Goals:

Learn about making speakers by building some 2 way speakers using some low cost drivers using ideas borrowed from the AudioKarma Econowave project. And make some full sounding floor standing speakers by virtue of big cabinets and large drivers.
Results:

BASS!!

And knowing a hell of a lot more about speakers than I did 6 months ago. Thanks to Col for all the help and hints in getting this off the ground.

Ingredients :

Pyle PH612 constant radiation horn

* Material: ABS Resin
* Nominal Coverage Angle (HxV)-6 dB:90°x40°
* Cut Off Frequency: 1000 Hz
* Throat Diameter: 26mm
* Mounting Type: Zinc Screw Insert 1 3/8”- 18 UNEF
* Dimensions: 6.4″h x 11.9″w x 4.4″d
We initially considered these to be the key to the Econowave sound.. however later reading shows its the sysnergy between this (and a few other) horn design and the Selenium D220TI driver is the Econowave design.

But as the Pyle PDS221 compression drivers were already ordered we continued on to check out what they sounded like, plus it would be interesting to document this completely unknown low cost compression driver.

* Midrange/Tweeter Compression Horn Driver
* Titanium Diaphragm
* Terminals 205-Type
* 1.12” (28.6mm) Flat Aluminum Voice Coil
* 20 Oz Magnet Structure
* Frequency Response: 800Hz-20KHz
* Sensitivity: 102dB @ 1W/ 1M
* 8 Ohm Impedance
* 150 Watts RMS /300 Watts Peak Power
* Fits Horms With 1-3/8” x 18 TPI Threads
* Overall Dimensions: 3.2” Diameter x 3” Depth

Pioneer A30GC50 52F Q 1 30cm woofer. This speaker appears to be mainly intended for sound reinforcement use, and was selling cheap from a Melbourne guy on Ebay. I got 2 of them.

Headed over to Cols and he measured them up with WooferTester 3

The parameters are:

* This data was exported from the Dayton Audio WT3 Woofer Tester
*
* Manufacturer:  Pioneer
* Model:   A30GC50 52F Q 1
* Piston Diameter = 272.0 mm
* f(s)= 53.83 Hz
* R(e)= 7.12 Ohms
* Z(max)= 52.84 Ohms
* Q(ms)= 3.794
* Q(es)= 0.591
* Q(ts)= 0.511
* V(as)= 100.500 liters     (3.550 cubic feet)
* L(e)= 0.52 mH
* n(0)= 2.53 %
* SPL= 96.13 1W/1m
* M(ms)= 41.24 grams
* C(ms)= 0.21 mm/N
* BL= 12.96

Entering this data into WinISD pro got good response curve using a 120 litre bass reflex cabinet with two 10cm diameter, 10cm long ports. Mostly flat but with a 1dB boost in the lower registers.

MDF Panels pre-cut to size by Allboard Distributors of Boronia

They did great job considering I wasn’t quite sure how to specify or measure the curvature of the rounded corners of the horn.. The 120 litre cabinets have a 25mm MDF front baffle, with the rest being 18mm MDF. There are 2 internal braces glued in for additional stability. I had to sand out the horn recesses a bit to get the horns to fit, but everything else fit together perfectly. I emailed them pencil diagrams of what I was after, they clarified a few points, and about a week later the parts were cut.

To be stingy I left out the terminal hole and bass reflex port holes from the Allboard spec, Col came over and cut them with a jigsaw.

Using Bostik MDF glue and a pile of borrowed clamps, I stuck the bits together:

Sanding:

This stage actually took me ages but not much to say.. I dont have any power tools to do it.. so a lot of elbow grease went into it. Also used some Bostik Heavy Filler to even out part of the bass reflex holes that needed it, and fill up some other tiny gaps.

Painting:

I used two coats of White Knight pavement paint from Bunnings, terracotta colour.

Considering I had no idea what I was doing the results came out OK. Extra advantage of Pavement paint is it didnt need and undercoat as it is intended for porous surfaces. And it should be durable.

Painting sucks. Well painting is OK but cleaning up after painting sucks.

Damping Material:

Used a discount shop staple gun to staple Altronics damping material inside.

Bass reflex ports:

Altronics  C3633 flared ports cut down to 10cm.. with a hacksaw…

Speaker terminals:

From Selby Acoustics I got some  gold bi-wire speaker terminals, the idea being I can keep the crossover outside the cabinets while it’s under development, then later using the metal straps to join if I decide to put the finished crossovers inside the cabinet.. or they might end up living on the back of the cabinets or something.

Measurement:

After playing around with pretty much every free measurement package I could get my hand on, Linux and Windows, ARTA seems to be the way to go. Easy to use, and the demo version can export FRD files that I can import into speaker workshop. Measurements done with a Behringer ECM8000 measurement mic, with a generic correction curve (for that model mic) applied. My positioning of the mic has varied a bit, but I’ve stuck to using measurements done in the same mic orientation when comparing or overlaying curves. Also all these were done in the loungeroom so room effects come into play as well.

Response of the Pyle PDS221 in the PH612 horn (with 33uF protection)

Response of the Pioneer  A30GC50 52F Q 1 measured in 120L bass reflex cabinet.

Crossover:

My first attempt didnt work out.. I’d developed an idea using a notch filter that made quite a flat response.. at the expense of  attenuating the output way too much.. so I had a fairly flat response that was way to quiet for the woofer.. also it was pointed out to me later on Audiokarma that I’d messed up the layout of the circuit anyway, too many late night revisions I guess… at the last moment I jumped from a 1st order low pass to a 3rd order lowpass

above: very hacky crossover – some of the inductors made by joining together ones from a loose bag of assorted inductors I got from Col with spools of Altronics enameled wire to make up the values.

Second attempt was pretty much a hack on the Econowave crossover circuit.. I say a hack as Zilch pointed out the capacitor values I was using for the HF compensation wouldnt do much. This version at sounds quite nice though, but a bit bright.

Third version (after quite a few iterations)  uses a HF comp cap but no resistor in series, but I still think I need to review the info pointed out to me in the Audiokarma thread to get my head around it, as I seemed to get the best results with just the capacitor. Still have the issue of the flatter I make the curve, the lower the total output of the HF section.. to the level that it will be quieter than the woofer. Lowpass remains first order as it helps taper down some of the frequency “bumps” before the crossover point.

• white: pds221+ph612 no crossover, just a 33uF protection cap
• black: calced total response
• blue: crossover horn response
• green: crossover pioneer woofer response

Inductors used are Altronics air cored 20awg.. some made by combing in series inductors purchased for previous circuit layouts (i.e. 2 x 1mH combined for 1 x 1.93 mH). Some of the inductors matched and increased in value by winding on extra lengths of Altronics enamelled wire.

Capacitors purchased from Rockby Electronics, who seem to have a grab bag of good audio capacitors at cheap cheap prices.

Build gallery (plus other random measurements and stuff)

the full set of pics and graphs….

RESULT:

Fine sounding speakers… especially the low end.. While they dont have sub-bass, the bass is real bass, dub techno and other music sounds awesome on them:

The Pyle Horns sound acceptable and quite listenable. but don’t appear to be in the league of the rave reviews the Econowave Selenium driver combos get. This could be that I’m just not getting the crossover quite right.. but they are also way cheaper than the Selenium drivers.

So Mk II of this system will deployed when the Selenium drivers I’ve ordered arrive.. then I can be lazier with the crossover as the Audiokarma Econowave people have done all the hard work,  I just have to integrate the Pioneer woofer into the curve.