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Old 11th May 2012, 07:30 PM   #21
njoak is offline njoak  Sweden
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Quote:
Originally Posted by boris81 View Post
Correct, when it comes to a cardioid response the boxless/muffler approach produces similar results to the box with side holes that is stuffed with absorbing material.

I was thrown off by the term "resistive vent" because that is used in an Aperiodic Loudspeaker Enclosure Design for bass tuning. With resistive ports on the side of the box an aperiodic enclosure should theoretically produce some type of cardioid response. Unfortunately, I'm not familiar with any research that specifies how different parameters can be optimized to arrive at a desired response.
Oh, I see. Right, resistive ports might be a more appropriate name, although they do the same thing but with different purposes. Considering the muffler terminology I would actually be tempted to call them sidepipes (referring to automotive terminology, in case you're not in to that kind of thing), but that sounds like bass reflex boxes instead... Many uses for holes in boxes; wonder what one can learn from models of the other ones?

Olsen [1] is often cited in this context, as is Holmes [2]. Holmes is more to the point in this context and likely worth digging into. I have not, yet, so can't tell how specific he gets.

[1] H. F. Olsen, Gradient Loudspeakers, JAES 21, 89, 1973
[2] T. J. Holmes, The "Acoustic Resistance Box" -- A Fresh Look at an Old Principle, JAES 34, 981, 1986
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Old 11th May 2012, 08:07 PM   #22
njoak is offline njoak  Sweden
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Originally Posted by speaker dave View Post
Not following your logic here. I think you are saying all would be well if the floor reflections have flat response, or that if speakers send messy response towards the floor that proves it must be inconsequential. That isn't true. Floor and ceiling bounce energy, no matter what the spectrum, will arrive at the ear just enough delayed to give very significant comb filtering.

The issue is one of psychoacoustics. We are inundated with reflections from all directions. If they come from the sides our binaural hearing lets us separate them very well from the frontal sound. We perceive them as added spaciousness or image spread. Anything that arrives on the median plane (the plane halfway between the two ears) we will have a hard time seperating out. It will be combined with the direct sound as a nonflat, comb filtered composite.

Vertical directivity of any form is useful. Lateral reflections, if sufficiently delayed, are pleasant and add spaciousness. Toole writes a lot about this, you should read his book.

D'Appolitos should be vertical!

David S.
I can't resist to comment that it would be cool with a symmetric-pair setup la Keele to control vertical directivity, combined with the side ports we are discussing here to control horizontal directivity!
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Old 11th May 2012, 09:16 PM   #23
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Quote:
Originally Posted by njoak View Post
Oh, I see. Right, resistive ports might be a more appropriate name, although they do the same thing but with different purposes. Considering the muffler terminology I would actually be tempted to call them sidepipes (referring to automotive terminology, in case you're not in to that kind of thing), but that sounds like bass reflex boxes instead... Many uses for holes in boxes; wonder what one can learn from models of the other ones?

Olsen [1] is often cited in this context, as is Holmes [2]. Holmes is more to the point in this context and likely worth digging into. I have not, yet, so can't tell how specific he gets.

[1] H. F. Olsen, Gradient Loudspeakers, JAES 21, 89, 1973
[2] T. J. Holmes, The "Acoustic Resistance Box" -- A Fresh Look at an Old Principle, JAES 34, 981, 1986
Another good paper is: Unidirectionally Radiating Loudspeakers by W. H. Idling from the 1972 AES Munich Convention.

He shows some pretty decent response with 10 to 13 dB rejection in the backwards direction. A response curve in front of a rear wall shows nicely improved response compared to a conventional speaker.

David
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Old 11th May 2012, 09:45 PM   #24
Paul W is offline Paul W  United States
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Don't know how much help this will be, but this is the bottom of a 3-way dipole/cardioid/monopole WG from 5-6 years ago. The back of the baffle was a semi-circular piece of 1" wool felt captured by heavy wire mesh inside and out. I used the felt to transition from a dipole (at ~DC), through ~cardioid mids, to ~monopole at the upper XO of around 1.2k.

Click the image to open in full size.

Click the image to open in full size.
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Old 11th May 2012, 10:42 PM   #25
njoak is offline njoak  Sweden
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Originally Posted by speaker dave View Post
Another good paper is: Unidirectionally Radiating Loudspeakers by W. H. Idling from the 1972 AES Munich Convention.

He shows some pretty decent response with 10 to 13 dB rejection in the backwards direction. A response curve in front of a rear wall shows nicely improved response compared to a conventional speaker.

David
Thanks for the ref, David, that sounds like a paper I might consider worth cashing out for. In fact, googling for it brought me to a patent by Idling in which I found a picture that made me reconsider a test bed for my little 3.5-ers:

Click the image to open in full size.

a slotted pipe, with larger size, similarly slotted pipe (or rings) slid on top. Turn the rings to adjust size of the vents. Could make for a fun looking array, actually. Now I just have to learn how to tame pipe resonances...

I am pretty sure I've seen this arrangement mentioned somewhere before, wonder where that was...
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Old 11th May 2012, 10:50 PM   #26
njoak is offline njoak  Sweden
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Originally Posted by Paul W View Post
Don't know how much help this will be, but this is the bottom of a 3-way dipole/cardioid/monopole WG from 5-6 years ago. The back of the baffle was a semi-circular piece of 1" wool felt captured by heavy wire mesh inside and out. I used the felt to transition from a dipole (at ~DC), through ~cardioid mids, to ~monopole at the upper XO of around 1.2k.

Click the image to open in full size.

Click the image to open in full size.
That's a very good looking speaker Paul! I for one would be very interested in hearing more about it (like what the results were, your tuning experience and if there were particular issues and problems), but I feel like I'm starting to hijack Boris' thread (sorry Boris)..
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Old 12th May 2012, 12:31 AM   #27
boris81 is offline boris81  United States
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Originally Posted by njoak View Post
Thanks for the ref, David, that sounds like a paper I might consider worth cashing out for.
http://www.ee.ic.ac.uk/naylor/LineSo...kers/iding.pdf

Quote:
Originally Posted by njoak View Post
That's a very good looking speaker Paul! I for one would be very interested in hearing more about it (like what the results were, your tuning experience and if there were particular issues and problems), but I feel like I'm starting to hijack Boris' thread (sorry Boris)..
No problem. I'm interested in learning more about it as well.
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Old 12th May 2012, 12:42 AM   #28
njoak is offline njoak  Sweden
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Originally Posted by boris81 View Post
Yep, I found it as well. Iding used copper mesh on side slits of a line array. And his response looks darn good to my untrained eyes.
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Old 12th May 2012, 03:06 AM   #29
boris81 is offline boris81  United States
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Originally Posted by AllenB View Post
We may not perceive vertical reflections well for imaging but they'll cause colouration, as will the horizontal reflections. Horizontal reflections usually are treated in a constant directivity design, by way of the directivity itself.

I don't agree that the ceiling reflection will be easy to equalise.
Quote:
Originally Posted by speaker dave View Post
Not following your logic here. I think you are saying all would be well if the floor reflections have flat response, or that if speakers send messy response towards the floor that proves it must be inconsequential. That isn't true. Floor and ceiling bounce energy, no matter what the spectrum, will arrive at the ear just enough delayed to give very significant comb filtering.

The issue is one of psychoacoustics. We are inundated with reflections from all directions. If they come from the sides our binaural hearing lets us separate them very well from the frontal sound. We perceive them as added spaciousness or image spread. Anything that arrives on the median plane (the plane halfway between the two ears) we will have a hard time seperating out. It will be combined with the direct sound as a nonflat, comb filtered composite.

Vertical directivity of any form is useful. Lateral reflections, if sufficiently delayed, are pleasant and add spaciousness. Toole writes a lot about this, you should read his book.

D'Appolitos should be vertical!

David S.
Dave and Allen,
Thank for patiently explaining the issue! I'm grateful for your input.

At first I was worried about the lobe in the vertical response caused by the crossover between the midwoofer and the tweeter. Now I'm starting to think that the woofer array might be causing more trouble than I hoped to solve. I plan to use it below 500Hz but I could move the crossover lower if that will help.

Aside from the obvious WWTMWW arrangement, what would you suggest for improving the vertical response?
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Old 12th May 2012, 10:44 PM   #30
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A good MTM geometry will give a reasonable amount of vertical directivity. Joining it with a woofer placed at floor level can allow a crossover, for the woofer, below the first null, and a crossover, for the mids, above their first primary null. This is much like the Allison speakers.

David
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