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PFM Special - a simpler and more affordable DIY loudspeaker design

Well, it's been just over a year since my last post regarding the PFM Special. Now that I've finished upgrading my Voyagers with QUDOS boards, I've decided to move ahead with this project in the fall.

I've had the Vifa Woofers in storage for many years, and I've just taken delivery of the other drivers, as well as the crossover components and associated connectors. The Scanspeak D2905/9300 is no longer available, but apparently the 9500 is a drop in replacement. Rather than banana plugs, I'm using Neutrik Speakon connectors.

I've done a fair bit of woodworking, but this will definitely stretch my skill set. I haven't got all of the tools, but fortunately there is a woodworking workshop here in town that I can join. In addition to the extra tools, I expect they'll be able to give me a hand with the trickier steps.

I'm wondering whether, instead of MDF with hardwood front panels, I could do the whole thing with Baltic birch. I've got built-in birch shelves in my office, with dark walnut trim. I could trim out the speakers in a similar fashion. I suppose I could use MDF for the inner carcass, to save a bit of money.

So you'll start to see pictures appearing here soon. I expect the project to drag out over several months, so it will be a nail biter with many cliff hangers. :D
 
You go Mike! Have fun, I sometimes wish I had the nerve to build my own speakers, have thought about, mulled over so many things, can see it in my mind. Yet if I did, they would look like a three year olds first birdhouse shop project-probably worse. Plus I would probably lose several body parts in the process as well. So....
 
Thanks for the vote of confidence, Tim. We'll see how good mine look when I'm done. Most of the stuff I've done required as much finesse as this does. I'm hoping that with the right tools and a bit of expert assistance, I'll be able to pull it off.
 
Go for it Mike and good luck. My Specials are still special, and will be more so once I get them up and running at my new house.

Looking forward to seeing the build.

I moved my build pictures https://flic.kr/s/aHsmmeFGoF
 
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Thanks, Garf. Kudos for that excellent document of yours. Between James and you (and of course, the rest of the community members who took part), there's no way I would have attempted such an ambitious project.
 
I shall watch your build with great interest, Mike.

The 9500 isn't exactly a drop in for the 9300, but it will be close. The good news is I have a pair of unused 9300 if you'd like to take them off my hands. I think the 9300 sounds more natural, having used both tweeters before.
 
Thanks for the offer, James. If I had known you the 9300 spare, I would have snagged them. I've already received the 9500s, and they would be a hassle to return.

If I'm not happy with the performance of the 9500, hopefully you can advise me on which alternative values to try in the crossover.
 
Mike Hanson said:
If I'm not happy with the performance of the 9500, hopefully you can advise me on which alternative values to try in the crossover.
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That might be a stretch, Mike. Since becoming a Mac user, I no longer have LspCAD to (re)model anything. Let's cross that bridge when we get to it. The 9300s I have aren't going anywhere, so that's always an option for you.
 
Question regarding the upper baffle: Does it need to be that rectangle? I would like to make it smaller and more curvaceous. Will that affect the crossover?

Note that I'm starting with the passive crossover as designed, but will eventually play with a MiniDSP active crossover, which will make the point somewhat moot.
 
The baffle affects how the drivers perform, and the crossover was designed for that particular complement on that particular baffle. I can't say with any certainty how much a differently sized and shaped baffle would deviate sound-wise. When I had my PFM-Specials, the open baffle part was screwed on and could be removed. Perhaps you can make your preferred baffle and swap the original one out when you're ready for active.
 
Thanks, James. Yeah, I did a bit of reading after posting my message, and learned that both the baffle area and driver position would impact the crossover.

I' may go with the same general dimensions, but introduce a curve that doesn't change the physics too much, yet softens the boxy look. I have access to a CNC router, so the possibilities are endless.
 
Here I am back again, and I can safely say the project is finally ready to begin in earnest. I was rather shocked when I noticed James started this thread 17 years ago. :eek: I've had the unobtanium woofers in storage for most of that time, and a couple of years ago bought the midranges and tweeters, along with the crossover bits.

I'll likely house the crossover externally, and use three SpeakON connectors on the cabinet. Then I can change it to an active design later, if I feel so inclined. It also keeps the passive crossover components away from speaker vibration.

Over the last year I've been working on various projects at the local woodworking club, and I think my skills are up to snuff. Their table saw is perfect for cutting the MDF sheets; their joiner and planer will help with the raw timber; the wall of clamps will be integral; they have a CNC Router to carve all the holes for drivers; and a topnotch router table for roundovers, etc. They've also tools for dowels, biscuits, or dominos, so there are options aplenty!

Now is time to finalize my design and order/acquire some wood. I'm a big fan of natural wood, and I would like to use solid timber for the bottom and top baffles. Walnut is plentiful here and lovely too. I'll also consider wood that has natural black/dark colors in the grain, to play off the black drivers.

Regarding the bottom baffle: Given the inner carcass of the bass bin is MDF, it's not going to expand and contract, but solid timber will. In addition to the woofer screws, I was considering using silicone calking to affix the wood panel to the MDF. Would this give it enough flexibility to permit that movement? Alternatively, could I sandwich some type of flexible sheet (sorbothane or neoprene?) between the two surfaces? That should help to further deaden resonances too.

This thread itself is an excellent resource, but unfortunately many of the images are no longer available. Consequently I'm working primarily from the fantastic document that @chiily sent to me, which includes the changes required for the Scanspeak tweeter. I've considered his visual design, with the arms on the side, and I think I'm going to go with the simple baffle perched on top. I might use a piano hinge to attach it to the bass bin, then add a strut or two to hold it in the correct position. Or I may go with James' original approach of the struts alone. I don't need to decide that today.

I have to check the dimensions of everything, as MDF sheets in North America may have a different thickness, and I may redraw the plans.

One question for now: Is it a good idea to use HDF rather than MDF? The cost isn't an issue for me, as my time during and satisfaction after the build are worth much more to me. If HDF would be beneficial, then I'll order that instead.
 
I wouldn’t use solid wood and mdf in the same cabinet, it’s ok if the grain is all going in the same direction but when you do a cross grain joint you will have movement to contend with.

Mdf will move, I made a mdf door with one skin and it bent like a banana when the mdf shrunk.

Pete
 
Pete MB&D said:
I wouldn’t use solid wood and mdf in the same cabinet, it’s ok if the grain is all going in the same direction but when you do a cross grain joint you will have movement to contend with.

Mdf will move, I made a mdf door with one skin and it bent like a banana when the mdf shrunk.
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Thanks for the warning. I was under the (perhaps mistaken) impression that MDF was stable.

What about Baltic birch? It's apparently hard to get these days, but that's also an option for me, and I know that it's very stable.

FYI: I'm thinking to use solid timber for the external front baffles, but I was planning to use wood veneer on the other surfaces of the bottom cabinet. Perhaps instead I could go with Baltic birch throughout, and veneer the whole thing. That would give me a wider choice of woods to use. I'm intrigued by the idea of exotic/extreme wood grain.

Alternatively, if I can get my hands on HDF, then I can use that instead of the Baltic birch. It should be strong enough for the top baffle. I'll see what's available locally.
 
The Oak front baffle on the bass bins of mine have a 2mm crack up the centre were the solid wood has moved and the MDF hasn't :(

If I had my time again I would go for birch ply all round....
 
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Hi Mike

Birch ply will be good it still needs to be kept where ever it ends up for a few weeks to acclimatise, so cut roughly to size bring in io the house stack with battens in between to allow the air flow around the pieces then cut to size.
The same goes for solid wood.

Pete
 
chiily said:
The Oak front baffle on the bass bins of mine have a 2mm crack up the centre were the solid wood has moved and the MDF hasn't :(

If I had my time again I would go for birch ply all round....
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I'm glad I asked. I'm thinking it makes sense to to birch ply or HDF (if I can find it). If I like the way they sound, then I can add veneer later. If I don't... well I'll cross that bridge when I come. ;)
 
Pete MB&D said:
Hi Mike

Birch ply will be good it still needs to be kept where ever it ends up for a few weeks to acclimatise, so cut roughly to size bring in io the house stack with battens in between to allow the air flow around the pieces then cut to size.
The same goes for solid wood.
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That's a good point. I'll be sure to acclimatize it to my house when I get it, then transfer it straight to the woodworking shop for cutting. It's "near" my place, so should have similar environmental conditions.
 
Looking forward to your build, Mike! Hopefully you are able to get some good pics snapped as you go along. Have fun, sounds exciting! Oh, and keep all of your digits! :)
 
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