A new home for Betsy -- build and measure - diyAudio
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Old 17th July 2013, 12:44 AM   #1
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Default A new home for Betsy -- build and measure

Hi folks --

Today a built a new home for my great Betsy 8" full-range drivers. I previously had been using them in 24" x 40" flat baffles with alpha 15 helper woofers, but I decided I wanted something more modular, and also with a narrower baffle to help with imaging. Plus, I was never really happy with the bass response from the Alphas on the flat baffle.

So. I started with s H-frame box for the Eminence Alpha based on MJK's design. 16x16" cross section, 7.5" deep on both sides.

The betsy now sits on top with a sloping baffle -- 20.5" high, 16" wide on the bottom and 9" on top. Pretty simple build.

I did get a chance to make some outdoor measurements with the new baffle, based on @gainphile's great article on measurement: Gainphile: Measuring Open Baffle loudspeakers

See the REW plots for the outdoor, windowed measurement. I'll attach -- basically it looks like the dipole peak is about 5 dB @ 500 Hz. Rolloff begins at about 300 Hz, if I am reading it right.

Some pics of the build and the measurement. Next step is to decide on a tweeter.

Maybe ESS Heil Air Motion Transformers?
Maybe Bohlender Graebener Neo3W?
Maybe a back-to-back tweeter arrangement?
Or maybe a super tweeter > 8 kHz, just facing forward?

Maybe something similar to this:
My new Beta 12LTA over H-frame Alpha build

I'm not sure, I would love some opinions and thoughts on the build. Currently bi-amping and using the MiniDSP for the crossover and filters.
Attached Images
File Type: jpg 7-16-13-V2BetsyBaffle-010.jpg (470.8 KB, 355 views)
File Type: jpg 7-16-13-V2BetsyBaffle-006.jpg (164.8 KB, 335 views)
File Type: jpg 7-16-13-V2BetsyBaffle-011.jpg (182.0 KB, 328 views)
File Type: jpg 7-16-13-V2BetsyBaffle-013.jpg (218.6 KB, 325 views)
File Type: jpg 7-16-13-V2BetsyBaffle-012.jpg (169.6 KB, 312 views)
File Type: jpg 7-16-13-V2BetsyBaffle-014.jpg (189.9 KB, 69 views)
File Type: jpg 7-16-13-V2BetsyBaffle-015.jpg (181.7 KB, 83 views)
File Type: jpg 7-16-13-V2BetsyBaffle-016.jpg (185.1 KB, 82 views)
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Old 17th July 2013, 12:53 AM   #2
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Here are the outdoor measurements -- see the dipole peak and dipole rolloff. The 4-8 kHz notch is a bit concerning, but it doesn't sound that bad on the baffle. I had a similar notch in my flat baffles, maybe a *feature* of the Betsy?

I'd like to cross-over low-ish, I still to make turntable measurements to see where Betsy is losing its dipole behavior -- maybe 1.4 kHz or so, I'm not sure what tweeter would fit the bill. I'd like to x-over passively, so I can keep my current amplifier setup.

Or maybe go higher -- 3-4 kHz right before the notch.
Attached Images
File Type: png OutdoorDipole.png (49.1 KB, 119 views)
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Old 19th July 2013, 12:16 PM   #3
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How do you compare the "H" frames to the OB?
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Old 19th July 2013, 03:17 PM   #4
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I like the H-Frames better. They are phsyically smaller and fit into my listening room better. Using MJK's design I am able to cross them over at 125 Hz, and use the resonance to extend the frequency response to about 300 Hz, where the Betsys take over.

I also like that they are modular. If I want to change up my top baffles, that is less of an issue. I think I have the Bass dialed in. I am still using a 20 Hz 6 dB boost to bump up the low bass response a bit, but that is pretty much the only EQ on the Mini DSP there. I'll post screenshots of my settings later this evening.

This is def. still a work in progress.
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Old 19th July 2013, 08:56 PM   #5
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Here are my Mini DSP settings.

Woofers are based on measurements in-room. Full-range is based on outdoor elevated measurements.

Crossover is 125 LR4 for the H-Frame (with a 15 Hz subsonic LR4). Using the resonance of the H-frame pushes this usable frequency range up to 200 Hz or so.

That is where I am crossing the Betsy 200 Hz LR4. I am using a 6 dB 25 Hz Q2 peak filter, which is similar to what is used in the FirstWatt crossover.

The full-range has some more work done to it. I have a 6 dB/octave low-shelf to combat the dipole roll-off. 1500 Hz High-shelf to tame the shout of the betsy a bit (although it may not need it). I have the 5.5 dB dipole peak EQ at 513 Hz (measured). Finally I have a -4 dB peak filter at 2000 Hz to flatten the betsy bump between 1k and 4k.

Also, in other news I went ahead and purchased the Neo3W -- going to mount those at the top of the baffles in dipole mode (by removing the back). Passive 6 dB/octave at about 11kHz (using a 4.0 uF cap).
Attached Images
File Type: png LF-W.png (65.5 KB, 48 views)
File Type: png FullRange-DP.png (72.1 KB, 24 views)
File Type: png FullRange-Notch.png (72.0 KB, 20 views)
File Type: png FullRangeBaffle.png (71.9 KB, 16 views)
File Type: png FullRange-betsyBump.png (71.1 KB, 17 views)
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Old 22nd July 2013, 04:31 PM   #6
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Looks good. I may do something similar with my Betsy... or not. Just about anything sounds great on top of H-frames. Once they are dialed in to the room and matched to the mains they produce great bass. In my current situation I may try a mono OB setup. I wonder if the imaging of a mono OB will prove impressive compared to a typical box. Right now I am listening to a TB Bamboo in a box... nice and smooth but not the same level of dynamics the Betsy/Alpha project above has.
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