orangeart
KJF Audio Ltd.
Ok here goes,my first speaker build!
Firstly I've no real idea what I'm doing so please don't blindly follow my recipe and then slag me off for designing a crap speaker! You were warned
I had intended on building James's PFM SII but alas James hasn't had the time to get it finished. This build is based loosely on his design ethos, sealed and dynamic floorstander.
I have borrowed elements of his box design but have ommitted a vertical brace as my box isn't as wide so no real room. It is also slightly smaller at 33l where James's is 42l. The box is closer to the box on this page, that whole site is a great resource in fact. My dimensions are slightly different because the 25mm mdf that the front panel requires in both the aforementioned boxes comes in 8x4 sheets which is more than large enough for all the panels to be cut from, so that is what I've done I've kept the intenal dimensions the same and adjusted the panel sizes acordingly. I hope the extra thikness will make a stronger and more acousticaly inert structure.
I also spent a lot of time reading over this design which is the basis for the popular madisound kit of the same name. I am using a modified version of this X-over to get started. The drivers I am using are the scan-speak 18W/8531G00 and the D3004/662001
The frequency response of the 66200 is flatter toward the top end and more extended than the 6600 used in the ZRT, the lower end is almost the same and most importantly, the impedance curve is almost exactly the same. All of this means that the cross over doesn't need re-designing, there is a impedance flattening notch in Zaph's design that'll do exactly the same job here and as the lower FR is almost identical the crossover point can remain the same. The only change I have made is to lower the value of the padding resistor from 6 ohm to 5 ohm because of the sensitivity difference.
Because I didn't have room for the vertical brace as per James' original plan i decided to add rigidity by rebating the rear and side panels as per the photo.
The rebates should be 12.5 mm as the board is 25 mm. However as you look at the image the board on the left is the side panel and on the right the back panel. I actualy made the rebate of the side panel 13mm wide x 12.5mm deep, and the back panel 12.5mm wide and 13mm deep. This gives a 1mm overhang at the rear, allowing me to run a router with a fluted bearing bit along the back ensuring an absolutely flush fit to save sanding and filling later. This took some doing as I don't have accurate plunge control on my router so had to use a lot of scrap wood and a set of callipers and swearing!! Here are my boys helping with the clamping to line all the panels up for routing (note the power tools are not plugged in
I have also rebated the side panels to allow the internal bracing and top and bottom panel to sit in their own rebate, adding further to rigidity.
The panels are all then glued and screwed together. I don't think screwing is really needed but as I don't own enough sash clamps to hold a drying box together I had no choice. I'll have to fill and smooth the counter sinks later.
The drivers, cable, stuffing, foam, crossover components, spikes etc are all coming from Wilmslow Audio. They have their own very similar design called the vogue and were happy for me to use this kit as a base for my component changes and adjusted the prices accordingly. This allowed me to get a very keen price for a kit of parts rather than buying a la carte, a significant saving. I went there in person to pay for the bits and Terry was a very helpful fellow, well worth speaking with if anybody does venture to recreate the PFM Ogre I. They also make cabinets as well but while they were well finished there wasn't anywhere near enough bracing IMHO for a project with this level of driver in. They sounded a bit like a drum with the old knock test. James had set the bar with his PFM SII box for stiffness and I wasn't going to settle for anything less. That said, if your woodworking skills aren't up to the job you could get one and just add some extra bracing, like this.
The cabinets have been lined with bitumen/acoustic foam laminates and now feel very solid when knuckles are rapped on the side. They sound denesly hollow but with none of the drum sound of the aforementioned Wilmslow boxes.
That is as far as I've got for the moment, the drivers will arrive late this week and then i can move on, I'll add more as I get more done. If there is interest I can post panel dimensions and provide a diagram, may even be able to make a few boxes!!
Finally, to prove that helping daddy in the shed isn't just the preserve of the lads here is my other little helper with a cabinet, this was after spending two hours helping me make a circle cutting jig for the driver holes - not just a photo op
Firstly I've no real idea what I'm doing so please don't blindly follow my recipe and then slag me off for designing a crap speaker! You were warned
I had intended on building James's PFM SII but alas James hasn't had the time to get it finished. This build is based loosely on his design ethos, sealed and dynamic floorstander.
I have borrowed elements of his box design but have ommitted a vertical brace as my box isn't as wide so no real room. It is also slightly smaller at 33l where James's is 42l. The box is closer to the box on this page, that whole site is a great resource in fact. My dimensions are slightly different because the 25mm mdf that the front panel requires in both the aforementioned boxes comes in 8x4 sheets which is more than large enough for all the panels to be cut from, so that is what I've done I've kept the intenal dimensions the same and adjusted the panel sizes acordingly. I hope the extra thikness will make a stronger and more acousticaly inert structure.
I also spent a lot of time reading over this design which is the basis for the popular madisound kit of the same name. I am using a modified version of this X-over to get started. The drivers I am using are the scan-speak 18W/8531G00 and the D3004/662001
The frequency response of the 66200 is flatter toward the top end and more extended than the 6600 used in the ZRT, the lower end is almost the same and most importantly, the impedance curve is almost exactly the same. All of this means that the cross over doesn't need re-designing, there is a impedance flattening notch in Zaph's design that'll do exactly the same job here and as the lower FR is almost identical the crossover point can remain the same. The only change I have made is to lower the value of the padding resistor from 6 ohm to 5 ohm because of the sensitivity difference.
Because I didn't have room for the vertical brace as per James' original plan i decided to add rigidity by rebating the rear and side panels as per the photo.
The rebates should be 12.5 mm as the board is 25 mm. However as you look at the image the board on the left is the side panel and on the right the back panel. I actualy made the rebate of the side panel 13mm wide x 12.5mm deep, and the back panel 12.5mm wide and 13mm deep. This gives a 1mm overhang at the rear, allowing me to run a router with a fluted bearing bit along the back ensuring an absolutely flush fit to save sanding and filling later. This took some doing as I don't have accurate plunge control on my router so had to use a lot of scrap wood and a set of callipers and swearing!! Here are my boys helping with the clamping to line all the panels up for routing (note the power tools are not plugged in
I have also rebated the side panels to allow the internal bracing and top and bottom panel to sit in their own rebate, adding further to rigidity.
The panels are all then glued and screwed together. I don't think screwing is really needed but as I don't own enough sash clamps to hold a drying box together I had no choice. I'll have to fill and smooth the counter sinks later.
The drivers, cable, stuffing, foam, crossover components, spikes etc are all coming from Wilmslow Audio. They have their own very similar design called the vogue and were happy for me to use this kit as a base for my component changes and adjusted the prices accordingly. This allowed me to get a very keen price for a kit of parts rather than buying a la carte, a significant saving. I went there in person to pay for the bits and Terry was a very helpful fellow, well worth speaking with if anybody does venture to recreate the PFM Ogre I. They also make cabinets as well but while they were well finished there wasn't anywhere near enough bracing IMHO for a project with this level of driver in. They sounded a bit like a drum with the old knock test. James had set the bar with his PFM SII box for stiffness and I wasn't going to settle for anything less. That said, if your woodworking skills aren't up to the job you could get one and just add some extra bracing, like this.
The cabinets have been lined with bitumen/acoustic foam laminates and now feel very solid when knuckles are rapped on the side. They sound denesly hollow but with none of the drum sound of the aforementioned Wilmslow boxes.
That is as far as I've got for the moment, the drivers will arrive late this week and then i can move on, I'll add more as I get more done. If there is interest I can post panel dimensions and provide a diagram, may even be able to make a few boxes!!
Finally, to prove that helping daddy in the shed isn't just the preserve of the lads here is my other little helper with a cabinet, this was after spending two hours helping me make a circle cutting jig for the driver holes - not just a photo op
