[ronny31]

I was thinking, the angle of a sound wave affects how much of the sound is transmitted through the wall. Thus, I reason that better sound transmission dampening can be achieved if the 2 channel stereo or surround system is position diagonally in a room instead of being on one wall, firing towards the parallel rear wall. Like this:

Anyone have experience with this?

I'll quote a comment from another thread (this thread)

I have applied his techniques with great results

https://www.youtube.com/watch?v=84Pf0ycbyBM

Even this guy says to put the speakers at a wall, and doesn't mention diagonal setups. Is it a particular reason or is it just because he haven't thought of it?

PS: Ignore perfectly square room as reason for it being bad. Also, speakers and speaker placement not to scale. Illustration purposes only.

 

[jaddie]

I was thinking, the angle of a sound wave affects how much of the sound is transmitted through the wall. Thus, I reason that better sound transmission dampening can be achieved if the 2 channel stereo or surround system is position diagonally in a room instead of being on one wall, firing towards the parallel rear wall. Like this:

Anyone have experience with this?

I'll quote a comment from another thread (this thread)


Even this guy says to put the speakers at a wall, and doesn't mention diagonal setups. Is it a particular reason or is it just because he haven't thought of it?

PS: Ignore perfectly square room as reason for it being bad. Also, speakers and speaker placement not to scale. Illustration purposes only.

What do you mean by "sound transmission dampening"? Transmission of sound through the walls? Or are you referring to some acoustic quality within the room?

Sorry, I can't devote over an hour to a video right now.

 

[Bill Fitzmaurice]

The bulk of through-wall transmission is in the low frequencies, below the baffle step frequency, which radiate omni-directionally, so which direction the speaker is aiming won't make any difference. For that matter where subwoofers are concerned, the major source of through-wall transmission, there's really no such thing as 'aiming' when the dispersion pattern is 360 degrees.

 

[ronny31]

The bulk of through-wall transmission is in the low frequencies, below the baffle step frequency, which radiate omni-directionally, so which direction the speaker is aiming won't make any difference. For that matter where subwoofers are concerned, the major source of through-wall transmission, there's really no such thing as 'aiming' when the dispersion pattern is 360 degrees.

So you're saying "for low frequencies, it won't lower sound transmission much if at all". What about in a room where the wall doesn't let much bass through from the star because its so solid, and then what about high frequencies?

The low frequency wave from the speakers will radiate omni-directionally, but it will hit the wall one tiny piece at a time, not all at once. Won't this lower the amount of vibration the pressure wave can bring forth in the material of the wall?

What do you mean by "sound transmission dampening"? Transmission of sound through the walls? Or are you referring to some acoustic quality within the room?

Sorry, I can't devote over an hour to a video right now.

Sound transmission is sound that goes through the material and out the other side.

 

[Bill Fitzmaurice]

The low frequency wave from the speakers will radiate omni-directionally, but it will hit the wall one tiny piece at a time, not all at once.

That's not the case when you're dealing with wavelengths from 10 to 50 feet long.

 

[ronny31]

That's not the case when you're dealing with wavelengths from 10 to 50 feet long.

Its still the case, but if the wavelength is 10 feet long the wall has to be twice as long to contain four sets of pressure regions (two high pressure two low pressure).
Even with just enough room to contain half a wavelength the pressure difference across the wall will be equivalent to half the peak to bottom pressure difference. The time to travel also makes some difference. a 10 foot sound wave has 1/114th of a second time difference between peaks. 1/228 of a second between peak to bottom, 1/456 between peak to centerline of the wave. So along a 10 foot wall section the first bit of the wall has the peak pressure, the middle has the bottom pressure, the end has peak pressure. Between the middle and each edge there's a no-pressure section which has the exact atmospheric pressure. And the pressure differences are gradual, not square waveforms. We can name each pressure region "a pressure region".

Compare these two figures, small circle indicates source of low frequency sound waves. Black circles represent the peak pressure locations.

Note the small pressure regions.

Note the much larger pressure regions where they would hit the wall.
If this is soft drywall then the small pressure regions are going to have a much harder time imparting a uniform force to the drywall than the large pressure regions. No?

Do anyone have some experience or papers to link to or something?

 

[RayDunzl]

Arny would know.

-

However, redraw your low frequency waves to the proper scale for the room in question and see what you get.

You might have something there if it is a large venue.

Those waves look to be maybe 500 to 1kHz for a residential size room.

 

[ronny31]

Arny would know.

-

However, redraw your low frequency waves to the proper scale for the room in question and see what you get.

You might have something there if it is a large venue.

Those waves look to be maybe 500 to 1kHz for a residential size room.

I want to understand this in all rooms, not one room. I could draw a low frequency (these are about 200hz) but then I'll have to include different pressures other than just peaks and bottoms. But you can get that from these figures by just imagining that the first circle represents one portion of the peak to peak pressure and the next circle represents the next portion, etc.

 

[RayDunzl]

200hz wavelength is 5.65 feet

So top picture, the speaker is 17 feet from the wall.

Bottom picture 45 feet.

As I interpret it.

Neither of those correspond very well to your initial picture with the speakers up against the wall, assuming a typical little room in a typical little house or aparto.

Carry on!

 

[kiwi2]

If your main goal is to reduce the noise in adjacent rooms then make sure you haven't got the listening position in a null for the lower bass frequencies. i.e. having the LP right in the centre of the room where the bass is usually the weakest. An AVR's auto calibration will turn the volume up on the subs a lot higher to get the level right for the LP in the centre of the room.


If you have such a setup and you walk over towards the walls when the system is playing you will notice the bass much louder around the walls.


Alternatively if you have the LP closer to one of those boundary walls then the AVR's calibration will have the subs at a much lower level than if you were sitting in a null somewhere near the centre of the room.

 

[ronny31]

If your main goal is to reduce the noise in adjacent rooms then make sure you haven't got the listening position in a null for the lower bass frequencies. i.e. having the LP right in the centre of the room where the bass is usually the weakest. An AVR's auto calibration will turn the volume up on the subs a lot higher to get the level right for the LP in the centre of the room.


If you have such a setup and you walk over towards the walls when the system is playing you will notice the bass much louder around the walls.


Alternatively if you have the LP closer to one of those boundary walls then the AVR's calibration will have the subs at a much lower level than if you were sitting in a null somewhere near the centre of the room.

My goal is to know what happens when you measure sound transmission of the wall and adjust the angle of the wall relative to the sound source and measuring device. I didn't find any experiments where only angle was the variable.

 

[jaddie]

My goal is to know what happens when you measure sound transmission of the wall and adjust the angle of the wall relative to the sound source and measuring device. I didn't find any experiments where only angle was the variable.

You probably won't find that data easily, mostly because in reality its not that much of a factor.

Transmission loss of a wall is frequency dependant, more at HF, far less at LF. Low frequencies pass through walls because the wall acts as a diaphragm. As wavelengths get longer they act like pressure waves which impact the wall/diaphragm pretty much without depending on the direction of origination. As wavelengths get shorter and frequencies higher they become less like just pressure, more like a wave that impacts a barrier, and in that case, direction will make a difference, though very little changes at +/- 45 degrees. But you really can't consider a wall without considering the total room as a system. There are flanking paths, penetrations, etc., all of which reduce the effectiveness of the wall against sound transmission. In the end, the angle of incidence is a very minor factor, and a non-factor at low frequencies.

This link helps a little with background, sorry I couldn't find something better. It doesn't deal with angles, but you can see what's going on with a wall across the spectrum.

https://www.soundproofingcompany.com/soundproofing101/understanding-stc/

 

[ronny31]

You probably won't find that data easily, mostly because in reality its not that much of a factor.

I know I probably won't find that data easily, that's why this thread is here. I'd like to know how much of a small effect it has, because it definitely has some effect compared to its cost of zero dollars.

 

[jaddie]

I know I probably won't find that data easily, that's why this thread is here. I'd like to know how much of a small effect it has, because it definitely has some effect compared to its cost of zero dollars.

Again, it's frequency dependent. Below 100Hz, 45 degree angle of incidence makes no measurable difference. Above 1000Hz, the factors that limit the maximum acoustic isolation dominate, so the slight difference in loss from a 45 degree angle of incidence are swamped by imperfect wall sealing, penetrations, flanking paths, etc. You also won't have that perfect 45 degree angle anyway unless your room is fairly anechoic.

But from an isolation standpoint, other factors dominate. For example, you build a theoretical 60dB STC wall, then punch a duplex outlet box in it, now you have a theoretical 40dB wall. Residential construction is horribly leaky, because they usually don't bother with separate stud systems, and there are often shared common spaces above and below the room. If the two rooms in question share HVAC systems, and there are no duct silencers, there's a huge source of leakage.

In a perfect situation the change in transmission from a 45 degree angle vs zero degrees will range from about 3dB max to zero, frequency dependent. And you won't have that perfect situation.

 

[ronny31]

Again, it's frequency dependent.

I want to find some papers that say precisely what circumstances they used to measure sound absorption due to angle, which also specifies the measured amounts along the frequency spectrum.

We don't regularly use HVAC in Norwegian homes, we do not have flammable gas in the average home.

 

[jaddie]

I want to find some papers that say precisely what circumstances they used to measure sound absorption due to angle, which also specifies the measured amounts along the frequency spectrum.

Let us know if you find them.

We don't regularly use HVAC in Norwegian homes, we do not have flammable gas in the average home.

HVAC ducts are only one source of leakage. There are plenty of opportunities for flanking paths, structure-born paths, penetrations for pipe or wires, etc.

I've tried to express why this information is probably not available, but you're welcome to search. The biggest problem I see with trying to develop transmission loss figures for different angles of incidence would be that the data would also have to include distance from the source to the partition, as well as the total size of the partition. This is because of the wavelengths involved. At 1KHz, the approximate wavelength is 1'. If you have a source 10' away from a 10' wide by 10' high partition, the wave hitting the wall will reverse phase every few feet along the wall. Moving the source to any angle doesn't change that, though the exact location and of the phase reversals will be somewhat different. The wall, in any case, is subject to the same type of mechanical stimulus, and assuming a wall of uniform stiffness, the amount of transmission loss through the wall will not change appreciably either. In other words, no appreciable change in transmission loss vs angle at an average of 10' from the source. If we bump that distance out to 1000', the wave front becomes nearly parallel to the wall, and changing the angle of incidence to 45 degrees would change the mechanical stimulus at the wall form a single unified wave front to several waves of varying phase, which could in theory change the measured transmission loss. Let us know if you get a 1000' by 1000' room in which to run those tests. Oh, buy the way, it should be anechoic.

If you lower the frequency, you change the number and location of wave phase reversals, until you get somewhere around the Schroeder frequency, then then there's no point in analyzing the number of phase reversals along a partition, it begins to act as a diaphragm at all frequencies below. And, by the way, the average wall is terrible for transmission loss at low frequencies.

Again, the issues that degrade transmission loss are many, and of far greater impact.

For all the above reasons, I personally would abandon the search for the data and concentrate on things that make a difference in transmission loss, like wall construction, eliminating perforations and flanking paths.

 

[ronny31]

Stop bloody telling me I shouldn't bother! Calories come in the form of cake and red meat and I can spend however many calories I want doing investigations into the effect of incidence angle on sound transmission no matter how pointlessly low the effect is compared to other things. Its a boring subject to hypothesize that I can get extra db sound transmission loss by doing all the things everyone already agrees works to that end.

I'll update if I find some data.

 

[jaddie]

Stop bloody telling me I shouldn't bother! Calories come in the form of cake and red meat and I can spend however many calories I want doing investigations into the effect of incidence angle on sound transmission no matter how pointlessly low the effect is compared to other things. Its a boring subject to hypothesize that I can get extra db sound transmission loss by doing all the things everyone already agrees works to that end.

I'll update if I find some data.

Read my last sentence. It says "I would abandon the search", not "You shouldn't bother." Bother away!

In acoustic isolation we deal with 6dB, 10dB, 20+dB changes because they are noticeable to those paying for the improvement. 3dB changes are around the area of measurement error, and not reliably reproducible. That's why I wouldn't bother. I was just trying to save you some frustration and time.

Why not research something that has at least some promise, like the application of active anti-noise as an augmentation in acoustic isolation?

But do whatever you want, ignore whatever you want, burn those calories in whatever way makes you happy. I'd never discourage the burning of calories!

 

[ronny31]

In acoustic isolation we deal with 6dB, 10dB, 20+dB changes because they are noticeable to those paying for the improvement. 3dB changes are around the area of measurement error, and not reliably reproducible.

Do you know what the profit margin is on something that costs nothing like a diagonal stereo?
Also, you never just sell one thing, you say "do you want a coke with that? Do you want to supersize? Do you want fries with that? Do you can bacon with that? Do you want onion-rings with that? Do you want (...)". So diagonal placement is just one more thing to sell. And if we know it works x amount in this and that precise circumstance, we can recreate it under those circumstances.

 

[jaddie]

Do you know what the profit margin is on something that costs nothing like a diagonal stereo?
Also, you never just sell one thing, you say "do you want a coke with that? Do you want to supersize? Do you want fries with that? Do you can bacon with that? Do you want onion-rings with that? Do you want (...)". So diagonal placement is just one more thing to sell. And if we know it works x amount in this and that precise circumstance, we can recreate it under those circumstances.

Agreed in principle, but I won't be "selling" it because my clients come to me wanting "sound proof" rooms, which there is no such thing in real life. I need to give them isolation on the order of STC-50 or better. If I build to that figure, I get between STC-45 and STC-50 if I'm really, really careful and no other contractor messes it up. Those are very expensive rooms to build, and very difficult to pull off and hit the target STC. At that level, creating a weird floor plan the wife will hate that may or may not gain 1dB mid band is simply not going to happen, and I'm not going to suggest it.

If you ordered a $50 steak and they offered you some sort of special salt that may or may not taste any different, but to use the special salt you have to stand on your head to eat it, what would you choose? We aren't up-charging for bacon, they're already ordering bacon, but we'd be up-charging for "special" bacon that may not taste any different, and making them walk across the street to get it.

There is such a thing as negative margin. It happens when you sell something that doesn't work, but you have to stand behind it anyway. It's not cost free, there's a cost in aesthetics, which are already at issue with things like a flock of huge subwoofers, perfectly neutral gray walls, etc. Each of those has a measurable and repeatable benefit, and they're hard to sell. I'm not going to suggest a wacky floor plan and fight for it unless there's a provable benefit that outweighs the cost...that's the cost in aesthetics.

My analysis based on physics and known partition performance data proves to me there's no benefit, none. It's not going to work X amount, it'll be 0.01X, and be below measurement error, making it irreproducible.

If you find other data, I'll reconsider my position.