucker for a good deal so when I saw these DCM Timeframe 350 speakers advertised in the local classifieds for a giveaway price I had to snap them up. I knew they would need a little tender loving care due to their age. With vintage loudspeakers most problems arise from either a blown tweeter, leaking capacitor in the crossover network and the most common issue deteriorated foam surrounds on the woofers. The DCM Timeframe 350 is what they classify as a transmission line speaker. It’s a lot different than a sealed or ported box design. Transmission line speakers are typically larger boxes but they can be best described as acoustical labyrinths where the rear wave of the woofer travels through a maze like enclosure and ports through a slot either in the rear bottom or front of the enclosure. Most older DCM speakers are a little more difficult to work on because instead of featuring a removable grille they use a removable back, top and bottom panels. The grille cloth can then be removed or folded down like a tube sock.

Day 1. After disassembling the speaker the foam surrounds on the woofer were rotted away so my first step was to order new speaker foams and adhesive. While I was waiting to take delivery of the new foams I carefully inspected the crossover network in each speaker for any cold solder joints and leaking capacitors. Luckily everything looked good so it was just a matter of waiting for the new foams.

Day 2. The new foams have been delivered so I carefully removed the old foams and any left over residue of old adhesive from the speaker cones and frames. When replacing speaker foam you have to take great care to make sure the voice coil is perfectly centered or the end result will sound like a scraping or tapping while listening to music. There are two schools of thought on how to center voice coils when re-foaming. The first is to remove the center cap on the woofer and use shims. The second way is to use a signal generator set to 50hz (cycles) fed into an amplifier set to a very low volume which is connected to the woofer you are working on. The signal generator doesn’t have to be an expensive piece of equipment. You can download free signal generator apps for iPhone, iPad or android phones and connect it to an amplifier with a cheap mini headphone to twin RCA connector cable.

The first step is to glue the inner portion of the foam surround to the woofer cone. You could center it visually. Let the glue dry for one to two hours before proceeding to the next step. The next step is to use either your fingers or in my case two 3/4 inch short dowels to prop up the woofer cone from underneath so that you can apply glue to the frame of the woofer. The next step will require a little patience. Remove the dowels and set your signal generator to 50hz and turn on your amplifier. The woofer cone will start to vibrate. Make sure you don’t have your amplifier volume set too loud. Now move the woofer cone around until you hear a clean tone (that means no scraping of the voice coil against the voice coil magnet). You will know when the voice coil is scraping against the magnet because it will sound like a tapping noise. Once you get the voice coil centered tack down about four sections around the perimeter of the foam surround. When you are sure that the speaker cone is vibrating without scraping on the voice coil you can turn off your amplifier and tone generator then finish securing the perimeter of the foam surround. Thats it now proceed to the next woofer. Be sure to let the glue totally cure before reinstalling the woofers back into the speaker enclosure.

Day 3.  Now that the glue has fully cured I was able to reinstall the woofers and pull up my socks (err the speaker sock that is). I was able to reassemble the speakers in about two hours taking my time to insure no wrinkles in the grille cloth. Now all that was left to do was to hook the speakers up to my system and give them a listen. I really wasn’t expecting much in the way of bass response being the DCM timeframe 350 speakers are a 2 way design featuring a 3/4 inch dome tweeter and a 6 1/2 inch woofer but I was pleasantly surprised when the music stated playing. I think DCM was really onto something when designing the transmission line enclosure because the bass was clean and punchy. The midrange and highs are what these speakers are known for but I’m quite impressed with the bass response.

So there you have it. A couple of days in the life of Joe’s head and workshop. I hope some of you fellow audiophiles whose woofer foams bit the dust will think about undertaking a similar project.

Audio, Entertainment, Joseph, Music, Photography

Woof..Woof

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10 thoughts on “Woof..Woof

  1. I see your still doing the things you love to do! That’s great! You always had a passion for photography and anything to do with audio. Of all the things you have taught me in my life, you just taught me a new thing! I didn’t know about this completely different concept in speaker design. The work you did to repair these speakers seemed quite tedious to get them to sound perfect, but you are a driven perfectionist! So where will you be putting these new additions?

    Liked by 2 people

    • Thank you Gale 😊 I’ve read about this kind of speaker but never had listened to a pair until now. I’ve never tried to design transmission line speakers because its difficult to achieve proper bass response without a lot of trial and error. I don’t want to experiment with building so many different cabinet sizes that I would be responsible for deforestation 🤣. Actually I bought these speakers to repair and sell. I’ve been buying amps, turntables and other gear to repair, restore clean up and sell. It keeps me occupied in the colder months.

      Liked by 1 person

  2. Timothy Price says:

    It looks like you did a great job. How do they sound? I’m still using a pair of speakers I built in the late 70s when I was building speaker cabinets and some complete sets of speakers. I have not found a pair of contemporary speakers that come close to the full sound and dynamic range of my old speakers. My studio monitors come close and they really accurate on their sound reproduction, but they are close proximity speakers and don’t sound very good in a large space.

    Liked by 1 person

    • Thank you Timothy 👍🏻 They sound surprisingly good, much better than expected. On my primary system I am accustomed to very accurate sound. I am using Canadian made Paradigm Reference Studio series speakers with a powered subwoofer to fill in the lower octaves and Canadian made Bryston electronics. I haven’t hooked these speakers up to my main system because of the difficulty reaching the speaker wires on my main power amp. I should have never installed my equipment in a cabinet but it was a compromise (I try to keep my hobbies wife friendly LOL). I tested the DCM’s on a vintage Denon integrated amp that I keep around for testing my various projects. The dispersion, all important midrange and highs sound spectacular on the DCM’s. What really was surprising was the amount of bass these DCM’s put out with only a 6 1/2” woofer. I guess there’s something to be said for transmission line speaker enclosures. It’s so cool that you used to build speakers because I did the same thing. Many of my friends are still using speakers I designed and built for them. When computer programs came out for speaker enclosure box volume and port sizes I was off to the races and built so many pairs of speakers. Now I have to get the urge out of my head to design and build a pair of transmission line speakers LOL.

      Liked by 1 person

      • Timothy Price says:

        I worked at a music store for a year in the mid 70s. A Bose rep had a great deal on cases of 4″ full-range, high watt speakers. I bought a couple of cases of those speakers. The magnets were 3.5″ by 1.5″. They were heavy duty speakers. I used most of them to build small monitors that could be mounted on stands and sold them to bands. I made a few enclosures for regular music systems that sounded fab and they could be really cranked up. I don’t think there are speakers anything like those little monsters made today.

        Liked by 1 person

        • I agree there are not many companies that build quality speakers for reasonable prices anymore. Sure anyone who has thousands of dollars to spend can buy great sounding and properly constructed cabinets. I’m a perfect example of that because I have the needle in pretty deep being an audiophile. The trick is to be able to offer great sound and properly constructed cabinets in the under $1000 per pair price range. Most companies selling speakers in the sub $1000 price range have the speakers made in China including PSB, Polk and Klipsch. Back when I first got into audio the American companies were all fighting to manufacture speakers that sounded good in the sub $1000 range. I guess everything is relative though because the price of audio electronics has gone up dramatically. A perfect example would be that I paid $1699 for a Bryston BP-20 preamplifier with an external power supply about 20 years ago and the BP-26 preamplifier sells for $3999 without a power supply. The external MPS-2 power supply is an additional $1899. There have been refinements in the sound but not enough to warrant the additional cost.

          Liked by 2 people

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