Value Buster Series 10" Two Way
Design description and goals:
Bigger Brother to the VBS-6.2 this is a similarly value oriented design, a 10" 2-way with a horn loaded compression driver and excellent sound quality and output. Ideally suited for theater use as mains or surrounds or for high output stereo use when paired with subwoofers. Drivers, horn & crossover costs come in just under $150 per speaker at the time of writing this page up.
After being very pleased with the results of the VBS-6.2 I wanted to try and tackle a larger companion again using drivers and a horn which I have yet to use design of my own.
The GRS 6PT-8 woofer really surprised me in the VBS-6.2 so I wanted to test out the larger GRS10PT-8 which again looked like a great value. It models well in a compact sealed enclosure, looking to easily reach the standard 80hz subwoofer crossover frequency which was my target. The published frequency response looked decent outside of a notch around 850hz but for a budget design I wasn't too worried and in the end that proved less problematic then it looked on paper. The driver also had plenty of xmax for a pro 10" (7.8mm listed in the spec sheet) which helps greatly in a sealed design like I was planning.
For the horn/waveguide I choose the Eminence WG-10 which recently went on sale for $15, hopefully they don't discontinue them. It's no longer available from Parts Express but can be found directly from Eminence as well as a few other retailers. The shape of the WG-10 looked very promising, large round overs at the mouth, smooth transitions from between the vertical and horizontal sides of the horn and a constant directivity design which accepts bolt on compression drivers (opens up driver options). The rated dispersion looked a little narrow on paper but I figured that would match the VBS-6.2 and both ended up measuring a little wider then rated.
I choose the Peerless/Tymphany DFM-2535R00-08 as the compression driver, this is one of the smoothest measuring compression drivers that I have tested and is an excellent value as well. Of course in the couple months since I ordered this driver Parts Express now shows it out of stock and clearance, hopefully that is a fluke like they showed with their dayton brand inductors.
Similar to the VBS-6.2 I wanted to use a fairly compact sealed enclosure though the GRS 10PT-8 woofer is also well suited for use in slightly larger ported enclosures. which could easily be an option if more extensions and output is desired.
I used polyfil damping in this enclosure, the loose pile of poly was about twice the size of the enclosure before stuffing it all in there. A light fill with fiberglass, rockwool or recycled denim would also be adequate.
I did flush mount both the woofer and the horn and placed a large 5/8" round over on the cabinet corners. Surface mounting both should not introduce too many issues but expect a little more ripple in the frequency response through the midrange, similar goes for the roundovers.
Cabinet Cut List:
The dimensions for the cabinet I ended up with are 20.5" tall x 13" wide x 10" deep using 3/4" material. This is just over 1cuft gross, probably a tad under 1cuft after subtracting for the drivers and bracing.
Baffle/Back - 20.5" x 13"
Sides - 20.5" x 8.5"
Top/bottom - 11.5" x 8.5"
Braces - (2x) 8.5" x 1.25" & 11.5" x 1.5"
Includes both inner cutout and outer dimension.
I wanted to crossover where the woofer and horn directivity would match up, so I was aiming for something in the 1200-1600hz range not yet knowing how the drivers would behave. It ended up working out right in the middle at 1400hz. I was worried this was a tad low for the 1.4" VC compression driver but it doesn't appear to struggle with it at all.
The low pass is 4th order with an LCR notch filter. Highpass is 3rd order on paper but due to the other filters I used to straighten out the response the electrical slope ends up near 4th order as well. Much of the high frequency padding is done in the reactive components of the highpass so very little power is wasted as heat in the resistors padding down the compression driver to match the woofer. This is why the impedance is 12+ ohms over much of the high frequency range though it drops back down at the top end where the sensitivity from the horn/compression driver is the lowest.
The horn has an on axis hole or perhaps better described as a dip between 9-15k which fills in just a little off axis. For this reason I did not want to make on axis response perfectly flat as then there would be high frequency peaking off axis.
PCB kit I've made for this for this crossover/speaker design (will add soon).
Individual driver response, sum and inverted response.
Somehow the dip seen here at 750hz vanished when I tested the speaker again with the finished crossover.
Impedance is 8 Ohm nominal, dipping to a minimum of around 6 Ohms at 20kHz, should be a very easy load for most amps and AVRs.
Measurements taken at 2.83v/2m and scaled up 6dB to approximate 1m level.
Measurements gated at 14ms and blended to diffraction compensated nearfield woofer response below 240hz.
Smoothing applied is 1/48th octave.
On Axis & 10 degrees off axis showing how the top end fills in slightly off axis:
CTA-2034 Style Spin:
Off Axis Horizontal + Normalized to On Axis & 10 Degrees Off Axis,
Directivity tracks extremely well through the crossover and besides the small hole on axis near the top end the wavegide is very linear as you move off axis.
Horizontal Polar Response - Normal, normalized to on axis & normalized to 10 degrees,
Judging by the normalized polar response I'd put dispersion of the waveguide ~80-85 degrees nominal with some pinching centered near 4k:
Vertical Response Above Axis & Normalized:
Vertical Response Below Axis & Normalized:
Vertical Polar Response - Normal, normalized to on axis & normalized to 10 degrees horizontal,
Ideally stay within +- 10 degrees to stay within +-3dB window:
Harmonic Distortion @ 80, 90 & 100dB/1m - measured at 50cm,
Distortion performance not quite as exceptional in the midrange from the woofer as the 6" VBS-6.2 but nearly as good especially around the crossover. Great performance from the compression driver especially 3rd order which is below 0.1% at 100dB over most of the range through the 2nd harmonic does rise towards the top end but it's still decent and that's out of the critical midband where we are most sensitive to it anyway.