Back Loaded Type Horns using Fostex 4 inch FE 103E Single Drivers.

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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/fostexdrivers/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 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.

Any feedback would be gratefully appreciated.

Best Wishes

dh
 
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/tlinespeakers/FAL/box-plans/buschhorn-Mk2.gif
 
frugal-phile™
Joined 2001
Paid Member
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
 
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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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
 
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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frugal-phile™
Joined 2001
Paid Member
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
 
frugal-phile™
Joined 2001
Paid Member
Hmm. No 103 box. We'll have to do something about that at some point. I've generally tended to overlook it in the past because it's not all that much cheaper than the slightly larger 126. I think the 107 has the same problem with the 127.

The 103 does have a die-hard following though & the midband is rather nice. Be interesting to hear a pair on one of Nelson's current source amps... next time Simon brings his Vampyrs to a meet I'll have to haul along my F2.

Sorry for the OT there...:eek:
 
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