I am not criticizing, at least it's not my intention. It was always my intention to look at all different designs objectively.gedlee said:
Providing data on dome tweeters would be really off topic. If anyone wishes to open a thread to discuss this issue. I'd be glad to post my data on an old Thiel tweeter.
As for this thread. I'm already posting more new data than probably any other member in the past few months. It would be nice if you could post more data than criticizing views that differ from yours, maybe calculation of impulse symmetry that you criticize others about?
Hello Soongsc,
What you said about someone preference that could be for "no foam" inside the waveguide make me remember of many experiments me and others have done on fiber filling ratio inside closed enclosure or bass-reflex. (no scientific study I know about this though).
Apart the different "tuning" required for the box volume (or/and the vents if any) a majority appeared to concluded that too much foam was detrimental to the sound...
I used to study ultrasounds transmission through porous rocks and I doubt that the only effect of the foam inside the waveguide is linear as it has been said. I would like to have access to a study of the shape of pulses at different angle from the axis, with and without foam...
Best regards from Paris, France
Jean-Michel Le Cléac'h
What you said about someone preference that could be for "no foam" inside the waveguide make me remember of many experiments me and others have done on fiber filling ratio inside closed enclosure or bass-reflex. (no scientific study I know about this though).
Apart the different "tuning" required for the box volume (or/and the vents if any) a majority appeared to concluded that too much foam was detrimental to the sound...
I used to study ultrasounds transmission through porous rocks and I doubt that the only effect of the foam inside the waveguide is linear as it has been said. I would like to have access to a study of the shape of pulses at different angle from the axis, with and without foam...
Best regards from Paris, France
Jean-Michel Le Cléac'h
soongsc said:
As I thought, it should be enough to know the frequency response in combination with the phase response. In this case one does not need the phase response to describe the foam/grille impact on sound, as they do not insert an energy storage element. So the sonogram/radiation diagram is an adequate illustration, isn't it?Jmmlc said:
Best regards, Timo
Hello Tiki,
I don't know if we can a priori say that the foam don't store energy... even if it is called "open cells" the foam contain cells with different links to neighbouring cells... it is not a continuum. Poroacoustics in such medium is not something we can a priori predict so easily...
But from another point of view, foam by definition possess a solid skeletton and the speed of sound in a solid is far larger than in air. We should verify if first arrival by solidian transmission is something that happens or not...
Best regards from Paris, France
Jean-Michel Le Cléac'h
I don't know if we can a priori say that the foam don't store energy... even if it is called "open cells" the foam contain cells with different links to neighbouring cells... it is not a continuum. Poroacoustics in such medium is not something we can a priori predict so easily...
But from another point of view, foam by definition possess a solid skeletton and the speed of sound in a solid is far larger than in air. We should verify if first arrival by solidian transmission is something that happens or not...
Best regards from Paris, France
Jean-Michel Le Cléac'h
tiki said:
And I actually have a sheet of 1cm thick open cell foam on the wall behind the speakers which does a great job absorbing higher frequency reflections allowing better image and soundstage depth. I have also played around with stuffing in an enclosure, and about 10% weight difference seems to start presenting audible differences when compared, but may be unnoticed when listened to individually.Jmmlc said:
In the simple sims I did with the BEM software, it seems that in order to obtain optimum design of a horn/guide, it is necessary to consider wave travel starting from the diaphragm. I am sure Earl realizes this, otherwise he would not have considered designing a phase plug as he mentioned earlier in this thread.
The length of the part from the diaphragm is critical, especially in an OS wave guide because the exit of the throat acts like a lip of a wave guide, only at a higher frequency. Too short, there will be HOMs above certain frequency. Too long, then there seems to be some kind of reflection from the throat exit. From what I can see based on sims, it would probably be very very difficult to get a pure plane wave at the smallest section of the throat at all frequencies. So right now, I'm really wondering what the third wave guide in my test will be.
What I refer to as resolution is the capability to resolve low level signals that exist in recordings. Unfortunately frequency response is not directly related with this although increased bandwith does seem to help. In video, there are clear definitions regarding resolution even though much is not known to the public. In audio, there seems to be not clear method of defining it.MartinQ said:
To give everone a feel as to what is going on, here is a new set of pics. Basically quite a ways back I posted a pic indicating how the throat, guide, size effect how dispersion is controlled which had inspired me. Also inspired by lot's of things mentioned in this thread by Dr. Geddes, this BEM software really is good to explore various options to get a general feeling what's going on. It's not coing to be accurate for a final call, but it's good enough for those without much math capability to get things rolling.
Attachments
Hello Jean-Michel,
Thanks!
Regards, Timo
Of course you are right - in principle. In my opinion the damping will dominate the energy storage, so the eventually existing resonances should be marginal. What else is the reason for using open cell foam like Basotect for acousting dampening purposes? Until now I did not notice any additional resonances by adding damping material in my (rare) measurements, even though the reflections due to acoustic impedance changes (they are low in most cases).Jmmlc said:
Hmm, as I believe to remember, soft materials can exhibit significantly lower speeds of sounds than air. The speed of sound along the way through the open cells will be lower too. But I did not measure, maybe I will do a "test" at the next opportunity.Jmmlc said:
Thanks!
Regards, Timo
Hell Tiki,
I never spoke of resonance as a feature that the foam could exhibit. The effect I think is more about delayed signals varying with frequency. This will be seen as a distortion of the shape of the pulse reponse.
As a difference to tuned pipe, the effect of reflected energy on the impedance curve of horn loaded driver are quite small, we must look at very tiny changes there (same as for the reduction of small parasitic impedance peaks due to internal stationary waves inside closed enclosure using dampening material).
I don't deny that the dampening of the HOMs by the foam could have a benefitial effect (I use to experiment a waveguide with and without foam and it was far less tiring with the foam than without...) on the sound of the waveguide. But the question raised by Soongsc, is: "is there some negative effects , by example on the dynamics- that were ignored until now using the foam plug inside the horn)..."
Best regards from Paris, France
Jean-Michel Le Cléac'h
I never spoke of resonance as a feature that the foam could exhibit. The effect I think is more about delayed signals varying with frequency. This will be seen as a distortion of the shape of the pulse reponse.
As a difference to tuned pipe, the effect of reflected energy on the impedance curve of horn loaded driver are quite small, we must look at very tiny changes there (same as for the reduction of small parasitic impedance peaks due to internal stationary waves inside closed enclosure using dampening material).
I don't deny that the dampening of the HOMs by the foam could have a benefitial effect (I use to experiment a waveguide with and without foam and it was far less tiring with the foam than without...) on the sound of the waveguide. But the question raised by Soongsc, is: "is there some negative effects , by example on the dynamics- that were ignored until now using the foam plug inside the horn)..."
Best regards from Paris, France
Jean-Michel Le Cléac'h
tiki said:
Hello Soongsc,
Any body have access to my spreadsheet at
http://ndaviden.club.fr/outils/axial.zip
so the best thing should be that you calulate the profile yourself and import it in your software, so the further process will be the same as the simulations you yet presented to use.
Best regards from Paris, France
Jean-Michel Le Cléac'h
Any body have access to my spreadsheet at
http://ndaviden.club.fr/outils/axial.zip
so the best thing should be that you calulate the profile yourself and import it in your software, so the further process will be the same as the simulations you yet presented to use.
Best regards from Paris, France
Jean-Michel Le Cléac'h
soongsc said:
Hello Soongsc,
in the sheet "entrée_et_calculs" you have 3 parameters to set:
1) "diamètre de gorge (mm)" which is the throat diameter. put 25,4 for a 1 inch throat.
2) "fréquence de coupure acoustique (Hz)" which is "acoustical cut off frequency of the horn" and by default is 160. You'll have to change that value to 650 (or whatever you want)
3) "coefficient T dans la loi d'expansion =" the T coefficient (when T >>1 you tend toward waveguides). Default value is 0, you'll have to change the value to 2,7.
Then you may go inside "profils" to look at the profile of the axial horn (in red, don't bother with the blue curve)
Then in the sheet "sous_echantillonage_de_points" (= subsampling of points of the profile) you'll find a subsampling of the coordinates of the points describing the profile are under the writtings:
"profil du pavillon dans le plan vertical".
Each point is associated with 2 coordiantes: "distance to throat" and "half width" (well that's english language...)
Best regards from Paris, France
Jean-Michel Le Cléac'h
in the sheet "entrée_et_calculs" you have 3 parameters to set:
1) "diamètre de gorge (mm)" which is the throat diameter. put 25,4 for a 1 inch throat.
2) "fréquence de coupure acoustique (Hz)" which is "acoustical cut off frequency of the horn" and by default is 160. You'll have to change that value to 650 (or whatever you want)
3) "coefficient T dans la loi d'expansion =" the T coefficient (when T >>1 you tend toward waveguides). Default value is 0, you'll have to change the value to 2,7.
Then you may go inside "profils" to look at the profile of the axial horn (in red, don't bother with the blue curve)
Then in the sheet "sous_echantillonage_de_points" (= subsampling of points of the profile) you'll find a subsampling of the coordinates of the points describing the profile are under the writtings:
"profil du pavillon dans le plan vertical".
Each point is associated with 2 coordiantes: "distance to throat" and "half width" (well that's english language...)
Best regards from Paris, France
Jean-Michel Le Cléac'h
soongsc said:
It makes me wish the girlfriend that studied French was around.