fostex FE206 in front horn (BD-Design)

by GC, Thursday, February 03, 2005, 19:37 (4731 days ago)

I have built a square front horn similar to what Bert had built prior to the current round Oris horn. The FE206 in it sounds nice, but it seems to have a dip in frequency response in the 1.6K to 2.5K range. I think the square shape of the throat is causing cancellation and therefore a dip. Bert what would you suggest I could do to minimize cancellation in the square throat?
Thanks

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fostex FE206 in front horn

by GC, Thursday, February 03, 2005, 23:26 (4731 days ago) @ GC

I have built a square front horn similar to what Bert had built prior to
the current round Oris horn. The FE206 in it sounds nice, but it seems to
have a dip in frequency response in the 1.6K to 2.5K range. I think the
square shape of the throat is causing cancellation and therefore a dip.
Bert what would you suggest I could do to minimize cancellation in the
square throat?

Hi BQC,

How did you mounted the driver to the throat? Can you show a picture of that?

To prevent severe standing waves is not to use a square throat so an option could be to split the throat by thin walls or such...another thing you can do is to add damping in the corners (some triangle shaped pieces of foam).

If you have a dip then you also have a peak (like most resonances caused by standing waves). Can you show a frequency plot?

Ciao,

Bert

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fostex FE206 in front horn

by GC, Friday, February 04, 2005, 05:01 (4731 days ago) @ GC


How did you mounted the driver to the throat? Can you show a picture of
that?

very close to the throat, I mounted the speaker on a piece of 19mm MDF and attach the MDF to the back of the throat, making the rim of the fostex almost touching the back of the flange of the horn throat.

[image]


To prevent severe standing waves is not to use a square throat so an
option could be to split the throat by thin walls or such...another thing
you can do is to add damping in the corners (some triangle shaped pieces
of foam).

If you have a dip then you also have a peak (like most resonances caused
by standing waves). Can you show a frequency plot?

I dont have a plot, but here is some rough measurement using test CD warble tone and radioshack SPL meter. Meter located 11 feet from horn

HZ dB
6000 75
5000 73
4000 74
3000 71
2500 72
2000 73
1600 72
1200 73
1000 74
800 78
600 77
500 80
400 82
300 77
250 83
200 83
160 82

Ciao,

Bert

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fostex FE206 in front horn

by GC, Friday, February 04, 2005, 10:03 (4731 days ago) @ GC

I dont have a plot, but here is some rough measurement using test CD
warble tone and radioshack SPL meter. Meter located 11 feet from horn

I read these warble tone measurements differently, I think that the horn is not too rigid or has a throat that is too small and is therefore too strong sounding in the lower range. If you use a back chamber then try to open it at the back to reduce the lower output, if not then you could make the throat larger for a better tonal balance.

Adding little pieces of foam in the corners will always be a good idea...

Ciao,

Bert

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fostex FE206 in front horn

by GC, Friday, February 04, 2005, 15:50 (4730 days ago) @ GC

I read these warble tone measurements differently, I think that the horn
is not too rigid or has a throat that is too small and is therefore too
strong sounding in the lower range. If you use a back chamber then try to
open it at the back to reduce the lower output, if not then you could make
the throat larger for a better tonal balance.

The strong response at around 160 hz is probably because the measurement was taken with the base unit turned on which is biamped and crossed over at 150hz. The throat
dimension is about 178 mm square, ie just about as big as the fostex diaphram as you can see in the picture. The horn throat used to be even smaller (127 mm square) and I have cut it to make the horn shorter and the throat larger to its current size.

Adding little pieces of foam in the corners will always be a good idea...

Thanks for the suggestions, I'll try that.


Ciao,

Bert

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