Highly provocative. I'm not sure Offenbach or G&S is bombastic or even Beethoven, even Brahms or Verdi. A lot of the time folk just play too loud, even in large halls. But perhaps that's a discussion for some other place.
However, it remains, even with folk like Purcell or Bach, if I'm going to get in end a really satisfactory presentation in my small place I'm going to have to produce, one way or another, an environment for the music to shine.
However, it remains, even with folk like Purcell or Bach, if I'm going to get in end a really satisfactory presentation in my small place I'm going to have to produce, one way or another, an environment for the music to shine.
One has to remember that the invention of those concert halls is a result of the commercialisation of symphonic music with the begin of the 19th century. The subscription concerts of the Wiener Klassik (with Haendel in London as a sort of predecessor) and the intention of the new wealthy bourgeoisie to rival with the gentry in artistic terms produced the need for larger auditoriums than before. It was only then when music really started to be a "farfield" event. For a span of 300 years before that artistic music had been played much closer to the (fewer) listeners. If you think of the stadium concerts of today, one has to think that over time music has constantly been removed from the crowds.
Same for "envelopment". Music in churches had always been meant to resemble the nature of god: ubiquitous, overwhelming and enveloping. That´s why the organ has its place in the church. But courtly music was never intended to be dominant in an "enveloping" manner. Even "late" pre-classical composers like Haendel, Bach and Purcell, when having the good luck of disposing of a larger number of musicians, would not cluster them in a large single "symphonic" orchestra, but preferred to distribute them into "double" or "triple" concerts.
Only when large crowds had to be drawn to the concert halls to finance them, bombast took over from sophistication and the volume had to be pumped up for those who confused better music with more SPL.
Porous absorber work only at locations where the velocity of a sound wave is high. For a certain frequency this is at and around 1/4 the wavelength from a wall. That's why porous absorption is more effective when mounted with an air gap.
But if the absorber is too thin, then you'll see "ripples" in the absorption curve, i.e. it's effective at certain frequencies but not at others (see pink curve below).
An externally hosted image should be here but it was not working when we last tested it.
What we need is broad absorption regardless of frequency. This can be achieved by making the absorber thicker. Problem is that thick porous absorber will become reflective at a certain depth. Sound waves can penetrate the material only to a certain degree. To allow the sound waves to pass through the whole absorber for maximum absorption, we need to reduce its flow resistivity. But lower resistivity means less aborption. So for each material there's an optimal thickness which depends on its flow resistivity value.
Good absorption has an α greater than 0.8. To get good absorption down to 100 Hz, the material has to be really thick and the flow resistivity very low. The material will be so fluffy that you have to find ways to hold it in place.
Best, Markus
"Porous absorber work only at locations where the velocity of a sound wave is high."
What causes the velocity of sound to change in a medium?
I was always taught that the velocity of sound is the same in a given media (ignoring temperature).
From Acoustic Treatment and Design for Recording Studios and Listening Rooms:
"As a sound wave travels toward a boundary, the pressure and velocity are reset at the boundary. Therefore the wave has a maximum velocity 1/4 wavelength from the wall. At half a wavelength the velocity is minimum. Then it rises again at 3/4 wavelength. This pattern repeats indefinitely."
"As a sound wave travels toward a boundary, the pressure and velocity are reset at the boundary. Therefore the wave has a maximum velocity 1/4 wavelength from the wall. At half a wavelength the velocity is minimum. Then it rises again at 3/4 wavelength. This pattern repeats indefinitely."
Wow! This is starting to sound easier than I thought it was going to be.
Thanks Stig,
Dan
From Acoustic Treatment and Design for Recording Studios and Listening Rooms:
"As a sound wave travels toward a boundary, the pressure and velocity are reset at the boundary. Therefore the wave has a maximum velocity 1/4 wavelength from the wall. At half a wavelength the velocity is minimum. Then it rises again at 3/4 wavelength. This pattern repeats indefinitely."
Your diagram is wrong.
Velocity does not change with the "phase" of the waveform, only pressure.
Also, the pressure minimum occurs at the bottom of the waveform (+90° phase), not the zero cross point (0° and 180° phase). At the zero cross point the pressure is the same as STP.
Last edited:
Folks,
And we have come full circle.
We are back at fixing the room, instead of fixing the source of the problems, that is the speaker.
So, how about we get back to fixing the speaker?
For example, it is possible to make a 15" X 30" X 15" (WHD) system that covers 80Hz to 600Hz with a 6dB DI (lower frequency response possible if we allow DI to degrade) and which hands over to a system at higher frequencies that also exhibits 6dB DI at the crossover point and then rises to a maximum of 10dB DI.
It is also possible to produce a larger version of the first device (24" X 48" X 24") that can cover 20Hz to 150Hz with a 6dB DI.
Either system exhibits a rear "null" that is at least 20dB below the front output.
I wonder how much absorbtion we can save by this little expedient of correctly designing a speaker to fit into a room?
Who here would agree that such a system with a DI of 6dB from 20Hz to around 1KHz and then smoothly rising to 10dB would be desirable and in "normal" rooms a "good thing" (a "good thing" is kinda like Winnie the Pooh saying "Hunny is good").
Ciao T
And we have come full circle.
We are back at fixing the room, instead of fixing the source of the problems, that is the speaker.
So, how about we get back to fixing the speaker?
For example, it is possible to make a 15" X 30" X 15" (WHD) system that covers 80Hz to 600Hz with a 6dB DI (lower frequency response possible if we allow DI to degrade) and which hands over to a system at higher frequencies that also exhibits 6dB DI at the crossover point and then rises to a maximum of 10dB DI.
It is also possible to produce a larger version of the first device (24" X 48" X 24") that can cover 20Hz to 150Hz with a 6dB DI.
Either system exhibits a rear "null" that is at least 20dB below the front output.
I wonder how much absorbtion we can save by this little expedient of correctly designing a speaker to fit into a room?
Who here would agree that such a system with a DI of 6dB from 20Hz to around 1KHz and then smoothly rising to 10dB would be desirable and in "normal" rooms a "good thing" (a "good thing" is kinda like Winnie the Pooh saying "Hunny is good").
Ciao T
Loudspeakers and the room ARE one system. So fixing only one part will never fix all problems. Furthermore depending on the loudspeaker concept, only room treatment will be able to fix certain problems. It might be just more practical to use room treatment.
Best, Markus
No. You can draw it as a function of velocity or as a function of pressure. Doesn't change the validity, just the labeling.
Velocity of what? It surely isn't the velocity of sound, which is constant in a medium of uniform density.
I don't understand your point.
Put that system in a room. Now, what is dominating the sound at the listening position? The loudspeaker or the room?
What about the region around the Schröder frequency?
That's because you don't understand the diagram. Nobody said that the speed of sound changes.
Please see Particle velocity - Wikipedia, the free encyclopedia
Lots of confusion above. There is a difference between partical velocity and phase velocity (speed of sound).
There is an excellent book by Uno Ingard on absorption. In the end all that matters for a dead hanging absorber placed away from a wall is its thickness and flow resistance and distance from the wall. Pleating the fabric makes its "virtual thickness the same as the fiberglass and its flow resistance is comparable. Hence, in theory (and here the theory is quite accurate), the two will act the same if done correctly. Get Dr. Ingards book if you really want to see the details, although its quite rare.
And yes Markus, I absolutely agree that the loudspeakers and rooms are one system and only when one looks at the problem in that way does the optimum approach present itself.
There is an excellent book by Uno Ingard on absorption. In the end all that matters for a dead hanging absorber placed away from a wall is its thickness and flow resistance and distance from the wall. Pleating the fabric makes its "virtual thickness the same as the fiberglass and its flow resistance is comparable. Hence, in theory (and here the theory is quite accurate), the two will act the same if done correctly. Get Dr. Ingards book if you really want to see the details, although its quite rare.
And yes Markus, I absolutely agree that the loudspeakers and rooms are one system and only when one looks at the problem in that way does the optimum approach present itself.
Now I understand your point and agree. However, I still think that diagram is wrong with respect to the pressure.
Let's assume that the cartoon illustration of the sine wave represents the sound pressure wave. Further, let's assume that the first zero cross on the right of the diagram is 0° phase angle and it moves right to left.
At 90° the atmospheric pressure is at its maximum. At 180° the pressure returns to normal room pressure (standard pressure). At 270° the pressure wave is at its minimum. At 360° the pressure returns to the standard pressure again and the process repeats.
One could change the diagram to read maximum positive pressure and maximum negative pressure, but the way it is annotated the diagram implies that the pressure is equal at 90°*and 270°, which it is not.
You quoted, "As a sound wave travels toward a boundary, the pressure and velocity are reset at the boundary. Therefore the wave has a maximum velocity 1/4 wavelength from the wall."
This I struggled with. I think the particle velocity at the wall boundary is immaterial. The wall simply acts as an acoustic mirror and reflects a portion of the initial wave back toward the source.
The particle velocity 1/4 wavelength from the wall is also immaterial. Indeed, it is entirely dependent on the phase angle of the wave when it meets the wall. That point when the wave strikes the wall boundary has equal probability of occurring at any phase angle.
What is important is that the reflected wave will be 180°*out of phase with the incident wave at 1/4 wavelength from the wall boundary. This is a wave node and provides cancellation at that point.
The cited article I think has some flaws describing the physics behind the principle. That doesn't mean that the effect does not work; it does! However, I think the supporting physics cited by the author is incorrect or incorrectly applied.
If I had more time I could sort it out for you, but I don't. Maybe later.
Go to http://www.falstad.com/ripple/ and draw a straight wall, then observe what happens in front of the wall.
Best, Markus
Best, Markus
Its called "Sound Absorption Technology"
In absolute pressure pressure terms you are correct, but no one in acoustics ever deals in that reference base. We always talk in terms of pressure magnitude "about" the ambient, and in that case Markus plot is correct. These is a reason for this and that is that it makes both the pressure and the velocity variables oscillate about zero. Considering the static pressure is an unnecessary complication.