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Squawker Driver Tests, K-55V, K-55M, K-51V, K-52H


BEC
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Thought I would try to work out a better way today to test drivers than I have had before. Always get a lot of reflections, so with enough baling wire and an air conditioner filter, today got the method working pretty good. I think I still have a bit of reflection/cancellation at about 450 hz. Either that or every driver I can get my hands on drops a bit in output at 450. I doubt that actually.

Bob Crites

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All drivers tested with bandwidth limited white noise. Spectrum Analyzer looking at 0 to 10 Khz in log function. Exactly the same signal into each driver. Nothing adjusted in the test setup during the entire test.

Tested drivers Left to right.

K-55V 2 piece phase plug, K-55V 1 piece phase plug, K-55M, K-51V, K-52H

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Good work.


The dip at 450hz is a mouth reflection back down the horn from too small of a mouth. This is reduced in practice by the flange it is mounted to in actual use. This may be predicted by using fig.5.10 from Olson. The K400 is very close to 'C' scaled for 275hz. PWK hoped the flange would give closer to 'D'. The K5J, and most commercial designs were similar to 'D', having more length and mouth area.


http://i56.photobucket.com/albums/g196/dkleitsch/Olson510and511.jpg

 

Modern designs, such as Duke's JBL2360A, have such a large mouth that they approach 'E'. This horn, intended for a 500hz crossover, actually has more mouth area than the LaScala bass horn does.


PWK thought the K400 was a good compromise, decades later many of us prefer the older designs.

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All on one. Really too many to be able to tell much about them this way, but each is a different color.

Bob Crites

what can be discerned from this insofar as the various tested drivers are concerned? Should there be obvious favorites? Any to move away from?

Or just leave well enough alone, knowing that the network designers voiced the entire setup including that particular network/driver/horn combo? (in other words, would it behoove someone with AA's in a LS with K55M to just change drivers or does the network have to follow the driver swap?

Michael

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Michael,

I would say that every driver tested here looks good for a Lascala or Khorn driver with the exception of the K-52H which does not go low enough. It looks good for a Cornwall or a Heresy.

As far as standouts, the K-55V with 2 piece phase plug has the cleanest trace and is very flat to 6.5 Khz. But, the particular one I tested at least gives up a couple of dB in output compared to the K-55V single piece phase plug and the K-55M.

The K-51V extends as high as the K-55V 2 piece phase plus and has a bit higher output than the others. Not quite as flat a curve as the K-55V 2 piece phase plug.

I am just surprised how really good these drivers are. I think the first four are pretty much interchangable. Once I got the test method down to very few test induced errors, the drivers look great.

Now, another surprise is the peak at 7.5 khz on the K-55M. If someone wants to get upset about the little peak on the K-55V 1 piece phase plug at 9 Khz, they should go nuts over the one for the K-55M. Also notice the one the K-52H has at 9.5 Khz.

Bob Crites

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"Now, another surprise is the peak at 7.5 khz on the K-55M. If someone wants to get upset about the little peak on the K-55V 1 piece phase plug at 9 Khz, they should go nuts over the one for the K-55M. Also notice the one the K-52H has at 9.5 Khz."

Very interesting results. I agree that those peaks are a problem. It's a shame that both the Type "A" and "AA" crossovers allow the squawker to "come back on" at such a volume. A crossover with a sharp cutoff slope between the squawker and the tweeter (or even a cutoff slope at all) would solve that problem.

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I hope I am not butting in here... being that this is my

first post and all. I recently started trying to catch up on your

forum.... there are so many interesting topics and so many great discussions.

I only have a pair of K55V drivers, but both offered fairly similar

results. My drivers are the ones with the spring clips so I guess that

means they are the 1 piece phase plug version.

My measurements are with the K-400 mounted on the baffle of a La Scala.

The mic was on axis ~1.5m from the mouth of the horn. The center of the horn was raised to five feet from the floor in a room

with a 10' + ceiling height so the first reflection was far enough away

that I was able to time window the measurement to achieve a quasi

anechoic measurement that is probably accurate to ~350Hz to ~400Hz or

so.

When I first looked at the plots I was taken back by the fact that they

are not particularly flat... I am not sure if this is due to their age

and likely abuse along the way or if it is typical of these drivers on

this horn. I will say that in the mid 70's the K-horn and La Scala were

spec'd at +/- 5dB... these horns and drivers are keeping within that

tolerance between 400Hz and 6500Hz, so I suppose they may still be

within spec.

I'll be very interested in your opinions.

Widget

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Hi Bob and Mr. Widget - out of curiosity I just pulled a Speakerlab K400 clone to compare to Altec 511.

The K400 clone's msooth expansion has more beaming giving a bit more HF EQ than the beamy 511--perhaps a Cobraflex would be similar up to a point.

I'm worried more about distortion in some old drivers - can't get one 1823M to play right - dunno if alignment issue of not but low end and high end are gone.

Posted Image

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I've had nasty sounding 1823s end up OK after dis-assembly, cleaning (that they didn't seem to need), and re-assembly. I think someone may have replaced the diaphragm at one time or another and didn't tighten the screws down snug, and then go back and torque them evenly. I've also seen a couple of loose phase plugs too.

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Put in any one of my network designs and the glitches above 6000 Hz on any of the drivers are filtered out. It's the AA that can't handle them! In other words, replace the network, not the driver!

Al K.

 

I agree.

I see too many posts about replacing drivers (single phase plug vs dual phase plug, etc) to reduce the effect of the "glitch".

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