I don’t understand the question.
With a slim wall mount the only thing that happens is that the chamfer reduces the ripple at the baffle step & the higher frequncy reradiation (as it approximates a round over).
dave
With a slim wall mount the only thing that happens is that the chamfer reduces the ripple at the baffle step & the higher frequncy reradiation (as it approximates a round over).
dave
Earlier I was responding to what WBS was beginning to say, and the point was that even though the table makes that shape look good in free space, the result isn't the same with a wall.
The point was that the less the chamfer is required in the first place, the better.. and that the result will not be the same with a wall.
I don't trust the images below to show the full effects, including the time delays and other issues that alter the perceptibility of the differences (also the degree of visibility doesn't necessarily relate to the degree of audibility). Only to show that there is actually a difference. (This example was randomly chosen.)
In addition, the front wall is considered by some to be the worst surface to have sound reflected from it, ie early reflections, when it comes to affecting imaging.
The point was that the less the chamfer is required in the first place, the better.. and that the result will not be the same with a wall.
I don't trust the images below to show the full effects, including the time delays and other issues that alter the perceptibility of the differences (also the degree of visibility doesn't necessarily relate to the degree of audibility). Only to show that there is actually a difference. (This example was randomly chosen.)
In addition, the front wall is considered by some to be the worst surface to have sound reflected from it, ie early reflections, when it comes to affecting imaging.
Attachments
True.
In the bass. Wavelengths get long enuff, it does not see the edge at all. The chamfer still gretly reduces edge reradiation at higher frequencies.
The nature of what you are attempting to depict is different as frequency changes. At LF & HF we know what happens. It is in the bafflestep transition range, a chamfer should still smooth that out as the “edge” is not well defined as it would be with an orthoganol edge.
By some. If a reflection is withing a certain time window (i’d have to look up the exact number), the brain just integrates it with the main signal. With the speaker right against the wall that number will be very small.
dave
That id good, lowering the frequency of the baffle effect closer to a point where the depth has become small enuff that it “disappears”.
Widening the baffle, usually means a smaller depth as well. one just wants to not make them so shallow that it starts to intrude sonically. Real world experience with some of our builds. In the 1st one adding a 3/4” supreBaffle was sufficient to mostly eradicate the issue.
dave
Widening the baffle, usually means a smaller depth as well. one just wants to not make them so shallow that it starts to intrude sonically. Real world experience with some of our builds. In the 1st one adding a 3/4” supreBaffle was sufficient to mostly eradicate the issue.
dave
I would disagree with you - the speaker will be slim enough to introduce coloration no matter off depth hence the priority of making it thinner. If its deeper it will not stay well to a flat screen tv.
In a typical room the 1st reflections off the side walls still fit within the integration window so the width of the baffle will not cause enuff delay to be an issue. And with a wide enuff baffle the wall behind effectively becomes part of the baffle.
dave
Even if they do, diffraction or reflections occuring in the vicinity of the driver can contribute to interference patterns that reach far from the speaker, modifying the timbre of early or later reflections.
That is why you want a big chamfer or roundover.
There are always issues, one has to choose their compromises base don paticular needs.
If teh baffle is wide enuff and the box shallow enuff, LFs don’t see the edge, the chamfer gretaly reduces the HF diffraction effects and smooths th etransition in between.
dave
There are always issues, one has to choose their compromises base don paticular needs.
If teh baffle is wide enuff and the box shallow enuff, LFs don’t see the edge, the chamfer gretaly reduces the HF diffraction effects and smooths th etransition in between.
dave
How about, take your four-inch drivers, array two of them in a DeAppolito WTW arrangement, tweeter in between of course...Getting some piping, your typical six inch "sewer pipe", in cement/concrete substance...it would stand about 350mm high, 150+ mm in diameter...???
---------------------------------------------------------------------Rick.............
---------------------------------------------------------------------Rick.............
One certainly has a different set of compromises, bu tif on ecan make it “look” like an infinite baffle it is always radiating into 2π space. Done well there will be NO diffraction, only room effects.
What frequency are you trying to illustrate?
dave
What frequency are you trying to illustrate?
dave
Nothing in particular. You could scale the example, which looks like a cabinet depth of around 1/3 wavelength FWIW.
Behaviour depends heavily on frequency being looked at.
At HF we have a 2π space, just as with any other position. And issues with what happens at the edge (edge diffraction). Best would be somesort of increasing radius curve, but a chamfer (or prefereable a 45° side) is much easier and close, particularily if you soften the initial edge).
At low frequencies the waveform does not even see the edge and the wall extends the baffle.
The only area we have to worry about is the stuff inbetween (normally the FBS(-3). Olsons work deals with shapes in 4π space. If we look at the sphere and the semi-sphere we can see that the ripple as one transitions from 2π to 4π space that the flat back edge of the semi-sphere is acting as the edge of the cabinet for some frequencies and we get much larger riipple tha the full sphere. against a wall there is no edge, we sort of have a “mirror” of the semi-sphere and should have little ripple. This supposition would need to be measured in the real world to see if it holds.
Further, we expect that the level of any waveform travelling across the surface of the baffle. Being a 2D space, this will be less than the 6dB in free space, probably close to 3D with every doubling of distance. The wider the baffle, the greater the attenuation leading to a reduction of any issues that occur at the edge.
That, and that as the width increases the affected frequencies drop, suggests that a wider baffle, with a slower transition to the wall, will have less effect.
dave
At HF we have a 2π space, just as with any other position. And issues with what happens at the edge (edge diffraction). Best would be somesort of increasing radius curve, but a chamfer (or prefereable a 45° side) is much easier and close, particularily if you soften the initial edge).
At low frequencies the waveform does not even see the edge and the wall extends the baffle.
The only area we have to worry about is the stuff inbetween (normally the FBS(-3). Olsons work deals with shapes in 4π space. If we look at the sphere and the semi-sphere we can see that the ripple as one transitions from 2π to 4π space that the flat back edge of the semi-sphere is acting as the edge of the cabinet for some frequencies and we get much larger riipple tha the full sphere. against a wall there is no edge, we sort of have a “mirror” of the semi-sphere and should have little ripple. This supposition would need to be measured in the real world to see if it holds.
Further, we expect that the level of any waveform travelling across the surface of the baffle. Being a 2D space, this will be less than the 6dB in free space, probably close to 3D with every doubling of distance. The wider the baffle, the greater the attenuation leading to a reduction of any issues that occur at the edge.
That, and that as the width increases the affected frequencies drop, suggests that a wider baffle, with a slower transition to the wall, will have less effect.
dave
Not necessarily, the shallower the enclosure the higher in frequency the relections and the easier they are to absorb.
But to absorb a frequency you need at least ~half wave thibk of approriate damping.
My comment was based on emprical results, every time we have built a box with walls too close you can hear that.
dave
My comment was based on emprical results, every time we have built a box with walls too close you can hear that.
dave
Lobing is associated with 2 sound sources producing the same frequency from 2 different spots. Here is would be primarily caused by the HF diffraction at the edge. A softened chamfer (45° side in this case) is way better than an orthoganal edge and effectly larger than any round over you can add. As per above an increasing radius would be a slight improvement, but much harder to implement. It would be horizontal lobing not vertical lobing. Further the reduction in level with the distance it would travel to get to the edge of a wide baffle would further diminish any effect.
I don’t see it as an issue — and with the FRs we use, little HF actually travels along the edge. It seems the best set of compromises to my mind. If it is still an issue one can use the felt around the tweeter trick.
dave
I don’t see it as an issue — and with the FRs we use, little HF actually travels along the edge. It seems the best set of compromises to my mind. If it is still an issue one can use the felt around the tweeter trick.
dave
Hi! Thank you for all the answers! Interesting discussions 🙂
Like said in the beginning and also implied in the discussion, this is a difficult thing to simulate. I'm aware of that. My intention was not to simulate and try to get a "perfect" result. My intention was to simulate with a rather simple crossover, and try to check that with some simulations that include baffle step and room gain or acustic effect. After that maybe do some adjustments, but I realize that the simulations would have to much uncertainties in them to have as a base for complex crossover build, trying to compensate all the different effects.
Anyway. I have found myself in a state of over analyzing this project, in all aspects. And sometimes when you find yourself in that state, it stops being fun. So I have decided to let this idea rest. Instead I going to build something using a pair of full range drivers, which is something I also been thing about from time to time 🙂
Like said in the beginning and also implied in the discussion, this is a difficult thing to simulate. I'm aware of that. My intention was not to simulate and try to get a "perfect" result. My intention was to simulate with a rather simple crossover, and try to check that with some simulations that include baffle step and room gain or acustic effect. After that maybe do some adjustments, but I realize that the simulations would have to much uncertainties in them to have as a base for complex crossover build, trying to compensate all the different effects.
Anyway. I have found myself in a state of over analyzing this project, in all aspects. And sometimes when you find yourself in that state, it stops being fun. So I have decided to let this idea rest. Instead I going to build something using a pair of full range drivers, which is something I also been thing about from time to time 🙂
Which FR drivers? I am just finishing up the 1st drawings for a 2nd Poplar, which is an ML-TL for against the wall — the simple version here of the original.
dave
dave