pete_mac Posted November 14, 2010 Share Posted November 14, 2010 (edited) I bought a really nice set of (almost vintage!) Sound Dymanics 300ti speakers from Victor (vmhf) about a month ago. I seem to have a penchant for old Canadian speakers. I've got some restored Energy's that sound nice, but the 300ti's are definitely a step above. Noticeably more detail in the midrange and top end. These speakers sounded surprisingly nice on Victor's monster setup when he demo'd them for me, and my vintage Sansui and digital front end drives them quite well too. Like most 20 year old speakers with foam surrounds, the surrounds on the 4.5" midrange drivers started to crack and perish. It's just one of those inevitable things when you're dealing with foam surrounds on speakers. Thankfully, the surrounds on the 8" woofers are quite good. They use a filled-fillet foam surround like the EV Sentry/Interface speakers, but the sizing is a little odd - the EV foams don't fit these unfortunately. If/when these die, I'll have to replace them with a standard foam surround. New foam surrounds are typically a poly-ether foam which lasts longer than the original foams. Anyhow, you can see how badly the midrange surround had perished: I removed the 'roll' of the surround in this pic: In this pic, most of the foam has been removed (as you can see by the pile of foam crap on the table next to the driver!). The brown/orange stuff is the glue that held on a foam trim ring around the edge of the speaker. The frame is scraped clean in the pics, but there is a little bit of foam residue on the midrange. I cleaned it further and wiped everything down with isopropyl alcohol after this pic was taken: It's pretty easy to refoam speakers to be honest (particularly if they have a wide voice coil gap). Many people recommend shimming, but I've got a 100% success rate with refoaming by using a battery to move the cone in and out to check for rubbing, or by using a 30hz test tone on woofers and a 1-2kz test tone on midranges. I'm yet to resort to the shimming method, mainly becuase it requires the dust caps to be removed. Tone generating software can be downloaded free off the interwebz. I use Audacity. First step is to glue the foam onto the speaker. Most speaker glues can be used like contact cement and are relatively tacky, so you apply some to both surfaces, wait for the glue to tack up, and then push the surround onto the cone. Make sure it is centred properly. Once this glue dries, you align the speaker cone using highly specialised speaker refoam alignment tools (ie. clothes pegs). Hold the surround in place on the driver frame/basket using 8 pegs or so, and check that the driver moves in and out without fouling on the voice coil. This is where the battery or test tone method works well. With most speakers, you can do it by feel once you know what you're doing. You then remove a few pegs at a time and apply glue under that portion of the foam (or on the basket). Re-fit the pegs and move to another section of the speaker. Work your way around the speaker and once finished, check the centering of the speaker again via the battery/test tone/by feel. Let the glue dry and you're ready to re-fit the driver! In the pic below, you will notice how messy the glue looks. I wasn't very happy with this outcome, so I later applied a light coating of the glue over this 'mess' which tidied it up a bit as per the very last pic. It's definitely not a show-stopper as it does not affect the functionality of the driver... but it's not quite as neat as it should be. I guess it doesn't look so bad given that the midrange driver has quite a lot of glue around the dust cap from the factory to behing with. BTW, the glue dries clear, not white. And the end result - re-installed back into it's home, and sounding exactly the same as before (which is just what I wanted ) Edited March 27, 2011 by pete_mac Link to comment Share on other sites More sharing options...
skippy124 Posted November 14, 2010 Share Posted November 14, 2010 Nice write up and result Pete.... looking forward to hearing these soon!! Link to comment Share on other sites More sharing options...
pete_mac Posted November 14, 2010 Author Share Posted November 14, 2010 Why thank you sir! Looking forward to seeing what you think about their sound. Link to comment Share on other sites More sharing options...
vmhf Posted November 20, 2010 Share Posted November 20, 2010 (edited) Hi Pete, The speakers look stunningly good now that you have refoamed them. I have to invite myself to your place to a listen to these 'reborn' speakers and vintage gear when I get the chance! Cheers, Victor. Edited November 20, 2010 by vmhf Link to comment Share on other sites More sharing options...
pete_mac Posted November 29, 2010 Author Share Posted November 29, 2010 Hi Pete,The speakers look stunningly good now that you have refoamed them. I have to invite myself to your place to a listen to these 'reborn' speakers and vintage gear when I get the chance! Cheers, Victor. Indeed... one day my friend! Link to comment Share on other sites More sharing options...
pete_mac Posted March 27, 2011 Author Share Posted March 27, 2011 Update time... I've now finished tweaking these speakers and I'm very happy with the results. The original tiny bipolar electrolytic caps have been forever banished from the crossover, with Mundorf M-Caps in their place. The metal woofer baskets have been treated with some Dynamat Xtreme self-adhesive damping material. Dynamat does its job by adding mass to resonant metal surfaces in order to reduce their resonant frequency and prevent sympathetic ringing. Prior to doing this, the baskets would ring noticeably when you tapped them, but they are now quite non-resonant and reply with a 'thud' when tapped. It doesn't look pretty, but it's a case of function over form. You dopn't see the rear of the speaker basket anyway I was careful to avoid placing the Dynamat too close to the edge of the spokes of the basket in case it created issues with interference/turbulence with the backwave of the speaker. You don't need to cover the entire basket to achieve reductions in resonance/ringing. Also, it would have been possible to apply multiple layers, but you quickly encounter diminished returns for your efforts. One layer is more than enough IMHO. Link to comment Share on other sites More sharing options...
pete_mac Posted March 27, 2011 Author Share Posted March 27, 2011 (edited) They aren't the most visually attractive speakers out there, but they punch well above their weight. The crossover tweaks have made a very noticeable improvement in the transparency of the midrange and tweeter drivers. I'm very happy with the outcome, and I'm really looking forward to setting these up in a proper listening environment in the near future - they are poorly placed at present. After having these out of action for a month or so, I forgot how low these go compare to the Usher S-520s. They have effortless bass reproduction down to 35Hz, and the midrange and treble response is now on-par with the Ushers after the crossover mods. I also have the original stands for these, so in future the current 'ghetto' stands will be ditched in favour of them. Although... I will perform listening tests first, as I bet the current stands are much more inert than the original metal stands! Edited March 27, 2011 by pete_mac Link to comment Share on other sites More sharing options...
pete_mac Posted April 1, 2011 Author Share Posted April 1, 2011 (edited) I've had a good listen to these during the week, and gee they sound great. They have far surpassed my expectations. They will not be going anywhere in a hurry methinks! I do love my Ushers to bits, but they certainly can't get up and boogie like a larger speaker can. These 300tis are effortless in how they produce their sound. They perhaps aren't quite as forward as the Ushers, but they certainly aren't all that different in their overall sound... apart from the additional low end extension. They are so pleasing to listen to, and such good fun!! Edited April 1, 2011 by pete_mac Link to comment Share on other sites More sharing options...
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