For the techies amongst you, here is an explanation of the process we use in sound file creation.
We have a vast sound effects library of many thousands of sounds at our disposal. These are real recordings and not some digitally created random noise. They are all recorded at 44.1kHz, which is a commonly used sample rate for broadcast audio.
We also are able to record sounds on location to this same high quality using our portable TASCAM stereo recorder.
Once the sound files are loaded onto our audio editing station, we can overlay, or multi-track the sounds, fading seamlessly from one effect to the next. Our mixer is capable of handling up to 99 individual tracks, although for these sound files we rarely use more than eight tracks. Each track is mixed with the others, all tracks having separate control over stereo panning and volume. Even though the Master Blaster is a monaural device, we keep the files in stereo should you which to play them back on another MP3 compatible stereo device.
Once we are happy with the final mix, we create one single master file, typically of around five to ten minutes in length, and export the file to MP3 format, ready to be copied onto your MicroSD card and ready for you to plug into your Master Speaker Unit. As you only have a single file on the Master Blaster at any one time, the sound file will continue to loop until the unit is turned off.
What is porting?
One reason why other sound effects units costing a lot more do not sound half as good as our Master Speaker Units is the manufacturer has concentrated more on the electronics. The speaker, the bit that makes the real difference, is an afterthought. I have seen all manner of weird and not-so-wonderful speakers being mounted in all sorts of odd ways. No wonder they sound so bad!
Speakers are transducers that rely on a space for the diaphragm to move air in order to create sound. So bolting a speaker against, say, a bulkhead of a boat is a recipe for very poor and muffled sound. The speaker in the Master Blaster unit is contained in a tube, giving it a porting ability, and allowing enough air around the unit to produce a precise yet powerful sound.
Applicable to Master Blasters only
As it happens, the old-style Master Blaster unit (the one with the five buttons on the front) and the 2016 model (same size and shape but with only three buttons on the front) are the same diameter as a cardboard toilet roll inner, ie 50mm. So, in true Blue Peter fashion, if you want to not only increase bass performance but also focus the direction of the sound, then stick (with Blu-tack) a toilet roll onto the top of the Master Blaster unit. Experiment with different lengths for differing effects. This is particularly useful for model boats.
If you have the Super Improved unit from 2015 (the little blue one with the controls underneath) this has a smaller diameter, so you will need to cut along the length of the toilet roll and wrap it over itself slightly to reduce its diameter, then stick it back together with tape or glue.
Another thing that you can do is to create a circular cut-out for your model. Once again, the handy toilet roll holder makes a perfect template for this! Or, if you have the smaller Master Blaster, you can use the lid of a WD-40 spray can. After this you can disguise the port hole by using thin wire mesh. This is readily available at Halfords, and it is the kind of stuff that is used to help patch up rust holes in cars' bodywork.