Room Acoustics – Live End Dead End ExplainedChristoph Thiers
Whether it’s a home hi-fi room or a professional recording studio; the goal is to create a listening environment that’s as neutral as possible; this way, the sound you hear has as much in common with the signal source as possible. But how do you achieve this neutral sound reproduction?
It is obvious that the loudspeaker itself plays a decisive role in this, so people are happy to spend some serious money on that behalf. However, what is often disregarded is the fact that the room acoustics have at least as great an influence on the sound! In other words: with bad acoustics, even the best loudspeaker has no chance! Setup, room symmetry, initial reflections, reverberation times, frequency response etc. have an elementary and often highly underrated influence on the listening experience. Newcomers to the subject of room acoustics usually find it difficult to correctly assess these influences, because poor room acoustics rarely have anything to do with perceptible reverberation tails. Fortunately, there is a simple way to achieve good-sounding room acoustics that has already proven itself in thousands of rooms: Live End Dead End, or LEDE for short. Here’s how LEDE works and how you can easily apply the acoustic concept to your own room.
Absorbers in the front, diffusors in the back?
The LEDE principle is rather simple: the front half of the room is designed to be acoustically “dead”, while the back half is kept “alive.” “Dead” is the name given to a room that absorbs sound in a wide frequency range. “Alive” is the exact opposite: a room that is designed with sound-reflecting surfaces and thus gives a variety of acoustic responses to a sound event. So, when setting up a listening environment or control room, the side where the speakers are is fitted with sound absorbers to minimize reflections. The opposite side (in the back of the listener) tends to be fitted with sound-reflecting surfaces designed to distribute sound waves in different directions – this is known as diffusion.
Room acoustic in the studio
How do room acoustics benefit from the LEDE principle? Let’s take a look at the objective of our project: we want to hear exactly what’s coming out of our speakers – no more and no less. Wouldn’t the most obvious thing then be completely anechoic room acoustics? Not quite. The sense of hearing represents an important orientation tool for the human organism, and the absence of acoustic reflections has an unpleasant and disorienting effect. In addition, we want a certain comparability, and since the rest of the world is not sitting in an anechoic chamber either, the completely absorptive approach is not promising (and would also be very costly to implement). However, acoustic participation “from behind” is also desirable to enable a stronger feeling of envelopment. After all, when music is heard live, reflections behind us also play a certain role in our perception. This is achieved with a stereo speaker setup by creating a reflection pattern that is as neutral (i.e., “diffuse”) as possible in the live end. So, it is not a matter of eliminating the influence of room acoustics in total, but only of coloring the direct sound from the loudspeakers as little as possible, thus creating a listening environment that is as pleasant and balanced as possible.
The biggest enemy of a clean, direct sound wave are close reflective surfaces. Through them, the sound from the loudspeaker not only hits our ears in a direct way, but also takes a detour via the reflecting surface, e.g. via the tabletop, the floor, the ceiling or nearby walls. The superposition of two (nearly) identical, time-delayed sound waves always leads to dips in the frequency response and to a strong sound alienation, the so-called comb filter effect. Close reflections therefore do not produce a beautiful reverberation as known from concert halls and churches, but a potentially strong alteration of the direct signal. Engineers and musicians are also familiar with the comb filter effect from effect devices such as the phaser or flanger, where it is used for creative sound design.
The more similar the level and frequency response of the two time-shifted signals and the shorter the delay, the more intense the coloration. Thus, the closer the reflection surface, the worse the effects on the direct sound. The first reflective surfaces near the loudspeakers and the listening position should therefore always be absorptive if possible.
However, the comb filter effect is not the only problem caused by near surfaces. In addition to the negative influence on the frequency response, stereo localization and depth detection also suffer, for example. The LEDE principle is therefore based on achieving the largest possible time gap between direct sound and reflection to avoid all these negative effects.
The rear part of the room, on the other hand, which has the largest distance to the loudspeakers, may be more reflective because in most rooms, the direct sound has found its way to the ear of the listener before any considerable reflection is to be expected from behind. However, one would also like to avoid bare walls and similar sound-hard large surfaces in order to avoid unpleasant flutter echoes and the like. The solution: diffusors! Or in other words: perfect acoustic chaos that distributes the sound in all directions.
Room setup according to Live End Dead End
How do I set up my room according to the LEDE principle? First, you should try to set up your speakers and work station optimally in terms of room symmetry. That basically means: as symmetrical as possible, with sufficient distance to the walls and corners in particular. Whether the listening position (the so-called “sweet spot”) is in the live end or the dead end, depends primarily on the size of your room. According to the original application in the 1970s, the “sweet spot” tends to be in the live end, but nowadays, people usually listen in the dead end. This has to do with aesthetics and listening habits, but mostly with room size. Those who don’t have a large room tend to prefer to sit in the dead end as well, to minimize the influence of lateral reflections. This is the case with most (home) studios these days.
Next, it’s a matter of “killing” the room acoustics in the dead end behind the speakers. This is a job for absorbers – acoustically specialized, porous materials that convert sound energy in the air into motion and heat energy. But you’d better forget about egg cartons and cheap pyramid foam. One is ineffective, the other counterproductive. After all, the crucial thing is not only that sound energy is absorbed, but above all that absorption is as linear as possible in a suitable frequency range. Unfortunately, however, most materials absorb different frequency ranges very unevenly. Some frequencies are absorbed, while others remain unaffected. If you pick the wrong product here, it usually results in heavily damped high frequencies and an uncontrolled mid and bass range! A good and linear effectiveness in the relevant frequency ranges is achieved with professional absorbers from about 8-10 cm thickness, such as the HOFA absorber. If the absorbers are mounted with some distance to the wall/ceiling, they can even be a bit thinner. Thus, HOFA ceiling sails with some distance to the ceiling achieve their high efficiency down to the low mid-range.
By the way: caution is advised regarding furniture and equipment in the dead end. Not only walls and ceiling can influence the direct sound, but also tables, screens, mixing consoles, etc. So in the best case, these reflections are also considered and minimized if possible.
However, the greatest attention in room acoustics is almost always paid to the bass range. This is because low frequencies generally require a higher level of absorption, and most rooms have unpleasant resonances in the bass. Specialized absorbers are needed for acoustic control in the bass range: the bass traps! These have a rather large volume and are made of materials that have a particularly high effectiveness in the low end of the audible frequency range.
Particularly relevant for bass absorption are the corners of the room. The effectiveness of an absorber is at its highest at boundary surfaces, and room corners have 2-3 such boundary surfaces! So: place your bass traps in the corners! And the more, the better. You can already get a positive effect with about 2-3 bass traps in the right spots, but if you want to perfectly control the bass range, you usually need more material. The individual need for absorbers, diffusors and bass traps can be determined by a professional acoustics planning.
As a rule, bass traps are stacked in towers to make the best use of the higher efficiency in the corners of the room. It often makes sense to equip not only the front, but also the rear corners (in the live end) with bass traps.
Now to the live end: diffusion is required here! The rear wall (i.e. at the back of the listening position) may be equipped with diffusors over a large area. If the distance to the listening position is larger, a big 1D diffusor can help, but for the vast majority of rooms 2D diffusors are more effective. These can also be designed point-symmetrically as a QRD arrangement, which not only favors the underlying mathematics, but also preserves symmetry in the room even in acoustic “chaos”.
By the way – even though the LEDE concept is primarily intended for control rooms and listening rooms, it can also be useful in recording situations: voice recordings, for example, can better be realized in the dead end, whereas acoustic string instruments benefit from the lively acoustics of the live end. If a modular system such as the HOFA Frame is used, the room acoustics can even be flexibly adapted to the current use at any time.
By applying simple strategies like the LEDE principle, your room acoustics can be greatly improved with absorbers, diffusors and bass traps in the right places. And of course, if you ever need a more complex acoustic concept, our HOFA acoustics professionals will be happy to assist you and plan your room individually according to your needs and requirements.