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-   -   Horn grouping question. (http://www.diyaudio.com/forums/subwoofers/226401-horn-grouping-question.html)

dustman96 25th December 2012 05:48 PM

Horn grouping question.
 
So I am having trouble making heads or tails of horn grouping given the plethora of differing opinions on horn loading. From what it seems to me you can truncate the length and mouth size of a horn (while keeping the flare rate) and group the horns to the needed mouth size for a given frequency to get equivalent performance to a full size horn, of course assuming a similar acoustic loading environment. Am I missing something here? What am I not taking into consideration? Thanks all.

weltersys 25th December 2012 07:31 PM

You can use multiple horns to make up for mouth size, but path length determines Fc.
You can not truncate the length without raising the horn cutoff frequency.

more10 25th December 2012 07:47 PM

If you design a horn for corner use (0,5 pi), u can use two of these for wall placement (1 pi), four horns for floor placement (2 pi) and eight for suspended placement (4 pi).

David McBean 26th December 2012 06:18 AM

Quote:

Originally Posted by weltersys (Post 3298836)
You can not truncate the length without raising the horn cutoff frequency.

Hi Art,

Just to clarify - it is perhaps worth making the distinction between the actual theoretical flare cutoff frequency of a horn, and the resultant practical low frequency response rolloff.

Horn length can be truncated without raising the cutoff frequency provided that the flare rate remains unchanged. For example, the following three exponential horns have the same throat areas and flare rates but different lengths - in each case, the cutoff frequency stays constant at 100 hertz.

S1 = 10.00
S2 = 2397.32
L12 = 150.00
F12 = 100.00

S1 = 10.00
S2 = 385.91
L12 = 100.00
F12 = 100.00

S1 = 10.00
S2 = 62.12
L12 = 50.00
F12 = 100.00

In other words, to be strictly correct it is actually flare rate that determines the horn cutoff frequency, not length.

As the horn is shortened however, the increasing mismatch at the mouth causes the ripples in the throat acoustical impedance to become larger, and the shorter length means that the ripples will be further apart in frequency. Both these things conspire to make the resultant response roll off at a higher frequency, even though the theoretical cutoff frequency of the horn has not changed.

Kind regards,

David

dustman96 26th December 2012 03:06 PM

So... Theoretically, one would be able to group 6 horns with an L12 of 100 and S2 of 385 and get nearly the same effective mouth area and response as the longer, larger horn?

What got me thinking about all this was looking at Olson's paper that had response charts for different lengths of horns with the same flare cutoff and throat size and the responses were relatively similar, not taking into account the major impedance fluctuations presumably caused by small mouth sizes.

Thanks again David.

David McBean 27th December 2012 06:53 AM

1 Attachment(s)
Quote:

Originally Posted by dustman96 (Post 3299630)
So... Theoretically, one would be able to group 6 horns with an L12 of 100 and S2 of 385 and get nearly the same effective mouth area and response as the longer, larger horn?

Hi dustman96,

I'm not sure that your observation above is strictly correct, but it seems you may get reasonably close - the black trace in the attached chart shows the Hornresp predicted power response for six 100 cm horns connected in a 2S x 3P array radiating into 2Pi space. The gray trace shows the response for a single 150 cm horn radiating into 2Pi space.

Kind regards,

David

dustman96 27th December 2012 11:21 PM

Hey David,

Thanks for running that through Hornresp and sharing. Pretty interesting. I wonder if the slightly smaller mouth area of the 6 horns as opposed to the long one makes the difference. I bet in the real world the coupling wouldn't be perfect so response might suffer slightly. I don't want to ask too much of you but if you have the time would you mind throwing just a single foreshortened 100cm horn onto that graph as well?

I don't know about you, but I find horns fascinating!

Dusty

David McBean 28th December 2012 05:12 AM

1 Attachment(s)
Quote:

Originally Posted by dustman96 (Post 3301367)
would you mind throwing just a single foreshortened 100cm horn onto that graph as well?

Hi Dusty,

For you, just this once only :-). My very strong preference is for people to spend a little time learning how to use Hornresp so that they can try these things for themselves - it is by far the best way to learn, and to understand what is going on.

That said - the black trace in the attached chart shows the Hornresp predicted power response for a single 100 cm horn radiating into 2Pi space. The gray trace shows the response for a single 150 cm horn, also radiating into 2Pi space. As expected, the response of the 100 cm horn is more "peaky" than that of the 150 cm horn because of the smaller mouth size and the resultant poorer mouth acoustical loading. Even though both horns have the same flare rate, and hence the same theoretical cutoff frequency, the longer horn has slightly better low-frequency extension for the reasons outlined in my earlier post to Art (weltersys).

Kind regards,

David

djk 29th December 2012 02:48 PM

http://i56.photobucket.com/albums/g1...n510and511.jpg

head_unit 29th December 2012 03:55 PM

Quote:

Originally Posted by David McBean (Post 3301621)
...My very strong preference is for people to spend a little time learning how to use Hornresp so that they can try these things for themselves - it is by far the best way to learn, and to understand what is going on...

You are correct.

However, we don't all have Hornresp. And I'm sure a lot of others, like me, really don't have a need to mess with it.

Nevertheless, although I'm not building horns, I'm really curious to see this kind of stuff --> thanks for running the sims and posting them.


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