very lage folded horn

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If you start with an 18" driver you've limited yourself to how much pressure you can develop. Sd, and thus Vd, can be equaled or exceeded by numerous smaller and probably cheaper drivers. The main consideration for efficiency is how high a compression ratio you can develop. If you can get 2:1 on an 18 without ripping the cone, you're doing good. Small 8" drivers you might go as high as 6.5:1.

A horn is an acoustical transformer exchanging pressure at the cone for volumetric displacement at the mouth.
 
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no prob.. Other types of 18" horns like the CerwinVega aren't really horns when you examine them. There's a point as you sweep down where the horn essentially disappears and all that's left is a sealed box (Vrc) which is mainly what the CV 18" horn is. I think of that just as a sealed box and made in a horn shape for marketing reasons. Ok, 120 Hz is nice and efficient probably around 106, but 30Hz is still at 91.. That's a good mid-bass, not really an efficient sub.

To get some true horn loading down to 20Hz requires a path length of around 6 meters. Mouth circumference would also need to be around 6 meters as well.

This is the part in the conversation where the compromising begins due to reality crashing in on us.

Can we assume the four cabinets you mentioned in the other thread? Can we assume these will be used outdoors in full 1/2 space (on the ground with no boundary reinforcement)? Will this be placed as a horizontal stack under a stage? By a 20Hz response, do you want it flat to 20, or some semblance of usable output there instead? 140db(SPL) @ 1M is most likely not possible given the dimensions you have... but are those dimension for one of the four cabs, or is that total space for all four?
 
Size 48D X 65H X 30 D

Total volume of that is 1,533 liters, btw, which is nice and big. A proper tapped horn for your driver appears to achieve 125dB at 20Hz. It is excursion limited @ 26Hz to 63Vrms of drive which equates to 500W. Four cabs would get you to 137dB.

The only downside to this sim that I see is the compression ratio at 3.6:1 which I don't know if it is too high or not.
 

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Here's what I get for an exponential horn (corner loaded) with:

throat area = 279 cm^2 (43 square inches)
mouth area = 4500 cm^2 (5 square feet)
length = 6m (20 feet)
back chamber = 216L (8 cubic feet)

Looks good without the back chamber, too (second pic).
Better cooling vs a bit more displacement below about 15 hz and some cancellation / interference.

edit: Oops, sorry, ignore red and blue - I forgot to erase them on second pic.
 

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well you should also consider portability, beasts as big as those will require some hands to carry them around :)
what is the rest of the soundsystem supposed to be? these ciares arent very sensitive and with an Fs od 36 Hz I doubt they would produce significant output below that anyway ...
 
i will be using it outdoor

Trying to generate 20hz outside is a great way to blow up a speaker I'm afraid. Even the labhorns were limited to about 30hz, and that was a VERY sophisticated design.

I'm not saying it can't be done, but it requires a LOT of excursion.

Remember, a horn behaves like a sealed box *below* it's cutoff. So pouring power into the horn to get it to play 20hz makes the driver go *pop*

If I were going to generate 20hz outdoors I would personally use a huge array of sealed or vented boxes. And when I mean huge, I mean a minimum of eight fifteens, and thirty two would be even better.

P Audio 15-inch subwoofer speakers and replacement subwoofers
The SN15B is nice, and it's on sale for $99

I've built a LOT of horns and tapped horns, and I don't even bother trying to get real output below 30hz. I know that it's nice to have a sub that gets down to 15-20hz, but the size of the sub gets goofy when it's any kind of a horn.

If you want to have your cake and eat it too, you might consider both. Use an array of sealed boxes for infrabass, and bass horns for 30-120hz. High pass the horns so you don't fry your woofers, then run the sealed boxes at reduced volume to add some "weight" to the presentation.

At very low frequencies it's easy to mix front loaded horns and sealed boxes, because front loaded horns BEHAVE like sealed boxes at very low frequencies.

 
This is the progression chart of my tapped horn. It assumes a 30" (29" internal) width. Use it to make a cut-out with graph paper and try making a fold for it.

Do you first cab in cheap 1/2" ply with plenty of bracing. Use a string for measuring path length to finalize your dimensions. Use screws through-out, but no glue. Use plumbers paste for fill so it can be taken apart should you want to modify the dimensions.
 

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I'm not saying it can't be done, but it requires a LOT of excursion.

Either excursion or loading from a very long and large cabinet. And hopefully with FLH he uses many boxes to get the mouth area up. I'm still assuming 1/2 space with no boundary effect.

Yup, kinda crazy, but about the only way, I feel, to explain this to him, is to follow what he requests to show him how impossible it is.
 
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Richard Long had a great 2 x 18 inch hyperbolic expansion folded bass horn called the Levan after Leroy Levan with influence from the early RCA theatre horn. The W bass box without the mouth expansion was called Bertha (the EAW BH 882 is fairly similar and they made some of Richard's cabinets including the bass horns at times). The drivers were custom made Emience's if I recall correctly (attempts to substitute " better " JBL , Celestion, etc drivers with incorrect driver parameters resulted in short driver life span - hours. The mouth of the standard 2 bend mouth version is 8 ft x 42 inches and I had 4 of the even larger 10 ft x 42 inch triple bend mouth versions double stacked for a 10 ft x 7 ft mouth - powered by crest 1800 watt mono blocks per side - band pass filtered at 20 and 100 hz. - as mentioned by Dave above you don 't want to drive a horn below it's bandpass nor above it's hf limit for a bass horn especially a hyperbolic - fastest expansion to a low cutoff F but also the quickest to generate hf distortion if you go too high. Not exactly portable unless you make the mouth seperatly and in 2 halfs that could bolt together on site
 
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Hi soundhead

That horn (in post 7) is a good match for the Ciare sw 18.
Response / efficiency should be excellent down to 30 hz, but dropping fast below that. (i.e. forget about 20hz) Do you really need to get to 20hz, though? What's it going to be used for? I think you mentioned using a bank of four outdoors?

btw: The back chamber wants to be about 2 cubic feet for this, which should actually make the woodwork easier - as far as I can make out, the plan calls for wasting some space, which may as well be put to good use.

I tried looking it up on tda-audio - PhotoFile.name / id: usr to get more details, but got lost - everything's in russian. Have you got a link to the page where you found this?

Cheers - Godfrey

edit: oops - missed a whole page of posts while I was simming and typing
 
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