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Old 19th June 2007, 03:14 AM   #1111
AJinFLA is offline AJinFLA  United States
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Quote:
Originally posted by SY
too woo-woo
Is that a scientific term?

I may have to brush up on my Chinese. Not familiar with that one.

cheers,

AJ
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Old 19th June 2007, 03:22 AM   #1112
ScottG is offline ScottG  United States
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Quote:
Originally posted by MJK


It is easy to take shots at Earl Geddes on the audio forums.

One other interesting observation about this particular thread, in my opinion there is a lot of talking and throwing out of ideas but not much engineering taking place. This appears to be a holistic design based on subjective opinions, conjecture and trial an error evolution and not at all on basic OB engineering design principles. This is easily demonstrated by reviewing who is contributing and who is not, there are not many posts from the people working on OB engineering and design methods. There is not much presented in the thread for the engineering people to become interested in discussing and participating. Basically this thread is ony getting one side of the exchange of ideas, the engineering technical side is missing.

My opinions
If you perceived my comment as taking a "shot" at Earl - you are mistaken. (.if not, my bad - and in any event no offense taken. )

I think an AES forum would be an EXCELLENT idea, don't you think so? (..it certainly wasn't intended to "shoo-off" Earl to some other forum - he has already stated he has no intention of participating here, and in fact *I* think he would be a very valuable addition if he was actually contributing to this thread's purpose.)

As to the design and progress:

This IS Lynn's thread, he will be doing the engineering when he wants to and is physically capable. (He has said so numerous times.) Despite that a few others have already started on their own designs as an "off-shoot" (..which is particularly nice because they can add information on what did and did not seem to work - concurrently with this thread).

And sure enough Lynn has done OB modeling, as have I (when making an OB suggestion) - and no doubt several others have as well. I'm also fairly sure Lynn has also done some modeling of a 2.5.5.5.5.5.5 (etc.) crossover to see whats possible/practical. (..remember, just because it isn't explicitly posted doesn't mean it hasn't happened.)

The KEY point though is that the design isn't finalized. Sure, the shear length of the thread is daunting and often filled with off-topic comments (like ours here).

IMO the point of this thread is gathering ideas and to act as Lynn's personal "sounding board" to see what gets the "nod" for the final design. In other words he gets to conceptually "kick the tires" here while he goes through post-op waiting and physical therapy.

When he actual does finalize the design - we can only hope that he does so in another thread here.

As to others participating on the engineering-end ..open baffles (in a myriad of forms), and horns with CD's have been in discussion continually though somewhat sporadically - sadly, most who could interject with greater engineering depth on either topic have not. Perhaps its the "noise" level or the length of the thread?

Bottom-line: I'm fairly certain the Ariel wasn't conceived and built in a day, or even a few months. Now add-in a currently "bed-bound" engineer/designer and the amount of time it will take before prototyping will even begin. So if you are in a hurry to see something actually take form - you are in for a bit of a wait. In the mean time why not suggest something on the topic of open baffles that hasn't been covered and/or is more in-depth with an engineering perspective?
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Old 19th June 2007, 04:02 AM   #1113
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The Mice Will Play - take off for a few hours to get a little fresh air, and things get really wild in here!

Later this summer, the magical MLSSA and supernatural SoundEasy will be churning out lots of pretty-looking graphs. Wizard's caps will not be required to interpret them. Whether this will overlap with the RMAF remains to be seen. At least I'll be out of the walker and wheelchair by then, at the rate I'm going.

Today I took my first step upwards into the house, a tiny but significant achievement. This replaces the sit-in-a-chair-and-swing-the-walker-around method of the last several months. Left-to-right symmetry on the walker is improving as well. I can also stand still, outside of the walker, and hold things in my hands, for the first time since January. Bit by bit, day by day, week by week.

I've been reading Augusten Burroughs (Running with Scissors, Dry, Magical Thinking, and Possible Side Effects). I think it's had an effect on my writing, and I'm not sure if that's a good or bad thing. (Fair warning to the tender-minder reader - some chapters in the first two books are not an easy read.) He's a stunningly good writer, and works in a difficult form - the memoir.
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Old 19th June 2007, 04:08 AM   #1114
ScottG is offline ScottG  United States
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Wow.. Your Physical Therapy must be moving along quickly - excellent!

(edit: I just realized that the abbreviation PT has another more common association. )
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Old 19th June 2007, 05:04 AM   #1115
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Most fascinating discussion of "horn honk", by Jack Bouska. The simple rolled-up magazine test (mentioned in Part 3) makes the point, I guess maybe that's the reason I've never warmed up to conical horns - the resemblance to a simple megaphone is just too close.

EG's patented technique is of great interest, and I suspect there may be other ways to address the issue as well.

A quote from the linked post:

"In addition to the criteria of flat frequency response, I believe that the second biggest influence on the subjective quality of horns or waveguides is the unpleasant phenomenon known as “horn-honk”. This has been incorrectly attributed to a variety of causes, such as compression chamber and/or throat distortion, resonances in the horn cavity or walls, and even abrupt changes of DI between cone and horn transducers in a loudspeaker system. While the previously mentioned mechanisms can contribute to poor quality sound, the real culprit behind horn-honk is caused by poor mouth termination, and/or rapid flare rate changes within a horn or waveguide. In answer to Ian’s comment on subjectively poor performance of some CD horns, I note that many of the commercial devices on the market rely on diffraction slots and abrupt internal slope breaks (flare rate changes), while also displaying poor mouth to baffle impedance matching, all of which are responsible for imposing varying levels of horn-honk to the sonic character. Unfortunately, good CD does not guarantee good sonic performance."

<snip>

"Dr. Holland concludes that the poor sonic quality of many horns is attributable to internal reflections between the mouth and throat. The horn-honk caused by these internal reflections can be easily detected as a distinct tonal aberration, similar to talking through a cardboard mailing tube, or a small tunnel. (Send me private mail if you are interested in this article.)

Addendum: Please note that in Post #5 of my oblate spheroid thread, I incorrectly described this comb filtering effect as a resonance. I apologize if I mislead anyone by my use of that misnomer, as horn-honk is not caused by an internal resonance, but rather by one or more discrete reflections, between mouth and throat. In contrast, a typical fundamental resonance mode would exhibit a response peak much lower in frequency, which even for short horns would be below 500Hz. (eg: a 13” long horn would have a resonant frequency of 250 Hz, and a 7” horn resonance would be just over 500 Hz)

The broad-band comb filter effect, associated with horn-honk, is created by reflection, and summation of delayed signals, which are added back into the primary acoustic output of the horn (with alternating polarity). The delay & addition of any broad-band signal with itself creates a comb filtering effect, which on a log scale amplitude plot appears as a sinusoidal ripple in an otherwise smooth response. The period of this sinusoidal pattern is related to the time delay of the reflection according to the equations:

Time period = 1 / frequency
(This period is measured between peaks on a linear frequency scale spectral graph).

The comb filtering effect can be band limited in the case where the internal reflections are not broad band. In Tractrix or Exponential horns, the higher frequencies beam down the center of the horn, and do not diffract or reflect from the mouth edge, and so the response ripples will be limited to the lower octaves of the horn bandwidth (which is in the human voice range, where we are quite sensitive). In the case of CD horns, if the mouth has some form of flair, or radius, the high frequencies will be presented with a better acoustic impedance match, thus limiting the reflections to the lower octaves, similar to Tractrix and exponential horns. The reflection induced ripples in the horn frequency response have the same root cause as the impedance bumps which might be observed in the first octave or two above cutoff, these are attributed to improper mouth dimension for a given flare rate."
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Old 19th June 2007, 05:15 AM   #1116
gedlee is offline gedlee  United States
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If I might suggest, the approach that I always take is to specify the objective, then see what of the alternatives best meet the objectives. It sounds to me like this thread has decided that "OB is the design, now whats the objective".

I have looked at OB several times with the idea to see if and how it meets the objectives. Every time I come up with one or more problems that seem to outweigh the advantages.

I really believe that to get to "the answer" we should first look at the "objectives". When those are clearly understood then it is much clearer how the design should follow.

A thread simply focused on "What should a loudspeaker do?" is long overdo. There is no simple answer here either since the room plays a very significant role and "there are many rooms". My expertise and focus is on "small rooms", they interest me the most as they are what we tend to live in on a daily basis.

Had I the time, I would start a thread on "The objectives of a loudspeaker in a small room" as this would parallel the central focus of my lifes work. I could start it, but I'm likely to disapear after a few days.
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Old 19th June 2007, 05:18 AM   #1117
Variac is offline Variac  United States
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It is certainly easy to come to the conclusion that this is another of those thrown together projects, with one idea after another suggested and then thrown aside to be replaced by another, with no testing or direction. There are indeed such projects, and I for one have been guilty of participating in them on occasion. -sometimes that's fun in fact!

BUT unless you have followed from day one, you may be unaware that due to his severely broken leg, Lynn was barely capable of getting out of bed at the beginning and while he has made much progress is unable to make test baffles, set up test gear, even carry boxes of drivers into his basement where his equipment is.

So we are all having a good time suggesting possible areas that Lynn can investigate when he gets better. Things have stagnated a bit but his condition should be kept in mind when critisizing this. At the same time he has gotten lots (too much?) information, much of it probably well worth studying when he gets serious.

It is pointless to try to design the system for him -Lynn will do that when he is capable - after all , it's his speaker. He has pointed out that in the process he will use MLSSA, etc. , make lots of mistakes, learn a lot..... but that process has barely started, because it really isn't possible for him to do so.

While some estalished authorities complain of attacks rightfully, sometimes it seems that they are used to only agreement and interpret any questioning as an attack. Other members attack seemingly without reason just because they can. This is a problem here as in other forums, but this place isn't static. As SY has pointed out, we have started a strong effort to have the most civilized discussion of all the audio sites, and we are getting positive results. More useful discussions are taking place and more people who are participating have meaningful knowledge to offer.

In the future, we hope to be able to "publish" papers by people that have worthwhile things to contribute and wish to do so in a structured way. Changes are happening, but in their own time I'm afraid. A lot of this is going on in the background so isn't visible to most members.

Mr. Geddes certainly sums things up well in his most recent post.

"Not everyone can afford to do ellaborate subjective tests, and not every advance has to be so proven. But, one must always be careful not to claim unproven opinions as facts. WHEN scientific data is available use it, when you only have your own personal observations, use them too, but ALWAY be sceptical of their validity because the human psychy is not to be trusted"

Too bad he seems to have so many irons in the fire!

I think that another thread on Open Baffles is certainly not too many, and might prevent Lynn's thread from getting too wide ranging...

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Old 19th June 2007, 05:20 AM   #1118
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Quote:
Originally posted by gedlee

Had I the time, I would start a thread on "The objectives of a loudspeaker in a small room" as this would parallel the central focus of my lifes work. I could start it, but I'm likely to disapear after a few days.
If you ever find the time, an "Objectives" thread would meet with great interest. It is, after all, the starting point of any engineering project, and the only way to keep a project on track.
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Old 19th June 2007, 05:36 AM   #1119
gedlee is offline gedlee  United States
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Default Re: This Is Too Good To Let Slip By

"the real culprit behind horn-honk is caused by poor mouth termination, and/or rapid flare rate changes within a horn or waveguide."

"Please note that in Post #5 of my oblate spheroid thread, I incorrectly described this comb filtering effect as a resonance. I apologize if I mislead anyone by my use of that misnomer, as horn-honk is not caused by an internal resonance, but rather by one or more discrete reflections, between mouth and throat. In contrast, a typical fundamental resonance mode would exhibit a response peak much lower in frequency, which even for short horns would be below 500Hz. (eg: a 13” long horn would have a resonant frequency of 250 Hz, and a 7” horn resonance would be just over 500 Hz)

The broad-band comb filter effect, associated with horn-honk, is created by reflection, and summation of delayed signals, which are added back into the primary acoustic output of the horn (with alternating polarity). The delay & addition of any broad-band signal with itself creates a comb filtering effect, which on a log scale amplitude plot appears as a sinusoidal ripple in an otherwise smooth response. "

My entire study of "waveguides" was aimed at one thing - to get rid of (God I hate this phase) "Horn Honk". Lets just say that "horns" have an unnnatural quality about them that it would be desirable to eliminate. In the late 80's I did several papers on horn modeling only to find that there was a big hole in the theory of "horns" that prevented me from really getting anywhere. Thats when I went the next step to "Waveguide Theory" which uses an entirely different set of equations than "Horn theory". This theory was in fact more complete and allowed for a better understanding of the details of wave propagation in these devices, but alas it was also far far more mathematically complex. SO complex, in fact, that the solutions were not really even know at the time of my first writing. This has indeed limited the understanding of this new approach as only a highly proficient mathematician can follow the development.

BUT, this new theory predicted some things that the old theory did not. That is the Higher order modes that can, and do, propagate in waveguides. These became of serious interest to me. I studied them for the next ten years - most of which was not published. Lidia nd I published our subjective analysis of these HOMs at the AES last year, but alas, as God would have it, we were BOTH called away to Lidia's mothers funeral and this paper was never presented. In it we showed how the ear is actually the nonlinear element and that the HOM, which are dispersive, are perceived as nonlinear distortion. Quite a revolutionary concept, it has received virtually no attention, and yet, to me, it is the answer to "Horn Honk".

Sorry for the complexity (I can't make brain sugery any easier), but after nearly 20 years of intensive investigation, I have come to this conclusion. And anyone who has heard my waveguides must agree they don't have the typical "Horn sound". They are as natural as any direct radiator. Mouth reflections are a factor (I would call this a "resonance") but HOM's are the real culprit to "Horn Honk". The current genre of CD (I say that with a smile) horns are based on diffraction which maximizes HOMs - net result, nearly CD with terrible sound. Virtually everyone today is steering away from diffraction techniques.

Well thats enough "lecturing" for tonight.
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Old 19th June 2007, 05:37 AM   #1120
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Lynn,

From the various prototypes that I went through with my current waveguides, I can't agree that horn honk has anything to do with the mouth termination, but instead is caused by reflections between the surfaces of the horn itself. That puts me firmly in Earls camp in that regard. I tried quite large roundovers and even tried significant foam padding near the terminus wrapping around to the back (similar to what Peavy does with its quadratic WG's). My current WG's also had that same unnatural tonality until I lined the interior surfaces with 1/2" foam, which cured the problem entirely even though I left the terminus as bare wood. It still have unresolved issues with the terminus, but they seem to affect imaging, not tonality, just as the edge termination does with any speaker.
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