Fill of the voids in the Khorn

[Wrench722]

On all my plans and some have it cut out and some don't? So witch way is the best way? Look at this Pic it show it cut out.

[colterphoto1]

Interesting topic in this thread. In what way would the performance of the Khorn be enhanced by this additional volume in the rear chamber of the K33?

M

I was going to ask you now that you work in tech support(?)

jw

I don't think we should endorse modifications of PWK's designs.

EDIT- that being said, I agree with what John has said about stuffing any of the woofer chambers, including the 'discovered' cavities. Adding stuffing of any significant amount will change the 'apparent' volume of the chamber to the woofer by the factors he mentioned. This is done frequently in Acoustic Suspension cabinet designs.

So I'd leave it unfilled. Insofar as building a new Klipschorn, I'd build it like PWK would, utilizing the additional chambers exactly as he did. Thumping as a test for cabinet resonance is not really a valid way of discovering sympathetic vibrations within the cabinet anyway. No woofer will hit the walls as hard as your knuckles. Those myriad small chambers of trapezoidal shape and braced as they are should not add any appreciable coloration to the reproduction of music.

Shinall or any other manufacturers or any other drawings do not reflect the Klipschorn end engineering or design. If you want Klipschorn, stick to the original. Accept no substitutes.

END EDIT.

[Wrench722]

Well this is not Pic I was going to use. But this is a pic of Shinall. But the way Klipsch does it they dont cut the corner off??

[Wrench722]

So what is the best way? What is the pro's and con's for both way?[8-)]

[John Warren]

The Klipsch factory units DO have the corners cut and anyone with a factory unit can see it (see Rick's post above) by simply removing the woofer access plate and looking down at them. The volume contained in the ski-slopes is added to the total volume behind the cone. Over the years, this has been a revelation for many (many) DIY builders.

There was a factory pic of a partially assembled Klipschorn bass unit posted some time back (from one of the plant tours). It clearly shows the corners cut. I have it somewhere, I'll post it later.

What is the best way? The volume behind the cone is important and determines the efficiency of the horn near Fc thus duplicating the factory design will provide a similar response near Fc. So if you define "best way" as duplicating the original, you have your answer, no?

[Erland]

I think this is the picture you are refering to?

[Deang]

looks like Shinall uses 3/4" plywood in those areas where I believe Klipsch uses 1/2". Maybe it's just an optical delusion.

[Wrench722]

No it is not a optical delusion. He use 3/4 on the whole thing. Makes for a very heavy unit.

The pic I was trying to put up is the one where Paul is standing beside a plexie glass Klipschorn.

[DizRotus]

Despite having owned 4 Speakerlab Ks in the 70s, I don't know if the back chamber vented into the ski slopes. Does anyone know for certain?

[John Warren]

looks like Shinall uses 3/4" plywood in those areas where I believe Klipsch uses 1/2". Maybe it's just an optical delusion.

Klipsch uses 3/4" on the two large panels that make up the "V" opposite the baffle. These panels resonate if made from 1/2" stock. The front face of the horn is also 3/4". I have 4 bass units and the stock is good quality multi-ply birch.

[WMcD]

I've said most of the below in one place or another.

There is the photo of PWK with the Plexiglass unit. He is wearing socks and sandals. Goodness. The Plexiglass unit does have the notch cut out. So the prisms or ski ramps are part of the back chamber.

The SpeakerLab plans I have show the notch on drawings and a comment to not make it. They don't explain why.

We'll have to look at the EV plans but I believe they too have the notch.

I do think that reactance annunlling is being focused on too much. One reason is that these finite length horns have both mass and capacitive effects. I.e. going plus and minus j. Granted the plus j is pretty high. This is to say things are by no means like finite length horns.

I seems pretty clear to me that PWK was concerned with squeezing out all the bass below Fc as possible. That means getting system resonance down to 35 Hz or so. The lower the better regardless of classical reactance annulling.

Gil

[Wrench722]

The Pic that I have he is in a suit and the speaker has the notches?

[ZAKO]

McDermott.......At that time Paul was trying to get system resonence below 30hz

[Wrench722]

Let see if I can post the Pic again.

You'r right he is in sox and sandals

[TRiv]

I've said most of the below in one place or another.

There is the photo of PWK with the Plexiglass unit. He is wearing socks and sandals. Goodness. The Plexiglass unit does have the notch cut out. So the prisms or ski ramps are part of the back chamber.

The SpeakerLab plans I have show the notch on drawings and a comment to not make it. They don't explain why.

We'll have to look at the EV plans but I believe they too have the notch.

I do think that reactance annunlling is being focused on too much. One reason is that these finite length horns have both mass and capacitive effects. I.e. going plus and minus j. Granted the plus j is pretty high. This is to say things are by no means like finite length horns.

I seems pretty clear to me that PWK was concerned with squeezing out all the bass below Fc as possible. That means getting system resonance down to 35 Hz or so. The lower the better regardless of classical reactance annulling.

Gil

I have a pair of Speakerlab bins that don't have the notches, and have a way to modify them to add the path to the sky slope area, a bit of a job ( they are not finished off yet) but do-able, question, will the extra volume be worth the effort in audible performance or by measuring with instrumentation only? I am using K33-P's and BEC type A crossovers, and do listen to some pipe organ stuff, maybe I'll mod one and compare to the other, though that is subjective to opinion and guess.

[WMcD]

I guess that question goes to me.

I built my bass units based on the SpeakerLab plans, but 3/4 inch ply. I did not make the notch.

My reason was the thought that the back chamber has to have a good air tight seal. Getting those two pieces made (cut) for what I call the prisms was a real bear. I was using a circular saw with the help of a guide. So it seemed wiser to not take a chance that I'd wind up with a leak because of poor cutting. I created a lot of scrap in the effort.

I might have been too cautious. Newer glues do fill a gap and you can get to the horn side of the prisms to caulk things off. This at least before you put on the tail board.

On the other hand, it is like you say, in my view. The prisms make a very small contribution to the overall volume in cubic inches. It may be a matter of squeezing out a few Hertz in the system resonance. That results in a small measurable improvement.

= = =

It looks to me that PWK at the time (late '40s) was in a 'war' of sorts with a builder of a scaled up version of the K-horn made by a fan which would have a lower Fc than the standard K-horn. The battle ground was around 32 Hertz and the note of lowest C on the organ which is around that.

Now you'd think that bigger is better. Somewhat like the Patrician (bigger EV K-horn) seems like it would win any such contest.

However, performance below Fc seems to rely mostly upon getting system resonance as low as possible, and indeed less than Fc of the horn. This requires a driver with low resonance (hence efforts to make the suspension as less springy as possible) and the biggest back chamber possible (which reduces acoustic spring).

Maron points this out about resonance. BTW, there is mention of St. Louis in old publications. Is that Maron? I'd like to think so.

- - -

If you look at the Klipsch papers, PWK had one about computing the resistance of a finite horn below Fc. There is some resistance which is small and dropping below Fc. This means that if the driver has output, the horn throat will absorb it and transmit it down the horn. Of course it is not like the very influential throat load well above Fc, but it is there.

Generally, driver excursion is max at resonance (a sealed box increases it) and drops off very quickly below. This is much of speaker bass design. In any case this must have been why PWK wanted to get resonance as low as possible. If you look at the Audio magazine review, resonance is about 35 Hz and output in a good room goes to 32 Hz.

As Mike B says, it is all about compromise. You get a bump up at system resonance. But if you go too low, there is not enough throat load to make it work. I suppose PWK had to make some decisions.

Gil

[TRiv]

On the other hand, it is like you say, in my view. The prisms make a very small contribution to the overall volume in cubic inches. It may be a matter of squeezing out a few Hertz in the system resonance. That results in a small measurable improvement.

However, performance below Fc seems to rely mostly upon getting system resonance as low as possible, and indeed less than Fc of the horn. This requires a driver with low resonance (hence efforts to make the suspension as less springy as possible) and the biggest back chamber possible (which reduces acoustic spring).

Actually, the prisms "could" be a substantial increase in total chamber volume (at least compared to the main chamber) only guessing, not doing the math, about 3/4 cubic foot each prism, the problem I see after looking at the cutaways awhile is the notches or 45 degree cuts only provide (two to each prism) provide, at best a 1 1/2 inch square opening to each prism. In pnuematics or hydraulics this would be an orifice, and flow would be restricted quit a bit, in this situation, actually, a pressure differential between main chamber and prism chambers, and it's hard to imagine seeing much "spring" effect from main chamber volume to the prisms through a 1 1/2 inch square hole, unlike the added volume on the sides of the Khorn interior which have large passages.

I don't mean to debate the design, it is a clever attempt to add chamber volume using the available space of the original Khorn, and maybe it helps somewhat, but is that audibly noticable? I am going to leave my bins alone for now, "sound" great to me as is, a bit of work for unknown performance increase, unless someone can convince me otherwise.

PWK obviosly had the back chamber volume needed calculated for desired system resonance and used the only available space to come closer to it without adding to the cabinet elsewhere, is that volume known? and what about the volume of the Khorn chamber as is? Must have been some math to figure the existing volume unless doing it like automotive engine head combustion chamber volume, fill it up (cc-ing)with liquid and measure amount needed to fill the cavity.

[John Warren]

This may give some idea as to the effect of the rear chamber volume on horn response. The predictions below represent the K33E driver loaded in a low frequency horn per Keele's lumped electrical equivalent circuit. The model assumes that the horn is straight and has an Fc of 35Hz. The red curve is with a rear chamber that is equal to the volume required for reactance annulling, the other two curves represent reductions in this volume. The horn front chamber is the cone volume.

As shown in the graph, the system resonance increases as the rear chamber gets smaller, thus bass performance should be reduced.

[grindstone]

Took a hack at modeling some of this today. Whole shot with notches is around 97L if I didn't screw-up. Less the ski slopes the total is around 82L. 61L or so for only the backchamber. No driver volume subtracted from any of this, BTW.

Edited December 15, 2013 by grindstone

[NBPK402]

deleted

Edited December 15, 2013 by ellisr63