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Old 11th May 2007, 04:22 AM   #51
Grahame is online now Grahame  United States
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I can now add the resistance values form my multi meter -
all values are in ohms

L1=(1163)=0.15mH=0.6R
L2=(1358)=2.16mH=1.3R
L3=(547)=0.33mH=0.6R
L4=(1359=3.68mH=1.3R
L5=(1358)=2.16mH=1.5R


I've had a look at the Capacitors at - parts express
Lots of choice, and lots of prices! - what would you recommend,
in terms of best value for the money - good audio qualities, but not silly money, please
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Old 12th May 2007, 12:06 AM   #52
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L1 look funny to me but im very interested in what Allen thinks, your doing great and sounds like we are going to make our beloved Celestions really sing......
I have not dealt with the top lip diffraction yet, but will post my findings soon, my thoughts so far is we may solve some key problems with baffle and phasing and with the addition of quality caps should give us a very nice recipe..........i think this tweeter will work great after that.

Pete
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Old 12th May 2007, 11:30 AM   #53
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Default Sorry, but a delay ...

Hi guys,

Excellent that you've got the Inductor values Grahame !

Sorry, but I am working in a country area town where I do not have computer access, thus I will not be able to reply to your several posts for at least 6 days, or 7 days from today.

But, don't worry, you have posted plenty for me to think about, thus I will reply !


tonedef2,

I suppose you have heard a difference with those ovals in place ?

Have you tried them in both their standing on end vertical orientation, and lying on side horozontal orientation ?

Given the proximity to the top of cabinet overhang, I'd expect the lying on side horozontal to work better, but what have you found to be the case ?

If you're undecided about which orientation you prefer, try them also at a tilt of 45 degrees -{falling over !}- but yes, I am serious, such is worth a try.

Note, the mentioned 10kHz effect of the original rings, and now spread across 8kHz - 12kHz for the ovals, that is they partially reflect sound !
I'd have made them from soft wool felt !!

regards,
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Old 12th May 2007, 05:38 PM   #54
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Hi Allen & Grahame

Yes Allen I did notice a positive difference, perhaps described initially as reduced attenuation / less noise, but we all know it can be better (side note> this mid dome is so wonderful in itís very wide sweet spot). Question> did you mean that this ring will reflect on the inner surface???? Itís very porous on that side... or absorb? Should I go with an audio type woolen felt material instead?

The instructions for the ovals say this up/down orientation is best, not considering the lip of course.

Grahame your really tearing into this just like I would love to, time permitting...let me know if you need any of my worthless help.
Grahame was I correct in L1 being way out?

Ok Allen, will wait till you get a connection.

ToneDef2 / Pete
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Old 13th May 2007, 02:32 AM   #55
Grahame is online now Grahame  United States
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I can wait for Alan to get back in the loop.

the L1-L5 names are from the PCB layout,

I'd be particularly interested in recommendations for brands of capacitors and tolerances.

The inductor measurements were what they were - I took several readings just to be sure.

Given we now have

1) The crossover topology
2) The values of the components in the crossover (L + C)

we should be able to stick the values into some software (suggestions please!) and see what the designers were attempting to do.

Also - this should show us the effect of changing the capacitor values
(6.2 -> 6 , 3.98 ->4) and if this is a good or bad thing - or irrelevant as the actual values would have a 20/10/5/1% tolerance anyway .

Pete - I'd be interested in your findings re: the acoustic treatment for the tweeter - then I can just follow your lead.

I'll see if I can get the DC resistance values of the speakers - disconnected - (tweeter, mid and sub) to complete the set of measurements.

I'd also be interested if Alan knows of anybody else whose expertise would benefit this thread.


Pete - does your crossover look like my PCB - its behind the Sub.
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Old 19th May 2007, 01:01 PM   #56
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Default Computer availability is brief today ...

Quote:
Originally posted by tonedef2
L1 look funny to me but im very interested in what Allen thinks,
Pete
0.15mH for an inductor in that position of the 3rd order electrical filter at about 5kHz is a size I would expect.

Grahame and Pete :-

When you have time, measure and post the DC resistances for both your tweeters, and I'll comment some more on that filter.

Similarly for the 4th order electrical filter to the woofer, when you have time measure both woofers' DC resistances and post.
The DC resistances of both L4 and L5 are significant in the behavior of this filter, and now we know those, thus need the value for the woofer itself.
__________________________________________________ __

The E.S.R. values of the electrolytic capacitors will be significant also, and likely need duplicating when replacing with the much lower ESR polypropylene capacitors, especially for the 72uF cap that is in direct parallel with the woofer, and perhaps for the other 72uF, and less likely for the 24uF -{which will have a lower ESR anyway}, and highly unlikely to be necessary for the 4uF black cap.

E.S.R. = Equivalent Series Resistance

This is not easy to measure, but can be estimated from other measurements.
I can explain how to do this, but you will need some specific test equipment, and a Standard - a known value resistor - for comparative voltage measurements.

Do you both have a 1%, or closer, Tolerance resistor that is of any value between about 6 ohms <---> 10 ohms ?

In 2 watt would be best, but hard to obtain ; 1 watt is OK, but even if you can only buy a 1/2 watt 1% tolerance resistor, it can be used to check the accuracy of your multimeters' ohm ranges, and then a 2% or 5% resistor in larger wattage can be measured and used for the Standard.

Buy 2 in case one gets broken.

Vishay VTA52 series is 1watt in 0.5% tolerance and is available in 10 ohm for about $6.50 in the USA.

There are much cheaper available in 1/2 watt in 1%, and probably in 0.5%.
__________________________________________________ __

For the AC voltage ranges of your multimeters, what does the owners' manuals list for :-
Accuracy ?
Frequency Response ?

There may be different Accuracy specifications for different frequency bands.

Are your meters "True RMS" for the AC ranges ?
OR is this not specified ?

What is the Digits' display ?

Eg:- 4 1/2 digits' display shows each range to a maximum of 1999.
And 3 3/4 digits' display shows each range to a maximum of 399.
__________________________________________________ __


Do you have Audio Frequency sweep oscillators ?
and their Wave type ? -{usually are in Sine Wave, some have Square Wave also}.
OR, do you have CDs with fixed, listed Frequencies in Sine Waves ?
If so, please list the available frequencies ..?..
__________________________________________________ __

All the above can be used to do measurements to be able to estimate the ESR values of electrolytic capacitors ; the pass-band Impedances of the speaker drivers - and this we do need to know if considering whether alternate tweeters would substitute for HF2000 ; the Fs's, and the magnitudes of Impedance at each, of the HF2000 and the MD500 - for if you want to know more about the cross-over slopes, and whether it may be worth deciding between 6uF and 6.2uF for that tweeter filter's cap., and some other matters ...
__________________________________________________ __

Grahame, I'll post about the safe-to-measure bandwidths for the HF2000s and MD500s as soon as I have time to,
and also about brands for capacitors, and the other things you asked,
hopefully next week-end.

regards,
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Old 19th May 2007, 01:25 PM   #57
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Default Diffraction and Reflections.

Quote:
Originally posted by tonedef2


Yes Allen I did notice a positive difference, perhaps described initially as reduced attenuation / less noise, but we all know it can be better (side note> this mid dome is so wonderful in itís very wide sweet spot). Question> did you mean that this ring will reflect on the inner surface???? Itís very porous on that side... or absorb? Should I go with an audio type woolen felt material instead?

The instructions for the ovals say this up/down orientation is best, not considering the lip of course.

ToneDef2 / Pete
Well, given the Designer's, or, Manufacturer's comments about their measured 10kHz effect - and then 8kHz <--> 12kHz effect for the oval shape - there is obviously either, or both, diffraction or reflection occurring from either the inside edge or the top surface of the oval.
A foam rubber is never fully porous - such usually have some sealed cells - visible as small flat sufaces.
Inspect the top and inside of the ovals with a strong magnifying glass.
Post whether you can see any very small flat surfaces in the foam, then we will know whether these ovals partially reflect, or only diffract sound waves.

Even small flat surfaces are sufficient to cause some reflections of the short wave-lengths' high treble frequencies, and,
any mass - even a porous one - has some acoustic impedance that is different to air, thus there will be some diffraction of part of the bandwidth of sound when the sound waves pass the junctions of air-foam-air.

Try the rolled up woollen sock under top of baffle lip idea I described, both with and without the ovals in place, and listen for preferences ...

Given the audio qualities of those MD500s is why we are continuing to pursue this restorations/modifications topic to such degree - I think they are worth this.

regards,
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Old 26th May 2007, 01:23 PM   #58
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Default Clarification of a recent post, and of an earlier ...

Quote:
Originally posted by alan-1-b


I can explain how to do this, but you will need some specific test equipment, and a Standard - a known value resistor - for comparative voltage measurements.

,

By "Standard", above, I mean as a Reference.

Though, if you don't mind working within the accuracy limits of the Resistance ranges of your multimeters, then you can simply use the 2% Dayton resistors that Parts Express sell for loudspeaker cross-overs.
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Old 26th May 2007, 01:26 PM   #59
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Default Made a mistake - now very angry !

Sorry, I have just now accidentally erased most of a very long post - I can't believe this, but I did !

It was part of the above appearing post, but only that part remained - I don't know how I did it !?!

I have no time left to do it again now, thus will have to leave till next weekend.

I regret this,
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Old 2nd June 2007, 12:57 PM   #60
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Default real drivers and cross-over considerations.

Back again !

In regard to matters raised about filter slopes and software for calculating cross-over components values :-

The text book formulae ; on-line calculators ; and various software for cross-over filters all require a constant Impedance across the driver's useable frequency bandwidth and a flat Frequency Response for at least 2 octaves past the cross-over frequency.
Most drivers, including the 3 active drivers in the Ditton 66, do not have constant impedance nor flat frequency response in some otherwise useable areas of their bandwidth.
There seem to be some software types that one can enter variable impedance and non-flat frequency response data into, but I am not familiar with those.

I cannot find frequency response nor impedance plots for any of the 66's drivers, so I will give examples of some similar drivers :-

go to www.celestion.com

click on Guitar Loudspeakers

look down the the left-side column and click on "Ask Dr Decibel"

scroll down the page to "Archive Specifications" and click on "G12M-70"

see the frequency response -{in red}- has a raised plateau in the 850Hz - 1kHz region, then a notch at about 1.3kHz, then a large peak centered on about 2.5kHz.
this is characteristic for 12" paper cones with a slightly ourved profile.
the woofer in the 66 will have similar, though possibly in slightly different areas of its useable bandwidth, and the upper midrange peak may not be as large - all 3 depend on cone mass ; cone stiffness ; voice-coil diameter, {as well as cone diameter}.

see the impedance plot -{in blue}- on the same graph.
see how it changes across the frequency bandwidth of the driver.
its minimum - in the 200Hz - 400Hz area is the Nominal Impedance of the driver, and this is usually about 20% larger than the driver's DC resistance which your multimeter measures.
the impedance is higher than the nominal value in the cross-over region if one was considering a 500Hz crossover freq. and the need for a constant impedance to beyond 1kHz so that the electrical filter will work as designed to.

Print or Store the G12M-70 plots so you can look at them beside the other plots I'll list below:-

go to www.moreleurope.com

click on "Drivers", and then at the bottom of the page click on "Click here for products overview"

click on 'midrange" and open the "product information sheet" for the MDM 55 dome.

see the Impedance Magnitude plot - large changes across the frequency bandwidth.
the hump at about 380Hz is the Fs for this driver.
As it is quite high, it is not highly damped, thus one cannot use this area of the frequency spectrum for any significant output level a it will simply distort, and probably damage the driver as it likely has a limited excursion also.
I do not know the Fs of the Celestion MD500, but it may be as high in frequency as 500Hz, however from tonedef2's description it seems it is very well damped, and it may have sufficient excursion capacity to reproduce significant output at its Fs -{woofers usually do, and some cone midranges do, but rarely do dome midranges and tweeters}.
see the "Sensitivity Magnitude" plot -{this is the frequency response}- and where the response rolls off at a slow rate slope below 1kHz, and where it rolls off at a higher slope rate above 6kHz.
this is typical of mid-domes of that size, and in this one it is very well controlled.

Print or Store those plots for comparison with the next:-

For a less well engineered upper end roll-off, but quite good lower end roll-off, AND, less change of impedance magnitude, go to:-
www.tymphany.com , and under "Products" cllick on "Peerless" in the left-side column, then on "midranges" and open the file for the D75MX-41-08 , and Print or Store to compare the plots for it to those of the Morel MDM 55.

I do not know the rate of roll-off slopes for the Celestion MD500, but as it has 2nd order electrical filters I think it will likely have moderate slope roll-offs at both its low and high ends.

next look at Peerless tweeters:-
look at APL25SC15-04, it has its Fs at about 1.5kHz, which is approximately where I think the Celestion HF2000's Fs will be, or it may be slightly higher in frequency.
see the Fs is not well damped, and this is also indicated by the hump in its frequency response in the region just above its Fs.
look at BC25SC15-04, it has a slightly better damped Fs -{at 1.32kHz}- and a flatter frequency response.

Print or Store the plots for the BC25SC15-04, then place 3 of these plots side-by-side :-
the G12M-70 - one of the mid-domes - the BC25SC1-04 tweeter, and try to imagine how these 3 can be crossed over at useable points in the bandwidth of the mid-dome, and then with the other mid-dome.
In theory, one has to make the impedance constant around the cross-over regions - that is usually done with resistors plus either or both capacitors or inductors - AND make the frequency resp. flat, which is possible only with the woofer in this example, and is done with some or all of resistors; capacitors; inductors.
In practice -{in most cases}- one can combine the functions of the required components for the electrical filters and the required components for the impedance and frequency resp. compensation components, and use less components, BUT these will be different values to what is given for simply the electrical filters' slopes.
This is what Celestion seem to have done.

For electrical filter on the woofer Celestion have used a 4th order slope, AND, this will include a larger than expected value capacitor for the cap. parallel closest to the woofer, to compensate for the rising impedance magnitude in the cross-over region.
That cap. may part compensate for the rising frequency resp. magnitude also, as likely does the slightly larger than expected inductor beside it -{2.16mH}.
The other cap. and induct. seem to be what I would expect for approximtely 500Hz cross-over for a driver impedance plus inductors' DC resistances to total of about 7.5ohm, -{but for some cross-overs the other cap. and/or induct. may be changed also}.
As there are no resistors used, I think the highish E.S.R. - typical of electrolytic caps, especially of that vintage, may be incorporated into the cross-over design.

The MD500 wll have its own roll-off slopes, thus Celestion need use only lower order electrical filters there to achieve total roll-off rates of 4th Order, and the cap. and induct. values seem to have been chosen to compensate for a non-constant impedance.

For the HF2000, at least one of the caps will have to be different than exected to compensate for the impedance hump at the driver's Fs, and to compensate IF a non-flat freq. resp. at least 1 octave both above and below the cross-over frequency.
As the inductor is about the value one would expect for a nominal 7ohm tweeter -{is it ?}- , I think the HF2000 will not have required a lot of compensation cicuitry, but as Celestion have used a Reversed Polarity connection for the tweeter I am wondering whether this is result of using less cross-over components than would be required for a Like Polarity connection for the tweeter.

All this is why it would be useful to have some measurements of at least the HF2000 if one is considering substituting another tweeter.
For the MD500 some measurements would be useful also to assist in integrating it with a different tweeter.
For both these drivers some measurements would be useful if one wants to know which option of the different capacitor values to choose, but it is not absolutely necessary.

I have run out of time and will have to go now as I am very late.
More next week.

Post some comments if this is, or is not, in the direction either of you wish to go !
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