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-   -   Wharfedale crossover question (http://www.diyaudio.com/forums/multi-way/224726-wharfedale-crossover-question.html)

MikeCobar 1st December 2012 08:27 AM

Wharfedale crossover question
 
Apologies if this sounds like a newbie question. I've just changed caps on Wharfedale Diamond III bookshelf speakers after changing blown tweeters some time back to 6Ohm PSB units. On my speakers the high pass consisted of 6uF and a 2.2uF in series, with resultant capacitance of about 1.6uF. This would appear to give a crossover frequency of in excess of 7000Hz with 8Ohm tweeter, yet the label on the back claims 5000Hz. I've seen pictures of different Diamonds and they've had 4.7 and a 3.3uF caps, not sure if in series or parallel.

In any case I put 4.7uF (actual value 4.9) caps in because tables suggested 5.3uF for 6Ohm tweeter with 8Ohm woofer and I had the 4.7s on hand (and I live a long way from any electronics outlet). I also changed the 450uF caps on the "low pass'' which apparently (according, again, to the label) give "5th order" characteristics to the crossover, but I've read it's mainly to protect the woofer. The new caps checked out at around 480uF (my multimeter only goes to 200 so I had some maths to work out with a known sub-200 cap in series).

Anyway the sound seems to be improved, which was the point of the exercise. Have I made any mathematical errors?

system7 1st December 2012 05:03 PM

6uF and 2.2uF in series is just a bit odd. It does of course make an overall 1.5uF or so. Fairly typical cheap and cheerful high first order tweeter crossover. 1.5uF to 2.2uF in series with tweeter is common enough and protects tweeter from low frequencies.

Such low slope that crossover point is almost meaningless and depending on the woofer rolloff.

The series 450uF low pass is designed to protect the woofer from subsonics. It may well have a 1mH series coil too, to boost the bass performance. Well, actually it rolls off the woofer in the midrange, which has the effect of making the bass relatively louder.

I think I used to have this tiny 2 way speaker. Lively performance if a bit ragged. Quite nice.

MikeCobar 1st December 2012 09:13 PM

Thanks Steve, yes, there is a 1.8mH coil, there (at least, that's what I measured it at). I have two other pairs of Wharfedale speakers (510s, which had issues, now sorted) and some 70s Lintons, which I gutted and replaced drivers and crossovers. While I didn't listen to the Lintons (only wanted the cabs to reduced the need for woodworking, not one of my strong points) the Diamonds and 510s have always astounded me in that they sound pretty good to my ears yet appear quite shoddily made in some respects. I bought the Diamonds and 510s new in 1989. They've been through a lot, including salt air and mouse infestation on a remote island. The Linton crossovers looked like they'd been thrown together with WWII bits, in 5 minutes.

I can only surmise that Wharfedale had a good supply of 6 and 2.2uF caps lying around when they put the Diamond IIIs together. They are the blue "Alcap" brand I've seen in other Wharfedales (pics online and the 510s).

I had a great couple of weeks in and around Portsmouth in '77, Queen's Silver Jubilee. It's remarkable that Elizabeth has passed Gold and Diamond and has been queen my entire life (and I'm approaching 60:)).

system7 1st December 2012 09:37 PM

Isn't that funny! I used some Linton cabinets for a complete rebuild too. Very solid! :D

If you're interested, there are some better tweeters around that might fit a small space:

Morel Classic CAT408

Monacor DT-28N

It's not hard to add an attenuator circuit to get levels right with wirewound resistors. I certainly like those little plastic bass units. You can stick rubbery carpet underlay on the sides too for the BBC sound.

Replacement capacitors are easy too:
Alcap 50V Low Loss Electrolytic capacitors for all audio and hi-fi loudspeaker crossover applications

I realise you're not in the UK, but you get the idea? :)

MikeCobar 1st December 2012 10:06 PM

Thanks for the links, Steve. I used some small (much smaller the the Wharfedale purple things) Miller and Kreisel buyout tweeters from the US in the Lintons, with some 6.5" carbon fibre woofers from a company here in Au/NZ called Jaycar. The original Linton 8" woofers had been replaced with cheap Jaycar-branded units, mounted at the rear of the baffle. I mounted the new drivers from the front, with a small ring to fill out the (surprisingly small) hole and rebated slightly so I could retain the Linton grilles.

These speakers were meant to be a reasonably cheap way to fill out the 7.1 set for AV, realising of course that one can buy cheap Chinese stuff even in my local electrical shop or from Ebay, but I wanted something I had made/assembled myself. The carbon woofers I had anyway, 4Ohm and designed more for car use although extremely heavy (despite the carbon fibre:)).

I hadn't thought that Alcap caps were still around (so many great British companies having folded) so will bookmark the site for future cap needs. I have bought some stuff out of UK, as with US postage can be really scary, especially for large drivers, but quite reasonable (at least for small/light goods) out of UK. And, the service so far has always been friendly unlike some of my contact with US sellers.

kgrlee 1st December 2012 11:22 PM

The Diamond III crossover is 18dB/8ve. There'll be a 0.2mH air cored inductor between the 2 caps & earth.

Don't bother trying to get values for classic filter circuits. The better speaker makers stopped doing that in the 70s and designed the xovers to match the units/box response.

Shame about your blown trebles. Are they the ones with a rectangular faceplate with rounded sides?

These are some of my favourite treble units. The diaphragm material is now Unobtainium.

system7 2nd December 2012 12:36 AM

Quote:

Originally Posted by kgrlee (Post 3266283)
These are some of my favourite treble units. The diaphragm material is now Unobtainium.

Actually it's not too hard to find plastic dome tweeters really:
DT 94 - 8 Ohm
DTW 72 - 8 Ohm
Vifa D19TD-05 3/4" Poly Dome Tweeter 264-500

I'm not too sure they are really all that good though. Just bright. :)

MikeCobar 2nd December 2012 01:47 AM

Quote:

Originally Posted by kgrlee (Post 3266283)
The Diamond III crossover is 18dB/8ve. There'll be a 0.2mH air cored inductor between the 2 caps & earth.

Don't bother trying to get values for classic filter circuits. The better speaker makers stopped doing that in the 70s and designed the xovers to match the units/box response.

Shame about your blown trebles. Are they the ones with a rectangular faceplate with rounded sides?

These are some of my favourite treble units. The diaphragm material is now Unobtainium.

Yes, there is a small inductor (I measured at 1.8 mH, but my meter is a cheap one) in the circuit.

I don't know if tweeters can "blow" as comprehensively as these ones (well, one of them at least) did. I pulled the grille off because the tweeter wasn't working- to find ferrofluid leaking in quite disturbing amounts. I opened the cab, to find that the magnet had actually fallen off the faceplate and was attached to the woofer's magnet. The tweeters are "truncated" i.e. a flattened circle, with a dome a little under 25mm.

The PSB units I obtained from US are aluminium-domed and a little "bright". My circuit would have differing requirements now with that 6Ohm tweeter. In retrospect the Dayton 8Ohm truncated plate units would have been a better fit. Anyway the Diamonds do sound better to my ear with a new 4.7Uf cap replacing the series 6 & 2.2UF caps, which were approaching 25 years in age, too.

I'd reckon Cooktown is a more pleasant place to be at the moment than where I am in western NSW. A week of 38-44C temps has left me frazzled, trying to catch up on outdoors chores now the temp's back to 32C- still drenched in sweat.

kgrlee 2nd December 2012 07:07 AM

Quote:

Originally Posted by system7 (Post 3266344)
Actually it's not too hard to find plastic dome tweeters really:

Plastic dome treble units are not created equal. I worked on that unit at Wharfedale.

mjf 2nd December 2012 09:14 AM

hello.
in this thread there is something about wharfedale crossovers......(post12, 16,....)
http://www.diyaudio.com/forums/parts...ml#post3266730


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