Yikes, can you post a link to where I said that?
My current sentiment is is that a driver larger than 8" can't quite make it to 2kHz without beaming. I might have been ignoring that issue at the time.
It's possible to do it with the "right" driver, but in general it doesn't integrate together with the tweeter as well as a 6" or 7" driver. For instance, my insane system with a 15" woofer crossed to 1" dome tweeter pair. That particular driver, used nude, could do it (barely). But I don't recommend it.
Yes, to some extent. The 15" is about 8" above the top of the M-frame. But I could not locate it any farther away or the tweeter would be way too high. It was already located pretty high, as shown in the picture. It was the best I could do at the time with that type of construction. The thinner the frame the less of a problem this would be. Mine was about 15" deep, which makes for a big surface. This is why I have changed my approach to a nude 3-way, with a large central H-frame subwoofer. That design avoids these problems.
A nude dipole driver will form a null to the sides. It's usually on the order of 20dB deep. This helps to minimize the issue with the surface, but it can't eliminate it. I just wanted to make you aware of the problem.
Not really, no. It might be 12" above or more, if possible.
The idea is to get it away from the floor so that the dipole pattern can also completely form below the driver. This should reduce/eliminate "floor bounce" because the floor is mostly in the null. It's not a complete null, but the effect is there beyond 45 degrees off axis.
Floor reflection is actually a quite tricky issue...
Floor/Ceiling Reflection Calculator
It is not problem for a typical multiway woofer, but the midrange!
Floor/Ceiling Reflection Calculator
It is not problem for a typical multiway woofer, but the midrange!
Not when the midrange isn't illuminating the floor. This is where a dipole system has a real advantage over a monopole one. The calculator you linked to assumes the source is a monopole, and isn't accurate for a source with increased directivity.
As evidence for this claim of mine, when I want to measure a driver for a project I suspend it about 1m above the ground outdoors, hanging from a pole that is placed between two extendable stands. The mic is places 1m or more away, and I sweep in a arc to get polar data. In a long walkway area alongside my home I can get resolution to and below about 50Hz. There is absolutely no sign of the "floor" in the measurement data.
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A driver is not a flat plane lying perpendicular to the source. The basket and motor are not flat, and aren't that large, and they are located in the deepest part of the null at 90 degrees off axis. It's still an issue to be considered, but an adjacent driver is nothing like a surface when it comes to reflections.
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I imagine that the dropping response of a dipole off axis as it approaches the null must mitigate this effect to some degree. At listening distance, the floor must be around 45 degrees off axis or so...does anyone know of this being investigated?
I would think it be reduced by about a third with a dipole, relative to a sealed midrange. It seems that in 3 way designs, a few have lowered the woofer/s near the floor to reduce bounce effects and gain some low bass.
Psychoacoustically, I would think we have evolved to use the floor/ground to give us clues about the size and height of the source.
Regarding driver spacing and position, and the overall height of the system: There is no requirement to stack the drivers in a straight line, one above the other. Instead, the woofer can be located to the outside of the midrange so that the mid can be located lower. E.g. looking at the LEFT speaker from the listening position, the midrange is located next to the 2 o'clock position on the woofer, with the tweeter right above it as usual. With a large woofer like a 15" this can reduce the overall height by 5 or 6 inches.
See attachment for quick drawing of this concept.
See attachment for quick drawing of this concept.
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Got it, therefore the dipole null negates most of the inter-driver reflection.
But wouldn't having driver so close to each other result into interaction between the rear dipole waves as in the attachment?
Mind you, I assume that the mixed waves are mostly directed at the floor and the ceiling, which should negate it.
D
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pursuit of 20-20k dipole thread, post #325:
Needless to say my intent is just to learn how/why your thinking evolved, to aid my learning. I think you already answered.
From earlier today:
Another great learning for me! Coming from boxed midbasses, I was getting my 18" nude midbass close to the floor for room gain. Now I know I shouldn't!! Also explains diypole's design with the 15" woofer offset to the top vs to the bottom.
My system will get tall. Now I will need to turn on the WAF solver and let it iterate until a solution is found
I have also thought about how to implement a Ripole type enclosure for the lowest (e.g. woofer/subwoofer) driver, with the Ripole lying down on the floor to minimize its height. It could work. I don't think you will have great success with an 18 driver in a Ripole, however. The resonance peak will be quite low in frequency. But if only need it to operate up to 80Hz that would be OK.
Still about floor reflections...
Dipole response will be substantially lower only at 60 deg or more off-axis. Here sims with listening distance of 3 meters and rough estimate of angles when radiator is at 40 or 80 cm height. Tilting of the mid is a way ot enhance reflection minimization - Jorma Salmi was a smart guy!
Dipole response will be substantially lower only at 60 deg or more off-axis. Here sims with listening distance of 3 meters and rough estimate of angles when radiator is at 40 or 80 cm height. Tilting of the mid is a way ot enhance reflection minimization - Jorma Salmi was a smart guy!
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What you are talking about is the same for any two non-coincident drivers that are reproducing the same signal at the same time. It's not unique to dipoles!
Good point. Yes, tilting the mid back a bit would help in this regard. It will also allow the tweeter (thinking a small planar tweeter a la Neo3) to be better aligned with the mid's acoustic center while located adjacent to (instead of behind) the mounting flange.
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