Some suggestions from Stu Lumsden
SeleniumFalcon
Posts: 3,779
I thought this suggestion would be of interest to CP readers. It's from the Polk Enthusiasts group of Facebook and written by Stu (for those not familiar, Stu was the head of Polk's engineering department and was instrumental in classic Monitor and SDA designs). The comment was posted in response to a question asking for recommendations for someone in the Boston area who could upgrade SDA speakers.
"Replace caps with same values but lower Dissipation Factor [DF] to reduce the effective HF DCR. We used Mylar caps in all the SDA HF sections. Want more air? piggyback a 10picoF silver/mica cap on the main HF cap. Hi Still muffled? Reduce the HF resistor value by 0.1ohm. Measure, don’t assume the written value is correct. +\-10% if I recall correctly. All crossovers were measured as an assembly which captured the tolerance stack up.
Hope this helps."
"Replace caps with same values but lower Dissipation Factor [DF] to reduce the effective HF DCR. We used Mylar caps in all the SDA HF sections. Want more air? piggyback a 10picoF silver/mica cap on the main HF cap. Hi Still muffled? Reduce the HF resistor value by 0.1ohm. Measure, don’t assume the written value is correct. +\-10% if I recall correctly. All crossovers were measured as an assembly which captured the tolerance stack up.
Hope this helps."
Comments
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I have found adding a HIGH QUALITY bypass of the highest quality, like duelund cast to a cap makes a great difference. .01uf duelund cast or the jdm line is great.
Some caps also have this built in as you move up the capacitor chain. The upper end duelund caps have a bypass cap already installed within the cap.
Is Stu active on that group?
Very cool!
- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit. -
I think I've seen him respond twice. Once was to someone who needed a tweeter repaired and this one. I'm sure there were more, but I didn't catch them.
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Nice! Keep the input coming Stu, even if indirect
George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
The problem with bypass caps is the "air" they add is in reality an artifact. It's not a natural sound one would hear at a live event and becomes rather annoying over time.
Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
So why use a bypass at all? There are actually components of very high frequencies in some audio waveforms. Some are high order harmonics. If you think of a square wave, the right angles at the top of the wave are extremely high in frequency. Sometimes there are high frequency components in very fast audio sounds, for example, the instantaneous tap of a drum stick on a cymbal. These are the sounds that should be "helped" by including a small-value bypass capacitor in a high pass crossover.
Well, I don't think so. If the 8 µF capacitor blocks frequencies below 5000 Hz and passes frequencies above 5000 Hz, why do we need what is actually another crossover for the same tweeter, but operating at frequencies already passed by the big cap? I am sure engineers have a very good reason, and a couple of them have tried to educate me on this subject. I respect the science and electrical theory on this subject, and my technical background helps me to understand it fairly well. But there is one small problem: the bypasses all sound bad! They add a quality that at first sounds like an increase in air and detail, but after a couple of hours becomes an intrusive harshness and discontinuity in the upper treble. Remove the bypass: all of the detail is present but without that grating and annoying sound. The high frequencies are cleaner, smoother, and much more enjoyable. It doesn't matter if the bypass cap is Teflon®, polystyrene, or common polypropylene, the results are very similar. And to be avoided.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
I agree with you until I tried the duelund stuff, well worth the investment anh provides a great balance of air and tone- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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Bypass caps? I'll take my Black Dragons straight, no chasers.Don't take experimental gene therapies from known eugenicists.
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This is a posting, by Stu, in response to a question about which speaker was best, SDA, SRT or L800:
"The L800 represent the most research and refinement in both simple faithful amplitude response and detail while also having the latest in SDA research and improvements.
The SRT will play the loudest. And has the means to modify the SDA (which I would leave fully active).
The SRS was the state of the art at of the advent of the SDA age for Polk. Wonderful work by Matthew and great in rooms with low ceilings because of the line arrays.
I Choose L800s."
