Boo to Boxes, Hurray for Art!

Unfortunately, the subwoofers require boxes, a construct to which I am both allergic, from an audio point of view, and challenged by, from a constructional point of view. The audio side of things is probably ok, they are just subwoofers, so the boxiness isn't going to be problem, I hope. The construction thing is much harder, because boxes require sawing, right angles, joints, all that kind of stuff. Once Upon A Time, I blithely built boxes for all sorts of speakers, but now I seem to be incapable of getting anything to meet squarely with anything else. I suspect this was always true, but maybe I'm just more critical now!

Anyway, I've knocked up the required 1ft cubes with open backs, as specified by SL. I deviated slightly from the Master Plans in that I've used 18mm MDF instead of plywood for the top/bottom/front, because that's what I had, but that shouldn't matter. However, I want to spray them the same flocked grey that I've used for the main speakers... and there's the problem. Unfortunately, I held the panels together with tape while I was lining things up (all part of the patented GoukBuild © method), and the dratted tape has picked up the surface of the crappy 6mm MDF I used for the sides. So now it has rough and smooth bits, which stand out a mile when sprayed. Farts. Yeah, I know, the boxes are utterly cack and completely utilitarian, with screws standing out and all sorts of horror, but I'm drawing the line here, ok?

What to do? My mate G suggested molten plastic, conceptually, which is a great idea but infeasible. Then I thought of gesso - a high-build, water-soluble paint-like material used by painters to smooth out canvas and stuff, with which I'm familiar via my wife's artistic endeavours. She happened to have an used bottle of grey gesso she'd been keeping on the off-chance of ever needing grey... And a foam applicator!

Bottle of instant gesso and applicator

Here's a shot of the boxes, showing one of the bits where the tape has lifted the surface of the MDF, highlighted by the raw gesso application. I'm never using MDF for anything ever again... Am I being fussy?? Hey, it's my project!

Box close-up showing lifted surface

And here are the boxes in all their glory, after two coats of gesso. More to come I suspect, although it goes on very easily, and dries really quickly. I started out using a brush, but the gesso is quite gloopy, and the foam applicator is much quicker and smoother. I'm going to slap lots of gesso on to build up a layer that I can sand back to smooth off the fluffy bits - hopefully! They're looking quite cool, in a "Rebel Alliance spaceship" kind of way... With the awesome ally-coned woofers, they're going to look amazing! Nobody will notice the uneven edges, variously-countersunk screws etc. etc. right?

Subwoofers with 2 coats gesso applied

Input Selection (part 2)

I've chosen to use 2x 2x4 miniDSP units for the 6 channels of DSP required for LXMini+2. Initially they will be used with purely analogue inputs...

All Analogue LXMini+2 Configuration, with RPi/CD sources

But there are other options...

The 2x4 with the miniDIGI input permits an interesting option. The miniDIGI is providing a set of digital inputs across the miniDSP units, but doesn't disable the ADC section of the miniDSPs, merely bypasses it. So it's possible to use s simple switch to select the digital source for the DSP section of the miniDSPs... which could be the miniDSP or ADC!

And then there's using the miniDSP 4x10HD unit, which provides 8 DSP channels in one box, with much more processing power than the 2x4. Because that uses a DIGI-FP for input, and a VOL-FP for volume control, you get multiple digital and one analogue input, with switching from the VOL-FP multifunction controller. And remote! That's available as a complete solution from audio phonics at £547 or you can buy the components (2x8 kit, VOL-FP, DIGI-FP and a suitable enclosure) for £450, with all the fun of building it ;-).

To Be Continued...

Input Selection (part 1)

It's been a while since I posted anything, largely because things have been parked for quite a bit. However, I've started up the subwoofer build again, of which more on another post, and also looked at the critical problem of Input Selection.

Basically, the miniDSP has a single set of stereo inputs, and it's quite likely that we need more than one source. Right now, switching sources (mostly between the RPi/DAC and the CD player) is performed in the analogue domain by (simply?! no...) unplugging/plugging the appropriate set of cables, whilst keeping the right stereo L/R relationships, not getting confused about the right sockets to use etc. Dull. So...

Here's the current situation, and a possible super-simple solution...

Current vs. Proposed Analogue Input Selection Mechanisms 

To that end, I've ordered a well-reviewed analogue 3-1 switch box and a few 1m RCA-RCA cables. Let's start with this...

The Subwoofer Units Arrive...

These are BIG, at least, in a normal home! And heavy... They look like very big brothers of the fiddly woofer units, with their aluminium cones and magnet setups.

Boxed - you can just see the cunning cone/surround protector plastic lid

Even the hole in the box looks like a dormant volcano...

Top view - A4 sheet of paper for scale

Side view - note the suspended spider and open voice coil

Costs so far

As of 2017-02-24, updated to include Subwoofer costs:

Thing	Cost
Speakers	£212.40
Pipes	£74.56
Wadding	£18.28
MDF (6mm)	£8.99
Fixings	£13.20
Cables, Plugs, Sockets	£34.17
MiniDSP	£93.00
Sony Amp	£35.00
Linkwitz plans $105 (forgot this earlier!)	£72.65
Wickes 4" clay to PVC couplers	£19.96
Push-on tag connectors	£2.00
Wire	£6.00
S/W Cables, Plugs, Sockets	£25.33
S/W Speakers	£393.00
Linkwitz plans $55	£44.84
Paint	£15.98
Total	£1,069.36

Ouch. Still, cheaper than a Quad rebuild, and remember, this includes the DSP and amp, unlike Dr. Frank's kit. And also the plans from SL!

24 Feb 2017:  Subwoofer adds about £450 to the cost, most of which is the enormous drivers, at nearly £200 each! They are astounding impressive though. Let's hope the sonic effects are as massive.

Remote control?

I'm also fiddling about with RPi audio. I'm not sure where this info should go, but it's here for the moment.

The cheap Chinese Hifiberry Digi+ knock-off board has an IR sensor on it, which in principle can be used to allow a remote control to do things to the system. Interesting...

A bot of research, and it seems you have to use lirc, the Linux IR Controller module. Acting on some hints/instructions in various fora, I've

• Modified my config.txt to include 
• dtoverlay=lirc-rpi (load the right module)
• dtparam=gpio_in_pin=26 (enable the GPIO pin IR sensor is connected to)
• Rebooted the RPi (took a couple of attempts, with an edit of config.txt for GPIO 26 from 27 - oops)
• Run mode2 -d /dev/lirc0
• Pointed my old Virgin Media TV box controller at it...
• Result! lots of pulse/space codes....

[root@Frontroom ~]# mode2 -d /dev/lirc0

Using device: /dev/lirc0

Using device: /dev/lirc0

Warning: Running as root.

space 16777215

pulse 10974

space 4670

pulse 753

space 577

pulse 731

space 551

pulse 726

space 586

Now I have to teach the lirc software the remote control buttons. It's a wet afternoon.

Update

I did managed to record something from the controller, a post on the runeaudio forum said irrecord didn't work on ArchLinux, but it seemed to for me. At least, it generated a file. I subsequently foundered on a number of errors from the lircd, like "can't find IR thing" and so on. Poo. Maybe I need to get it to work with another platform first, like Raspbian. At least I can now see how it could control the Rune player - it's basically scripts that use mpc, invoked when a specific event is detected.

Digital Ins and Outs

The miniDSP 2x4 kit, miniDigi and cheap Chinese Hifiberry Digi+ knock-off have arrived. Hurray! Let's see if any of this works...

The first thing is to get the Digi+ SPDIF/Toslink interface going on an RPi. I happen to have a spare one (of course!), so I've cloned the SD card from one that works, popped the Digi+ hat on top, and wound it up. Oops - no sign of the Digi+ in the MPD config menu... So time for a quick SSH onto the RPi, vi /boot/config.txt, edit the dtoverlay param so that it includes the hifiberry_digiplus, and now it's recognised. Hurray. You might think the smart money would be on trying something known to work first, like my Focusrite Firewire audio interface with SPDIF out, but hey.

miniDSP 4-way Advanced application

Now for the miniDigi and 2x4. The miniDSP documentation is a bit dodgy, and needs careful reading. I rigged up the miniDigi and 2x4 using the provided 30-way headers, connectors and ribbon cables - there are two sets of connections, only one of which is documented much. This is the I2S interface, I assume the other is about power connections and so on. Time to select 1) input - Toslink initially because they gave me a cable! 2) output - looks like it's ok. I powered it all up from the Mac USB connection, and cranked up the 4-way Advanced configuration application. Bleuch - nothing!

Check the manual - oops, need to ensure I2S Master and Slave relationships set correctly. Set miniDigi to Master. Now there's sound, but a horrendous crackling that drowns out music, and it's constant. 

Check the manual again - check 2x4 MCLK master/slave setting, which is currently Master. Poo - should be Slave (this is not intuitive, but hey... what use is intuition in these matters?). Switch to slave, re-stack boards. Hurray!! Sound, clean, no noise, expected selection of Left/Right on 4-way Advanced interface.

RPi SPDIF i'face, stacked miniDigi/2x4

miniDigi (top) and 2x4 stacked (SD card over bright blue LED!)

Summary

1. RTFM properly!
2. miniDigi - I2S Slave
3. 2x4 - MCLK in Slave position (I2S signals coming from miniDigi)

See what I mean about it being non-intuitive? I guess the difference is between MCLK - the signalling rate indicator, and I2S Slave - who's boss on the interface.

Next Step

Make up the custom connectors, since the provided ones only allow for a single 2x4 to be connected to a miniDigi. More on this to come...

Now for the Big Boys...

Right. I like the LXMini. Could it be better? Apparently yes - there are various flavours of subwoofer available, all of which offload the (fairly small, TBH) lower mid/woofer for the last couple of octaves, and thus allow it to perform better. The SEAS drivers are pretty amazing (see here for some info on that), but the laws of physics will not be denied!

The choices are:

1. Relatively cheap omni subwoofers in 1 cu ft boxes - ok, but does their directivity or lack of it really match the carefully planned LXMinis? They're not a Linkwitz design, but from one of the guys on the OPLUG forum, people seem to have good results, but they would say that! About £130 for the chassis speakers (Peerless 830668), so a bargain
2. LXMini + 2 subs - these are from the Linkwitz design stable, and require the stonking Seas L26RO4Y D1004-04 woofers, at a wallet-busting £370 the pair!! However, they are dipoles and thus more amenable to room placement and more fitting with the LXMini directivity
3. LXStudio - again, from the SL stable, basically the LX521 woofer setup running in parallel to the LXMinis; these require 4 of the aforementioned WFW (Wallet Busting Woofers) at £740, and thus very much a nice to have... Again, the directivity is more fitting with the LXMini

All of these require 

• 2 more DSP outputs i.e. 2 more than I currently have, bummer
• 2 more power amps - now those I do have! The trusty Sony has two spare channels, hurray! You'd almost think I planned it. I don't have enough  power the LXStudio, since that's 2 massive 4ohm woofers per channel

DSP options include, but are not limited to:

1. MiniDSP 4x10HD: SL's choice, a very useful bit of kit, which includes analogue and digital inputs, volume control, selection between multiple stored configs; however, it's another WBO (WB Option...), at a stonking €650 from Audiophonics (not including shipping, but no customs duty (yet!), or $500 direct from miniDSP, in which case no idea about customs, but certainly VAT i.e. $600 before any customs/shipping! No. Not this time.
2. MiniDSP 2x4: Supported by Dave Reise on OPLUG, this is another of the DSP units I already for this project, paralleled by using one each for Left and Right channels, so it gets the same analogue input as the current one. Fairly cheap option, €85 from Audiophonics in board-only form, or boxed from CPC for £95 as last time. This gives me a total of 8 channels of DAC/DSP, which is plenty.
3. Hypex DLCP: excellent 6-channel DSP from these guys, but requires some building work; it has 6 (6!) analogue inputs (balanced - super!), USB/Toslink/SPDIF/AES-EBU digital inputs, loads of horsepower, and it's the basis of a much superior setup, including the Magic521 Powerboxes. It's about £530, without shipping and a good box to put it in. Hmm. I can also get it from Magic521 with the DLCP config file already loaded. If I was starting from scratch, or thought it would sounds loads better (it might :-( ) I'd be tempted. 

I've purchased the LXMini + 2 and Studio subwoofer plans, because they're fairly cheap ($55). Call me impulsive, but I've also bought a miniDSP 2x4 board from Audiophonics in France. Hey, useful anyway, right? It's a good way to try things out, without the massive expenditure of the other options. 

I've also purchased, because it looked interesting, and provides an alternative input mechanism, 

• A miniDSP miniDigi; this provides a digital input to the miniDSP 2x4, resampling the input to 48kHz using standard chips. I'm not sure if it does more than 16 bits, that would be interesting, but I think unlikely
• An Audiophonics digi+ for RPi; this provides a digital output capability for a Raspberry Pi, using S/PDIF or Toslink, and therefore avoids a DAC/ADC cycle when using RPi with the digitally-enabled 2x4. Worth a try, and I can in principle use both inputs with a bit of switchery in the 2x4

The miniDigi also provides a dual 2x4 capability, in that cunning use of its internal switching matrix and outputs will allow me to drive the two 2x4s from a single digital input, in fact that's the only way to do that. Some cunning-ness required, but hey, let's keep this complicated.

Done!! Well, almost

It's Sunday, and very wet outside, so what else would you do, if not finish up the build?

First job is to assemble the second speaker, like the first. Trickier - the hole for the woofer tube was a much tighter fit, and took some serious clouting with the rubber hammer!

Then the wiring completion, basically 

• Cut to length, leaving plenty inside the woofer tube to enable removal of the speaker units at some future date
• Check the polarity and wiring with a 1.5v battery
• Fit the crimped on tag connectors
• Push them onto the Speakon terminals
• Screw the Speakons into the bases

Speakon connector in place

I also cut the 2x5m Speakon connector cables - one 10m length with a plug on each end, now cut into two, and prepared the ends, bare wire being required for connection to the Sony output terminals. I also plugged the connectors into the speakers and re-checked the wiring and polarity with the 1.5v battery. Success!

All done, in the front room for a team picture

The initial setup and so on was quite fraught - I haven't used the Sony amp much, and various bits seemed not to work, but eventually I checked all the wiring, connections, input settings and so on and - bingo!! The Kraken wakes!

Speakers in initial operation

And here they are. They are in front of my Quad ESL63s and existing amps/sources. The Sony amp and miniDSP are on the floor between them.

What do they sound like? Good! At least, not utter shyte, which was always possible. Good bass, more punchy than the Quads. Top end seems ok. They don't sound like boxes as I perceive them (result). Jen and I listened to lots of music, and got very aurally tired! Do they replace the Quads, the original design brief? I'm not sure yet, but it's possible... It's conceivable that a better DSP/Amp setup could add a lot, but let's see how it goes. The subwoofer would also improve the bass and free up the current woofer to do a better lower midrange job.

Almost done? Yes, well, I haven't checked for air least yet with a 10Hz signal - I had to get them connected to the amp to check that, and then got carried away listening! Tomorrow??

I have also had a fiddle with the gain structure again. I suspect the miniDSP is about 16db hotter than the Sony inputs can handle, but it doesn't seem to be a problem. I've looked at the Sony circuit diagrams to work out where the input attenuation takes place, if it's in the right place then just turning it down is sufficient to prevent distortion, but it's not obvious to me. Otherwise, the miniDSP input meters show that most material appears to be getting near the 0dB level, which is pretty scary. I re-ran the tests with the HiFi News signals off a CD and the REW signal generator, and the miniDSP levels appear fairly close to accurate, which is pleasing. At least I can ensure that the miniDSP doesn't clip, as it's ADCing the input - that would be dull! I guess I could get a miniDSP miniDigi and strap it onto the miniDSP so that I skip a DAC/ADC step. Another time...

Final Assembly - One Down, One To Go!

Right, here goes... This turns out to be quite tricky.

Firstly, I have to assemble the FR tube onto the mounting plate. I had a couple of goes at this, because getting the levelling screws a) level (!) b) at the right height was a bit tricky. This also involved running the cable through the tube and blocks, which required an additional reaming with the 5mm drill bit to straighten the holes up.

Initial FR tube mounting on plate

Running the FR wires through the block is tricky, and adds to the complexity of putting the nuts and washers on the retaining bolts. But...

Attachment bolts with FR wires, showing tightness of spot!

After that the wire needed to be run through the hole in the coupler - this was also a bit hard! The wire is not very bendy and needs eventually to turn at right angles a) at the exit from the mounting plate b) on the inside of the coupler, after it's come through the side.

View of FR wire transit from mounting plate to coupling 

Of course, I aligned the speaker terminals with the rear of the coupler, right where the FR wires come through... this increased the level of difficulty by about 5! But eventually I coaxed it into place, and worked the 1m of wire through the hole.

FR wires enter right beside Woofer speaker terminals!!

Now it was time to assemble the woofer tube to the base, and then the rubber coupler to the woofer tube. This is/was made difficult by the need to run the wires through the base, whilst not actually connecting the coupler to the woofer tube. Fortunately the dining room table is about the right height to support the heavy speaker assembly whilst the tube and base are unstressed and can be assembled.

Speaker units resting on table

I used the "dodgy" glue because it's pretty darned good on anything but EPDM, and can be more easily applied than the pretty gloopy acrylic stuff. I also checked the tube's orthogonality using a set square, and pounded it into the hole with a rubber mallet!

What I haven't included pictures of is the teasing out of the two 1' x 2' pieces of MDM4 wadding - that was a major component of the time, and was pretty tiring, just pulling at the wadding to open it up. Eventually I got it done, rolled up and stuffed down the woofer tube...

At which point I was able to put the coupler on the woofer tube and tighten the stainless steel band. Hurrah!

Completed speaker assembly

And here's the result. I still have to remove the draughting tape that marks the 1" level of the coupler on the tube, and fill the coupler and base wire holes with sealant. Then it's done!

I'm really impressed - it looks great, really solid, and the colours work brilliantly, giving a kind of solidity and technical "function over form" appearance. It's not an eyesore, and quite neutral.

Damn! The wrong kind of glue...

I was a bit suspicious about the glue I'd used for the woofer EPDM (synthetic rubber) couplers. The glue (Evostick "Sticks Like ...") just didn't seem to be setting where it was in contact with the EPDM, and some investigation today proved that it was useless. A quick Google on EPDM revels that only cyanoacrylate (superglue) really sticks to EPDM, because it's slightly oily, being made out of, well, oil. The next best stuff is acrylic glue - and at that point I recall that the Magic521 kit includes some acrylic glue...

A quick scan of the Magic521 instructions reveals they are supplying Soudal Fix All, or at least, that's what I worked out after some judicious Googling. And Screwfix has various types. Hurray.

An hour's worth of pulling apart and careful scraping cleans up the couplers and the mounting rings. At least, I hope it does. It's hard to know. And I do have to be careful because the speakers are of course still glued into the mounting plates, and are easily damaged with a scraper or screwdriver blade. I have managed not to damage them, unusually.

So tonight I've reglued the couplers and mounting plates, using Soudal Fix All High Tack, which is incredibly thick and hard to use. It is, however, clear, which is handy, and smells a lot more pleasant than the Sticks Like, being solvent-free. Let's see how these look tomorrow.

UPDATE: The new glue appears to stick really well! Success. Phew. 

Getting close! Woofers, bases... Almost done

It being Sunday afternoon, and a few moments to myself, time for a little more assembly. 

I glued the woofers into the mounting plates, after clipping the wiring onto the back of the units - it would be really hard to do that afterwards. Prior to that I also drilled holes in the backs of the couplers to pass the FR unit wires through so that everything runs inside the woofer tubes. That was actually quite hard - the coupler material is extremely tough and resilient - I ended up using a sharp knife to cut some material out of the holes.

Woofers newly glued into the mounting plates

I also attached the feet onto the bases. I had been going to use 3 feet, on the basis that they wouldn't need levelling or truing, but since I wanted two get at the front and the back one would have gone where the Speakon socket is, I went with four. 

Attached base feet - it's underneath, right?

The feet look quite good, IMHO! 

I also resanded the woofer tubes and put a ring of tape 1" from the top, in readiness for mounting the speaker units on the top. I suspect this final stage is going to be the trickiest, since it involves

• Mounting the FR tubes on the mounting plates - I have to adjust the height/levelling screws too; MagicLX521 suggests using a 5mm drill bit to get the height right, good idea
• Finishing running the wiring from the FR and Woofer through the woofer tubes - involves running it through the FR tube mounting blocks and the couplings/woofer mounts, and then down through the holes in the bases; hopefully I've left enough wire spare for this! MagicLX521 glue the tube to the base first, then run the wires through the base; this is probably a good idea, since will allow me to push on the top of the tube to get it into the hole! I'd better check I can reach down the tube far enough to push the wires in the holes in the base...
• Putting the filling in the woofer tubes - the MagicLX521 kit suggests just pushing it in from the top, rather than from the bottom like Linkwitz. Since that uses a similar mount for the tubes (a hole in the base, rather than the original cup), I shall likely do the same. 
• Attaching the woofer tubes to the bases - a one-time job since it will use the acrylic glue, so better get this right...
• Attaching the couplers/mounting plates to the woofer tubes - that doesn't sound too hard, does it :-p
• Cutting the wires to length, attaching the crimp-on connectors, attaching to the Speakon connectors and screwing the connectors into the bases
• Filling the FR tubes with damping; I won't have any MDM-4 left, since it all appears to go into the woofer tubes! I'm going to use BAF that I already have, let's hope it has the right effect, otherwise acquiring another pack of MDM-4 is going to be very expensive (relatively). the MagicLX521 kit also uses two packs of MDM-3 (originally), the same size as the MDM-4, and just says "use both both sheets; stuff the FR tube with lots of wadding" without pointing out exactly where the FR tube wadding is coming from. Ha! I guess I could email them for a pointer.

Some progress - building the FR tubes!

It's been slow over the holiday period, all those dratted people requiring attention ;). I'm not sure that things would necessarily have gone any better, I'd have just screwed up sooner!

I spent this afternoon building the FR speaker enclosures. Firstly, the slightly misaligned bolt holes make it tricky to get the hardboard pads in the right place. Hopefully they're OK. I also thought I'd try double sided tape instead of hot glue to attach the pads to the units, as last time the glue seemed to come off very easily! However, it doesn't provide any filling effect so the pads are liable to move around a bit and also rock if not exactly centrally pressured, which they're not. Boo. We'll see. Additionally, it's very hard to tighten the nuts on the nonslip washers, no spanner I have fits and allows the turning of the nut in the available space.

I've also (gulp) glued the rubber couplers onto the mounting plates. They are currently drying under the mild pressure of a box of champagne - amazing what you find in the garage. I have yet to drill the holes for the FR wires to go through them, I'll do that when they're dry. I think it's a good idea to glue couplers and speakers separately, it enables me at least to get the former well-attached!!

Hopefully, the various cruddinesses will neither make the end result non-functional or too horrible in appearance. We'll see!!

Slow progress with Bozo AKA yet more mistakes!

Grimness. I am actually Bozo the clown... I checked the alignment of the FR chassis units in the FR tubes, having managed to stick the hardboard pads on with a hot glue gun. For some reason, I couldn't make the speaker be the right height in the tube - the pads were too high! Then I looked again at the plans - I'd drilled the stupid holes at 0.5" from the top, not 0.25"! Fool. And there isn't really space for a new 5mm hole beside the old 5mm hole without breaking through the side...

Fortunately, I'd gone for a 3 bolt solution, with two bolts at the bottom and one centrally at the top. So I was able to reverse that, so now it's one at the bottom and 2 at the top. And I remembered this time to use a 4mm drill, and use the 5mm taps I have to tap a proper 5mm thread into those holes! So it was kind of a result. Some pictures...

Set screws looking cool in the new tapped hole

Originally specified bolt in tapped hole - original hole also visible!

Set screw screwed in vs. cap screw

The set screws are pretty cool looking, if only I'd put the holes and the taps in the right place the first time! Sigh...

I ended up taking the pads off the speaker units of course, because they are now in the wrong place. Fortunately the glue didn't appear to have adhered too well, and they came off far too easily!

I've also been spraying the various parts over the holiday on the occasion that it's not too cold or wet outside, and there are no micro-people around who will DIE if they inhale overspray. They required an additional can of paint - the bases are really sucking the paint up, but typically MDF is never going to accept a finish on the cut edges without some kind of primer. Ha! I don't care. It's industrial chic, right?