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Old 22nd March 2012, 04:21 PM   #1
Simon B is offline Simon B  United Kingdom
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Default Horn loaded reflex guitar speaker box

Is anyone on here familiar with the design of guitar speaker whose cross-section is shown here?

Image1.gif


I built one of these a long time ago, following a design in "Sounds" weekly music paper, published in the UK, sometime roughly around 1977 to 1979.

As the diagram shows, the front of the speaker is open, and the rear works into a compression chamber that vents into a constant width, increasing height horn.

I don't have the speaker or the original article now, but it worked very well indeed, great tone and very efficient. Any information gratefully received!

Rear loaded folded horn is another name that these things seem to go by.


Last edited by Simon B; 22nd March 2012 at 07:47 PM.
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Old 22nd March 2012, 07:42 PM   #2
Simon B is offline Simon B  United Kingdom
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Years later I had a West African Djembe drum, which reminded me of it in some ways. Wikipedia says this:

"The djembe can produce a wide variety of sounds, making it one of the most versatile drums. The drum is very loud, allowing it to be heard clearly as a solo instrument over a large percussion ensemble.
"

Which sounds just pretty much ideal for a guitar speaker too!

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Old 23rd March 2012, 01:06 PM   #3
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Nope, haven't seen one of those, but it looks plausible. Don't try to make it any smaller though, from my work with transmission lines, I think the horn length needs to be about 3 feet, minimum, for a guitar.

I think a Djembe is a bass reflex, or a box with transmission line. The taper isn't great enough to act as a horn. Cool drums, though.

Speaking of speakers and drums, check these out:
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Old 23rd March 2012, 06:08 PM   #4
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Music Man made 1x15, 2x12 and 1x18 cabinets like that in the late 70's. JBL also made a large "Scoop" cabinet with 2x15. There is usually a null somewhere in the upper bass region where direct radiation is canceled by port radiation.
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Old 23rd March 2012, 06:32 PM   #5
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Sunn also made cabinet of such of a design.
The Sunn 215.
I was just digging out My old guitar rig and I am starting to get it back together with some new drivers.

Right now I have some old Altec Lansing's in the 215 and I used to have some 400/800 watt MCM Select's in it.

I have a set of some Pyle PPA10's that I will be installing in the 610.



jer
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Old 24th March 2012, 12:44 AM   #6
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Cool, Gerald, any idea how old the top cabinet is?
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Old 24th March 2012, 01:08 AM   #7
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That's gotta be a pre mid-69 2000S cab on the bottom. A little different from what the OP posted because the port doesn't flare at the face. Sunn gave up on that design around 72 and made cabs with the flare like the OPs diagram. The 6x10 is probably mid 70's vintage.
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Old 24th March 2012, 01:58 AM   #8
Simon B is offline Simon B  United Kingdom
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Hi, and thanks for all of your responses so far, certainly helping my thinking about this, it's been a long time since I designed any speakers, and I built this one with with just about no knowledge at all of how it was really working.

Keriwena, point taken about the djembe. I also once had a "goblet drum" where the tube was a completely straight cylinder, no flare at all. The sound was quite different, a more rigidly defined resonance I thought, at the time. Of course there were other differences between the two.

My knowledge of acoustics is still pretty ropey really, wasted too much time on this electrickery stuff. I do understand the idea of a ported reflex or acoustic guitar body as consisting of box with compliance (electrical analogue capacitor), then port/hole with inertance (electrical analogue inductor).

Could you give me any pointers towards likely areas of study to understand more of what happens as the port changes from a straight constant section tube, to one dimensional linear taper (like my speaker diagram ie area increasing linearly along length
), to two dimensional or conical taper, and on towards a "true" horn?

I'm definitely not ready for boundary element methods yet, and in any case I suspect that that would give me numbers without much understanding.

Loudthump, interesting what you were saying about there often being a null somewhere in the upper bass, from what I remember of the sound of my cab that might well have been going on, it definitely got a thunder and lightning sort of sound.


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Old 24th March 2012, 10:51 AM   #9
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On the one hand, since commercial cabinets are seldom "designed", and are mostly "the smallest box we could fit all the speakers in", it's not that hard to DIY 'better' enclosures.

On the other hand, the Thiele/Small stuff and all the programs based on it don't take into account two features of guitar cabinets that don't apply to hifi cabs - the speakers and cabinets are non-linear. That is, the T/S parameters of the speakers change when you crank them to levels that will compete with a drummer, and the cabinets themselves become "translucent". That is, they leak a lot of sound through the walls, no matter how thick you make them. Well, within reason... I suppose you could use cinderblocks, but then you'd need a forklift instead of a hand truck to load in at a gig.

Still, the basic math applies, it's just you can't take the calculated sizes as gospel. It does help, though, to know if you should make the box bigger, longer, or make the port smaller. I find Augspurger's TLwrx easy to use, and playing with it will answer your questions about taper, etc, rather neatly.

Other toys you might want include PE's WT3 to measure the T/S parameters, something like HOLMimpulse to measure the finished speakers, and an SM57 - not a typical test mic, but it won't cry when you crank your amp.
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Old 24th March 2012, 03:02 PM   #10
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I am not sure of the date on the 610.
So I will look and see if I can find the markings.
I am guessing around 70 or so maybe.
I got it in 76 when I was just 13 with the Concert Lead Head.
I think the amp head had a date of 72.
I paid $400 for it used back then and I think I paid $200 for the 215 with the Anvil Road Case with no drivers.
I still have the original Speaker frames for the 610 but the magnets are much too weak to invest in a re-coning job.
I have re-coned those things three time already.
Sadly that head is long gone, But I do have two Concert Slave amps that I normally run on the stack.
The 215 cabinet if I remember correctly has a date of 68 I have only been inside of it like 3 or for times since I got it.

I think Acoustic used a similar style of design as well.
I have only experienced two of those systems so far.
One was a guitar rig that I played on one night when they had just come out,again I was just 14!! he,he,he
And the other one was used by the bass player in Yasgar's down in Florida when I did the sound for them.


jer

Last edited by geraldfryjr; 24th March 2012 at 03:13 PM.
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