Geddes on Waveguides

[BHTX]

From some pics I've seen and the pair I seen in person last week the fit and finish is terrible.

Really disappointed to hear that.
Would you happen to have those pics?
Anyone else care to comment?
Thanks for the reply.

 

[soongsc]

Well, that has been the "religion" fore as long as I can remember

But I have seen measurements that showed a smoother FR with a "frontgrille"(frame with cloth?) in place than without it

I dont think its a scientific fact that you loose any details with frontcloth ... if the speaker is designed to use it

There are other issues related to a normal speaker with frontgrille with cloth ... such as diffraction problems from the frame

Some have even placed thin toilet paper in front of a tweeter, instead of resistor padding ... is supposed to work ok ... you may also say that you loose detail with tweeter series resistor, you should know that

Compare impulse response shape and you can probably understand what I mean. Putting something in front of the diaphram does help suppress some high frequency resonances, but you lose some transient detail. This is the same as putting foam in a horn. I would prefer trying to solve the problem without anything in front of the diaphragm that effect the impulse onset. But it's only my preference.

 

[SunRa]

Compare impulse response shape and you can probably understand what I mean. Putting something in front of the diaphram does help suppress some high frequency resonances, but you lose some transient detail. This is the same as putting foam in a horn. I would prefer trying to solve the problem without anything in front of the diaphragm that effect the impulse onset. But it's only my preference.

Hello,

What is the reason for loosing transient detail? The foam acts like a filter for some frequencies? And how did you come up with this conclusion?

Thank you!

 

[soongsc]

Hello,

What is the reason for loosing transient detail? The foam acts like a filter for some frequencies? And how did you come up with this conclusion?

Thank you!

This will get into detail discussion that diverts from the main topic. But if you cannot measure a difference in impulse response, and cannot hear the difference. Then it may mean nothing. I think first one needs to be convinced there is a difference, hear the pros and cons of each, then look into the data to see what's going on.

 

[graaf]

Graaf,
Your attitude is becoming worse and worse. Please stop.

You mean "stop asking questions"?
Am I annoying?
Please forgive me but isn’t asking questions and discussing them something that the forum is all about?

Have you read the paper in question? Apparently not, based on your comments.

not only apparently
I have openly admitted that the paper is unavailable to me because I haven’t got US credit card
EXACTLY THEREFORE I ASKED A QUESTION to a person that supposedly "knows it all"

WHAT IS WRONG WITH THAT?

I like to learn
couple of pages back in this thread I asked similar question about JBL "acoustical lenses"
Dr Geddes kindly responded and I was grateful

This is how I understand normal way of things in a thread like this one – interested audiophiles ask questions concerning waveguides and Dr Geddes is helpful as He always is

I wonder why this is not the case with my latest question
first Dr Geddes sarcastically joking without knowing/remembering what is in the paper I asked about (He admitted it Himself that Hi didn’t know what is in it)
then His suprising reluctance to check it

and now You came out shouting at me: "Behave! Behave!"

what is going on?

As Dr. Geddes pointed out, the paper is largely an advertisement in disguise.

yeah, You forgot to mention that He pointed that out without knowing what is inside the paper

The main thrust is that the throat is round (to match the driver) and the mouth is rectangular (to make it look "conventional", as near as I can tell).

and impulse response measurement is there to prove that it the look is conventional?

They make passing reference to reduced "multi-path ghost distortion", but do not define what it is

and what can it possibly be? Doesn’t the definition follow from the exact meaning of the phrase "multi-path ghost distortion"?

anyway, they define it elsewhere exactly in the same way as Dr Geddes defines HOM
so they understood it exactly the same
I posted links above

Have You read my posts above? Apparently very selectively

nor how to measure it.

so what is the impulse response measurement there for?
apparently they were of opinion that the distortion or lack/reduced amount of it can be seen in the measurement

They show an impulse response that is slightly cleaner than the impulse response of some other unspecified horn. That is all.

well, isn’t "slightly cleaner", "slightly better in this or that way" something that high fidelity engineering is all about?

They *cannot* have been aware of the importance of avoiding diffraction, as the mouth of the horn has very sharp edges.

nowhere above I have suggested that they were aware of the problem of avoiding "diffraction from mouth edges"
I have sugested that they might be aware of HOM but HOM strictly speaking is something different: "waves that propagate in a waveguide that do not go down the axis, but travel by bouncing off of the walls" in Dr Geddes’ own words

In short, the paper is a joke.

wele, very nice, but what exactly is a joke? cleaner impulse response?

BTW are "joke papers" something typical in AES publications or is it extraordinary case with this specific paper?

Please stop harassing Dr. Geddes

"harassing"="asking questions"?

in what dictionary?

regarding something you know nothing about.

I ask questions EXACTLY BECAUSE I don’t know much

Making such unfounded accusations as you have is quite insulting. You owe him an apology.

You owe me an apology Mr Hansen for shouting at me and for Your unfounded accusations of "harassment" and "insuting accusations" of Dr Geddes

Please quote examples of those "accusations" directly from my posts in this thread

or APOLOGIZE

 

[BHTX]

*sighs* ...

 

[FrankWW]

Graf, Hansen is right. You don't know what you're talking about because you haven't read the paper.

Why don't you exert yourself and get a copy? It's certainly available in your country. Or be a little creative, and have a friend buy it for you - lots of your countrymen do business on the internet...yes, even into the US!

Then you can read it and tell us all about it.

Right now, you are reduced to writing unpleasant innuendo in hopes of having Geddes or someone else read it for you.

I don't believe for one second you can't get the paper or access to all of the journal.

 

[soongsc]

Graaf,

I have to admit it is more appropriate to have enough understanding of the paper you are referencing before asking Geddes to read or comment. It's normal for people to address certain outstanding aspects of the paper that one agrees or disagrees with, thus allowing people answering to focus on the specific issues rather that having everyone read the paper without having a clue what the purpose is. If you find things in the paper that is more reasonable than what Geddes has described, the address them specifically. If you are paying for Geddes and others to read for you, then that's a different issue.

 

[dlr]

Which position to you actually take on this?

Whenever anything is added to the fron of the wave path, you can expect loss is detail transients.

I would also ask on what basis you make this claim? Do you have any supporting evidence, as in valid studies for which no exceptions have ever been found, or is it all anecdotal, as this appears to be?

But if you cannot measure a difference in impulse response, and cannot hear the difference. Then it may mean nothing.

This seems to be in contrast to your first claim of expecting loss in transients. On the one hand, you tell someone to expect a loss. Soon after, you qualify that earlier, unequivocal statement. Sometimes your position is rather erratic. In which do you actually believe, the equivocal one or the unequivocal one?

I think first one needs to be convinced there is a difference, hear the pros and cons of each, then look into the data to see what's going on.

One does not have to be convinced of anything before delving into the data. This sort of dogma is only supportable by anecdote, much like your first point. Do you have any data (measurements and/or valid studies) of any kind for either of your positions on this?

Dave

 

[gedlee]

Responses:

Yes, I sell waveguides, but I prefer to sell the kits as I think that you will end up with a better system in the end.

Graaf - you really can be overbearing at times. I don't respond to impolite posts.

Songsc - I see no reason that placing something in the waveguide or in front of a transducer inherently degrades the transient response. It can if not compensated for, but it can also be a vast improvement if done corectly. I've never believed the traditional beliefs and in my own experiments with foam I have found the exact opposite to be more the case.

 

[Salas]

If there is some porous mass in front of a sound wave I can only think it can slow it down a bit. If there is amplitude vs frequency compensation we get back to original emitted impulse. Don't we?

 

[gedlee]

If there is some porous mass in front of a sound wave I can only think it can slow it down a bit. If there is amplitude vs frequency compensation we get back to original emitted impulse. Don't we?

There is a small delay, but only a few cm max. There is a small loss from the friction, but this is easily restored in the ccrossover. What appears to be the major efect is the foam attenuates secodn order things which when we correct the first order ones leaves the second order ones at a lower level.

 

[graaf]

Responses:
Graaf - you really can be overbearing at times. I don't respond to impolite posts.

yeah, You are right
I know I can be overbearing
I am sorry

but I hope that You know that it is sincerely never my intention to be impolite

anyway, I apologize

best regards,
graaf

 

[Salas]

There is a small delay, but only a few cm max. There is a small loss from the friction, but this is easily restored in the ccrossover. What appears to be the major efect is the foam attenuates secodn order things which when we correct the first order ones leaves the second order ones at a lower level.

I figured out that the small loss is restored with compensation, and the side benefits remain with foam. Thanks for explaining further.
What is the distortion pattern named HOM, in a sense of harmonic distribution? Does it have an IMD component too? Is the foam plug totally killing it in high SPL? If no by what percentage?

 

[gedlee]

I figured out that the small loss is restored with compensation, and the side benefits remain with foam. Thanks for explaining further.
What is the distortion pattern named HOM, in a sense of harmonic distribution? Does it have an IMD component too? Is the foam plug totally killing it in high SPL? If no by what percentage?

HOMs are a linear phenomina. They are very short time delayed signals, which can be highly audible. The foam attenuates them, nothing can actually get rid of them entirely.

 

[Salas]

Is it the high SPL 'splashiness' of most PA horns?

 

[soongsc]

Re: Which position to you actually take on this?

I would also ask on what basis you make this claim? Do you have any supporting evidence, as in valid studies for which no exceptions have ever been found, or is it all anecdotal, as this appears to be?



This seems to be in contrast to your first claim of expecting loss in transients. On the one hand, you tell someone to expect a loss. Soon after, you qualify that earlier, unequivocal statement. Sometimes your position is rather erratic. In which do you actually believe, the equivocal one or the unequivocal one?



One does not have to be convinced of anything before delving into the data. This sort of dogma is only supportable by anecdote, much like your first point. Do you have any data (measurements and/or valid studies) of any kind for either of your positions on this?

Dave

The way you express yourself still holds a very provoking taste, the only thing I can respond to talk like this is that if you find a tweeter that extends to at least 20KHz and decays to at least 12db or more from the second peak of an impulse, than do listening tests and additional measurements on your own. Then try a tweater with similar bandwidth and sensitividy, but much worse decay performance. Then you can draw your own conclusions.

 

[soongsc]

Responses:

Yes, I sell waveguides, but I prefer to sell the kits as I think that you will end up with a better system in the end.

Graaf - you really can be overbearing at times. I don't respond to impolite posts.

Songsc - I see no reason that placing something in the waveguide or in front of a transducer inherently degrades the transient response. It can if not compensated for, but it can also be a vast improvement if done corectly. I've never believed the traditional beliefs and in my own experiments with foam I have found the exact opposite to be more the case.

HOM masks detail without the foam, so when you add foam to reduce HOM, you remove detail as well. So I can't figure out how one knows what is missing other than HOM.

 

[dlr]

Re: Re: Which position to you actually take on this?

The way you express yourself still holds a very provoking taste, the only thing I can respond to talk like this is that if you find a tweeter that extends to at least 20KHz and decays to at least 12db or more from the second peak of an impulse, than do listening tests and additional measurements on your own. Then try a tweater with similar bandwidth and sensitividy, but much worse decay performance. Then you can draw your own conclusions.

This doesn't address your comments whatsoever. Plus, I'm not looking to draw conclusions, I'm curious to learn how you came to your conclusions. There is no connection between them and your reply in this post.

I posted as I did because you frequently make comments that are absolute in nature with little or nothing to support them other than personal anecdote. There is no evidence of which I'm aware to support the absolute position that you first stated (expect loss of transient detail), then qualified later (actually contradictory to an expectation of loss). How should someone react to either the initial absolute statement or the later contradiction?

Dave

 

[soongsc]

Re: Re: Re: Which position to you actually take on this?

This doesn't address your comments whatsoever. Plus, I'm not looking to draw conclusions, I'm curious to learn how you came to your conclusions. There is no connection between them and your reply in this post.

I posted as I did because you frequently make comments that are absolute in nature with little or nothing to support them other than personal anecdote. There is no evidence of which I'm aware to support the absolute position that you first stated (expect loss of transient detail), then qualified later (actually contradictory to an expectation of loss). How should someone react to either the initial absolute statement or the later contradiction?

Dave

If one does not listen to the detailed revealed during live performance as in small lounges, then they will not have appreciation of what detail they are missing, so it really does not make sense to convince them they are missing something becasue they really don't miss it. But because some people don't miss it or care about it, it does not mean the detail cannot be revealed?

So the point that I wish to make is, if you are satisfied with what you are hearing, it is meaningless to explore issues regarding revealing more detail.