PFM Special - a simpler and more affordable DIY loudspeaker design

[AshleyD]

James,

Hmmm, I'm a few square meters short in the present room... look forward to seeing some comparative photos, but don't do your back in.

Ashley

 

[James]

Not to worry, Ashley. I won't be moving the E-VIIIs. Picking an E-IV will be easy, but that will have to wait until next weekend.

James

 

[chiily]

Well done Garf, excellent job, you'll enjoy them for years. My speaker search finished when I got my Ergo's up and running, it will only start again if I get a much bigger room for the music system, Jame's would then be my first port of call.
Enjoy them,
Ashley

Thanks. I am pretty proud. I even got the briwax out and gave them a rub down on Friday.

I've not had a huge amount of time (about 20 mins so far this weekend) to sit down and listen. I've been enjoying the thrills of flat-pack for two days. I've two bedrooms to fit out and my other half is great for, 'You know Garf an extra shelf in that wardrobe would be useful.', or 'Would it be possible to fit it right in to the corner/the other way round/on the other side of the room/etc.'

My 20 minutes was sat listening to "Township Jazz'n'Jive'. Strange collection of Township music. Some of it really raw in the recording. I'm pretty fond of it. Anyhow the Specials did a marvelous job. There some great acoustic double bass which was little trouble for those 10" bass units. The bass is beginning to come on song.

I'm still foot tapping.

Ah, well. Tomorrow is mine.

PS Found a link http://www.afromix.org/html/musique/artistes/township-jazz-n-jive/township-jazz-n-jive.en.html

 

[James]

I've been enjoying the thrills of flat-pack for two days. I've two bedrooms to fit out and my other half is great for, 'You know Garf an extra shelf in that wardrobe would be useful.', or 'Would it be possible to fit it right in to the corner/the other way round/on the other side of the room/etc.'

Flat-pack ain't too bad. If a man put his skills/tools/resources to good use to maintain harmony at home, it must be a good thing. For my sins of building a truck-load of loudspeakers and collecting a garageful of tools, I built a 50 sqm deck for the family. Took me all the spare time I had between Christmas 2006 and Easter 2007.

It's safe to say I've got the all clear for my next loudspeaker project.

James

 

[RustyB]

Well done James. I'm looking forward to enjoying a barbie on that magnificent structure next time I'm down.

Perhaps some outdoor speakers could be your next project???

 

[James]

Rusty,

I had been meaning to ask when you'd be down next. I don't think you've heard the E-VIIIs in anger, have you? I recall you really liking what the E-IVs did. If so, the E-VIIIs should be a treat.

James

 

[RustyB]

If the VIII's are the wide boys, then yes I have, at an early period in their gestation.

 

[James]

They're the wide ones, alright. But for some inexplicable reason they sound completely different with their made-up XO.

James

 

[rontoolsie]

The first thing I noticed in the picture was not the deck, but the G17 antenna on the roof.

 

[James]

Well spotted, Ron. Thanks to Marc Newmann, FM radio plays all day via a little NAT02 in our second system.

James

 

[James]

Garf,

I hope your absence on PFM means you're way too busy playing music. Is there a tweak you'd like to effect on your 'Specials that I can help with?

James

 

[chiily]

James,

I'm certainly enjoying these Specials. I still can't believe how foot tapping they are (spot on timing) and how much emotion they can portray even at very low volume levels. Don't you just love that goosebump feeling...

Time to sit in front of them is pretty limited at the moment, work is hectic and I can't quite squeeze a day 'working from home'.

I've just finished spiking 'em up this weekend. Drilling holes for the spike inserts in the undersides was not my idea of fun. They are now perched a top two slabs of granite, better known as Tesco's worktop protectors. Whether it is the spikes or just the running in of the drivers, but the Specials have gained a certain clarity in the lower mid. I had noticed a slight muffling, a missing of sound previously. Where did you get the idea for this little Seas mid? Lovely driver and getting some pretty good praise for the price. So spikes are a must for this speaker.

The spikes have had no effect on the treble quality, which remains effortless, lots of texture. Vinyl gets treble so right, and all from a spherical diamond too (Denon 103R). However, I'm looking to tweak that tweeter resistor in due course, 'cos I can! I can't remember what I set it at during the build.

Foolishly I thought that the concrete floor would have been level, but the two granite slabs are not sitting flat. They rock side to side, not good. The original idea was based on your experience with the slabs earlier in this thread. I'm going to remove the granite and use my original spike shoes directly to the floor.

I did have a happy hour yesterday adding a more stuffing to the bass bins. I was finding the bass a touch boomy and still a little thumpy in the lower reaches, but I'm not use to hearing bass this low and with a degree of clarity, I did use Epos 14s before. (anyone want to buy my old Epos 14s?)

Sadly I've only had a short time to listen to gauge the effect of the changes, one half an album (LP). I am beginning to suspect that it is my LP12/Akito (not the best arm in the world) that are contributing factors. My LP12 still is head and shoulders above my AA5.

Couple of technical points for uneducated me:

Checking for leaks - I was very careful about sealing the inner box. The overlapping joints between the inner and outer boxes I'm sure helped. I'm quite certain that I have no problems there. But pushing the speaker cone in, now I don't know what I'm expected to feel, could you explain a little more please.

Dry Bass - I would like to try a dryer bass sound, just to see, preferably through resistor changes.

Cheers.

 

[James]

Garf,

However, I'm looking to tweak that tweeter resistor in due course, 'cos I can! I can't remember what I set it at during the build.

The series resistor works in tandem with the resistance (together with the resonance trap) in parallel. Be wary of changing this value too greatly. +/- 25% should be a sensible limit.

I did have a happy hour yesterday adding a more stuffing to the bass bins. I was finding the bass a touch boomy and still a little thumpy in the lower reaches ... Sadly I've only had a short time to listen to gauge the effect of the changes, one half an album (LP).

If you are finding the bottom end still a bit too thumpy for your liking, that would indicate to me you need a lower system Q. The easiest way to achieve this is to increase electrical damping by replacing the woofer inductor with one of a lower DCR (same inductance) to give better amplifier control. Madisound makes a steel laminate inductor with half the DCR of the iron core you are using. Finding space for it might pose a little challenge, but I'm sure you'll work something out. I'm certain it will produce a dryer bass.

Checking for leaks - I was very careful about sealing the inner box. The overlapping joints between the inner and outer boxes I'm sure helped. I'm quite certain that I have no problems there. But pushing the speaker cone in, now I don't know what I'm expected to feel, could you explain a little more please.

Sure. Push on the woofer cone with about as much force as you would to close, say, a drawer. Hold that force constant and see if the woofer sinks in over a short time. If it does, and it returns to the normal resting position slowly, that indicates a leak. If it sinks very slowly and returns to rest in more than 5 seconds, the leak is insignificant. Anything less might contribute to incorrect bass loading. If you have a perfect seal, the woofer will not sink in under constant force, but will have the effect of a linear air spring, which is what you'll feel. I hope I have explained it reasonably clearly.

James

P/S: The MCA15RCY is a mid-only version of the CA15RLY, which I had used to stunning effect on the E-IIIs that both Mr Tibbs and I adore.

 

[James]

Ooops, the steel laminate inductor has 1/3 the DCR. It's rather more bulky than the iron core, and so should be considered carefully if additional stuffing hasn't helped.

James

 

[chiily]

James,

Cone pushing - Well, I push 'em in and they spring back out, <0.5s. I do have to push 'em both quite hard (all relative before I hear you scream!). Even if I hold them in for say 5 secs then the spring back out <0.5s. I believe I could push 'em to their back stops with a far amount of force mind you, but I haven't.

One thing I did notice was that the neoprene sealing tape was quite flat around the bass units.

The stuffing appears to have done the trick, in fact I may have stuffed 'em a bit too much. One change from your original design was that I stuck carpet underlay to the side and back walls behind the bass unit and in the little pocket above it.

As a consequence of stuffing last night I was just running through a couple of Hendrix albums and was amazed to hear that a previously heard bass 'slide' did in fact have about 6 bass notes in it. I just love finding things like that.

It appears that I have just about cured the thump, the touch of boom is my room (positively convinced now). However I am tempted by those Steel Laminate inductors, only $17.55 each. I could squeeze those in pretty easily.

For the resistor R3051 I bought these resistor values: 5, 6, 3.3, 4.7, 5.6 and 3.5 ohm. I have the 4.7 ohms installed at the moment.

 

[James]

Garf,

Cone pushing - Well, I push 'em in and they spring back out, <0.5s. I do have to push 'em both quite hard (all relative before I hear you scream!). Even if I hold them in for say 5 secs then the spring back out <0.5s. I believe I could push 'em to their back stops with a far amount of force mind you, but I haven't.

OK, it either sounds like you have a very good seal or a crappy one. I'm inclined to believe the former. If they didn't sink in slowly with a constant force/push over several tens of seconds, but spring back immediately when you release the force, then all is good. The key here is to push the cone in (gently) and see if the enclosed air can find a way out of the enclosure. With a good seal, you should feel a far stiffer resistance than the drivers themselves normally offer. No need to find back-stops though.

One thing I did notice was that the neoprene sealing tape was quite flat around the bass units.

Leaks, if you have them, are mostly around panel joints and wiring holes.

The stuffing appears to have done the trick, in fact I may have stuffed 'em a bit too much. One change from your original design was that I stuck carpet underlay to the side and back walls behind the bass unit and in the little pocket above it.

It's OK to stuff the cabinet completely. Just make sure the stuffing is not overly compressed. Otherwise, it has the opposite effect. Sounds like you have achieved a better result.

As a consequence of stuffing last night I was just running through a couple of Hendrix albums and was amazed to hear that a previously heard bass 'slide' did in fact have about 6 bass notes in it. I just love finding things like that.

I love hearing about things like that too.

It appears that I have just about cured the thump, the touch of boom is my room (positively convinced now). However I am tempted by those Steel Laminate inductors, only $17.55 each. I could squeeze those in pretty easily.

If the stuffing has addressed your concerns, I'd suggest you leave the inductor change out for now. The change to the electrical damping is quite dramatic and it might swing too far to the lean and light side. But if you're itching to fiddle, now that the build is finished, I guess it couldn't hurt to experiment.

For the resistor R3051 I bought these resistor values: 5, 6, 3.3, 4.7, 5.6 and 3.5 ohm. I have the 4.7 ohms installed at the moment.

Speaking of experimentation, the original design called for a 4.0 ohm R3051. If you aren't finding the treble overly emphasised, you could try lifting the output a little. It might help balance the bottom-end too.

The other thing to check for is positioning of the loudspeakers. If they are optimally positioned, they should pressurise the room evenly. By this, I mean there shouldn't be big variations of bass levels at different locations. If you're getting heavy bass reinforcement in the corners and cancellation in the middle of the room, then you have some scope for further experimentation before you decide if the 'Specials need further tweaking.

James

 

[MarkS]

Leaks, if you have them, are mostly around panel joints and wiring holes.

A pinhole is worthwhile in a sealed cabinet to allow it to maintain equal pressure with its surroundings.

 

[James]

Agreed. Could be rather disconcerting to see the woofer popping out with an approaching storm front otherwise.

James

 

[chiily]

I take it all back about the thumpy bass.

I replaced R3051 in the tweeter network this evening. Swapped out a 4.7Ohm and dropped in a 4Ohm. The difference is startling.

I now have super, groovy bass. The whole sound stage has opened forwards and upwards. Really quite spectacular. I've yet to hear the Specials slur a bass note.

I just don't have the words to describe the change.

James, how sensitive are these speakers? I never get my 32.5 volume dial past 9 o'clock and there's plenty of sound pressure.

 

[James]

I just don't have the words to describe the change.

I thought you did quite well, really.

James, how sensitive are these speakers? I never get my 32.5 volume dial past 9 o'clock and there's plenty of sound pressure.

The M26WR is good for 89dB/2.83V @ 1m. Should be at least twice the sensitivity (+3dB) compared to ES14s. If you think that is loud, you should hear what a quad of M26WRs do.

James