LAR’S REPORT #5 ON WEISS PS2000 K-COUPLER

"-Dear Group,

The PS2000 taper rate is 4.23 1/m corresponding to a frequency cut-off 116 Hz.

A horn for this rate suitable to the dimensions of the PS2000 (throat area St=500 cm^2
[77.5 in^2] and length L=30 cm [11.8 in]) would have a mouth area Sm=1760 cm^2 [273 in^2].

For comparison the area of the tapered opening of the PS2000 is 256 cm^2 [40 in^2]
and the area of the terminating PS2000 'mouth' is Smk=90 cm^2 [14 in^2].

The horn radiates sound determined by the mouth real impedance.

The PS2000 radiates through the real impedance of the tapered opening, and the end area Smk
(nose area). If the horn is short, or if a lot of energy is left behind in the wave front
before it reaches the nose area in the K-coupler, a lot of reflections take place.

This is well known to all of you. Some more information on the PS2000 speaker.

The mechanical resistance of the driver motor is 5.7 N*sec/m. The mechanical resistance of the driver
suspension losses is 1.6 N*sec/m. The mechanical resistance of the back chamber load (vol. = 5 liters)
on the speaker is 1.65 N*sec/m.

Those resistances determine the SPL together with the real mechanical impedance of the throat.

The optimal (horn) throat area for max. efficiency of the system is 85 cm^2 [13 in^2] which
would give a max. SPL 1W/1m close to 107 dB. The actual PS2000 St is 4 times larger, lowering the SPL.

Based on well known horn equations I estimated the complex input impedance of the above horn.
Then I applied the Poppe equations (which also are the well known horn equations if there
is no loss through the tapered opening), but adjusted for loss - and this is where the transmission
line theory comes in handy - , and from that I also estimated the throat complex impedance of the PS2000.

I had at this point to assume that the K-coupler was a tube
(I have not worked out the clam design yet - so it is a first approximation).

It should also be noted that the PS2000 K-coupler is very short. For all energy to emit through
the tapered opening the length should be about 90 cm [34 in] for that specific taper rate,
so one would expect a lot of reflections.

I found the k_coupler acoustical characteristic capacitance to be Co=9.9*10-^8 m^5/N
and inductance Lo=6.6 N*s^2/m^5.

Due to the tilt of the panel (and square form) Co would decrease and Lo would increase compared
to the tube form assumed. The overall effect would be a relative increase in
throat impedance in the clam type box compared to a tube. At the same time more energy would be forced
out through the tapered opening.

The resulting SPL for the horn as well as the PS2000 was about 103-105 dB.

The cut-off for the horn was the assumed 116 Hz, however, the cut-off for the K-coupler
was - as expected - shifted upwards to about 200 Hz.

I clearly found a broad lower K-coupler resonance centered about 400 Hz (100 Hz above measured,
first approximation) and the upper peaks and dips. Also the plots did not show the on-axis response
below the cut-off where the speaker may behave more like a closed box design.

In conclusion: Yes, the PS2000 K-coupler has some significant horn characteristics,
and no, it is not optimized.

We only begin to understand the theory, however, we have some rough models to play around with.

I may have made a lot of errors! However, I have scanned the plots and will send them together
with the contour plot to anybody interested (Fred and Carl have asked).

I think can get them through the (local) fire-wall by know.

Take care! Lars"

K-patent holder Alan Weiss "Rocket" speaker

an ~copy loaded with Sammi 8" wideband - it could play louder than this video - I didn't have the gain that day to crank it - up close mine sounded rather echoey - but back a bit and it rocked as a noisemaker

Karlson Evangelist