mid-size open baffle plus "FIN" design prototype - diyAudio
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Old 20th October 2014, 12:06 AM   #1
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Default mid-size open baffle plus "FIN" design prototype

I've put together the first prototype of a new open baffle speaker that I have been developing, along with a DSP crossover and some other custom electronics described in this thread:
PROPOSAL: wireless digital loudspeaker with remote volume and on/off control

The speaker is a three-way (plus subwoofer(s) not shown) open-baffle/nude design using a novel mounting method for the midrange and fullrange/tweeter that I am referring to as a "fin". I machined holes in the edge of the fin into which I sank tapped tubes. The drivers are mounted to the tapped ends, the midwoofer by its frame and the tweeter using a small adapter that attaches to its magnet. The fin is bolted on to the frame that supports the lower baffle. A 12" woofer located in the tilted-back baffle is "aimed up" at the listening position. Overall the construction provides a very clean and minimal visual profile.

I will post more info and measurements when I have them. For now here is a picture (attached) of the prototype.
Attached Images
File Type: jpg C.Laub prototype open baffle with fin loudspeaker.jpg (298.0 KB, 275 views)
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Old 20th October 2014, 12:20 AM   #2
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I like the very low visual pollution! Make the mids adjust relative to the base?
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Old 20th October 2014, 12:57 AM   #3
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Make the mids adjust relative to the base?
Not sure what you mean. There isn't anything that is adjustable per se. Moving the drivers relative to each other would effect the frequency response around the crossover point(s).
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Old 20th October 2014, 02:43 AM   #4
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I've started to do the crossover development. I can simulate on and off axis responses using my ACD tools and some (yet unreleased) extensions and see how the family of responses change as I tweak the crossover filters and EQ. See the attached pic for a preview of the frequency response on axis, and at 23, 45, and 67 degrees off axis (in the horizontal plane).

This would normally mean I have to measure the drivers on multiple axes. Luckily this is not the case with the "nude" mounting since I already did lots of measurements when I was selecting these particular drivers, and did them in the "nude" mounting style. I'm assuming that the response will be the same here, and it should. I also had done a bunch of preliminary crossover and EQ development on each driver separately many months ago. All of this data is still valid, and I only needed to play with the digital delay on one of the drivers to bring them into phase alignment around the crossover point.

The results look pretty good - there is a general constant directivity trend with some slight widening (1kHz-2kHz) and narrowing (3kHz) of the pattern. In general this looks like a good balanced response, and I can easily shape the overall trend using global EQ once I have the full system up and running and can take some measurements on it.

I plan to take some measurements of the woofer's response tomorrow, and then I can try to integrate it with the midrange and see what happens.
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File Type: png preliminary crossover 1 MT responses.png (46.9 KB, 230 views)
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Old 20th October 2014, 07:32 AM   #5
Juhazi is offline Juhazi  Finland
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Very nice Charlie! There seen to be some widening of response around 3kHz but it is very smooth. (Response widening = less spl attenuation off-axis, in graphics lines are closer to each other)

In my Ainos I had lots of trouble in that region, but it was obviously the tweeter-waveguide being too near. I have measured a 3" mid's off-axis response without a baffle in my hand and then it is smooth up to dipole null around 6kHz.

Where are your xo-points now, what configuration?
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Last edited by Juhazi; 20th October 2014 at 07:37 AM.
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Old 20th October 2014, 02:32 PM   #6
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Originally Posted by Juhazi View Post
Very nice Charlie! There seen to be some widening of response around 3kHz but it is very smooth. (Response widening = less spl attenuation off-axis, in graphics lines are closer to each other)

In my Ainos I had lots of trouble in that region, but it was obviously the tweeter-waveguide being too near. I have measured a 3" mid's off-axis response without a baffle in my hand and then it is smooth up to dipole null around 6kHz.

Where are your xo-points now, what configuration?
The midrange rolls off at around 500Hz, 4-5th order with sort of a Butterworth type of character and at around 2kHz with more of a Linkwitz-Riley character, 4th order. The tweeter comes in around 2kHz, 4-5th order. All slopes mentioned are the combined acoustic slope.

Thanks for the correction on "widening" and "narrowing". I had that backwards I guess.
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Old 20th October 2014, 02:42 PM   #7
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Will these be playing on Saturday?
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Old 20th October 2014, 02:50 PM   #8
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Will these be playing on Saturday?
Yes.
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Old 22nd October 2014, 03:03 PM   #9
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Will these be playing on Saturday?
Due to time constraints and some delay in getting new PC boards I won't be bringing the full on electronics system to the event Saturday.

I will have the speakers, crossovers, and built in amps. These will be operating over using wireless SPDIF but without the volume control system or the preamp side electronics (input switching, etc.). Since this has traditionally been a loudspeaker meeting, I thought I would pair it down to the essential loudspeaker bits and go with that. If I had another couple of weeks I could get all the other stuff ready, but at this point even the amps and crossover will be in an "extreme DIY" form rather than like a polished final product.
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Old 23rd October 2014, 03:19 AM   #10
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About the same as I'll be bringing - speakers, external amps, MiniDSP 4x10. Wired SPDIF or analog inputs, I'll have a laptop and sound card if I need to use my own signal source.

A quick pic is attached. The thumbnail is horizontal but it opens vertical on my computer, I hope it does for others!

Bill
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File Type: jpg P1020842.JPG (174.3 KB, 60 views)
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Last edited by lousymusician; 23rd October 2014 at 03:20 AM. Reason: grammar
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