June 23, 2013 at 6:20 am #416266
No it doesn’t stand for what you might think.
PMS akaPoor Man’s Strad originally designed by Troels Graveson and inspired by Sonus Faber’s Stradavari.
Rather than doing a direct copy of Troel’s version I have done a little redesign to accommodate drivers that are readily available here in New Zealand.
As the name implies the idea is a cost effective, but top performing speaker.
I have opted for a design that is in terms of size. Rather than use a 10 or 12 inch driver the PMS ( my version) will be based around an 8 inch (200mm) woofer, 5 1/4 inch (135mm Kevlar )mid range and a 1 (25mm) inch Titanium tweeter.
The design calls for a 49 liter enclosure, of which 7 liters are for the mid/tweeter enclosure, with a further 4 liters for internal framing and speaker displacement.
Minimum requirements for the woofer enclosure is 38-40 liters, tuned to 41.62Hz.
Today I drew the plans onto some 3 mm Mdf sheet, made the pattern for the interior frames, and constructed the mid/tweeter enclosure and locked it all together with some stabilizing edging. Once the laminated curved sides have been made and fitted, the stabilizer sides pieces will be removed and some hardwood edging will be fitted. Solid hardwood will be used for the front and rear baffles, with Rimu veneer for the sides
First sub-frame ready for the sides & baffles.
Bare frame dimensions are 1020mm x 498mm (final sizes will be larger in width once edge trim is fitted.)
Frame & speaker positioning.
A Recovering Audioholic ---- " Geez I Missed You 33 & 1/3rd"June 23, 2013 at 9:42 pm #416282
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A pal made a set of Troel’s PMS a couple of yrs ago.
Used Seas drivers IIRC.
Dark Lantern blog - http://darklanternforowen.wordpress.comJune 23, 2013 at 11:26 pm #416283
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Plenty of pics, please! I do like a good speaker build.:D
WellingtonJune 24, 2013 at 5:40 am #416300
Will do, I usually take a whole lot of pics as its a way of being able to visually refer to at a later date.
A Recovering Audioholic ---- " Geez I Missed You 33 & 1/3rd"June 24, 2013 at 6:59 am #416304
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Awesome! Will have to come out and have a listen to your builds some time. Good luck with this one.June 30, 2013 at 5:14 am #416548
This weekend saw the finishing of the sub-frame and the beginning of the skin process.
As I didn’t want to risk having the possibility of lines showing using Troels version I have opted for a 6 ply skin comprised of 3mm Mdf with a Rimu ( or similar ) veneer to finish. The baffle will be a textured matt black, as will be the rear of the enclosures. The wood veneer sides will be stained, possibly Rosewood or a dark red of some sort. Alternately I could use some nicely figured Macrocarpa and go for a lighter finish. Any thoughts?
To date total workshop time is 9 1/2 hours.
As it was woefully cold this morning I modeled the basic crossover layout.
Suggestions always welcome. More next week hopefully.
A Recovering Audioholic ---- " Geez I Missed You 33 & 1/3rd"June 30, 2013 at 5:18 am #416549July 3, 2013 at 1:39 am #416629
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Looking damn good. All these DIY speaker projects are giving me ideas….expensive ideas…July 7, 2013 at 9:56 am #416816
The skinning process didn’t work too well so I have used slotted Mdf as Troels and others have. Spent today sanding and filling air gaps and sealing around the mid/tweeter chamber. I doubled the amount of cuts in the Mdf and that smoothed out the shape very nicely.
As its my birthday today, I’ve been a little lazy, but I have been remodeling the crossovers for a variety of different drivers and configurations. Did the same to the box model and now have what I think should be the final design for the tuning and port size/length worked out.
Box tuning is 42.30 Hz and F3 is 42.85 Hz which should make for a very flat response from the woofer. This turns out to be very close to Troels models as well, so it seems I have it pretty much right.
I moved the crossover point for the woofer from 350 to 750 Hz and this gives a lot flatter overall response, and allows a higher cross to the tweeter at 4000 kHz, which keeps the vocal range nicely in the mid-range drivers zone.
An added filter for the tweeter to pad down its upper end will be added to the HF section prior to the L-Pad. The tweeter has a rising response from 15000 to 20000 kHz and climbs to 96dB so a contour filter needed to be added. Titanium tweeters can be prone to this and without this filter get too shrill for my taste.
Thats about it for now. More skinning to be done and some drivers to order, then I will need to assemble the crossovers prior to a trial run. I’ll add more photos as we go along.
A Recovering Audioholic ---- " Geez I Missed You 33 & 1/3rd"July 7, 2013 at 9:33 pm #416822
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kiwilistener;185417 wrote: The skinning process didn’t work too well so I have used slotted Mdf as Troels and others have. Spent today sanding and filling air gaps and sealing around the mid/tweeter chamber. I doubled the amount of cuts in the Mdf and that smoothed out the shape very nicely.
‘Kerfing’ as they used to call it
Dark Lantern blog - http://darklanternforowen.wordpress.comJuly 8, 2013 at 7:42 pm #416861
Some still do, over at the woodwork forum you still see the term used frequently but it seems to have fallen out of use with mainstream vocab and become more trade orientated.
A Recovering Audioholic ---- " Geez I Missed You 33 & 1/3rd"July 22, 2013 at 6:05 am #417734
Due to work and family, things on the PMS build have been a little slow.
However I was able to get out on Sunday and get some more done.
Both the speakers have had their rear skins fitted and the removable panels for the mid chamber have been pre-fitted and shaped to match the rest of the skin’s shape.
Slotting ( or kerfing ) 18 mm mdf is easy and at 20 mm intervals makes for a smooth shape with no fold lines. All panels are glued and screwed for rigidity. You may think screwing as well as gluing is overkill but I want total rigidity and given the pressure exerted by the woofer everything needs to be solid and well sealed, as seen in the images below.
Once everything is fixed in position the holes are filled with my newest favorite filler. If you haven’t used Selly’s Rapid Fill I suggest you give it a shot. This stuff is very good to work with, and dries and sands really nicely.
Once I’m happy that all the holes are well filled and sanded back they will get some matt black applied. I do this with a wool roller and if done slowly will create a nice textured finish rather than a drab flat looking finish.
Tonight I sanded back the filler and re applied the odd small amount on holes where I had trapped a little spot of air. It gets 80, 120, 220, 400, and a final cut at 800 grit prior to painting.
You will note in the lower images the stuffing position and that the walls are covered. This will include the woofer chamber although it wont contain stuffing. All the kerf lines and seams around the woofer chamber, both inside and outside the chamber are fully sealed.
A Recovering Audioholic ---- " Geez I Missed You 33 & 1/3rd"July 22, 2013 at 6:20 am #417735
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Isn’t nice when things go as planned – not like my day of diy at all.
I tell you, we are here on Earth to fart around, and don't let anybody tell you different. KVJuly 22, 2013 at 7:44 pm #417757
What happened to your day of DIY?
A Recovering Audioholic ---- " Geez I Missed You 33 & 1/3rd"July 23, 2013 at 4:15 am #417793
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