All of the hand waving audiophool explanations about "aperiodic enclosures" notwithstanding, the amount of sound radiated by any enclosure is proportional to the pressure in the box.
My opinion about aperiodic enclosures and the foolish BS that surrounds them is not because of a lack of understanding about how they work. A damped resonance is still a resonance...
My opinion about aperiodic enclosures and the foolish BS that surrounds them is not because of a lack of understanding about how they work. A damped resonance is still a resonance...
Nice.
Loudspeaker is not rocket science. You may wish to consider Beranek speaker model. Then you'll see there is not any kind of magic in electrodynamic speaker and enclosures and none in "flow resistance" either. Practically speaker in sealed enclosure with a hole "acoustically dampened" is a third order hi pass filter which can be tuned for a Qts to yield a flat Butterworth characteristic for ex. thereby "saving" volume. However the acoustical output is unaffected it is still predominantly moving piston.
Buried in this document, which decribes the process of developing probably th emost advanced aperiodic speaker, is some real meat, including some significant measurements. A biy of a slog, but quite interesting. From a time before cheap, easy to use computer kit.
https://www.pearl-hifi.com/03_Prod_Serv/PR2/Refs/PR_2_Expanded_Info.pdf
dave
https://www.pearl-hifi.com/03_Prod_Serv/PR2/Refs/PR_2_Expanded_Info.pdf
dave
Aside from the historical papers which have some value, on a really quick skim the beginning of this is written by someone with advanced i-did-it-itis, the disease by which a person who develops a product and is confident in every decision is incapable of looking at it objectively. Written in a conversational tone with many "firsts" and "exclusives", it reads more like ad copy than anything else.
Let's assume a 28L box is built with 1" mdf and 100W is used to power it with a given song. With the amount of sound radiated by any enclosure being proportional to the pressure in the box, as you have suggested, what do you suppose happens if the same box is built with 2" mdf? Apply 100W of power using the same music, and the amount of pressure inside the box is still the same. It would seem that the amount of sound that was radiated from the 1" box with 100W is now less with the 2" box using the same 100W.the amount of sound radiated by any enclosure is proportional to the pressure in the box.
Nice.
Although I can see how you misunderstand, implicit in my statement is that the box is rigid so that it does not matter how thick the walls are.
If you have a given driver in a given size box, whether aperiodic, sealed, or vented, and it is producing 90dB at the same frequency, the pressure inside the box is the same. The force on the walls is thus the same.
If you have a given driver in a given size box, whether aperiodic, sealed, or vented, and it is producing 90dB at the same frequency, the pressure inside the box is the same. The force on the walls is thus the same.
I can imagine a woofers travel being greatly reduced to almost no movement at all at the box tuning frequency, but is it also correct that there is no pressure?
At this point hasn't the air volume in the port effectively plugged the port, likening it to a sealed enclosure? This is coupling right? If so then I cant see how there can be any Fb without maintaining that pressure?
In my project Alternative DIY speaker project i have a 20 cm woofer with T/S as such that for Butterworth 4th order it requires box tuning 38 Hz and box volume 50 litres in bass reflex. I have 28 litres thus Qts must be reduced. This works by reducing Qes with "negative resistance" of driving amp. Then i am at Butterworth alignment but it comes at a price. Due to cone excursion/displacement limitation the max power must be reduced to a mere 6 Watts at 40 Hz which is the -3dB. That requires a clever soft limiter which is standard in every active monitor speaker. The low pass filter for that is somewhat tedious to calculate if it is analog. I experimented then with aperiodic enclosure. While Jordan's electrical analog is correct it is also an idealisation. I found that the diameter of the Jordan vent should be 1/4 to 1/5 of the woofer diameter so 5 cm is a good start. But box damping and vent damping are somehow interacting so it is a cumbersome thingy but can be done. However as the mid/hi is a Jordan broadband which takes over at 300 Hz the electrically Qts tuned reflex is easier. It needs no damping the construction efforts are at the electrical side.
Of course not, otherwise there will be no sound.
Nope, at this point the port is doing all the work of pressurizing the box and the coupling between port and diaphragm are what causes the diaphragm to stop.
My statement is more general than just at the port frequency, though.
The quote from Beranek goes something like this: "The sound pressure produced at faraway points is proportional to the volume velocity necessary to pressurize the box." Beranek says this in relation to bass reflex enclosures. Benson also proves this result and extends it to "regardless of the number of apertures in the box"
The only way a box can have lower pressure, is if it has lower SPL.
There is nothing wrong with an "aperiodic" design, but it doesn't have magic or physics-breaking properties. You could also call it a damped vented box or a leaky sealed box. It isn't really even third order (gasp!) as a resistance isn't an energy storage device. Resistive damping can be especially useful for jamming woofers in too-small boxes, but there is nothing really "aperiodic" about them....
aperiodic in terms of speaker enclosures means critical damping. Critical damping provides the shortest return to zero motion. But some 197x models of ScanSpeak speaker boxes which had been using sort of Variovent showed a deep mismatch of measured frequency response and listening tests as bass appears to be very thin, however precise. But there are no acoustical musical instruments producing "precise bass" that is physically impossible perhaps except very long organ pipes. Human hearing is also unprecise in terms of dynamic and frequency resolution in frequency range below 100 Hz.In psychoacoustics the attack and decay of bass tone is assessed as the size of the sound source and this is the reason why some speaker enclosures give "thick" bass, that is not considered as good bass reproduction
Aside from Trump's Mar-aLago living room most living rooms act as a pressure chamber due to size (0r "spatial dimensions") for low frequencies.
The difference between a "free air" measurement of a critically dampened bass box and then same box in living room is although to be expected yet startling. The actual Qts is almost without effect.
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