I sometimes wonder if what people call a "box coloration" is really just the same ol' stuff people talk about here all the time - differences in power response, room reflections, diffraction.
I realize that a poor box can have abberations visible in the impulse response, but i'm not sure it's audible stuff once it's attenuated.
I realize that a poor box can have abberations visible in the impulse response, but i'm not sure it's audible stuff once it's attenuated.
Box coloration sounds different from room coloration, since the time-delay of the reflected energy is longer in a room than in a speaker box, and the standing waves in a room happens at lower frequencies. But yes, it's basically the same problem.
The problem is how to attenuate it below audible levels. Even the best absorbtion materials placed close enough to the sound source (the speaker cone) will give reflections that are clearly audible.
If you don't design boxes for "flat to 30 Hz" and keep them well off the wall, half of that "box coloration" will be gone. Both above issues are already cared for by most dipole users. I wonder who has built dipoles with two "boxes" and still found "boxiness" a problem?
If box coloration is about resonating box walls, OBs often have a much harder time to get their baffle "silent", when there are no stiffening side walls.
Last point: In most cases changing from box to OB/dipole is tied to a radical change in room interaction. StigErik just pointed to that. My ears/brain find it really difficult to strictly separate one from the other.
If box coloration is about resonating box walls, OBs often have a much harder time to get their baffle "silent", when there are no stiffening side walls.
Last point: In most cases changing from box to OB/dipole is tied to a radical change in room interaction. StigErik just pointed to that. My ears/brain find it really difficult to strictly separate one from the other.
Every dipole has "reflections" off the baffle edge, which are at the same SPL level as the direct sound. You can see it very prominently in the impulse response. I don't find that "clearly audible".
Rudolf
Do you have any measurements that show this? I've never seen such reflection on my own measurements on dipoles.
I suspect that's exactly right.
It's worth noting that there has been one test comparing dipoles, monopoles, and omnipole-ish speakers on their ability to recreate an auditory scene, by David L. Clark. His presentation is here.
There was also a DIYA thread about it. It's, as one would expect from these things, quite long.
While some of the setup details puzzle me - a table between the loudspeakers and the listening position? Nobody interested in high-fidelity reproduction at home is going to compromise that far! - the salient facts are as follows:
(1) Three speakers with different radiation patterns, EQ'ed to the same listening-position response, were tested blind.
(2) No statistically-significant preference emerged from the test.
From that, it seems more likely than not that the biggest reduction in "box coloration" comes from the speakers' owner seeing with her/his own eyes that there isn't a box around the drivers.
IMO, a really bad box is audible. A box designed along sensible-but-not-heroic lines is not. The exception to that rule may be monopole planars/ribbons, simply because the diaphragm is a large flat piece that is less resistant to localized bending than a conical or dome-shaped structure.
At least, the only time I've heard a box being a serious issue was when I tried to fit the old BG "Acculine" planar magnetics in the A-pillars of a car. In free air, they sounded great. In a slim box, one could really hear colorations that can really only have come from reflections coming back through the diaphragm, which was of course thin, light, and not very rigid. Even when it was stuffed. While I didn't try any "cabinet" deeper than about 4" (because 4" deep A-pillars already looked awful)
The pernicious influence of backwave reflections on a planar driver might be the real reason why Dr. Murphy loads the current iteration of that driver, BG's Neo8, in an open tunnel. For a cone midrange, I've never noticed it to be a problem.
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I wrote "reflections" in quotes because it is edge diffraction really. Did you ever compare impulse responses of the same driver in baffles of rather different size?
These are impulse responses of a small FR driver, taken from sweep measurements at 50cm distance. Green for the "naked" driver, blue with a cup on the back not larger than the driver, red with the driver centered on a square baffle.
Impulse response of on of my dipole speakers shown below.
(Floor reflection at 8 ms)
(Floor reflection at 8 ms)
An externally hosted image should be here but it was not working when we last tested it.
An other one done with MLS. FIY, this measurement signal only contains the positive half of the impulse.
The speaker is a Philips RSQ8P planar tweeter/mid.
The speaker is a Philips RSQ8P planar tweeter/mid.
An externally hosted image should be here but it was not working when we last tested it.
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I believe we were talking about effects happening in the first millisecond:
So we would need a still higher resolution of your impulse responses to "see" the dipole edge.
My point is that you don't hear a separate reflection within 1 ms of the original sound - as would be the case inside a speaker box. What you possibly hear is the decaying resonance which may have built up inside a box.
Rudolf
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I read the pdf and the thread. I may have read it too quickly but I got the sense that the test was attempting to determine listening preferences based on certain criteria. Box colourations was not one of the criteria so we would have to believe that any colourations would have had an impact on some of the criteria being measured. This may be OK on the face of it, but as humans we tend to notice things far more if we are actively looking for it and if it's something we don't like then we become even more sensitive. So a blind test such as this may not have highlighted any issues with box colourations, but a test designed to demonstrate box colourations may have lead to a different result. Maybe box colourations have no impact on AS ?
I also suspect that listening tests have to be conducted over a longer period and I've also read that humans are much better at choosing what they like when presented with only 2 choices, no more than 2.
Edit: I must add that my respect for Linkwitz went up after seeing his willingness to have his products participate in such a test.
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Yes. However, IF there was a material difference caused by the presence or absence of a box, it would have materially affected preference rankings. That change in preference may have gone towards the boxes, or towards the dipole. For these purposes, the direction of the effect is uninteresting. The presence or absence of any trend differentiating the OB from the box speakers is what's material.
(Note also that there were in fact three configurations in that test: mostly or all dipole, depending on the Orion version used; hybrid monopole/dipole box in the Berry - monopole above tuning/dipole below; and all monopole in GE's box.)
It is not an unreasonable inference that "box colorations" (I'm putting that in quotes because I think the general existence of such things is very much in question) will materially affect the following criteria:
-Speakers disappear
-Local acoustics not heard
-Images lateral localization
-Images depth localization
-Ambience non-localized
-Freedom of movement.
Disagree?
IOW, if, for instance, there is such a thing as "box coloration," then wouldn't speakers with "box coloration" be less likely to disappear compared to speakers without "box coloration"?
I'm not sure that's true.
I think what is likely true is that people think they notice a given thing when they're looking for that specific thing.
Whether that thing is actually there or not is a separate issue. Often, it's not there at all, but many seem to nonetheless find it. See, e.g. the Audioquest "Boombox" wire demo.
As for the rest of it, you're grasping at straws rather than trying to understand the obvious implications of this test, as well as Linkwitz's more recent words about the importance of constant directivity.
There are many things known in loudspeaker design to not be dead ends, such as Grant's list above: design-axis FR, power response, diffraction, and room reflectivity. It seems to me that the smart DIYer will work to optimize those, using whatever tools are at hand (which may or may not include OB or cardoid configurations in a given room) rather than devote much effort to aspects of decidedly lesser import.
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As we look at this topic we also need to look at http://www.diyaudio.com/forums/multi-way/214896-gentle-cue.html
OBs cannot exist alone in a system
OBs cannot exist alone in a system
An open baffle and nothing else is gonna be very quiet, that's for sure!
You do have quite some sense of humour
. Yes all speakers need HAL amplifiers. They are a must have
Depends on the system. Even human beings can exist alone in certain "systems".
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I don't have enough experience or knowledge to say that "I know" but my thought is that box colourations would be perceived as an additional signature to the music and may not necessarily impact the items you've listed - except in the extreme case that the box makes enough of a discordant noise it spoils the first item on your list.
Anyhow, I started this thread because I'm not sure I've seen any evidence that box colourations are a real issue, there isn't any measurement data to show that it's an issue (except perhaps in facetious examples). And we know how full of BS this hobby is
Why do I even ask in the first place - well because I'm very intrigued by persistent reports from people who have built different types of speaker that OB is their preference. One of the reasons often stated is lack of box colourations.
I'm becoming more convinced that the 'box' is an issue in the mid-range, because this is where it has the most chances of creating problems with impact. At high frequencies the boxes commonly used don't resonate (and unless designed poorly should not allow h.f. to reflect back through the cone). At low frequencies the room becomes the box and it's harder to 'blame' the box for issues. So it's the mid range where the issues are and where OB is most helpful. I think that's what Cal said.
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Ok , we rely on what Cal might have said
Anyone else ?
Is that little cube ahead of a speaker producing some reflections ?
Well , move it away ...!
decreases fast .
Anyone else ?
Is that little cube ahead of a speaker producing some reflections ?
Well , move it away ...!
The diaphragm is transparent , but to low tones ,not high ; if the example is a closed box , the energy of the short waves ( 1 KHz = 38 cm )after bouncing
decreases fast .