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PFM Special - a simpler and more affordable DIY loudspeaker design

I like the looks of that design! The only thing that I'll likely do differently is to use bare wood on the front baffles, rather than leather cladding. I'm also toying with the idea of using plywood rather than hardwood, as I kind of like the layered edge look, especially when it's shaped a bit. We'll see...

-=> Mike Hanson <=-
 
Mike,

There are two further reasons, besides the aesthetic one, for using MDF and leather for the baffles.

The first and most important is the damping of the surface. MDF is an excellent self-damping material and if a different material such as leather is bonded to its surface, it becomes incredibly dead sounding, which is what you want for loudspeakers. The sound, and hopefully music, should be coming from only the drivers - perfectly blended by the XO of course. When I rapped the upper baffle of the PFM-Special, it sounded distinctly woody with a louder and higher pitch than the leather-clad MDF Ergo baffles. Whether this adds significantly to the acoustic output is difficult to determine without a different variant against which to compare. But one thing is certain IMO - it would be preferable to have an overdamped baffle than an underdamped one. Note that I've also made the E-VI baffles almost twice as thick, and I haven't discounted true constrained layer damping with a lead or bitumen sheet sandwiched between the MDF layers.

The second reason is air-sealing. It's not so important with a finished design, but if there is a chance that you need to experiment with the amount of stuffing, or rewire the internal bits - then using mastic or sealant to provide an air-tight interface between the woofer flange and cabinet is a lot more hassle than leather.

I'll see if I can persuade Steve to draft another set of drawings to capture the E-VI design in more detail, and perhaps colour in the bits to make it look more real. Then, I think you might find that the blackness of the leather (assuming you use black of course) provides welcome relief and textural contrast to the wooden surfaces to yield a well proportioned and purposeful looking loudspeaker. The use of black leather also softens the grill-less look of exposed drivers (which will ALWAYS sound better than clothed varieties) and is one less useless accessory to worry about.

You are planning to teach your son the golden rule of "Don't Touch Daddy's Toys", yes?

James
 
I've never got along with that "black leather in the center, with wood panels on the sides" look. I can appreciate the sonic benefits of your design, though, and I'll probably end up using that approach.

BTW, is there any reason why the upper portion of those side panels doesn't extend further back? Wouldn't it succeed in making the baffle more "infinite". You could take them at least half-way back, and still maintain the same basic look (i.e. smaller on top than on bottom). It would also help to hide the "guts".

For that matter, you could place a board across the back (within the side panels), to further enclose the upper baffle. I suppose this leads to the issue of whether the top baffle should be sealed completely, or left open at the top and bottom.

-=> Mike Hanson <=-
 
Mike,

"BTW, is there any reason why the upper portion of those side panels doesn't extend further back?"

Yes, and it's an effect called cavity resonance. I had thought that swept back wings could work and look nicer to boot, but in practice that totally destroys the dipole effect, which requires the front and back surfaces to be as close to identical as possible. If the back is partially enclosed with extended side panels, then at certain frequencies, the echo arising from cavity resonance will colour the overall acoustic output. A totally flat surface would be ideal, but such will still need structural rigidity. I may experiment with metal plate inserts if I can get the right sized pieces, and do away with the vestigial 'struts' in the E-VI version.

James
 
I read this in all its glory a little while ago & have now come to the conclusion that I need to head in the direction of sealed speakers because of room, um, eccentricities in the resonances department, chiefly because of positioning requirements of the speakers. That positioning requirement being right up against a wall. Which I have a feeling is not a good idea with these speakers, them being open-backed... I'd love to have a go at one of the Ergo series, but am rather nervous about the sound of the EBAT test, that even assuming that James would be happy for yet another clone to be allowed out of Middle Earth!
 
Nom,

If you are anywhere near AshleyD, I'm sure he wouldn't mind letting you know a bit more about the Ergo Building Aptitude Test. Heck, he might even show you the fruits of his labour. The E-IVs work just fine against the wall if you cannot accommodate the PFM-Special away from boundaries. PM AshleyD, Mr Tibbs or me if you'd like to know more. I'm happy for another Ergo clone to be built as long as it's done correctly.

James
 
Thanks James! Boundaries are all I've got at the moment, sadly...
I think Ashley is nearest - will throw him a PM shortly & will go from there!
 
Moving an old thread up as I'm interesting in building a set of speakers.

James, are the PFM specials still in use? Was the tweeter ever changed? Did anyone in the UK build one of these?

The design looks good and reasonably cheap.
 
chiily said:
James, are the PFM specials still in use? Was the tweeter ever changed? Did anyone in the UK build one of these?

The design looks good and reasonably cheap.
Click to expand...
Unfortunately, no. I have enough difficulty accommodating three spare pairs of loudspeakers. Besides, I wanted to recycle the Vifa M26WR woofers into a pair of these ...

4028437-lg.jpg


No-one built the PFM-Special, but Mike Hanson came close; he bought a pair of M26WRs. The (bass) cabinets now collect dust in my garage and occasionally serve as a platform for my drill press. The difficulty with trying to build the PFM-Special is getting a pair of M26WR-09-08s. They've been out of production for a while now, and I'm sure NOS stocks must be depleted by now.

James
 
Thanks for the update.

I'm just looking for a diy speaker, reasonably simple to build, but with a great sound to rival my ES14s. I've listened to a few speakers over the last few months and not heard anything (unless we are talking lots of money!) that makes think about selling the Epos.

I just want to save some cash and have some fun building a pair of speakers.
 
chiily said:
I just want to save some cash and have some fun building a pair of speakers.
Click to expand...
Unless you have all the requisite tools, time and patience, DIY loudspeakers don't actually save you any money. What's fun for some may turn out to be sheer frustration, but there is no denying the personal satisfaction of building something from your own hands and efforts. Eventually.

If you can find yourself a pair of Vifa M26WR-09-08s, you're more than welcome to have a go at building the PFM-Special. Just don't make the aesthetic mistake I did by having the top baffle in a different colour to the bottoms.

James
 
Hi James,
Grant from Sydney, Au here. I'm very interested in your PFM Special and have some questions please, if you have the time!
I have two ancient Vifa P25WO-00-08's which I wonder could be used instead of the M26's? My main boxes are only 40 Litres (too small for P25 according to WinISD) and baffles are 32cm by 74cm. Your open TM baffle would sit on top.
(the P25WO is here: http://www.sea.vg/vifa/ )

I hope to buy the MCA15RCY's soon and err.....Seas 27TFFC tweeters. I have a reason for choosing the Seas tweeters and indeed their response and parameters look similar to the Vifa D27TG's, imho, I think? I'm wondering please if these new T&W's would have any chance of success with your existing
xo and identical T/M baffle? Unfortunately, I'm a relative beginner and can't do measurements (although I can sim xo's in Speaker Workshop). I was using most of the FRC tools at the Library until I lost access to the Excel Pc! Aarrgh!

Please don't spend much time on my questions as I know you are very busy! A generalized yes/no type answer would be great! Many thanks, and great Ergo designs!...grant
 
Hi Grant,

I'll need to do some investigation and see how close the T/S specs are this weekend. Let me get back to you.

James
 
Grant, the Seas and Vifa tweeters may have similar response, etc, but don't sound anything alike.

I originally used Seas 27TFC's in my MTM design, but replaced them with a pair of Vifa D27's courtesy of James. The Seas are quite explicit, the Vifa's sweeter and integrated much better with my Vifa C17's.
 
RustyB said:
... replaced them with a pair of Vifa D27's courtesy of James.
Click to expand...
Now I remember where they disappeared to.

The Seas are quite explicit, the Vifa's sweeter and integrated much better with my Vifa C17's.
Click to expand...
I found the D27's top end somewhat grainier than I'd like. But it still sounded like music, which is not a bad thing.

To answer Grant's question, the D27 is a lot closer to the 27TFFC than the P25WO is to the M26WR. I think the XO for the PFM Special would accommodate the Seas tweeter. The odd resonance hump should not matter too much with a cross at around 3kHz.

The P25WO will need to be reflex loaded if you want to get any bass from it. I haven't done the maths to calculate box volume, vent dimensions etc. However, the cross between the woofer and mid is critical, and need to take into account baffle dimensions and the natural roll-off of the driver. I'd be more comfortable advising the M26WR than going with the P25WO. Have you checked with Mike Hanson to see if he still has his pair for sale?

James
 
Wow, thanks James and Rusty! For your speedy replies.

My drivers are probably 20? years old, I found this site by googling D75MX ( mine have no version on driver!).
The tweeters I have are ancient Vifa D25TG-55-06's , but no specs available. I should mention that I am a
55yo retiree with very limited funds, and I was thinking of modifying Troels Gravesen's Poor Mans Strad (PMS)
for my (too small existing *vented* boxes for the P25's?), with the Seas MCA15RCY and 27TFFC's.
(James, I was hoping to emulate your M26 xo response graph with the P25...looks straightforward...LR2 @ 500?)

The PFM Specials really appeal to me! Somehow, a modification maybe seems just do-able? There are issues
of course! James , thank you for your comments on the D27 / 27TFFC comparison. Unfortunately, as a beginner
I really don't know how resonance/impedance affects response, except Fs should be low, (and Zaph's 'Tweeter Mishmash').
Or, Rusty, I have no clue as to how different tweeters sound. I wish I knew!

Very IMHO!, the P25 in a too small 40 litre vented box, might give me some bass extension with a proper port without sounding
'boomy'? The M26 was tested in an infinite baffle, but the the P25 was in a 50Litre (closed?) box. So thats why I thought
it might be OK? I guess I'm just hoping for something great sounding for a cheap price! James, unfortunately, I don't
have the cash for the M26's. I was just curious as to the possibility with the P25's. If its not possible, then no problem!
I've been admiring your 'beauty contest' photo of your Ergo designs....wow! Stunning craftsmanship.

Please don't waste any time on it! But your help is/has been very much appreciated! Thanks so much, grant, in Sydney, Au
(PS - I'm new to this site - how do you post jpegs?)
 
grantnsw said:
(PS - I'm new to this site - how do you post jpegs?)
Click to expand...

You don't directly. Find somewhere that will host your jpeg for free (I use Flickr, but there are lots of photo sharing sites).

Then you use the IMG tags to point to the URL of your image.

If you use the full editor, there is a little picture button, which puts the tags and and prompts you for the URL.
 
Grant,

grantnsw said:
James, I was hoping to emulate your M26 xo response graph with the P25...looks straightforward...LR2 @ 500
Click to expand...
Yes, that's about right but I did factor in some baffle step compensation. Taking a closer look at the P25 vs M26 conundrum, I note that they have materially different voice-coil inductance and DC resistance. This means the crossover I had designed would result in a different transfer. You could try simulate an LR2@500Hz crossover, but unless you have measurement and CAD software, you could be taking a risk in putting money into a project that drives you around the bend. I'm also reluctant for you to undertake such a venture with two out of three different drivers. If you lived near me, I could make the crossover modification for you, but alas NSW is more than a drive.

Keep an eye out on eBay or check with the Australian importers of Vifa (Wes Components). They might have M26s on special, and you should be able to sell your P25s and recover some of your cost.

James
 
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