Stacking horns

[rob]

Here's one for the PA guys out there!
I have some 10" Foster woofs with a fairly high Vas and low Fs, but low power handling capacity, and thought some rear loading may help. I've also got 50 x 4" mids and 30 small tweeters which were purchased with a line array in mind.
If I were to build say five pairs of small 3 way horns (1 x 10", 2 x 4", 3 x tweet) then stack them vertically a la line array, would the horn"s cut off frequency be determined by the overall horn dimensions (ie, five times taller than a single horn) or the individual dimensions of each horn?
If its the individual dimensions, is there a way of,say, adding some length to the horn(s) to combine the individual horn mouths into a single large mouth. For example, if I had the horn mouth to the side, I could corner place the stack, attach a vertical panel between the back of the stack and the side wall and fit a top panel, extending the length of the horn, making use of the side wall and firing into 1/8 space which reduces the required mouth area.
Comments?
Cheers,

rob

[Judd]

would the horn"s cut off frequency be determined by the overall horn dimensions (ie, five times taller than a single horn) or the individual dimensions of each horn?

Yes, the effective mouth would be the combined circumference.
You still need to have a length greater than 1/4 (some would say 1/2) wavelength of the lowest frequency you intend to use. Reactance nulling can extend the low frequency cutoff but this is at the expense of greater diaphragm displacement.

Look up McBean's horn calculator, i'm not sure if it will do back loaded horns though.

[Klaus Stock]

Here's one for the PA guys out there!

Well, since we live in the age of cheap amp power and high power/high efficiency drivers, PA bass horns aren't that popular any more. Since PA horns should be transportable, their dimensions and therefore their performance gains are rather limited. It is easily possible to achieve similar or better results with an array of small boxes ("small" compared to a horn, of course). And since we live in the age of cheap digital controllers, use of an array also allows for beam shaping.

The problem with high power high efficiency drivers in horns is the excursion limit. When operated at "nominal power", modern drivers will quickly rip their diaphragms apart.

Notable exceptions may be the EV MTL4 and the Intersonic BT-7, but both systems aren't really popular either. Both systems are rather compact....and expensive. However, they can't really be compared to the usual bass horns. The BT-7 uses a special driver (the servodrive, or "motor bass"). And the MTL4 isn't really a horn - the idea behind the design is to cram more drivers into the same space without getting array effects.

If its the individual dimensions, is there a way of,say, adding some length to the horn(s) to combine the individual horn mouths into a single large mouth.

As far as I understand, you wish to design something like the JBL 1530 (http://members.aol.com/xxbase80a/rutsche.1.15/box.html), operated sidewards? In that case, it is possible to simply eliminate the divinding walls between the indivdual boxes, like in the JBL 1520 (http://members.aol.com/xxbase80a/doppelrutsche.2.15/box.html).

However, even with the dividing wall removed, the box will still be quite heavy. Even in the case of the 1530, simple "lightweigt constructions" often rattle or resonate in an unwanted way. Making the construction wider and leaving out the walls between the individual sections makes the whole thing more floppy, requiring additional efforts to maintain it's stiffness. In other words, it's still quite an amount of wood and woodwork! You might end up finding out that it's cheaper to ditch/sell the Fostex drivers and invest into a more suitable driver for your needs, which will work in a "normal", much cheaper enclosure.

BTW,

Look up McBean's horn calculator, i'm not sure if it will do back loaded horns though.

that would be http://mywebsite.bigpond.com/dmcbean/.

Best regards, Klaus

[rob]

Hi and thanks for the replies.
The crux of the problem with these drivers is their low power handling (40W) and large Vas (6cu ft+). I placed one into a 3cu ft box in place of a 10" Vifa and it sounded OK so I figure its worth pursuing at some stage. It wasn't as loud as the Vifa and probably would benefit from an EBS alignment but excursion would be a problem then. So I got the idea for some small horn loaded boxes which may be suitable as HT satellites but could be stacked to form a larger, more efficient pair of fronts if so desired. Horn loading could improve the efficiency of a single 10" vs a pair of 4" mids and stacking to form a line would take care of power handling. Satellites would require a sub but the horn may suffuce (no I know it wouldn't be large enough for true "sub" unless I could utilise the corner an walls, perhaps).
Alternatively, I could sell them and have thought about going to the local speaker repair shop and offering up all my collected drivers. In that case "that would that" as I don't really need more speakers, I just have the drivers sitting there - you know the score. I also have a new job which gives me access to a proper table saw and a supply of used, largish lumps of mdf.
Anyway, the horn mouth looks promising and digital XO plus amps are getting cheaper all the time so better finish the house painting and kitchen reno...
rob

[bond09]

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