Subwoofer Simulation problem calculating resistance of enclosure due to absorption

[SoulMagnet]

Hello,

I am trying to simulate a subwoofer using matlab...
I couldn´t find how Resistance of enclosure due to energy absorption is calculated (the Rab or Rmo in bibliography).It´s alwsays taken into account while calculating various parameters, but I can´t see how it´s calculated or its approximate value...

Any help appreciated

 

[weltersys]

Standard air-proof enclosures don’t absorb sound, though absorptive materials may be used inside and outside for various purposes.

Enclosure walls do flex, which can reduce or increase sound output at various frequencies. With proper bracing, flex can be reduced to a the point where effects are negligible.

Everybody has hobbies, curious why you are trying to use matlab for simulation when there are many good simulation programs already available for free?

 

[Djim]

Hello,

I am trying to simulate a subwoofer using matlab...
I couldn´t find how Resistance of enclosure due to energy absorption is calculated (the Rab or Rmo in bibliography).It´s alwsays taken into account while calculating various parameters, but I can´t see how it´s calculated or its approximate value...

Any help appreciated

Hi,

I'm not sure how precise these absorption figures need to be. Normally DIY's don't dive into this area since the influence is very subtle. But if you need precise values you will end up with many paramters/ variables. Every type of wood has its own absorption values (material characteristics). The way you construct and finish these materials (paint, fabric around them, wood layering,) are all of influence to these absorption figures. Also these figures are not frequency constant, which makes it more complex. If it is just for the 'loss' figures you can try to get standard industrial datasheets from wood manufacturers. Acoustic companies (especially those who build studio's, concert halls and or measuring rooms) do not share such kind of information since they often have to pay themselves for detailed measurements.

 

[SoulMagnet]

Well to begin with thank you for the reply1

You see I´m an engineering student and in the first part of my thesis I´m attempting to program a matlab GUI which kind of duplicates the funtion of simulation programs such as BassBox pro etc....
So I need to develop matlab code for closed box and vented box loudspeaker systems....
I´ve read the Thiele Small papers some work of Aarts as well and keep studuying.
Im not experienced in audio engineering so pardon me if I sound naive.

Well, it is under my consideration that it´s the leakage losses I should be concerned about (the Ral resistance).I suppose I could model that with it´s mathematical formula or just with it´s typical value....

So I´m not interested in reducing it ( yet ), but model its behavior.

Will be glad to hear from you again both.

 

[sim696]

Hi Soul,
I found your post while googling for the same matter.
For what concern Rab (the acoustic resistance of the enclosure losses caused by the energy absorption of the filling material) wold be great to find a table with resistivity values for each material! If you find it, let me know.

Anyway you can find an interesting reading in http://usir.salford.ac.uk/19489/1/Improved_Membrane_Absorbers__Rob_Oldfield_MscThesis.pdf

I have not read it yet but I found some interesting references.

For what concern the Ral I think you can neglect it.
In a closed box would be advisible to leave a small leakage for compensate changes in atmospheric pressure, but usually the porosity of loudspeaker membrane is sufficient for that.

 

[Ron E]

You see I´m an engineering student and in the first part of my thesis I´m attempting to program a matlab GUI which kind of duplicates the funtion of simulation programs such as BassBox pro etc....
So I need to develop matlab code for closed box and vented box loudspeaker systems....
I´ve read the Thiele Small papers some work of Aarts as well and keep studying.
Im not experienced in audio engineering so pardon me if I sound naive.

G Marshall Leach gave an equivalent circuit for a stuffed box. Most programs (Even expensive ones) just treat loss terms as a (constant) parameter for user entry. Small's work gives some typical values for drivers ~1970.