Best Practice - What exactly does ‘Acoustic Treatment’ mean?

In the world of AV, the most misinformation and uninformed opinions are about acoustics and ‘acoustic treatment’

So much of what gets specified into a high performance entertainment space is binary. Is it 4K? Tick. Is the screen big enough? Tick. Are there four subwoofers? Tick. Is there acoustic treatment? Tick. Hang on a second though, because none of the above really tells you very much about the performance that will be achieved. And whilst looking at a screen and seeing if it’s big enough is easy, that tick in the ‘Acoustic Treatment’ box really tells you absolutely nothing about the audio performance of the room.

Everything in a space is an ‘acoustic treatment’ because everything in a space has an effect on acoustics regardless of if this effect is intentional or not, or beneficial or not. There is much discussion on The Internet about ‘acoustic panels’. I have no idea what these are. These could be frames covered with acoustically transparent fabric that hide a loudspeaker. These could be panels hung on the wall made from 50mm thick fibreglass covered with fabric designed to deliver some absorption. The description of ‘acoustic panel’ tells you nothing.

In any room used for enjoying entertainment content, the single biggest factor affecting sound quality is the room itself. Given that around 60 to 80% of the total sound power reaching your ears has first bounced off one or more room surfaces, managing those reflections carefully with respect to frequency (are reflections managed across all frequencies), amplitude (how loud are the reflections), and time (how do the reflections decay over time) is critical. Oh, and before you ask, yes electronic digital EQ can help but it’s still the basic physics of the room that dominates the sound.

I can’t within the scope of a short article describe everything about acoustics, the problems inherent in rooms, the solutions, and how to design them. This takes years, well decades really, of studying and experience. I can, however, tell you the number one reason why acoustic treatments can make a room sound worse, rather than better. This happens when people randomly specify ‘Acoustic Panels’. When inexpensive 50mm (or less) fibreglass or foam absorbers are placed all over a space, high and mid range frequency reflections will be absorbed but bass (below around 250Hz) will barely be touched. This will give you a dead (because high and midrange frequency reflections have been over absorbed) and boomy (because bass has hardly been absorbed) room. Not ideal…

There is masses of engineering that should go into acoustical design for rooms. Every room is different - These £299/€299/$299 packages of bits of foam could very well make the room sound WORSE due to the reasons stated above. I have spoken to many people who no longer believe in ‘acoustic treatment’ because they have heard too many ‘treated’ rooms that sounded terrible. I too have had the same experiences. Dead and boomy rooms as the result of just sticking some absorption on the walls without paying attention to any form of engineering. Can 50mm thick panels help? Sure. If used correctly they can help bring the room’s RdT (Reflection decay time) at high and midrange frequencies down to acceptable levels. They will do little to nothing for bass performance though and if too many are used in conjunction with all the other absorbers in a room (carpet, curtains, sofas, rugs, people, furniture etc) the room can quickly become over absorbed at high and mid range frequencies.

Bass is really difficult to absorb in real rooms because -

1. The absorption (impedance) of the room’s structure is really difficult to predict in advance.

2. The modal response (Where the peaks and nulls are at bass frequencies in the room) is really difficult to predict because of the difficulty in predicting the room’s structure impedance to bass.

3. To absorb enough bass to be useful, large surface areas of absorption are needed. if this area of absorption also absorbs high and midrange frequencies (Foam in the corners of rooms. Yuck…) then you may have a problem.

4. Where the bass absorption should go in a room is really difficult to predict in real rooms.

5. Some bass absorption (often called a ‘bass trap’) only works at specific narrow frequency ranges.

The advantages of bass absorption are - 

1. More even bass frequency response across multiple seating positions.

2. The EQ in your processor can work far more effectively at EQ-ing and smoothing the bass frequency response.

3. Bass sounds faster and tighter because bass energy is being absorbed fast rather than being left to reflect around a room. This not a subtle effect.

‘What about absorbing the first reflection’ I hear you ask? This is not a simple question, but an extremely complex one. In a 5.1 or 7.1 system with LCR speakers that are well behaved off-axis (If a speaker manufacturer publishes its off axis data in the form of a spinorama or polar response plot, you can learn a LOT about how the speaker will behave in a given space) then arguably leaving the first lateral (side) reflections largely unabsorbed will give the impression of a wider soundstage. Again, this needs to be an engineering decision based upon objective data. Not an ‘I read it on The Internet once’ decision. The upcoming CEDIA RP22 recommended Practice for Multichannel Audio Room Design will for the first time recommend target acoustics metrics including how linear RdT (measured as an RT60 number) should be. This will change the conversation from Internet chat nonsense conjecture, to objective engineering.

So far, i’ve made the argument that - 

1. The phrase ‘Acoustic Panel’ is meaningless without more information and context

2. 50mm foam or fibreglass is great at absorbing high and mid range frequencies, but will do little for bass

3. Putting too much high and midrange frequency absorption into a space will make it sound dead. Having too little bass absorption will make it sound boomy.

4. EVERY application of any specialist acoustic materials or products requires some deep engineering knowledge, skill and calculation.

5. You shouldn’t necessarily absorb the first lateral reflections

Now let’s answer the question - ‘What exactly is acoustic treatment?’. The answer is ‘any thing or materials within a space that affects the acoustics of that space’. Not very helpful, eh? Sorry, but that’s the reality. This is what to do about it…

Let’s not talk about specifying ‘acoustic treatments’. Let’s start talking about holistic acoustic engineering that takes everything in the room into account and comes up with a broadband (meaning all frequencies including bass down to ~60Hz and even below) strategy to maximise the performance of the room and its installed system. There are many opinions on how this could and should be done. The joke is that if you ask 10 acousticians for a design, you’ll get at least 12 different answers! I can’t talk for the others, but at HTE we take a very unique and holistic approach that combines the interior design, acoustic design, and modular room fit out. We call it Acoustic Interior Design™. We don’t sell ‘acoustic treatment’. We design and sell complete room systems that combine the interior design, and acoustics. If you come to us wanting to buy some ‘acoustic panels’ to randomly hang on the wall then sorry, you’ve come to the wrong place. If you want the best possible sounding and best possible looking room then let’s talk. Our system and its included technologies is completely unique in the industry. Our rooms sound and feel fresh - The kind place you just want to kick back in and read a book. Our absorption is really linear from high frequencies down to low bass. They are the least dead and boomy rooms you’ll ever experience as our approach to low frequency absorption is totally unique, and extremely predictable in real rooms. The results we get at industry shows, where most years our rooms win ‘Best of show’ awards both for their sound quality, and design, are testament to the results we predictably deliver in the real world.

So, when someone says ‘Acoustic panel’ to you, answer with ‘what exactly do you mean by that?