Pass Slot Loaded Open Baffle Speaker Build Underway

dcbingaman · « **on:** 13 Sep 2019, 12:13 am »

I am working on a Pass SLOB (Slot Loaded Open Baffle) with a 15" Eminence driver on the bottom and a Cube Audio FC8 full range driver on the top. Jeff McCabe will build the cabinets for me. The baffle board itself is 1/2" thick clear acrylic which has better damping than MDF or plywood, and you can see through it !

The X-Over will be built into a DIY preamp using PC boards from DIYAudio, and Pass's LxMini and NuTube circuits. The NuTube will provide the gain, volume and balance controls and input selector switching. The LXMini will provide the crossover and EQ, based on Pass's experiments at his studio in Sea Ranch, CA. Level setting between the upper and lower amps will be accomplished using pink noise, an iPhone hosted RTM app, and the Studio Six Digital iTestMic2.

Amplifiers: Low pass: Aleph 5 (90 watts) and DIY First Watt F5 Turbo V2 (140 watts). High pass: First Watt J2 (25 watts), DIY Pass / Sony VFET (15 watts), and an Elekit TU-8600 (9 300B watts) I am building. It should be ready for audition later this fall. I plan to have a GAS Music Session sometime in November (after Halloween). I'll keep you guys and gals posted.

Here's some pics:

FullRangeMan · « **Reply #1 on:** 13 Sep 2019, 12:25 am »

Seems a great OB plan, what is the Eminence woofer?

dcbingaman · « **Reply #2 on:** 13 Sep 2019, 12:41 am »

It's the Eminence Definimax 4015 ULF-8. Pretty beefy looking devil. Pass loves this one.

FullRangeMan · « **Reply #3 on:** 13 Sep 2019, 01:05 am »

Nice thanks, this is a complex xover.

dcbingaman · « **Reply #4 on:** 13 Sep 2019, 09:29 am »

Yeah, I thought so too. It is a Pass designed, 2nd order Linkwitz-Riley type, but also includes equalization for both drivers, based on Pass's experimentation with the cabinet and drivers I am using. (He got to do all the "ear" work, and I am just building what he concluded was required.)

Couple interesting notes - 1) the crossover frequencies are staggered on the low and high pass to get a better match, and 2) the drivers are wired IN PHASE. Pass found that the only full range drivers where this works are the Cube Audio drivers. Other full-range drivers (Lowther, Fostex, etc.) are radiating 180 degrees out of phase with the electrical input in the crossover region due to the dynamics of the diaphragm. Pretty crazy. Turns out that the Cube Audio drivers use a very unusual "spider", (it is NOT a typical set of concentric pleats in a cloth "donut"), but is a patented stiff linear suspension which looks like a set of spiral arm "leaf springs" of relative long length which connect the top of the voice coil to the outer frame, resulting in low deflection angles. The driver cone surround is a very compliant foam half-roll, similar to the type used for high excursion in bass reflex applications. This results in a very linear response curve with no significant hysteresis or phase reversals.

rollo · « **Reply #5 on:** 13 Sep 2019, 12:45 pm »

NICE !! Go get um. Like the design and designer. Have fun.

charles

justauby · « **Reply #6 on:** 9 Dec 2019, 03:43 pm »

Did you get your Pre/XO built for this Binger? I thought about doing this too except utlizing a DSP module into the Pass Pre we built. Looking forward to seeing the new gear!

bladesmith · « **Reply #7 on:** 9 Dec 2019, 04:58 pm »

Folsom · « **Reply #8 on:** 10 Dec 2019, 01:54 am »

Your baffle is so small that it is ineffectual. All the bass frequencies are simply going around to the front. Basically this does nothing but make the polar a little uglier.

It takes 1/4 wave length to make directionality. Here is a calculator http://www.procato.com/calculator-wavelength-frequency/

dcbingaman · « **Reply #9 on:** 11 Dec 2019, 06:15 am »

The baffle size is set for the full-range driver - it is sufficient for its range but not so big as to screw up the room acoustics - a big issue for big baffle and panel speakers. The bass driver is slot-loaded so that the impedance of the forward face is several times that of the back face. This gives a 3dB improvement in gain at the listener position. EQ in the electronic X-over takes care of the rest. The speaker / X-over combination is essentially flat from about 35 Hz to 20Khz.

Big baffles have limited utility because of the very wide spectrum of wavelengths loudspeakers must cover, (>50' to <0.5") Below 100 Hz (~10' in wavelength) you are in the acoustic Rayleigh region where all speakers become omni-directional and the room acoustics dominate, thus the effective lower limit for dipole operation is about 100 Hz unless you are in free space (say, your backyard). Hence baffles larger than 20" x 40" are pretty much a waste of lumber.

This particular speaker was designed jointly by Nelson Pass and Siegfried Linkwitz (RIP). I trust their judgement. Herb Reichert of Stereophile has heard it and speaks very highly of its performance.

Folsom · « **Reply #10 on:** 12 Dec 2019, 04:20 pm »

Pass uses much wider baffles for SLOB. I'd like to see measurements. You're getting a lot of dipole effect.

dcbingaman · « **Reply #11 on:** 13 Dec 2019, 08:25 am »

This is, EXACTLY, Pass's baffle size and design - 20" x 40". He gave me a copy of his drawing.

I will not give it to you - you need to get a copy from Pass directly. Good luck !

Blackmore · « **Reply #12 on:** 13 Dec 2019, 01:18 pm »

I also have the design dimensions from Pass and Don's 20 by 40 is correct for this version of Nelson's SLOB. Folsom, you may be thinking about the first generation SLOB that was much bigger.

Folsom · « **Reply #13 on:** 20 Dec 2019, 05:31 am »

Ya I would have to see the design... the 40x20 is the baffle for the fullrange on yours.

mjmsound · « **Reply #14 on:** 22 Dec 2019, 02:10 am »

Folsom, sometimes it is good to check out what is being designed before cutting it down!!!

genestl · « **Reply #15 on:** 22 Dec 2019, 06:14 pm »

And who knows?? Maybe even take a listen to it for a while.

Jcowling · « **Reply #16 on:** 2 Jan 2020, 01:50 am »

I, for one, am excited about this project. Having built the Linkwitz LX521, I trust Linkwitz and Pass on the design.

LeoA · « **Reply #17 on:** 11 Aug 2020, 06:15 pm »

How do you like them?

dcbingaman · « **Reply #18 on:** 17 Aug 2020, 04:52 am »

They sound wonderful. You need either a miniDSP 2x4 HD or an analog EQ / crossover to bi-amp. The Cube Audio only needs about 15W. I use a First Watt J2 for the high pass. The woofer needs about 100W. I have used both a Pass Aleph 5 (60W into 8 ohms) and a FW F5 Turbo V.2 which makes about 140W. Here is a new picture. The 1/2" thick acrylic baffle lets me keep an eye on the cat !

Bumpy · « **Reply #19 on:** 16 Nov 2021, 07:48 pm »

How is this project going now?