There is no simple answer to your question.
In terms of PSIG, yes +P and -P.
In terms of the ideal gas Law PV=NRT pressure is absolute, there is no such thing as negative pressure.
When it comes down to it, steam and air are nowhere near ideal gases.
Through in adiabatic heat of compression and enclosure stuffing, things start getting more complex. Simulation starts getting more difficult. Results are more empirical, the theory gets lost in the weeds.
I put a fist full of soft pillow stuffing in the enclosure, installed the driver and measured using a frequency sweep and a current sensing resistor. The measured Total Q and resonance frequency were not even close to the simulation. On test; Q = 0.64 and resonance frequency was 50hZ.
Thanks DT
FYI
https://phys.libretexts.org/Bookshe...cs/3.07:_Adiabatic_Processes_for_an_Ideal_Gas
Thanks. Why I'm asking is that from the above discussion, it seemed like the pressure situation was only a problem when cone goes inwards in box - I found that strange...
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These pressure variations are called sound. Graphic presentation is soundwaves, pressure variation per time scale. Pressure gives amplitude (spl) and time frequency.
Those better in maths can say if pressure variations in a closed box are linear or log, in and out and with increasing amplitude.
Those better in maths can say if pressure variations in a closed box are linear or log, in and out and with increasing amplitude.
Hello,
It is not about linear or Log. It is about the forces pushing the cone in, as opposed to the forces pushing the cone out, the forces are asymmetrical causing distortion.
The air is a poor quality spring.
Thanks DT
I'm asking if closed box volume gives different counterforce vs. out of box infinite volume. I suppose it does affect low freq behaviour... a bass driver open air vs. free - making compression and distortion at high excursion if box is "too" small.
Hello All,
It is a Goldilocks kind of thing, too small, too large or just right.
My thought today is that Q = 0.64 is just right with the use of a sub-woofer.
https://www.dltk-teach.com/rhymes/goldilocks_story.htm
https://audiojudgement.com/sealed-enclosure-closed-box/
It is a Goldilocks kind of thing, too small, too large or just right.
My thought today is that Q = 0.64 is just right with the use of a sub-woofer.
https://www.dltk-teach.com/rhymes/goldilocks_story.htm
https://audiojudgement.com/sealed-enclosure-closed-box/
the relevant question is how stiff the air spring is and how linear it is (symmetry does not mean linear ). The box air spring is typically much more linear than the suspension of a driver. It does not have mechanical hysteresis like suspensions have.
The driver Sd is modulated by the box pressure and this modulated the stiffness that the driver experiences - air stiffness scales with Sd squared. For a conventional half roll this is the issue to worry about. The Purifi surrounds offers an almost constant Sd even at high box pressure
hmm that audiojudgement post on sealed box is not that great. The graph comparing sealed and reflex is bot good: reflex will have a lower corner frequency but steeper roll off. should have same sensitivity at higher frequencies.
their post on reflex alignments is really good : https://audiojudgement.com/bass-reflex-alignments-explained/
Hello Dr. Lars,
Thank you for your insights regarding sealed and bass reflex enclosures.
I am pleased with the distortion measurements of your 6-1/2 inch 8R mid-bass driver in sealed Denovo 0.55 cubic foot enclosures. Pluss the Frequency Response is just right for late night listening. Fewer complaints from she who sleeps.
This may not be your target market, there is space on my test bench for a pair of mini Purifi 2-way speakers. There is also a sub-woofer tucked away on the shelf below.
For future experiments I have 4, Purifi 6-1/2 inch passive radiators to tryout.
Thanks DT