How to build a spherical speaker?

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#223
olsond3 said:
Certainly recordings exist that were made with just two microphones expertly placed in front of an orchestra in a venue with fantastic acoustics. You get a wonderful window into such a recording with uniformly narrow dispersion speakers, E. g. a pair of Dutch & Dutch 8C, in a non-reverberant room. How ever many many more recordings are made with a microphone jammed two inches away from each performers mouth and the instruments are also close mic'd or they are directly wired into the mixing board, some without a microphone , avoiding the capture of any venue ambient information. If such recordings have not been processed with heavy handed artificial ambience the ability to produce that performance in your room or any room is provided by omni directional speakers. So with the omnidirectional speakers you get a good approximation of what you might hear if a small group where to actually perform in your room if they were sitting on a line between your speakers. This idea that only one radiation pattern or directivity angle is correct is short sighted. It seems many people have developed a taste for a specific radiation pattern without knowing what it is. The wide dispersion produced by small diameter drivers, on small baffles, E. g. BBC LS3/5a, or the large baffle speakers with large drivers with wave guides or horns having narrow dispersion E. g. Klipsch. Not to forget the open baffle crowd or speakers with rear firing ambience drivers. The mixed dispersion speakers are also out there, ultra wide high frequency, narrow midrange and omnidirectional bass E.g. B&W 802 The best way to play back recorded sound depends heavily on how it was recorded as well as how you want it presented when you are listening. The idea that all should agree that this single radiation pattern is best misses out on a lot of fun listening possibilities and ignores the wide variation in how recordings are made. I have yet to audition a pair of Beolab 90's but there was a dealer in Portland with a pair. I may make it out there this fall. It would be fun to flip that switch while listening to different recordings.
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Trinity sessions, cowboy junkies...recorded with akai portable dat.
 
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#226
wesayso said:
If I were to invite someone to play in my room, I'd expect to hear them play in my room. If I were to record that, the room effects would
be in that recording. So if I want to hear it played back, I wouldn't want to use onmi's for that.
However, if I listen to a large orchestra, I wouldn't want to hear them play in my room. I'd rather "be transported" to the recording venue.
Not going to happen in an untreated room with omni speakers. So I'm not really interested in that.

We each have our own preferences. But I'd welcome anyone to come play in my room and promise I won't put them in a box.
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I agree on this - but how to manage that you would like to play both types in the same room?

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#232
TNT said:
But the problem is not diffraction...

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But is, in different ways. It is not just that diffraction changes the frequency response in one spot, because that could be corrected. The problem is that it changes the frequency response from spot to spot, and there is no correction for that.

For example, take an MTM configuration with the tweeter closely mounted between two mid drivers. In this setup, the sound of the tweeter gets reflected by the midwoofer cones and both wave fronts will interact. This will produce recognizable diffraction peaks and dips, different for every location you measure them from. It is my conviction that this diffraction pattern can reveal the loudspeaker location by providing audible cues and should thus be avoided as much as possible.

The outside of an enclosure can impact as much as the inside. Speakers that are absurd from a diffraction point of view, such as the larger Watt's, will only sound good in a tight spot. Good, little diffracting speakers are rather insensitive to toe in differences. Speakers like the big Watts require a special team to get them positioned right. That is, for your listening chair only.
 
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#233
TNT, AllenB, me, others, I think there is just semantic difference between statements of diffraction increasing or decreasing while a sphere, or just a rounded edge.

Diffraction is simply sound bending at the edge and when the bending is reduced, edge rounded, there is less of the secondary sound source forming at the edge. One could view this as diffraction increasing as "more sound" goes around the edge, or less diffraction as less of the secondary sound source forms. Both mean the same thing, more sound around means less secondary source, energy must preserve.

Wikipedia page linked above says at the very beginning that diffraction is defined by the interference, or bending of waves.. duh, not mucho help.
"Diffraction refers to various phenomena that occur when a wave encounters an obstacle or opening. It is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave."

I see rounded edges as less diffraction because ill effects we see on frequency response reduce, interference reduces in amplitude which means the secondary sound source got attenuated.

Since the definition seems vague in this sense it would be helpful if we described what we mean while talking diffraction to avoid confusion and unnecessary debate, like "effects of diffraction reduce" or "diffraction related interference" or something like that. This is what is the meaningful part for loudspeaker systems, the interference, the secondary sound source. Sound that bends is not that interesting as its out of harms way mostly propagates as direct sound, but the secondary sound source has dire effects. There is also some importance what goes to the back of enclosure but not as much as what the listening window is. Its the secondary sound source made by diffraction that is meaningful in loudspeaker context, you didn't buy it or install it, yet its still there making speaker emit unwanted stuff all around 🙂
 
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#235
Yeah Olsens drawings show effects of diffraction 😉 Secondary sound source interference with direct sound, also "loss" of low frequencies aka baffle step as long wavelengths just don't mind the enclosure at all and radiate to all directions.

Actually, thinking baffle step as loss of lows is wrong and its because we usually inspect on-axis frequency response and see the bafflestep as drooping lows. If one measures frequency response from back of the speaker its all about lows, its loss of highs there! One should think the highs reflect forward making boost instead, imagine it as half of "high frequency sound sphere" cannot go around the baffle and instead reflects combining with the another half going out from the baffle. Measure all around and calculate emitted sound power (average to all directions) and its roughly constant, its just more lows on the back, more highs on the front.

All sound naturally propagates to all directions and go around objects, diffract, reflect, its just that the effect varies depending on wavelength relative to size of the object. Very interesting stuff and in the core of loudspeaker constructs.
 
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#236
Yeah diffraction happens when wavelength is about the size of the object and its on all waves like water, light, gravitation etc 😉 but the effects can be changed, round the edge to reduce the secondary sound source and enjoy problem free diffraction.
 
#237
Hence (repeated - sorry...)

glob.jpg


But I plan for a small coax - like the 4" SB perhaps...

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