Crossover nightmare!!!!!!!

[alan-1-b]

Originally Posted by wintermute

Lucas,

If you add impedance compensation you will almost certainly change the sound of the speakers. The impedance compensation will basically present a more uniform impedance to the filter meaning it will work the same (more or less) at all frequencies. If there was no comensation the original network will get less effective as the natural driver impedance rises... This may or may not be desirable depending on how the overall original design was arrived at. Also You will probably get an overall cut in the output level of the woofer, which will likely then necessitate changes in other areas of the crossover to comensate.

Tony.

Hello Tony,

Celestion didn't bother with additional impedance correction circuits often then,
and few manufacturers do unless it is absolutely necessary, and does not cause the cross-over to be more complex than necessary.
When high-slope filters are needed, and thus a lot of parallel connected components, there are audible colourations caused by caps resonating with inductors, including with the inductance of the driver's voice-coil.
Such types of multi-path circuit cross-overs were used by B&W and KEF in several of their loudspeakers during the 1970s and 1980s, and most of them sounded worse when used with their moving-coil drivers than the simpler circuits used by Celestion with theirs.
Too much Science was incompetantly applied, and not sufficient listening to the results, but trying to impress tech-head buyers by showing photos of impressive looking cross-over circuitry !
{there are a few classic KEF and B&W models than do not sound bad, but not all their old models.}

The woofers used in Celestion's 44 and 66 models have significant rise in output as the frequency response increases, thus the large parallel caps,
in conjunction with the large series inductors, to pull down the output rise which starts from a little above 200Hz with those woofers.
Those woofers were developed from Public Address and Electric Guitar 12" speakers.
They were not like other developed for bass only applicable 12" drivers.
Celestion's main business was manufacturing drivers for Public Address and Electric Instruments' amplifiers then, and it still is to large degree.
But there are significant differences between the 12" in the 44 and those used in Marshall's guitar and bass cabinets,
and the Hi-Fi versions would not live long if driven hard by Rock Musicians' amplifiers -{so don't try it !}.

One could redesign the bass filters in the x-over and use a Zobel in parallel with the woofer,
but then one would have to change the values of the inductors and of the cap to ground in between the inductors.
Would the final result be any better ?
It would be different, but as a lot of listeners like the basic sound of these old 44s and 66s -{and see the ridiculously high prices that some are selling for}- then why change the design ?

What I am attempting to do here is to restore the Celestions to as close as possible to their original liked sound, but with using modern longer life components -{when the budget allows}.

If one wants to Improve on the original design then one will have to measure ALL the drivers and redesign the x-over.

There is some Zobel type Impedance Correction present in the bass filter, and that is the ESR in the 72uF electro-caps.
{Celestion's design engineers knew about ESR.}
That obviously worked well enough when those caps were new, and similar type new electro caps will have similar ESR now,
-{but not all new bipolar electros do now, thus why I specified the particular ones in this Thread, and NOT the Elnas and Nichicons which are intended for lower impedance applications}.

If one wants long life, then install poly caps, but with the necessary series-connected resistances to keep the relative impedances correct in this crossover.

*******************

I'll get to your inductor winding question next time Lucas.

[LucasAdamson]

Sense as always Alan. Just like those tractor boys from Ipswich.

[tinitus]

I use 5watt wirewound cement fore tweeter series attenuation, no problems, XT25 sounds just sweet
Also 5watt ditto on midrange zobel, no problems
5watt does seem to sound better used in particular these two positions

20watt wirewound cement everywhere else
Also, 20watt seem to sound better in all these other low frequency "high power" positions

None of them ever gets hot or even slightly varm, so no problems at all

I have no idea about durability of film resistors

As said, I will never accept multiple paralelled components
They mostly sounds worse than choosing the closest standard value, if not too far off
The trick is to choose the best closest standard value, which I admit takes some experimenting
Thats all

[tinitus]

Originally Posted by alan-1-b

significant rise in output as the frequency response increases, thus the large parallel caps,

Using two equally sized caps value in paralel with inductors
Been there, done that, and its a never again, and noone else does, if they have brains

[alan-1-b]

and neither did Celestion's engineers !

See the schematic for this crossover in Post #82 .


I'll re-phrase my explanation to:-

"thus the large shunt caps".

[tinitus]

Originally Posted by alan-1-b

and neither did Celestion's engineers !

See the schematic for this crossover in Post #82 .

Pardon me if wrong, but are there not TWO equally sized value 72uf in paralel on woofer ?
Its pretty daft
If it at least dont ruin response too much, it certainly will screw up phase
I dont understand how they left it like that
I bet almost anything else works better
But at the time I believe it was one of those slick ideas some believed in

Man, there have even been very skilled guys who made 2ways 12db with equally sized mirror imaged reversed values on woofer and tweeter, or whatever we should call it

[LucasAdamson]

Tinitus, enough already! It's not helpful. It's not fun. It's pretty discouraging.

Have you ever heard Celestion Ditton 66 or 44 speakers? They are VERY good. You can bet all you like how awful they might sound, but the fact is, Alan and I own some, and we like them a hell of a lot, as does everybody that's heard mine. The bass is in fact highly renowned on both models. I'm trying to get the best out of mine, and Alan is helping out with his FIRST HAND EXPERIENCE of rejuvenating this particular combo of crossover and drive units, and it's the kind of advice that makes sense to me.

[wintermute]

Originally Posted by alan-1-b

Hello Tony,

Celestion didn't bother with additional impedance correction circuits often then,
and few manufacturers do unless it is absolutely necessary, and does not cause the cross-over to be more complex than necessary.

Hi Alan, I've only played around with impedance compensation on my current project, and didn't care for it that much. Sorry if my post came across as supporting the idea of putting in impedance compensation, that was not the intent.. The intent was simply to state that adding it would more than likely change the sound, and possibly also necessitate making other crossover changes. Something I didn't think Lucas really wanted to do.

Tony.

[tinitus]

Originally Posted by LucasAdamson

They are VERY good.

You can bet all you like how awful they might sound, but the fact is, Alan and I own some, and we like them a hell of a lot

Thats a completely total misunderstanding

I said, "I bet almost anything else works better", which was regarding using double 72uf caps
I thought that was quite clear

I have never commented on the sound of your speakers as such, or said anything about sounding awful

But if you want my silence fine, no problem

Take care

[LucasAdamson]

Tinitus, I din't mean to be rude, but maybe I was, so I'm sorry for that.

I find that Alan has personal experience of these units and has done what I am trying to do, so he can be less theoretical in his advise about what to expect, and I find that reassuring.

You place more doubts and questions in the air, which may be based on your extensive experience but these questions can't be answered, as you have said yourself, without listening, and all of that just leads to a negative feeling that there's no point to it all and it will make a mess of my speakers. That's not what I need to hear, sorry! Maybe you're right. Maybe they're a terrible design and I should really change them a lot, like removing caps completely and changing values, but you're contradicting your earlier advice not to change much, so it gets very confusing and not helpful in the end.

Again, sorry if I was rude. I know you were trying to help, and I may look back later and see that you were right about some things.
Lucas