The Mill - Acoustics & design

Gus had particular requirements for acoustics that matched the studios he enjoyed working in. He had a studio that he liked to do his recordings at because of the musical quality, and there was The Marquee control room in Wardour Street, in which he liked to do all his mixing. Gus’s brief was to replicate the acoustics of these two rooms. This was something that, at this time, had not been done before. Measuring techniques at that time were fairly primitive by today’s standards and even measuring rooms to a degree of accuracy that would enable one to start designing some form of replication proved a bit challenging. Bruel & Kjaer were experimenting with fast transform analysis and were persuaded to loan us one of their prototype kits to do some measurements to see if we could make some sense of the characteristics of the existing rooms and this actually proved quite interesting and rewarding. The kit was difficult to set up but it did produce some useful values and also showed us what we needed to do to produce the acoustic qualities that Gus was looking for.

That then took us into the realms of design and the fairly enormous task ahead because computers hadn’t really taken off at that time. We ventured into placing an order and took delivery of an HP 9845. We soon had a couple of useful programmes that we could use as calculation for reverberation times so we could experiment with different forms of treatment and to a degree, the position of the treatments. That was revealing because it showed us what the effects on the room were by introducing absorbency at different positions in the room. It quickly developed our understanding of the behaviour of sound in rooms and the influence of shape and absorption. We had already experimented with ceiling shapes previously, and created what had become known as the compression ceiling, which was essentially an upside down pyramid where the lowest point was over the listening position, focusing particularly the low frequencies and increasing the effective power of the low frequencies over the listening area. We decided to use this because it was useful to the shape of the room and the indication that we should get the sort of bass response that Gus was looking in the listening area. The Mill was quite strange in its shape; we couldn’t change the exterior and the interior of the room was pretty much controlled by the exterior walls, but it was quite favourable in terms of the shape of the control room, being wider at the front and narrower at the back, although subsequently, we reversed that.

The net results of the control room were that we obtained the characteristics that Gus was keen to have and the way we designed it departed from a lot of the tradition at that time. Evidence of the room shows that it’s not always necessary to start off with an aircraft hanger to end up with a small box; that you can actually do a lot in a small room, and also control the low frequency end. We looked at how to propagate the mid bands across the space, and a lot of this was taken care of with the compression ceiling to ensure that the early reflections are strong and in good proportion to the direct sound. The reflections following on from the early ones are absorbed and taken away as quickly as possible. This gives a fairly even tempered room and one quite pleasant to work in and also favourable to microphones.

We used the ceiling to convey the early reflections, together with the surface of the console and that got us all within the first 60 milliseconds and after that, the surfaces of the room attenuated the energy quite quickly. We needed to get quite a quick slope and we were looking for a reverberation time of around 0.3 to 0.35 of a second.

Gus wanted the acoustic of another room that he enjoyed recording in. The room had a particularly bright mid range, it had a bit of excess low frequency, but a particularly bright mid range which we thought was the particular characteristic that Gus had affection for. Gus was keen to have an even tempered studio and in order to cater for the range of instruments that Gus normally worked with, we created a drum trap in one corner of the room which was pretty good at soaking up the LF end.

The floor of the room was terraced, so there was a low section. This was helpful in creating the acoustics we were looking for. At the far end of the studio to the control room the floor sloped downwards thus creating more volume to the room. This helped in creating the brighter mid band, without creating edges and other apparent echoes.

We were able to produce both a control room and a studio that achieved wishes of the client and design goals.Gus was delighted with the studio and impressed with the results.

The Mill control room was quite unusual. The ceiling was between 4-5ft thick concrete. There was a brickwork faced wall around the speakers and then there was the fireplace, situated under the left hand monitor speaker with a chimney going up through the workshop on the above floor.

The monitors at the Mill sounded wonderful, and many engineers recorded there with no subsequent alteration of tonal balance needed. Gus's mixes were often cut flat or with half a dB here and there by Ian Cooper at The Townhouse. The tapes mixed there appeared to show an accurate acoustic balance.

I watched Gus and Eddie Veale align the monitors one day. The critical part was done by ear with Gus listening carefully to music and calling for small changes here and there, with Eddie altering the crossover pots and then checking the balance with pink noise and a microphone/spectrum analyser. This process was repeated several times until Gus was happy with the result. The spectrum analyser showed a pronounced tilted curve but closely resembled the reverb time curve.

It was a common occurrence that halfway through side two of an album playback, the Crowns would go in to thermal shutdown as they were being driven so hard. It was always very loud and there were no fans near the amplifiers.

Monitor Speakers

The large speakers were designed by Stephen Court and were customised JBL 4130 units, built into the brick faced wall and covered with a brown reticulated foam grille. They were fed from Crown DC300 amplifiers, and contained passive crossovers. The drive units were special JBL 15" LE15B units (two per cabinet) chosen for their extended linear excursion properties, giving low distortion at higher levels. The rest of the drivers included an 8" midrange unit coupled with the popular 2105 slot tweeter.