Analysis of Klipschorn and La Scala cabinets with several drivers

[Edgar]

....doesn't decreasing the cross-sectional area increase velocity related distortions?

In applications such as ports on vented boxes, yes. In horns, I think that the predominant problem with small throats is "horn throat distortion", which is related to nonlinearity of air at high pressure. While that can be a problem at the high SPLs used in sound reinforcement, for home use I doubt it.

Klipsch and company seem pretty adament about using rubber throats in all their horns. I can't tell if it's for decreasing throat overload, and/or controlling HF polars, or maybe something else?

Yes, even Roy has said that PWK was quite fond of rubber throats ... though for the life of me I have never been able to figure out why.

Greg

[Edgar]

Here are the best five performers that I was able to find, out of dozens that I tried. Parameters as indicated in the lower right corner of each plot. In each case the K33E in the stock horn is shown in gray for comparison.


The absolute best of the lot is the Altec 515-8GHP, but I wasn't even going to include it because I thought that it was unavailable. But this morning I was browsing the Great Plains Audio site and discovered that they're now making them again!


The BD-15 is within about 1 dB of the 515, but is quite expensive.


As far as I can tell, the B&C 15PE40 is not available in North America.


I don't know about availability of the Ciare 15NdW1.


The EV DL15X should be readily available. If not, the DL15ST is essentially identical.


Greg

[hulkss]

Here are the best five performers that I was able to find, out of dozens that I tried. Parameters as indicated in the lower right corner of each plot. In each case the K33E in the stock horn is shown in gray for comparison.

The absolute best of the lot is the Altec 515-8GHP, but I wasn't even going to include it because I thought that it was unavailable. But this morning I was browsing the Great Plains Audio site and discovered that they're now making them again!

The BD-15 is within about 1 dB of the 515, but is quite expensive.

As far as I can tell, the B&C 15PE40 is not available in North America.

I don't know about availability of the Ciare 15NdW1.

The EV DL15X should be readily available. If not, the DL15ST is essentially identical.

Greg

The Altec is a 16 inch driver and is too big and does not fit.

The BD-15 is only available from one source in the Netherlands and is very expensive.

I am now listening to the Ciare 15.64NdW1. It mounts identically to the K33E and bolts right in to a La Scala II cabinet. I did have to open up the access hole a tiny bit to get it in. You can see in the photo where I filed on the opening. It is availabe here for $158. Ciare at Assistance Audio.

[Edgar]

The Altec is a 16 inch driver and is too big and does not fit.

It looks like it will fit in the KHorn woofer chamber. However, I currently have neither a KHorn nor a 515 with which to check.

Greg

[PrestonTom]

Edgar, Thanks for measuring and posting these items.

I have done something similar for the bass bin outlined in the JAES, 2000 article (which later became the Jubilee bass bin). I am confused about something however. When I plotted the cross-sectional area as a function of distance (the expansion) and also plotted the appropriate exponential functions, the "rubber throat" was clearly evident. The initial section (first 20 cm) had a cross section that jumped from 0.029 cm2 (at the throat) to a factor about double in that distance. IOW a flare rate of nearly 100 Hz (as described in the paper).

I do not see that rapid flare in your graph for the Klipschorn. I thought the Klipschorn also had a comparable rapid flare in the initial section.

Regarding the other question: Yes, I also believe the rubber throat was to minimize the 2nd harmonic distortion that is created when the relatively small volume of air (near the throat) does not symmetrically oscillate in pressure variation. Others have suggested the rubber throat is a way to cheat and shorten the "necessary" length of the horn. However, when you look at the exponential (at 38 or 40 Hz flare) next to the measured values (with the rubber throat), the length really has not been shortened.

Again, thanks for your efforts on this,

-Tom

[Edgar]

I do not see that rapid flare in your graph for the Klipschorn. I thought the Klipschorn also had a comparable rapid flare in the initial section.

There are a couple of possible explanations.

- First, I didn't measure a Klipschorn; I measured a Speakerlab K from a set of 1980 plans that I have. It is possible that the Speakerlab was not a completely accurate copy of the KHorn. It is also possible that the KHorn internal design changed with time. Or it is possible that the KHorn didn't actually use a rubber throat.

- Second, in the KHorn (Speakerlab K), the woofer opening is 39in², but that dumps directly into a horn whose throat is 78in². Perhaps that is what someone has called a rubber throat?

Greg

[dBspl]

The original Klipschorn had a woofer baffle opening of roughly 6" X 12". The baffle opening was cut in half at some point (probably in the 50's) to improve the upper frequency response of the bass horn.

I believe the first horn section in the Klipschorn (between the baffle opening and the first bend) does flare faster than the last two sections, but I can't be sure. My understanding of the purpose of a "rubber throat" was to control the horn resistance in a way such that it results in a flatter passband repsonse, but I've never seen any experimental evidence to suggests that it actually works.

dbspl

[andrea]

Excuse me

Why the hornresp parameters of pag 1 and 2 for k-horn are differents (see for ex Vtc)?

thanks

[drboar]

Modeling vs measurement.

I have a horn similar to the LS and to my surprise the low pass is way higher than calculated byt the mass rolloff.

See my blogg at "http://drboar.blogspot.se/"

Do note that a classical horn driver like the Beyma falls below 100 Hz using "worse" drivers with lower Fr and higher Q gives more bass output but also a hump at the high pass band

Corner reflectors:

I added both corner reflectors as well as a reflector in front of the driver. Attached by double sided tape

I tried no 1. No reflector 2. Just in front of driver 3. Just corner reflectors 4. Both infront and corner

I expected the effect to be additative 1 worst 2&3 better and 4. Best. Not so, it varied with the driver what combinations that worked best!

[moray james]

Don't know if you noticed that this is an old but good thread> I am sure there are others who are interested in your findings though. I expect that with folded hors as with straight horn that reflections from inside the horn as well as from the horn mouth have a significant impact. i have been experimenting of late with blocking reflections frome getting to the diaphragmand with very good results. I look forward to reading your future post. Welcome to a great forum. Best regards Moray James.

[drboar]

I realised if I do the talk I better walk as well[H]

This is the setup with the horn set against a back wall. XTZ Room Analyser II connected to my macbook (with WinXP in Bootcamp). Microphone is center line about 70 cm in front of horn opening.

The driver in the back is the Beyma G320 (Fr= 52 Hz and Qes= 0.2) built to be a horn driver. The other is a Fane Crescendo 80W Silmilar Fr but a Qes of about 0.5

Starting with the Beyma horn driver With no reflector(green) and then adding the bisector in front of the driver (blue),not much happens below 1 kHz

Adding corner reflectos add some dB jsute below 1 kHz and a huge bump around 2 kHz

Adding both the bisecting reflector and the corner reflectors, brings us back at square one!

Here we have the impedance plot Dayton Woofer Tester 3. System resonance at 77 Hz and medium Q value of 0.8 Note the gently sloping response below 200 Hz

Turning to the Fane driver with a higher Q adding a bisector. Note the hump in the bass just above the HP. Here there is about 4 dB added both at 400 and 900 Hz by the reflectors

Then adding both (I missed measuring just the corner reflector) Either some few dB added 200-800 Hz by te reflectors (blue) or back to square one

Impedance plot show a Fr 10 Hz lower and higher Q of 1.4

Tossing in a Vintage driver with a Fr of 30 Hz Qes of 0.4 and Vas of 300 Liters! The setup is different the green line is tha Beyma and the green is the vintage driver that is a theoretical mass rollof of 150 Hz but a practial one is this case of 1200 Hz

The images are cropped for some reason.

The system with this driver has a Fr of 67 Hz and a Q of 1.4 suggesting having a low Fr higher Q driver might be better than adding ports and stuff. I also note that Klipsh original driver is far from the classical horn driver of say 50 Hz an a Qes of 0.2

[moray james]

Have you tried a driver with similar values as the old original K33 or enc=en the current K33? P>W>K> spent decades fine tuning the LaScala to work with the K33 and he was a very clever man. Those values might be a good place to start. I understand an Altec 515 also works very well in this horn. Looking forward to future posts. Best regards Moray James.

[djk]

"P>W>K> spent decades fine tuning the LaScala to work with the
K33 and he was a very clever man. Those values might be a good place to
start. I understand an Altec 515 also works very well in this horn."

LOL.

What constituted a K33 changed with the phases of the moon (almost).

90% of the performance is the horn, not the driver.

I'd like to see you get a 515 into a LaScala, 16" in 1978 (and later), 15-5/16 before that (but the original 515B only 35W rated and 16Ω), LaScala motor board only 15-1/4" wide.

[moray james]

A bud simulated the driver and I was thinking about putting them in my Peavey FH-1 lots of room there, the two designs have similar volume dog houses.. I never looked that hard at the LaScala internal though I know it is narrow and that some drivers have to ground to fit in. I don't have one here and like the build of the Peavey. Still the LaScala manages to do very well no matter how you look at it Klipsch did a good job on it. Lots of little unsaid ideas there I imagine. Did you ever learn wht that little 3'4" step is just before the sides of the dog house meet the two parallel sections you know the lip you wondered why they left there like that? Was there ever any recorded discussions by Paul about that? I have not found any maybe someone has a copy of something somewhere.

I appologize for my mistake I have some LD's and it can be a task to stay on top of them sometimes more so then others and I am glad that you caught it but it is just a simple mistake and thanks to you that you caught it saving some poor guy who might have taken my say so and bought a pair of 515 Altec's. I am not good with numbers Dennis and details often slip past and I don't notice. I do make an effort but I don't have your ability for fine detail conbined with a fantastic memory and I do appreciate the task that you have so generously taken on fixing mistakes made by people like me. I don't think in details I see pictures for the most part it's hard to explain. I imagine your efforts go thankless for most of the time. For audio details you are more reliable than the wikipedia and you are a great resource and one of the reasons this is such a great forum and I know that you do the same job at a lot of other forums.So thank you for that. I will continue to do my best but I can't do it like you do so thanks again. Best regards Moray James.

[Guest " "]

Sometimes when we don't know something can't be done, we screw up and accomplish it. Once you router out the lascala motor board, you can get a very large horn in there.