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Old 2nd December 2012, 11:43 AM   #11
system7 is offline system7  United Kingdom
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Quote:
Originally Posted by kgrlee View Post
Plastic dome treble units are not created equal. I worked on that unit at Wharfedale.
Aw, come off it! Secret sauce added, I suppose....No, I'm not having it. Tweeters are tweeters.

The Monacor DT19-SU is a current polydome that people seem to like.

Click the image to open in full size.

Rather similar to the KEF T27 IMO.
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Old 4th December 2012, 05:22 AM   #12
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Quote:
Originally Posted by system7 View Post
Aw, come off it! Secret sauce added, I suppose....No, I'm not having it. Tweeters are tweeters.
System, if you believe that, you'll believe 'xovers are xovers' and the classic filter stuff can be used for all treble units.
Quote:
Rather similar to the KEF T27 IMO.
I worked for KEF too. There were several different versions of T27, some of which look the same to anyone not versed in the art. I'm sure your views will interest all current and former drive unit designers and manufacturers ... and the system designers too.

BTW, I'm not dissing the Monacor units. They may well be excellent. But there is a lot of important stuff that never appears in a spec sheet. Not that its of interest to you cos 'Tweeters are tweeters'.

Last edited by kgrlee; 4th December 2012 at 05:25 AM.
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Old 4th December 2012, 05:42 AM   #13
system7 is offline system7  United Kingdom
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kgrlee, you doubtless know a thing or two about tweeters, but to imply your own design was without peer is just a tease. Tell us about it so DIYers can find some good substitute rather than just try to look clever. Seems to me you just mix up magnets, coils and domes and ferrofluid and materials in different proportions and sizes really.

Robin Marshall doesn't find it hard, and like most people who really know what they are talking about, can explain it simply:
Quote:
Atkinson: I said earlier that you make your own drive-units, including the 26mm dome for the ES-14 and the 32mm for the old '20. I've always been told that tweeter manufacture is fraught with problems because of the very close tolerances required on something so small. You went into that . . .

Marshall: Foolishly.

Atkinson: Did it take you a long time to get a good tweeter into production?

Marshall: No, not really, because it's just an engineering problem. There's nothing difficult really about it. The only difficulty in making a tweeter is that all the masses are so low you've got to be very careful with adhesive bonding to make sure you're not changing the masses of things and introducing compliances. It's only an engineering problem. There's nothing difficult in licking that, providing you have the experience and the resources to do it. I think most people are scared off unnecessarily. Most manufacturers say "Well, we can make a bass driver, but a tweeter, hmm, no." They've never tried it.
I find his notion that cone tweeters might work better interesting too:
Quote:
Atkinson: You're probably aware that metal-dome tweeters are controversial here in the USA, with many designers feeling that their advantages are only obtained at the expense of problems elsewhere. What are the specific reasons you chose to use them?

Marshall: Let me first of all say that I'm beginning increasingly to think that dome tweeters might not be the best way of doing things. I'm beginning to think more and more that, should we not be looking at cone rather than dome tweeters? But having decided that you're going to make a dome tweeter, you want at least to keep the diaphragm bending modes out of the audio passband. And there is no other material, no usable material, other than a metal, where that is possible. You could probably make a tweeter diaphragm out of ceramic, which would be, perhaps, quite wonderful, but the prospect of making it is daunting.
So what is good about that little plastic Wharfedale cheapie? I would add that I used to have this speaker, and liked it.
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Old 4th December 2012, 07:09 AM   #14
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Quote:
Originally Posted by system7 View Post
kgrlee, you doubtless know a thing or two about tweeters, but to imply your own design was without peer is just a tease.
System, I didn't say it was without peer. I said it was one of my favourites. You may be aware that Celestion & Wharfedale made some of the best metal dome treble units too. Celestion was the first. The same people were involved with both companies.

Wharfedale also made a good ceramic dome treble unit and yes, it has the advantages that Robin Marshal ascribes to it including the daunting manufacture

Quote:
Tell us about it so DIYers can find some good substitute rather than just try to look clever. Seems to me you just mix up magnets, coils and domes and ferrofluid and materials in different proportions and sizes really.
I wish it was that simple. I've been a beach bum for more than a decade so have no flag to wave for any company but still have friends in the major UK manufacturers.

All of them would find your beliefs amusing.

Quote:
Robin Marshall doesn't find it hard, and like most people who really know what they are talking about, can explain it simply:
I'm not sure you get anything useful about how to choose a treble unit from his interview.

Quote:
So what is good about that little plastic Wharfedale cheapie? I would add that I used to have this speaker, and liked it.
The secret sauce was the diaphragm material. As it is the secret sauce in our bass units.[*] Both materials are now Unobtainium Though we were the biggest European manufacturer at the time, it was 1/2 days production for ICI to produce several years supply for us.

I could bore you with the Scanned Laser Doppler Interferometry and FEA work that led to the specification of the material but then you would accuse me of showing off.

Let me tell instead, what I'd do if I was starting manufacture again in a small way. I'd look at what was available from the better Far East manufacturers. I'd want to visit their factories and talk QC with them. Certain factories in Guangzhou make some of the most consistent units in the world since the demise of the Wharfedale Leeds factory. I know, cos I helped set some up more than a decade ago.

After choosing suitable examples for test, I'd measure them for response, distortion & directivity. The leading contenders would be tried with matched xovers in the system I was working on. Discuss small changes with the factory to ensure anything requested tied in with their manufacture & quality.

I'm sorry if this isn't much help to a DIYer but I wouldn't have spoken up at all except your statements that
  • 'Tweeters are tweeters' and
  • the implication that standard filter circuits for xovers are OK
are both wrong and likely to result in poor speaker systems.

Try Design of Optimized Loudspeaker Crossover Networks Using a Personal Computer for some of the issues.

I spent most of my previous life trying to understand speakers but I'm not sure I'm any better suited to pick a drive unit from info on the internet.

Of course I have my own prejudices which would influence what I'd choose to look at first. Practically any treble unit of the right sensitivity that fits in the hole could be made to 'work' PROVIDED you had some means of providing the information to a programme like Schuck's. But that isn't a guarantee that it would sound good.

[*] There are other important ingredients like the way they are assembled but none of it is relevant today as the units are Unobtainium.
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Old 4th December 2012, 08:03 AM   #15
sreten is offline sreten  United Kingdom
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Hi,

The simple fact is mixing and not matching replacement bass units
and tweeters with the original croosover is just hoping that it works.

You don't know if it will work well and what problems may be lurking.

Replacing tweeters generally though isn't too problematic. 3rd order
electrical at 5KHz will suit smaller cheaper types very well like the
Dayton ND20 or HiVi T20, no real point going bigger / "better".
(Or the classic Audax used in the earlier Diamond.)

rgds, sreten.

Is more likely the x/o is worse than better, if you change
component values based on false premises, I'd sim it using
TinaTi to see what you done to the 3rd order roll-off.
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Last edited by sreten; 4th December 2012 at 08:18 AM.
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Old 4th December 2012, 08:21 AM   #16
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Thanks, sreten, I'll download and have a look.

I replaced the tweeter some time before I'd investigated crossover networks very much: it's very early in my learning curve still.
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Old 4th December 2012, 09:18 PM   #17
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Quote:
The Diamond III crossover is 18dB/8ve. There'll be a 0.2mH air cored inductor between the 2 caps & earth.
Quote:
Originally Posted by MikeCobar View Post
Yes, there is a small inductor (I measured at 1.8 mH, but my meter is a cheap one) in the circuit.
The 1.8mH will look like L1 in this pic. The 0.2mH will look like L3.
http://www.deviantpics.com/images/2012/11/30/2.jpg
The Diamond 3 xover is similar to Laser 90B but without the 0.05mH inductor. In its place may be a small resistor.

If the 0.2mH is missing, you need to replace it. If the treble units were blown, the treble capacitors will probably be blown too.

As sreten says, none of this is likely to give the correct response except with the genuine Wharfedale unit.

But it will be better than 6dB/8ve xovers (without the 0.2mH) which are truly evil.
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Old 5th December 2012, 07:09 PM   #18
system7 is offline system7  United Kingdom
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Kgrlee, I've gotta say that it is very enjoyable to talk to you online. Evidently you are one of the last people who believed that Britain was founded as a manufacturing nation, and that Mrs. Thatcher (Gawd bless her in most respects, a politician who had actually had a real job at some stage...) was totally wrong in killing off our factories.

I used to bump into Sir John Harvey-Jones, Chairman of ICI and lover of bright ties, on a regular basis. It was always his belief that REAL WEALTH is created by MANUFACTURING alone. Sound man.

I just "crunched some numbers" on the Wharfedale Laser 90B speaker in the thoroughly modern Visaton Boxsim simulator.

Click the image to open in full size.

Pretty awful filter, TBH, though it might work with a valve amp. That coil at the tweeter input is just not good. I used the plastic dome DT-94-8 ohm which has a phase plate to correct the typical frequency peak around 10kHz of plastic domes. The Monacor DT-19SU behaves predictably for another plastic dome without phase plate. Usually you notch this one electrically instead.

Tweeter ARE tweeters. Filters depend on circumstances. Your plastic Wharfedale jobbie was OK as it goes. I enclose some pictures, worth a thousand words, of one that fell apart.

The last image is a Robin Marshall design AFAIK. Plastic bass, metal tweeter with diffuser. Dig that convex tweeter mounting plate.

There is a bit of a hierarchy in speaker materials. Broadly plastic is well damped and slow and gets away with simple filters, paper optimal, and metal fast and buzzy needing great attention with filters to be well behaved.

I modelled a Visaton W170S paper bass and very efficient DT-94 plastic tweeter here. Quite nice really, but as I said, I have doubts if plastic tweeters are really all that satisfying though they are inoffensive. But they will integrate nicely with a plastic bass.
Attached Images
File Type: jpg Wharfedale_Diamond_3_Drivers.JPG (29.8 KB, 57 views)
File Type: jpg Wharfedale_Diamond_3_Tweeter_Plate.JPG (30.2 KB, 59 views)
File Type: jpg Wharfedale_Diamond_3_Magnet.JPG (32.2 KB, 58 views)
File Type: jpg Mordaunt_Short_MS821C_Front.jpg (91.4 KB, 16 views)
File Type: png Wharfedale_Sim_FR.PNG (20.5 KB, 25 views)
File Type: png Wharfedale_Sim_Network.PNG (11.6 KB, 29 views)
File Type: png Wharfedale_Sim_Phase.PNG (19.3 KB, 23 views)
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Old 5th December 2012, 07:28 PM   #19
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Quote:
Originally Posted by kgrlee View Post
The 1.8mH will look like L1 in this pic. The 0.2mH will look like L3.
http://www.deviantpics.com/images/2012/11/30/2.jpg
The Diamond 3 xover is similar to Laser 90B but without the 0.05mH inductor. In its place may be a small resistor.

If the 0.2mH is missing, you need to replace it. If the treble units were blown, the treble capacitors will probably be blown too.

As sreten says, none of this is likely to give the correct response except with the genuine Wharfedale unit.

But it will be better than 6dB/8ve xovers (without the 0.2mH) which are truly evil.
I replaced all the caps. The change I made was to replace the two in series, giving 1.6uF, with a single 4.7uF cap (bearing in mind that I changed 8Ohm tweeter for a 6Ohm unit). There is a resistor in the circuit, measured at 2.5Ohm, couldn't decipher what was printed on the actual resisitor.
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Old 5th December 2012, 07:35 PM   #20
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Interesting pics and data, Steve. My Diamond look pretty much the same as you've posted- and the dead tweeter also looked much like the pic you've posted, fluid leaking and magnet fallen off. My crossover network is simpler than the Laser schematic although I see Wharfedale also uses the 450uF cap on the woofer.
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