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Analytical Analysis - Room Gain

Ismapics

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Promoted to home page. OP title upgraded as well. :)

@amirm : could it be possible to have the people from Kippel and ASR to write us an article about speakers, headphones in general or about the development of their test rigs. Maybe there is no more to add but it would be interesting.
 
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René - Acculution.com

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@amirm : could it be possible to have the people from Kippel and ASR to write us an article about speakers, headphones in general or about the development of their test rigs. Maybe there is no more to add but it would be interesting.
It is difficult to write general post about loudspeaker, but a little easier to tackle more specific topics within the field. Is there anything in particular you are interested in knowing more about?
 

Ismapics

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It is difficult to write general post about loudspeaker, but a little easier to tackle more specific topics within the field. Is there anything in particular you are interested in knowing more about?
Hello René,
My thoughts were to see if either Kippel or ASR which are the 2 measurement tools for speakers and headphones could give a technical / maybe a recount of the development of these tools. No going into trade secrets but just a makes point of view of their road to development and (I am sure they had plenty) trial and error process to arrive at what is used today. Sure @amirm has written about them, but I was thinking a bit more into the development side. Cheers. im
 

DonH56

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@René - Acculution.com : COMSOL is a great tool to look at speaker (driver, cone) modes and breakup. I used to have links to some presentations showing the modes forming and then breakup occurring on some drivers; if you could do something like that, a lot of folk might appreciate it. Or at least me, being a lazy soul disinclined to do the work again myself. :)
 
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René - Acculution.com

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@René - Acculution.com : COMSOL is a great tool to look at speaker (driver, cone) modes and breakup. I used to have links to some presentations showing the modes forming and then breakup occurring on some drivers; if you could do something like that, a lot of folk might appreciate it. Or at least me, being a lazy soul disinclined to do the work again myself. :)
Sure, and I can add the Phase Decomposition that is otherwise only used in Klippel’s package, with which you can see how a complex movement can be broken further down. Also , next week I will be presenting a the Comsol Acoustics Day and I can write up a post based on that. It has shape and topology optimisation also.
 

DonH56

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Sure, and I can add the Phase Decomposition that is otherwise only used in Klippel’s package, with which you can see how a complex movement can be broken further down. Also , next week I will be presenting a the Comsol Acoustics Day and I can write up a post based on that. It has shape and topology optimisation also.

That'd be great, thanks!

Many years ago I had the opportunity to be a beta tester when COMSOL was released but I was never proficient, or even competent, with it.
 

ppataki

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-Introduction-


-Conclusion-
Room gain is not some esoteric effect that the acoustic text books do not cover; it is actually a simple subset of known modal analysis combined with loudspeaker characteristics. For a sealed room we will have flat low frequency pressure response for a transducer with flat volume displacement, and a sealed sub gives us exactly that below its operating range.

I wonder what the situation would be with sealed push-pull subwoofers?
 
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René - Acculution.com

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I wonder what the situation would be with sealed push-pull subwoofers?
If there is just one port looking out into the room, it would not short circuit so it should act as a sealed box. If two drivers are in a sealed sub but only one driver front sees the room that should be the case also. If both drivers have their front into the room and both push outwards in sync that would also give a flat curve.
 
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ppataki

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If there is just one port looking out into the room, it would not short circuit so it should act as a sealed box. If two drivers are in a sealed sub but only one driver front sees the room that should be the case also.

There is no port, totally sealed box with 2 drivers
One in the front side of the box with correct polarity and one in the rear side of the box with inverted polarity
I am thinking about this design since it is supposed to reduce distortion by 40%
 
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René - Acculution.com

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There is no port, totally sealed box with 2 drivers
One in the front side of the box with correct polarity and one in the rear side of the box with inverted polarity
I am thinking about this design since it is supposed to reduce distortion by 40%
As long as one pushes outwards as the other one also pushes outwards it will act as a monopole. So if one has inverted polarity it must also be mounted with its rear side pointing outwards.
 

ppataki

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Thank you, I see - here it is clearly not the case; one driver will push outwards while the other will push inwards at the same time
Do you know what the 'consequences' will be with regards to your original conclusion?
 
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René - Acculution.com

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Thank you, I see - here it is clearly not the case; one driver will push outwards while the other will push inwards at the same time
Do you know what the 'consequences' will be with regards to your original conclusion?
At low frequencies as one drivers gives minus the volume displacement of the other, I would expect it to act as a ported speaker with regards to room gain. Do you have a link to this type of woofer?
 

ppataki

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This is how it looks like in the manual of Bass Box Pro 6:
1621364671288.png


I guess I have misinterpreted the concept since both drivers are moving outwards at the same time! So this should act as a normal sealed subwoofer then
 

richard12511

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Wow. I'm learning a lot here lately. Up until a few weeks ago, I had assumed room gain was a given, but it seems I have some big misunderstandings. I'm still not sure I understand(the math is over my head). All of my rooms show a rising bass response below 100Hz. The cause of this is due to those modes below 100Hz? What I don't understand is, shouldn't I be seeing an "average" trend line downwards from high to low? For example, my main room has a few sealed subs with a natural anechoic downward slope from 100-10Hz, but the in room slope is positive from 100-10. I would expect to see (with enough sources to smooth it out) a slope that is similar to the subwoofer's anechoic response? Or am I misunderstanding?

I've also noticed that companies like Revel design a fairly heavy downward sloping response(Salon2 is a good example) in the bass. I assumed they did this to counteract room gain, but now it just seems like a poor design choice/limitation? I do notice many actives designs are often flat in the bass.
 
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René - Acculution.com

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Wow. I'm learning a lot here lately. Up until a few weeks ago, I had assumed room gain was a given, but it seems I have some big misunderstandings. I'm still not sure I understand(the math is over my head). All of my rooms show a rising bass response below 100Hz. The cause of this is due to those modes below 100Hz? What I don't understand is, shouldn't I be seeing an "average" trend line downwards from high to low? For example, my main room has a few sealed subs with a natural anechoic downward slope from 100-10Hz, but the in room slope is positive from 100-10. I would expect to see (with enough sources to smooth it out) a slope that is similar to the subwoofer's anechoic response? Or am I misunderstanding?

I've also noticed that companies like Revel design a fairly heavy downward sloping response(Salon2 is a good example) in the bass. I assumed they did this to counteract room gain, but now it just seems like a poor design choice/limitation? I do notice many actives designs are often flat in the bass.
Whether you have one or many sealed subs, as you describe, you would (theoretically; perfectly sealed room and everything) see a flat room curve, as they all act together as volume displacement sources. I am not sure why it rises, perhaps you are not seeing enough of the curve towards DC?

The slope is given by the particular loudspeaker topology (sealed, ported), and so you might get better free-field performance for your datasheet with one than the other, but in-room it might be different.
 

Newman

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an

Thank you for your useful analysis.

Can you show the effect on the above blue graph if the room is ‘realistically leaky’? (I presume an open door / window returns to the slope of the red line below 35 Hz?) But what about a room with doors and windows closed, but ‘typical air gaps’ under doors, around door frames, or into an airconditioning vent?

cheers
 
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René - Acculution.com

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Thank you for your useful analysis.

Can you show the effect on the above blue graph if the room is ‘realistically leaky’? (I presume an open door / window returns to the slope of the red line below 35 Hz?) But what about a room with doors and windows closed, but ‘typical air gaps’ under doors, around door frames, or into an airconditioning vent?

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

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Very cool stuff, but not sure how much I appreciate seeing those Greek functions I buried deep since my grad acoustics courses... :)

Is your Matlab script available publicly?

You may want to have a play with LowFAT by Dr Adam Hill:
http://adamjhill.com/lowfat/

It’s a MATLAB-based application which uses the Finite-Difference Time Domain method to produce 2D or 3D data for in-room low frequency behaviour. You can position multiple virtual point sources of monopole, dipole or cardioid response, choose from some pre-defined absorption coefficients for surfaces or enter your own, then visualise the output for a single frequency as a ‘wave pool’ style animation, plot the spatial variance, or auralise the response.

Like a lot of software that comes out of engineering disciplines, it won’t win many awards for UI design, but it’s super useful to visualise your thoughts in a similar way to the excellent first post in this thread.
 
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