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In Reply to: Ignorant speaker cap questions. posted by DavidLD on December 28, 2003 at 07:52:53:
David,I'll know more about the mylar vs. non-polar electrolytic soon as I plan to experiment with the series caps in the high pass section of my Polks. From playing around with the Advents, replacing a non-polar electrolytic with a polypropylene film cap added considerable extra brightness. So I went back to the NP. We'll see what happens with the Polks.
On your plan with the Lafayette drivers. I have Bose Acoustimass 5 series 2 speakers and I did open them up and make some measurements. Their bass enclosure is a 6th order bandpass, there is a rather steep roll off at around 250 Hz on the woofer port output. The two drivers are buried nside and do not radiate directly (you probably knew that, already). There is no electrical rolloff on the woofers, it's strictly acoustical filtering by the enclosure. Also, it is wired as one woofer per channel. The L+R summing is done acoustically inside the enclosure. The mid/tweeter modules are acoustic suspension and have a second order electrical filter and what seems to be a 4th order acoustic rolloff. Classic L-R. There is an LRC notch filter at around 1 kHz. Otherwise, the 2" mid/high drivers run full range above 250 Hz.
Now, getting back to your planned sub-sat system. I doubt the Lafayette midranges will get down low enough to be able to get a good transition between the sub-woofer module and the mids. Since both woofers will operate well up into the mids, directionality and consequent localization of the bass will be a serious problem. It's there with a 250 Hz crossover on the Bose, but not too seriously. The fact that Lafayette crossed over at 6 kHz argues that the midrange is really a tweeter and the other is a super tweeter. Do the woofers have a whizzer cone? They sound like augmented full range drivers with a coupole of tweeters rather than a woofer/mid/tweeter combo.
Simple three ways from the 60's and 70's. JBL L-100: 2 caps and two L-pads. JBL L-110: three first order filters and one second order plus some impedance compensation. Bozaks were mostly all first order. Yes there were a lot of nice 3 ways in the late 60's and into the 70's. AR 3a, 5, 2ax, 11, 10pi, 91, 92, etc. Boston A-200, A-150. Numerous ADS models. Infinity, KLH 5, Epicure 3.0, Rectilinear III, lots of JBL, several varieties of Jensen and Altec, Klipsch, and on and on.
I can think of several reasons for the current trend toward 6.5 and 7" drivers. Narrow cabinets which are easy to place and have a higher WAF, cost, and the potential for eliminating one crossover point and the cost and complexity that goes with it. Big and bulky three ways live on in the "high end". But in the wares from Circuit City and Best Buy, the cabinets are slender. I think it really has to do with costs and the decorating aspects of slender cabinets.
As to the craze to use 6.5" and 7" drivers in the DIY arena, I think a lot of it has to do with the much greater difficulty of building a 3 way that's as smooth and flat as a two way. But then you need to add a sub (usually) and end up with a 3 way anyway plus the problems of integrating a sub.
Follow Ups:
If I can't find anyone to take the MCS I may mail you those drivers too. Do you want some pics????
If anyone is interested they are your's but be forwarned shipping charges DO apply if you want the cabinet and all.I'll email you on the side about the MCS crossovers, Lottsa parts!!
charles
I'm gonna end up with too many projects to complete at this rate.Let's first see if there is anyone here who would want and could use the MCS speakers whole for the shipping charges. I hate to see those nice units cut up and they would make a great speaker for a rec room.. Guys what these really are is 3-wat Technics speakers dating from the early 80s.
At last count I have 12 pairs of conventional speakers in operation somewhere in the house plus a couple more pair in a closet. So I'm not really in need of yet another conventional design.
Bose has this other all-in-one deal thats not a Wave radio or three-piece--maybe that would be a better starting point. Many small console stereos from the 60s had side-firing low-range units, and then mounted the other drivers toward the front. If I made a single cabinet about 24 inches long I could mount the woofers in either end, and directionality would be enhanced as they would be aimed in opposite directions. Then I could mount the other drivers in two small separate boxes that could sit atop or near the woofer cabinet not a long ways from the woofers.
Hmm... kinda an updated console.
Side firing or off axis firing gives the effect of removing the higher frequencies without the use of any crossover. This would let the lower frequency, which has a lesser directional quality, pass while shooting the more directional higher tones into no where land, or off a wall or something. I think this was the early version of a 6th order bandpass. Bose really mastered this trick early on and did a very good job using 4 inch drivers.
Consider downward firing the woofers. Or even rear and forward.
c
Kind of a combination sub-woofer speaker stand.
You cuuld then aim the directional speakers easily or even tilt them back slightly.
Some interesting ideas.
Bill
....
If it doesn't work you can remove the woofers and do the saw people in half magic act with it.
Bill
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