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should I build this one?

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Category: Plans
Forum Name: New Projects Forum
Forum Description: Forum for new speakerplans projects, in memory of Tony Wilkes, 1953 - 2014
Printed Date: 29 February 2024 at 3:07pm
Software Version: Web Wiz Forums 12.06 -

Topic: should I build this one?
Posted By: _Natty_
Subject: should I build this one?
Date Posted: 03 September 2018 at 2:26pm

front loaded 1segment horn, for 150hz 1000hz use.

loaded with b&c 12mh32 (i will use 4 of them for each colum).

25kg each circa to be lift at 1,9mt circa....

Its my very first horn building so id like to understand howto not waste time,
these are the sims result:

Posted By: Keen
Date Posted: 03 September 2018 at 11:46pm
smaller rear chamber will smooth out response.

Also go into options and choose directivity plot to see on axis response. Changes quite a bit in good way, go 20 off axis

Posted By: fatfreddiescat
Date Posted: 04 September 2018 at 9:09am
Very similar to the TDA MT121 and half of the speakerplans MT122

Posted By: _Natty_
Date Posted: 04 September 2018 at 9:34am

you are right...the inspiration start from smtp tda version, but big moods on every part.

the question is for people that have build horns of this size, and if they found more problems than db or long trow....

Im afraid by the tiny troath, and if is good to put or not a one more expansion at 3/4 lenght of the horn path.. even im curios about the back chamber that is not so little but seems to have best result over this simulation!

Posted By: Keen
Date Posted: 05 September 2018 at 6:01am
can you show us the input data?

Posted By: _Natty_
Date Posted: 05 September 2018 at 11:00am
not so complicated

back chamber 22l circa
back panel 19 cm circa

s1 under 200sq cm
s2 around 1500sq cm circa
con 52cm circa

Posted By: Keen
Date Posted: 06 September 2018 at 7:27am
s1 200 is fine 

don't worry about the second expansion at 3/4 length. but give the mouth termination a lip 

Posted By: _Natty_
Date Posted: 06 September 2018 at 9:13am

what you mean by "but give the mouth termination a lip"

the horn lenght is based in:
-back chamber lenght + horn lenght < 75cm (is the es18bph lenght so to be fit best to stay under this lenght)

some one suggest me to give a second expansion at 3/4 of the horn lenght like you said, but to me there is no such help in the lower part of the response (under 400hz) that justify the big works to do a second expansion... the carpenter was very happy when I show him just a straight horn instead of many expansion style...
even to me expansion helps directivity that is not such needs for a horn like this one that is cutted at 1khz.

For s1 better result is under 200, from 80 to 170cm^2, so very small, and for that reason maybe design a troath reduction could be good... but I've no idea if I simply cover the mouth with planar reduction or a phase plug... where I can find some reads about that?

The s2 is designed like that because is the area of the back chamber too, so less wood, less problem to fit the horn in the box... and ive seen that again due the low upper cutoff there is not such advantage to make it larger.

final step is the back chamber, many said small volume, but mine sims give me best result with something around 20l, and is even simpler to build!

it will be an expensive project for me, so before cutting id like to be confident in what i project on paper.
many thanks

Posted By: snowflake
Date Posted: 06 September 2018 at 3:14pm
if you want to avoid beaming and fingering in the off axis resonse you need to double the flare rate in the last section of the horn. I think it was Keele who did a good paper about this. It does take up more volume to do this. you might want to consider how you are arraying them and how that will work. On some of my boxes I had more expansio in the vertical axis but not on the horizontal. I thought I could get rid of the fingering by using the right splay angle to get the fingers to fill in the gaps of the neighbouring box. I didn't get it quite right but I think it's an approach that might work if tweaked.

Posted By: _Natty_
Date Posted: 07 September 2018 at 8:23am
please can you link me this paper, thanks!

Posted By: odc04r
Date Posted: 07 September 2018 at 9:17am
I think the paper in question was probably Keele - "What's so sacred about exponential horns". Towards the end of it he proposed a dual flare horn from exponential to conical. Haven't read it in a while but was probably about a smoother termination to free air and less reflections at the air/mouth abrupt boundary." rel="nofollow - (1975-05%20AES%20Preprint)%20-%20Whats%20So%20Sacred%20Exp%20Horns.pdf

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