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Multi-Way Conventional loudspeakers with crossovers

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Old 28th July 2007, 05:56 PM   #81
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See eBay for celestion 662 parts!!! over in 2 days!

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Old 30th July 2007, 02:54 AM   #82
sba is offline sba
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I only had time to test 2 of my speakers for DC resistance. Both pairs of 66's are in the same room...one pair on top of the other in a tower arrangement. The lower pair I'll call "blacky" because of the black front, and the upper pair I'll call "woody", for the wood front.

left woody:

left blacky:

...and from a spare woofer: 4.2-4.3
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Old 30th July 2007, 02:54 AM   #83
sba is offline sba
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here is a pic of woody's crossover:
Attached Images
File Type: jpg woody x over.jpg (91.4 KB, 456 views)
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Old 30th July 2007, 02:54 AM   #84
sba is offline sba
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here is a pic of blacky's crossover:
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File Type: jpg blacky cross over.jpg (82.9 KB, 436 views)
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Old 31st July 2007, 12:38 AM   #85
sba is offline sba
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"...we add a series resistor to each polyprop. cap to simulate the ESR of the electro's so the impedances, including the phase angles, will be the same as Celestion's original, so that the drivers will cross over at the original design frequencies."

So...it seems then that replacing electro caps with polyprop ones necessitates the use of an added resistor.

Since this is my foray with crossovers, I'll sit here on the side and wait for brand, size, value, etc recommendations.


Scott / sba
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Old 2nd August 2007, 02:54 PM   #86
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Location: Midlands
Default incorrect spelling

Originally posted by alan-1-b

So, why not simply use new electrolytic caps which have the higher ESRs ?
Well, electrolytic caps also have high Dielectric Absorbsion.
What is that ?
It is a Memory effect. Basically when the electro cap is charged by the signal {music} it retains part of that charge and does not fully discharge and charge to the opposite polarity when the signal changes polarity.
It does charge and discharge and re-charge etc, but always lagging the signal by a much larger time interval than the Time Constant of the circuit.
The audible consequence is a muddying of the music owing to the mixing of delayed release information being added to new information.
{this is a simplification of the full process, but it's sufficient to give you the idea}

Polypropylene caps have very very low dielectric absorbsion. That is one reason why they are so good for audio signal use.

I don't know why I cannot remember how to spell some words that I have read a sufficient number of times to remember !

Correct spelling is :- absorption
This is for Dielectric Absorption, as discussed above, and which I correct here in the event readers want to research that phenomena in capacitors.
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Old 2nd August 2007, 03:17 PM   #87
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Default Diffraction control

Originally posted by tonedef2

News> I finished messing around with the diffraction problem> net result was, attaching the audio wool to the upper grill works best and did have a good affect, I will describe as less blurring of the high freq energy, note: if you listen with grills off........then I simply used a custom cut wool with very little Velcro to slip under the top over hang (your grill will fit a little tighter), works great and am now working on the aesthetics.....

2-I will post some picks of the grill soon for analysis as im pretty sure as the audio wool loosens over time we have a ringing affect at moderate attenuation.

Pete, I'm pleased you have heard the effect of reducing the diffraction.
What you have reported is what I had expected would occur, and how I hear such myself.
I would also describe it as "clearer" {as distinct from "brighter" which can be caused by diffraction in some circumstances}.

If you try a strip down both front edges of the baffle panel from where-ever you have stopped in the tweeter area to down past the mid-dome a few inches, then you should be able to hear similar benefits in the mids' reproduction.
The strip will need to be at least 3" wide for the mids, as it has to absorb sufficient part of the longer wavelengths of the lower frequencies there.

Sound should be clearer with the grilles off, but if listening with the grilles on, than the tighter fit you mention should reduce vibration of the grille frame.

I am puzzled by the "ringing effect at moderate attenuation" you mentioned.
Is this when the wool is loose, or when the grille is looser fitting ?

Are you listening with those oval/rings around the tweeters still in place, or them off and only the wool on now ?

Yes, do post some pictures, as that will show us what you have done, and may help to see how to solve the ringing effect you have mentioned.
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Old 2nd August 2007, 03:56 PM   #88
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Default the DC resistances, and the large orange-red capacitors.

Great stuff sba !
thankyou indeed for posting the DCR's , as this confirms the figures Pete has posted also for those, and the two different vintage samples are of interest also.

Is your "blackie" 66s older than your "woodie" set ?
There may be a Date, or some type of Date Code printed on either the front or back of the cross-over boards.

Capacitor C7 - the parallel pair of large orange + small black is probably a 20uF electrolytic cap {orange} with the black cap the same 4uF type as C5 on one of Grahame's set of boards.

The large red-orange caps in the treble filter section of "blackie's" board I do not recognise, but possibly these are a Paper-in-oil capacitor type, as such were used in cross-overs years ago, and are said to give better sound than Electrolytics and some plastic types.
Can you read what is printed on them, and post here ?
I may be able to identify them from the lettering.

Some paper-in-oil types do not have as high dielectric absorption as electrolytics, but this depends on the type of material{s} used to make the paper, and the type of oil.
Main problem of paper-in-oil types over period of time is they develop leakage, and especially if heated.
Heating is less likely in a speaker x-over than in a tube amplifier chassis, unless the speakers have been played very loud for long periods, but as yours are quite old do look closely around all joins in their coatings, ends of and around the wire holes for any sign of a substance leaking.
There is also Electrical Leakage - of charge. That is a different phenomena and occurs to some degree in all capacitors, but less so in well made ones, but is to some degree dependant on type of capacitor.

Pete, you know more about the vintages/versions of the Ditton 66 than I do.
Those two sba has seem to be older types than Grahame's pair, and yours - {if yours are the same as Grahame's ?}, ?

"woodie's" board has the two sets of old type plastic film caps in the treble filter the same as on those 2 boards that Grahame bought from the e-bay seller.

Notice that the DCR of the tweeter in "blackie" is lower than in "woodie" and in Pete's later model 66.
I wonder if this is simply co-incidence, as we only know 1 tweeter sample from "blackie", OR, if Celestion changed the voice-coil in a later version of their HF2000 tweeter ...

What-ever the case, and I do not know for sure but I think paper-in-oil caps have larger ESRs than even those old plastic caps, thus the ESR of the paper-in-oil cap may be sufficient to add to the DCR of that lower DCR tweeter to give effectively the same resistance at the 5 kHz cross-over frequency as the higher DCR tweeter + very low DCR of the plastic film caps ...

More on this when I post about capacitor selections, soon I hope .
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Old 4th August 2007, 05:25 AM   #89
Grahame is offline Grahame  United States
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I'm back - sorry for the gap.

Alan - thanks for your very informative posts. I hope you haven't been affected by the recent flooding in the UK.

sba - welcome to our little gathering. Quad 66's - now that must sound impressive!

Interesting that Celestion seemed to go through so many crossover styles. Continuous improvement, or whatever they had in the parts bin /the supplier delivered- who knows?

sba - good to see that your crossover has the zip-tied green capacitors - I wasn't certain if they were originals on the crossovers I won on ebay - but this would seem to indicate they were.

One side effect of all this measurement is that I noticed that one of the MD-500s was cutting out intermittently - traced it down to the red/black wires on the outside must have been pinched at some point in all this opening / closing of the cases and would make / brake if you wiggled the wire . Solution - solder another wire in parallel from the connection on the back of the front plate to the tab at the base of the case - seems to have done the trick. Did it on both sides to be sure.

With all this assembling /disassembling are there any better solutions for semi - permanent connections that the rather flimsy seeming tab / folded spade arrangement ? Anything mil-spec designed for the task or better more modern solutions - or am I just being fussy? I could solder it in place + then just use the new form of connection where required.

Ok, now onto DC Resistance - which is where it gets interesting ... or not.

LEFT Speaker
HF2000 (high) = 4.6
MD500 (mid) = 6.6
12"(low) = 4.2

RIGHT speaker
HF2000 (high) = 9.2
MD500 (mid) = 6.8
12"(low) = 4.2

Should I be concerned in the difference in R for the HF2000's ?
Any possible causes? any significance in the fact the values differ by a factor of 2?

To these cloth ears there doesn't appear to a gross difference -in fact they still sound fine to me - given that their placement is not ideal due to room / WAF constraints

I'm hoping to get some objective frequency response plots - so I can see if there is a difference, and what form it takes - if any.

tonedef2 - look forward to your pictures - then I can try the same thing at this end.

Glad to be back,

P.S. if there are any other 66 owners lurking please speak up - the more the merrier - especially as I've noticed quite a few pop up ebay.co.uk - pity they all seem to be buyer collects
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Old 4th August 2007, 08:31 PM   #90
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Have read the new posts and will respond soon in more detail......that 9. DCR on the HF2000 of Graham's may be a problem when taking his measurements? Alan? No time, more later...

Ringing/vibrating due to the grill cloth/wool (i think it's wool?)loosening over time on the metal frame, more later...

Where making good progress gentlemen....

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