From: bill@verdix.com (William Spencer)
Subject: Re: Anyone successfully using Jordan 50mm drivers?
Organization: Verdix Corp.
Date: Tue, 7 Apr 1992 22:53:26 GMT

In article <1992Apr6.202026.6536@mercury.cair.du.edu> troby@diana.cair.du.edu (Thorn Roby) writes:
>Long ago I built a pair of speakers using the 50mm Jordans in a 96 cubic inch
>(long,skinny) particle board box lightly stuffed. I finally abandoned
>them several years ago when I could no longer ignore the fact that they
>had a nasty buzzing resonance around, maybe, 1 KHz. I was crossing
>them over at 150 Hz. I replaced them with a satellite made from a 5"
>mid and a SEAS tweeter. They sound fine, but I've always wondered whether
>there was something I could have done to make the Jordans work. Anyone
>have any suggestions? I never drove them very hard (a few watts, max) 
>and they show no signs of damage (except for the one the cat got hold of).

Jordan no longer recommends the 150 Hz crossover. Using 4 or more per side,
preferably ported, or at low levels you can make that low frequency work,
but you're best off going up to 300 Hz or higher. You don't say how many
drivers per side you used.

I presume these were the old version Jordans. They have a protective
mesh over the front, strangely attached to the moving cone, which is
a straight flare with a seam. I was not impressed to see these, although
I'm sure they can be used as decent midranges -- still should compare very
favoribly to dome mids. The high frequencies tend to be rough and limited.

More recently Jordan has improved the drivers. They are now updated quite
often in fact. The new ones have seamless curvilinear cones and rubber 
surrounds and a strange looking phase plug that looks like a nail head
sticking out of the middle. They are also slightly larger. I have heard
that Jordan now has a version that goes out to 30 kHz -- from a 2"
cone! I heard last year's version, and I thought it was good (the owner
was not finished with his speakers yet however). The line array of 4
drivers per side was directional, but I could detect no comb-filtering
like effects.

I have been experimenting with, and enjoying listening to, a different
50mm module made by Bandor. The company is run by Mr. Jordan's ex-wife.
These are like industrial strength versions with bigger magnets, thicker
faceplates, etc. A conventional spider is substituted for the rear suspension
of the Jordan. I use one per side with a 4th-order crossover at 340 Hz.
These sound great, but it was very tricky getting them to the point they are
at now. They are the 3/4" voice coil version -- avoid the older 1/2" VCs.
Xmax is 4mm, so they can pump out relatively low frequencies far better than
you might expect. Free-air resonance is 80 Hz; new versions are rated 50 W.
Boxmodel predicts ported-box
alignments that go as low as 55 Hz! Of course SPLs would be minimal.

As you can see, the frequency response of these drivers goes far lower than
the desired crossover. But extension well below crossover is a great aid to 
crossover design. After playing with these drivers, most tweeters seem
ludicrous, with their resonances in the 800-2.5K range. Such drivers push the 
crossover frequencies up to 3K and higher and still don't have the extension
for sensible crossover design. The kilohertz region results in short
wavelengths at crossover, therefore extreme sensitivity to interdriver spacing.
The result is great changes of frequency response with vertical movement
of the listener and audible incoherence due to movement of the source over 
frequency. I have considered that some of the claimed superiority of planar
designs is a result of avoiding high frequency crossovers. Now you might say
there will be a problem with a driver covering such a wide frequency range,
but it seems that those who make that complaint are not so concerned by 
normal two ways whose woofer covers a very wide range. The 50mm drivers allow
an equal split between woofer and tweeter.

My only gripe with Jordan and Bandor is the drivers have a personality
crisis. The same driver can be used for a midrange or a tweeter or both
-- in fact even a woofer, if you have the bucks for a lot of them --,
but they're not really optimized for either. Normal tweeters, on the other
hand, tend to be overly specialized and require high crossover frequencies.
It seems almost impossible that there are drivers capable of treble response
with resonance frequencies above 700 Hz and below 100 Hz but none in 
between. If speaker makers were to take a lesson from Jordan they could build
superior drivers, but they don't. 

Bill Spencer