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Baffle Diffraction
Baffle Diffraction
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Old 2nd December 2019, 01:10 PM   #571
Pallas is offline Pallas  Pakistan
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Originally Posted by 33Polkhigh View Post
The size and shape of the box changes the tone of the speaker. I use computer based dsp, and you can't equalize out the tonal difference.
Why would you expect otherwise?

What you're really doing is varying the size/shape of the waveguide and then wondering why DSP EQ (presumably of the axial response) doesn't affect directivity.
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Old 2nd December 2019, 03:49 PM   #572
33Polkhigh is offline 33Polkhigh  United States
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Yes, so I guess it isn't about the FR?
Its not entirely about FR. Because a bigger speaker will start becoming directional at a lower frequency. When this happens the sound is emphasized and we hear it differently

This goes back to my initial point that one doesn't want to have the baffle step shift in an area of cone break up. Big baffles help with this but they are better from a distance.
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Old 2nd December 2019, 10:30 PM   #573
AllenB is online now AllenB  Australia
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Originally Posted by 33Polkhigh View Post
a bigger speaker will start becoming directional at a lower frequency. When this happens the sound is emphasized and we hear it differently
I don't think I'm convinced about that.
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Old 3rd December 2019, 11:38 AM   #574
homebuilder is offline homebuilder  United States
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Default Baffle diffraction

33Polkhigh:

According to your theory concerning audible diffraction, would a driver mounted in a very large baffle, ie a wall, exhibit considerably better performance in a large room? Would it make sense that a large driver would realize more benefit from this type of mounting than a small driver? Say, 15" versus 6"-8" units?

Sorry if some of us have high-jacked parts of your thread, but the reality is that many posts on this forum have value to others in ways that may not seem readily apparent. Especially when one is trying to learn from others, and then apply that to their own situation. With that said:

Badman: "The larger cone of the 15" provides a directivity advantage as well as meaning the horn (cone) is moving less for the treble for a given SPL. The measured responses are superb on the DIYSG polars, equivalent to some very good horn/waveguide 2 ways (only the top octave gets very slightly wonky).

In my opinion, for what I'd expect from straight sound quality, that 15" is a straight upgrade to the JBL solution, which was previously one of the best for coaxial continuity and directivity."

Badman: Thank you for your response on the DIYSG coaxial. Based on your comment, would it seem like a reasonable idea to mate that driver up with JBL 2404 bi-radial crossed over at about 7kh? (I have 4 of these new in box) This would be a very easy, and elegant solution for my room. And the high efficiency of the drivers would allow me lots of options for amplifiers. to remind, you, these would be flush mounted in the end wall of a 24' x 36' room, off-center on the shorter wall.
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Old 3rd December 2019, 04:01 PM   #575
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Badman: Thank you for your response on the DIYSG coaxial. Based on your comment, would it seem like a reasonable idea to mate that driver up with JBL 2404 bi-radial crossed over at about 7kh? (I have 4 of these new in box) This would be a very easy, and elegant solution for my room. And the high efficiency of the drivers would allow me lots of options for amplifiers. to remind, you, these would be flush mounted in the end wall of a 24' x 36' room, off-center on the shorter wall.
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I'm not sure you even need the 2404 with that coax. It's not perfect in the top octave, but it's not bad at all.
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Old 3rd December 2019, 05:46 PM   #576
33Polkhigh is offline 33Polkhigh  United States
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I don't think I'm convinced about that.
I'm not sure if I can convince you of something that is perceptual. But if you were talking to a person in a very reflective room. And they turned their back to you or moved around their voice would change. More direct sound that is closer is more intense than if it is reflected.

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Originally Posted by homebuilder View Post
33Polkhigh:

According to your theory concerning audible diffraction, would a driver mounted in a very large baffle, ie a wall, exhibit considerably better performance in a large room? Would it make sense that a large driver would realize more benefit from this type of mounting than a small driver? Say, 15" versus 6"-8" units?

Sorry if some of us have high-jacked parts of your thread, but the reality is that many posts on this forum have value to others in ways that may not seem readily apparent. Especially when one is trying to learn from others, and then apply that to their own situation. With that said:
Sure, i don't think any of us remember who's thread this is. My initial point about diffraction was that you can use the ripple to your advantage with certain baffle shapes. You put a diffraction "dip" where a cone peak is. This seems almost common sense to me.

As far as infinite baffles. I do like them from what I've heard. They don't have that typical baffle step transition that creates problems with small baffles. That said its hard to say whether what you want to do will sound good. A 15" driver will be directional fairly low in frequency.
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Old 3rd December 2019, 05:58 PM   #577
badman is offline badman  United States
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Originally Posted by 33Polkhigh View Post
Sure, i don't think any of us remember who's thread this is. My initial point about diffraction was that you can use the ripple to your advantage with certain baffle shapes. You put a diffraction "dip" where a cone peak is. This seems almost common sense to me.

<<SNIP>>

That said its hard to say whether what you want to do will sound good. A 15" driver will be directional fairly low in frequency.
Whose thread? The DIYaudio community! The idea of a threadstarter "owning" a thread is silly IMO.

Regarding using the diffraction that way, that's all well and good on a few angles. A few specific angles. The only consistent solution is to create smooth transitions, use absorption, and minimize baffle artifacts, be it broadband ripple or discrete reflections.

Directional low in frequency is generally the goal for many of us. Very few have big rooms to use so we tend to go for directional solutions to limit room interaction in the mid/HF.
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Old 3rd December 2019, 10:37 PM   #578
AllenB is online now AllenB  Australia
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if you were talking to a person in a very reflective room. And they turned their back to you
Then you'd lose the direct arriving higher frequencies. Not a clear comparison for speakers. Also dependent on response.
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Old 4th December 2019, 05:58 AM   #579
33Polkhigh is offline 33Polkhigh  United States
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Whose thread? The DIYaudio community! The idea of a threadstarter "owning" a thread is silly IMO.

Regarding using the diffraction that way, that's all well and good on a few angles. A few specific angles. The only consistent solution is to create smooth transitions, use absorption, and minimize baffle artifacts, be it broadband ripple or discrete reflections.
Some angles and frequencies matter much more than others. A direct sound peak in the 1-2 khz region can ruin a speaker imo. A simple roundover can eliminate any diffraction in the 8-16 khz, but there isn't much content up there anyways.
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Old 4th December 2019, 06:43 PM   #580
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I have been away for awhile, but I'd like to comment on the discussion several pages back.

The Toole reference was interesting, but I don't think that it is evidence that baffle diffraction is not audible.

First, while the infinite baffle shows only small difference from the unbaffled case, the other example shows significant differences. In this second case, the aberrations are baffle diffraction as well, so the two examples seem to show contradictory things, but neither is conclusive as regards the audibility of diffraction.

Second, and this is the most important, there is no reason to believe that a small visual aberration means that the perception is equally small. It may well be that small diffraction aberrations are far more audible that the FR differences would lead one to believe (my research shows that.) I think that it is important to note that diffraction effects are always delayed in time and that can make a huge difference in perception.

Lastly I want to clarify my comment about open baffle diffraction. In thinking it through, I believe that an open baffle will have significant diffraction, in general, but because of symmetry, it may not show up as a large FR aberration on axis. But since the diffracted wave emanates from a very large source, the baffle edge, it will have a much different polar response than the un-diffracted wave. This means that the effect could be quite large in some places and much smaller in others. The more I thought about this issue the more complicated it became and I want to go back to basics and search out the exact nature of the diffraction from a disk (it can be solved in closed form.) This will help me to better understand the importance of diffraction from an open baffle as it relates to perception.

I will also add that in my system I have attempted to eliminate diffraction not only from the speakers but from nearby room components as well. IMO this has paid big dividends in perception, especially in "image". "Tone" to a far lessor degree.
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Last edited by gedlee; 4th December 2019 at 06:45 PM.
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