Back Loaded Type Horns using Fostex 4 inch FE 103E Single Drivers. - diyAudio
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Old 17th December 2009, 12:49 PM   #1
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Default Back Loaded Type Horns using Fostex 4 inch FE 103E Single Drivers.

Hi

I am thinking about making a pair of Back Loaded Type Horns using Fostex 4 inch FE 103E Single Drivers.

Fostex provide a comprehensive design PDF

http://www.madisound.com/catalog/PDF.../fe103erev.pdf
I was wondering if anybody had built this set up. As the manufactures have supplied the design I am hoping it will be fairly foolproof.

The one think that I donít understand is the use of MDF steps rather than laminated curves on the Horn Mouth. Is this just to simplify construction or is there some sound audio logic I fail to understand going on here? Would not these step set up standing waves? I am very happy to take the mid point and substitute two curves to form the Horn Mouth.

Any feedback would be gratefully appreciated.

Best Wishes

dh
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Old 17th December 2009, 05:27 PM   #2
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I believe the steps help break up higher frequencies so you only get lower frequencies out of the horn mouth. Although I have not built any of the Fostex-supplied box plans, I have seen mixed reviews of them on this site.

There are some other designs for the FE103E on this site if you do some searching. One in particular is the Buschhorn MKII.
http://homepage.mac.com/tlinespeaker...chhorn-Mk2.gif
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Old 17th December 2009, 05:47 PM   #3
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Quote:
Originally Posted by davidhugo View Post
Hi

I am thinking about making a pair of Back Loaded Type Horns using Fostex 4 inch FE 103E Single Drivers.

I was wondering if anybody had built this set up. As the manufactures have supplied the design I am hoping it will be fairly foolproof.

The one think that I don’t understand is the use of MDF steps rather than laminated curves on the Horn Mouth. Is this just to simplify construction or is there some sound audio logic I fail to understand going on here? Would not these step set up standing waves? I am very happy to take the mid point and substitute two curves to form the Horn Mouth.
Not to discourgae your quest but,

1st. We have built this horn. It is not very good.

2nd. Each step in this manifold horn, and each square bend acts as a low pass filter. Curves would mean HF getting out the mouth, something you don't want to.

3rd. If you build this out of MDF it will be even worse than it is when properly made with the specified plywood.

Do you have the FE103s already or are you just looking to do a small horn? The FE103 is a nice driver, but not best suited to a horn, but there are some that work way better than the Fostex. The B-Horn Chuler mentions, and probably the Frugel-Horn with appropriate tuning of the air cavity.

dave
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Old 17th December 2009, 07:24 PM   #4
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Quote:
Originally Posted by planet10 View Post
Not to discourgae your quest but,

1st. We have built this horn. It is not very good.

2nd. Each step in this manifold horn, and each square bend acts as a low pass filter. Curves would mean HF getting out the mouth, something you don't want to.

3rd. If you build this out of MDF it will be even worse than it is when properly made with the specified plywood.

Do you have the FE103s already or are you just looking to do a small horn? The FE103 is a nice driver, but not best suited to a horn, but there are some that work way better than the Fostex. The B-Horn Chuler mentions, and probably the Frugel-Horn with appropriate tuning of the air cavity.

dave

Did I miss it, or has no-one mentioned that of the 2 Buschorns, the MKI is probably a better sounding design for this driver, or the FE126E for that matter?

I've built at least one pair of all 4 designs ( BH MKI & II, Fostex's "hybrid", and many pairs of the Frugels), and listened to them extensively in a couple of different systems and rooms, so this is subjectively biased of course, but not idle conjecture.
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Last edited by chrisb; 17th December 2009 at 07:26 PM.
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Old 17th December 2009, 07:45 PM   #5
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Note that the B1 that Chris mentions is a version scaled to fit a 4" driver, and that all of our trials were with FE126eN (better suited to horns than FE103)

The plans for this are on the very last page of the Frugel-Horn plans.
dave
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Old 18th December 2009, 03:02 PM   #6
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Default Thanks for the Links -Whats wrong with 15 mm MDF ?

Thanks for the advice. I will look at the links you all surgested.
Sadly 15 mm Ply is very hard to find in the UK. So What so wrong with MDF ?
I have always used it for speaker projects. It seem likethe perfect 'dead' material. 15 mm MDF is easy to purchase were I live.

Best Wishes

dh
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Old 18th December 2009, 04:25 PM   #7
BL21DE3 is offline BL21DE3  Scotland
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If your based in Scotalnd (just a guess from your chosen country flag) you might want to check out these guys Rembrand Timber Limited - Scotland's largest independent timber merchant they stock 15mm birch ply. Elsewhere in the UK you could try Avon Plywood or even a local builders merchants, that's where I source my ply from.

Regards,
Ewan
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Old 18th December 2009, 04:55 PM   #8
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Default Thanks

Thanks for the Rembrant timber Link. I normlally use Thornbridge Sawmills who told me they could not supply that product.

dh
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Old 18th December 2009, 05:14 PM   #9
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Re MDF, its basic problems are high density and lack of stiffness, which at the kind of thicknessess usually used (1/2in - 3/4in) usually puts panel resonance slap-bang in the middle of the bandwidth the cabinet is operating over. For e.g., to equal the stiffness of 3/4in BB ply, you would need about 1 1/4in of MDF (stiffness in a material increases at the cube of thickness), and you still have (an even worse) issue WRT high mass.

For once, I'm going to disagree with Dave WRT the 103 not being ideal for BLHs. From my POV, it's no more or less so than, say, the very popular, slightly larger FE126E. Mass corner is acceptably low, & with its miniscule linear travel & small cone area (and more controversially, its very high theoretical acceleration factor of over 2100 m/s^2 per ampere) if you want to run it sans LF support then a decent BLH is about the only option you have if you want to keep distortion within vaguely reasonable levels.

I do concur that Fostex's published design for it isn't great though. There's nothing wrong with manifold horns, but that one isn't a particularly distinguished example sadly.
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Last edited by Scottmoose; 18th December 2009 at 05:34 PM.
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Old 18th December 2009, 05:55 PM   #10
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Quote:
Originally Posted by Scottmoose View Post

For once, I'm going to disagree with Dave WRT the 103 not being ideal for BLHs. From my POV, it's no more or less so than, say, the very popular, slightly larger FE126E. Mass corner is acceptably low, & with its miniscule linear travel & small cone area (and more controversially, its very high theoretical acceleration factor of over 2100 m/s^2 per ampere) if you want to run it sans LF support then a decent BLH is about the only option you have if you want to keep distortion within vaguely reasonable levels.
I defer to Scott (since his key involvement in any horn work i do -- the usual situation is Scott doing the horn, me doing the drawings and suggesting detail improvements)... my comment was based more on the fact that Scott & i have never done a horn specifically for the FE103.

Be nice to see someone verify its performance in the Frugel-horn

dave
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