gedlee, have you investigated if speaker's box vibrations have influence on waveguide's high frequencies output?
do you think it makes sense to decouple waveguide from woofers' box? thanks.
do you think it makes sense to decouple waveguide from woofers' box? thanks.
MisterTwister said:
In detail I know of no such studies. But this much seems intuitive to me, that a vibrating waveguide would not be a good thing. But none of my waveguides could vibrate. If you have not seen one of them then you should as they are extremely solid and well damped from the construction. So decoupling them would be of no advantage.
We did look at the audibility of box vibrations and found that the boxes were low enough in vibration as to be past the point of diminishing return, because we could reduce the damping and it had no effect.
The waveguides that are typically sold in the marketplace would be a big concern for vibration because they are anything but solid. Fiberglass, unless it is backed up by several inches of foam, is NOT rigid enough. This is the reason that I mount my drivers completely differently, so as to allow the wavguide to be several inches thick at the critical throat. And the injection molded devices, well those need serious work.
In conclusion, yes, vibration in a waveguide would be a significant issue if it were not controlled. In all my designs it is well controlled.
Earl,
Incorrect again!
I yet published few directivity curves in one discussion you were an inevitable protagonist. You'll find them one more time in attached file to that message.
Never I did say that the foam impedance was "purely reactive" but only that it was "reactive", doing such I admit that it can possess a real part added to an imaginary part.
About the longer path travelled by the Homs, surely I didn't invented that. Here is another example of citation of your work from
http://www.htguide.com/forum/showthread.php4?t=16026
"Over the last several years Dr. Geddes has worked on ways to further reduce the HOM in his waveguides. This has resulted in the Refractive Sound Plug or RSP (™ and Patent Pending). This plug is made of very low density open cell polyurethane foam. The
idea is to absorb the HOM as they travel down the waveguide. Since the HOM travel a longer path in the device than the axial wave, the HOM will experience more sound attenuation that the axial wave...."
Best regards from Paris, France
Jean-Michel Le Cléac'h
Incorrect again!
I yet published few directivity curves in one discussion you were an inevitable protagonist. You'll find them one more time in attached file to that message.
Never I did say that the foam impedance was "purely reactive" but only that it was "reactive", doing such I admit that it can possess a real part added to an imaginary part.
About the longer path travelled by the Homs, surely I didn't invented that. Here is another example of citation of your work from
http://www.htguide.com/forum/showthread.php4?t=16026
"Over the last several years Dr. Geddes has worked on ways to further reduce the HOM in his waveguides. This has resulted in the Refractive Sound Plug or RSP (™ and Patent Pending). This plug is made of very low density open cell polyurethane foam. The
idea is to absorb the HOM as they travel down the waveguide. Since the HOM travel a longer path in the device than the axial wave, the HOM will experience more sound attenuation that the axial wave...."
Best regards from Paris, France
Jean-Michel Le Cléac'h
gedlee said:
Attachments
Jean-Michel
You said:
"Also when replying to the question about the modelisation of the foam Earl indicated that the BEM should should not be modelised as an acoustically resistive material but as a reactive material ..."
This clearly says that the material is "NOT" resistive, but "reactive" (your words). "reactive" impedances DO NOT have a real part. And that is still not what I said, I never said anything about impedance only wave speed and that it should be complex. You say things that are incorrect or ambiguous on purpose? Its hard to know what you are saying then.
And yes, your quote is correct, but in no way is contradicted by Musical Noise.
You said:
"Also when replying to the question about the modelisation of the foam Earl indicated that the BEM should should not be modelised as an acoustically resistive material but as a reactive material ..."
This clearly says that the material is "NOT" resistive, but "reactive" (your words). "reactive" impedances DO NOT have a real part. And that is still not what I said, I never said anything about impedance only wave speed and that it should be complex. You say things that are incorrect or ambiguous on purpose? Its hard to know what you are saying then.
And yes, your quote is correct, but in no way is contradicted by Musical Noise.
Interesting graph. I would make two observations. It makes it abundantly clear that it is anything but CD, makes me wonder why you would be so intent in discussing it in a thread about a CD device as a goal. It also indicates that there will be a very narrow range of angles in which there isn't significant deviation from a relatively linear response. Equalizing it on any particular axis results in a similarly small range.
Dave
From the data shown, the foam is not doing that to reduce HOMs. It does have a filter effect as shown in the curves with and without foam, but it actually serves to diffuse the pressure wave front so that pressure is smoother throughout a range of angles.Jmmlc said:
I wonder what the true definition CD is regardless who's design. I interprete it as "Controlled Directivity" which means that you control the directivity to the extent you see fit. Currently there is no "Contant Directivity" device that covers the whole audio spectrum. So really, any for of directivity can be discussed here.dlr said:
soongsc said:
How do you get that? I see the opposite! I guess we see what we want to see.
soongsc said:
CD means Constant Directivity, lets not change the deffinition to suite our arguments. Your definition makes it meaningless since everything is CD is I say it is. And the fact that CD cannot be maintained full bandwidth is also unimportant and completely beside the point.
soongsc said:
I understand that point, however the goals seem to me to be in opposition. The goal of the OS waveguide/foam plug is, if I understand correctly, is a device that when equalized in the off-axis position and aimed as recommended will provide a wide coverage of relatively consistent response due to the characteristics created by the foam plug and OS shape for multiple listeners. All of that is separate from the HOMs, of course.
In contrast, the data as just posted by Jmmlc is antithetical to this goal. That is, his has an extremely narrow control area and cannot exhibit a similarly broad area of coverage in typical room listening environment. It certainly will not provide a similar room response.
Dave
dlr said:
As I have said before, the foam has no significant effect on the directivity, that is completely controlled by the waveguide. The foam is purely for sound quality and not directivity. You are correct in your understand otherwise.
That's why it's "Controlled Directivity" Let's not create illusions of perfect "Constant Directivity" unless there is a more quantifiable definition that well documented. Other than that, it just seem like advertisement tactics.gedlee said:
soongsc said:
CD has always meant Constant Directivity, everywhere and by everyone. You are the one who is attempting to change it. The fact that it doesn't suit you opinions is beside the point. Yes, CD for Constant Directivity is totally abused in the marketplace with horns that aren't even close to being CD being called that, but my waveguides ARE Constant Directivity (as close as anyone has ever come) even if the woofer is not, but that's a seperate discussion. For the context here (waveguides) CD means Constant Directivity.
But the directivity is constant within the range the device is designed for. CD is pretty clear to me.
Nick.
Nick.
Hello Jean-Michel
I did not say anything that contradicts what Dr. Geddes has said. That reply being a response to Soongsc’s incorrect conjecture about varying absorption rates for different angles and its implication on directivity control, was about coverage thus he could not have been talking about HOMs (or so I hope). Indeed, I did not mention HOMs in that post and wrote only about the uniform absorption of the entire main wave as it travels through the foam plug.
I did not say anything that contradicts what Dr. Geddes has said. That reply being a response to Soongsc’s incorrect conjecture about varying absorption rates for different angles and its implication on directivity control, was about coverage thus he could not have been talking about HOMs (or so I hope). Indeed, I did not mention HOMs in that post and wrote only about the uniform absorption of the entire main wave as it travels through the foam plug.
That's why it's "Controlled Directivity" Let's not create illusions of perfect "Constant Directivity" unless there is a more quantifiable definition that well documented. Other than that, it just seem like advertisement tactics.gedlee said:
My browser is getting as confused in this discussion as I am.😀
I guess I'll just go on with my work.
I guess I'll just go on with my work.
Hello,
Someone said this thread was Earl's thread.
Earl's insisted that I show those directivity curves and I did. Now you are saying that I should not show them! That's madness.
Best regards from Paris, France
Jean-Michel Le Cléac'h
Someone said this thread was Earl's thread.
Earl's insisted that I show those directivity curves and I did. Now you are saying that I should not show them! That's madness.
Best regards from Paris, France
Jean-Michel Le Cléac'h
dlr said:
Hello musical noise.
HOMs cannot be separated from the main direct wave and they participate also to the directivity property of the OSwaveguide.
Then am I alone to remind that Earl said that the HOMs have longer path through the foam? No, as we can see from the link
http://www.htguide.com/forum/showthread.php4?t=16026
Best regards from Paris, France
Jean-Michel Le Cléac'h
HOMs cannot be separated from the main direct wave and they participate also to the directivity property of the OSwaveguide.
Then am I alone to remind that Earl said that the HOMs have longer path through the foam? No, as we can see from the link
http://www.htguide.com/forum/showthread.php4?t=16026
Best regards from Paris, France
Jean-Michel Le Cléac'h
musical noise said:
Hello Jean-Michel
I am sure that Earl will answer in more detail, but I do not recall where it was said that HOMs participate in the directivity. I do know from his writings that not only are they separate waves but have different wave velocities as well. I would think that he is looking at velocity as a vector rather than a scalar quantity, as I can’t see wave phenomena in the same medium having different propagation speeds (please elaborate a bit on this Earl if you could).
I am sure that Earl will answer in more detail, but I do not recall where it was said that HOMs participate in the directivity. I do know from his writings that not only are they separate waves but have different wave velocities as well. I would think that he is looking at velocity as a vector rather than a scalar quantity, as I can’t see wave phenomena in the same medium having different propagation speeds (please elaborate a bit on this Earl if you could).
Jmmlc said:
I suppose that this will be argumentative, but I didn't see any insistence, only a comment that you had not made them, not quite the same thing. Having followed this thread, I couldn't recall having seen them in the past myself.
Either you missed my point or are side-stepping it. You now show quite explicit data of your own measurements that shows your design to be exceedingly highly directional and highly frequency dependent as opposed to the pattern desired in an OS waveguide as I understand it and that your design in no way has the properties nor even the goals put forth for the OS waveguide. It is as I said above, antithetical, not necessary bad. So excuse me if I am a bit puzzled as to your intent in the discussion. Are you trying to show some kind of superiority of design in some form over the OS waveguide concept or is it something else? Maybe you'd like to clarify that.
Dave