HTB Sound Design

SFL Deliver a Complete Sound Design and Installation for Holy Trinity Brompton

A Story of Excellent Sound
Written by Mark Payne

First Impressions

I was first asked to look at the main part of the church at HTB back in 2006. Like many churches HTB's sound system has evolved over the years. What I found a mismatch of JBL, ElectroVoice and Community speakers with Wembley PA subs driven by an assortment of amplifiers and bits and bobs processors! The control side was fine (and is still in use as I write) This is made up of an Allen and Heath GL2800 mixer and some basic compressors at FOH.

From memory I think Tim Hughes was not long joining HTB as Director of Worship and in general the church were looking to 'raise the bar' with strong contemporary worship running alongside the more traditional music forms.

The sound system I found in place did 'make noise' and made it everywhere(!) but it was hardly representative of the excellent art and heart of the musicians and congregation alike.

Three Words: Acoustics, Acoustics, Acoustics

We looked at the acoustics of the HTB space first as the venue ambience and diffusion characteristic becomes the platform on which quality sound is built.

My sound systems designs have to be holistically matched to the venue space. If you have fundamental acoustic problems in the room then a £150 speaker and a £2500 speaker are going to sound equally horrible!

I found that HTB was a little too reverberant (a mid frequency RT of around 2 Seconds) to make contemporary music sound 'tight'. The space is however well diffused due to the obvious (and beautiful) architectural complexity of the building.

At the time I recommended, and we researched ways of pulling the RT down slightly (but not by too much) but it was felt that there would be compromises to the more traditional choral and organ ambience in the church and there was not the will or the budget in this case to change it.

In response to the slightly over reverberant nature of the space, I later decided on using the d&b Q7 speaker as the main provider of sound energy at HTB. The Q7 has a degree of headroom that I would not need at HTB but the vertical control of dispersion would improve intelligibility by reducing the sound energy being sent up into the roof spaces.

Working for Faculty

Any changes to the fittings and fabric of a traditional church space have to first seek faculty approval in partnership with the DAC. As part of the design we were required to provide details on the look and fitting details of the new speakers. More details on faculty approval and the work of DAC can be found here www.london.anglican.org/DACOffice

Computer Modelling

I have years of experience of understanding speaker system choice and placement coming from countless events, installations and venue exposure but with a permanent sound design I like to inform my own thinking whilst developing and sanity checking my ideas. After all, I am capable of being wrong (or only nearly right) in the first iteration!

I do this using EASE models for SPL (sound pressure levels), making sure there is sufficient system headroom at all frequencies for the music genre in question. During this phase I am also checking for even sound field coverage to achieve a balanced distribution of sound energy in the venue. I want all members of an audience (in this case the congregation) to have the same aural experience.

Sound System Choice

As the pictures show, I designed around the use of the d&b audiotechnik Qi7 speakers as the main providers of sound energy into the open centre of the downstairs level with further Qi7 mounted up high for the left and right balconies.

d&b QSubs have been hidden under the stage and also mounted high and 'out of the way' near and above the upper balcony Qi7 to keep the bass warmth on the second floor.

The under balcony areas on the ground floor have been kept in coverage with a distributed array of d&b Ci80 speakers pretty much on every pillar. This keeps the detail in the audio under the balcony shadow and also makes up for the further acoustic shadowing caused by the pillars themselves. Ci80 has also been used as fill speakers on the upper level to ensure even coverage throughout the side and rear balconies on the second floor.

When you use so many speakers in a distribution it is critical to use good time alignment taking advantage of the Haas Effect (rule of precedence) to 'remove' the fill speakers from the perception of the listener. The focus of sound at HTB remains on the altar. Each speaker needing different time delay is driven by an individual d&b 'Epac' amplifier which contains the DSP I need to tweak the time alignment and EQ on a speaker by speaker basis.

The setup and relative balance of the system is set by me firstly using critical listening by ear, then by accurate time/space measurement using SIA Smaart Live software to nail down the time alignment of all components to a chosen reference point.

The system is then equalised and rebalanced again by ear to get the relative levels in all parts of the building to match. It's at this point that I like to walk away and come back a number of times to ensure I am listening fresh. The final tweaking can only be done with a real live event and a live congregation in place as the acoustic absorption and focus of the building does change somewhat as it fills with people.

Once done, the system setup, alignment, balance and EQ is locked away in the DSP amplifier settings and cannot be changed by accident. Now the sound engineer can mix at the desk position knowing all members of the congregation are hearing the same image.