The Caves of Arne Saknussemm (A Journey to the Bass of the Earth)

[WMcD]

Thanks for the nice words Tom. I'm pleased to have a chance to talk about it.

Making up the story seemed to be far more work than construction. I'm sorry to not have done more these months.

Actually there was far less engineering in advance than you think.

One reason for using 15 inch drivers was that I had a lot of EVM-15s left over from the K-Horn and Bigger Belle project. I eventually replaced them in that project with a Pyramid. This was to get something a bit closer to the K-33. I intend doing some experimentation on the Fat Jubilees. Fatter in that they are 3 inches wider.

The second was that I didn't want to just make a Jubilee. Some variation was a target.

The third is that I wanted a more classic exponential horn without the rubber throat. I just wanted it that way.

Reading the AES Jubilee article, it appear to me that Paul and Roy were aiming for the same footprint and height as the K-Horn. It looked to me that the prototype used 15" and the same footprint. [Edit: Looking at the article drawings again it looks like they were 12 inchers in the original prototype.] Then they found the splayed mouths didn't focus the highs forward and went to the final form. The AES article says about as much.

It seems to me they realized that with the forward facing mouths there is a real problem with the doghouse and the interior ducts and keeping the footprint. There is no real choice but to use 12 inch drivers. And then you need a rapid flare which is the rubber throat. That is my guesswork. Roy may well step up and say it was part of the plan from the start. [Edit: Well, if the original prototype use 12 inchers, this argument doesn't quite make sense, but I do still suspect the rubber throat was something they were compelled to use.]

Re flare: This is a difficult subject. Paul and Roy's article has a table which winds up with a number based on throat and mouth and lenght at the end. That is one way of characterizing it. In the 1940 article on the rubber throat K-Horn it is described as a horn with a high Fc feeding a horn with a low Fc. At low frequencies the rapid flare small throat is not effective, at high frequencies the rapid flare and small throat is effective. Therefore the effective mouth size is different at different frequencies. It stretches. Hence the term rubber throat. This may help high frequencies.

Anyway . . .

I made up a spreadsheet with actual area of the Jubilee and mine - and also hyperbolic horns of varous T (?) and Fc. Then put them up on a spreadsheet graph. One can vary the parameters of the hyperbolic and play to see which hyperbolic graph most closely matches the as built units.

The rubber throat Slim Jubilee is tough to match along the entire length. I can't find that spreadsheet now. It may have been lost on a cranky floppy.

My Fat Jubilee is close to Fc of 29 Hz with slightly better than exponential flare. This would be close to all but the initial flare of the Slim Jubilee, too. Of course with finite lenght horns this is really not as much of a gauge of performance as you see on infinite lenght horns.

Back chamber. I did not do any formal study before. It is bigger because of the extra three inches of width.

Passband. I have a graph which I'm not sure of. It was done in a room. Generally, the system resonance is at 42 Hz which is the Fs of the EVM driver. Bass is good to about 35 Hz and up to 500 Hz. There are some peaks in the middle which may or may not be room effects. Stuffing with pillows had no effect.

The plan is to try other drivers are on hand but setting up controlled tests are a monumental project.

I'd like to include fiberglass stuffing just to be able to dismiss claims by others that fiberglass, or indeed stuffing, is a tweek. People with no technical training and no instruments always seem to pop up with the suggestion and then want someone else to prove they are wrong. Grr.

I've overall got the same problem PWK had. Finding a very low Fs driver and more back volume.

High Freq. Horn.

I have made some but they and the drivers need work. Another big project. My "source of income" work, and family, always get higher priority. And if the Professor and the crew are going to explain it, well, that is another part of the work. I enjoy it but it gives one respect for movie makers.

One alternate to the HF horn is to put some K-600s and tweeters in the mouth and preserve the clean prism shape of the unit.

Grills:

I made some grills and put on Klipsch black cloth. That was a real bear too. The cosmetics are tough.. I hope to show off all of this in the future.

- - -

As mentioned by me elsewhere, I enjoyed integrating old articles and basing the story a bit on Jules Verne, Journey to the Center of the Earth. We really are following the footsteps of Paul and Roy.

Best,

Gil

[jwc]

Gil. Thank you for updating this thread.

I wish you could explain how you figured an Fc of 29Hz. I would think the physical horn length would be about 150cm. I know it is an 1/8 space horn and the mouth is made up with the room but I still can't figure how you got to 29Hz. Also what is the throat of each driver? Slot cutout? I know you tapered some corners of the slot.....it must be a big slot.

Yes, it is tuff to find a driver with the low Fs and requiring a large Vb. It is interesting how the Pioneer drivers I find on Partsexpress have a low Fs and large VAS.....and maintaining a low Qts. It is hard to accept that you could imagine putting a Pioneer woofer in a horn cabinet but I have been surprised with the pair of their 12 inch woofers in my jub clone.

Anyway you could estimate the volume of the inner chamber? The Jub is 37 liter/driver. You think 42-43 liters?

You don't have any EVM-15B's you would like to load or sell do you? Are the T/S parameters available?

Thanks.

jc

[BEC]

jc,

Do you want to borrow a pair of K-31s?

Bob Crites

[jwc]

Yes Bob.

You have a PM coming.

[jwc]

Actually, I emailed you

[DrWho]

Passband. I have a graph which I'm not sure of. It was done in a room. Generally, the system resonance is at 42 Hz which is the Fs of the EVM driver. Bass is good to about 35 Hz and up to 500 Hz. There are some peaks in the middle which may or may not be room effects.

Would you be willing to share these graphs? Generally speaking, i wouldn't expect room induced peaks to be any greater than 3-5dB in magnitude. You can also verify if it is room induced by moving the mic around.

[WMcD]

Since Mike asked . . .

I fooled with my graph and the AES graph to line them up so the frequency ranges match.

It is somewhat good to see I can claim a favorable comparison. On the other hand, the testing conditions are not comparable.

I was a bit concerned that mine does not have the sustained treble output like Roy and Paul's. More later.

Gil

[jwc]

Gil,

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Was this a raw bass bin response?

Where is the mic?

Strange how that after 200Hz there is a dip then a consistent flat response out to 500Hz. I am assuming this was done a while ago. What are your thoughts on this. The only real difference I can see from your design is the increased width of the horn at the initial flare and an increase in chamber size too. I would assume the latter to be driver dependant.

Yes there is this splay angle difference toobut I wouldnt think this would play to much on your curve unless at 1 meter there may be a loss of coverage for the higher frequencies.

Now my bass bin DIY project has a dip a 200Hz but comes back up. Roy had some very interesting comments about this on page #17 on this thread:

http://forums.klipsch.com/forums/17/810222/ShowThread.aspx

Do you have two bass bins or one?

jc