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Multi-Way Conventional loudspeakers with crossovers

Active Bookshelf with SBA MW16P-4 & TW29R
Active Bookshelf with SBA MW16P-4 & TW29R
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Old 8th October 2018, 05:29 PM   #1
rscamp is offline rscamp  Canada
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Default Active Bookshelf with SBA MW16P-4 & TW29R

I hope it is okay that I'm starting a new thread as the design stage of the project originally scoped out in this thread:

MW16P-4 vs MW16P-8 & TW29R vs SB29RDC-C000-4

As the title suggests I am ready to start this project. The drivers have been received (pictured). I broke open a cheap pair of two-way speakers to connect in biamp configuration (pictured) and started playing with the miniDSP. Very cool.

Any comments, criticisms, or advice on the way forward will be graciously accepted!

Firstly, here are the results of some guideline checks that others have suggested. It is my understanding that these rules can be broken within reason and/or with good reason:

ka=2 (beaming) rule for midrange/midwoofer - circumference of the midrange cone divided by wavelength of crossover frequency shall not exceed 2.
- 1774 Hz

lobing rule - center-to-center distance between tweeter and midrange shall not exceed the wavelength of the crossover frequency
- center-to-center distance 157mm, crossover wavelength 193mm @ 1774 Hz

power handling rule - at the tweeter's resonant frequency (Fs), the crossover slope is at least -18dB down
- tweeter Fs = 600 Hz
- first order 18 dB down @ 222 Hz, second order @ 443 Hz, third order @ 887 Hz

distortion rule - make sure neither the tweeter nor the midrange is pushed to play with excessive distortion
- can't go too low with the tweeter due to quickly rising distortion below about 2 kHz

time alignment - align electronically and/or mechanically near the crossover frequency
- data published by SBA for TW29R/MW16P - 61 us or 21mm

baffle step - accommodate the baffle step by coordinating the baffle effect and filter/DSP algorithm
- -3 dB down at 489 Hz for 9.5" wide baffle

lobing - TBD
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Old 8th October 2018, 05:37 PM   #2
rscamp is offline rscamp  Canada
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Here are sketches of the front baffle and enclosure. Net volume is approximately 17.5 litres. I plan to experiment with both vented and closed box configurations.
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File Type: jpg Enclosure Side View 18-10-08.JPG (162.1 KB, 340 views)
File Type: jpg Enclosure Top View 18-10-08.JPG (97.3 KB, 328 views)
File Type: jpg Capture2.JPG (154.7 KB, 323 views)

Last edited by rscamp; 8th October 2018 at 05:42 PM.
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Old 11th October 2018, 10:24 PM   #3
rscamp is offline rscamp  Canada
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I started cutting wood! I made a larger double-ended jig to cut the shapes that form the top, bottom and internal ribs.
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Old 16th October 2018, 08:54 PM   #4
rscamp is offline rscamp  Canada
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Do you guys normally solder your speaker connections?
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Old 16th October 2018, 09:06 PM   #5
ernperkins is offline ernperkins  United States
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What DSP are you going to use?
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Old 16th October 2018, 09:24 PM   #6
rscamp is offline rscamp  Canada
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Quote:
Originally Posted by ernperkins View Post
What DSP are you going to use?
miniDSP 2X4 HD
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Old 17th October 2018, 01:36 AM   #7
rscamp is offline rscamp  Canada
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Still making parts...
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File Type: jpg IMG_1415.JPG (87.5 KB, 24 views)
File Type: jpg IMG_1421.JPG (113.0 KB, 31 views)
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Old 17th October 2018, 06:13 AM   #8
camsemp is offline camsemp
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Awesome work. You've already used some build techniques that are interesting. I saw on your other thread that you used a similar box shape on the practise ones. Is that just thinner MDF clamped into a curve on the sides?
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Old 17th October 2018, 06:15 AM   #9
Mayuri is offline Mayuri  Finland
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Interesting project.
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Old 17th October 2018, 11:45 AM   #10
rscamp is offline rscamp  Canada
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Quote:
Originally Posted by camsemp View Post
Awesome work.
Thanks but you are not seeing how long it takes me to do this! . I still have a few things to do before I can start putting it together including mounting holes/fasteners for the drivers.

Quote:
Originally Posted by camsemp View Post
You've already used some build techniques that are interesting. I saw on your other thread that you used a similar box shape on the practise ones. Is that just thinner MDF clamped into a curve on the sides?
Yes, exactly. 1/8" thick (about 3mm). It will bend easily over the near 36" (914mm) radius.

I also turned off part of the external vent tube flange and will use it on the inside. I think the internal flare without the mounting flange will look better on the outside.
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