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Old 5th June 2005, 11:54 PM   #21
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Onur,

I wish I could hear all the different designs, but there aren't any DIY meets here in Costa Rica and the only horns I've ever heard are PA junk. I have a pair of 206's and want to try them in a horn, but I want my initiation to horns to be a good one. That leaves me with trying to gain enough information to make an informed decision about which design to try.

I like the layout of your 206 horn and I believe it would make a fine looking speaker. My concern is the short horn length and the use of a large compression chamber as the low pass filter to generate deeper bass, essentially through some horn loading bandpass output. Can you please explain the difference in character between RLH's with large vs small compression chambers ?
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Old 6th June 2005, 07:38 AM   #22
Onur is offline Onur  Belgium
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Default horn length and rear chamber volume

1/8 tuning is another alternative. I have used it in my horn design. My main concern is the acoustic resistance seen by the cone of the speaker unit. When you make the horn longer you increase the acoustic impedance effecting the cone, also, when you build a small rear chamber, you get the same result. If you think horn lenght and rear chamber volume are two functions, they have an intersection, which we can call an optimum. While one is getting smaller and the other one longer, they intersect at a certain point. And when you examine the acoustic resistance at that point, you see that it has reached to a minimum. That is how I decide the lenght and the volume. I didn't think in terms of acoustic filtering though.
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Old 6th June 2005, 08:00 AM   #23
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My understanding is that the Fostex horns (OK, I know that strictly they aren't 'real' horns, but let's not get bogged down with semantics) use right angles for 2 major reasons. 1) It allows a greater length for a given box-size 2) the edges are there to act as diffusors. (I'm not convinced that curves make an audible difference, except in pycho-accoustics, but diffusors certainly do) That's most likely why the people who smoothed the internal edges were unhappy -they hadn't realised that they are a vital part of the basic design. Better still, they make construction quick and simple (for a horn). Fine with me.
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Old 6th June 2005, 01:11 PM   #24
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Onur,

Very interesting approach for determining chamber volume and horn length. Is that one of those well guarded secrets to horn design? Are the response graphs on your site measured or predicted ?
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Old 6th June 2005, 01:47 PM   #25
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Default not a secret I suppose !?

Friendly, I am not good at maths, the good point of this is that, I am aware that I am not good at maths In order to close the gap I go for the secure way and play trial-error. God knows how many enclosures I have built and measured before I found a corrolation between the simulated results and my measurements. (Just to give you an idea, I have built over 60 enclosures, these are the ones that I have recorded, there are ones which are not recorded) My predictions from those experiments can be wrong, however, since they are based on pure observations.

On the other hand, please visit this link,
http://www.yildiz.edu.tr/~ilkorur/sp...tex_fe127e.htm

Here you are going to find both simulation graphs and measurement results. In both SPL graphs, if you put the peaks and dips aside, you see that the enclosure reaches to 60 Hz. The impedance curve is different since I have added more absorbing material then I have entered to the simulation software. This enclosure came up in 2 hours time. I have measured the T/S of the driver, placed those variables in AJ-Horn, fiddled with the knobs for a while and then generated the dimensions in AutoCAD. The result was and is very good. I can say that it came out to be just as I expedted or maybe even more. What I am trying to say is that, I am very much familiar with AJ-Horn now, I can carry the same simulation graph to real life. So, you can look at those graphs and think that they are very close to real life test results.

/Onur
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Old 6th June 2005, 03:40 PM   #26
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Onur,

For your 206 horn, what do you think about a "<" shaped brace centered behind the driver? It would serve 2 purposes. Of course add some extra rigidity to the compression chamber, but the main benefit would be to totally eliminate direct reflections from the flat rear of the chamber back to the cone. Since I've become an open baffle convert, reflections back to the cone are of great concern to me.
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Old 6th June 2005, 04:33 PM   #27
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Default rear radiation pattern of driver

I wish I could show you my simulation result but I am working on to code a *.avi output of my simulation code.

All I can tell you is, midrange or the frequencies, which are causing reflections in the rear chamber and radiating back to the listening room from the thin cone of the speaker unit, are originating from the sides of the driver. Therefore it is better to cover the side panels with absorbing materials rather then rear panel. Also, rear panels of these enclosures are far away from the driver unit as compared to more problematic ones.

As for the "<" shape, the wave length of low frequencies are very long and that "<" brace is invisible for those, according to my oppinion.
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Old 6th June 2005, 05:20 PM   #28
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Just an idea, since damping in the chamber is problematic also. Re low frequencies, I don't believe they are a factor because I'm not sure they can really even reflect in such a small space due to the long wavelengths.
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Old 6th June 2005, 05:30 PM   #29
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Default this is my point of view

I have solved this question in my mind in this way. Think of horn throat. The acoustic resistance must be low in order to radiate through it. When there is a standing wave (resonance or reflection) occurs inside the horn, the throat resistance increases and you can not radiate energy. The energy which couldn't be radiated to the horn streses the rear chamber and the driver causing distorsion? No ?
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Old 7th June 2005, 09:34 AM   #30
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Onur,

I have been looking at your response curves for your two FE-206E designs. A couple of things don't make sense to me so I thought I would ask some questions.

First your TL design :

1) I assume that AJ-horn is calculating into 2 pi space. if this is correct you will have almost no usable bass response once you add some baffle step loss (say 2 or 3 dB in a room) to the already falling bass output below 500 Hz. Why try and tune this design so low?

2) Assuming you have designed a TL, where are the peaks in the impedance curve due to the higher harmonics?

3) I assume that there is no damping fiber in your line based on your double humped impedance curve, why is your SPL response so smooth and not a very ragged response due to peaks and null associated with the line resonances?

4) Why are there not more nulls in the driver displacement plot?

Second your BLH design :

1) This design looks a lot like the Replikon horn discussed a few weeks ago, a big back chamber coupled to a short horn that acts like a hybrid bass reflex/horn design. This is concluded from the double humped impedance curve. So I ask again, where are all of the ripples due to the higher modes?

2) With your large coupling chamber, how did you eliminate the standing waves in this volume? Standing waves will have a significant impact on the driver's SPL response and the output from the horn mouth.

3) With your over under horn mouth arrangement, did you account for the floor loading of the lower mouth and not the upper mouth? Are you concerned about the two horns seeing different mouth acoustic impedances and how it will impact the SPL response from each?

These are questions I am addressing in my own designs as they are evolving. Since you are posting response plots based on a commercial design tool, I assume thet you have answered some of these same questions. I would be interested in your experiences.
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