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Re: LFTVIIIa crossover mods

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.

Greg in Minneapolis

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