In that case, there is also absolutely nothing to be discussed about, see answer previously.
Case closed.
I agree, and this is what I meant with Linkwitz' hypothesis, but there are plenty of more modern stories for this as well.
With a bit of simple logic and basic physics, we can already know for sure that the entire idea is very debatable at most.
So to be very honest, some of those smart guys actually do make things up.
That's most definitely not meant on a negative way.
But again, without any real practical data to back it up, it's nothing more than just a hypothesis with no numbers to show any significance.
I think that is a bit overly simplified tbh.
Science by definition is not a religion, so there is also nothing to believe in.
I once had a teacher who said; believing is what you do in church but not in science.
But we can be sure about certain things with a certain predictability.
Meaning that there is also never a full true or false, often just grey scales.
The more complicated and complex subjects become, the more difficult it this is going to be.
Standard straightforward thermodynamics is most definitely NOT one of those fields.
You most definitely also don't also don't have to refer to the AES for this kind of stuff.
Just your standard high-school physics book will be fine.
btw, what other method would you propose?
Because all other alternatives, are just all about believing without as objective as possible working methods?
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I can tell about my experiences with small air leaks during my experiments with ports (and I did several of those!).
Small air leaks appeared sometimes when sloppily installing ports with play-dough or when the port adapter-boards did not seal properly because of loose screws or when I even just forgot one of the screws (screw hole air leak).
I would estimate the cross section surface of those air leaks being around 1-10 mm².
I should mention that I only tested ported speakers at the respective resonance frequency, which means there was a very high peak pressure in the enclosure - higher than in a similar sized sealed speaker with similar input voltage (*).
without exception all of those leaks were clearly audible at higher volumes. They make an annoying modulated whistling sound.
even more interesting was that I could immediately tell there was an air leak, because of unnaturally high H3 distorsion noticed at the measurement, even at very low levels.
I always found the air leak, either by visual inspection or by turning up volume and listening closely around possible leaks. I even used a wet finger or wet lips to detect the air movement.
I could imagine that an air leak at the back of a sealed speaker will probably not have such a big impact.
But I am now very aware of how important sealing a (low frequency) speaker is.
(*) to get an idea of the pressure just imagine a very high Q ported speaker. at the resonance frequency the diaphragm moves very little, the air in the port however moves very much - but in opposite direction. so the total pressure in the speaker is so high that it more or less counteracts the force of the voice coil.
Small air leaks appeared sometimes when sloppily installing ports with play-dough or when the port adapter-boards did not seal properly because of loose screws or when I even just forgot one of the screws (screw hole air leak).
I would estimate the cross section surface of those air leaks being around 1-10 mm².
I should mention that I only tested ported speakers at the respective resonance frequency, which means there was a very high peak pressure in the enclosure - higher than in a similar sized sealed speaker with similar input voltage (*).
without exception all of those leaks were clearly audible at higher volumes. They make an annoying modulated whistling sound.
even more interesting was that I could immediately tell there was an air leak, because of unnaturally high H3 distorsion noticed at the measurement, even at very low levels.
I always found the air leak, either by visual inspection or by turning up volume and listening closely around possible leaks. I even used a wet finger or wet lips to detect the air movement.
I could imagine that an air leak at the back of a sealed speaker will probably not have such a big impact.
But I am now very aware of how important sealing a (low frequency) speaker is.
(*) to get an idea of the pressure just imagine a very high Q ported speaker. at the resonance frequency the diaphragm moves very little, the air in the port however moves very much - but in opposite direction. so the total pressure in the speaker is so high that it more or less counteracts the force of the voice coil.
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Things are not always as they seem.
If you want high pressure and very high "Q" start with a small sealed speaker enclosure.
If you want a bass reflex speaker the volume of the enclosure is close to doubled and there is a added tuned enclosure duct. You end up with a impedance curve with two much lower "Q" peeks with a saddle in between. The lower peek is from the reduced speaker resonance frequency. The higher separate impedance peek is from the tuned port, there is no direct connection between the VC and this port resonance. Think of blowing across the mouth of a 40 OZ beer bottle.
Back to the sealed enclosure with high pressure and very high "Q", drill a single 1/4 inch hole. The back pressure inside the enclosure will be as high as it will be. The resonant frequency will be its' highest. The air velocity and local noise at the leak will also be their highest. Drill a second hole, back pressure will fall, air velocity and noise will also fall. Drill additional holes all that stuff will continue to fall. The resonate "Q" peek and frequency will also fall. Also with a given input voltage the excursion of the driver will increase. All this gets complicated pretty fast. One example is that Force Factor is a function of excursion (Bl(X)).
As Erin says; drill, measure and then repeat until you reach the desired result.
Thanks DT
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Great post! There may be a consensus between scientists, and scientific evidence.
But as soon as someone mentions "scientific consensus", you know he knows not what science is.
Scientists should read Popper.
I suppose I could say the same.
Another way of looking at it:
Whatever sealed enclosure (small, high Q) you take you'll never have an interior pressure high enough to inhibit the diaphragm from moving or only allow it to barely move. And here the diaphragm movement has other counteracting forces besides the internal enclosure pressure: the suspension and the exterior air weight and pressure. So movement is only partially limited by internal enclosure pressure.
A ported enclosure however will inhibit the movement of diaphragm by posing a high enough internal pressure on the diaphragm, so it barely moves. No driver suspension force or exterior air weight and pressure is acting on the (mostly immobile) diaphragm.
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Can't have it both ways:
1) "will inhibit the movement of the diaphragm by posing a high enough internal pressure on the diaphragm"
2) " No driver suspension force or exterior air weight and pressure is acting on the (mostly immobile) diaphragm."
Highlight by me.
Visualize this speaker test:
Place the measurement microphone in the direct field. Sine sweep the speaker/enclosure with the analyzer / test amplifier.
The enclosure resonant tuned port will continue to ring like a bell long after the test frequency sweep is complete. It is not about the driver, It is about the enclosure / port resonance. Pressure inside the enclosure on the back side of the driver plays no part yet the resonate port continues to ring.
moving on to the next topic.
Thanks
And in between is the concept of damping. In case of a ported system it could become a aperiodic system i believe. I am a sealed enclosure user so i am not sure.
Another twist: Linn used to seal and bolt the drivers in their isobarik speaker systems in the 70s, 80s & 90s so thoroughly with silicone that getting out a blown or damaged one was a major challenge. They insisted such sealing was necessary for proper performance. When a bass driver cone in a Linn isobarik speaker was pushed in, the resistance was very high, and the cone bounced back quickly when released. In contrast, doing this with most other sealed bass speakers of the day would result in a slow in, then slow release of the cone back to normal position, indicating small air leakage. Repair technicians were trained to reseal these Linn systems back to factory air-tightness.
I admit to never putting this to the test by comparing a leaky vs tightly sealed isobarik system.
I admit to never putting this to the test by comparing a leaky vs tightly sealed isobarik system.
Next Topic: Passive Radiators
Not a lot unlike a Bass Reflex. Passive Radiators have moving parts and weights that you can put your eyes and hands on. They are physically and visually easier to understand. But still there is no direct relationship or link to watts put into the voice coil. There is no levers springs or pulleys connecting the driver to the passive radiator.
There is no linear direct relationship between air pressure in the enclosure and the passive radiator motion. There is a transfer function. The enclosure internal air pressure is not high as in a sealed enclosure. But there is sufficient enclosure air pressure to ring the resonance bell of the mass of the passive radiator.
Thanks DT
https://www.klippel.de/fileadmin/kl...ement_with_Multiple_Drivers_ and_Ports(2).pdf
https://www.klippel.de/fileadmin/klippel/Files/Know_How/Application_Notes/AN_57_Passive_Radiator.pdf
Not a lot unlike a Bass Reflex. Passive Radiators have moving parts and weights that you can put your eyes and hands on. They are physically and visually easier to understand. But still there is no direct relationship or link to watts put into the voice coil. There is no levers springs or pulleys connecting the driver to the passive radiator.
There is no linear direct relationship between air pressure in the enclosure and the passive radiator motion. There is a transfer function. The enclosure internal air pressure is not high as in a sealed enclosure. But there is sufficient enclosure air pressure to ring the resonance bell of the mass of the passive radiator.
Thanks DT
https://www.klippel.de/fileadmin/kl...ement_with_Multiple_Drivers_ and_Ports(2).pdf
https://www.klippel.de/fileadmin/klippel/Files/Know_How/Application_Notes/AN_57_Passive_Radiator.pdf
In my limited understanding, the air in enclosure is the spring between the driven and the passive.
Exactly!
And at the tuning frequency both driver and PR are nearly in sync, that means both move outwards/inwards in sync, they both add to the total pressure in the enclosure.
David McBean just informed me how to plot in-box pressurewith hornresp. I will provide some examples, but in my port investigation thread!
I agree for the most part, but we have to keep an open mind for exceptions. People are designing enclosures using plastic (even diy guys are doing so using 3d printing). Taken in conjunction with drivers with non-paper cones (polymer, titanium, etc.) a hermetically sealed enclosure is not impossible to achieve. And for these, differences in air pressure are significant.
I live near a hill station, and have noticed while driving down that the nearly empty plastic water bottle that I closed at the top of the mountain is noticeably squished by the time I get to the bottom. I do not want that sort of thing to happen to my drivers.
It's very difficult to get 3d prints airtight ... but I understand your concern. It's still difficult to get all cone-surround, surround-basket and mainly the driver-enclosure joints perfectly airtight. And maybe that's good!
That's why I don't take sealed speakers with me when mountain hiking 😊
The atmospheric air pressure variations due to low or high pressure situations is not a problem. Large altitude variation ( take it up a mountain or in an airplane ) can cause a problem , that i can understand.
A small "leak" in case of sealed boxes is not a problem during use the system. Leak as f.i. mdf (is not airtight) is not a problem, a drilled hole i am not so sure.
My current boxes are airtight. Would i ship it, I would drill a hole and put some fibrous damping in it, or untight one of the screws/bolts of each driver. (And when arrived at destination thighten these bolts). Atmospheric air pressure variations are rather slow in my understanding.
A small "leak" in case of sealed boxes is not a problem during use the system. Leak as f.i. mdf (is not airtight) is not a problem, a drilled hole i am not so sure.
My current boxes are airtight. Would i ship it, I would drill a hole and put some fibrous damping in it, or untight one of the screws/bolts of each driver. (And when arrived at destination thighten these bolts). Atmospheric air pressure variations are rather slow in my understanding.
I bet that temperature changes (even sunlight/shadow) affect internal pressure more that height/atmosperic.
I've read about a small hole receommendation before and a 1-2mm hole on the bottom or near cable posts should't do any noise. I haven't made those, I believe that I'm just a lousy carpenter 😎
I've read about a small hole receommendation before and a 1-2mm hole on the bottom or near cable posts should't do any noise. I haven't made those, I believe that I'm just a lousy carpenter 😎
Veneer work is nearly done. Next is working on the base and feet.
