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New Open Baffle Project: Gainphile S20z
New Open Baffle Project: Gainphile S20z
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Old 9th July 2013, 08:13 PM   #1
danvprod is offline danvprod
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Default New Open Baffle Project: Gainphile S20z

I've decided to take on a new open baffle build. I'd love to brainstorm with you folks here about my ideas.

I really like Gainphile's most recent OB design, the S20Z -- Gainphile: S20-Z Compact Open Baffle using Zaph Kit

The basic design is a hybrid active/passive 3-way bi-amped with a miniDSP and passive crossover.

I plane on modifying the design a bit.
  • Think about swapping the 2-way MF/HF section with a single Mark Audio Alpair 10.2 that will better work with my SET amp.
  • Build the box in two pieces like Gainphile did so that I can experiment with different top speaker configurations like he did.

Basically, I was curious about how sensitive a LF dipole configuration is to the absolute dimensions. I was planning on using 12" x 8' 3/4 particle board for a prototype, and making the footprint 9" x 12" x 23" for the LF section.

I'd make the top baffle about 9" x 15" for a 38" total height, and place the Alpair at about 33" to be a seated ear height.

My biggest challenge will be calibrating them and setting the crossover. The LF drives I chose and ordered were the parts express 10" subwoofers he recommended:
Dayton Audio SD270A-88 10" DVC Subwoofer 295-486

What do you think? Any thoughts before I pull the trigger on buying the Mark Audios, anyone have experience with the Zaph kit from Madisound? $200 for the pair with crossovers seems more than reasonable.

Signal chain is my Turntable > Tube Preamp > MiniDSP > SET Amp for HF (Decware) and Rotel RB1050 for LF section.

Many thanks in advance!
-Dan

Last edited by danvprod; 9th July 2013 at 10:32 PM.
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Old 9th July 2013, 11:40 PM   #2
gainphile is offline gainphile  Australia
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The most critical eq of a dipole is the notch to compensate for dipole peak. This relates directly to driver width and baffle width. The larger the baffle, the lower in frequency it would be (which may be undesirable!) and is a tradeoff between polar response and SPL.

From the datasheet Alpair 10.2 is similar size to ZA14? and 9" ~ 22cm ish. The notch I used in the speaker 650Hz/-4.2dB/1.4Q should be OK. Finding this notch is painful as it requires outdoor measurements.

I've never worked with 5" full-range driver. How is their HF quality? In other hand you'd gain better symmetry between front and rear radiation (the zaph kit only has 1 tweeter firing to the front).
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Last edited by gainphile; 9th July 2013 at 11:45 PM.
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Old 10th July 2013, 11:29 AM   #3
danvprod is offline danvprod
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Thanks, @gainphile.

On your site, you say the following re: full-range drivers. In your "Practical OB design practices" (Gainphile: Practical OB design practices)

"All dipoles will exhibit a dipole peak. The 1st peak can be tamed using notch filter, but the next peak-and dips are not. The idea is to use the response before and just above the dipole peak. The consequence of this is usually the need of tweeter which can be crossed low, at about 1.4kHz."

This would lead me to believe that the full-range driver would not be ideal, and rather using the two-way kit as you've suggested would be better.

I know you've used tweeters back-to-back to increase the dipole radiation frequency, and you have not used that on your latest design. Do you have any thoughts on that vs you bigger, S19 speakers?

I hope to start construction of the bass boxes this weekend. Here is my current plan for the LF boxes.
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Old 11th July 2013, 12:11 AM   #4
gainphile is offline gainphile  Australia
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Yes, fullrange is not ideal because it will use those frequency portions above the dipole peak. But so are all typical dome tweeter implementation. Not ideal at all, and the resulting polar response is fondly known as the "klingon bird of prey" sonogram.

That's why JohnK developed NaoNote and SL with his recent LX521 and their peculiar looks. Also those dipole nudies in this forum.

Is it audible though? I don't feel they're too much of a problem. The original Orion had been around for more than a decade and no one were complaining. The best way for you I guess is to build one and see/hear.

... Then let us know
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Old 11th July 2013, 12:21 AM   #5
danvprod is offline danvprod
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Thank you -- I went ahead and purchased the wood for the bass bins today -- going to try and bang them out this weekend and get those measure/calibrated.

Do my physical measurements look OK to you? I ended up picking up 3/4" birch ply for the main pieces and 1/2" birch ply for the top and bottom.

I've been playing around with some simulation programs to module the dipole peak -- The Edge and The Diffraction and Boundary Simulator

Subwoofers came today from Parts express, they look quite nice.

I noticed in your build log you measured the quarter wave resonance indoors. Is that OK?

A few clarification points:

Will I need to measure my configuration to determine the proper Linkwitz transform or can I use the •coefs you posted on your blog?
•I think it is still reasonable to use the 220 Hz LR4 X-over.
•Will the 6 dB/octave dipole EQ be about the same for my slightly modified dimensions?
•I will have to measure my drivers to determine the quaterwave notch -- It prob won't be 330 Hz, will it?

I'll post some pics as I start construction...

I'll prob make a temp baffle and use the 8" Betsy drivers I have on-hand from my last open-baffle project.
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Old 11th July 2013, 08:32 AM   #6
gainphile is offline gainphile  Australia
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I noticed in your build log you measured the quarter wave resonance indoors. Is that OK?

Yes, just measure it nearfield at the mouth of the enclosure like this.


Will I need to measure my configuration to determine the proper Linkwitz transform or can I use the •coefs you posted on your blog?

Sven had used the Daytons and provided me the LT coefs. You should be able to use it but as always, it's best to measure.


•I think it is still reasonable to use the 220 Hz LR4 X-over.

Yes, 200ish Hz for LPF. It's a tradeoff between lobing and midrange SPL.


•Will the 6 dB/octave dipole EQ be about the same for my slightly modified dimensions?

Dipole subs would operate below dipole peak, so certainly 6db/oct boost. You need to adjust the SPL accordingly to the midrange.


•I will have to measure my drivers to determine the quaterwave notch -- It prob won't be 330 Hz, will it?

Sven's build using the Daytons measured ~350hz, so very close. Again, best to measure but 330hz should be a good test/start.

What is impressive is that the Daytons almost need no EQ. Later you might want to target a sub HPF of 20hz LR4, instead of 20hz LR2. JohnK advised this and I had tried and used it for months (I don't hear group delay). More SPL goodness

To do this, first apply Driver LT using biquad with Fo=20hz, Q=0.707 and add another biquad with Fo=20hz, Q=0.707.


I'll post some pics as I start construction...


Great !
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Last edited by gainphile; 11th July 2013 at 08:39 AM.
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Old 12th July 2013, 02:38 AM   #7
danvprod is offline danvprod
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Default Started construction

Started construction tonight, had a few hours to work on the speakers. Successfully cut the baffles out and driver holes. Decided on a recess so that the woofers will be flush with the front baffle.

I should be able to make some more good progress tomorrow. Plan is to cut out the rest of the pieces and glue up the front, back, sides and hopefully top and bottom. If all goes well, I should have the unfinished cabs ready by the weekend to wire up and measure.

As you can see the drivers fit nicely. Those Dayton drivers have a really really fat outer baffle dimension to cutout. As you can see I had to cut the circles slightly off center, in order to be able to glue the 1/2" plywood to the backs without clipping the drivers. Because my 2x2 board was actually 23 31/32 and I lose 1/8" with my circular saw blade, I ended up going with 11.75" deep for the baffles. I still plan on being 9" wide in order to keep with the S20z design. The bass boxes will be 24" tall, which is the height of the wood I was able to get at Lowe's (trying to limit the circular saw cuts).

The routing took forever but I think it was worth it to have the flush-mount drivers.
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Old 13th July 2013, 01:42 AM   #8
danvprod is offline danvprod
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Default Progress...

Made a bunch of progress this evening. Slower than I thought, though, but that is OK.

I got one completely assembled. Came out pretty good. Ended up making the cabinet a bitter wider than planned -- about 9.75" vs. 9" to accommodate the bumped back plate of the dayton woofers and my recess.

Too late to measure tonight, but I'll prob. finish building the second enclosure tomorrow and do some basic measurements.

This is my wiring diagram -- daytons are 8 Ohm/coil, but the wiring should be the same. Going to use Cat5 for hooking up the woofers.
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Last edited by danvprod; 13th July 2013 at 01:45 AM.
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Old 13th July 2013, 11:55 PM   #9
danvprod is offline danvprod
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I finished the second bass box today. My Zaph kit comes tuesday, so I am done until then. I did manage to do some measurements and quickie-calibration.

My quart waver resonance was a bit lower than what @Gainphile measured -- I get about about 265 Hz -- so I may need to cross-over a bit lower than 220 Hz to avoid that. Also had a couple of nulls and roll-off that wasn't measured by @Gainphile. It's def a work in progress, but I have a quick crossover and EQ setting. We will see how everything works tuesday when the rest of the speakers come.

Here is my measurements and MiniDSP settings.
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File Type: png NullFix2.png (178.5 KB, 26 views)
File Type: png X-Over.png (183.7 KB, 35 views)
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Old 14th July 2013, 01:08 AM   #10
gainphile is offline gainphile  Australia
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Great progress there! Seems like dimension is critical as I got 300hz peak, Sven 350hz and you 265hz!

I did also measure secondary peak and dips which seems to be an artifact of slot loading. I do not EQ them though.

I like your choice of speaker cables!

Btw I thought you're using Alpairs?
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Last edited by gainphile; 14th July 2013 at 01:13 AM.
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