Valhalla - A large floorstander

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GOAL: Excellent Engineering solution to mimic a full range point source.

The $32K KEF Blade speaker uses four 9" woofers arranged as counter-force vibration reduction pairs above and below a coaxial tweeter-midrange. Large radius on front baffle edges to reduce distortion.

REVIEW: “The KEF Blade vanishes in the room” The large radius low diffraction baffle plus coaxial TM point-source perform the magic
 

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Your large C-to-C Front-Rear counter-force woofers will favor placement several feet away from the rear wall.

Rear wall reflections affect the sound for this bipolar design because the lower crossover is ~250Hz, and the cabinet is 60" tall. An 80Hz woofer crossover frequency would be more tolerant to rear wall reflections and longer woofer-woofer C-to-C spacing.
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The FaitalPro 6PR160 with triple roll suspension and low Le=0.28mH looks like a good match around 2.0 - 2.3kHz crossover for the TPL-150, but the 6PR160 Fs=90Hz will move the lower crossover to around 250Hz.

The 6PR160 in a sealed enclosure at 2.83 V and at a voltage level sufficiently high enough to increase cone excursion to Xmax + 15% (3.5 mm for the 6PR160) produces a F3 frequency of ~229 Hz (F6 = 179 Hz) with a Qtc = 0.6 for the sealed enclosure, and –3 dB = 213 Hz (F6 = 176 Hz) for the vented box simulation. You want a sealed midrange box!

To avoid any lobing(250Hz quarter wavelength = 13.5") among your 8 woofers, the woofer C-to-C should ideally be less than 13.5" apart. Most designers accept 27" C-to-C separation. Your current 60" tall cabinet puts two woofers ~40" C-to-C.

The KEF Blade engineers used side-side woofer pairs to reduce vibration, reduce woofer C-to-C distance, move bass reflection problems from front-rear to side-side room symmetry. SO, keep the KEF Blade front baffle and side woofer pairs. Maintain a rectangular rear box.
 
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@LineSource,

Thanks! I have the option to use either the 6RS140 (16 ohm) or the 6PR160 (8 ohm), the former will allow me to cross lower, in a 5 closed box I arrive at the following; Q=0.5, F3 170Hz for the 6RS140 and a Q=0.4, F3 of 300Hz for the 6PR160.

I was meaning to cross around 200-300Hz, so either driver would work well in that regard. Worst case would thus be a wavelength of around 100cm (343Hz). With the rule of thumb of the minimum spacing between the drivers being <= 1/4 wavelength, the mid and woofers should have a center to center spacing of no more than 25cm.

That's what I was shooting for and that works out well for the front drivers, obviously the rear drivers see a larger spacing. I could indeed opt to mount the drivers in the sides, but that would look somewhat awkward, I've not decided on what the best approach would be yet, and that includes the esthetics of the loudspeaker.

Below are a few more renderings of the design, showing the internals and also showing some ideas on different styles and colors of finishing.
 

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GOAL: Excellent Engineering solution to mimic a full range point source.

The $32K KEF Blade speaker uses four 9" woofers arranged as counter-force vibration reduction pairs above and below a coaxial tweeter-midrange. Large radius on front baffle edges to reduce distortion.

REVIEW: “The KEF Blade vanishes in the room” The large radius low diffraction baffle plus coaxial TM point-source perform the magic

Havent heard blades must be good speaker.
side woofers with 350hz crossovers does sound odd to me, sure it is omnidirectional under 350hz and front coax start to make some directivity.

gotta listen these some day if side drivers with quite high xo can be located
 
Hi Sander,

Nice concept, but I have some remarks, important ones IMO.

You have to be aware that for all the woofer drivers, there is a vertical distance of about 80 cm between two driver pairs and a horizontal distance of about 50 cm between two arrays of 4 driver each at the front and back side. 80 cm being half a wavelength at 215 Hz and 50 cm being half a wavelength at 345 Hz, close to your intended x-over at 200 – 300 Hz.

To get an idea of the horizontal and vertical dispersion I did a simulation in Leap of it. I used a box of W x H x D = 22 x 180 x 40 cm. 7 inch drivers with a distance of 80 cm between the driver pair centers.

In the plots:
- the horizontal SPL response 0 - 30 - 60 deg in red - green – blue. The pink curve is the infinite baffle SPL response of 1 woofer driver, to compare with and to get an idea of the cabinet response.
- the horizontal SPL response 0 – 30 – 60 deg and the average SPL in the single horizontal plane (power response) in black.
- the horizontal polar diagram at 10 - 80 – 160 – 220 – 320 – 640 Hz normalized to on axis
- the vertical polar diagram at 10 - 80 – 160 – 220 – 320 – 640 Hz normalized to on axis
- the Directivity Index in the single horizontal plane

Analyzing all the plots shows that the x-over frequency has be chosen not higher than about 120 Hz. SPL, DI and power are not flat anymore above this frequency.

Maybe it is better to choose a midwoofer that can operate down to 100 Hz and use the two woofer arrays as a kind of subwoofer.
Putting the woofers on the side is an option, but it doesn't compensate for the vertical distance between the driver pairs.

Paul
 

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@Paul Vancluysen,

Thanks! Appreciate you’ve made the effort to run these simulations. However I don’t plan to run all of the woofers as a simple series/parallel array. The idea was to run the two inner woofers at a higher XO than the others, just to prevent exactly what you’ve shown here. The approach I feel should work here is simply adding a series inductor for the top and bottom and rear woofers.
 
Alright, new project, dubbed 'Valhalla'. It is to be a floorstanding loudspeaker, about 6 feet, 1.80m, tall. It'll use eight (!) SB Acoustics SB17NBAC35-4 woofers in a impulse compensated configuration. A FaitalPRO 6PR160 mid and the legendary Beyma TPL-150 AMT compliment the woofers.

Here's a few 3D sketches of the drivers, and the first attempt at a design. I'm going to model the entire loudspeaker in 3D first, to try different design ideas so I can better visualize what the loudspeaker will look like in reality.

Comments and suggestions are welcome!
Woow! Did you model thsese drivers yourself?! They look perfect.
Would you mind sharing the files? I'd like to use the SB17nbac in Google sketches as well. Right now there is just empty space lol!
 
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