Crossover nightmare!!!!!!!

[alan-1-b]

Originally Posted by LucasAdamson

I am putting the 5 watt wire-wound resistors in tonight and will let you all know whether this worked. They are large MOX type resistors.

MOX is Metal OXide, and not metal wire.

Some listeners like the sound of metal oxide resistors, at least when those are new, but I am wary of them because the connections between the internal oxide and the metal end caps can become electrically faulty more easily than internal resistance wire does to end connections.
This is more likely to occur if the resistors get hot in use because the junction changes its electrical characteristics during the hot-cold cycle, and more-so over a long period of time of many hot-cold cycles.
Very well designed and constructed metal-oxide resistors of the oxide formulae and assembly/construction used by Caddock -{and probably also by Vishay}- will work well for very long periods because those are designed and engineered to work in critical Military, Aerospace and Medical equipment applications.

[alan-1-b]

Originally Posted by LucasAdamson

Maybe L-pads would be good, one for tweeter and one for mids, each with a few resistor choices ????? It always seemed to me that you can discuss the "tone" of your amp and record deck and pre-amp and all the other stuff in your hi-fi, and you're talking about tiny details, but the sound of speakers is MUCH less uniform and can vary enormously and the range of tonal balance with speakers is vast compared to everything else, so it makes sense to be able to adjust the tonal balance to taste..........Opinions on l-pads anyone?

The problem with L-pads is that the resistive element wears thin after more than a few turns and to a greater degree than it does inside an amplifier's volume pot for the same number of turns,
because there is much higher electrical current flowing though an L-pad than through an amplifier's volume control in its quite different circuit position.
High current requires very large contact area to be maintained intact, and that is difficult to keep when a tight fitting contact point is continually moved over a deposited track of carbon or spiral of wire -{depending on the type of resistive element used in the L-pad}.
Over time L-pads cause lower quality sound as they wear out - I heard this in my own loudspeakers years ago, and eventually the L-pads connections became audibly intermitant.
Also, there is more heat generated as Power has to dissipated in an L-pad, and most are not made to sufficiently high power rating to have a very long life.
Use an L-pad to experiment in the design stage to find the best comprimise setting, then measure the resistances and substitute fixed wire-wound resistors of those values in place of the L-pad.

[alan-1-b]

Originally Posted by alan-1-b

Hi tinitus !


The PCA Cap you posted the Link to -
do you know what Dielectric is used in them ?

I emailed to freQuence a while ago and received a reply which includes a Specifications' list in English language.
The PCA caps are metalized polypropylene types, thus the dielectric is polypropylene.

There is little on the freQuence web-site about the assembly of the caps, thus it may not be equal to the very best,
but at their prices they will likely be as good as any other axial polypropylene cap at the same price, and may be better.

If anyone trys them, please do Post the audible results in comparison with what was previously used, and where used in the circuit.

[LucasAdamson]

Yes, sorry Alan, you make a valid point. I was only referring to the tweeter 0R5 resistors. I placed them at the crossover in the end. I think that it's the right value for the tweeters, by the way. I'm less sure of the midrange ECR values though.

Lucas

[alan-1-b]

Hello Lucas,

as I was reading all the older Posts to see what I had not addressed, and if any other loose ends, I wondered whether you have installed 3 resistors for each crossover or only 2 ... ?
I intended 2 for the mid's filter - such as where you now have a 2ohm -{or 2.2 ohm ?}- plus a 2.7ohm with the 6uF cap
-{see #71 on Page 8 of this Thread - at the bottom of that Post}.

The 0.5ohm to the tweeter is the 3rd resistor.

If you have only a single resistor in the mid's filter and are happy with the sound result, then that is quite OK, but as you now have two spare 1.5ohm resistors you could try them in Series with the 6uF mid's cap if you have no resistor there - you may like that more or you may not.

Do Post how many resistors you have used, and where, so that others who find this Thread later can get some idea of what to expect.

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I'll not Post about inductors now, as you seem to be quite happy with the bass sound,
and the inductors currently in there are quite OK for sound until driven very hard with high volume playing to a greater degree than may be pleasant in your room.
New ones may not be any better for the volume levels you like, and its possible they may not produce as likeable sound at those volumes, though that will depend on the DCRs of whatever new inductors.

[kevinkr]

Originally Posted by alan-1-b

The problem with L-pads is that the resistive element wears thin after more than a few turns and to a greater degree than it does inside an amplifier's volume pot for the same number of turns,
because there is much higher electrical current flowing though an L-pad than through an amplifier's volume control in its quite different circuit position.
High current requires very large contact area to be maintained intact, and that is difficult to keep when a tight fitting contact point is continually moved over a deposited track of carbon or spiral of wire -{depending on the type of resistive element used in the L-pad}.
Over time L-pads cause lower quality sound as they wear out - I heard this in my own loudspeakers years ago, and eventually the L-pads connections became audibly intermitant.
Also, there is more heat generated as Power has to dissipated in an L-pad, and most are not made to sufficiently high power rating to have a very long life.
Use an L-pad to experiment in the design stage to find the best comprimise setting, then measure the resistances and substitute fixed wire-wound resistors of those values in place of the L-pad.

Strange, every single L-PAD I have ever disassembled was a concentric wirewound type with large sliding wipers. They can become intermittent over time, but this is usually because the wiper itself oxidizes. They usually clean up pretty nicely with a couple of rotations, and worst case seem to respond well to a dab of any good contact cleaner. (Caig Labs)

There are plenty of inexpensive, good quality L-PADS rated at 25W or 50W at Madisound, Parts Express, etc. In most applications except for extension speakers they will never see significant power levels in normal use. (A club would be the typical exception.) Most of the power in music is typically found in the lowest few octaves and most mid-range drivers and tweeters are reasonably efficient.

I've had 50yr old JBL speakers with the original L-PADs on the tweeters and they worked just fine.

You shouldn't be adjusting them on a regular basis after all the system response does not abruptly change - although changes in room furnishings and the like may have some minor influence.

L-PADs aren't ideal in other respects as there are several contacts in the signal path and arguably replacing these with a fixed attenuation L-PAD should result in better long term stability and just possibly a slight audible improvement. (I haven't heard any as long as I keep my adjustable L-PADS clean.)

I think the overall recommendation to replace the L-PAD with a fixed set of resistors is a good one though, just make sure that the LPAD reflects the proper resistance back to the X-O otherwise the performance of X-O itself will be compromised. (it is not a simple potentiometer see first link)

Note that you should probably measure the AC attenuation across the L-PAD in circuit (convert to dB) and then use one of the several online calculators to get the correct resistor values. Here's one:

L-PADS

And another:

L pad calculator - attenuation dB damping impedance decibel loudspeaker - sengpielaudio Sengpiel Berlin

These are the best I've found online so far..

[alan-1-b]

Thanks for Posting your experiences with L-pads Kevin !
- and it has reminded me that I should have mentioned I was discussing only variable-potentiometer types and not fixed resistor types,
nor even switched resistor types which its possible Lucas may have meant.

The variable-pot L-pads that deteriorated to unusable in my old loudspeakers were in the mid-driver circuit !
I probably tried a contact cleaner in them, as I did squirt contact cleaner in the pots in my electric guitar at times then -{until those deteriorated beyond salvation !}- however I have forgotten.

I have not seen the types in old JBL loudspeakers, and at the then JBL prices I would have thought longer life types would have been used.

I Posted about low-power rated types because that is what was in my old loudspeakers and in various low and mid-price loudspeakers I have seen since, and in particular I am Posting for UK buyers who don't want to buy from overseas' suppliers - for whatever reasons some have enquired such
of me - though I do buy from USA and elsewhere myself for what is not available in the UK.

I didn't adjust pot-type L-pads very often, but it seems some users do want a type they can adjust each time for different recordings they play,
but I think deciding a compromise fixed resistance is better for the long term, and if one owns an amplifier with tone-pots or filters it seems the adjustments are usually better done there.

Thankyou also for Posting the Links to the calculators.
I had not seen the second one previously, and I will look through that web-site when time is available.
www.lalena.com has an L-pad calculator in its audio pages, and it looks to be a correct one to me,
{though I have not used it as I always calculated using some mathematical formulae I found in a diy article in a magazine years ago}.
Do you have any comments about the Lalena site's calculator ?

[speedie]

tinitus why! go there

[LucasAdamson]

Originally Posted by alan-1-b

MOX is Metal OXide, and not metal wire.

Some listeners like the sound of metal oxide resistors, at least when those are new, but I am wary of them because the connections between the internal oxide and the metal end caps can become electrically faulty more easily than internal resistance wire does to end connections.
This is more likely to occur if the resistors get hot in use because the junction changes its electrical characteristics during the hot-cold cycle, and more-so over a long period of time of many hot-cold cycles.
Very well designed and constructed metal-oxide resistors of the oxide formulae and assembly/construction used by Caddock -{and probably also by Vishay}- will work well for very long periods because those are designed and engineered to work in critical Military, Aerospace and Medical equipment applications.

Do you know what, Alan, I've tried equivalent values between MOX and Welwyn wirewound, and the MOX sound much nicer, in my opinion. They sound freer and more musical. I think I may revert back to them.

Regarding values, I have 0R5 in the tweeter and in the mids I have 2R7 after the 6uF (to earth), with 2R2 immediately after the 33uF, but I am not entirely happy with the mids. I want them a touch louder generally, and less tight sounding. I may swap the 2R2 for a 1R5 and the 2R7 for a 2R2. I'm going back to MOX too. Sorry if that's dumb, but to my ears they are better sounding. I expect that to be near the end of the resistor road for me. I hope so anyway, as I need a completed reference speaker for when I reassemble and test my amp.

All the best
Lucas

[alan-1-b]

Its not "dumb" to use the type of resistor that one prefers the sound of !
Given that you have hearing capability to discern the difference between the sounds of the two types, you may as well use the type you prefer.
I posted the warning about MOX type resistors because I cannot guarantee they will remain sounding the same after a long period of use, for the reasons I gave.
My consideration was, because you had previously requested low price components, I thought you wanted a resistor that would not need replacing after a period of hot/cold cycling, and that is what a lot of low budget listeners ask me to recommend.
As for sound quality, well you will know that some enthusiasts use valve{tube} amplifiers because they prefer the sound even though valves wear out and have to be replaced.
Some other listeners do prefer the sound from valve amplifiers but say they cannot afford the maintainance costs of replacing valves, so they buy solid state.
It is often difficult for me to know what to recommend because of this Cost versus Performance trade-off, thus I play it safe and recommend long-life components unless I am asked to recommend otherwise.
For resistors the only oxide types I am confident to recommend for long life are those manufactured by Caddock.

There is audible differences between different types of wirewounds, even between different Series from the same manufacturer.
Please Post and tell us for the use of all readers, which Welwyns did you try -
W__ series, or WA__ series, or WP__ series, or another series of theirs ?

And the MOX type you prefer, which Manufacturer's name is stamped on them ?
or if no known manufacturer, then which Company did you buy them from ?

If you have bought a sufficiently high power rated MOX it will not get hot whilst music signal through it and thus, if it has been well constructed, it's connection contacts may not deteriorate and the sound may remain as good as when new for a very long time.

I prefer Mills brand wirewounds over other wirewound brands I have heard, but some diyers do not want to pay the price for those, and in the UK only the very large 12watt Mills are available and some UK diyers will not buy via Mailorder from USA to obtain the smaller size 5watt Mills, thus why I recommend Welwyn for them, if they want long life.

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For slightly louder mids, do try the 1R5 after the 33uF cap, but retain the 2R7 to ground after the 6uF cap because lower resistance of 2R2 there will cause small attenuation of part of the midrange, however if you wish to hear the nature of the differences then do try both and listen for what you prefer, as you have resistors in all these values now.