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Old 7th December 2012, 04:24 AM   #31
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Join Date: Nov 2011
Location: Cooktown, Oz
Quote:
Originally Posted by system7 View Post
Yes, Robin Marshall IS a hero of mine. I love his stuff. Maybe that's because I understand it.
system, perhaps you are actually a guru masquerading as a beach bum. A lot of what you say is so nearly true. (sorry. Couldn't help that)

But does Robin Marshall share your opinion on treble units?
____________

In the face of all this expert knowledge, I'm just going to try and ensure, Mike has the correct value inductor at the proper place in the treble xover.

I won't say anything more unless someone proposes a xover which might cause damage to whatever unit Mike chooses.
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Old 7th December 2012, 05:12 AM   #32
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Quote:
Originally Posted by system7 View Post
Well, Mike, if you listen to my learned friends here, you will abandon all hope of knocking that simple little speaker into shape, obviously far too difficult to try at home....

Tina TI is an op-amp simulator circuit that would interest me if I ever picked up amplifier design again. It does have a good filter modeller in it, but not one that has much relevance to loudspeakers, lacking FRD (Frequency Response and Phase) and ZMA (Impedance) loudspeaker modelling data.

My simple-minded approach relies on well-behaved standard sorts of drivers with published data and frequency response plots. Cabinet solutions are based on simple optimal stuff that works. It is not simple-minded at all, of course. More clear-minded. I leave it to the forum windbags to debate 0.618:1:1.618 or 0.8:1:1.25 cabinet ratios.

To solve a problem, the best approach is to simplify it. That is what I suggest. Treble filters are really not hard. I use Zobels and an input resistor because they just work with most stuff and it's not hard to look up tweeter inductance.

Bass filters vary a little and I assume you're working with the usual 0.6-0.9mH units. Plastic is a slow material which responds to simple filters. A simple coil and capacitor circuit will work passably well with little need for a notch as with the Wharfedale Laser 90B design. With paper bass, it helps to notch the AAL3 Resonance to reduce the annoying bass cone-breakup sound which is around 5kHz for 6" paper units.

Yes, Robin Marshall IS a hero of mine. I love his stuff. Maybe that's because I understand it. And like Lynn Olson, Joachim Gerhard and John Linsley-Hood, he can explain it simply. Good players make any game look easy. So does Troels Gravesen with this SEAS CURV plastic bass design:
SEAS CURV
Thanks for the info, Steve. Actually some of the stuff I find on this site makes my head spin! While I am a technical officer (working in meteorology) my academic leanings are to the humanities, the electronics are a challenge for another part of the brain perhaps, but it has to be in small doses or I faint
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Old 8th December 2012, 06:01 AM   #33
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Join Date: Nov 2011
Location: Cooktown, Oz
Mike, I'm going to conquer my fear of system and try & take you through what I did for speaker design before I joined the industry and had facilities to measure response, bla bla.

After more than half a lifetime doing this for real, I still think its a good procedure.

But if system or anyone else wants to take over, I'll bow out as it's impossible to follow 2 gurus.
__________________

In order of importance.

1) Have you identified the elusive 0.2mH inductor?

2) Have you chosen your replacement treble unit? If not, Jaycar CT2005 looks good value. Will it fit?

3) Can you use a router?

4) Can you borrow a working 'good' speaker of similar size? What is it?

5) Do you have or can beg borrow a microphone with associated preamp?

6) What model & brand

Last edited by kgrlee; 8th December 2012 at 06:08 AM.
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Old 8th December 2012, 07:40 AM   #34
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Quote:
Originally Posted by kgrlee View Post
Mike, I'm going to conquer my fear of system and try & take you through what I did for speaker design before I joined the industry and had facilities to measure response, bla bla.

After more than half a lifetime doing this for real, I still think its a good procedure.

But if system or anyone else wants to take over, I'll bow out as it's impossible to follow 2 gurus.
__________________

In order of importance.

1) Have you identified the elusive 0.2mH inductor?

2) Have you chosen your replacement treble unit? If not, Jaycar CT2005 looks good value. Will it fit?

3) Can you use a router?

4) Can you borrow a working 'good' speaker of similar size? What is it?

5) Do you have or can beg borrow a microphone with associated preamp?

6) What model & brand
Hi kgrlee,
1) Yes, there is only one, I measured at 0.18mH
2) Yes, it was fitted around six months ago. This is it: PSB Speakers G Design 1" Aluminum Tweeter s GT1 GB1 GC1 | eBay

It wasn't a "good fit", but then I hadn't expected any tweeter to go in easily (although the Dayton truncated 8Ohm would have been the closest fit).
3) Yes, with a high degree of inexperience. Never owned or used one until this year.
5) No. I live in the outback although possibly not as remote as you, being 9.5 hrs by road from Sydney.
6) Not applicable.

Cheers,
Mike
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Old 8th December 2012, 09:21 AM   #35
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Location: Cooktown, Oz
Quote:
Originally Posted by MikeCobar View Post
1) Yes, there is only one, I measured at 0.18mH
That's much more like what I'd expect from a DMM measuring inductance of the 0.2mH

Quote:
2) Yes, it was fitted around six months ago. This is it: PSB Speakers G Design 1" Aluminum Tweeter s GT1 GB1 GC1 | eBay
This is actually quite a good choice. The front plastic plate is designed (like the Wharfedale unit) to be mounted directly on the box front panel.

Can you post a pic?

Jaycar CT2005 for instance, would need to be recessed into the front panel so the plastic plate was flush. That's the reason for asking if you could use a router.
__________________________

Now we have the treble unit mounted properly and the xover bits in good order, the next thing is to decide what phase the treble unit should be.

For this you need a source of Pink Noise. Download http://www.realtraps.com/nti_minirator.exe This free application is useful for loadsa other stuff too.

On your 2 speakers, play the PNOISE signal through each speaker & check that they sound similar.

Then change the phase on ONE treble unit and compare the 2 speakers again.

The correct phase will sound like "shuuush". The wrong phase will sound like "sssssssss".

What is happening is that with the wrong phase, the outputs of bass & treble cancel out & there will be a big dip at the crossover point (the "shuuush" frequencies) leaving the "sssss" high frequencies to stand out. On music, the wrong phase will make voices sound laid back and whispy.
___________________________

The reason for asking
4) Can you borrow a working 'good' speaker of similar size? What is it?
is to determine the correct level for the treble unit.

Compare the speaker (with correct phase) with a known accurate speaker and adjust the resistor at the input of the treble xover until they sound similar. Use music to do this rather than Pink Noise.

With a lot of experience, and a really good 'reference' speaker, you can do a lot of xover work by ear too.
___________________________

That's as far as you can go without some means of measuring response.

BTW, all the stuff I've described will be done by a good speaker designer even when he has all the fancy gear & automatic programmes too ... just to check the supa stuff is making sense.
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Old 8th December 2012, 11:00 AM   #36
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Hi kgrlee,
The link came up with: "REALTRAPS PAGE NOT FOUND". I'll keep trying tomorrow though.

I know about recessing tweeters (and other drivers) because I built a large 3-way (using an off-the-shelf crossover) with Peerless India (Bought out of UK- Willy's HiFi) mid and woofers with Dynavox tweeters:
Dynavox TD2801XL 1-1/8" Silk Dome Tweeter 275-200

Posting a pic is above my ability level, the url has several pics:
PSB Speakers G Design 1" Aluminum Tweeter s GT1 GB1 GC1 | eBay

The speaker build was very testing and taxing as my electronics knowledge is quite low, and my woodworking ability almost non-existent. I am one of those people who set themselves challenges (not the sort which can be fatal, however, like "extreme sports") because life is boring without surprises and challenges.

Not sure what qualifies as a "good" speaker. My Wharfedale 510s are "good'' albeit with new tweeters (Vifa ring radiator). Same impedance as originals and I didn't play with crossovers. My ignorance of things Hifi is such that I ran the 510s for 23 years on an NEC amp rated 8-16 Ohm (510s are 4 Ohm) and eventually the tweeters blew. While they are still "good" I've moved them to the AV amp for their own safety (and the safety of my amp which I like very much- cost an arm and a leg, before amps got cheap).

You've probably noticed that I have an assortment of tweeters (also have some horns sitting in a box), I saw all the different sorts and thought I'd try them. To be honest, I like the ring radiators the best so far, but anyway it has been a revelation listening to speakers with good, functioning tweeters.


Cheers,
Mike
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Old 8th December 2012, 11:44 AM   #37
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Join Date: Nov 2011
Location: Cooktown, Oz
Mike, I wanted to see how you mounted the PSBs in your Diamonds.

The 510s if original would have been a good choice as reference speakers. Unfortunately, we have no idea if the treble response of the system with the Vifa's is flat or even at the right level.

Can I suggest you get some Polyswitch Speaker Protectors: Jaycar RN-3460 and put them at the input to the treble sections of your xovers.

They should be in series with the resistor on the Diamond xover. I think there is a similar resistor on the 510. If not, the Polyswitch should be in series with the first capacitor on the input of the treble xover.

These won't guarantee the treble units won't die but they will help a lot.
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Old 8th December 2012, 07:58 PM   #38
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Thanks again kgrlee. The Diamonds, I'm pretty sure, have a polyswitch in the crossover circuits. I'm almost certain the 510s do not. Unfortunately the 510s have the worst crossover access known to man, in fact they were the cause of me joining this forum as I was completely stumped as to the method of accessing the cabs. The tweeters have a plastic cover which hides the screws (glued on) and the mids and woofers aren't screwed on- they "cam" onto the baffle, presumably using a special tool like the small ones used for removing watch backs, for each different sized woofer which, needless to say, I do not have. Not an experience to be repeated! The 8" sound woofers wonderful, and I believe the frames are cast aluminium- which is nice, but after 23 years, often in harsh environments, the frames were covered in surface corrosion.

Since I'm at work photos of the PSBs in place will have to come when work finishes this afternoon, sorry, misunderstood your request.

Last edited by MikeCobar; 8th December 2012 at 08:04 PM.
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