The relationship between air volume and SPL

[Onur]

Hello,

I have examined this web page;

http://www.angelfire.com/comics/illustartions/

There you can find a relation between the air volume and SPL. Can somebody please explain me how it is possible to calculate the needed air volume which needs to be moved in order to achieve certain SPL value?

Thanks in advance
Onur

[fpara]

You should add: "for open baffles"

[noodle_snacks]

It would depend on frequency too.

[Onur]

It is depended on the frequency and the volume of the space in which the sound is generated, am I right? Without knowing the volume of the space in which the pressure wave is generated, how could he came up with such results?

However, if there is a way to calculate the needed air volume which needs to be moved for open baffle speakers for a specific frequency, I would like to examine that. Can somebody forwar a link?

/Onur

[bzfcocon]

Check this out:

http://www.linkwitzlab.com/models.htm#A1

Scroll down, there is an explanation as to how the displacement is related with frequency and some theory.

[bjorno]

Just my 2 cents, Calculations only valid on axis and no baffle considerations made and I could be wrong when not understanding fully what you want to compare? See the picture:

b

1(1)

[bjorno]

More odd shortcomings:
Look again at the table for 112 dB where 100 cu in equates 645.16 cu cm, that is 1 cu in= 6.45 cu cm and obvious wrong as 1 cu in = 2.54^3 and about 16.4 cm^3, then all the tables are systematically erroneous.

But worse is this assumption:

‘…For a totally open-baffle ELF design, the roll-off rate will be 18dB/octave (room gain not taken into account). For an aperiodic design such as the one I'm proposing, it will be much closer to 12dB/octave…’

...as the SPL losses, when loading aperiodic from 18 dB to 12 dB/octave is not included.

b

[sreten]

Hi,

The maximum levels a sealed box driver can produce at low frequencies
assuming it has enough juice to get it to excursion limits is solely
determined by the Vd (volume displacement of the driver) Sd x exc.

Maximum levels obviously drop with frequency, the actual levels are
fairly arbitary, usually they are calculated at 1m into half space.

Reflex loading makes a big positive difference. Open baffle loading
makes an ever increasing negative difference, combined with the
reducing levels available as you go lower it becomes obvious open
baffles (of reasonable size) cannot do low bass at decent levels.

Try WinISDbeta for illustrations of excursion and related max levels.

sreten.

[Ron E]

Some hints, wouldn't want to just give you the answer and spoil the "discovery" for you.

Relation of volume velocity to SPL is perhaps the proper question.

All over the 'net there are equations relating excursion with SPL, and volume velocity (U-m^3/s) is just excursion * Sd * frequency.

In reality SPL is directly proportional to piston acceleration, not velocity.

think of sinusoidal motion.
Excursion:
X(t)=X0*sin(wt)

Velocity = dX/dt:
V(t)=w*X0*cos(wt)

Acceleration = dV/dt:
A(t)=-w^2*X0*sin(wt)

[Onur]

During my search for inline passive (before amp.) crossovers I found myself reading this article :

http://sound.westhost.com/qb5align.htm

It would be more scientific to know how the kp (the power output constant) is calculated. Any ideas?