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In Reply to: RE: Design parameters I hold dear... {Lynn Olsen} ... posted by Cleantimestream on September 01, 2014 at 09:31:10
Cleanstream
I've been following the current discussion with great interest as I am a fan of Lynn Olson's (correct spelling?) writings concerning amps. The first thing I've ever read of his was a very good article from Voice Coil magazine (re-printed in the now defunct Valve magazine as I recall) which presented the case that speaker induced resonances were amplified through an amp with negative feedback through the feedback network, but not so with an amp with no negative feedback. I've been less enthusiastic concerning Lynn Olson's comments about horn loaded loudspeakers following this however. So the question I have in the current discussion is: how do you feel that horn loaded speakers are "...hard-to-drive" as you have stated? As to speakers which are hard to drive for an amp, Quad electrostats immediately come to mind (and I like them, though they have been described as "...like driving a capacititor"), and vented direct radiators compared to closed box too (and I've heard examples of both I've liked). Comments regarding the relative difficulty of driving a properly horn loaded woofer are welcome.
Paul
Follow Ups:
Lynn stated that, and is just conjecture on my part that he meant the wide variance in impedance plots (they look like the Andes)common with horn systems,indeed, I have a 'swamping' resistor in my modified Forte's so
my 45 SE amps have more power...
The Mind has No Firewall~ U.S. Army War College.
C
Horn mids (& tweeters) are frequently paired with reflex/vented woofers like your Klipsch Fortes, and large (mountainous) impedance swings can be expected with woofers with this kind of bass enclosure, and impedance compensation networks can be used to address this.
The German magazine Stereoplay (9/81)* published a comparison test of several horn and horn hybrid speakers with graphs showing the minimum and maximum impedance. Two are good representatives of the horn mid/tweeter with a vented woofer: Altec 19 (Max. 49.2 Ohms, min. 8.4 Ohms) and the EV Sentry lll Series 2 (max 68.7 Ohms, min. 6.1 Ohms). Compare these figures with a kit built K Horn (max. 13.4 Ohms, min. 4 Ohms), and the Klipschorn KDBR (max 32.1 Ohms, min. 4.8 Ohms). Also tested was a kit built Fostex mid horn along with what looks like an Altec A5/A7 replica for the woofer, which is horn loaded on the front of the woofer and vented on the back (max. 56.3 Ohms, min. 5.5 Ohms), and the EXA Studiohorn 3/60 B EXA which has a backloaded bass horn with direct radiator from the front of the woofer (max. 24.7 Ohms, min. 5.7 Ohms).
From this data it seems clear that horn loaded woofers can have more consistent impedance variances than comparable speakers with vented box woofers. Now it's unclear (with my college German) whether any of the speakers had impedance compensation networks, which would have skewed the results, but looking at the the 1981 time frame it's unlikely that they did, and no schematics of the crossover networks were provided.
The reason for the generally better impedance behavior of the horn loaded woofers is that the acoustic resistance of the horn dominates the performance of the woofer, and it is relatively consistent across the pass band of the horn. The direct radiator woofer is mass controlled in order to give the driver nominal flat response instead of an increasing high frequency response, along with the acoustic resistance of the box and the vent at the lower end, which are all variable according to frequency. At least this is a rather simplified take on what is a rather complex subject.
Paul
*A scan of the magazine article on a german website (Selbstbau, 11/14 2003) was linked to on the Hi-E forum here some time ago, however it's since disappeared. If anyone's interested, perhaps a deep search with the Wayback can turn it up (I made a paper copy for reference). To my knowledge Stereophile has never fully tested a speaker with a horn loaded woofer, and viewing Ed. John Atkinson admitted skepticism towards horns it's unlikely they will, unless Art Dudley shows up with a K Horn.
Indeed, Paul
I use KHorn bass bins and JBL 2360 Horns with 2445H drivers crossed @ 430 ... still experimenting/seeking the right balance.
The Mind has No Firewall~ U.S. Army War College.
It looks like I've been preaching to the choir ; ) K Horns, with their sealed reactance-annulling back chambers, should present a more stable load to an amp than the Forte's, as long as the K Horns are in a corner. Those german guys probably did their test the old-school way with an oscillator, test box, multi-meter and graph paper. In the present time we have Room Eq Wizard (REW, which is a free download for Mac and PC) and, along with a simple DIY test box, it can do an impedance graph in some 30 seconds or so. I would expect the test results between the K Horn and the Forte's would be similar to what the German test found.
Paul
There is nothing, I repeat, nothing... that recreates the bottom end like KHorns ... in the right room... many others disagree... perhaps I just hear things differently... the only downside is when they run out of steam/punch around 375 hz.
The Mind has No Firewall~ U.S. Army War College.
Edits: 09/05/14
For life like dynamics it takes a horn to catch a horn. If you get a chance you should hear one of the horn loaded sub woofers like the Edgarhorn Seismic, or Tom Danley's Labhorn or Tapped Horn. The only direct radiators I've heard that can run with them are the thirty inch EV 30W, and Tom Brennan's former dual JBL 4648 sub rig.
Some K Horn guys go with JBL mid drivers. I had some JBL 175's on test some time ago. There was a problem with one (apparently the diaphragms have to be hand tweaked with an oscillator) but the other one went down to 400 Hz on my home made tractrix horn (with similar dimensions to an Edgar "Salad Bowl" mid horn). I've heard some K Horn replicas run with TAD's on LeCleach mid horns which sounded very good. The crossover region between the mid and bass horn is always a challenge with a K Horn as you can't easily get the woofer and mid drivers aligned in phase unless you use digital delay. And you loose power handling capacity crossing over that low too of course, but that's probably not a problem if you're using low powered tube amps, which gets us back on topic here.
Paul
Are you saying the realm above 375 Hz is problematic?
Yes Sir, the horn loaded woofer simply runs out, I can hear it when my Horns were configured stock, I have heard that problem was solved with the Jubilee.
The Mind has No Firewall~ U.S. Army War College.
Edits: 09/06/14
In my opinion K-horn with the right driver (I used Altec 803A) has a phenomenal midbass. The performance with K-33-E is only passable and the potential of the cab is mostly wasted IMHO. K-horn will never do bass ,(it will boom along with K-33E) and by the nature of the beast everything over 200 hz will be compromised but 50-200hz ? -out of this world !I sorely miss it .
Rgrds, W
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