Order of the Bath

When planning a video projector system for a church, or anywhere else for that matter, you need to do things in the right order. The first thing to decide is what sort of material you are going to project: is it cinema type video, detailed business type presentations or are words of hymns the main objective. These determine the shape and most importantly the size of screen that you require. This must come before choosing your projector. Most online advice guides ignore the first criteria—type of presentation.

For the cinema type of experience you will probably want a 16:9 format screen and most of the advice online will be able to assist you to decide the size. The consensus seems to be a screen height 1/6^th the distance to the back row of seats. You may also want at least a partial blackout.

For a business presentation you would probably want a 4:3 format and, unless you wanted very fine detail, you could probably go to a screen height 1/8^th the distance to the back row.

For a system primarily for the words of hymns and scripture then it is a different prospect altogether. Doing the calculations for our church, which is 24m from front to back (we don’t have a chancel/choir area), we get a screen 7m x 4m for cinema and 4m x 3m for business. Without exaggerating — this is HUGE. Even the smaller would completely dominate the front of the worship area and the larger would block out all view of the East window and generally annoy everyone including the diocesan architects.

Fortunately we consulted a good professional contractor who knows churches and he put us right (in fact we consulted two and got similar answers). The difference is that you are rarely showing more than a dozen lines of text on the screen at once. Any more than that and the reader will lose their place. Hence you can use very large text sizes which reduces the necessary size of the screen. You can still do video clips and pictures for illustration but you are not aiming at that all enveloping cinema experience. Many years experience also tells me that only about half the members turn up to church business meetings so pack them into the front when you want to display the detailed financials.

So, taking the advice, we determined that we only needed an 8′ wide screen (that is about 2.4m) and I have been holding off posting this item until I had seen it in action: he was right! The benefits were great. It was much cheaper (both screen and projector), it is not overly obtrusive, and it folds away neatly when not in use. I can just about read it from the middle without my glasses and I my sight is pretty poor. It is perfect from right at the back with them on.

One thing that complicates the running of church sound is the requirement for multiple mixes for different purposes. In addition to the output to the main speakers you often need a feed to the induction loop, a tape recorder and perhaps the crêche and other parts of the building. The requirements of each are slightly different, and to do this effectively you need more than just a splitter on the main outputs—some stereo, some mono, some with an “ambient” mic mixed in etc.
When looking at some church systems I was struck by the complexity and the involvement required by the operators. The most common arrangement I have seen for recording or a hearing-aid loop is complete separate mixes on auxiliary-sends. This requires the operator to be aware of two or more levels on every channel and, if they are doing it properly, monitoring each one separately each time something changes (even if you do have them ganged by using a post-fade auxiliary). There are too many opportunities for error doing it this way.

The “ambient” additions are what we use the last mixer group for (see my earlier post on Group Mixing for Church Audio). These are microphones for signals that you do not want to go out to the main loud-speakers and can include high level microphones suspended above the congregation to pick up the singing, perhaps a microphone or direct feed from the organ (because even an electronic one normally has its own speakers rather than go through the PA) and once I even had a radio microphone in the bell tower. This group is switched so that the “Send to Mix” button is not pressed and there are connections to the group output sockets.
There are other ways to achieve this result, for instance using a auxiliary-send (containing only the “ambient” channels), a direct-out socket if there is only one microphone or even a separate small mixer, especially if you have limited channels available on the main one.

So now you have four wires and you need to generate the right signals for your various destinations. When we first installed our system I built a custom distribution box using mixer modules and line drivers from a range of modular units sold by Maplin. This got to be less than reliable due to my poor construction skills and we had to find a better solution. When it became critical I discovered the perfect solution by browsing around the shops and internet—the Citronic Z-5DM. It is small, in a 1U rack mount, very good quality not disturbing the signals at a critical stage, versatile and modestly priced. It is intended for background music in bars and hotels where two different stereo sound sources are required in up to five different areas but there is no harm in employing it for a different purpose. There may be other brands but I haven’t come across any and you may need to go to a specialist supplier to get one. There are similar devices called matrix-mixers which offer multiple inputs and outputs but these are often too complex and quite expensive.

The way it is connected is to take your main desk output, left and right, into the Line 1 inputs and the secondary “ambient” mix, left and right (or split from a single output), into the Line 2 inputs. You can then adjust the level of these for each of the five zone outputs independently, select stereo or mono for each and connect to your outboard equipment and amplifiers as required. The outputs will work balanced or unbalanced as required and, as each one is driven separately at low impedance, the loading from one amplifier will not affect the others and the distances can be quite long allowing the use of powered speakers for instance.
A typical arrangement would be

• Zone 1 — Line 1 only, stereo, balanced outputs, to main amplifiers.
• Zone 2 — Line 1 only, two mono, balanced outputs, to powered speakers in the side aisles and transepts.
• Zone 3 — Line 1 and 2, one mono balanced output, to hearing aid loop amplifier. Adjust the relative levels to suit the user’s requirements.
• Zone 4 — Line 1 and 2, one mono balanced output, to 100V line amplifier for distribution to crêche, chapel and other small rooms.
• Zone 5 — Line 1 and 2, stereo unbalanced outputs, to compressor then on to tape and CD recorders. Preset the levels by monitoring the recording.

All the levels can be adjusted from the convenience of the mixing console area without having to touch anything in the amplifier rack, though once they are set they can generally be left alone. I am told that this sort of multiple output facility is now available on some mixing desks but what we have done here is a simple solution which can easily be retrofitted to an existing system.

This, as best as I can determine, is the current position in the UK.

VHF Radio Mics

The licence free (deregulated) frequencies are (MHz)
173·800*, 174·000, 174·200, 174·400, 174·600, 174·800*, 175·000*.
Older equipment may be using the 5 frequency set of
173·800*, 174·100, 174·500, 174·800*, 175·000* which, apart from those that are the same (marked *), can’t be mixed with the current set. I am told that, for reliable operation, you can only use four at once. The extra frequencies are there to avoid local interference problems. The relevant regulation is MPT 1311 which limits the power to 2mw and 180KHz bandwidth.

UHF Radio Mics

The licence free (deregulated) frequencies are (MHz)
Ch13 = 863.100, Ch14 = 863.900, Ch15 = 864.500, Ch16 = 864.900
They are usually switchable to find a free channel and are limited to 10mw and 300KHz bandwidth. Many available microphones for sale and hire also have channels 1 to 12 but these should not really be used without a licence. Despite being higher power and bandwidth than the VHF units, the performance is very similar in practice, but with a stricter “line of sight” requirement. Due to variations in the actual frequencies used, transmitters and receivers from different manufacturers are often not interchangeable.

US Radio Mic Frequencies

Grey imported equipment commonly has frequencies named by U numbers (MHz)
U1 = 801.375, U2 = 801.875, U3 = 803.125, U4 = 803.750, U5 = 804.500, U6 = 805.750.
These should not be used in the UK [unless licensed].

For all I know this may be a well known practice but, as I haven’t seen it elsewhere, I thought it worth publicising for others. It is used for big live concerts but not commonly on smaller systems.

I am talking here about medium sized churches (say 100-300 congregation) with sound systems that have an active operator. In most cases the microphone users can be separated into two distinct groups; the leaders speaking and the worship team singing and playing instruments. Some churches may have a separate system for each group; this often happens when the musicians organise their own PA, but here I am considering an integrated sound system with one mixer.

It struck me that there was a frequent requirement to switch from one section to the other so, for instance, during prayers you would want all the band off to reduce hum and other distracting noises and during singing the minister should be off so that he is not performing a solo. It is inconvenient and error prone to switch/fade all the mics separately so I wanted a way to control them as a group.

Mixers in the middle of the market come in two distinct types; live and studio. In simple terms, live mixers allow the setting of each channel and feeding it to a stereo output pair. Studio mixers have additional features designed for multi-track recording which normally you would think were not needed for a church service but they can be exploited to solve the problem above. How they work is that each input channel has a set of routing buttons to direct the signal either to the main mix or one or more recording tracks (called groups). There are usually four or eight in stereo pairs so there are three or five routing buttons including the main “mix” routing. Further across the desk are a set of group faders, usually in pairs, which control the master output level to each track. You can see from this how a multi-track tape recording is made. The feature that makes it useful for our application is that each group output or pair also has a “send to mix” button which does exactly what it says—sends the group output to the main mix controlled by the master fader(s).

So what we can set up is, for example, all leaders mics routed to groups 1/2 and all musician inputs routed to groups 3/4. Then we can fade up or down each section as a whole using the relevant group faders. The channel levels can all be preset to their optimum and all the operator is doing during the service is fading in the right group at the right time. To make it even easier, all the levels can be set so that the group faders are full up to the stop when live so there is no doubt where it should be positioned. I suggest colour coding the caption on each input to show which group it is routed to with corresponding colour captions on the group faders. You don’t use the group output sockets at all and, although it is possible, it is not helpful to have any channel routed to more than one group at a time or main mix.

In practice we use an 8 track desk and use the four group pairs for

• 1/2 (Blue) Leaders—lectern, pulpit, communion table, clip radio mics etc.
• 3/4 (Red) Band—instruments and solo singers
• 5/6 (Green) Choir
• 7/8 (Yellow) Other—see later
• Direct to Mix (White)—CD, tape player and video inputs

The reason for separating the choir from the band is mostly to do with timing, but also the band section is not required for hymns using the organ. Consider a normal service sequence … reading — song — sermon —: The operator sequence would be …

• During the reading have 1/2 up.
• As the song is announced fade up 3/4 so that it is ready for when the band starts playing
• They play the intro and the choir find their pages and stand up
• Just before the first word, fade up 5/6
• Then fade down 1/2. You could cross fade here with two hands but it is not necessary, there is plenty of time
• During the song you have 3/4 and 5/6 live. The choir/band balance can be fine tuned if necessary on the group faders
• As the song ends, fade up 1/2 to be ready for the minister
• Fade down 5/6 (not too quick, allow for natural resonance)
• Fade down 3/4 when done unless another song is due in which case leave them.

You see the sequence — always “up before down,” so there are always live mics. With practice this becomes second nature and allows for most unexpected things e.g. the minister’s mic is already live if he decides to ask for that last verse again, though if you have a worship leader who talks over the singing then they will need to be on the band group not the leaders one. Even on a recording the fades will seem natural and “up before down” means you never get dead air. While a group is off it can be reconfigured for the next item e.g. cutting the lectern and enabling the pulpit before the sermon.

What doesn’t work with our current desk (SoundCraft Spirit Studio LC 16, quite old now)—relatively minor problems:

• The Aux Returns (reverb and FX) are not routable so stay live direct to mix even when the band group is off sometime giving odd effects. We use a foot pedal “FX cut” to control this but sometimes forget to switch it back on again.
• The group faders are in pairs but for this application you really want them ganged. A single stereo fader would be even easier.
• It is difficult to see quickly which routing buttons are pressed and which are not.
• The channel fold-back Aux Sends are still live even when the group is off which means the band gets the minister’s solo singing even if the congregation don’t. On a previous desk (StudioMaster) we had Post-fade Aux Sends on the groups. This allowed us to fold-back the whole of the leader’s group to the musicians so they could hear what was being said when needed but on the current desk we have to do individual channels. This is mainly a problem with clip radio mics.

I haven’t investigated if other desks have better facilities.

The last group, 7/8, we use for inputs that are not wanted on the main mix at all. The “send to mix” button is not active on those groups and we use the group output sockets. They are channels that are only required for the recording and other destinations. How this is organised will be the subject of another post.

Visual Liturgy, the package published by the Church of England to make the current version of the prayer book available electronically has been branded as spyware by Norton Anti-Virus. One feels sympathetic towards vicars who had their lifeline software disabled automatically, but perhaps it will teach them not to use Norton. I can’t count the number of times I have had to remove it from systems because it caused problems of one sort or another.

In the computing, telecoms and professional audio/video business the 19″ rack is ubiquitous for mounting equipment. This standard, named after the equipment size, came originally from the cabinets used to house telephone switchgear and has resisted metrication largely due to the dominance of the USA in computing. There is however enough slack in the dimensions to allow a fairly crude conversion to metric units though you do come across modules that are a bit “tight” when mixed with others.

The fundamental dimensions are the overall width to the outside edge of the flanges which is 19″ and a height, edge-to-edge, of a multiple of 1¾”. This height is known as 1 unit or 1U so pieces of equipment are specified as, for example, 3U which is 5¼”. The standard actually says that every item (however large) should be 1/32″ shorter to allow for clearance but this can be ignored unless you are manufacturing them.

The flanges (or ears) have holes for bolting to the rack rails and the horizontal distance between centres is 18 5/16″ though the holes are usually drilled oval which allows quite a bit of sideways movement. For a neat effect you should loosen the screws a little after installation align the units before final tightening. The minimum clearance between the rails and other obstructions should be 17 ¾” though some are a very close fit.

The fixings are most commonly M6 cheese-head bolts (in Europe) and corresponding “cage-nuts” inserted into the 3/8″ square cut-outs in the rails. You do sometimes see drilled and tapped rails but this is usually on proprietary racks used by the bigger computer manufacturers. The rails can either be steel or aluminium and it should be noted that they require different cage-nuts to allow for the metal thickness. The bolts are usually steel and plastic washers can be used to protect the finish. If earth isolation is required then nylon bolts (for light equipment) or plastic flange washers are available, but otherwise it is general practice to earth the rails with a strap.

The hole spacing on the rail is complex. Each U has provision for three holes, though the middle one is rarely used. The spacing to the centres from the top or bottom of the unit is ¼”, 7/8″ and 1½”. This means that they are uneven, some being ½” apart and others 5/8″, making it VERY important that units are correctly located in their proper U positions, not offset by one or two holes. To help with this, many rails have a small notch cut out of the edge of the central square hole in each group to identify it. The cage nuts allow a small amount of vertical movement which may be needed when installing fractionally oversize modules.

The smaller equipment (up to 3U) is usually secured by two bolts on each side. 1U and 2U cases usually use the outer hole positions, 3U cases use the inside ones, being 2¼” apart. Larger modules use four or more bolts in various positions (but again, rarely using the central hole of each U.) It is worth noting that when installing equipment, it is the lower screws that should be inserted first and removed last because it is those that “take the weight” and stop the case from twisting, bending the flanges.

Many racks also have back rails to support heavier equipment; there is no standard depth though 31½” is quite common. Equipment that requires front and back mounting often has movable brackets or is dedicated to one brand of rack. Using runners is quite common for large equipment as it allows maintenance without complete removal, though care should be taken to avoid the rack tipping forward.

When installing equipment it is important to read the ventilation requirements. Although it is possible to butt the units up tight together they may cook, so you may need to leave gaps (with blanking plates for neatness). Fan modules are available for situations where a lot of heat needs to be removed.

This standard leaked for a short while onto the domestic audio market in the late 1970’s when it was fashionable to have the flanges even if you had no rack to install them into. This lingers in domestic circles with “full size” components being 430mm wide which potentially could have flanges attached for rack mounting though many of the cases would not be strong enough. They do, however, fit quite neatly onto rack shelves. Semi-pro gear often has rack mount kit options, though beware that they are often overpriced.