Inductors in series

chris · Post by **chris** » Wed Dec 17, 2014 3:18 pm

I have some old WAD kls 10's that I want to fit some new Millennium tweeters, the crossover has changed some what in the new design and I was wondering if it's better to replace with new inductors to the correct specfications or add another inductor in series to obtain the new value..

Cheers.

Scottmoose · Post by **Scottmoose** » Thu Dec 18, 2014 9:34 am

You can add another in series to make up the desired value, although that may push DCR up to unacceptable levels depending on what was in there in the first place. On that basis, I would be more inclined to replace it with whatever the [re]designer (presumably Peter C.?) specified for the mH & DCR value for the new inductor.

chris · Post by **chris** » Thu Dec 18, 2014 6:01 pm

Thanks for your reply Scott, I did not take into account the DCR value that can differ from different types of inductors and that can add or subtract resistance in the circuit. I have only this attached file of the crossover designed by Peter Comesu to go by.

Scottmoose · Post by **Scottmoose** » Thu Dec 18, 2014 10:58 pm

Without having the measured impedance + FRs of the drivers on the baffle, can't comment on the XO itself other than to say that Peter knows what he's doing & his filter designs are good examples of their type. Not exactly news.

The filter is roughly what I'd anticipate for this sort of design; 2nd order electrical + split padding on the tweeter & a hybrid electrical on the midbass incorporating a tank & a degree of 2nd order into the shunt elements. The series inductor on the midbass isn't particularly large, so they're presumably voiced for optimal performance near boundaries.

Be that as it may. I'd just buy new values; the sizes aren't large so costs will not be excessive. I'd be inclined to use a quality cored inductor of the lowest possible / practicable DCR for L1; you don't want too much resistance in series with the LF driver or system Q / tuning will be affected. So keep that down. Make sure it's a good quality inductor though. L2 could (should) be an air-core; since DCR is not specified (an unfortunate omission), presumably it is not being used as a functional part of the HF transfer function, so again, this should be kept minimal which means a reasonable winding gauge ( >1mm^2). Fortunately, 0.27mH is quite a small value, so it shouldn't be particularly expensive. In the absence of any other information / spec., keep its DCR < 0.2ohm.

rowuk · Post by **rowuk** » Sat Dec 20, 2014 1:54 am

Replacing parts in a speaker is not trivial if the result is supposed to be better than it is now.

Voicing the speaker generally needs more than one shot. I have had good luck using a mini DSP and a couple of amplifiers to get the general voicing right, then duplicating what I determined to be good sounding passively. For my own system, I have the passive analog crossover in the amplifiers. The original testing was done with the MiniDSP.

The chance of just mixing and matching parts needs more luck than I have had in my whole life. In that case nothing can replace experience and purpose. Regardless, following basic rules will get audible pressure at most desired frequencies.

shane · Post by **shane** » Sat Dec 20, 2014 9:31 am

KLS10 wasn't one of Peter's designs. He only produced WD25A onwards.

Scottmoose · Post by **Scottmoose** » Sat Dec 20, 2014 9:48 am

Nobody said it was. Chris did however imply that Peter did a redesign of the filter at some point to allow the Seas T25CF002 Millennium tweeter to be used (as he once did with the KLS3). The general configuration of the filter design he attached also closely resembles a general typology Peter appears to favour / frequently employ, lending further credence to this.

shane · Post by **shane** » Sat Dec 20, 2014 10:02 am

I stand corrected

Scottmoose · Post by **Scottmoose** » Sat Dec 20, 2014 10:07 am

rowuk wrote:Replacing parts in a speaker is not trivial if the result is supposed to be better than it is now.

Voicing the speaker generally needs more than one shot. I have had good luck using a mini DSP and a couple of amplifiers to get the general voicing right, then duplicating what I determined to be good sounding passively. For my own system, I have the passive analog crossover in the amplifiers. The original testing was done with the MiniDSP.

The chance of just mixing and matching parts needs more luck than I have had in my whole life. In that case nothing can replace experience and purpose. Regardless, following basic rules will get audible pressure at most desired frequencies.

That may be so, but it's not a case of 'upgrading' an existing filter; it's a different tweeter & complete new XO that was designed to go with it.

In the absence of further information (such as inductor DCR) all one can do is employ standard engineering practice / common sense & a little knowledge of what the filter's designer uses as their typical approach. Peter (assuming it was he) generally used quality ferrite inductors on the LF leg to minimise DCR & magnetic fields, with air-cores for smaller values on the mid / HF leg. Since no DCR is specified for that either, it is reasonable to suppose that it is not a part of the transfer function, and should be minimised. That is as far as we can realistically go. Chris could always try a foil, or some complex braided-wire air-core for the HF shunt inductor if he felt so inclined -depends if you believe they make any difference or not over a more standard air core type.

Outside that, we are in the realms of generalised inference. If this filter was done when Peter was at WD, then caps would most likely be assumed as Soniqs polypropylenes, likely the SAX type. They could be exchanged for alternatives with possible subtle changes. Resistors are unlikely to have been more than standard ceramic types unless otherwise specified.

chris · Post by **chris** » Sat Dec 20, 2014 1:08 pm

I really appreciate the input that has been made, without it I would have made lots of basic errors. I really have to slow down and make sure that I take the given advice.

Hi-fi World June 8

Since I updated a reader’s KLS10 Gold bookshelf speakers last year I’ve had more than a few e-mails asking whether the SEAS Millennium treble units I installed in place of the gradually declining Audax HD-3P Piezo units could be used in the KLS3 Gold as well.

Whilst the simple answer is ‘yes’ I pointed out that a crossover change would also be needed, particularly for the treble unit crossover and possibly, also to the midrange crossover to perform a perfect match.

This dismayed all but one correspondent who was so eager to refurbish his KLS3 Gold MkIIs that he delivered them to the World Designs Lab so that I could perform the necessary measurements and revise the crossover.

Scottmoose · Post by **Scottmoose** » Sat Dec 20, 2014 9:04 pm

Ah, I've found the page you cited the information from (a link might've been simpler

). Confirmed that it's one of Peter's then.

In which case, looks essentially confirmed. Almost certain to be ferrite on the bass leg, an air-core for the HF, lowest possible DCR for both. Soniqs SAX caps, probably standard resistors. The latter two you should be able to change if you felt inclined. Differences (if any) will be subtle, assuming you use quality components.

chris · Post by **chris** » Sun Dec 21, 2014 12:09 pm

Thanks Scottmoose, not able to put down links just yet...have to become a trusted memeber. The information you have given to me will really make a big difference to the end results, I will select some inductors after Christmas.
Yesterday I managed to cut a larger radius as the new tweeters are slightly bigger, the speakers were originally made up of 25mm of solid oak so I did not want to mess up, so was glad that it was without any problems.
I was thinking of changing the cheap plastic input panels for a slab of aluminium then just drill some holes for the binding posts.

chris661 · Post by **chris661** » Sun Dec 21, 2014 1:01 pm

If you're re-doing the backplates, consider using Neutrik SpeakOn connectors.

Very high current rating, very low contact resistance, and no chance of shorting out.

Also cheaper than the "audiophile-grade" binding posts if you happen to be so inclined.

Chris

chris · Post by **chris** » Mon Dec 22, 2014 2:21 pm

The Neutrik SpeakOn connectors look like sensible engineering, not expensive very high current handling with solid connection.
I have made up some copper foil speaker cables which are not so easy to connect to binding post of limited design. I am going to use 8mm aluminium plate and just router a rebate to drop it flush with the back of the speaker, then drill some holes for the binding post, am not sure to leave the aluminium as is or paint it black then use some gold allen bolts.

Scottmoose · Post by **Scottmoose** » Mon Dec 22, 2014 4:54 pm

Sensible engineering is exactly what they are. I stick with ordinary binding posts for convenience, but then, I'm constantly fooling with different speakers.

That is (no offense) more than I can say for copper foil used for speaker wire though. At best it's a solution in search of a problem, and one that causes a few problems of its own. Depends on the geometry. If you space the conductors apart (side by side, or, at its most extreme, pulled well away from each other) then inductance is significantly raised. So they form a low-pass filter, rolling off the HF -how much depending on how extreme the end geometry is & the length involved. Conversely, if you've got them close together, e.g. face-to-face, inductance will be pushed to vanishingly low levels, but capacitance will be through the roof to the point that you might need to stick an RC Zobel on it to get some semblance of stability back, since crazily capacitive wire rarely does anything any favours at all. If you like the sound of it, fair enough. But neutral it isn't.

audio-talk

Inductors in series

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