Fostex FE103 Sigma for Mid Horn? - diyAudio
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Old 30th October 2015, 05:45 PM   #1
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Default Fostex FE103 Sigma for Mid Horn?

I bought a pair of vintage FE103 sigma's with the intent if trying them in a wood mid horn in my 3 way setup. If it doesn't work, then they will reside as a bookshelf speaker.
These units peaked my interest because #1. I've never seen a this sigma model for sale before. It has a very flat response and its double magnet might mean its powerful enough for front horn loading.

#2. I've heard what a cone/horn can do with another project using JBL pro midranges, but felt it lacked the delicacy a lighter cone, with less power handling might have.

The horns I'm looking at building are either a bi-radial like a Yuichi a290 or a constant directivity horn.

Operating range will be the primary vocal range, limited to 300-600hz to about 2-3khz via a passive crossiver.

Altec 416 on the bottom, Altec 802 on top.
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Last edited by croweproductions; 30th October 2015 at 05:51 PM.
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Old 30th October 2015, 07:29 PM   #2
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Very nice pair of vintage FE103s you have there… picture from the front?

dave
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Old 30th October 2015, 11:13 PM   #3
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Old 31st October 2015, 12:06 AM   #4
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How flexible are the surrounds?

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Old 31st October 2015, 03:17 AM   #5
djk is offline djk
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If they were stiff they would still be fine for use in a horn.

They would work best in a non-constant directivity horn, which at best would only add about 4dB or so to the lower midrange.
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Old 31st October 2015, 09:34 AM   #6
Scott L is offline Scott L  United States
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Quote:
Originally Posted by djk View Post
If they were stiff they would still be fine for use in a horn.

They would work best in a non-constant directivity horn, which at best would only add about 4dB or so to the lower midrange.
I'm surprised only 4 db. Is it because of the type of horn ?

I had always thought that horns lift between 6 and 10db depending upon
the particular configuration.

I have for a long time, wished to experiment with putting a small Fostex driver (3 or 4 inch unit) on a huge round tractrix, just to see what it sounded like.
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Old 31st October 2015, 10:04 AM   #7
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Interesting.

I recently tried Fostex 83 in my large Azura 340 horns. The sound was clean and easy, though laid back. A lot less detailed than a standard compression driver. Andrew
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File Type: jpg fostex 83 up close 2.jpg (64.0 KB, 167 views)
File Type: jpg fostex 83 up close.jpg (50.7 KB, 43 views)
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Old 31st October 2015, 11:37 AM   #8
Scott L is offline Scott L  United States
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Quote:
Originally Posted by atilsley View Post
Interesting.

I recently tried Fostex 83 in my large Azura 340 horns. The sound was clean and easy, though laid back. A lot less detailed than a standard compression driver. Andrew
Andrew, thanks for that !

Had you considered using a back chamber ? I only ask because I have heard a few systems like that, with the rear wave splashing about, and it's just not my cup of tea.

Your horns are really really nice ! So, what driver have you found that you like the best ?
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Old 31st October 2015, 02:08 PM   #9
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According to Hornresp, a compression chamber effects the front wave high freq extension greatly (not reflected sound, but loading of the driver). Maybe that is why it sounded so "laid back"?
My plan is to build an adapter and try both the Altec 288-8G compression driver and the fostex.

I think the biggest drawback will be efficiency compared to the rest of the system. The 416 Onken is around 100dB. So no chance of getting 10dB gain?
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Old 31st October 2015, 04:10 PM   #10
GM is offline GM  United States
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Wide BW point source drivers designed for baffle or ~3-4 dB BLH loading usually can't tolerate any real compression loading beyond a 2:1 ratio throat and then only with conical [preferably parabolic] wave-guides, so little wonder Andrew's are 'laid back' as we would be too if our motions were always being pushed/pulled by a high pressure, wide frequency range wind 'tunnel' A/C pulse.

Bottom line for best overall performance, any [minor] BLH loading or FLH wave-guide baffling of such drivers should be limited to below its upper mass corner [2*Fs/Qts] to maintain its wide range output and due to driver design this holds true even in limited BW apps.

That said, there are [were?] some 'FR' drivers that are designed for modest compression loaded and are easily spotted due to having a prominent phase plug combined with a very strong motor [low Qes] and stiff suspension [abnormally low Vas], but even then best limited to a relatively large tractrix with a compression chamber.

If loaded with a 'weak' motor [higher Qes and/or coupled to a high output impedance], then use either a suitably large semi-aperiodic or sealed compression chamber; and for high Q drivers, 'gapping' them at the driver/horn junction to 'bleed off' some of its 'Q-ness' similar to a R-J BP alignment has worked well IME, especially if there's a filter to further damp it once the right 'vent' dimensions are found empirically. I wonder if AkAbak or similar can sim this.

GM
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Last edited by GM; 31st October 2015 at 04:21 PM. Reason: punctuation
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