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I'm toying with the idea of doing a 1-1 parts swap to higher quality components in the crossovers in my lft-viiias. I have a couple of questions for those that might have undertaken this endeavor themselves before i pull out the woofer and end-up with a bigger job than i'd hope to find.What's the dcr of the inductors, and how important is it to get a 100% match? The only 1.25mH inductor i can find is from madisound. The manual for the speakers seems to indicate that the crossovers are not removable. Is this true? Are they constructed on terminal strips? Are the resistance values listed on the schematic for the panels themselves or are they actual resistors? Finally, what's stock component quality like? Are upgrades really worthwhile?
I realize i could just ask bruce thigpen for this info, but i'd rather not bother him if possible.
Follow Ups:
Parts Connexion will unwind a higher value Alpha-core inductors to a specific value for a small nominal fee. I had them do this on two of the coils I needed for upgrading my LFT-VI xover.I used Northcreek Audio's Zen caps to make up the 470uf in my VIs. They still list 200uf and 100uf values on sale... while they weren't cheap, it was a good upgrade and a lot less expensive than any other high-end capacitor upgrades I know of. The other options I looked at were Solen's (the Zen caps were less expensive and from the comments I've heard, I think the Zen's are better sounding, but I haven't compared) or the Nichicon bi-polar electrolytics available from Michael Percy. BTW, they are some seriously LARGE caps!
See my comments on the upgrade in my response to the LFT-IV review posted a few weeks ago.
Based on my experiences, for the panel xover parts, the lower DCR of upgraded coils won't be a significant factor. For the dynamic woofers, you can always add small value R's in series to bring the DCR back up to spec... but I'd sure try it without the added R 1st, it might be an improvement for a simple xover like the one in the LFT-VIIIs (This would probably not be true in a more complex xover).
Glad to see you believe simply adding a resistor adjusts for a change
in quality of a larger coil but it doesn't change the laws of physics
and the change this causes. By increasing the diameter of the coil
you are changing the RELUCTANCE of the coil as well as DCR. Considering you are not crossing over to a coil based woofer with
your VI's you do not have the same result either. I hate to say
it but I am getting tired of seeing people screw up their systems
because they don't believe in adhering to the design they purchased.
Again resistance is not the same as reluctance.
XL= 2TTFL ( excuse my notation)
Jazzbeat,I am not an electrical engineer, just an experienced eq tweaker. I'll have to trust you on resistance vs reluctance.
OTOH, I think that replacing capacitors and coils with 'supposedly' better parts can produce good results in certain situations.
Why?
1. The variation in speaker cable resistance, amplifier damping factor, and component precision can be pretty large to begin with. I know that the caps labeled '470uf' in my LFT-VI's measured in at '590uf' on my B&K meter. When I asked Bruce Thigpin about this, he said it wasn't too critical and that the 'specified' value was probably better as it reduced the low-frequency power to the mid-panels, reducing the chance that I'd damage them with high volumes. Hmmmm... I thought these were supposed to be 10% parts too!
2. This is my opinion, but I don't think that most speaker manufacturers do a great job of looking at all areas of crosover/speaker interaction in designing their speakers. I know that some do and that it's easier to do today with the availability of modeling software, but when I see how many speakers can't pass a recognizable step indicating that they are not fully time and phase coherent, I despair.
3. My understanding (and I am willing to be wrong and further educated here) is that with 'simple' 1st order xovers, the difference the more complex parameters make in the system response is pretty small and that a lower-resistance coil can make an improviement in driver damping and perceived sound quality in a manner similar to a higher-damping-factor amplifer. Again, my understanding is that with a more complex crossover, the situation is more complex and you may change the crossover in a way you don't want with the substitution of a lower-R coil.
I would be very interested in seeing tests that show how much difference a change in a crossover coil to a lower resistance one makes in speaker alignment and response and what the subjective changes are. Generally, the anectdotal comments I've heard have generally been positive, but I have not seen much subjective and measured work on this. It would also be interesting to do these tests first with just variations on the same component type (18 gauge magnet wire coil versus 12 gauge of a similar wire) and then compare different component types (18 gauge magnet wire coil versus 18 gauge poly-insulated ribbon-type coil versus 12 gauge of the same) to get a feel for how much of a difference the 'traditional EE' parameters make and how much the 'audio tweaker' parameters matter.
Back to the original question, I'd have no problem recommending a capacitor upgrade for the LFT-VIIIs and only add the caveat of 'it will most likely be an upgrade, but there is a small chance it may change your woofer response in a way you won't like' for an inductor substitution. I will say they both made nice improvements in my LFT-VI's, and in my MG-III's, ML CLS's, and Acoustat 2's, 2+2's, and 1+1's before them.
P.S. I see I implied that my xover mods all included inductor changes. Only the MG-III and the LFT-VI mods changed inductors... the others didn't have any inductors to change!
An interesting description of a fairly involved crossover upgrade can be found at the Northcreek Audio site for their B&W 801 crossover upgrade.Greg in Minneapolis
Looks interesting but prices are a bit extreme. Looks like if someone builds it someone will pay for it..
My gut feeling is that if you own 801's, this is not a big expense.Of course, I may be wrong...
Later!
The components are mounted directly behind the woofer on a panel
and are screwed (terminal strips) and hot glued in place. The coils
appear to be adequate in size and are custom made at his plant
from what it shows on the website. As for the caps there appears to
be enough space to locate new and physically larger caps. As for the
470UF cap this is quite a large one and replacement with mylar versus
the electrolytic used could be rather costly (all the rest are mylar). Let me know how it goes I had been thinking about doing this
upgrade also.
Thanks for all of the info on the effect changing the resistance value of the inductors has on the resonance characteristics of the crossover. It's not something i had studied in sufficient detail.I believe i've decided to leave the inductors but still may change the caps to either auricaps or a mix of auricaps and jensens. I might upgrade the wiring, also.
Anyone have any details on the construction of the crossovers? Are they removable and made on terminal strips?
Also, what might be some recommendations for the 470uf cap in the crossover? Go with a combination of film style caps (quite pricey) or a bipolar electrolytic?
As a simple response to this question. DCR stands for DC resistance
for the coil. This is the static resistance that the coil has to
non frequency induced signals, IE a DC source.
In regards to the chenge in value I would leave well enough alone
in my opinion . I presently own the VIIIA and have thought of
doing a capacitor upgrade on these. Changing of the coils as stated
by Mart can and will change the characterstics of the crossover
and will change the Q loading of the woofer. This will change the
curve that the crossover uses to go from the mid panel to the woofer
( could be steeper or less steep ) as well as changing the loading the woofer represents to the amplifier. If you read the notes
concerning the woofer used it has a Q of .56 as I remember and has
been upgraded and custom made to match the panels characteristics.
This is a part of the design concept that has been employed in these
speakers to give a seemless transistion from the woofer to the panel.
Which is as a smooth as I have heard. Changing the DC value will
alter this characteristic, one which in my opinion should be left
well enough alone. Why mess with perfection?
The "E#" values are the planar driver impedances that are virtually purely resistive. The "W1" value is probably the working nominal impedance of the dynamic woofer . Reducing DCR of the inductor coil makes the woofer punch more (increases speaker Q), allows the amplifiier to better control piston motion (increases damping factor), and makes it louder. More info than you want to know.
♪ moderate Mart £ ♫ ☺ Planar Asylum
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