I've been moving to a perspective that a lot of careful bass performance planning is futile: what is needed is to have tools of adjustment* available to apply after the box is situated in your room. So my suggestion is to create a screen which can be adjusted once REW and a mic are ready.
How do you think Hafler did it?
B.
* DSP crossover and EQ
How do you think Hafler did it?
B.
* DSP crossover and EQ
I have no idea, please tell us ... I am particularly interested in knowing, and I imagine that many others also ...
Sorry. I don't know how Hafler (the guiding spirit of Dynaco) did it. I was asking.
My guess is he just made a little BR box and added resistance to the port until it was a reasonable compromise between BR and sealed box to a listening panel, at least the best compromise possible with a small box.
But things are different for manufacturers compared to DIYer. If I were building, I'd figure out how to change the resistance of the port by repeatably controlled steps. That way, you measure and then listen for a while and then go up or down in resistance and be able to return to your preferred resistance.
B.
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Tannoy has an adjustable system between "sealed" and BR in the Prestige Canterbury SE model
Here you can see the description of the system, it seems to be an exquisite solution. I had the opportunity to hear it and see the system, it is a wooden slat sliding on one or both sides.
I do not remember that detail well...
" How to adjust the Variable Distributed Port System for yourmusic in your room "
Grille Removal; Loudspeaker System Adjustment - Prestige CANTERBURY SE Owner's Manual [Page 6]
PS:For a moment I thought the browser would allow me to watch Hafler's Play Boy for free!
I did not succeed ......😡
It was Hefner!?
Here you can see the description of the system, it seems to be an exquisite solution. I had the opportunity to hear it and see the system, it is a wooden slat sliding on one or both sides.
I do not remember that detail well...
" How to adjust the Variable Distributed Port System for yourmusic in your room "
Grille Removal; Loudspeaker System Adjustment - Prestige CANTERBURY SE Owner's Manual [Page 6]
PS:For a moment I thought the browser would allow me to watch Hafler's Play Boy for free!
I did not succeed ......😡
It was Hefner!?
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Weird and very disappointing. The manual is clearly a case where the engineering department does not have the power to proof-read the manual for egregious nonsense and "talking down" to customers.
More shamefull is the section on breaking-in. What they are deceptively not saying is that if you listen to this speaker for a while, you'll come to consider their sound the norm, even if you don't like it when new.
Hard to tell about the ports, but that sounds more like re-tuning than changing port resistance (although a good way to introduce resistance is by using a lot of little holes as the port).
Might be that a leaky sealed box is the best way to sequester the rear wave. Not readily sim'able.
B.
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Right, basically the Goodmans/Ted Jordan ARU [acoustic resistance unit] design in the few I've seen.
Agreed and historically 'we' recommend a screen 'sandwich' where the outside screen can be removed to adjust damping [coffee filters are popular].
GM
Nothing new under the sun, this was the industrial solution to the idea of wearing socks inside the tuning tube ......
The acoustic vent
May 2014: The Variovent is out of production but you can still get the same thing from using a conventional port and stuff it lightly with acoustilux. I suggest a 68 x 200 mm port (Jantzen Audio). Cut it to 10 cm length. Now, the question is how much acoustilux should be added? I suggest for a start rolling a 10 x 20 cm piece of 30 mm acoustilux at insert it into the port. If you can do an impedance plot you add damping material until you get the same impedance profile as can be seen below. If you cannot perform measurements, you have to tune by ear. No damping will make a boomy bass peaking 4 dB at 63 Hz from a 65 litre cabinet and Fb = 30 Hz. Stuffing the port really hard (closed box) will reduce the bump by 2 dB. The full length - non-stuffed - port (20 cm) will make a Fb = 22 Hz. Try it out.
The Variovent consists of two grilles with some damping material stuck in between. Simple as that. The diameter, amount of damping material and the compression of the material determines the air flow properties = acoustic resistance. The late Gilbert Briggs (Wharfedale) made slits in the rear panel and added damping material over the slits. Works the same and costs nothing. But you have to be able to follow the impedance of the system to tune the amount of damping material needed.
The Variovent is a device sometimes causing much debate. What is an acoustic vent? Well, an acoustic vent allows some ventilation at low frequences and virtually none at higher frequences. So what's that supposed to be good for? Neville Thiele studied the Variovent in detail and concluded it didn't offer any advantage over a properly designed vented systems. The general advice on the use of acoustic vents is simple: Try it! Which offers little comfort to those addicted to math. But box calculation based on Thiele/Small data really only apply for speakers with a Qt = 0.35, which only counts for very few drivers. Based on experience we use speakers with high Qt in cabs too small and drivers with low Qt in cabs too large compared to strict box simulation.
Comparing the impedance peaks of a driver in free air and a perfectly closed and empty box should reveal the same peak height, so we have no loss in the closed box. Obviously the resonance frequency is higher. Adding damping material to the closed box we see a decline in peak height; now we have some loss. Adding an acoustic vent may produce a significant reduction in peak height depending on how open the vent is. So, the system Q-value is lowered (= more loss) from applying an acoustic vent although we really can't speak of a Q-value of an aperiodic system. Basically a closed box has 2nd order roll-off, a vented system a 4th order roll-off and the aperiodic system a 3rd order roll-off.
JBL L100 Century,
The acoustic vent
May 2014: The Variovent is out of production but you can still get the same thing from using a conventional port and stuff it lightly with acoustilux. I suggest a 68 x 200 mm port (Jantzen Audio). Cut it to 10 cm length. Now, the question is how much acoustilux should be added? I suggest for a start rolling a 10 x 20 cm piece of 30 mm acoustilux at insert it into the port. If you can do an impedance plot you add damping material until you get the same impedance profile as can be seen below. If you cannot perform measurements, you have to tune by ear. No damping will make a boomy bass peaking 4 dB at 63 Hz from a 65 litre cabinet and Fb = 30 Hz. Stuffing the port really hard (closed box) will reduce the bump by 2 dB. The full length - non-stuffed - port (20 cm) will make a Fb = 22 Hz. Try it out.
The Variovent consists of two grilles with some damping material stuck in between. Simple as that. The diameter, amount of damping material and the compression of the material determines the air flow properties = acoustic resistance. The late Gilbert Briggs (Wharfedale) made slits in the rear panel and added damping material over the slits. Works the same and costs nothing. But you have to be able to follow the impedance of the system to tune the amount of damping material needed.
The Variovent is a device sometimes causing much debate. What is an acoustic vent? Well, an acoustic vent allows some ventilation at low frequences and virtually none at higher frequences. So what's that supposed to be good for? Neville Thiele studied the Variovent in detail and concluded it didn't offer any advantage over a properly designed vented systems. The general advice on the use of acoustic vents is simple: Try it! Which offers little comfort to those addicted to math. But box calculation based on Thiele/Small data really only apply for speakers with a Qt = 0.35, which only counts for very few drivers. Based on experience we use speakers with high Qt in cabs too small and drivers with low Qt in cabs too large compared to strict box simulation.
Comparing the impedance peaks of a driver in free air and a perfectly closed and empty box should reveal the same peak height, so we have no loss in the closed box. Obviously the resonance frequency is higher. Adding damping material to the closed box we see a decline in peak height; now we have some loss. Adding an acoustic vent may produce a significant reduction in peak height depending on how open the vent is. So, the system Q-value is lowered (= more loss) from applying an acoustic vent although we really can't speak of a Q-value of an aperiodic system. Basically a closed box has 2nd order roll-off, a vented system a 4th order roll-off and the aperiodic system a 3rd order roll-off.
JBL L100 Century,
Perhaps I am compulsive about good methods, but you really want something where you can return the exactly the favourite damping after doing trials. I have no intuition about coffee filters, as suggested earlier, but the count of filters is reproducible.
B.
B.
Ditto scraps of the dense grill cloth I'd strip off the discarded '40s, '50s consoles as folks 'upgraded' to stereo separates.
GM
GM
I have used the funny perforated thin pad sold for use under rugs and for stopping wood workpieces from buzzing and sliding under power sanders on a whoompy powered sub to good effect.
Really?! Interesting! Went out and blew threw my '60s era one and could discern no resistance of merit until folded to a very thick six layers, though looking at what's available nowadays it looks like some of these would be the 'hot ticket' for flattening an intentionally under-damped alignment like I've been suggesting just recently, especially if rigid acoustic fiberglass pads [O.C. 703] were 'sandwiched' in.
Thanks!
GM
Thanks!
GM
I have only one layer and the sub is still whoompy so I'll double up and report. Too chilly in the garage for this kind of fiddling lately.
Funny how the world keeps doing the duality deal. Some of us insist on the port output being maximized since resistance is inherently bad; others have the notion that undamped resonance is evil. I fall in with the second group, being an old stuffed shirt - I mean stuffed TL guy. So port output is supplemental not primary for me. My pro sound buddy had JBL 2245s catch fire from being driven too hard too long at the port tuning frequency, which caused the drivers to barely move while the full power of the system was being poured on. He remains a fan of minimum damping, btw, but has moved on to 8 Labhorns for his bottom end.
Funny how the world keeps doing the duality deal. Some of us insist on the port output being maximized since resistance is inherently bad; others have the notion that undamped resonance is evil. I fall in with the second group, being an old stuffed shirt - I mean stuffed TL guy. So port output is supplemental not primary for me. My pro sound buddy had JBL 2245s catch fire from being driven too hard too long at the port tuning frequency, which caused the drivers to barely move while the full power of the system was being poured on. He remains a fan of minimum damping, btw, but has moved on to 8 Labhorns for his bottom end.
You can make an number of folds in a towel or piece of air filter (kitchen), before you roll it up and stick it in the port; with more folds, the tighter the plug is and the more air is blocked.
I'm a port blocker 😀 and see 2 reasons for it;
1) To correct bass reflex subs which have a flat response outdoors, but sound boomy indoors; to get a nice low end roll off to compensate for room gain, more like sealed.
2) To dampen port noise
Are there other reasons this is done?
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