What I'd like to know is how the Dynaco A35 arrangement with its very small damped vent (~11.2 sq.cm.), behaves at higher input power and higher cone excursions. Would that vent which couples the two chambers "choke" and cause the speaker to see only the first chamber's volume ?
Here's the impedance of that SEAS driver in a regular 28 liter sealed box
Here's the impedance of that SEAS driver in a regular 28 liter sealed box
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I see this is a special interest of yours freddi. Your knowledge of Dynaco aperiodic design exceeds mine. I'd no idea that the damped vent inside the A35 has such a small area.
I am unable to answer your question on whether double chamber aperiodic loading is workable in the extreme conditions imposed by a subwoofer.
As you know, Dynaco fed a large excursion, 5Hz square wave into the A35 and adjusted the damping of the vent to achieve the desired bass response.
They did not quantify how big an excursion can be tolerated by this type of loading. I suspect that, with a powerful subwoofer, the vent area would have to be larger and that experimentation is the order of the day.
Sorry I can't be of more help. 🙁
I am unable to answer your question on whether double chamber aperiodic loading is workable in the extreme conditions imposed by a subwoofer.
As you know, Dynaco fed a large excursion, 5Hz square wave into the A35 and adjusted the damping of the vent to achieve the desired bass response.
They did not quantify how big an excursion can be tolerated by this type of loading. I suspect that, with a powerful subwoofer, the vent area would have to be larger and that experimentation is the order of the day.
Sorry I can't be of more help. 🙁
my knowledge is very poor. I looked at Planet10's excellent pages on Dynaco's aperiodic enclosures and used hornresp step feature to make the two chambers and connecting duct.
I'd imagine enclosures using holes or narrow slots (but no cloth or foam) like Karlson's 2nd K12 having a distributed port consisting of narrow slits, will at small signal, have input impedance which looks like a reflex but under dynamic conditions, the drag will cause the first impedance peak to disappear at some point.
Karlson's K12 with the slit vent, if driven by sine in the vicinity of Fb, produces very high vent velocities which would blow out a candle up close with 1 watt input. Also, there are many strong overtone harmonics created with sine drive and the slit vent K12. Those would not be there with a single vent. I perceived them as harmonic distortion but Dr. Geddes says the correct term is "modulated noise". Can this modulated noise alter the way music sounds? - or are the transients usually too quick to excite the effect?
Its an interesting technique for higher Q speakers. Your rule of hole diameter, spacing, and number to drill sounds like a good place to start.
I'd imagine enclosures using holes or narrow slots (but no cloth or foam) like Karlson's 2nd K12 having a distributed port consisting of narrow slits, will at small signal, have input impedance which looks like a reflex but under dynamic conditions, the drag will cause the first impedance peak to disappear at some point.
Karlson's K12 with the slit vent, if driven by sine in the vicinity of Fb, produces very high vent velocities which would blow out a candle up close with 1 watt input. Also, there are many strong overtone harmonics created with sine drive and the slit vent K12. Those would not be there with a single vent. I perceived them as harmonic distortion but Dr. Geddes says the correct term is "modulated noise". Can this modulated noise alter the way music sounds? - or are the transients usually too quick to excite the effect?
Its an interesting technique for higher Q speakers. Your rule of hole diameter, spacing, and number to drill sounds like a good place to start.
Here is the front and rear of the Altec 604 enclosure. I was not attempting a port, I was hoping to achieve a rear wave reflection off the wall to add a sense of 'airiness'. I was hoping to avoid the 'tubey' sound you often get with a simple open back. The boxes have rockwool damping like a regular box but they are not aperiodic.
I am sure it helps with heat dissipation to boot.
I am sure it helps with heat dissipation to boot.
Attachments
I based my empirical 'rule' on Briggs' designs for DP cabinets.
His designs suited a driver such as the Super 12/RS/DD which had a low Q (thanks to its powerful magnet system) and a very large Vas.
No kiddin'. See the size of those flakes? They might as well call that stuff plywood.
Good stuff, microphones have used arrays of holes to control Q forever but at the high end of the frequency range. Just scale everything the air molecules are still small enough to act macroscopically.
Just ask the naysayers to provide a cogent counter argument using non-linear acoustics and turbulent flow. 😉
I am currently reading this paper to help me get to sleep at night.
MODELS OF NONLINEAR ACOUSTICS VIEWED AS AN APPROXIMATION OF THE NAVIER-STOKES AND EULER COMPRESSIBLE ISENTROPIC SYSTEMS
It is proving extremely effective! 😀
I have indeed SJ! I can just about understand the impedance curves on the final page!
http://www.ejjordan.co.uk/PDFs/A-Cabinet-of-Reduced-Size-with-Better-Low-Frequency-Performance.pdf
http://www.ejjordan.co.uk/PDFs/A-Cabinet-of-Reduced-Size-with-Better-Low-Frequency-Performance.pdf
seems like that would have been a large box not to move the Z peak up much - ?
here's dampedd vent in hornresp with a LAB15 variant at 85 and 170 liters.
There's some sort pf PVC pipe grill which might make nice looking "variovent" copies.
Cheese-cloth was used in the old days to damp vents ( I think)
Other than not quite knowing how to weigh small amounts of polyfil to check against simulation
hornresp's "Wizard" can be used to see what things may be. LAB15 did not like the 164sq.cm. damped vent in a 170 liter box.
Using the Wizard's slider with S2 and S3 locked together showed 39sq.cm. to be good for the case below:
here's dampedd vent in hornresp with a LAB15 variant at 85 and 170 liters.
There's some sort pf PVC pipe grill which might make nice looking "variovent" copies.
Cheese-cloth was used in the old days to damp vents ( I think)
Other than not quite knowing how to weigh small amounts of polyfil to check against simulation
hornresp's "Wizard" can be used to see what things may be. LAB15 did not like the 164sq.cm. damped vent in a 170 liter box.
Using the Wizard's slider with S2 and S3 locked together showed 39sq.cm. to be good for the case below:
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probably - or perhaps sandwich the damping material beween two of this piece called a "termination grill" - It has the ludicrous price of $15.58 at US Ebay - They might be tough to press fit and keep in place - ?
here's more mucking with hornresp - looks like those grills might have too much area for some use ? - or just need more resistance.
here's more mucking with hornresp - looks like those grills might have too much area for some use ? - or just need more resistance.
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one interesting I saw with the example in the previous post was that box fill really didn't do much to the impedance. It was about the same with an empty box and the damped vent alone.
My point in starting this thread, was to explore the fact that, above a certain frequency any opening/s in the box stop acting as a port/s.
This because hole/s length/s size/s required are too small to fit. In order to not affect the lower frequencies, the openings must be calculated with due regard.
Try to sim hole/s etc, without them altering the frequency response etc etc. When you do, you'll discover what hole/s size options are available to consider.
From what i can see, the opening/s would be too small to have much/any effect of reducing thermals. And in any case, they seem to result in negative lengths !
Utilising methods to damp etc ports, are still tailoring the lower range/s, but not taking port/s out of the equation. So making openings affect the response, unless they are tuned really high. But that then negates the purpose of reflexing etc.
Catch 22 anyone ? 😛
This because hole/s length/s size/s required are too small to fit. In order to not affect the lower frequencies, the openings must be calculated with due regard.
Try to sim hole/s etc, without them altering the frequency response etc etc. When you do, you'll discover what hole/s size options are available to consider.
From what i can see, the opening/s would be too small to have much/any effect of reducing thermals. And in any case, they seem to result in negative lengths !
Utilising methods to damp etc ports, are still tailoring the lower range/s, but not taking port/s out of the equation. So making openings affect the response, unless they are tuned really high. But that then negates the purpose of reflexing etc.
Catch 22 anyone ? 😛
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