Measuring HD at low levels is difficult. What test protocol would you suggest?
If it is something similar to crossover distortion we are after, then maybe simply looking at the zero crossing for some low level would be adequate?
Hm, seems like it would introduce HF resonances in the cylindrical gap between pole and former...
Why would this be? Noise? If you can't measure the harmonics because of the noise floor then it is hard to believe that they would be a significant audible effect. If there is significant stiction then the harmonics should increase in % as the signal level falls. This should not be hard to measure. Go near field if you have to, although that wouldn't be ideal. You could use synchronous averaging techniques if you had to to measure below the ambient noise floor.
The nonlinearity is on the velocity (that's what stiction is) so the "zero crossing" would be when the velocity goes through zero which is not when the diaphragm goes through zero.
It could show on the step test as the diaphragm recovers especially towards zero. Also try this with a cold driver then with it warmed in a warm room.
Different things happen at different frequencies, I have not been able to see a good solution over a wide band yet, but looking at phase plugs of many drivers, there is a large area near the diaphragm that causes asymmetric damping in the compression process. I think with 3D printing be momism popular, it could be cost effective to try different designs as long as you don't heat the driver up.
I would also try to design the diaphragm, but it is going to take lots of simulation up front because some of the simpler tools don't have much flexibility to create more complicated diaphragm shapes. If a 3" can go wide range with a direct radiating driver, I wonder whether it can do so in a horn.
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Even without the possible midrange FR change, better highs can make other registers sound better. Most of us have heard a new tweeter make the bass better.
It's psycho-acoustics, and it's real.
Even without the possible midrange FR change, better highs can make other registers sound better. Most of us have heard a new tweeter make the bass better.
It's psycho-acoustics, and it's real.
Is phase response a psycho-acoustics?
Wow, I had no idea that throwing out the idea of "stiction" in the spider and surround would get things off on such a tangent.
What puzzles me is why low-efficiency direct-radiator loudspeakers can sound energetic and lively at 80 to 90 dB levels, and dull and lifeless in the 50 dB range. By comparison, electrostats and horn systems (including hybrid horns) sound more consistent as the level changes. Why? The previous post about "stiction" was just a guess, nothing more.
The real mechanism? I don't know. Why would a direct-radiator perform less well at low levels? I can only think of a few possible mechanisms that would do this. It's just a short-travel linear motor with a primitive suspension. In principle, IM distortion (and spurious noise from spider and surround) should go down monotonically with level. (It should sound clearer at low levels, not worse.)
Subjectively, though, electrostats and horns have a sound that stays consistent with dynamic level, while direct-radiators, particularly low-efficiency systems, can sound opaque and toneless at low levels. An illusion? Maybe, but the dynamic difference between electrostats & horns, compared to low-efficiency direct-radiators, seems pretty noticeable, and not in favor of the direct-radiator.
There's something going on with dynamic tracking that is not at all obvious.
One similarity between electrostats and horns is the dominance of the air-load in the driver performance, while direct-radiators are not as well coupled to the load. No idea how this would affect dynamics, though.
What puzzles me is why low-efficiency direct-radiator loudspeakers can sound energetic and lively at 80 to 90 dB levels, and dull and lifeless in the 50 dB range. By comparison, electrostats and horn systems (including hybrid horns) sound more consistent as the level changes. Why? The previous post about "stiction" was just a guess, nothing more.
The real mechanism? I don't know. Why would a direct-radiator perform less well at low levels? I can only think of a few possible mechanisms that would do this. It's just a short-travel linear motor with a primitive suspension. In principle, IM distortion (and spurious noise from spider and surround) should go down monotonically with level. (It should sound clearer at low levels, not worse.)
Subjectively, though, electrostats and horns have a sound that stays consistent with dynamic level, while direct-radiators, particularly low-efficiency systems, can sound opaque and toneless at low levels. An illusion? Maybe, but the dynamic difference between electrostats & horns, compared to low-efficiency direct-radiators, seems pretty noticeable, and not in favor of the direct-radiator.
There's something going on with dynamic tracking that is not at all obvious.
One similarity between electrostats and horns is the dominance of the air-load in the driver performance, while direct-radiators are not as well coupled to the load. No idea how this would affect dynamics, though.
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Correct me if I am wrong here but a major difference between a dynamic driver and a compression driver would be the rarefaction that occurs in the area between the diaphragm and the phase plug and no equivalent function in a normal direct radiator. The air loading on the diaphragm is multiple factors higher in a compression driver and this would to me be the major contributor to the difference in perceived dynamic response of the two different approaches.
Soongsc,
I think that besides a few rather old designs you will find that the majority of compression driver diaphragms are made of a rigid metallic material, aluminum, TI, or even Be. I don't think it has anything to do with the mass of the diaphragm as any compression driver including most 1" drivers will have much more mass in the diaphragm than any 1" dome tweeter diaphragm could approach.
My "belief" is that the air loading on a direct radiator is so low that this is the effect that we are hearing at low levels, very poor transfer efficiency between the moving diaphragm and the air column in front of it requiring a higher peak output to cause any true compressional waves to be produced.
Soongsc,
I think that besides a few rather old designs you will find that the majority of compression driver diaphragms are made of a rigid metallic material, aluminum, TI, or even Be. I don't think it has anything to do with the mass of the diaphragm as any compression driver including most 1" drivers will have much more mass in the diaphragm than any 1" dome tweeter diaphragm could approach.
My "belief" is that the air loading on a direct radiator is so low that this is the effect that we are hearing at low levels, very poor transfer efficiency between the moving diaphragm and the air column in front of it requiring a higher peak output to cause any true compressional waves to be produced.
I have mentioned this a few times in the thread, the material has more to do with low level listening that Lynn just mentioned. Soft material absorb energy transferred from voice coil movement.
You can always argue that some things are not audible. My approach is, if the theory looks like it might improve sound, and it does not cost an arm and a leg to try it, well just do something and see what you hear, then put the pieces together and establish some design criteria. In this case, someone removed a phase plug and likes the sound. I always avoid putting anything in front of a diaphragm as a basic criteria. But who knows, maybe I will one day.
Also compression drivers can compress 2 to 5 times the normal air density i.e contracts and expands as it drives the air in and out of the horn throat. It is effectively an AC or rather irregular i.e music signal driven almost adiabatic heat engine. It can be better or worse than a direct drivers in terms of losses. But the frictional losses may favour the pressure tweeter in being lower, and thus in allowing movement of the diaphragm at low signal inputs. FWIW
Excellent ... thanks for that, Rob ...
This is all very vague; electrostatic speakers are direct radiators. Accelerate equal surfaces areas of any type of direct ratiator at same rate and air reacts exactly the same; same effective air load. Power requirements for accelerating different unit area mass of membranes from different types is readily calculated.
Electrostatics are very flat, very light, not very rigid, and very limited in displacement. For large membrane, encounters with returning room reflections is like ripples in water with reflections from uneven bottom, standing waves and traveling waves are set up on the membrane resulting in charge distribution of both membrane (unless electret material, and in conductive grids that provide reactive electric field. Distribution of drive state becomes perturbed. Seems this would have complex effect on radiation from membrane compared to plane wave idealized in electrostatic concept.
Energy from room radiating back into horn encounters continuously increasing impedance; much energy reflects back out again as pressure wave continuing onward to driver increases in pressure. In apex of horn returning wave may encounter a compression drivers phase plug, or a suitably stiff direct radiator. With direct radiator case, yet more energy is reflected from it, and a driving force against it with ensuing electromagnetic reaction......
Dull and lifeless with low efficiency driver at 50dB? Specific examples would be helpful. Late night I can play low efficiency drivers peaking -60dB to lively daytime levels with great detail and measured linearity at both levels. At low level playback all the quieter signals sink cleanly into the ambient noise floor. At low level I can compress the signal dynamics to bring lowest signals back to audibility within the room noise. I can boost the base to compensate for hearing curves.
Sound from room entering back into
Lynne
My take on this is an effect that I have often noted, but cannot explain completely. That is, for each recording piece there seems to be an ideal gain control setting. This is two things: first each recording has a different loudness for a given gain, but, and this is the real point, each recording seems to have an ideal SPL level.
When I listen to music I use a playlist. But I have to keep the volume control right next to me to adjust each recording for its optimum playback level - the one where the song sounds best. Auto leveling just not do the job.
Now why would there be a different SPL level at which a song sounded best? My only explanation is that this is the level that the recording was mixed at and at this level the mix just clicks. Now one could easily attribute this effect to the loudspeakers, but I don't.
I listen to music much louder than my wife likes, but to me lower levels just sound flat and unappealing. Thank goodness that my room is sound proof!! It could be my hearing I suppose, that's what she says it is.
My take on this is an effect that I have often noted, but cannot explain completely. That is, for each recording piece there seems to be an ideal gain control setting. This is two things: first each recording has a different loudness for a given gain, but, and this is the real point, each recording seems to have an ideal SPL level.
When I listen to music I use a playlist. But I have to keep the volume control right next to me to adjust each recording for its optimum playback level - the one where the song sounds best. Auto leveling just not do the job.
Now why would there be a different SPL level at which a song sounded best? My only explanation is that this is the level that the recording was mixed at and at this level the mix just clicks. Now one could easily attribute this effect to the loudspeakers, but I don't.
I listen to music much louder than my wife likes, but to me lower levels just sound flat and unappealing. Thank goodness that my room is sound proof!! It could be my hearing I suppose, that's what she says it is.
That would also explain why longer horns seem to bring more "dynamic" at low levels than shorter ones (on-axis response being made identical).
Better impedance matching lowers frictional losses?...