This is only a suggestion. If you make a non-factory mod to the baffle on your PMC's then they will be much harder to move on the resale market. Seeing you are unhappy with the PMC's why not look to sell them and trade up?
I am not unhappy as such - the supplied tweeter is quite good. However a ribbon might be much better given what I have heard recently. I wouldnt modify the front baffle - so I could just swap the old tweeter back in. I dont really think there is anything to trade up to - the pmc bass and midrange are peerless.
Had a friend convert the soft domes in his Dunlavy's. He found some that were a direct fit but required lots of playing with caps and resistors to pad them in. Fried one or two in the process. Even replaced the ribbon elements with aluminum foil.
Nick, forget it -- unless pmc themselves help you out with indispensable info on their speaker "voicing", the crossover schematics and the characteristics of the tweet you're now using.
In order to replace the tweet with a ribbon you need to mate it seamlessly with the other drivers.
This is difficult to do in yr present application anyway as ribbons are best cut higher than their cone, dome, etc counterparts.
You don;t seem to have been designing & building speakers as a hobby or otherwise. Ergo, let things be as they now stand UNLESS you wish to take on a new hobby and use your present speakers for experimenting. IMO you'll need lots of help in the beginning -- and do some reading of your own.
The "best" ribbon driver doesn't exist. "Best" is matter of applications. Some ribbons look better on paper than others; Alian ribbons are amongst the latter
The speaker is active so I can do it all in the electronic crossovers. I have room measurement equipment and software and a couple of guys on hand that design there own speakers and can help me out with the upgrade. I beleive info on the existing tweeter is in the public domain as well according to my contacts. I would crossover at 4khz.
What do you think? Any recommendations for reading?
Sounds risky to me...you are messing with a very high quality and well respected speaker which may be worthless after all your modifications....
Since you are a beginner at this, my suggestion would be to get a speaker kit from someone like Wilmslow audio...I remember they used to offer ATC 100 kits...not sure if they do PMC clones...
Alternatively, try canvassing PMC to offer an upgrade path to their Vifa tweeter.
I would mount the unit via an adapter plate to the existing screw holes so it would be completely reversible. I would keep the original tweeter. Apparently the PMC uses a modified audax tweeter not vifa as I originally stated in the active speakers - apparently the bbc loves it.
Measure the existing audax. 4kHz isn't a bad xover point; I would choose the cheapest (i.e. Chinese) true ribbon that has the right nominal sensitivity (i.e. ~equivalent to the audax -- or higher).
Can you find out the hi pass particulars and if there's any "taming" (notches, paddings and the like) taking place?
Fo a much used and tried model, there's the Raven (1 or 2, both expensive).
The problem you may have is the ribbon not matching sonically (the perception of "speed" is often the problem) with the next drive unit. Phase anomalies can raise their ugly head... that's why I recommend cheap first.
Also beware of high wattage; ~30 is a safe max & you're best starting out with a 24db LR cut.
The PMC looks very well thought out as is, you see. What are the other drivers, BTW? Volts?
Since that PMC is all active, perhaps the DEQX would help with the conversion, among other things.
Volt radial bass driver and PMCs own midrange.
Yes I might use the deq to help out as well.
I agree with Gregm, matching the tweeter to the other drivers is very important ... I am not sure what the effect is called but "speed" is a very good word for it...in essence the match affects how instruments with some HF harmonics sound to the ear. An instrument will have a tangible sounding timbre when this is well matched...almost real. If poorly matched then the instrument feels less tangible or real....although this depends on the listeners experience with the timbre of real instruments.
Yes I think they need to match - I was looking at one of the hivi isoplanar ribbons perhaps as they are more like conventional tweeters in shape and dispersion.
Rather than replace rhe Vifa tweeter you might be better of supplementing it with a ribbon used as a semi-super tweeter.I have found this works very well,especially with the 19mm Vifa tweeters.You can just sit the ribbon on top of the speaker and use a 0.5 mF cap to protect it and roll it off below 12000hz[approximately if it is 8 ohm].I would be hesitant to use anything of higher value than 0.5 mF .There is some risk of damage with first order crossover below this point,although I have used 1 mF on my Fountek JP2 without problems.
Here is a site you may want to look at:
He does a lot of driver testing and is pretty well respected in terms of his knowledge of drivers and DIY designs. Be prepared though, he's not of the "audiophile" camp and pretty much wants to attibute what he hears to what he measures. That can irritate some folks. Still, knowledge is valuable and he does present some interesting data.
I'd be careful with tweeter swaps. There are a few things working in your favor. I don't know the PMC's very well, but if they are truly active to all drivers with no passive components you might stand a chance of this working out. Not sure how much tailoring is possible. Also, your highish x-over point is working in your favor as ribbons get ever more unhappy the lower you cross them.
The big hurdle will be making this mod look halfway decent. You are going to have to move the tweeter center up because you can't center them in the current hole or you'd need to cut into the midrange driver. Moving them up means some trickier woodworking will be needed to make good round holes (or rectangular) in the new locations.
Also, since you are now increasing the center-to-center spacing you will change some of the interaction with the midrange. This may or may not mess with the resulting sound. (That's the reason they cut into the midrange flange in the first place when they designed these things. The higher the x-over point the closer together the drivers need to be for good integration.)
Go with a raven r3 and shit can the rest and start over.This would yield a better sounding loudspeaker than adding a ribbon to a loudspeaker designed for a diferant transducer. Ribbons sound wonderful but system needs to be design as a whole. Not just a add on.So maybe sell the PMC and DIY your own system based a r3. Would work very well with a 10-12in hieff woofer as a 2 way.Founteks neo pro 5i is a great ribbon almost as good as r3 but can run into the midrange and is 102db 1 watt. It also costs less.If you search about on tube amps or my adds. I have a 5i based system pictured maybe it will spark you into DIY.I have used most of the ribbons you mentioned and many others raven and 5i are the best I have heard.