On Dec 28th I will be taking delivery of a pair of 18" drivers and thus will be in possession of a full complement of drivers for what is supposed to be a ~full range constant directivity no-baffle speaker. Trouble is, I don't want it to look like a no-baffle speaker.
My woodworker guy is waiting on me to pull the trigger on the design, but I am uncertain about how to make something that looks like a baffle but does not interfere with imaging in any way shape or form. Would the baffle need to be perforated or would a "reasonable" open slot around the driver be enough?
I will enclose a pic below to make myself understood. The drivers are planned to be suspended. Necessary ropes not shown.
For reference, crossover points are planned at 150 Hz and 750 Hz. Mid driver is an Audio Nirvana CF Super 10, compression driver is 18Sound ND 1480 A on XT1464 horn. 18" are FH510 from Faitalpro (yes, low QTS). System will be fully active for time alignment and EQ.
My woodworker guy is waiting on me to pull the trigger on the design, but I am uncertain about how to make something that looks like a baffle but does not interfere with imaging in any way shape or form. Would the baffle need to be perforated or would a "reasonable" open slot around the driver be enough?
I will enclose a pic below to make myself understood. The drivers are planned to be suspended. Necessary ropes not shown.
For reference, crossover points are planned at 150 Hz and 750 Hz. Mid driver is an Audio Nirvana CF Super 10, compression driver is 18Sound ND 1480 A on XT1464 horn. 18" are FH510 from Faitalpro (yes, low QTS). System will be fully active for time alignment and EQ.
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Hi, you could consider it as a design piece and forget the minute acoustic details for cosmetics (accept as a compromise), or the other way around. If you want to make acoustically and visually good piece, prepare to make many prototypes since you really need measurements of a finished speaker to evaluate the acoustic performance (and to work out the crossover!). Sounds like a fun project! 🙂 I'd go with visual design if it must be done without prototypes and just live with the resulting sound. Big speakers are fun even without everything being acoustically perfect.
Cool design! I think those narrow gaps are going to be more or less invisible to the sound waves as far as dipole cancellation goes. A 750Hz wave is still 18" long. The acoustic short circuit will probably cost you a few dB of output though.
IMO the structure around the woofer will not change the radiation pattern very much at all, although you will get a bit more bass reinforcement and smoothness from the rectangular baffle area. That's good.
The mid will probably behave mostly as if it were on a solid baffle too, maybe that's not good for constant directivity at its high end. The general rule is baffle should be no more than 2X the diameter of the cone (actual radiating area) so you may be OK.
But your horn is a rather tight pattern of 60 degrees. A perfect dipole response would be a 120 degree pattern (-6db at 60 degrees off-axis) So that may be a directivity mismatch you can't do anything about.
Have you seen this paper? Great overview of dipole baffle effects.
http://www.dipolplus.de/downloads/Open baffle 1.pdf
IMO the structure around the woofer will not change the radiation pattern very much at all, although you will get a bit more bass reinforcement and smoothness from the rectangular baffle area. That's good.
The mid will probably behave mostly as if it were on a solid baffle too, maybe that's not good for constant directivity at its high end. The general rule is baffle should be no more than 2X the diameter of the cone (actual radiating area) so you may be OK.
But your horn is a rather tight pattern of 60 degrees. A perfect dipole response would be a 120 degree pattern (-6db at 60 degrees off-axis) So that may be a directivity mismatch you can't do anything about.
Have you seen this paper? Great overview of dipole baffle effects.
http://www.dipolplus.de/downloads/Open baffle 1.pdf
I'm afraid that midrange will need wider gaps between the frame - think about wavelength.
A prototype and measurements during holidays?
Masked frame is an alternative, but not as good looking NaO Note II RS Details
http://musicanddesign.speakerdesign.net/images/Note_II_RS_UnderA.jpg
A prototype and measurements during holidays?
Masked frame is an alternative, but not as good looking NaO Note II RS Details
http://musicanddesign.speakerdesign.net/images/Note_II_RS_UnderA.jpg
So, the baffle material needs to be acoustically transparent for all or part of the baffle. Frame and cloth?
Ah, my fears about the relationship between the remnants of the baffle and wavelengths have been confirmed. I guess I was hoping a little bit that maybe the pressure change coming through may have some alleviating effect.
I will test with a partial baffle and see what is the effect. If baffle step is noticeable I will see if I can have the baffle perforated. I really want the things to be a visual treat for my dearest...
I will test with a partial baffle and see what is the effect. If baffle step is noticeable I will see if I can have the baffle perforated. I really want the things to be a visual treat for my dearest...
The woofer could be mounted to a ring of clear Lexan which is then mounted to the white baffle. This would give you the look you seem to be looking for.
Juhazi is probably right about the mid - it will need to be more open to get the acoustic effect you want. You could probably just increase the gap between driver and baffle by some tens of mm. Unfortunately this is something that is probably very difficult to simulate, so build and measure will probably be the way to go.
Juhazi is probably right about the mid - it will need to be more open to get the acoustic effect you want. You could probably just increase the gap between driver and baffle by some tens of mm. Unfortunately this is something that is probably very difficult to simulate, so build and measure will probably be the way to go.
I had nearly similar (not by design) 3 way OB speakers. To get it play with normal SPL response is needed about 20 dB compensation of bass in lowest region and midrange on his lowest point. If you make it with DSP you will lost about 20 dB headroom.
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