Really enjoying this thread keep it up chaps :)
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Really enjoying this thread keep it up chaps :)
Some more progress this morning:
First of the new plinths made and fitted. For now I've just fitted the base with the steel domed feet removed from the original base until I drill and fit the castors.
Just need to fill and lightly sand to a decent finish to accept the veneer. Fit is exact. The new plinth sits very precisely to the old one with no steps or gaps, so the veneer which will go across both sections should fit very well and it will look like a monolithic construction:
http://i1140.photobucket.com/albums/...psca9d741a.jpg
Front View:
http://i1140.photobucket.com/albums/...ps75f0a15f.jpg
To give an idea of scale, the speaker now stand a whopping 43 inches high (1.1m) without castors. The castors will raise them to 45 inches (1.1.5m). The base is also very heavy and stable. With the drivers fitted, these will be a 2 man lift job.
Makes my Contiboard efforts look a bit crap..:scratch:
I could mess things up yet Dave! The only thing I hadn't thought through was the type of castor. I've bought standard 40mm dia plastic wheeled castors. They'll most likely crack every porcelain tile in the utility and kitchen as I move them to their resting place in the living room! Empty cabs must weigh in at 30 to 35Kg now.Quote:
Originally Posted by hifi_dave
A little more progress this week:
http://i1140.photobucket.com/albums/...psb54622fd.jpg
Both plinths now completed and castors fitted to bases. Bases filled and sanded to get a perfect finish prior to applying Sapele veneer.
Rear view showing joint with existing base:
http://i1140.photobucket.com/albums/...ps1412fac5.jpg
http://i1140.photobucket.com/albums/...psef930ee4.jpg
Silver plated binding posts fitted to crossovers:
http://i1140.photobucket.com/albums/...ps9da43f82.jpg
New Mills wire wound resistors on order to replace the existing 50 Ohm ones (one has a nasty looking bulge in it).
I've gone the whole hog and am fitting new crossovers in a few weeks (custom built using foo caps etc) but wanted to have the originals functional too as these stay with the speakers for the eventuality they may get moved on later.
Speaker drive units inspected in detail. One driver shows signs of wear to the suspension, probably as the result of being driven with the foam surrounds gone so I've bitten the bullet and decided to have them re-coned and new suspension fitted. Also have on order a new 4-pin connector for the new crossovers.
Long lambswool/polyester mix internal wadding will replace the sponge foam internal padding which is really rather poor at controlling resonance and in reality does little to attenuate anything other than HF. LF cannot be attenuated using this type of foam so the lambswool mix is targeted at prevention of LF standing waves within the cab.
It's looking good Paul, and interesting.
Shame the cones need replacing. Still, once it's done they'll last indefinitely. Will you be able to tailor the tweeter output with the new crossovers? There can be too much output from the compression driver in relation to the bass in some systems.
I'm thinking of building a couple of short plinths for my Cheviots, to get them off the deck by three or four inches, I'm not getting bass boom, but it may make a difference.
Loving the attention to detail, Paul!
Glad you've decided to make some 'fooey' crossovers too, and retain the originals, should you sell the speakers. That's exactly what I'd have done, and you'll now *really* hear what those drive units are capable of! ;) Castors are also the way to go, too!
Look forward to following the rest of the journey, as it unfolds :)
Marco.
It is a shame but to do the job properly, the whole units need refurbishing really and once done they'll just need a re-foam in perhaps another 15 years time. I haven't gone for the HE surrounds as this can destroy the magic of HPD/MG drivers but stuck to original spec with improved voice coils.Quote:
Originally Posted by walpurgis
The crossovers aren't tuneable save for manually changing cap values if needed. Mark Pitcher is designing and making them up for me only because I have no frequency generator or oscilloscope to test them on afterwards. mark will test and tweak from 20Hz to 20KHz. I'll eventually get round to desoldering all the components from the standard crossovers and replace everything like for like. The cost of the components is around £55 per crossover.
Raising your speakers off the ground ideally should be done to get the tweeter at ear level when seated. It does make an appreciable difference (improvement). Bass boom where it exists is more likely due to cab internal dimensions/padding and some cabs suffered with it, some didn't. I'm told that for ported enclosures the recommended volume for 12 and 15 inch drivers is 150 to 170 litres for best response and for sealed cabs with my 12 inch HPDs its much smaller...from 70 to 110 litres. Mine are 115, so a little extra wadding should improve LF, but it's suck it and see. I've bought enough to redo both cabs completely but may end up only using a fraction of that.
Loving the attention to detail, Paul!
Thanks Marco...yes, attention to detail is something of a fixation with me, a hang-up from my engineering days where it mattered! (...and still does!). Cabs are too big and heavy to man handle around the room so castors seemed the obvious solution.Quote:
Glad you've decided to make some 'fooey' crossovers too, and retain the originals, should you sell the speakers. That's exactly what I'd have done, and you'll now *really* hear what those drive units are capable of! Castors are also the way to go, too!
Look forward to following the rest of the journey, as it unfolds
Marco.
Interesting Paul and in this case, I await your findings with bated breath, as it's wonderful to see such careful dedication to the restoration of vintage gear like this :)
When did these models go over to foam surroundss? I remember the last of the pre HPD models did, but cannot remember when.. These cabs would have been originally fitted with the corrugated ones IIRC, tightening the bass at the expense of a bit of extension and giving a touch more sensitivity as a result. Up to you of course and practical experience of the difference is lacking this end, as it wasn't until 1973 that I first heard these both at Radiolux in Watford (decades before they became a solus B&O shop) and also KJ Watford who took Tannoy on six months or so before the "Girdacoustic" HPD models were launched - the Lancasters and Chatsworths they had were sold through pretty quickly I remember.
The thing is, you still have? the Turnberry to use as a modern DC reference, so it'll be great to read what the differences are to you :)
Quote:
Originally Posted by DSJR
Thanks David,
These were made in 1974 at the London factory using arguably the best quality of the HPDs and with the foam surrounds boast a sensitivity close to the Turnberrys (91dB V's 93dB). They have a self-resonance of 20Hz and in sealed cabs can drop lower than 35Hz before any appreciable roll-off kicks in. The sealed cabs also help with timing...they're meant to be far more agile than the Cheviots or Lancasters as well as more powerful in the bass. I still have the Turnberrys (they're not going anywhere soon) so it will be interesting to see how close the Mansfields come. They don't have the power handling of the Turnberrys but in most domestic situations, that's not too relevant.