PFM Special - a simpler and more affordable DIY loudspeaker design
- Thread starter James
- Start date
Rico,
Fyi...
I believe James already answered your question some threads ago in the audio room. It was in the midst of an argument you two were having about the merits or otherwise of modding equipment. I seem to recall he responded somewhat dismissively, unfortunately, as I was interested too.
If I may say so....such internecine strife in a far-flung corner of the world, what a shame. Can't you two just kiss and make up?
Regards,
JonR
PS: Lest I be accused of sticking my nose in where it isn't wanted, I apologise. I was only trying to help. My latter question above is genuine.
James
Lord of the Erg\o/s
"They must be sounding good."
Ashley, unfiltered loudspeakers sound, um, bland. I've just placed an order for all the XO bits and should expect delivery by the end of this week, just in time for some weekend assembly. Then we'll know how they sound.
"What's the ballpark cost per sheet of the marine ply? Is it a particular grade, or does all Marine ply come with decent grain per your cabs? I'm also interested in what the oil is you're using for the finish."
NZD100 per 2.44 x 1.22m sheet. I use marine ply that is graded to BS1088, which lay out all the requirements including finish. All my loudspeakers are finished in Danish Oil.
"I seem to recall he responded somewhat dismissively, unfortunately, as I was interested too."
Jon, my apologies for the poor form. In general, I don't dismiss people easily. I value friendships and enjoy the camaraderie that is obvious in PFM. I will defend my friends to the best of my abilities, but if it is not appropriate to do so, say when I'm in disagreement, I will remain neutral and not take the opposing side. Unfortunately, some don't have the same sense of loyalty as me. It is my flaw that I don't suffer fools gladly.
James
Ashley, unfiltered loudspeakers sound, um, bland. I've just placed an order for all the XO bits and should expect delivery by the end of this week, just in time for some weekend assembly. Then we'll know how they sound.
"What's the ballpark cost per sheet of the marine ply? Is it a particular grade, or does all Marine ply come with decent grain per your cabs? I'm also interested in what the oil is you're using for the finish."
NZD100 per 2.44 x 1.22m sheet. I use marine ply that is graded to BS1088, which lay out all the requirements including finish. All my loudspeakers are finished in Danish Oil.
"I seem to recall he responded somewhat dismissively, unfortunately, as I was interested too."
Jon, my apologies for the poor form. In general, I don't dismiss people easily. I value friendships and enjoy the camaraderie that is obvious in PFM. I will defend my friends to the best of my abilities, but if it is not appropriate to do so, say when I'm in disagreement, I will remain neutral and not take the opposing side. Unfortunately, some don't have the same sense of loyalty as me. It is my flaw that I don't suffer fools gladly.
James
James,
Thanks for the response to Rico's query and also for your gracious apology.
I have to admit to some concern that you "don't suffer fools gladly" when I say what a complete 'fool' I am when it comes to speaker engineering, design and build, something of which you clearly excel. Having said that, I have said in the past how much I enjoyed reading about your exploits on the Naim forum and equally I am incredibly impressed and fascinated by your threads on PFM. I always enjoy reading about your latest updates!
Therefore I hope you wouldn't mind if I ask one other question. The design of the crossover that you've been going into above - how does that influence the way the crossover actually gets built in practice? Ie. does it affect materials used, the way they are wired together, etc. Also, what is meant by a first-order or second-order crossover, or fourth-order?
Many thanks in advance for any reply.
Regards,
JonR
Thanks for the response to Rico's query and also for your gracious apology.
I have to admit to some concern that you "don't suffer fools gladly" when I say what a complete 'fool' I am when it comes to speaker engineering, design and build, something of which you clearly excel. Having said that, I have said in the past how much I enjoyed reading about your exploits on the Naim forum and equally I am incredibly impressed and fascinated by your threads on PFM. I always enjoy reading about your latest updates!
Therefore I hope you wouldn't mind if I ask one other question. The design of the crossover that you've been going into above - how does that influence the way the crossover actually gets built in practice? Ie. does it affect materials used, the way they are wired together, etc. Also, what is meant by a first-order or second-order crossover, or fourth-order?
Many thanks in advance for any reply.
Regards,
JonR
James
Lord of the Erg\o/s
Jon,
"I have to admit to some concern that you "don't suffer fools gladly" when I say what a complete 'fool' I am when it comes to speaker engineering"
Fear not, I'm not at all averse to inquisitive minds and genuine interest. In fact, I welcome constructive debate and discussion. The fools I refer to tend to have an opposite raison d'etre.
"The design of the crossover that you've been going into above - how does that influence the way the crossover actually gets built in practice? Ie. does it affect materials used, the way they are wired together, etc. Also, what is meant by a first-order or second-order crossover, or fourth-order?"
By way of example, a second order crossover has an attenuation rate of 12dB per octave beyond its cutoff frequency, 3rd order is 18dB per octave, 4th order is 24dB per octave, and so on. The point of confusion for most people is that it is the final acoustic crossover that matters. All loudspeaker drivers are passband devices, which means they will naturally roll off at their frequency extremes. So, if a driver is used up to the limits of its flat frequency response, then the effect of its natural roll off combined with any electrical filters in place will yield the actual acoustic attenuation slope.
There are many different slope shapes that, in symmetrical pairs, yield a different phase, acoustic, and power response. I have a preference for Linkwitz-Riley crossovers because they sum flat and if properly implemented maintain phase integrity of the crossover.
To achieve the acoustic transfer target, I have to first measure the native (acoustic and electrical) response of each individual driver in situ on the cabinet, and then use CAD software to model the filter components needed to achieve my design. I also strive to use as few components as possible to preserve the integrity of the musical signal and yet meet my design targets. As a result, the PFM-Special uses a single inductor on the woofer (in concert with natural roll-off) to yield a 2nd order transfer at 500Hz, just two inductors, a single capacitor, and two resistors in the midrange filter to realise a second order LR cross at 500Hz and 3kHz, and a single series capacitor with a resonance trap (resistor, capacitor and inductor in series across the driver) to achieve a second-order LR transfer at 3kHz.
When I'm happy with the result, I will publish the filter circuit here so everyone can see how it all hangs together.
James
"I have to admit to some concern that you "don't suffer fools gladly" when I say what a complete 'fool' I am when it comes to speaker engineering"
Fear not, I'm not at all averse to inquisitive minds and genuine interest. In fact, I welcome constructive debate and discussion. The fools I refer to tend to have an opposite raison d'etre.
"The design of the crossover that you've been going into above - how does that influence the way the crossover actually gets built in practice? Ie. does it affect materials used, the way they are wired together, etc. Also, what is meant by a first-order or second-order crossover, or fourth-order?"
By way of example, a second order crossover has an attenuation rate of 12dB per octave beyond its cutoff frequency, 3rd order is 18dB per octave, 4th order is 24dB per octave, and so on. The point of confusion for most people is that it is the final acoustic crossover that matters. All loudspeaker drivers are passband devices, which means they will naturally roll off at their frequency extremes. So, if a driver is used up to the limits of its flat frequency response, then the effect of its natural roll off combined with any electrical filters in place will yield the actual acoustic attenuation slope.
There are many different slope shapes that, in symmetrical pairs, yield a different phase, acoustic, and power response. I have a preference for Linkwitz-Riley crossovers because they sum flat and if properly implemented maintain phase integrity of the crossover.
To achieve the acoustic transfer target, I have to first measure the native (acoustic and electrical) response of each individual driver in situ on the cabinet, and then use CAD software to model the filter components needed to achieve my design. I also strive to use as few components as possible to preserve the integrity of the musical signal and yet meet my design targets. As a result, the PFM-Special uses a single inductor on the woofer (in concert with natural roll-off) to yield a 2nd order transfer at 500Hz, just two inductors, a single capacitor, and two resistors in the midrange filter to realise a second order LR cross at 500Hz and 3kHz, and a single series capacitor with a resonance trap (resistor, capacitor and inductor in series across the driver) to achieve a second-order LR transfer at 3kHz.
When I'm happy with the result, I will publish the filter circuit here so everyone can see how it all hangs together.
James
Mike Hanson
Trying to understand...
Yes, they're quite handsome, and look like they'll last forever. <grin> Compared to the other drivers in that shop (they make "cool" speakers for car audio buffs), their appearance is positively plain.
-=> Mike Hanson <=-
P.S.: I intend to put some type of grill on mine. I'm not sure how that will affect the world. The reason? I don't like being distracted by the movement of speaker drivers, and I've got a 1-year-old son. <sigh>
vuk
\o/ choose anarchy
james.
thanks for all this! looks like something i could possibly attempt. i still wish, however, you'd do something with a tannoy dual-concentric driver. just think, you would have been finished after constructing the first box.
bwt--i don't believe i thanked you for those CDs. i was expecting guys blowing into long bamboo tubes and then really became worried when i saw the dolled-up young girl on the one cover, but she's actually very good. the jury's still out on those "mutton choppers(?)" though ;-)
cheers,
vuk.
p.s. is that fastening system of the mid drvier on the MDF mock-up something you plan to stick with? i've been told that driver screws should not go into any sort of metal.
thanks for all this! looks like something i could possibly attempt. i still wish, however, you'd do something with a tannoy dual-concentric driver. just think, you would have been finished after constructing the first box.
bwt--i don't believe i thanked you for those CDs. i was expecting guys blowing into long bamboo tubes and then really became worried when i saw the dolled-up young girl on the one cover, but she's actually very good. the jury's still out on those "mutton choppers(?)" though ;-)
cheers,
vuk.
p.s. is that fastening system of the mid drvier on the MDF mock-up something you plan to stick with? i've been told that driver screws should not go into any sort of metal.
James
Lord of the Erg\o/s
"Secondly to James for the concise and understandable reply. Now I nearly understand it too ... did you get my PM finally ?? (router book)"
No problems, Mike (the jetsetting one). If I can't persuade you lot, then at least I can try blind you with science. I got your PM a while ago, not sure if I responded or if your Inbox was full. I have a couple of router books, but I find that nothing beats practice. The router is a wonderful tool when it all goes to plan, but a slip cannot be easily hidden in the finished work.
"I don't like being distracted by the movement of speaker drivers, and I've got a 1-year-old son."
I can understand your concern, Mike (the Canuck). The good thing about using a large sealed driver such as the Vifa 26WR is that cone movement will be visible only if you are playing extremely loudly or very deep notes. For the same note and amplitude, the big Vifa (with around 340 sq cm of swept area) will excurse less than half the distance a typical 7 inch driver will with 150 sq cm of swept area, and less than a third the distance a typical 5.5-inch driver will with 100 sq cm. You'll also find that bass generated by air gently but firmly moved will sound more real than the same note from violently agitated air. A bit like stirring paint with a paddle vs thin stick. BTW, a simple pi-r-squared calculation will not yield effective area (Sd) numbers. These are normally specified by the manufacturer, taking into account surround thickness, cone profile and dust cap arrangements.
As for grills, there is no problem putting a grill on the woofer, but I'd be cautious about a grill on the mid-baffle. The introduction of additional edges in a grill frame WILL change the response, and the cloth used itself will modify the tonal balance as well. Having raised two children with my hi-fi intact, I think training them from young not to touch certain things is a far safer bet.
James
No problems, Mike (the jetsetting one). If I can't persuade you lot, then at least I can try blind you with science.
I got your PM a while ago, not sure if I responded or if your Inbox was full. I have a couple of router books, but I find that nothing beats practice. The router is a wonderful tool when it all goes to plan, but a slip cannot be easily hidden in the finished work."I don't like being distracted by the movement of speaker drivers, and I've got a 1-year-old son."
I can understand your concern, Mike (the Canuck). The good thing about using a large sealed driver such as the Vifa 26WR is that cone movement will be visible only if you are playing extremely loudly or very deep notes. For the same note and amplitude, the big Vifa (with around 340 sq cm of swept area) will excurse less than half the distance a typical 7 inch driver will with 150 sq cm of swept area, and less than a third the distance a typical 5.5-inch driver will with 100 sq cm. You'll also find that bass generated by air gently but firmly moved will sound more real than the same note from violently agitated air. A bit like stirring paint with a paddle vs thin stick. BTW, a simple pi-r-squared calculation will not yield effective area (Sd) numbers. These are normally specified by the manufacturer, taking into account surround thickness, cone profile and dust cap arrangements.
As for grills, there is no problem putting a grill on the woofer, but I'd be cautious about a grill on the mid-baffle. The introduction of additional edges in a grill frame WILL change the response, and the cloth used itself will modify the tonal balance as well. Having raised two children with my hi-fi intact, I think training them from young not to touch certain things is a far safer bet.
James
James
Lord of the Erg\o/s
Vuk,
"i still wish, however, you'd do something with a tannoy dual-concentric driver. just think, you would have been finished after constructing the first box."
There is always the next project to tackle. I seem to recall the problem being difficulty in sourcing new Tannoy DC drivers given that they don't supply to the DIY market. Do you know something I don't? (More than likely )
"the jury's still out on those "mutton choppers(?)" though"
I'm glad you got them. You are referring to the Muttonbirds, who are a classic Kiwi rock band. I feel the Envy of Angels album is one of their better works. What are your preferred musical genres? I might be able to find something more to your liking.
"is that fastening system of the mid drvier on the MDF mock-up something you plan to stick with? i've been told that driver screws should not go into any sort of metal."
The mid baffle is only around 18mm thick, and once the rebate is cut to flush mount the driver frame, there's about 13mm of material left. Short wood screws could work into solid wood (which is what I'll be using) but for MDF and other man-made particulate material, a more secure method is machine screws into nyloc nuts. I'm not sure what the issue is with driver screws going into metal. Can you please explain.
James
"i still wish, however, you'd do something with a tannoy dual-concentric driver. just think, you would have been finished after constructing the first box."
There is always the next project to tackle. I seem to recall the problem being difficulty in sourcing new Tannoy DC drivers given that they don't supply to the DIY market. Do you know something I don't? (More than likely
)"the jury's still out on those "mutton choppers(?)" though"
I'm glad you got them. You are referring to the Muttonbirds, who are a classic Kiwi rock band. I feel the Envy of Angels album is one of their better works. What are your preferred musical genres? I might be able to find something more to your liking.
"is that fastening system of the mid drvier on the MDF mock-up something you plan to stick with? i've been told that driver screws should not go into any sort of metal."
The mid baffle is only around 18mm thick, and once the rebate is cut to flush mount the driver frame, there's about 13mm of material left. Short wood screws could work into solid wood (which is what I'll be using) but for MDF and other man-made particulate material, a more secure method is machine screws into nyloc nuts. I'm not sure what the issue is with driver screws going into metal. Can you please explain.
James
vuk
\o/ choose anarchy
"I seem to recall the problem being difficulty in sourcing new Tannoy DC drivers"
james.
i will see what i can do. i'll also think carefully about a fastener solution. the problem was explained to me by a capable DIYer who has screwed drivers into threaded inserts instead of wood/MDF and discovered it to be a bad move (though one would expect the opposite). the logic may not apply in this configuration, but it's also easier to try a few alternatives without damage. we know we need
a set of plain holes to begin with, what goes through them is open to creativity.
btw--you're a lucky bastard to have all those tools (not to mention the nice barbie).
vuk.
james.
i will see what i can do. i'll also think carefully about a fastener solution. the problem was explained to me by a capable DIYer who has screwed drivers into threaded inserts instead of wood/MDF and discovered it to be a bad move (though one would expect the opposite). the logic may not apply in this configuration, but it's also easier to try a few alternatives without damage. we know we need
a set of plain holes to begin with, what goes through them is open to creativity.
btw--you're a lucky bastard to have all those tools (not to mention the nice barbie).
vuk.
James
Lord of the Erg\o/s
Vuk,
"the problem was explained to me by a capable DIYer who has screwed drivers into threaded inserts instead of wood/MDF and discovered it to be a bad move ..."
I think that bad move is generally associated with T-Nuts, which have a tendency to fall out with repeated reomval and reinstallation. I still use T-Nuts with my other designs, but take extra precaution in gluing them into place before fastening the drivers. I've yet to have one fall out.
"you're a lucky bastard to have all those tools (not to mention the nice barbie)."
Surely you jest. Let me think about this for a bit. Power tools, wood and dusty assault on my nose vs camera, half-naked women and, um, visual delight on the eyes? Yes, you jest. Bastard!
James
"the problem was explained to me by a capable DIYer who has screwed drivers into threaded inserts instead of wood/MDF and discovered it to be a bad move ..."
I think that bad move is generally associated with T-Nuts, which have a tendency to fall out with repeated reomval and reinstallation. I still use T-Nuts with my other designs, but take extra precaution in gluing them into place before fastening the drivers. I've yet to have one fall out.
"you're a lucky bastard to have all those tools (not to mention the nice barbie)."
Surely you jest. Let me think about this for a bit. Power tools, wood and dusty assault on my nose vs camera, half-naked women and, um, visual delight on the eyes? Yes, you jest. Bastard!
James
Mike Hanson
Trying to understand...
Yes, I was somewhat concerned about the sonic effects of grill. As to training my youngster, I don't have a problem with that. However, his friends (when they arrive) might not be so well conditioned.
-=> Mike Hanson <=-
James
Lord of the Erg\o/s
The actual mid baffles are cut from (jointed) 19mm thick Sapele timber for stiffness and aesthetics. Since the drivers were measured and the XO is modelled from a specific orientation on the baffles, these were replicated from the mock-up, including the 12-degree lean which is supported by four bits of Sapele offcuts carefully shaped to provide a good balance of strength and minimal clutter. These are biscuit jointed to the mid baffle.
The only dimensional difference from the original mockup baffle is a roundover applied to the edges to soften the effects of diffraction. It is also for this reason that the driver array is offset to create a different distance to each edge. Here they are finished in the first coat of Danish Oil and basking in the long rays of our summer sun for their photo shoot.
The XO bits have arrived from USA and awaiting customs clearance and payment of GST. I should have them tomorrow and be able to cobble together the first iteration of the XO for an initial listen after the weekend.
James
The only dimensional difference from the original mockup baffle is a roundover applied to the edges to soften the effects of diffraction. It is also for this reason that the driver array is offset to create a different distance to each edge. Here they are finished in the first coat of Danish Oil and basking in the long rays of our summer sun for their photo shoot.
The XO bits have arrived from USA and awaiting customs clearance and payment of GST. I should have them tomorrow and be able to cobble together the first iteration of the XO for an initial listen after the weekend.
James
James
Lord of the Erg\o/s
Ladies and Gents,
I'm proud to annouce today that the PFM-Special have been born. Their XOs have been assembled, wired-up and they now have voice. First impression was one of rawness, but a wonderful sense of presence. There is musical energy that is reminiscent of the E-IVs that escapes my version of the E-IIIs to a small extent. The midband is absolutely spot on with the right balance of body, weight and texture. If there is a flaw, the treble seems slightly exaggerated, but I'm certain it's the character of the (cheap) Vifa tweeter. Time will tell, and if running in does not smooth out its character, then a simple change of a series resistor will dampen its enthusiasm to any degree needed.
Well, I'm truly buggered now, having spent the whole day and half the night planning the XO layout, drilling holes and 'stuffing-the-board' with carefully trimmed components, I've been able to take only a few quick (flash assisted) pics. I'll try natural light and better close-ups tomorrow.
Here's the front view ...
Followed by the rear view. Note the mid abd tweet wires disappearing into the XO cavity via holes drilled in the lid ...
This is a rear-quarter view showing where the loudspeaker cable is plugged into the cabinet. There is no provision for tri-amping or silly crap like that ...
Finally, a side view shot showing that there are indeed a pair of them. Shame about the scratch in the back. Will need a fresh lick of Danish Oil to lose it ...
James
I'm proud to annouce today that the PFM-Special have been born. Their XOs have been assembled, wired-up and they now have voice. First impression was one of rawness, but a wonderful sense of presence. There is musical energy that is reminiscent of the E-IVs that escapes my version of the E-IIIs to a small extent. The midband is absolutely spot on with the right balance of body, weight and texture. If there is a flaw, the treble seems slightly exaggerated, but I'm certain it's the character of the (cheap) Vifa tweeter. Time will tell, and if running in does not smooth out its character, then a simple change of a series resistor will dampen its enthusiasm to any degree needed.
Well, I'm truly buggered now, having spent the whole day and half the night planning the XO layout, drilling holes and 'stuffing-the-board' with carefully trimmed components, I've been able to take only a few quick (flash assisted) pics. I'll try natural light and better close-ups tomorrow.
Here's the front view ...
Followed by the rear view. Note the mid abd tweet wires disappearing into the XO cavity via holes drilled in the lid ...
This is a rear-quarter view showing where the loudspeaker cable is plugged into the cabinet. There is no provision for tri-amping or silly crap like that ...
Finally, a side view shot showing that there are indeed a pair of them. Shame about the scratch in the back. Will need a fresh lick of Danish Oil to lose it ...
James
