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TOPIC: Re: Measurement results.

Mini DSP Betsy-k, Alpha 15a open baffle project 6 years 8 months ago #7980

I am in the process of building a pair of 2-way actively crossed-over bi-amped open baffle speakers, which utilize the following for drivers:

Betsy-k by Wild Burro Audio Labs -- $110/pr
Eminence Alpha-15a 15" Driver -- $129/pr

Right now my current amplification scheme is a battery-powered 15 watt/channel Class D amp from Jerry's Electronics (with upgraded caps). This powers the Betsy-k speakers. The Alpha 15a speakers are powered with a Rotel RB-1050.

I'm using a Mini-DSP 2x4 with the 2-way advanced plugin. My DAC is currently an Apogee Duet firewire interface from my laptop.

Designed my final baffles and built them from 3/4" birch ply.

I've attached the plans. Basically a copy of the lowther baffles -- 24" x 48" with 16" deep sloping wings. The wings have a 2" set-back for time alignment of the drivers. 3" flat top and bottom and angled back towards the bottoms.

Also, finally got some proper tools -- new Bosch router, Jasper jig, dewalt circular saw and rip cutting jig. This made the build MUCH easier than what I've tried in the past. Gave a nice 3/8" radius around the edges and the wings. Wings are held on with glue and also 1.5" chair cleats in bronze metal.

Everything is nicely flush-mounted and is looking good. I did not do a detailed measurement by rather set the minidsp by Nelson Pass' B5 crossover settings -- LF to the alpha @ 200 Hz, 20 Hz +6dB Q2 peak filter. 15 Hz Subsonic filter. 12 dB for the LP, 48 dB for the 15 Hz HP. Betsy K has a 12 dB/octave filter at 200 Hz. -3 dB Q 0.5 @ 1800 Hz to take away the betsyk honk.

First impression is these baffles have a very rich sound, deep bass and good imaging. Will take some more measurements tomorrow and tweak a bit more.

I need to work on improving the driver blending -- I'd like to cross the Alpha 15a drivers lower, like 130-150Hz. Midbass sounds a bit bloated on certain things. I may move the HF X-over up to 180 Hz - 200 Hz to flatten it out.

I'm curious about the best way to measure and set the crossover and EQ settings. I do love that with the miniDSP I have so much flexibility, but right now I have a bit of analysis paralysis. I gave up last night taking IRs and just listened to music. :)

Also, I am thinking it might be better to go digital into the minidsp. (How do I do that?) and then have 4 channels of external DACs from the digital outputs. It would be really cool to integrate everything into a single rack unit box -- S/PDIF in to the minidsp, 4 channels of Sabre DACs, integrate my little 15 watt Class D amp, and a 12v SLA battery to power it all. Is that feasible?

Looking forward to comments and suggestions!
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Re: Mini DSP Betsy-k, Alpha 15a open baffle project 6 years 8 months ago #7982

Here are some additional pics.
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Re: Mini DSP Betsy-k, Alpha 15a open baffle project 6 years 7 months ago #8074

  • devteam
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Hello DanvProd,

Great setup and thanks for sharing! Wild Burro does have some neat speakers... We talked to them initially a long time ago. Cool seeing a project with these.

Your description of your project is very well done! thanks for sharing.. Did you by any chance end up making some measurements? that would be great if you could post them as well.

Enjoy your system!
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Re: Mini DSP Betsy-k, Alpha 15a open baffle project 6 years 7 months ago #8095

I hope to have some time to make detailed measurements this weekend. It's been a busy week at work. I'll post as soon as I have the measurements available.
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Re: Mini DSP Betsy-k, Alpha 15a open baffle project 6 years 7 months ago #8113

Here are some impedance measurements of the drivers in the baffles.
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Measurement results. 6 years 7 months ago #8121

Here are some measurements of the system with my updated crossover settings.

I'm not really getting the bass extension I expected out of the betsyK speakers -- even with no low-pass, it seems to be rolling off about 18 dB/octave at 250 Hz. So that is what I'm working with.

I'm crossing the BetsyK speakers at 250 Hz, with a 3 dB high shelf at 1 kHz to tame the rising response.

The Alpha15as are crossed over at 250 Hz as well with a 6 dB boost at 20 Hz, Q2. I am also cutting 4 dB at 125 Hz, because there was a big bump there.

I need to listen to my settings a bit more tonight. I'm getting pretty decent bass response down to 35/40 Hz, which I am happy with.

Would love any thoughts...
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Re: Measurement results. 6 years 7 months ago #8144

  • sladi
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Thanks a lot for the measurements.
danvprod wrote:
I'm not really getting the bass extension I expected out of the betsyK speakers -- even with no low-pass, it seems to be rolling off about 18 dB/octave at 250 Hz. So that is what I'm working with.
Did you mean without highpass instead of lowpass?
Could the rollof be due to the fact that dipoles cannot pressurize a room below its fundamental mode? Also 15 Watts might be too weak to EQ them flat in the bass too? Anyway the roloff is so low, it is quite nice.
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Re: Measurement results. 6 years 7 months ago #8145

You are correct - I mis-typed. I meant without a high-pass x-over to the betsy they were rolling off at 18 dB an octave from 250Hz.

15 watts may not be enough, is the other option. Agreed.
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