rtsound

It can be a bit difficult to find commercially available speakers which work off DC or batteries, in fact the only one I know of is the Remote Audio Speakeasy, which isn’t easy to get hold of over here, or cheap.

I normally use a dB technologies L80 if I need to use a speaker, although it’s mains powered only- it’s a 35W amp driving 4ohm speakers and loud enough for most situations. Having taken a look inside, the main transformer outputs 23V, and I’d have to use regulators to get that from my battery power.

After a bit of a rummage around drawers I remembered I had a board for a 25W Tripath 2020 Class-D amp (you can get these off ebay for about £20, and they’re rather good) which ran off 12V.

I’ve got a little Yamaha NS10MM centre speaker, which I normally use as a ‘Grot Box’ monitor which I bought from Hard-Off  (yes, it’s called that, and it’s brilliant) in Japan for about £12 (it still has the label).

I soldered together a few connectors, hooked them up to a 12V Li-Ion pack (another cheapo ebay job) and, as I didn’t have a suitable case for the amp, and the speaker is likely to get chipped, put it all in a camera bag:

I also found out my passive DI works backwards, so can send balanced line out to this or hook up a wireless receiver to the bag

Here’s my bag- every sound recordist’s is a bit different and I thought I’d give you a tour:

Mixer

Logically, I’ll start in the middle.  The mixer’s essentially the ‘heart’ of a sound recordist’s kit- with it the recordist can control the level of signals, so that a healthy signal to noise can be maintained but the signal is not distorted.  It also has analogue limiters which will compress the signal during peaks (such as shouting)- this is one of the main differences between mixers built for broadcast and those built for music (in addition to build, powering options and outputs)

Each of the three larger knobs control the level of each signal being sent to the mix, whilst the gain knobs set how much each signal is amplified.  LF cut is a filter which reduces the amount of lower frequencies present in the signal (which can be increased by microphones being placed close to the subject), this can also cut out some noise from the microphone being moved around and wind noise.

It will also power microphones and amplify their signals

Mixer ‘input side’:

Here’s a view from the left hand side of the bag.  Here the inputs are going into the mixer on the left.  The cable at the top goes to the boom microphone, whilst the cables with red and green bands come from a radio microphone receiver.  The thinner red cables provide power and the black cable going into the recorder on the right comes from the mixer’s digital output

Mixer ‘output side’

This particular mixer (Sonosax SX-M32) has ‘direct outputs’, which means each of the amplified microphone signals can be sent out before they are mixed.  This can give post production more options. Here the top cable, with the darker red ring sends a mix to the recorder and the other three send pre-fader direct outputs. The smaller ‘mono out’ usually goes to a radio transmitter, sending out a 1 channel mix.  There are also a couple of other connectors out of view which include one for a sending a 2 channels to a camera and receiving one back so that I can hear what is being recorded to camera, when not using a separate recorder, and a smaller one which sends the mix digitally to the recorder.

Recorder

This is the box at the bottom of the main picture.  Although it is also possible to plug microphones directly into this particular model, the quality and flexibility is not as good as using a separate mixer (there are a few recorders becoming available which can also operate as a mixer).  This one (Edirol R-44) can record 4 channels of audio, as digital .wav files.   Some recorders also have timecode generators which can be synchronised with cameras, making it faster to synchronise video and audio in post production. I also own a 2 channel recorder with timecode facility

Wireless

There are a number of situations where it is impossible, or extremely difficult to capture quality audio without using cables.   Although the most expensive and advanced wireless systems are not as high quality or reliable as a cable, they’re close- and allow microphones to be placed where they couldn’t without wires.

This particular box (Wisycom MCR42) actually has 4 receivers inside, 2 per transmiter- selecting the one with the strongest signal.  It also has emulation modes for other brands of receiver (Sennheiser and Audio Limited) and a very wide bandwidth, making it suitable for international use

Radios can also be used for sending signals, such as an feed to a director, boom operator, script supervisor or camera to aid with sync (or to send a timecode signal).  There’s also a transmitter for this purpose on the right and second receiver on the left (single channel) for a third radio mic.

Powering

Inside the pocket at the back of the bag is the battery and distributor

From here the battery power is split between the mixer, recorder and 2 channel radio  receiver.  Here is the whole bag opened up:

Here you can see the red cables running to the recorder, mixer and radio receiver in the front pouch

I’ve just made a new addition to my self-made power distribution system- a small voltmeter (the display with the numbers on the left, by the recorder).  This allows me to see exactly how much battery power I have left  They’re available from a number of sellers in China on ebay

I just soldered the red and green wires (+ power and voltage reading point) to the positive pin and black to 0V) on my power distribution box and it all works

Here’s the distribution box and battery:

It’s essentially a load of locking DC connectors wired in parallel

I’ve done a comparison of the various models of (reasonably) high end radio microphones available in the UK which will work with DC powering.  As a number of them work with 2 transmitters to 1 receiver, I’ve also made a cost comparison (most competetive I could find, including VAT) of 2 sets and put in the weight of the transmitters.

Transmission systems:

Analogue: Up until recently all radio microphones were analogue.  They use a compander circuit which compressed the audio signal on transmission and expands it in at the receiver.  The circuits need to be compatible on each end to match

Digital Hybrid:  Here a digital signal processor performs the companding (and usually some other fancy noise reduction etc) at both ends, although an analogue signal is transmitted.  They can also program in different compander algorithms, which can mean the receivers can work with other equipment.  The conversion and processing adds some latency (time in ms)

Digital:   With ‘pure’ digital systems, the signal is converted into a digital signal and compressed using a high-speed codec (like mp3 but faster to read/write and maybe better quality) before transmission.  This means they don’t use a compander at all and there are less analogue to digital conversions than with hybrid systems.  They also have a short latency

Diversity:

This effectively means that the receiver has two goes at picking up the signal and picks the strongest, however the point where this happens depends on the receiver design (all receivers here have diversity in some form).  ”True” diversity requires two separate receiver circuits, whereas antenna diversity switches between the signals from the two antennae.  In analogue systems it is often audible when switching between antennae, although I’m not certain with digital systems.  Also only two systems have true diversity in a dual channel receiver (4 receiver circuits), the Wisycom and Audio ltd EN2.

Bandwidth:

Although UK Channel 38, which we’re all supposed to be using next year is only 8MHz from 606-614Mhz, if you’re doing any work abroad or getting site-specific licenses you may have to be more flexible (or if things like ‘white-space’ devices start popping up).  The Wisycom, Sennheiser and  Audio Wireless systems have larger bandwidths (at a cost)

Remote:

Some of the systems have methods of remotely monitoring and/or controlling the receivers, and a number of them require buying a separate add-on or device.  Both digital systems will allow full control of transmitters from the receiver and the Sony system will allow you to name transmitters. The other systems require things like infra-red remote controls (which may not penetrate costume).  The Lectrosonics system uses audio tones through the attached microphone.

Output:

A few of the digital systems will allow digital output to recorders/cameras which have it, which can free up some more channels and reduce conversion processes.  Only the Sony system has word clock, so can be used in multiple instances in a system without sample rate converters.

Notes:

One of the main differences between the Zaxcom system and the others is that it can do some things which would require additional hardware.  The transmitters also act as 2.4GHz receivers so talkback and timecode transmission can be used with them if the receiver has the IFB option (or from a Zaxcom recorder).  Finally, some of the transmitters have recording facilities (for backup purposes) and will transmit in stereo (but EU law doesn’t allow for the wider bandwidth).

Also, finally- if you are buying radio mics in the UK, make sure they’re Channel 38 compatible (606-614MHz), the current band, Channel 69 (854-863MHz) is probably going to be sold to mobile phone companies after the olympics.  Also the (otherwise lovely looking) Lectrosonics D4 isn’t available here as it uses a current GSM mobile band, so it won’t work.

I’m really excited about a job I’ve got coming up, I’m off to France for a week to follow Team Strakka around for the Le Mans 24 hour.  Not only is it going to be taxing on me, especially for the race- but also for powering my kit.  So far I’ve managed to get by on AA batteries (bulk bought duracell procell from ebay or Kingsland waste market in Dalston), but it’s really not going to be practical for a week.

First of all I’ve found a way of getting a bit more from the AA’s- you can buy chargers which will get a few more goes out of alkaline batteries.  I’ve just had a couple of these arrive and they’ve got some of the spent batteries in them at the moment.  Both the mixer and recorder seem to give up when they get down to around 1.3V.  They’ll still be useful for the radio mics and as a backup.

For a while I’ve used a cheapo chinese Li-Ion 12v battery “6800mAh” designed for CCTV (with a polarity reverse cable) which’ll get a couple of hours out of the recorder. I think the 6800mAh quoted might be for something like 5V though (or just lies).  The connector is jut a 2.1mm barrel connector though so I really don’t trust it.

From having a look at what was available my choices were:

7.2V DVcam batteries- small, long lasting (although the equipment may drain more at a lower voltage, depending on the regulator), locking connector. Reasonable price

9V/12V consumer DVD player/CCTV batteries.  Cheap. Non Locking connector

Professional 14.4V NP1/V lock/gold mount etc. Big. Locking connectors.  Expensive

Unfortunately 7.2V wasn’t enough to power my recorder (even though it only gets 6V on AA’s), so that was out.  The consumer stuff would involve risky connectors and look cheap so I’ll see if I can do pro stuff.

I also found a full length NP1 doesn’t fit in my bag (I’ve got a couple of old ones).  The V-lock batteries etc were even more expensive and wider so that may not have been an option either.

Fortunately Hawk-Woods make a ‘Stubby’ NP1 style battery, the NP35 which will fit.  Shopped round a bit and got them for £70 each.  However they’re Li-Ion and my (broken) NP1 charger only recharges Ni-Cd and NIMH.

So, new charger.  They can get really expensive (up to £700…and they just recharge batteries?!?). Got a no-name chinese one off ebay (*hope it works*) for £80 which will recharge 4 batteries after just missing out on a 2nd hand PAG.

Finally to hook it up to my kit.  I’ve just bought a Hawk-woods NP1  shoe (rather than the full regulated distro) and I’m going to sort out a custom cable for it.