And yet, back in the 1960s...
Wharfedale specially recommended the use of a "distributed port" enclosure for their Super 12/RS/DD which had a low Q (thanks to its powerful magnet system) and a very large Vas.
The distributed port consisted of a slotted back covered internally with felt cloth to provide additional acoustic resistance - a form of aperiodic loading.
Although, they were talking of enclosure volumes of 3 to 5 cubic feet for these 12" full range drivers.
A popular commercial application of the distributed port was the Wharfedale Airedale, but it was designed to sit in a corner!
Perkins PR-2 took that concept to a new level, and other than a long welll damped pipe (TL) works best in my experience.
dave
Once upon a time, I had hands-on experience with Variovent - it does help boxes with too large Qtc. I duplicated the Variovent behavior with simple hole covered with dense foam. Variovent is not "tunable" (for optimum damping), but port with dense foam/rockwool is.
Yes, aperiodic loading does help.
https://diyaudioprojects.com/Technical/Aperiodic/
A Good Startpoint is this PDF
(The last link on this side)
A Cabinet of Reduced Size with Better Low Frequency Performance - E.J. Jordan
A Good Startpoint is this PDF
(The last link on this side)
A Cabinet of Reduced Size with Better Low Frequency Performance - E.J. Jordan
You are preaching to the choir 😉
Born in '52 I grew surrounded by such resistive aperiodic cabinets, some with fiberglass covered slots in the back , or smaller cheaper ones found in ubiquitous combination Radio_Grammophones), only dyed in the wool HiFi fans used tuned "Bass Reflex" cabinets.
Closed or straight open cabinets were considered too primitive.
Closed cabinets only became mainstream after Acoustic Suspensión invention, and literally bookshelf cabinets with any kind of Bass were considered a miracle.
My first foray into loudspeaker building in the mid to late 60s was a 5 cubic foot enclosure traditionally tuned by way of a large rectangular duct to the 40 Hz resonance of a 12" Fane driver.
Oh, the bass!
It's been downhill ever since! 😀
I made Bass Guitars speakers and the way to tune them for best perceived Bass, best combination of depth and SPL, was to cut a large slot on the back panel , say 10 cm by 40 or 50 cm, partly cover it with a piece of plywood held by clamps, so it could be adjustable, and try different positions until the best sound was found.
Once it was found, a new back panel was made and those dimensions were used from then on, until a new design was needed.
State of the art design, not kidding.
Another trick was putting a candle 1 meter away from port or duct and sweep an oscillator to find box resonance.
VERY visible results.
Tuning any and all Bass cabinets to 40 Hz, no matter what, was an old trick used by Fender.
It has something going for it.
Not flat response optimization but minimizing cone excursion at the lowest Bass Guitar frequency.
Oh the good old days.
Last year I tested and auditioned two pairs of small speakers for a local company. One had a resistive vent. Of course to hear the difference the music had to play the few low notes that were in the range changed by the vent. The effect was subtle. The highpass Q was lower for the speaker with the vent. The modern way to accomplish this is with digital signal processing. An asymmetric second order shelf filter can be used to cancel the natural high pass response of the woofer in the box and the desired Q and cutoff frequency can be achieved. I have been equalizing to a cutoff frequency of 20 Hz with a Q of 0.3 in my system recently and the results are great.
Somewhere it was mentioned that an aperiodic cabinet has a roll off not of 12 dB/oct as in a closed box, but of 18 dB/oct. A boost that a CB has if it is too small for the driver installed there (Qtc > 0.7) is flattened with a damped opening and the frequency range is extended downwards, right?
The behavior reminds me strongly of something that in German is called GHP - Geschlossen mit Hochpass, in English this is probably called passively-assisted sealed alignment, a topic on which there is actually a thread here.
What do you think of this similarity?
Best regards,
Michael
Translated with help from DeepL.com (free version)
The behavior reminds me strongly of something that in German is called GHP - Geschlossen mit Hochpass, in English this is probably called passively-assisted sealed alignment, a topic on which there is actually a thread here.
What do you think of this similarity?
Best regards,
Michael
Translated with help from DeepL.com (free version)
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Coffee break thoughts on aperiodic enclosure:
on impedance measurement peak at system resonance is due to backEMF, basically at the resonance cone moves relatively much with the voltage supplied making huge backEMF in comparison which keeps current low, impedance is just relation ship between voltage and current, so is high. This means the current from backEMF essentially dampens the resonance just fine as long as impedance in series with the driver is low, in other words amplifier output impedance is low and there is no passive parts or cabling that would increase series impedance with the driver at the resonant frequency. Now that there is electrical damping, and system response is nice, there is no need for additional damping the vent would provide.
So, for system damping aperiodic vent is not necessary in this sense, and one could just EQ the system Q (response) to liking. On the other hand if you have a tube amplifier with high output impedance which means less electrical damping, the vent could be nice to help with system Q. Or if it is too small of an enclosure for given driver with annoying peaking response, and for some reason cannot fix it with EQ.
Besides what happens at resonance, the vent could affect "box sound", perhaps relieving some modes inside the box or something like that. Perhaps it could reduce heat buildup inside the box as well. On the other hand since there is penalty for bass you'd be tempted to give more current for more bass and make more heat.
So aperiodic vent seems unnecessary with modern gear, so why not take full advantage of such vent and tune it so that system turns into gradient system which could help also with room modes? In this case aperiodic vent would be useful even today. On the other hand, one could deliberately use high output impedance amplifier to reduce driver motor distortion, and use aperiodic vent to add damping to the resonance, which is now missing.
So, depending on which amplifier, which environment, which sized box, how much bass is needed for given volume occupied, the aperiodic vent could be nice, or just unnecessary complexity. Given that we do not see aperiodic vents on practically any commercial products is a tell tale it's not very useful today, and likely due to abundance of low output impedance amplifiers, preference of reflex boxes over closed ones.
Perhaps there is other reasons why to make one, perhaps it sounds better, haven't tried one. Logically from above reasoning aperiodic box is a solution for situation where there is old low motor power driver, high output impedance tube amplifiers and no DSP.
Above is reasoning only, I have no auditory experience on bass box with aperiodic vent.
on impedance measurement peak at system resonance is due to backEMF, basically at the resonance cone moves relatively much with the voltage supplied making huge backEMF in comparison which keeps current low, impedance is just relation ship between voltage and current, so is high. This means the current from backEMF essentially dampens the resonance just fine as long as impedance in series with the driver is low, in other words amplifier output impedance is low and there is no passive parts or cabling that would increase series impedance with the driver at the resonant frequency. Now that there is electrical damping, and system response is nice, there is no need for additional damping the vent would provide.
So, for system damping aperiodic vent is not necessary in this sense, and one could just EQ the system Q (response) to liking. On the other hand if you have a tube amplifier with high output impedance which means less electrical damping, the vent could be nice to help with system Q. Or if it is too small of an enclosure for given driver with annoying peaking response, and for some reason cannot fix it with EQ.
Besides what happens at resonance, the vent could affect "box sound", perhaps relieving some modes inside the box or something like that. Perhaps it could reduce heat buildup inside the box as well. On the other hand since there is penalty for bass you'd be tempted to give more current for more bass and make more heat.
So aperiodic vent seems unnecessary with modern gear, so why not take full advantage of such vent and tune it so that system turns into gradient system which could help also with room modes? In this case aperiodic vent would be useful even today. On the other hand, one could deliberately use high output impedance amplifier to reduce driver motor distortion, and use aperiodic vent to add damping to the resonance, which is now missing.
So, depending on which amplifier, which environment, which sized box, how much bass is needed for given volume occupied, the aperiodic vent could be nice, or just unnecessary complexity. Given that we do not see aperiodic vents on practically any commercial products is a tell tale it's not very useful today, and likely due to abundance of low output impedance amplifiers, preference of reflex boxes over closed ones.
Perhaps there is other reasons why to make one, perhaps it sounds better, haven't tried one. Logically from above reasoning aperiodic box is a solution for situation where there is old low motor power driver, high output impedance tube amplifiers and no DSP.
Above is reasoning only, I have no auditory experience on bass box with aperiodic vent.
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If one looks at the box (either as a leaky sealed box, to as a vented box with a vent having a seriosu amount of R), the roll-off should be somewhere between (how much depending on how close to aperiodic you get).
But of interst is Bill Perkin;s claim, based on measurements his PR-2 (probably the most researched aperiodic box in existance) thjat it can actiully be less than 12dB/octave. https://pearl-hifi.com/03_Prod_Serv/PR2/PR2_Content.html
dave
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I had a good experience with the Supravox 165-2000 (Qts 1.1) in an 'aperiodic' enclosure, essentially open backed with various thickness and density of foam at the back.
https://www.diyaudio.com/community/threads/supravox-165-2000.326720/page-3#post-5713548
Free air driver
Supravox 165-2000 (2-A) by Robert Seymour, on Flickr
In the resistive back encosure
Supravox 165-2000 (2-A2 in cabinet - 2x Layer 36mm foam & Pillow) by Robert Seymour, on Flickr
https://www.diyaudio.com/community/threads/supravox-165-2000.326720/page-3#post-5713548
Free air driver
Supravox 165-2000 (2-A) by Robert Seymour, on Flickr
In the resistive back encosure
Supravox 165-2000 (2-A2 in cabinet - 2x Layer 36mm foam & Pillow) by Robert Seymour, on Flickr
Probably closer to being described as a Boffle.
http://p10hifi.net/tlinespeakers/forum/boffle-RadioElectronics.pdf
http://p10hifi.net/tlinespeakers/forum/Boffle-patent.pdf
dave
I have tested aperiodic vent in both midrange and bass.
In bass enclosure, both time my conclusion was this: I much prefer classic closed cabinet. I tested with the expensive scanspeak ones. Added less damping to the vents etc.
Of course maybe depends on application. But, for example I cannot think of even one commercial speaker that has aperiodic vent in the bass.
In midrange i have found decent good results with aperiodic vent. Maybe because it relieves the midrange a bit from the preassure in closed cabinet. Not sure I will use it again.
In bass enclosure, both time my conclusion was this: I much prefer classic closed cabinet. I tested with the expensive scanspeak ones. Added less damping to the vents etc.
Of course maybe depends on application. But, for example I cannot think of even one commercial speaker that has aperiodic vent in the bass.
In midrange i have found decent good results with aperiodic vent. Maybe because it relieves the midrange a bit from the preassure in closed cabinet. Not sure I will use it again.
wonder if there's a ready-made grate disc to fit inside a this standard 4" round drain grate ? - maybe a piece
of 1/4" grid hardware cloth would suffice to hold a layer of damping material - ?
https://www.amazon.com/NDS-11-Plast...3f-b6bd-da4aa56a9f74&pd_rd_i=B000BO8OAI&psc=1
of 1/4" grid hardware cloth would suffice to hold a layer of damping material - ?
https://www.amazon.com/NDS-11-Plast...3f-b6bd-da4aa56a9f74&pd_rd_i=B000BO8OAI&psc=1