Analytical Analysis - Room Gain

[loudnoise]

What a great resource

 

[abdo123]

I just discovered this thread! I can’t believe the mode at 0Hz can provide as much as 60 dB of gain free of charge!

Makes me want to study the physics behind it. Great write up and thank you for sharing!

 

[René - Acculution.com]

I just discovered this thread! I can’t believe the mode at 0Hz can provide as much as 60 dB of gain free of charge!

Makes me want to study the physics behind it. Great write up and thank you for sharing!

Good to hear. More topics coming soon.

 

[Newman]

I think I will tackle this at a later point, so I have put a pin in it.

Thanks. I hope you do get around to it, because ‘real life audio effects’ are very interesting.

cheers

 

[spalmgre]

I have posted a link to this thread on a Finnish HiFi group on FB. I tried to give e short explanation in Finnish as I know that not everyone is able to understand the explanation given here.

People have problems understanding this as Roome Gain is understood as a broader feature than what this thread's initial post is discussing.
People write that room gain is also there with a vented box when it is in a corner.

I would refer this to as "Loudspeaker Spatial Loading" but it is kind of difficult to explain that it does not represent Room Gain as it also makes the speaker sound louder in a room.

True Audio Speaker Topics: Spatial Loading

This Tech Topic reviews the Spatial Loading of loudspeakers.

trueaudio.com

 

[René - Acculution.com]

I have posted a link to this tread on a Finnish HiFi group on FB. I tryed to give e short explenation in Finnish as I know that not everyone is able to understadand the explenation given here. People have problems understanding this as Roome Gain is understood as a broder feature than what this thread's initial post is discussing.
People write that room gain is also there with a vented box when it is in a corner. I would refer this to "Loudspeaker Spatial Loading" but it is kind of difficult to explain that it does not represent Room Gain as it does also makes the speaker sound louder in a room.

As some loudspeaker companies have found an interest in the forum post here, I will be making an audioXpress article showing pretty much the same steps as here. Hopefully that can clear up the confusion that there might be. There is nothing going on that cannot be explained by traditional acoustics theory, but it might still be difficult to take in. There is a gain for a vented speaker too, but the roll-off is different than the for the sealed enclosure. The point in this post was to show why a sealed box can give a constant pressure even though it has a anechoic roll-off, but in the article there will be both a sealed and a vented box. If there are question on the fb site, feel free to translate them and put them here.

 

[spalmgre]

The most common question concerning 0Hz. I tried to explain that don't think about the 0Hz but what happens when you move towards 0Hz. But this seems to be difficult to understand.
AudioXpress is not available to everybody so consider publishing elsewhere also.

 

[Newman]

There is a gain for a vented speaker too, but the roll-off is different than the for the sealed enclosure. The point in this post was to show why a sealed box can give a constant pressure even though it has a anechoic roll-off,

Is this not already well-known?

Sealed box rolls off at -12 dB/oct, room gains at +12 dB/oct, summed = flat to DC. But only true if:-

1. Sealed box is designed to match the rolloff frequency with the frequency where room gain kicks in (relatively easy to design), AND
2. Room is fully sealed so it pressurizes (difficult to achieve in normal rooms and not realistic in practice).

And not applicable to vented box because its rolloff is -18 dB/oct.

If the above is your topic, it is nothing new or esoteric?

cheers

 

[spalmgre]

If the above is your topic, it is nothing new or esoteric?

And not applicable to vented box because its rolloff is -18 dB/oct.

It has not been explained in this way and is therefore interesting to many of us.

Did you read why the vented box doesn't benefit from Room Gain as it has been explained here before?

 

[Newman]

I’m not sure I understand your question.

 

[abdo123]

1. Room is fully sealed so it pressurizes (difficult to achieve in normal rooms and not realistic in practice).

Corner loading (or just two boundaries) are usually enough to counteract this condition. My room doesn't even have a door and i get a flat measuring response with my subwoofer.

 

[Thomas_A]

Corner loading (or just two boundaries) are usually enough to counteract this condition. My room doesn't even have a door and i get a flat measuring response with my subwoofer.

Just curious, how do you get there? Or out?

 

[spalmgre]

I’m not sure I understand your question.

"And what about the ported sub? When the driver moves inwards at low frequencies below the driver resonance, air will just be pushed out of the port, and so there is no net volume displacement; there is an acoustic short-circuit, just as you have for a dipole. So again it makes physical sense that we cannot take the same advantage of room gain as for the closed enclosure case."

 

[spalmgre]

Corner loading (or just two boundaries) are usually enough to counteract this condition.

This is the understanding I think most people have of what "Room gain" is: Spatial loading Pii, Pii 2, Pii4...

To me, this thread explains something else. But René also calls it "Room gain".

I really like to get a comment on when or what are we supposed to call Room Gain".

 

[René - Acculution.com]

Is this not already well-known?

Sealed box rolls off at -12 dB/oct, room gains at +12 dB/oct, summed = flat to DC. But only true if:-

1. Sealed box is designed to match the rolloff frequency with the frequency where room gain kicks in (relatively easy to design), AND
2. Room is fully sealed so it pressurizes (difficult to achieve in normal rooms and not realistic in practice).

And not applicable to vented box because its rolloff is -18 dB/oct.

If the above is your topic, it is nothing new or esoteric?

cheers

Well, I am not the right person to ask about what is well-known or not, as I have worked with vibroacoustics for to many years to be surprised about much. But I see it being discussed, and so there must be an interest, I guess? A vented box has a fourth order roll-off, not third, but otherwise, sure, they both see the same room environment, but the results is not the same, because the sources are different. They both get a second order "boost" in some sense. The math has been there for decades, so not very esoteric, no.

 

[René - Acculution.com]

It has not been explained in this way and is therefore interesting to many of us.

Did you read why the vented box doesn't benefit from Room Gain as it has been explained here before?

I should have put a figure showing the response for the vented box, as it also of course has a different slope than anechoically; both are affected by being in a room. But room gain was seemingly discussed as the effect of 'flat output from a sealed box' so that is what I wanted to show the most.

 

[René - Acculution.com]

This is the understanding I think most people have of what "Room gain" is: Spatial loading Pii, Pii 2, Pii4...

To me, this thread explains something else. But René also calls it "Room gain".

I really like to get a comment on when or what are we supposed to call Room Gain".

Yes, but I will call that effect Boundary Gain in the upcoming article: Infinite boundaries that constrain the source to limit the solid angle it looks into, will change the acoustic power and other acoustic quantities (4pi, 2pi, ...), but that is different from having a room totally enclosing the wall with modes occuring, and different again from SBIR (boundaries(s) as well as distance from the source to the boundary(s)), so I will show these steps towards what is ultimately just the room at low frequencies acting as an acoustic compliance, with an impedance that decreases with frequency, and with displacement increasing with frequency for a flat velocity, the two counterbalance each other. So lumped or modal, the result is the same, as it has to be.

 

[René - Acculution.com]

The most common question concerning 0Hz. I tried to explain that don't think about the 0Hz but what happens when you move towards 0Hz. But this seems to be difficult to understand.
AudioXpress is not available to everybody so consider publishing elsewhere also.

The 0 Hz mode is certainly there, and it is clearly seen that it has the same characteristics as the other modes, with an increase in pressure when the frequency gets closer and closer to it. With negative frequencies included, this might be illustrated even better. But one can also just think of the room as a capacitance being fed a current of "Volume velocity divided by i*omega) for a constant displacement. There might be a video on the way where a loudspeaker company and myself discuss it, and perhaps an available paper. I did not know that this little topic was of much interest to anyone, but I can offer a YouTube live or something an evening??

 

[Thomas_A]

What would be interesting to know is whether there are any studies of what the optimum alignment would be (as preference)? Should it be flat, sloping down or up?

 

[abdo123]

Just curious, how do you get there? Or out?

there is just a gap in the wall to other rooms.