New Frugel Horns: Tuning Problems - diyAudio
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Old 14th September 2007, 01:06 AM   #1
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Default New Frugel Horns: Tuning Problems

Just completed my Frugel Horn beta kits...first horns I have ever built. Put in a brand new pair of FE126e, stock...added 1/4" wool felt to the wall directly behind the driver, no other driver mods yet. Driving them with a signal source and SE 2A3 amp of known high quality.

First impression was not very good...male vocals sounded very "boxy," or hollow...as if singing through cupped hands. I pulled the baffles out and put a handful of Dacron polyfill in just behind the driver, in the compression chamber but not in the throat. OK...MUCH better now, but still sounds "boxy" compared to my FE-103s in a BR cabinets. Still, the horns sound promising...there is something"magical" about them.

What am I witnessing here? Is this a typical problem before tweaking a BLH? I am unfamiliar with horns, but I'll guess that baffle step is causing a dip before the low-pass of the horn starts kicking in, and this "dip" in response is giving me the "boxy" sound. Adding polyfill must have raised the LP frequency of the horn and filled in the dip? Am I on track here?

I ordered a pair of the "SupraBaffles," which in theory should mitigate some of the baffle-step effect. Will be trying them next week to see if it clears up the problem.

Cna anyone more experienced please comment on BLH horn tuning, baffle step effect and how one goes about getting all this tuned properly?

Thanks,
Dennis
San Diego
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Old 14th September 2007, 08:42 AM   #2
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The baffle-step point of the Frugalhorn, sans suprabaffle, is 658Hz with 18mm side-panels. So you're right in guessing that there's a dip in the response before horn-gain kicks in. The baffles will solve that problem.

Give the drivers about 100 hours to loosen up. You'll be surprised at the difference it can make. The Frugalhorn controls the driver excursion far better than a reflex etc box, so it'll take longer for the suspension to break in.

Depends what volume chamber you've selected as it's adjustable in the Frugalhorn. The larger the chamber volume, the lower the horn's upper-cut-off will occur. So if you're running the full back-chamber volume, try reducing it by adding something (the plans suggest wooden blocks) to adjust the upper cut-off frequency of the horn.

While you're at it, I'd pull out the stuffing from the chamber, and try line the back, top, bottom and one wall of it instead with damping material like carpet underlay, which should kill any unwanted resonances in the chamber (adding blocks should help break them up too). If you feel it needs more damping, add some of the polyfil back into the chamber. If you find it over-damped, remove some of the lining material. And so on.
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Old 14th September 2007, 02:02 PM   #3
hm is offline hm  Europe
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Hello,

that is a problem of material,
the same effect by Lowther and other horns they sound coloured,
because also the frequencies you donīt want getting
louder ~150 Hz, the bass gets weak because it is
covered by the freq. over 100 Hz.

Therefor I use WEICHFASER softfibre the first m of the horn to reduce the "Schallschnellen" over 4/lamda of 100 Hz.

http://www.hm-moreart.de/11.htm in the middle
and look my horns.

One desisive point is for a horn you need min. 1 mm Xmax,
I write it several times. Therefor is a simulation with AJ horn
helpful.
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Old 14th September 2007, 02:54 PM   #4
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Interesting material. Thanks for the heads-up Horst. I'm not sure how easy it is to obtain outside Germany -I've never seen it, but I'll now be looking. I don't like too much damping in cabinets -loads of damping is just a lash-up fix for sloppy design IMO, so this looks ideal.

It's been a while since I looked at AJ Horn. Does the latest version now have facilities for simulating corner-loading, wavelaunch from the baffle, curved mouths and deflectors?

BTW -could you clearly set out your reasoning why a stroke 0.0394 inches is an decisive requirement of every driver in every cabinet? I've asked before, but you've simply pointed me to your Saxophon page, which frankly wasn't much use. I'm not trying to be unpleasent, just curious as to why you claim this figure to be universally applicable, and everything else is completely wrong.

Best
Scott
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Old 14th September 2007, 03:17 PM   #5
hm is offline hm  Europe
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Scottmoose,

the material is made of the rest of woodworking,
very cheap, a sound reducing board, may be you get
it not in 12-13 mm with paper, but because itīs made by
waste, it must got everywhere.
Ask you joiner.

Please ask mr. Jost, I use AJ 4.0.

Remember we analysed this several times,
I make around 100 simulations in different
horns with different drivers, most need 0,8 mm
at 70 Hz and 0,5 mm ~150 Hz stroke for 1 Watt.
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Old 14th September 2007, 04:57 PM   #6
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Cheers for that Horst, I'll keep an eye open for it.

Ah, now I see where the reasoning comes from. Fair enough for those boxes -it's not universally applicable though. Depends on the design and the room influence. I've done more sims than I care to remember in MathCad and not every box makes those demands. Here's a quick example I've got on the PC at the moment. 0.2mm 150Hz, 0.5mm 70Hz, total excursion (/2 for one way) at 1w input. It's for a BVR type of horn actually, so a long-path version with hyperbolic expansion should beat it.

To be honest, I reckon people get a bit hung up over Xmax sometimes. Best not to pass it if possible, I wholeheartedly agree -but so long as something really daft isn't being attempted, breaching it mildly isn't automatically going to ruin the sound. That depends on the distortion characteristics of the driver of course. Some are worse than others. The Fostex units are pretty forgiving in this respect.
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Old 14th September 2007, 06:06 PM   #7
hm is offline hm  Europe
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super,
can you give us the data of the horn and which driver,
than I can simulate it in AJ.
I canīt see that the room influence the movement.
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Old 14th September 2007, 06:24 PM   #8
Svein_B is offline Svein_B  Norway
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If you are offering to do a horn simulation, might I suggest that you sim the Frugal-horn with the FE-126e.
... since that was the original subject of this thread

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Old 14th September 2007, 07:06 PM   #9
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Surely. The driver is the Eminence Beta12LTA 12in wide-band unit. The cabinet is a double-mouth (over-under layout) BVR style horn called Maria, that I'm working on with Dave at the moment, intended for for semi PA purposes. The plans aren't uploaded on the 'net yet, but it's about as simple as it gets, so shouldn't take too long. Great unit for the price actually. Not quite 'hifi' but a lot of drive-unit for the money.

The room has an influence on driver excursion if it forms part of the horn expansion (corner horns for example). So it needs to be taken into account if possible, or as close an approximation as can be done, as a 1/2 space or anechoic sim effectively is only simulating a part of the enclosure.
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Old 14th September 2007, 07:22 PM   #10
hm is offline hm  Europe
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I didnīt have the data of the horn.

Scoutmoose,

I need
Horn throat,
horn mouth,
length

Your explanation show your horn is very very large?

I remember Freddy done a simulation.

The constructor must have a real measurement,
if he donīt, think about why not.
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