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Old 25th May 2010, 02:09 AM   #1211
Bluto is offline Bluto  United States
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Location: WI.- near the Dells

Please tell us about the speakers with the oval drivers! I like the look, wondering what you have going on there?
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Old 26th May 2010, 07:03 PM   #1212
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Location: Moscow, ID
Here are my Wild Burro Betsy-K "bookshelves." They have planet10 phase plugs (thanks Dave!) and will eventually get some further treatments once I get a better feel for the sound. They will eventually go on rolling stands constructed of baltic birch with sand filled legs. I plan on using them in the near field and listening to them about 30 degrees off axis, and wheeling them outside for some background dinner party music on occasion.

This is the third enclosure I have had the Betsy-Ks in. I ran them full range in fairly large OBs, and I had them in sealed 1.5 ft^3 enclosures. To me their largest weakness was the bass. When they were in the sealed enclosures I tried to pair them with some Dayton sd215-88s at 200Hz but decided it smeared the midbass too much. (It would have helped if I still had my dcx2496, but I still think it would have been far from ideal or too complicated to implement to be practical.)

These boxes use to hold my Usher 15HMs. In a life before that they were display stands in a local department store that went out of business. I think I got them for something ridiculously cheap ( if memory serves it was $12 each). Externally they measure 24" W x 18" D x 32" H They are constructed of 3/4" particle board with melamine laminate on top. I added extensive bracing to the back, side, and top. On the front I added an inside layer of 3/4" MDF. Rather than haul them off to the dump or try and find someone who wanted them I decided use them for my Betsy-K fullrangers.

Each box after subtracting for bracing is about 5.5 ft^3 (I think, I guesstimated for the bracing). The ports are 3.75" in diameter and 4.25" long which tunes them to a little over 40 Hz. The magenta WINISD trace shows the predicted response. Ignore the yellow trace, it has a highpass filter applied. The boxes are damped with 2 layers of 1/2" carpet pad. Towards the back, sides, and top there is about 3" of polyfill. Between the ports and the upper part of the cabinet are two layers of 3" fiberglass insulation to help lowpass what comes out of the ports. The box might seem overly dead to some ears, but I think it is a good match for the Betsy since it already has enough "character" without a lively enclosure.

In the SynRTA figure the red curve is from 1.5 meters with the back of the cabinet 1 meter from the rear wall. The green curve is from the mouth of the port. The yellow curve is with some baffle step compensation.

Subjectively, I am quite pleased with the Betsy-Ks in this configuration. Bass extension and quality is completely satisfactory for music. If I was starting from scratch I would have probably opted to build BIBs, but seeing as how I had the enclosures lying around I am pretty satisfied with the end result. I can also highly recommend the phase plugs. In AB comparisons they sounded much less hollow with the plugs. They also went in pretty smoothly. The whizzers make contact with about 1/16” of the top inside of the former. If you cut straight down you can get the dustcap off without taking the whizzer with it. In comparison to my CSS WR125ST with alnico piezos (salvaged from Zenith Allegro 3000s) I can tell you the Betsy-Ks are way more dynamic sounding. The caveats being it is much easier to get bass out of the CSS drivers, and the CSS drivers are cleaner sounding to my ears.
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File Type: jpg IMG_0589 (Custom).JPG (90.0 KB, 2469 views)
File Type: jpg IMG_0591 (Custom).JPG (66.6 KB, 2424 views)
File Type: png winisd.png (48.3 KB, 2358 views)
File Type: png betsy.png (23.6 KB, 2288 views)
File Type: png sketchup.png (82.9 KB, 359 views)

Last edited by roger_lew; 26th May 2010 at 07:19 PM. Reason: added some details
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Old 27th May 2010, 02:21 PM   #1213
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Hi roger_lew, I love the very retro look and proportions (and the back-mounted driver and driver brace).

1. Is the 70Hz peak from the room, do you think?

2. To my newbie eyes, it looks like you would get a much flatter response if you could somehow roll off the port's high frequency output. However, you've already done so much internal damping toward that end. Is there anything else that can roll off the HF of the ports?

Really cool project.
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Old 27th May 2010, 07:20 PM   #1214
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Location: Moscow, ID

I'm not really sure about that peak at 70 Hz. I neglected to take a nearfield measurment in my haste.

The trace from the port also has some contribution from the driver. Of course there is always room for some tweaking.

They do sound a bit bright straight on, but off-axis they sound nice and full.

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Old 27th May 2010, 08:20 PM   #1215
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70-80 hz issues are usually from the room heihght of typical rectangular north american rooms. Take them outside, i bet it goes away.

community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
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Old 27th May 2010, 11:06 PM   #1216
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Yep, I definitely agree with Dave that it is definitely caused by a room mode of some sort.

I mostly did the measurements to verify the ports were tuned about where they should be since my margin for error on the volume of the enclosure was rather large. Once I get them up on stands I should take them out and try and get some cleaner measurements.

I personally don't really stress over measurements too much. I just use them to get into the ballpark and for insight.

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Old 29th May 2010, 12:43 AM   #1217
Defo is offline Defo  Norway
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Scan-Speak 10F

Click the image to open in full size.
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Old 29th May 2010, 01:59 AM   #1218
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Great looking pieces!!!
Randy Kunin
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Old 29th May 2010, 06:17 AM   #1219
h@kan is offline h@kan  Sweden
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Defo > Wow!
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Old 29th May 2010, 06:26 AM   #1220
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Location: Bristol, UK
Very clean an minimal enclosures. Can you tell us more about how they are used, what they do best, system set-up etc.?
Keep a green bough in your heart, the singing bird will come.
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