QUICK AND CHEAP WAYS TO FIX THE ROOM – NOT THE MIX…
GUERRILLA ACOUSTICS I CALL IT…
This was originally written with school music departments in mind, but frankly, all the techniques involved will work for anyone!
It’s a fact of life that the majority of spaces used for music recording, listening and mixing are less than perfect. Although the current regulations encourage new build facilities in education to be fit for purpose, they rarely are – and what about the rest? Well there is hope, and in the coming paragraphs I hope to show you how to significantly improve the sound of your room(s) without breaking the budget!
Firstly – a quick lesson in definitions: There are 4 significant issues that affect the usability of a room for sound recording or mixing.
- Isolation: keeping noise in – or out.
- Background noise – whether from the building, surrounding – or students…
- Reverb time: Both High Frequency and Low Frequency.
- Room Shape – the cause of odd noises such as booming low notes and flutter echoes between parallel walls.
Now some of these are simply not addressable without major engineering. Certainly if the library next door complain about your drum lessons then its time to move the department! Isolation works are major construction issues; there is NO quick fix – NO simple stuff you can ‘stick on’ the walls to stop the noise.
However for the rest, there are some simple experiments and tricks that will yield considerable improvements – let’s start with the most common:
Rattle & Roll
Most of the issues to do with intelligibility are caused by High Frequency (HF) reverb – typically above 500hz. If you are attempting critical listening in a reverberant environment chances are that apart from students immediately in front of the speakers the rest are hearing more of the room than the speakers! Solutions however are simple.
- Prove you can improve matters: Hang some borrowed sleeping bags or duvets on the walls or hang them over microphone boom stands set up in a T shape – try to cover at least 1/3 of the wall area – this should radically improve matters and should allow you to demonstrate to whoever holds the purse strings that you need to invest in some sound deadening panels made of sheepswool or rockwool slabs. You can experiment with positioning so you know where best to fix the panels when you buy them – note most foam panels are hard to fix permanently, are easy to damage, and often do not have the smoke/fire rating for an education environment so are not recommended.
- Consider carpet: Hard floors not only reflect noise – they cause it – shuffling feet and chairs are huge distraction. The simple act of laying industrial grade carpet or carpet tiles can help a lot by minimising these noises and also helping reduce the reverb time of the room. However – beware of thinking this means you can use them on the walls! A carpet tile only absorbs sound over a narrow range of frequencies – so the effect of completely carpeting a room can leave mid frequencies unchecked and actually sound worse than an untreated room! Also – if your recording space suffers footfall noise from classes above – simply carpeting the offending space may remove the problem just as effectively as isolating your classroom!
- Work closer: If you can get the speakers and students into the same 1/3 of a room then a lot of the main reverberation effects – especially at lower frequencies – will be in the unused part of the room. This isn’t a permanent fix, but certainly can be used quickly to improve matters when one is required to teach in unsuitable spaces.
Flutter & Boom
Hard parallel walls cause 2 particular problems: Flutter echoes and Low Frequency (LF) bass boom at certain very particular frequencies.
- Flutter can be dealt with in exactly the same way as the HF reverb – by placing soft panels on the walls. The most efficient arrangement is as a checkerboard pattern on each facing wall with one wall being the inverse of the other, i.e. each soft panel facing an untreated bit of wall opposite.
- Boom is caused by what is called the ‘axial modes’ of the room – i.e. the 3 parallel dimensions of a rectangular room each exhibit a note – a bit like an organ pipe. For example 11 feet will give a note of approx 100hz (roughly where all the bass detail in rock music is centred), 22 feet – 50hz etc etc. Sometimes the problem is worsened by dimensions of the room being all the same (cubic) or harmonic multiples of each other (e.g. twice as long as high etc). The bad news is that these cannot be properly removed without reshaping the room, however, once the problem frequencies are known, and the offending dimensions identified, it is possible to build and place specifically tuned bass traps in such a way as to minimise the problems. The measurement of such issues requires the services of a studio acoustician; however the construction and placement of the traps should be well within the capabilities of the average school handyman or woodwork department.
It is now accepted that good schoolroom acoustics are a major contributing factor to the learning experience all through the school – not just in the music department. However – it is in music that the inadequacies of building design are thrown into starkest relief. The government provided guidance to all these requirements in 2003 in Building Regulation BB93 – however this regulation is only a statutory requirement in new build projects, not renovations. The good news however is that all these issues outlined above can be dealt with in the design stage, and frequently the cost of implementing good acoustic design can be barely more than that of ordinary construction.
In the meantime however a little ingenuity and rockwool can go a long way….
Master Handbook of Acoustics, F. Alton Everest, McGraw Hill. ISBN 0-07-136097-2
BB93 is available on paper as ISBN 0 11 271105 7 from the Stationery Office (www.tso.co.uk).
Or can be downloaded free of charge from: www.teachernet.gov.uk/acoustics.
Howard Turner has over 30 years experience in the studio business, and for the last 2 decades, his Studio Wizard Organisation have been at the forefront of the development of effective & affordable designs and solutions for studios. Further information: +447803666789 web: www.studiowizard.com
Edge Studios Drum Room – Showing the use of soft panels and carpet to control room acoustics. www.theedgestudios.co.uk
3d rendering of an education facility – showing non-parallel wall arrangements to minimise flutter and bass resonance, along with floating isolation shells.
The main control room in the finished facility – Bath Spa University Music Lab.