How do aperiodic enclosures generate more bass?

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Ramista

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Joined 2020
#1
Can someone please explain how an aperiodic loudspeaker generates additional bass? A closed box (acoustic suspension) is easy enough to understand. Similarly with a ported speaker - more bass due to the air in the port resonating at a frequency lower than fs and adding to the bass being produced by the bass unit. But an aperiodic enclosure doesn’t have the supporting bass resonance, and if designed correctly, the flow resisting vent will lower the drive unit amplitude. So how is the extra bass generated? There’s obviously a fundamental piece of information I’m missing because it really makes no sense at all!
 
#4
Aperiodic boxes have tuned leaks(i.e.'resistive vents'). They act similarly to a sealed box, until lower frequencies where the leak lowers the effective Qb
and prevents the boominess normally caused by a high Q.

So the output is lowered where it was too high, no output is raised, although you may tolerate turning it up higher without the boominess.
 
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#5
An aperipdic box does not extend frequency.

But, given the common use of lowering the Q of a too small box* one does exchange the bump for “some” initial bass extention. But that is not why you use it.

*(or to flatten the impedamce amd suck up the back wave (aperiodic TL)

dave
 
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#7
But how much bass is lost, when the aperiodic vent, vents into a second, sealed chamber instead of the room? Presumably it would still have less bass than the same driver in a sealed box. Would it be more effective to have two chambers connected by a passive radiator, tuned to dampen the main resonance of the main driver, surely this would flatten the impedance and frequency response better than just a restrictive vent between the two ?
 
#8
I might be able to explain this with an electrical example. Here is the equivalent of a closed box:

1. Blue, a regular closed box 100Hz/0.9
2. Yellow, with resistive leakage
3. Red, leakage goes into another box

Untitled.png
 
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#9
Yes, the partitioned box is better. Kinder to the amp also.
See the larger Dynacos like the A35 & A50.

My friends used to put 400w/ch into a pair of A50s in a stone building.
Concert level sound from a big, fast reel-to-reel.
Why I like early Allman bros loud.

No Cerwin-Vegas, but they liked the motto: Loud is Beautiful. If it's Clean.
 
#10
cracked case said:
But how much bass is lost, when the aperiodic vent, vents into a second, sealed chamber instead of the room? Presumably it would still have less bass than the same driver in a sealed box.
Click to expand...

I don’t believe that is the case. At the lowest frequencies the aperiodic vent becomes invisible and the box acts like a sealed box of the same size (more or less), and a smaller box at HF.

Why? I am still not sure. I have seemn marketing stuff from those such as NAIM, but i am still not sure.

a passive radiator
Click to expand...

Not a fan of those. Given that it is essentially a BR vent, that works against the heavy aperiodic damping, so i don’t see it.

dave
 
#13
No, it's an analogy. I was going to use LtSpice with resistors for loads but Xsim was handy to do the same thing.

Are you thinking what I'm thinking, that by the time you add the second box you're not saving the space that aperiodic was supposed to save you in the first place?
 
#14
What would happen if you went the other way, did something half way between an aperiodic, and an open baffle. Say if you removed the back panel of a speaker box and stuffed if full of wadding. Presumably the wadding would slow the speed of the rear sound wave, increasing the effective size if the speaker, thereby improving bass, and also dampening the driver.
 
#15
It's interesting you mention that because there's an old trick where you lay cloth across the cutout before you push the speaker in and the rim holds it tightly in place. This creates a resistance which acts upon the cone as it moves.

Like you say, the effect is to lower the Q the same as with other forms of resistance. It takes energy out of the resonance, or in other words increases damping.
 
#17
I seem to be struggling to find formular to calculate aperiodic box volume (vented to open air), I think I saw an equation on diyaudio, but I can't find it. I'm thinking of a Visaton BG 17, augmented by a sub underneath each speaker. The BG 17s have been delivered today, so I can't opt for different drivers, but I suppose I could do a boffle.
 
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