How directional is dipole midbass up to let's say 400Hz? This is John's NaO Note:
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markus ... if the sub/woofer is xo'ed to mains around the Schroeder frequency what would be the point of rotating a mid/woofer in the mains? In a 2-way dipole main this would be problematic .. no?
My mains are HP to independent sub/woofers (in U frames) @116hz (LF cutoff) 4th order. I can't be the only person doing something like this.
There are still detrimental modal effects at higher frequencies. It's a gradual change, not a matter of on and off.
I'm still not sure about that nearfield usage for subs, I've never tried it. I would be very concerned with localization of this source due to higher order effects that are not an issue for a distant sub. Closed boxes do minimize these effects. Port noise would make their use in this application untenable.
Dipole midbass is no issue. So it will be a real dipole behavior and the directivity gain is 3 times over a monopole.
Attached is a near field measurement of a monopole vs. a dipole. Red is about 1ft. in front of the speaker, green and yellow 2ft. to the left and the right.
The modal effects are clearly visible in the monopole case. Overall the near field response is remarkably smooth in both cases when compared to the far field.
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What do you mean by "Dipole midbass is no issue"? Placed at the wrong location there can be detrimental modal effects regardless of source type.
I meant that at 400Hz it is easy to produce a real figure 8 pattern. That is not so easy let's say above 1.5KHz, where the directivy can vary which results in a different directivity gain.
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It sounds like subwoofer position and room dimensions matter the most.
There are a bunch of simple room mode calculators out there but maybe we should make a sophisticated software simulator that would tell people what is the ideal subwoofer position for their particular room.
We can start simple with a simulated SPL map of the room at various frequencies and let the user pick different monopole subwoofer positions. Ideally we would want to simulate multiple sources, different source configurations (monopole, dipole, cardioid), irregular room shapes, furniture and sound absorption.
A scaled physical model should give some insights as well. I read on Linkwitz's site that he initially picked up the 2" Aura tweeter to do room modes simulation with a small room model. During his experiments it occured to him to try the that driver as a fullrange in the Pluto speaker.
A dipole is a dipole and does not change directivity at all (in theory), especially not at long wavelengths
That's why I told you where it typically starts to change.A dipole is a dipole and does not change directivity at all (in theory), especially not at long wavelengths
Again, the topic was LF. One can make the dipole null "point" in different directions by rotation. This shouldn't change the direct sound significantly but it will alter the way the dipole couples to modes. This can't be done with a monopole. To my knowledge there is no dipole speaker that would exploit that advantage.
P.S. No, don't rotate the whole speaker, just the LF unit.
There are such speakers commercially available and they come from Finland. They have been on the market already for almost 20 years.
You sure you never seen one ?
Hi,
There's at least the Gradient Revolution loudspeaker with rotatable dipole bass.
Revolution
Another point about cardioid bass. Is it not more likely to couple to maximum number of modes as it will excite both the velocity and and pressure modes? Meanwhile the dipole or monopole may be sitting in a null. I think I read this in some AES paper by Backman. Any thoughts?
There's at least the Gradient Revolution loudspeaker with rotatable dipole bass.
Revolution
Another point about cardioid bass. Is it not more likely to couple to maximum number of modes as it will excite both the velocity and and pressure modes? Meanwhile the dipole or monopole may be sitting in a null. I think I read this in some AES paper by Backman. Any thoughts?
You sure you never seen one ?
Now I did. Great idea. I'm wondering why it's not more widespread amongst dipole users. Especially in the DIY community.
Again, it does not matter what the topic is as long as the radiation pattern does not change. But nevermind. Let's stop this.
Every dipole speaker can do this where
a. The sub is "separated" from the rest
b. the sub goes up to your desired F.
To get to the Schröder F (or a little beyond) with reasonable output you might require already 2 drivers per side.
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