Tweeter Quest

Getting there. I reckon it would be better on shellac now overall but still not as good in the bass. I will disable all the dc servos next...

Hmm could I fit it where the mb2 mid is? Some stuff I saw on the forums was detailing the fact that many ribbons dont perform well below a few khz. Perhaps it just means tweeter ribbons?

 

Yes I suspect it means tweeter ribbons. Most start to have a longer decay rate below 2KHz. Look a the cumulative spectral decay of the RAAL 140-15D. The same is true of any driver when it starts to go towards its lower limit though.

No way could you fit the mid ribbon where the PMC mid is

 

Hi,

Regardless if there is the Vifa 1" Softdome or the AUdax 34mm Tweeter in there, much room for improvement exists. The AUdax unit especially is better considered an upper midrange, lower treble driver in a 3-Way unit, with a supertweeter, similar to what Spendor did in the BC-1 (which did not use the Audax I hasten to add). No doubt the PMC mods help, but the dome is just too large and heavy to get a good HF performance, quoted spec's non withstanding.

What the BBC (and I) liked about the Audax was the combination of (for it's time) above average power handling combined with above average sensitivity and a decent "trow" for a tweeter, meking it robust and capable of handling high levels. The BBC felt the need to add a supertweeter though for TV duties, as otherwise tv line frequency breakhrough was hard to spot, suggesting the limits of the actual performance of that tweeter.

When I messed with big active PMC's in the mid 90's we used the Focal TC-120Tdx as replacement for the 1" Vifa, it was at the time IMHO the best readily available tweeter for high performance.

In this day and age I would be very tempted by the RT1L in the kind of application PMC use, it goes down to around 3KHz flat with a textbook 2nd order rolloff below and it should match mostly the radiation pattern of the tweeter it replaces. It should also fit (possibly with minor modifications to the faceplate) the hole in the box. A version of the same driver was found in a number of neat 2-Way speakers BTW....

The actual driver Nick heard at my place is the larger linear ribbon with waveguide, basically the same Ascendo use in their super expensive speakers. This would need a completely new cutout or perhaps mounting on the side of the Box or such. In this case it may be most prudent to re-house the Ribbon and the Midrange from the PMC into a new box and to make covers that close the xisting holes and place the woofer sections side by side, with the new midrange/treble box on the actual woofer section.

But if you do you might was well ditch the midrange from the PMC as well in favour of a large planar and so on, untill you in effect might as well sell the whole setup, buy a digital X-Over, a bunch of really good drivers (eg not ATC, Scan Speak/Vifa/Peerless or Seas) and build up a completely new system from scratch.

Hence my recommendation of the RT1L as "drop in" upgrade and the fact that it only costs around $ 45 per piece from partsexpress means if it does not work out not too much money has been lost....

Ciao T

 

Yes might be a good idea in terms of integration and lack of expense. I dont want to mod the box just yet .

 

Thorsten I have taken my own measurements that show the PMC version of the Audax extends perfectly fine to 20KHz and without beaming much when the phase plate in there.

I would think a tweeter that goes lower than 3KHz would be a good idea too, since the Xover is 3.8KHz even with a 4th order electrical slope it would not mate too well when you don't have full control of the crossover.

I would definitely use the B&G Neo3 for a test ‘cos it will fit easily in the current hole and then if I liked that I would probably get the RAAL and the Hi-Vi and see which I liked more. I'll buy the Neo3's off you at a nice discount if you want to get rid of them hehe

 

Is the raal undamped? Is there any colouration?

The tweeter T was using sounded very clean and precise.

 

Undamped? The RAAL has a critically damped chamber behind it, so it is a closed unit.

I have not heard the RAAL but I have heard a lot about it and those that have heard it worship it. I know the Hi-Vi tweeter is good but to be honest, the RAAL will be in another league. The Hi-Vi is VERY good for the money, the RAAL is supposed to be the best regardless of money.

There are no comercial speakers using it at the moment but it is very popular with top studios around America at the moment according to the designer.

 

Hmm ok - I wonder if it can fit in the hole... still as T says maybe its best to try a cheaper option first.

 

Its probably worth just asking you this question Thorsten, is it alright to drive a ribbon like the RAAL direct from a normal amp like the Bryston? I don't mean direct like removing its transformer, I just mean going right from the amp to the Raal's transformer inputs. Someone once said it wasn't a good idea for some reason... capacitive loading or something. It's the only time I heard it said though. I guess they thought it better to use a passive crossover?

 

Essentially it will be driven by one channel of a modifed bryston 3b-sst

 

Hi,

Hmm, not sure if the phaseplate makes enough of a difference. Anyway, i was not refering to MEASUREMENTS in the first place. According to the BBC their tweeters also measured fine, BUT they made picking lTV-line frequency noise breakthrough difficult to hear DESPITE the high reaching FR, which is why a supertweeter was added to a number of speakers using this driver ONLY for TV use (in FM radio use they where considered adequate without).

It will do not much harm, but with a 4th order electrical slope you should find that problems are minimal, as at 1.9KHz the attenuation from the filter is already 30db and 6db at the crossover frequency (to which the driver adds respectively 10db and 0db attenuation). You will find that in practice the integration will be pretty normal.

In this cas you need the version with the rear chamber and front panel. Also, the new dispersion pattern between the original tweeter and the Neo3 are unlikely to match all that well.

Ciao T

 

Hi,

Depends what the manufacturer says. In practice, usually yes.

BTW, my problem with "true ribbons" vs. Isoplanars is that true ribbons have in essence no suspension, no limitation to movement and minimal restore forces (and of course a metallic tone which is fine with metal cone drivers, less so with others).

While these features may superficially appear to be beneficial, they are in reality not, especially if a reasonable amount of level is expected, which causes ribbons to "flutter" (visibly - basically dynamic offset) and can in extreme case end up with deformed ribbons and before that with nasty distortion when the ribbon hits the mechanical structure.

So, Ribbons are very nice for "civilised" music (as Les Wong so charmingly calls it), but are a less ideal choice when things tend towards musical hooliganism... :MILD:

Ciao T

 

The brystons have zero gain at dc and high damping factors which must be a plus, along with the active drive.

 

Hi,

Ribbons, Isoplanars and the like have so "poor" (or light) coupling between radiating element and magnet that they operate in essence indepedent of any damping from the Amplifier, hence the relevance of build in mechanical damping and protection against excessive excursion....

Ciao T

 

Interesting!

 

The electrical damping wont make much difference to a ribbon.

I know the larger Raal was measured to do 120dB with a 4th order Xover at 1.8KHz so I bet the smaller one can do that easily with a Xover at 3.8KHz. I don't think things will push it too hard in that setting.

Who needs mechanical suspension when the diaphragm moves freely at the whim of the magnetic field around it? The suspension would only pull against what the signal is actually doing (especilly if the magnetic coupling is poor). Wouldn't it?

If a true ribbon has a metallic sound do the isoplanars have a plasticy sound?

I don't know which will be better but I would bet on the Raal over the Hi-Vi. I have not seen many real high end speakers use isoplanar but many use ribbons there must be a reason, and the Raal pushes the boundaries on that...

Oh plasma tweeters... hehe fun things!

http://www.diyaudio.com/forums/showthread.php?s=&threadid=76377&highlight=

Oh Thorsten this is the AMT I couldn't remember the name of that can go pretty low and might suit your speaker.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=2651

 

Hi,

One would think the answer was self explanatory, given your statemennt...

The way typhical isoplanars are "suspended" they have a fairly wide range where there is no specific suspension stiffness. If the planar attempts to move beyond this range the suspension progressively stiffens (material elasticity etc.) thus limiting the range of movement caused for example by dynamic offset, a phenomenae that both ribbons and planars are subject to.

Yes, they do, of course. This is a pet theory of mine, but it generally seems to suit the observed facts....

If "coherence" is desired from a multiway system with a crossover in the critical range (250Hz - 8KHz appx.) the best course of action is to use radiation surfaces made from identical materials or materials with identical or highly similar material sound.

So, paper cone tweeters with paper cone woofers (note that many Altec VOT users swear that phenolic diaphragms sound better and more integrated than metal ones!), plastic Domes/Planars with plastic cone woofers and metal ribbons or domes with metal cone drivers.

This way the same "material tone" applies to all parts of the sound spectrum.

I find that speakers having different cone/diaphragm/ribbon et al materials with a crossover in the critical range give rise to what some have described to "woofer/tweeter" sound.

We humans actually get quite easily used to mild material sound colorations (a bit of "paper cone" sound, or plastic "quack" or such) if they are consistent across the whole critical range, have different sonic signatures for lower midrange and upper midrange and you are asking for trouble.

Actually, you did not look well. In germany (where we are usually a decade or so ahead of "the market" elsewhere) AMT's and Isoplanars are everywhere in the locally designed "high end" speakers.

I am familiar with this one. The price is one that makes me consider the manger over it most days... ;-) It is pretty good though but also pretty hard to get and being a dipole it is not easily applied.

Ciao T

 

Ahh okay so the suspension is really just a safety measure.

Do you have any measurements for the tweeter you are using? Impulse response, distortion vs. frequency, decay, etc?

I just have this hunch that the Raal will outperform it and usually I follow my hunch's above all else.

The ESS is in the price range of the Manger? :O I didn’t realise!

 

Hi,

No, it also makes sure that overload compresses gently, instead of creating nasty noises.

That depends on many factors and application as well of course what you seek. I would not use it unless I intend to use a Metal Cone woofer.

Ciao T

 

I don't think I really subscribe to the idea that materials sound a certain way. It completely depends upon the design of the driver.

Certain materials have common distortions when used in a similar way, but use the same material in a different way and it will sound completely different. A cone and a ribbon are pretty different so I'm not sure it follows. If it were a dynamic metal cone and a metal dome then maybe... In practice I think the way it performs under measurements shows more about its sound than the material its made of.

Manger is metal, does it sound it?