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Artichoke Horn
Artichoke Horn
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Old 27th October 2016, 08:54 AM   #1
hollowboy is offline hollowboy  Australia
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Default Artichoke Horn

This is a re-packaging of info from an old horn build - not mine. The original info is scattered across the High Efficiency Speaker Asylum, I'm just piling it into one place. The "Artichoke Horn" was Greg B's speaker at a late 90's Burning Man festival.

I saw a photo of this system years ago, and was quite intrigued. I recently realised that a horn of this scale would be a perfect fit for a shipping container, and would make a nice (giant) outdoor boombox. This got me intrigued all over again.

Dimensional info follows. These lists are direct quotations (apart from my text in brackets), and can be found with a search of the High Efficiency Speaker Asylum:
  • it was a 15' long straight bass horn
  • Think it was about 16-17 ft long including back chamber. I lost the plans.
  • 8x8' mouth
  • it is roughly exponential, or as close as possible given two days of labor and reasonably economical use of standard size plywood
  • it was theoretically a 30hz horn
  • I used ~1:1 compression ratio, including the vent area as part of the driver area
  • throat is ~ 16-17 in sq i think (which would be bigger)
  • Box was 6 cu ft with two 3" radius vents, IIRC

More comments made by the builder (Greg B), on the build / location / setting:
  • it started out as just a folded baffle to control directivity, and then we kind of got carried away
  • Built 4 or 5 years ago when I didn't really know what I was doing. Got lucky or had good instincts (that quotation is from 2003)
  • I have plans somewhere, I'm not quite as subjective as I seem to come across. Unfortunately, I have no idea where they are (so the previous comments were probably partially in jest)
  • Driven by a quite ordinary eminence Kappa15, with Altec horn for HF. Old phase linear 400 powered it. One channel for LF and one for HF
  • We actually were big enough geeks to bring a signal generator and SPL meter to the desert. I was wandering around checking out the festival when my friends were geeking out testing it though. They said audible response into the upper teens, I think the F3 was like 25 or something, but I don't remember really
  • sound quality was great. really loud and low distortion. made the ravers' rows of multiple 4 x 15 cabinets sound like mushy overpriced ghettoblasters
  • we went prepared to block the vents and adjust the comp chamber volume if needed, but it wasn't (from these last 3 points, the vent must have worked well, despite Greg B not being able to sim it)
  • this monster horn most definitely had directional bass. It could barely be heard from the back side
  • if you're going to the trouble of making a -straight- horn, I'd consider crossing it over higher (800?) rather than just using it as a sub. Half the fun is the midrange dynamics/impact
  • Early on [at Burning Man] there were lots of home made flamethrowers and buzzjet go carts, big nasty machines, drive-by Barney shooting range, fire everywhere on the burn night

The sim info is from Hornresp, using a ~1:1 throat and excluding the vent, otherwise driver and dimensions are as given above. I'm happy to patch up any errors or omissions that I am alerted to. Also: if someone can get the venting part to sim well, that'd be good.

Pictured: inputs, and output for the exponential horn.

I also pictured a sim based on two rough changes:

1) a conical approximation I came up with (literally my first attempt - there is no optimisation)
2) rear box reduced from 175 litres to 75 litres

...not to attempt to re-create the exact shape of the original, but to show that even with quite rough and ready changes from the 'perfect' horn, the difference in output is trifling. Even throat size (the confusing part of Greg B's info) is benign - when I tried doubling the throat on the conical horn, Hornresp shows a 1.5dB dip at 65Hz.

So to me, it looks great, particularly for a horn that can be put together in two days, in a desert.

For a similar (temporary / desert) build, the only improvement I can see as worthwhile (time : benefit) would be piling some weight, possibly sandbags, on top.

For a permanent build (shipping container), I'd make a few changes: beefier & heavier materials, I'd lengthen the horn slightly (adding LF extension and LF ripple), and I'd prop the container doors open as mouth extensions (reducing the ripple).

For bass-only use, I'd add a J shaped (90 degree bend) bend at the throat. A quad of opposed drivers would then mount into a separate box that simply dropped onto a throat plate. The driver box would essentially be a 'normal' PPSL enclosure rotated 90 degrees.

Note: am not about to build this. Just appreciative / speculative, at the moment.
Attached Images
File Type: jpg HR inputs.jpg (65.5 KB, 1356 views)
File Type: jpg HR output.jpg (59.5 KB, 1332 views)
File Type: jpg HR conical.jpg (38.6 KB, 1313 views)
File Type: jpg HR overlay.jpg (60.6 KB, 1309 views)
File Type: jpg notated artichoke.jpg (96.7 KB, 1343 views)
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Last edited by hollowboy; 27th October 2016 at 08:56 AM. Reason: One pic failed to 'go'
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Old 27th October 2016, 09:15 AM   #2
xrk971 is online now xrk971  United States
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Artichoke Horn
Did you say shipping container?

Matterhorn:

http://www.youtube.com/watch?v=o36Kp6veJ6c&sns=em
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Old 27th October 2016, 11:34 AM   #3
hollowboy is offline hollowboy  Australia
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I watched the Matterhorn video a few days ago. It is an interesting way to squeeze a lot of bass capability into a relatively compact space, but since it was built to satisfy an odd mix of requirements, it doesn't seem to have much to it that can be applied to a normal budget and application.

If I ever did anything of this sort, it would use about 2% of the Matterhorn's budget: a few drivers and many tons of enclosure, rather than the other way around.
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Old 27th October 2016, 02:48 PM   #4
Pano is offline Pano  United States
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Thanks for the info and the photo!
Interesting build, with it being sort of half a horn against the ground. FWIW, the famous W.E. 15A horn is 15 feet long, but curled up. The mouth is about 1/2 that size I think.

Wonder what it sounded like.
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Old 27th October 2016, 03:40 PM   #5
weltersys is offline weltersys  United States
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Quote:
Originally Posted by hollowboy View Post
1) If you're going to the trouble of making a -straight- horn, I'd consider crossing it over higher (800?) rather than just using it as a sub. Half the fun is the midrange dynamics/impact[/LIST]2)The sim info is from Hornresp, using a ~1:1 throat and excluding the vent, otherwise driver and dimensions are as given above. I'm happy to patch up any errors or omissions that I am alerted to.
3)Even throat size (the confusing part of Greg B's info) is benign - when I tried doubling the throat on the conical horn, Hornresp shows a 1.5dB dip at 65Hz.
4)So to me, it looks great, particularly for a horn that can be put together in two days, in a desert.
For a similar (temporary / desert) build, the only improvement I can see as worthwhile (time : benefit) would be piling some weight, possibly sandbags, on top.
1) True, but when you run a LF driver near or past Xmax (as we tend to do ;^) )it causes A.M. (amplitude modulation) distortion, which makes vocals sound like they are "gargeling". That said, if you don't push the driver too hard, it can sound fine, but the dispersion upwards of 400 Hz is quite narrow on a long exponential horn as described.
2) If the horn is to be used up to 800 Hz or so, the throat should be narrowed to around 6 inches wide for better dispersion and phase response, or better yet, use a phase plug as shown in the photos below. When building/testing the Kangaroo Horn in the parking lot of a big-box lumber store with a parking lot adjacent to the St.Paul motel I lived at, I asked an interested shopper to participate in an A/B test with or without the phase plug, the better clarity the phase plug provided was obvious to him. This type of phase plug is similar to the ones Dave Gunness designed for the 10" mids in the EV MT systems from the mid 1980s.
3) As usual, lower compression ratios reduce output.
4) Large horns can be built in sections in the relative comfort of one's shop, then assembled on site, either using screws, ratchet straps or clamps. Sand bags or fill to reduce cabinet vibrations works well, but is rather labor intensive.

Back in the 1980's I designed an efficient horn system similar to the one you describe, though smaller. By today's standards that system did not go very low, probably an Fc around 65 Hz. It was built on the Island of Tonga for a pop group The Jets, originally from there, who returned to play a free concert.
Hiring in a system would have been too expensive, as the nearest large sound system was in Australia at the time, so the Jets brought 8) EV 15B and 8)JBL 2460 HF drivers on fiberglass copies of McCaully 482 exponential horns, using two stereo amplifiers for the entire sound system. Total cost of the used drivers, HF horns, and local plywood was under $2000 USD for a system that covered Tonga's outdoor soccer stadium with better sound than the islanders had ever heard.
Greg Huber built the pair of huge 4x15" bass horn cabinets with local carpenters, when they fired them up with pink noise the local kids feared that the island kingdom's volcano was starting to erupt, and ran for cover.
The free concerts went well, filling the stadium many times over during multiple shows over several days, though it ultimately cost the Jets some $250,000 dollars between chartered airplane, import/export tariffs, etc.

Art
Attached Images
File Type: png Kangaroo Phase Plug.png (488.5 KB, 727 views)
File Type: png Kangaroo Phase plug driver side.png (157.2 KB, 360 views)

Last edited by weltersys; 27th October 2016 at 03:52 PM.
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Old 27th October 2016, 03:51 PM   #6
Pano is offline Pano  United States
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Tongans are big people, they deserve big speakers!

Thanks for the story, Art.
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Old 27th October 2016, 04:04 PM   #7
weltersys is offline weltersys  United States
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Quote:
Originally Posted by Pano View Post
Tongans are big people, they deserve big speakers!

Thanks for the story, Art.
You are welcome!

The father of the Jets, a very big Tongan who lifted weights equal or greater than his own, was once arrested and handcuffed behind his back for multiple parking violations. I don't think he read English, parking signs and meters were not "on his radar". He said to the police officer "cuffs hurt wrists, take off". The officer replied in the negative, so he broke the cuffs off and handed them to back to him. The officer did not attempt to put another pair back on for his ride in the back seat to the station.

Art
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Old 27th October 2016, 04:38 PM   #8
tb46 is offline tb46  United States
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Hi hollowboy,

Thanks for bringing this up, I have seen this picture off and on, and wondered about the context.

Did you try to draw the horn from the picture to arrive at the Hornresp data? Are there any other pictures, e.g.: an orthogonal side view?

Either way, looks like someone had fun.

Regards,

P.S.: Hi Art. You sure get around. :-)
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Old 27th October 2016, 08:25 PM   #9
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by hollowboy View Post
For a permanent build (shipping container), I'd make a few changes: beefier & heavier materials, I'd lengthen the horn slightly (adding LF extension and LF ripple), and I'd prop the container doors open as mouth extensions (reducing the ripple).
Deceiving.. a standard container has the length and the mouth size so that it won't need to be folded. Folding the horn and using the container walls was cursorily discussed in the other thread but unless (maybe) you cut open the side to use as the mouth and therefore won't need to build the open doors into an extension then this whole thing could be built into a fraction of the volume.
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Old 28th October 2016, 02:43 AM   #10
hollowboy is offline hollowboy  Australia
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Quote:
Originally Posted by weltersys View Post
1) True, but when you run a LF driver near or past Xmax (as we tend to do ;^) )it causes A.M. (amplitude modulation) distortion, which makes vocals sound like they are "gargeling". That said, if you don't push the driver too hard, it can sound fine, but the dispersion upwards of 400 Hz is quite narrow on a long exponential horn as described.
I haven't heard gargle in years, since I moved up from bookshelf speakers. But yes, I was thinking it would be one of two options-

Like the original: straight throat, large bandwidth, maybe 30-800Hz, ~110dB peaks

As a sub: two or four drivers, J-shape throat, maybe 20-100Hz, ~120dB peaks

Using a modular throat, one could try swapping between these options.

Quote:
Originally Posted by weltersys View Post
2) If the horn is to be used up to 800 Hz or so, the throat should be narrowed to around 6 inches wide for better dispersion and phase response, or better yet, use a phase plug as shown in the photos below.
Interesting. You mean a slot throat (6' wide, 15' high)?

Your axe-head shaped 'plug' looks like a do-able project (without getting fancy with CNC or casting). Would there be any negative to continuing that division for the first metre (or more) of the throat - like a multicell? I've long been curious about applying the multicell concept to a cone driver.

Quote:
Originally Posted by weltersys View Post
3) As usual, lower compression ratios reduce output.
Yea, but I was surprised by how little. The shonky model I tried (dodgy expansion, bigger throat, smaller rear chamber) was a 'torture test' to see how an imperfect horn might perform. The deficits of multiple compromises appear negligible - especially compared to the in-room bass variances of normal systems.

The horn as modelled is excursion limited, and excursion is only high at cutoff, so it appears that one could equalise a 1.5dB hole at 65Hz without any harm.

Quote:
Originally Posted by weltersys View Post
4) Large horns can be built in sections in the relative comfort of one's shop, then assembled on site, either using screws, ratchet straps or clamps. Sand bags or fill to reduce cabinet vibrations works well, but is rather labor intensive.
I had to look up ratchet straps. Cool.

If I ever made a project like this, the shipping container would be the workshop

The container would be primarily a tool shed and an anchor point for shade cloth (it gets pretty hot here). I'd cut a door into one side, so I could continue using it for storage; the horn would only use the front 1/3 of a full-sized shipping container.
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