Pressure vs Sound Quality
I simulated a TH(Fb20hz) and a Sealed enclosure of similar size and volume matched at 30hz
Potentially, the 30hz note will generate more pressure derived 2nd order distortion and IMD in TH than the Sealed enclosure.
Excursion is minimal in both models....
I simulated a TH(Fb20hz) and a Sealed enclosure of similar size and volume matched at 30hz
Potentially, the 30hz note will generate more pressure derived 2nd order distortion and IMD in TH than the Sealed enclosure.
Excursion is minimal in both models....
In my endeavor to find a reason to not vent. It would appear that Pressure is a non issue within the realm of good vented designs....The 2 lines are, the Similar sized Sealed and Tapped Horn.
The "mouth" of the vent of a design has a CSA. That CSA corresponds to a Radiation Mass size...
"At very short distances (known as "near field"),movement of the fluid follows that of the membrane. Inertial force then largely dominates, and the reaction on the fluid corresponds essentially to the mass of the fluid thus driven, called "radiation mass"
When a Driver plays near Fb, the coupling takes place, closer and closer the mouth of the line. I don't know this for sure but it is my thought at this time. Where the excursion dip takes place, is likely where the air mass coupled to the driver, reaches the mouth.
Since we are dealing with bass. Dispersion will virtually the same. So it would seem that a radiator that was small vs one that is large. There would be no difference in perception, once volume matched to the listener...
Spl being the same at listening. Is it unanimously accepted that SQ is not affected by the radiator size, in this case, the radiation from the CSA of the vent line/mouth, in the omni part of the spectrum of the Line???
As soon as it hit post (for the first time lol) my mind was like....Hey! What about the efficiency of the enclosure. A larger CSA vent is more efficient!
The "mouth" of the vent of a design has a CSA. That CSA corresponds to a Radiation Mass size...
"At very short distances (known as "near field"),movement of the fluid follows that of the membrane. Inertial force then largely dominates, and the reaction on the fluid corresponds essentially to the mass of the fluid thus driven, called "radiation mass"
When a Driver plays near Fb, the coupling takes place, closer and closer the mouth of the line. I don't know this for sure but it is my thought at this time. Where the excursion dip takes place, is likely where the air mass coupled to the driver, reaches the mouth.
Since we are dealing with bass. Dispersion will virtually the same. So it would seem that a radiator that was small vs one that is large. There would be no difference in perception, once volume matched to the listener...
Spl being the same at listening. Is it unanimously accepted that SQ is not affected by the radiator size, in this case, the radiation from the CSA of the vent line/mouth, in the omni part of the spectrum of the Line???
As soon as it hit post (for the first time lol) my mind was like....Hey! What about the efficiency of the enclosure. A larger CSA vent is more efficient!
The dip is due to the resonance of the port with the box. I don't see (or I don't understand) your view of the situation.
At Fb the impedance of the box on the driver goes very high, which is why the cone hardly moves. When the cone ceases to move, the back EMF goes very low and the impedance dips - the impedance peaks being entirely due to back EMF since the static impedance is flat in that region.
ALso, regarding enclosed air nonlinearity, this nonlinearity is of very low order, dominantly 2nd order, which is all but inaudible in most cases. Air nonlinearity is essentially a non-issue.
Isnt there an air column directly associated with coupling? A certain volume of air per frequency and coupling?
I has 1/4wl resonance in mind but maybe they both work similar?
Also on my mind... is it true that Fb cares not about frequency and only velocity? Meaning that a driver moving 10mm at 20hz or 2000hz... 2000hzmm would obviously generate more pressure? Vs what happens at neutral playback as we know it
I has 1/4wl resonance in mind but maybe they both work similar?
Also on my mind... is it true that Fb cares not about frequency and only velocity? Meaning that a driver moving 10mm at 20hz or 2000hz... 2000hzmm would obviously generate more pressure? Vs what happens at neutral playback as we know it
^ I can't understand your questions. The port air column is "coupled" to the driver through the box volume. This creates two "modes" one with the port and driver in-phase (lower) and the other with them out-of-phase (upper).
But I don't understand "A certain volume of air per frequency and coupling?"
But I don't understand "A certain volume of air per frequency and coupling?"
Anyone have the video with the guy demostrating 1/4wl resonance through a clear tube filled with smoke? @Ro808?
Please forgive me if I'm misusing words... or confusing ideas. It is only the air column that is couple to the driver that maintains the same velocity, intensity and whatever else, as the transducer... beyond the coupled air column, radiation impedance drops off significantly
The borders of the coupled air column, are essentially the radiating surface, and as always when an energy change takes place, their is distortion. Group delay and decay.... but also in some cases like a horn or waveguide, the resulting csa of coupled air column is now larger than the transducer, increasing efficiency
Please forgive me if I'm misusing words... or confusing ideas. It is only the air column that is couple to the driver that maintains the same velocity, intensity and whatever else, as the transducer... beyond the coupled air column, radiation impedance drops off significantly
The borders of the coupled air column, are essentially the radiating surface, and as always when an energy change takes place, their is distortion. Group delay and decay.... but also in some cases like a horn or waveguide, the resulting csa of coupled air column is now larger than the transducer, increasing efficiency
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The above is never the case for a port (air column.) The ports relationship to the driver is complex, but it is only closely the same at frequencies well below Fb.
Rereading what I said, I see how it doesn't make sense, in particular when compression is involved. Is port specific to BR and Helmholtz resonance?
We agree, I may have just written it down in a way that I didn't get that across.
All I was trying to say is that despite all the variables for a system to be able to generate realistic playback levels, still it seems to me this tiny djembe produces way more sound than I think a speaker can with the same Vd properties. So either I am overlooking a factor(s), or I haven't implemented things well enough to include the variables good enough. These factors could be things like wrong implementation of Room Equalization, but it could as well be underestimating the effect of room interaction (a speaker directing the energy towards you as the room interaction with a djembe anywhere in the room generates, let's call it a dipole bass reflex loaded instrument. This could make for a different perception as well.
Also: with most factors accounted for, the snare and djembe sound equivalently alive and with the right amount of "snap" etc when there's a little bit too much top end applied and a bit less of LF. When that correction is applied, music seems too thin with too many albums. Now we all know all albums can't be taken as a reference but we do want most records to be playable, listenable right?!
I'm not quite there yet, if I find the solution, I'll let you know, but it might be just the room or system specific or just the amps not matching well, who knows?
To me that's distortion modulated by other distortions and is not most of it called IMD instead of THD?
Not sure if all of it is, trying to get my lingo straight. Opinions?
I need to revisit quarter wave theory. The first thing I need to realize is that A reflection is needed for standing waves....So no matter if the pipe is open or closed from the radiation source......a reflection will be sent back towards the transducer...Correct?
And then pressure....looking at a driver played into a open end line. Pressure seems to modulate.... How?
It seems to be based off of harmonics....It would seem to me that pressure would be relative to diaphragm velocity, nothing less. I guess I am not factoring in the reflected pressure....sometimes more or less energy is reflected back, that must be the harmonic part. My guess is that peak pressures are a combination of standing waves where the 2nd reflection is in phase with the source signal, the 2nd reflection being the one coming from the open end, and rebounding off of the transducer or just in phase on the way to the transducer????...and the increase of excursion required to make bass neutral to our ear.
And then pressure....looking at a driver played into a open end line. Pressure seems to modulate.... How?
It seems to be based off of harmonics....It would seem to me that pressure would be relative to diaphragm velocity, nothing less. I guess I am not factoring in the reflected pressure....sometimes more or less energy is reflected back, that must be the harmonic part. My guess is that peak pressures are a combination of standing waves where the 2nd reflection is in phase with the source signal, the 2nd reflection being the one coming from the open end, and rebounding off of the transducer or just in phase on the way to the transducer????...and the increase of excursion required to make bass neutral to our ear.
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This is correct, but the reflections of these two conditions are 180 out of phase with each other, so very different things happen. And then there is the radiation loss to consider. But at any rate, you seem to be talking more about transmission lines than base reflex. Very different things.
Ok Ok Ok ok, I know that there is something I am missing, and my confusion has to do with looking at waveguides and how directivity is corresponding to Wall angle at the axial point to where coupling takes place......OK I think I confused myself by neglected the CSA....
I like this visual for standing waves
I think if X remains static....pressure increases in an line with frequency.... outside of the cancellations.
I like this visual for standing waves
I think if X remains static....pressure increases in an line with frequency.... outside of the cancellations.
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Your not grasping that the boundaries make big differences. A driver at the end of a tube looks, acoustically, nothing like fig 4.23.
What is this discussion about? I thought that it was ports and tuning. Is there another question in there somewhere that I am missing.
What is this discussion about? I thought that it was ports and tuning. Is there another question in there somewhere that I am missing.
Heres confusion.... CSA relates wavelength "size".....Yes SPL relates to amplitude of oscillation..
I think my confusion is; tying amplitude to a physical dimension instead of leaving it as amplitude, which is amplitude of pressure.
I deleted that.
I think my confusion is; tying amplitude to a physical dimension instead of leaving it as amplitude, which is amplitude of pressure.
As long as this is true...its all making sense so far....
I am trying to find the issues of using a smaller radiation source vs a larger one.... if we remove the topic of THD and chuffing, since we are talking about the mouth of Transmission lines and the mouth of the Port, as the source of radiation
I know that a larger Port or 1/4w line is more efficient, so thus they should create sound with less energy, when the tuning note is the same. For example; a straight Line tuned to 30hz that has an ending CSA of 100cm2 vs 500cm2...the larger CSA is more efficient.
I thought of Radiation Mass/Impedance... When we volume match to the listening point, and the reproduced signal is of Omni character for both the 100cm2 and 500cm2 mouth.... Outside of efficiency....there is no effect on SQ and perception? In a small room?
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For an equal Volume Velocity (VV) in a large and small radiating area, the larger area is more efficient (let's call it R) at LFs, but since the radiated power goes as R * VV^2, it's the VV that is the key. You are trying to get the most VV you can at the ports radiating opening.
Thus, if the power output (volume) is adjusted to be equal, then the radiating area is almost irrelevant.
Thus, if the power output (volume) is adjusted to be equal, then the radiating area is almost irrelevant.
This is a sample of the dynamics from front seat at the Imax tonight showing of Black Adam
@gedlee My dilemma is that I watch the spl meter display numbers (80-90db range) I can hit at home but the experience is unsimilar. The way the LF felt in the theater, is not on par with my experience of LF, so far, with the single dual 18" sub in nearfield...I feel that the difference is attributed by high Sd but I would like to be certain and understand it on a technical level...
I've hypothesized some other things as well but it really means nothing without science backing it.... radiation mass/impedance is interesting but maybe its this; The larger room of the theater, reduces reflective energy, increasing the portion of direct energy to reach desired levels... that actually sounds like a likely conclusion.
Keeping thd at a low percentage, I predict that 90db bass, outside, is a much different experience than 90db bass in a domestic room. Direct vs indirect being the metric of significance, and not so much Sd.
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A well designed vented cabinet, either direct radiating or front horn loaded, is very hard to beat.