Moving forward :-p

Cracked on a bit this morning, trying to get that long list of things to do down a bit.

Base plates, FR tube mounts, FR jig blocks and FR unit spacers

• Cut the mounting plates out
• That was ok - bit wobbly with the jig saw but not too bad. 
• Chopped out the FR mounting blocks, FR unit spacers and fitting jig blocks
• Not too bad - using the big circular saw which is always a bit hairy!
• Got the woofer tubes to fit in the bases - didn't take too much more work, so they're a tight fit, which is what we're after
• Trimmed up the bases
• Got them lined up on the marks, clamped them and then screwed them together first
• Did this with my electric plane - a wonderful bit of kit! Took off 0.5 mm per pass, so didn't go too mad
• Sanding these MDF parts seems to work ok BUT you need a really good mask - I have one!
• Glued and screwed back together
• Trimmed up the mounting plates
• This was not so successful! Managed to take a big chunk out of one of them with the power plane, so the rear of one of them is at a bit of an angle. Hopefully it won't show too much. I could make a new part but...
• Matched up the mounting blocks
• Hand tools are crap really - the circular saw had not done an especially good job of keeping straight (like it's its fault...) and these needed a bit of work!
• Drilled lots of holes
• FR mounting blocks, including the wiring holes - these were tricky and needed a second go because I hadn't held the piece sufficiently stable so the holes weren't parallel
• Bases - wiring holes
• Mounting plates, including wiring holes
• speakon socket holding screw holes - tricky, too close to the edge in fragile MDF on one side, so a bit dodgy, hope they'll be ok
• Took some time finding Speakon socket attachment screws, used some #4 18mm ones which seem ok

There was lots of time spent looking for things, cleaning up the horrendous dust as I went, moving things around and so on - I worked out the front in the sun, so I could watch the front of the house while I wait for Amazon to deliver a Kritical Kristmas Konsideration, and also minimise dust transfer. Drank zero (0) cups of tea, had zero (0) wees.

Learning Points

• Drill press is really good, but you need to work quite hard at holding the work steady; use more clamps in future!
• MDF is utter shyte and very delicate; I dropped one piece and there is a big ding in the edge now, and generally it's incredibly easy to mark. I don't know how I would prevent this, other than having a proper workshop and being completely meticulous - oh that's how you do it!
• If there's some way to cut 2 pieces so they are exactly the same, I need to know what it is; considered various approaches e.g. cutting them all as one, but that's not really possible with a hand tool
• When planing edges that are substantially smaller than the bottom plate, put some longer sacrificial material on each side and clamp to support plane before  it reaches the piece, otherwise it might come in at a funny angle ;-)
• DO NOT scrimp on masks - I spent £25 on this one, with renewable filters; fits really well, and you can breathe very easily through it

Possible Issues

1. Because I've put the speaker-end connectors on the wires, I'll have to thread them through the various holes from what is frequently the longer end - bummer. It might be worth cutting them off, getting some more connectors and doing it again - except the man at the SotB said I'd bought the last of them!
2. I haven't got any satisfactory candidates for the FR tube alignment screws - maybe #6-1" or similar would be good, Pozidrive so I don't slip and gouge the tube!

To do

Things remaining to be done:

1. Bases
1. Attach feet to bases
2. Paint
1. bases
2. mounting plates
3. FR tube mounting blocks
3. In rubber couplers, drill wiring holes below mounting plate location
4. Stick 
1. mounting plates onto rubber couplers
2. woofers onto mounting plates
3. leave for 12 hours!
5. Drill 1mm pressure relief holes in Woofer tubes
6. Glue pressure pads to FR driver (hot glue!)
7. Mount FR driver in FR tube
8. Mount FR tube on mounting plate
9. Lead all wires through holes into Woofer tube
10. Mount rubber couplers on Woofer tubes
11. Check wiring works with battery
12. Put stuffing into woofer tubes
13. Push all wires through base holes and out through Speakon hole
14. Glue Woofer tubes into bases
15. Put connectors on wires
16. Attach wires to Speakon socket
17. Screw Speakon socket into hole
18. Stuff FR tubes with wadding
19. Testing... check, 1, 2...

Readying the tools

Pedestal drill at the ready

There are some holes to be drilled in the FR tubes that really need a steady hand that I don't have, or a pedestal drill. As luck would have it, I have one of those, inherited from my uncle in 1989. Works well, used it maybe once in that time, so here it is in its glory, all ready to go. Can't get in the freezer at the moment, but hey... I'm here on my own until Wed night at the latest!

Cutting the bases

This bit is more tricky than the specified approach, because I've decided

• to use two thicknesses of wood so that the pipe can be seated in one
• to put the Speakon socket on the back of the base!

The former means that I have to cut a 4.5" hole in the top plate, which fits the pipe tightly and allows it to be vertical.
The latter requires use of a hole-drilling tool, borrowed from my son!

Partly finished cut of Speakon socket hole

Another view of the Speakon socket hole

Pipe standing in hole, to the correct depth

The results look quite good on the first one completed, which is the second Speakon hole and first pipe hole...

Base roughly assembled with Speakon socket in place

Of course, cutting the first Speakon hole was hard and not very tidy. The second was easier and came out great. The first tube socket is pictured, and came out pretty good with a little adjustment. The second is a total pig, being undersized after I'd cut it, and thus hard to rescue. I'm giving up on that for today! I might even redo that base altogether, since that one also had the first, crappy, Speakon hole :-). And it will take me almost no time to do it this time!

Maybe I should get a new jigsaw, mine is pretty crap.

Cables and connectors

Since I had to wait in for the heating fixing man to arrive, and working outside on MDF bits means I can't easily hear the front door bell, thought I could taunt myself by making up the speaker cables. It's always nerdy fun building this stuff, making the result as tidy and robust as possible. 

Speaker Cable and Connector

Here's the female Speakon plug, with some very nice Posidrive #1 screws which I'm going to hack up with a Philips #0... The wire is pretty chunky!

The finished result

I simply put the plugs each end of the cable, so I'll just cut it in half or cut it to length when I want it. The Sony amp end, incredibly, is a bare wire connection!

Getting serious

My, that's a serious face!

Got some overalls today - I keep doing things in my reasonable street clothes and messing them up.... They work really well!

Test painted MDF and pipe

I tried painting some MDF with Halfords Grey Texture spray paint, looks quite good. I might keep the pipes plain, just rub them down a bit to remove the more egregious scuffs. They are a darker grey, not as black as it looks in the photo!

Mounting plates...

Mounting plates with circles cut, ready for gluing

Here are the mounting plates with the coupler and speaker mounting circles cut out. They're made in two halves and glued together to make the whole plate. Gluing is currently underway in the garage :-). They are then cut around the outside to make the appropriate shape.

Update: The following day I discovered I'd not clamped one of the plates very well, so the two parts had slipped and got out of alignment. So I made a new one today which took much less time... Except  that in the rush (rush!! Ha!) I forgot to cut the clearance slot in the edge of the lower half to allow for the tightening clamp of the rubber coupler. Bugger. I can fiddle that though, and it doesn't show.

Moral? More haste, less speed. Enjoy the trip, dude.

Let's get started!

Main parts cut out

I cut the main parts today

• 2 x 31" x 4.5" pipe
• 2 x 5" x 90mm pipe
• 4 x 6mm x 8" x 12" MDF - I decided to go with the spec, as 2x6mm seemed pretty stiff
• 4 x 12mm x 12" x 12" MDF - 2 off is part of my plan to support the woofer pipes

It all seems to have worked out ok, apart from the clouds of MDF dust I've had to vacuum up, wearing a face mask!

Gain structure continued - solved?

Late last night and this afternoon I tried using controlled signals from REW to check the gain levels through the system.

Using a chain of REW/MacBook/ODAC/miniDSP, I was able to test the sensitivity of the miniDSP vs. the ODAC. The ODAC certainly drives the miniDSP to clipping - I have to have the REW output set to -3dB to prevent > 0dB on the miniDSP input gain. This cascades onto the miniDSP outputs, where, with no crossover or EQ, both output levels track the input pretty exactly. Marv.

From there to the Sony - I can certainly get enough volume from that I think, running music signal through the above chain into the test speaker.

So the question is, why does the RPi/ODAC combo not work as well? I've just realised, while writing this, that I have been using the software volume control on Rune... Right now the RPi is switched off because the ODAC is elsewhere, but I bet that's the constraint. Bah!!

Update: Nope. Volume control was set on 100%, because I specifically wasn't  using the software volume, only the hardware on the crappy powered PC speakers I'd been using it with in the office. Bummer.

Anyway, I think this lot is ok, what I really need is the actual speakers to try it on. I'm not too impressed with the sound of this setup with the test speaker, I hope it's the crappy speaker and not the Sony... Still, I was thinking to replace it with something better, like a Hypex UCD or NCore setup when the basic arrangement was functioning.

Further Update: Trying my Focusrite Saffire, with an alleged 16dBu nominal 0dBFS output, into the miniDSP results in exactly matched inputs, so that the REW output level is exactly matched by the input level shown by the miniDSP. Hurrah. Or maybe boo. I dunno.

Nuts Screws Washers and Bolts...

M5 75mm bolt, nut, washer, M3 bolt, screw, rivnut

Here's the hardware that arrived today. Sadly I think the 3mm bolts and set screws are too skinny or too short, and the rivnuts are not going to work. So I've ordered 5mm socket bolts, set screws, nuts and lockwashers, in 12mm length. 

Hmm... Gain structure problems?

OK. Gain structure is the amount of amplification or attenuation applied at each stage in the signal chain, and the resulting headroom or overload.

Figure 1 shows the prototype setup I've just tested. Pretty much a possible setup...

Figure 1: Prototype Setup

From source to speaker:

• Music sources are Radio3 streamed from the Beeb, and digital music streamed from a music server (MinimServer running on an RPi)...
• Streamer is Rune installed on a Raspberry Pi, connected by USB to...
• An ODAC USB DAC, connected using RCA analogue connections to...
• miniDSP 2x4 Inputs 1 & 2, where crossover and frequency response adjustment are performed, and Outputs 1 & 2 for Woofer & Tweeter respectively on the RCA outputs, to...
• Sony amp via the Direct Inputs RCA sockets, using Front L and Surround L inputs, to...
• A 2-way test speaker which I'm using in active mode, Front L to Woofer, Surround L to Tweeter

Basically, this isn't playing very loud! I'm testing it in a small (tiny!) room, and the Sony amp is set to 0dB i.e. max. There is vast amounts of hiss from the tweeter i.e. the amp is NOISY. I've even set the Sony amp to 8Ω rather than 4, because I believe the speakers are about that. Time for some thinking, and maybe some more structured testing - bugger. Inevitably, I was hoping it would just work! Silly me.

Right. Here's the input/output specs of the various devices that count:

• ODAC
• Output: 2.1V RMS into 5KΩ or higher
• miniDSP 2x4
• Input: 2.0V RMS, 6KΩ 
• Alternative setting 0.9V RMS, could change this, but need to ensure no overload
• Output: 0.9V RMS (2.5V P-P), 560Ω impedance
• This is fixed, I can only turn it down from there! 
• 2.5V P-P => 1.25V peak => 1.25*0.707 RMS => 0.88V RMS, so that's cool
• Sony STR-DB1070
• Input: 150mV, 50KΩ impedance
• SNR is only 96dB, hmm
• Output: Allegedly 90W into 8Ω
• This is 16.4V RMS, from V=IR, I=V/R, W=VI, W=V2/R, V=⍻(WR)
• Amplifier gain, from 150mV RMS input is therefore 20*log(16.4/0.15) = 41dB
• SL reckons you need a damping factor of >20; there is no hint of this on the amp spec!

I think I need to run some tests, using a known signal level, probably generated by REW directly into the ODAC, that will show the levels in the miniDSP. Back to the hut...

More stuff

Wadding, cable and connectors arrived today :)

Neutrik (pricey!) Speakon 4-pole plugs & sockets, 8m 4x2.5mm cable and 2 packs of MDM-4 wadding 

When I opened the packet I thought maybe I should have ordered the screw terminated chassis connector, but that isn't airtight - choices!! The connectors use 3/16" push-on spade connectors, and I've just tested the ones I have - great fit! Far easier than soldering, and airtight means I could amount them on the woofer tube if I wanted to. The cable is pretty cool, if a bit chunky, good job it's 4-in-1. 

Actually, when I reviewed the NL4MP sockets and found the ST version, I also noticed that a 10m 4x2.5mm cable with "Neutrik-alike" Speakloc plugs was only £20. I could have bought one and cut it in half - the Sony amp takes bare wires anyway - would have saved myself £15 and had an extra 2m of wire... 

Only the bolts to come now, I'll have to actually do something soon. Maybe just make the cables up :-), a nice way to pass the darkening afternoon. After all, this morning I got the old freezer out into the garden making rom for the shiny new one on Friday, and got all the decorations down from the loft, and spent an hour teaching kids to programme rolling background games in Scratch at the Code Club. I deserve this... 

Wickes-style Fernco 4" clay to PVC connectors, made by FlexSeal, a Fernco company 

Popped around to Wickes and lashed out on the rubber connectors. I've tried them on the woofer pipe and hurray - they fit really well, so I'll be going with these. Need a bit of a cleanup but hey, no problem.

2.5mm wire capable 3/16" and 1/8" tag connectors for Speakon-speaker wires

On the way to Wickes I dropped into The Shop On The Bridge and acquired these connectors for Speakon to speaker wires, with 2.5mm capacity and the right tag sizes. Except I screwed up and didn't get all fully insulated, might exchange four of them tomorrow, the four blue with uninsulated connections. Otherwise the connections on the socket are a bit close. I guess if the -ve ones aren't insulated it won't matter.

The connector colours refer to the wire sizes they fit, rather than an polarity indication - you'll have to look at the wire colours if you want to see what's happening, guys! Strangely the little red ones are HUGE for wire, rather than 1.5mm as the colour would indicate, even the SOTB man was surprised.

Getting exciting!

Some parts have now arrived, with more on the way - hurray!

Woofer and Full Range Drivers

View of open spider and voice coil

They look pretty cool - I especially like the aluminium cone of the woofer. The "open spider" is a bit weird, reminds me of old-time loudspeaker units, usually dusty and forgotten in mysterious corner cabinets! The white plugs are just nylon spacers to stop the cones being damaged in transit.

2x3m of drain pipe!! And some MDF...

Pipe ends - pretty thick!

Pipe stock did the business - ordered Friday, delivered Monday, service only outdone by Falcon Acoustics (ordered Friday, delivered Saturday!). This looks like a lot of pipe - I'm using less than 50% of it in fact, so if anyone needs any high pressure PVC fat pipe, like for making a spud gun or something, feel free to get in touch. Some will be used experimentally for paint and finishing tests of course.

Hopefully the MDM-4 wadding, stainless steel bolts (ooh, I love those!!), cabling and connectors will be delivered tomorrow!

Design detailed thinking

It amuses me to think about some construction details in the evenings... There are some problems, sorry, opportunities to be solved/taken advantage of.

Some design thoughts...

1. 6mm MDF for the woofer support seems to be a bit flexible - it's not the original design spec "hardboard" which is HDF really, so I've considered using 6mm on the top of the sandwich, with 12mm below. That would leave the drivers in the same relative position but with more rigid support
2. Holding the woofer tube in place without the specified (and unavailable or ridiculously expensive) "cap hub" - how about another MDF base circle, with a 4.5" hole as a tight fit for the tube, and glued in? This would also make the speakers heavier in the base and thus more stable
3. The specified feet are just short lengths of 1.5" rod, and there are 5 of them; how about 
1. Only 3 - that would make them less likely to be wobbly, since anything more than 3 feet only makes for levelling problems
2. Spikes - a traditional way of seating loudspeakers
3. Sorbothane feet - moderately expensive on Ebay, and a great way to decouple from the floor
4. Rubber feet from Screwfix - 10 for £1.49!! Gotta be worth a go...
4. Some people have successfully bolted the woofer to the support, rather than gluing it, in order to simplify repair/modification - how to do this? There isn't much, if any, space for bolts/nuts above the rubber coupling. The only way I can to do this is to use very short bolts and countersink the nuts into the lower face of the support. That won't leave much of a thickness of MDF to hold the woofer...
5. No drawings of this, but there's the placement of the Speakon connector to be addressed. Choices include
1. On the base, on a longitudinal axis, on a separately attached support; this requires wires to be fed into the base and then up the woofer tube, with some visibility
2. In the base, vertically, easy then to feed the wires into the woofer tube
3. In the woofer tube! I saw one build that did that; provided it doesn't look too crap with a mismatch of curved tube vs. flat connector socket surround this could be the winner
6. The quantity of MDM-4 wadding will apparently just cover the woofer tube damping - there will be none left for the diffusor tubes :-(. I do have some Bonded Acetate Fibre (BAF) which is worth a try, otherwise it'll mean incurring more postage from Cybermarket, boo. I'll only know when/if I measure the speaker response and compare it to that specified by SL

The Build

Right, time to crack on. I was getting pretty cheesed off with this vague, cloudy project, and the Quads are starting to crackle and spit as the diaphragms start to break up with age!

DSP

Interesting as the pursuit of computer-based DSP has been, and I've acquired and even read a lot of books on the subject, since this was already complicated enough, I decided to go for the originally-specified MiniDSP 2x4. 

I did consider its considerably more expensive ( >2x! )brethren, 2x4HD and 4x10HD, on the basis that a) they both allow for fully digital inputs, thereby removing a D/A/D stage b) the latter has additional channels which can be used to feed subwoofers when/if that happens. But I'm very aware of requirements creep from my past life in large-scale IT projects, and how much that can screw up the achievement of any useful results. 

So, KISS!! £93 from CPC, quite a bit but I have other projects I can use it on, and keeps it all very simple. 

Amplification

Inspired by The Rational Audiophile, and not really willing to take on the building of amplifiers in order just to get the speakers to work, I looked for a suitable 6/7 channel AV amp. Luckily, Gumtree had an old Sony STR-DB1070 with a broken volume knob (works with remote still), that has 6 channels of amplification, and the right pre-amp spec to match the MiniDSP 2x4 - £35 to you, mate, from a Polish lady who works at Reading University. Too bad I had to drive to sodding Woking to get it, on an M3-closed-for-repairs day.

Loudspeakers

Cutting a long story short, I have decided to go for the DIY route. Yes, it's nominally cheaper (£100+ on a £6-700 total with amps, DSP etc.), but it's more that I fancy the challenge! So yesterday I spent a long time online, at

• Falcon Acoustics - chassis speakers; incredibly, these arrived 24 hours later!! Nice bits of kit, and very unusually structured - the rear spider that keeps the cone in place is actually separate from the magnet assembly on both types. Gosh.
• Pipestock - purveyors of PVC and ABS pipe to the gentry and other less salubrious individuals/organisations. Should deliver my 3m apiece of 4" and 3" PVC soil pipe on Monday. Some substitution required...
• 4" Class D PVC pipe, 3m length
• 90mm 9bar PVC pipe, 3m length (for 10" requirement!)
• Studiospares - connectors and 4-way speaker cable; rather than two separate sets of of wires per speaker, one for each chassis, I've gone for 4-way cable and 4 pole Neutrik Speakon connectors, largely because they look really cool and keep it all nice and tidy.
• Wickes - MDF, and the hard-to-source 4" PVC to Clay rubber couplings so easy to get in the US but not here...
• Kay's Fasteners, via their considerably cheaper Ebay shop, for stainless fixings i.e. bolts, nuts, and "rivnuts", a kind of captive nut that is a bit of an experiment, but that's why we're doing this right? Again, some substitution of US measurements required
• M5 75mm partial threaded bolts, nuts, lock washers
• M3 grubscrews, nuts, rivnuts
• M3 socket head bolts, in case grubscrews don't work
• Cybermarket - the original specification for the damping material is AcoustaStuf, not available in the UK; Dr. Frank uses Monacor MDM-3, which has been replaced by MDM-4; that's really hard to find, I eventually emailed Monacor UK who pointed me at Lawrence at Cybermarket, who was able to come up with the goods - hurray!

Remaining Issues

I haven't sourced

• The PVC-to-Clay rubber couplings; I'm going to see how the Wickes ones fit on the pipes when they arrive, then pursue an alternative if necessary
• The ABS 4" pipe cap hubs - these don't seem to be available in the UK for less than £50 apiece, so forget that... I'll use some other approach to attach the bass pipes to the stands
• Anything to cover the rear of the full range diffuser tubes, to stop the wadding coming out; it needs some sort of grill or mesh. No idea yet, but it will have to be very coarse, to prevent any sonic effects through effectively closing off the pipe.

I realised that I have got the wrong size (diameter) of screws to hold the FR speaker in the FR diffuser tube, 3mm rather than 5mm, owing to misreading my spreadsheet. Boo. I'll see how they go, it's easy to order some alternatives at Kay's.

Build vs. Kit vs. Buy

I've been interested in audio since my late teens, and even "built" a pair of KEF Concerto-like speakers, KEFKit 3s, from a kit when I was about 17/18. Maybe I should do this myself...

I bought the design/build plans from SL online, and joined the OPLUG forum, the Orion/Pluto User Group. O & P were his previous designs, now superseded by the LXMini and LX521. Hurray! They don't seem TOO complicated... But the main structural components, although easily available and ridiculously cheap in the U.S., are not available or horribly expensive in the UK. Bugger. Was there an easier alternative?

It turns out that Dr. Frank, a Lufthansa airline pilot and audiophile, markets complete kits with all the right stuff, ready to build, at www.magiclx521.com for €600. Nice. That would save me lots of effort and concern about having the correct components.

Of course, Dr. F also sells the speakers fully assembled, in which case they are €2130!! Not really competitive with a Quad rebuild.

Since Dec 2015 then, I've been deliberating between the DIY vs. Kit alternatives. It wasn't until the last couple of weeks that I've really worked at sourcing the materials for myself, and pricing them up. So far, I'm at about £400 all found, for the loudspeakers themselves. It's been quite a slog, primarily because of the need to balance cost and accuracy of specification - the US-style pipes are available, but can be very expensive.

And there's the issue of amplification and DSP. Did I mention that these are "active" speakers, in that each individual chassis speaker has its own amplifier, feeding it an appropriately tailored signal? Since these are 2-way loudspeakers (in the first instance, maybe 3-way later...), that means 4 channels of amplification. Should I build or acquire these amps? I looked at "chip amps", base on the LM3886 series, I looked at used 6-way hifi amps like the Nad 906 on ebay, I looked at AV amps used in combination with the HDMI Out of a RaspberryPi (see below)...

And the signal tailoring requires Digital Signal Processing, which can be done by the SL-recommended MiniDSP 2x4 or any other means, including RaspberryPi, Linux box or even MacBook Pro! Choices, choices...

And all with very different cost profiles, complexity and length of build etc. Argh! All this deliberation on top of the DIY vs. Kit choice - no wonder it's been a year in the planning.

Background

About a year ago, I realised my Quad ESL-63 loudspeakers were going to require a service shortly - an expensive service, usually about £1000+. That's not as expensive as buying new, modern Quads ESLs, they run at £6000/pair upwards, so probably quite good value... But it's still a lot of money. Could I replace them or do better somehow? And if so, with what, and what kind of budget?

Anyway, I really love the sounds of the Quads, largely because they don't sound like boxes. That's probably because they aren't - they are based on electrostatic attraction/repulsion, rather than the electrodynamic "electric motor" mechanisms of conventional cone loudspeakers. That means that rather than being in a box, they are a large flat panel, which radiate as much energy to the back as to the front, with very little at the sides due to the mutual cancellation of in-phase front/out-of-phase back radiation at the sides. This is a dipole radiation pattern, and it contributes to the relatively benign in-room diffusion pattern which enables them to sound so open and uncoloured - not like a box!

So any loudspeaker that I were to acquire would have to be as good as or better than the Quads in terms of their realism, imaging and "sonic invisibility" - that remarkable experience where one is joined in the room by the musicians in a recognisable sonic environment, which for me contributes significantly to the listening experience. I'm not a "the music comes second to the sound" person - I can, and do enjoy music on crappy radios, headphones etc., but it sure has more effect when the people are with you, especially on operas, vocal music, chamber music and large-scale orchestral works - oh, that's just about everything...

I became aware of Siegfried Linkwitz, a highly respected name in the "rational audiophile" community (rather than the "flat earth" subjective mob), who has published a number of DIY designs over the years. His loudspeakers are generally dipoles (good plan...) and carefully manage the in-room dispersion characteristics through careful design and appropriate choice of drivers. The fact that he was a great fan of the ESL-63s and wanted to improve on them was quite encouraging.

Anyway, because I only have a (relatively) little house, of SL's current designs the LXMini looks like a good starting point... Here goes!