I just joined this forum a few weeks ago, seeking answers to some problems regarding crossover rebuilding difficulties I was having with my Polks and other vintage speakers.
I received outstanding advice--I replaced the SL-3000 tweeters in my Polk RTA-11TLs with RD0198-1 silk dome drivers, which alone alleviated my main complaint (high end harshness). I've made one additional change since I last posted--after listening for a week things still sounded a tad strained on the high end. I had installed 14awg Goertz foil inductors, which I metered out at a bit less DCR than the stock air coil wire inductors (0.2R for the foils vs. 0.8R for the wire units). I tried some 5W resistors in series with the foil inductors (from 0.5R-1R) and interestingly they made little if any difference. So, since I haven't yet permanently mounted the new crossovers I ordered a pair of 0.3mH 19awg wire air-core inductors from Madisound (better, I felt, than the stock ones) and found that these $3.50 coils actually sound better than the $15 foil inductors, added resistors notwithstanding.
So I've learned yet another expensive lesson--the audible qualities of inductors are not due to DCR alone, which surprised me.
It's been an interesting process, since I've modified several other quality vintage speakers with simple substitution of premium caps, inductors and resistors and was rewarded with immediate positive results--by 'quality' and 'vintage' I mean speakers from Klipsch, Celestion, AR and others old enough to employ electrolytic caps in the crossovers. Those required surprisingly little fine-tuning, but the Polks for some reason are the most sensitive to small changes in crossover characteristics that I've come across.
Which brings me to my question--After reading the many articles extolling the benefits of crossover bypassing (mostly published by high-end cap manufacturers) in my original crossover rebuilds for the Polks I used AudioCap PPT Thetas to bypass the caps, using caps about !% of the base value, the general rule of thumb for bypassing. Although I was at first impressed--I heard significantly more detail than before--I found that my listening enjoyment was very dependent on source material...direct-digital vocal, jazz and classical CD's sounded great, as did many vinyl records, but the story was different with AAD CD's (remastered from analog sources) and less-than-perfect LP's (and since I've collected LP's for close to 40 years, many are in less than perfect shape). In any case, the bypassing revealed the harsher aspects of many recordings, and this improved greatly after I removed the bypasses altogether.
However except for the hash and hard edge of some recordings, I really liked what I was hearing, the bypasses revealed subtleties in vocals, acoustic guitar and piano I had never before noticed.
Has anyone else had a similar experience, and was my error perhaps in my choice of bypass caps? Up until recently my primary hands-on audio activity has been rebuilding and upgrading classic tube and mosfet amplifiers, and by trial and error I've learned where judicious use of certain brands of metallized film and film/foil caps makes an audible improvement, For bypassing and coupling in electronics I've used Audiocaps, Kimbers, Auricaps and even cheap Daytons. None of these cost more than about $7 ea, while esoteric brands can cost $50 in .01uf values, something I figured was for people with more money than sense.
However, several companies (such as Hovland Musicap) make caps specifically intended for speaker construction and I'm wondering if my opinion of bypassing might be different if I gone with these instead of the Audiocap PPT Thetas, which although excellent in HV electronics might not have the best characteristics for crossovers, where absolute speed and accuracy is NOT necessarily the quality I'm looking for. The Hovlands run about $16 ea, and I certainly don't want to throw another $60 at my crossovers when I've already tried and rejected other rather expensive components, it's just that I now know I can still make my RTA's sound better--as I said, I loved the speakers bypassed with Audiocaps with some material, but for across-the-board use they just didn't cut it. I'm looking for a mellower bypass cap, if anyone has any suggestions.
I should say that I'm a fairly experienced builder and upgrader of audio electronics and (to a lesser degree) speakers, and I've learned to take the majority of high-end claims with a large grain of salt. More money does not equal better sound. I only believe what my ears tell me, and they inform me that there are indeed significant benefits possible from bypassing. Speaker design, I'm learning, is more like alchemy than electrical engineering in many regards and the formulae involved are as much due to trial and error as they are to physical equations. Quality transducers are musical instruments like a fine violin or guitar, not simple electrical devices.
Excuse me for waxing poetic, I'm just interested in experiences others have had in bypassing and in any specific comments on applicability of different capacitors.