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This question was stimulated by Airtime sending me the drivers from a pair of Lafayette L-2 speakers, a 39.95(!!!) 3-way (!!!!) design dating from 1976, featuring an 8-inch woofer, cone mid-range, and cone tweeter.I got to thinking about speaker building today with the emphasis on 6 1/2 inch woofer (or smaller) 2-way designs and how the catalog stores were able in the 70s to build 3-way designs and sell them at very modest prices. Ask a DIYer today about building a 3-way and you get a long story about how incredibly difficult this is to do and no one but an utter fool would try to develop one from scratch. But in the 70s, inexpensive and in many cases quite nice sounding three-ways were everywhere. The notes I have in the Lafayette catalog on the L-2 indicate that it had a "capacitor crossover" at 6000 and 9000 Hz. The 6000 Hz figure seems incredibly high for an 8-inch woofer design, and what they call the super-tweeter basically covers only an octave. Its a very tiny cone in a larger sealed metal frame with a quite big magnet on it. The "mid", also sealed, has a much tinier magnet but a slightly larger cone. I can't believe that in a $39 speaker they woulda used more than a couple of caps which would have made this a first order design with no real band-pass as such on the "mid".
The other thing I'm not sure about is the type of capacitor. I gather the common capacitor used in these kinds of designs were inexpensive Non-polarized capacitors that for reasonable values cost between $0.30 and $1 in the PE catalog. Was this what was normally used at this point in time. Again, my friends in would cringe at such parts, but the interesting thing is in the 70s they seemed to work pretty well. Can I substitute the inexpensive Mylar caps I picked up surplus at Madisound for these?
For a woofer that operated up to 6000 Hz, the inductor, if present at all, would be very tiny, maybe 0.2 mH, and cheap. The woofers are actually quite nice, they have good-sized magnets and they have what appear to be textile surrounds, but are different from the other cloth surrounds I have seen in that they arent crimped and look like an inverted foam surround.My current thought is to build a single sealed partitioned box double the size of the original boxes for the woofers and aim the woofers in opposite directions at either end of the box. The original boxes were sealed. This is going to be my faux "acoustimass" module. Then build the mid and tweet into small satellite boxes. MY hunch is that these mid and tweet drivers are at least the equal of what Bose uses in their satellites. If there is some directionality with the bass, so what--thats true of the Bose as well....LOL
Follow Ups:
Just one 2.2uf's. One to the mid and the other to the tweeter in series. The woofer was open. The type of cap was your basic 35V axial, almost PCB sized caps. About 1/2-3/4 inch long.I think the older designs were of a very basic principle. They had a simple SPL graph and had a simple formula to mate drivers with MAYBE one cap to adjust for rolloff.
That's why I have so much trouble with working with DIY projects with 4th order LR designs. WHY????? is there a need for SO MUCH crossover if driver matching would seem to be MORE important that just stuffing parts on a crossover board.
David, have used 12 uf non-polarized caps on a myriad of tweeters in two-way designs for the better part of three decades now! They sounded great with those Utah Cadence drivers(with their seamless bass-midrange tonal transition), and later with replacement Ratio Shaq drivers installed into various wooden cabinets(don't forget to remove the stuffing, and let those cabs breathe)! Black, made in Mexico 12 uf 100 volt np caps used to be ubiquitous in electronics parts emporiums here in NorCali(Altecs and JBLs also used 12 uf nps, though they were monster sized)! Later discovered that 15 uf np caps coupled with 8" and under woofers added thumpability, and a slightly crisper high end from the tweeters! After a friend gave me his auld Advents several years back, started experimenting with 13uf np for those who wanted that Advent tonal flavour! Recently bought a pair of Sansui Classique 900s for KDVS' 14G sound room. Replaced the shot woofers with 12" Titan thumpers, which thundered when 15uf, 13uf, and 12uf np caps were coupled to the midrange driver. So tried 10uf np(which Celestion Vintage 30 and Electro Voice Force 12 drivers favour in two-way configuration)on the midrange, and 4.7 uf np on the tweeters! KDVS' general manager liked them so well, she now utilizes them as studio production monitors. Those modded Sansuis do sound impressive via Denon amplification! David, let that DIY crew use their computer computations to design complicated crossover loads, since that's what their hearts' desire! Auld skool cap crossovers, coupled to quality drivers, will let you hear your amp's sonic signiature!
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.
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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