Monthly Archives:

January 2021

DIY Projects

Speakers – exponential tapered horns

January 30, 2021

Though not strictly part of filmmaking or sound recording, ultimately playback is on hi-fi speakers (well for those not limiting themselves to earbuds!) and having something decent on which to check mixes other than nearfield studio monitors is critical. To me, speakers means DIY and I have been playing around with them since childhood: an early speaker project around undergrad days was a long-throw horn using WEM drivers (and I remember meeting the modest PA pioneer Charlie Watkins when I went to his largely one-man factory to get a driver re-coned), and then a few years later, when a thick cold meant I wasn’t feeling much like working on the thesis, I made my first exponential tapered horn speakers, loosely inspired by Laurence Dickie’s famous Nautilus B&W speakers. The rationale of the Nautilus design (and subsequent speakers using this approach) is to use tapered tubes to absorb the rearward sound produced by the drivers, to stop it being reflected back (as in a conventional speaker cabinet) through the driver again, adding unwanted resonances and colour.

The 1990s old snake speakers, with B&W drivers and that chipboard aesthetic

These first tapered horn speakers weren’t snail shaped like the Nautilus (too complex and derivative) but, rather, vaguely snake shaped, built simply out of chipboard, and had more of the WEM PA speakers: they weren’t very hi-fi at all. But modifications quickly followed. I was given some spare B&W drivers (I think for their 802s, but they are marked ‘prototype’ on the back), so modified the snakes to take them, and then some backroom boffins at B&W kindly stuck them in their anechoic chamber, stuffed them properly (I was too tentative with my wadding), added plasticine under the tweeters to take out a nasty reflection, and designed and built crossovers to suit: this might seem unusual, but I was brought up in the small Sussex market town of Steyning, where B&W’s R&D centre was located, so enthusiastic and generous research staff were thick on the ground.

I’d always meant to house the speakers in something rather nicer than chipboard, but the decades slipped by (actually over 25 years) and it took the Covid-19 lockdown for me to get round to it. Somehow the project rather developed: instead of re-housing the early 1990s B&W drivers (or, actually, similar: I had a spare set), I was offered some rather more modern and better (indeed, world-class) drivers (including metal-coned pistonic bass/mid drivers) actually designed for this type of speaker, and, again, some technical support (e.g. on crossover design and build). I’ll draw a discreet veil over which (different) manufacturer gifted them this time (those interested can probably guess), as they don’t supply for DIY use: again, these were some spares knocking around – acoustically fine, but not quite pristine looking.

Half-model for the new design

For the new speakers I decided to go for laminated plywood construction. I like the aesthetic of varnished laminated plywood sculptures and it seemed an achievable way of building a complex curvaceous shape: there would be no flat sides this time round. Also, with laminated construction I could create fairly thick and inert walls. The overall form is similar, nonetheless: a rearing snake (or a large number 2 if you want to be more prosaic) and a two-way design with passive crossovers. And the underlying principle was the same. That is, the form was defined entirely by eye and a gut feeling that the exact taper of the tube isn’t critical, so there is no scientific analysis behind it! Work began with drawing in AutoCAD and was followed by the production of a 0.3 scale half-model – shades of boat building. After sanding this so it looked right the laminated sections were each scanned on a flat-bed scanner, and then inserted into the CAD drawing to allow tweaking of the shape of the templates.

Then construction for real started, with endless hours of cutting plywood just with a circular saw and, mainly, a jigsaw: with 30 pieces of plywood per speaker I was soon cursing the frugal approach that precluded handing it all over to a CNC-equipped workshop (partly due to lockdown-derived impoverishment and partly due to the fact that I wanted to build them myself). Then gluing the plywood sections together to make half-speakers: it sounds easy, but the awkward shape and slippery glue were a difficult combination, resolved by adding a few laminations at a time and holding things in place with piles of books. Fiddlier still was making the front plywood baffles for mounting the drivers: the drivers sit in rubber O-rings with fixings via threaded bolts out of the back of the speakers, so millimetre precision was needed (achieved by spinning my router round a nail). Then back to hard graft: heavy sanding – mainly with a belt sander – to get into something near the final shape. I must have clocked up more hours with a mask on in my own garden than anyone else in lockdown. With initial sanding done it was on to stuffing the lower half of the tapered tube with woollen jumpers (almost solid at the bottom), add cables, and then, without stray bits of wool mucking things up, glue the two halves together: more wool and then – for the top part – speaker wadding was added through the bass driver hole.

Setting out paper templates, and working how to fit to the 8ft x 4ft plywood sheets
Plywood laminations cut for one half-speaker
The not-so-sophisticated gluing process: lashings of Titebond and precariously-balanced books.
The first half-speaker nearly finished, with drivers loaded. The tweeter has its own (plastic) exponential tube fitted, and both drivers are held in place by bolts through the back of the cabinet – requiring careful alignment and rubber fittings to avoid resonance issues. The interior was intentionally left with a stepped effect since sanding (which would have been difficult) would not have improved the performance.

With one speaker roughly made, it was time for loading the drivers for testing. With no access to a handy anechoic chamber this time, the garden on a windless day was the next best thing – getting away from any nasty indoor reflections. The neighbours must have thought it odd as I fed sine-wave sweeps through the speakers: aliens in the village? Measurement (bass driver and tweeter separately) was via a Dayton Audio EMM-6 measurement mic, using its individual calibration data and REW software (useful not just for measuring room EQ). The results were looking hopeful, so data was sent to the crossover designer (a renowned loudspeaker designer, so in safe hands), then the crossovers were assembled for me (using hand-wound inductors, made on a slowly spinning lathe), and the tests run again, this time with both drivers in unison: superb results, with impressive waterfall plots revealing negligible resonances and reverberation. During the to-ing and fro-ing of crossover design and build, I ground on with construction of speaker no. 2, and then both speakers were given the finer finishing sanding, crossovers were fixed, and then the speakers were treated to several coats of high-gloss yacht varnish.

Gluing the two half-speakers together: not the easiest shape…
Measuring a speaker in the garden: the poor man’s anechoic chamber.
Almost there: soldering connectors to one of the varnished speakers.

And the sound? After teething troubles with one bass driver (an elusive intermittent distortion caused by a loose connector in the driver – as I said, these were spares, and had been knocking around on a shelf for a few years) were sorted, absolutely superb! REW results indoors were exactly as anticipated and aimed for. But, more to the point, listening reveals the sound to be uncoloured, responsive, clear, with a good stereo image, and easily sufficient bass (something I was wondering about) for the size of room. At some points the complexity of utilizing the new drivers seemed daunting (compared to the old B&W ones), but, in the end, it was worth it: not only was there an aesthetic upgrade (the original plan), but an equal acoustic one. For the cost of several sheets of ply, a lot of glue and jigsaw blades, some crossover components, a tin of varnish and countless hours (which were going free during lockdown anyway), I’ve ended up with some unique-looking speakers that to better performance-wise would cost upwards of £20k. And such a satisfying feeling. Given that the mark 1 snakes served over 25 years, these ones will see me out.

Ah, I forgot to mention, though, that there is one drawback: this time round you can’t balance a mug of tea on the top of the speakers…

Film Projects

Rolling-ball sculptures

January 16, 2021

Rob Moore has many talents – artistic, musical and practical. Over the last three years I’ve enjoyed making short and simple videos that showcase some of his amazing rolling-ball sculptures: that is, sightly whimsical, but endlessly fascinating, kinetic sculptures drawn in stainless-steel wire and given motion by balls raised mechanically and then descending under gravity. Rob’s most ambitious creation to date has been his ‘Kinetic Lungs’, but, in early 2021, he is just about to start on a far more complex sculpture still: the Brain.

There is a small number of like-minded individuals making these kinetic sculptures, spread across the world and linked mostly by the internet. Many of the videos posted showing these sculptures have soundtracks dominated by music, but, to me, the noise of a rolling-ball sculpture is a significant part of its character: the background rumble of the mechanism that lifts the balls up; the swish of the balls as they descend the tracks; the clunks and thuds as gates and switches move; and the frantic spinning of balls in cones. So my approach to the films has been to focus on the sound, tracking, as it were, an individual ball through the sculpture, in a slightly hyper-real way. In each case I recorded the mechanical lift system separately, then turned this off and recorded the progress of an individual ball close-up, section by section with a spaced pair of mics giving a rather exaggerated stereo sound, as if leaning in close to the sculpture. This was then pieced together, overlain with the mechanical rumbling track (with this turned down, to match more closely how you perceive the noise in the flesh) and (and this is the complex bit) multiplied and synchronized with the multiple balls in the video. The video itself in each case has the whole sculpture shown as a static reference shot, with a split-screen showing changing close-ups, but all synchronized: a complexity of audio and visual synchronization that gives a very simple-looking end result, which lets Rob’s rolling-ball sculptures do the talking.

With the upcoming Brain the filming requirements will be much more complex, with pieces to camera by Rob and behind the scenes filming of its making. I’ll post more about the filming and sound-recording aspects of what will be a long build: and Rob will doubtless post updates on his progress on his Facebook page.

Film Projects

Colin Bygrave – painter and printmaker – 1933-2020

January 12, 2021

Christmas brought a few sad notes in cards, telling of deaths earlier during the year, with families having to cope – on top of all else – with constrained funerals amongst Covid-19 restrictions. One such death was that of Colin Bygrave, well-known in Norfolk as a painter and, especially, etcher. Colin was a friend and, for several years, a neighbour (I even have one of his aquatints of the side of our house viewed from his). Back in 2013 Colin and I made a film on etching. Divided into five short sections, this was intended as a guide to those interested in etching and, especially, aquatint, perhaps thinking of having a go themselves, so it follows a simple step-by-step structure. I’m so glad we did this, not just for the purpose of being a Youtube guide, but also since it captures something of Colin’s gentle enthusiasm and skill as a lifelong teacher.

Filming in Colin’s purpose-built garden studio was appropriately low-key, over a few shortish sessions (Colin was already over 80): I used a single Nikon DSLR, while another friend (Adam O’Grady) with an interest in etching (he had previously attended a course or two run by Colin) operated the boom mic.

For a commemoration of Colin’s life and work, see https://colinbygrave.uk/

And here is Colin’s brief five-part guide to etching and aquatint:

Audio Gear

Omni mic pair in a single blimp

January 8, 2021

I’m a fan of omni SDC pairs for outside recording. For music I will often use these in Rycote Baby Ball Gags mounted on a stereo bar, itself on a substantial stand (usually the Manfrotto 1004BAC). But where I want something more portable and more windproof, I mount the two omni mics end-to-end inside a single windshield – the Rode blimp Mk1. Joining the two mics end-to-end is easy with a rewired and drilled female-to-female xlr coupler (well, actually, the female-to-female XLR connector is actually not off-the-peg, but made up of three items: two Neutrik NM3FXI and one Neutrik KM. Neutrik’s own female-to-female XLR connector doesn’t unscrew). This places the mics  (a pair of Rode NT55 mics with the excellent NT45-O omni capsules) at a 360mm spacing, which renders a good stereo image and is exactly the ideal length for the Rode blimp (i.e. the same length as the straight part of the blimp). Being pure pressure omni mics there is, of course, no phase issue arising from the fact that they are pointing different directions.

So the end result: a simple robust set up, less fiddly and more portable than common field-recording set-ups for ORTF pairs etc. and – being all enclosed – more windproof. It’s not something I have seen or read about, but I imagine – or hope – others are doing the same.

And here’s a detail of the easily modified connector: just drill a couple of holes for the cables.

Live Music

A European tour

January 8, 2021

An acoustic performance next to the Halle aux grains in Auvillar

With Brexit on its way, in 2017 I organized a small European tour for local band Rattlebox (for which I am sound-engineer). This was an exercise entirely determined by fun and entente cordiale: free gigs in some fairly random and mostly very small places in France, Andorra and Spain, largely determined – though not in all cases – by one of us having some connection; and six families, and a few extras, with us on what would be their summer holiday. Even so, there were practical issues to sort: arranging gigs (much helped by my French-speaking and living elder daughter), accommodation (largely campsites: this was a budget tour), power supplies, intermediary stops (this was part holiday, remember) and, of course, the PA. Anyway, here’s to the gigs:

Fri 28 July: Sainte-Sévère-sur-Indre (central France, midway between Bourges and Limoges). A fitting start to the tour: the gig was in the open-sided market hall in the square of the village made so famous by Jacques Tati’s 1949 film Jour de fête. We were a little nervous about the gig as we had no previous contact in the village, and had just had a few – hard won – emails with the mayor’s office. But they came up trumps, and had set out the market hall with benches (which filled up), put up posters, and even produced a few slabs of beer. We felt as welcome as the fair folk in Jour de fête. After a little electric shock (a reminder that wiring isn’t always what it should be), the technical side went OK: the PA was a combination of Alto and Proel speakers, with a Soundcraft mixing desk, all fairly basic but fine for what is a slightly raucous folk band. Beers after at a bar, then all of a hundred yards to the village campsite with its profusion of Swallowtail butterflies. Perfick, as Pop Larkin would have said.

Sat 29 July: Auvillar (Tarn-et-Garonne, south-west France). A weekend here in this most beautiful of small towns, courtesy of an old friend (a retired French general) and the indefatigable efforts of Gilles Compagnat. Unknown to us beforehand, Gilles organized everything, from a short taster acoustic session by the circular Halle aux grains (where our carefully transported English cider – yes, we took a present of booze to France – went like lightning), paella for all in the square, the main evening gig to an audience of 200 (then a record for Rattlebox) outside the church with its natural ampitheatre (with lights set up specially too), and a Sunday morning acoustic gig in the Place du Château. Having no PA to run on the Sunday morning, I set up a couple of omni mics and recorded the band outside, ambience and all. Goodness, were we sad to leave.

Tues 1 Aug: Vinça (Pyrénées-Orientales: southern France, near the east end of the Pyrénées). After stops at Carcassone, Lagrasse and, for some, the Med, this more workaday small town had a great lake and, by the side of this a lively bar  – the ginguette d’Aquagliss au lac. A compressed stage, but, who cares, there was more paella and dancing for the first time on the tour.

Thurs 3 Aug: Andorra la Vella. It had always been an ambition of Danny (of Rattlebox) to visit Andorra, and as we pitched up in a very urban campsite next to the national football stadium in insanely hot and humid conditions, we wondered why? But the evening gig in the Harlem Bar (organized by the remarkable Pierre Infante Lagrave and the bar owner Josu Adanez) was a great success: small, extremely sweaty and with enthusiastic dancing. What more can you ask for?

Sat 5 Aug: Junzano (near Huesca, Spain). Courtesy of  the sister of Simon (also of Rattlebox), a long-time resident, of this small village, we were part of the municipal fiesta, and welcomed enthusiastically yet again. A bigger stage and, for the first time, other acts: yet more paella (at least in Spain this time), dancing and, afterwards, sad farewells before the long journey home.

During all the mayhem of keeping things on track, running the PA, being the roadie, and occasionally snatching bits of holiday – all in the unremittingly fantastic weather – there wasn’t really any time for serious filmmaking, but here’s an extremely rough film (largely an aide-mémoire for us) that captures something of the fun and, indeed, the welcome: the eternal question down the pub is where next?