I have been looking for some time for an approach that leads to a loudspeaker with good omni directional properties as well as accurate stereo imaging.
I hope this can be achieved with the this concept:
note: for the simulations I used the possibility in Boxsim to simulate a rectangular enclosure. So, if practice and simulation disagree: blame Boxsim
The argument goes as follows:
If we tilt a conventional speaker 90 degrees backwards we hear at the listening position the signal 6 dB softer and high-frequency filtered.
The cutoff frequency in the listening direction depends solely on the cone/dome diameter of the speaker ( Fc Ξ 1/d ). For amplitude, box size, form and driver location don’t matter. For phase however it does, and that’s important.
This low-pass filtering is a sort of “free lunch”.
Woofers and tweeters can be placed on the cube. Below a possible configuration of 2 tweeters and 2 woofers is given with its corresponding spl at the listening position. Besides the cone/dome diameter, the drivers are considered ideal.
On top and bottom we have 2½-inch woofers and at front and rear ½-inch tweeters, all placed at the centers of their baffles. The tweeters are high-pass filtered (Fc= 4 kHz, Q=0.7). The woofers are not filtered.
The spl already looks reasonable and can be further improved.
After trying some placements for the drivers for a while I found a placement that gave a quit nice results:
The system distinguish from a conventional 2-way systems by a much better directivity.
In the simulation, this concept produces a loudspeaker with good omni directional properties and a fairly flat spl in the horizontal plane over a reasonable angular range, which should give a wide sweet spot and decent stereo reproduction.
The crux of the concept is that, for every viewing angle, never more than 1 woofer and 1 tweeter are in direct “sight.” This eliminates direct interference between drivers. It seems simple, or am I missing something ?
I want to work out this approach a bit further with a concrete example and hope to post it on this thread soon.
I hope this can be achieved with the this concept:
note: for the simulations I used the possibility in Boxsim to simulate a rectangular enclosure. So, if practice and simulation disagree: blame Boxsim
The argument goes as follows:
If we tilt a conventional speaker 90 degrees backwards we hear at the listening position the signal 6 dB softer and high-frequency filtered.
The cutoff frequency in the listening direction depends solely on the cone/dome diameter of the speaker ( Fc Ξ 1/d ). For amplitude, box size, form and driver location don’t matter. For phase however it does, and that’s important.
This low-pass filtering is a sort of “free lunch”.
Woofers and tweeters can be placed on the cube. Below a possible configuration of 2 tweeters and 2 woofers is given with its corresponding spl at the listening position. Besides the cone/dome diameter, the drivers are considered ideal.
On top and bottom we have 2½-inch woofers and at front and rear ½-inch tweeters, all placed at the centers of their baffles. The tweeters are high-pass filtered (Fc= 4 kHz, Q=0.7). The woofers are not filtered.
The spl already looks reasonable and can be further improved.
After trying some placements for the drivers for a while I found a placement that gave a quit nice results:
The system distinguish from a conventional 2-way systems by a much better directivity.
In the simulation, this concept produces a loudspeaker with good omni directional properties and a fairly flat spl in the horizontal plane over a reasonable angular range, which should give a wide sweet spot and decent stereo reproduction.
The crux of the concept is that, for every viewing angle, never more than 1 woofer and 1 tweeter are in direct “sight.” This eliminates direct interference between drivers. It seems simple, or am I missing something ?
I want to work out this approach a bit further with a concrete example and hope to post it on this thread soon.
Attachments
The practical implementation appeared to be trouble-free.
Chosen is for affordable drivers. The drivers proposed are:
1 x DA175-8, 6 in inch driver as subwoofer (in a 30 liter closed box)
2 x DMA70-4, 2½ inch full range woofers (together in a 1.4 liter closed cube)
2 x ND13FA-4, ½ inch dome tweeters placed on the cube
The optimized placement of the drivers on the cube is shown in the following figure.
It was just a matter of trial and error until finding positions giving a reasonable result. (probably, with some more effort, better results are possible).
Furthermore, the passive crossover can be very simple, note that the midwoofers are not filtered at all.
The simulation results were similar to those in the first post, so I don’t show them again here.
The cubes have to be placed at ear height. Because of the relatively high Fr of the cube, it is necessary to give each cube its own subwoofer. They have to be placed directly under the cube on the floor. The stand between subwoofer and cube should be thin so as not to stress the radiation pattern of the down firing driver too much.
Chosen is for affordable drivers. The drivers proposed are:
1 x DA175-8, 6 in inch driver as subwoofer (in a 30 liter closed box)
2 x DMA70-4, 2½ inch full range woofers (together in a 1.4 liter closed cube)
2 x ND13FA-4, ½ inch dome tweeters placed on the cube
The optimized placement of the drivers on the cube is shown in the following figure.
It was just a matter of trial and error until finding positions giving a reasonable result. (probably, with some more effort, better results are possible).
Furthermore, the passive crossover can be very simple, note that the midwoofers are not filtered at all.
The simulation results were similar to those in the first post, so I don’t show them again here.
The cubes have to be placed at ear height. Because of the relatively high Fr of the cube, it is necessary to give each cube its own subwoofer. They have to be placed directly under the cube on the floor. The stand between subwoofer and cube should be thin so as not to stress the radiation pattern of the down firing driver too much.
I like LX-configuration a lot, upper driver acoustic center directly over bottom driver center, as close as possible. Time-alignment simplifies XO design; even XO-less. I posted several to the fullrange photo gallery, all quite different.
I'll need to study your design seriously.
I'll need to study your design seriously.
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You’re going to have to high pass your midwoofers or else the system will be severely SPL limited…..those little 2.5” drivers simply cannot do much below 200hz.
I believe your artist view brings in some harsh reality in that your sims will not reflect the actual in room response with the wall behind reflections…….the early reflection from the rear firing tweeter will be significant………..a good speaker for ambient background listening but not much else.
I believe your artist view brings in some harsh reality in that your sims will not reflect the actual in room response with the wall behind reflections…….the early reflection from the rear firing tweeter will be significant………..a good speaker for ambient background listening but not much else.
Hmmm... Experiments like this are fun and informative but it might be wise to wait until you hear them before dismissing the radiation pattern used by the pros in studios. I predict the high frequencies are going to make your ears bleed unless you introduce a downward sloping on-axis response.
Speakers with a wide radiation pattern can introduce an increased sense of space compared to conventional speakers but this tends to come at the expense of imaging and perceived tonal balance. It's a different set of compromises and how to get it to work reasonably well isn't clear (to me). In the 70s I head some Sonab speakers that significantly increased a sense of space but the perceived tonal balance was way off with intrusive high frequencies. In 00s I heards some MBLs in a large room that worked pretty well but how much of that was the large room? I have also heard several other brands with a wide radiation pattern that did little to enhance a sense of space but degraded the imaging and tonal balance. I don't think it's straightforward to get a good balance but believe it is possible. For example, although people tended to focus on the Orion and the Behringer in this listening test the speaker that perhaps performed best was one with a wide radiation pattern using mulitple cheap wideband drivers. Not too far removed from what you are proposing.
Thanks for the warning.
I assume that the downward sloping response applies not only on-axis but to all directions.
You could do this with the tone control on your amp, for example.
I assume that the downward sloping response applies not only on-axis but to all directions.
You could do this with the tone control on your amp, for example.
Thanks for your comments.
Totally agree that the midwoofer should be high-pass filtered. This can be done outside the cube in the subwoofer, so that is not a problem.
Further, as can just barely be seen in the artist impression, the subwoofer has wheels. For good quality stereo, I move the speaker about a meter away from the wall.
Simulated performance comparison between omni cube and a traditional 2 way system.
Both systems have the same drivers, the DMA70-4 2½” woofer and the ND13FA-4 ½‘’ dome tweeter. Crossover was at 4000 Hz.
The traditional system was compensated for baffle step. Omni cube needs no baffle step compensation.
The subwoofer was not included in the simulation.
Both systems have the same drivers, the DMA70-4 2½” woofer and the ND13FA-4 ½‘’ dome tweeter. Crossover was at 4000 Hz.
The traditional system was compensated for baffle step. Omni cube needs no baffle step compensation.
The subwoofer was not included in the simulation.
Will you do a (prototype) build? It looks very interesting. I am intrigued by speakers with different from normal directional patterns (omni, sphere, cardioid, dipoles), but still have a lot to try/learn.
I hesitate. Making the boxes is not a big deal if it's just about proving the principle.
However, if the behavior of the speaker differs greatly from what the simulation showed, it is a waste of time and money.
A possibility is a step-by-step approach, e.g. first one box with one midwoofer and test if the original assumption by BoxSim was correct, and so on.
However, if the behavior of the speaker differs greatly from what the simulation showed, it is a waste of time and money.
A possibility is a step-by-step approach, e.g. first one box with one midwoofer and test if the original assumption by BoxSim was correct, and so on.