Part 2 : A close-up "under the hood" look of what makes it work so well !
In our article yesterday about Anagram Acoustics' showroom, you may say that all this looks very good on the outside, but for those of you who really want to dig into and understand the details of what makes this auditorium work, we think it deserves a more in-depth approach with a fuller description of the techniques and equipment involved .
The design and construction of this auditorium has been described step by step in Patrice Congard's series of articles "Un auditorium zero mode", in the ten sections of "Un Home Cinema de A à Z" (which will soon be available here in English). The cooperation between Patrice and the Anagramme company has now gone one step further, as Patrice has joined Anagramme to develop the consumer "Home Theater" activity.
The first step in this project was the global approach for the design of the volumes defining the room itself. It has been achieved in cooperation with Bruno Soudan, acoustical engineer, and Jean Pierre Charrier, Design manager of Anagramme.
From a concept they have elaborated together, they have defined a model on the Architecte 3D program, which provides a general presentation in 3D, with a realistic positioning of the volumes, the furniture and various elements to be installed in the room. Corresponding data (positions, dimensions) was then fed together with the acoustic characteristics of each of the elements (absorption, scattering) into the simulation software E.A.S.E.
View of the simulated auditorium as a project
Transferring the results back and forth with step-by-step corrections from one software to the other has led to the design of a complete virtual room with known acoustical behaviour. At the same time, Jean Pierre designed the room decoration to create a whole coherent concept including the acoustical design.
The initial acoustical design is based upon rather innovative and what might be considered as radical ideas, which were feasible in the present case as nothing existed at the start, not even the walls. In practice, of course, the existing physical constraints if each individual client's room can be handled by the designer who can find solutions using this same method and approach.
These concepts are expressed as design criteria, including :
Total absence of room modes, echoes, reverberations or the like Absence of early reflections, delayed by less than 10 milliseconds with respect to the first wavefronts emitted from the 3 front (LCR) loudspeakers (Note: this criterion is typically used in the design of LeDe control rooms design for recording studios)Purely acoustical, fundamental electroacoustic criteria were imposed :
Cinema type surround layout Location of the 3 front loudspeakers behind the projection screen (acoustically transparent), for total coherence between the sound and the image Active digital crossover for the front loudspeakers, including precise delay adjustments (allowing a precise tuning of the lip-sync).Finally, the idea to have a rather pleasant, yet "standard" type of decoration, and when added to the above technical criteria, globally sets the guidelines and defines the aspect of the room. The project was now on the move to making the decision as to what components would be used to optimize budget and performance.
The loudspeakers needed to be of the "In-Wall" type to satisfy the initial criterion above, and provide for bi-amped active crossover for the 3 front ones. Looking for excellent quality (why not !) they have been designed and manufactured by AcoustiCraft based on Anagramme's specifications.
The selected digital crossover is the Behringer DCX 2496, (24 bit, 96 kHz for these who know) which has the advantage of offering three inputs and six outputs, exactly the required configuration for bi-amping 3 channels.
Other crossovers are available, offering similar features and equivalent performance, but they are much higher in price, and would have really exploded the intended budget. All crossover adjustments have been made on site by Patrice Congard using a Clio 6.5 measurement system.
The speakers perform through the acoustically transparent screen by Screen Excellence, fixed-frame, velour-finished, 240 cm (7.9 feet) width, 1.78 aspect ratio).
Beyond the impressive range of possible and easy access adjustments, another advantage offered by the digital crossover is the fine tuning of the lip-sync.
In practice, any videopojector delays the video signal by at least half an image (be it an interlaced or a progressive frame) for processing it. This delay is then 20 milliseconds in PAL and 17 milliseconds in NTSC. To this, one should add the difference in time for a sound wave to travel from the screen to the centre of the audience in a cinema (about 45 to 65 feet) and in a home cinema (about 12 to 16 feet).
Most "reasonable" AV processors provide an adjustable input delay, but the adjustment is by steps of, for instance, 20 milliseconds… This is not fine tuning!
Having set the input delay at 20 milliseconds on the A/V processor, we have finely tuned the lip-sync of the front channels to 18 milliseconds on the crossover.
Beware, if you undertake this kind of adjustment: some film directors (in particular, Luc Besson) deliberately delay the image or the sound by one image (42 ms.) to create a specific effect, a sort of "signature"! So, you have to be certain of the movie you are using for the set-up.
The surround sound
We have made the choice to stick as much as possible to the public cinema technologies. This leads to using many unipolar surround loudspeakers placed in a position significantly higher than that of the audience. Such unipolar speakers, fortunately, are much easier to integrate in a wall than any dipole type of speaker.
6 AcoustiCraft Rear One loudspeakers have been used according to the following layout:
Two loudspeakers on each side, with inverted polarity, reproducing the rear left and right channels. Two centre rear loudspeakers installed inside the Shroeder scattering wall, connected with the same polarity, reproducing the rear centre channelAs there is no digital crossover on these passive loudspeakers, adjusting the delay can only be done with the A/V processor. To compensate for the added 18 ms delay on the front channels, the distance has been set to minimum (11.7 inches) on the surround channels and significantly larger than real on the front and sub channels. As the processor performs the inverse compensation by adjusting the delays… we get what we want !
All the surround loudspeakers have been placed at a height of 7.4 feet from the floor.
The subwoofers
There are two subwoofers. Only one is handling the LFE channel, the other one extending the bandwidth of the 3 front loudspeakers (in "LARGE" configuration). This avoids the mixing of the low frequency content of the 3 front channel with the LFE channel (performed by the Bass Management in the A/V processor if the front channels are set in "SMALL"). Such a mix tends to blurr the bass reproduction, which is obviously not desirable if it can be avoided.
This implies either to have front loudspeakers having a well extended bass response (with sufficient power handling) or to use two subwoofers, which is our choice because of the limited range In-Wall main loudspeakers.
The two subwoofers are the AcoustiCraft Solo type, fed by a B&K OMP 1000 amplifier (550 W into 8 Ohms) via a QSC DSP3 2 channel digital crossover module. These channels are delayed to be in phase with the main loudspeakers after the lip-sync adjustment.
All components in the system (see list yesterday's article) have been selected for their excellent quality/price ratio, provided they were up to the stringent required standards we set at the outset of delivering film-like video and the best cinema sound.
The total budget, although on the high side, remains a realistic figure of 25,000 £, including design, simulations, components and installation.
Installation diagram :
If this is a bit complicated or you want to take another look at the final results, click here for the first article where you will also find a full list of all of the components.
>>> Take a Virtual Tour in 360° photography of the Anagram Acoustics auditorium <<<
For further information or to book an appointment :
Anagram Acoustics
Patrice Congard
Tel : +33 (0)1 43 00 53 40 / +33 (0)1 41 00 19 50
Fax : +33 (0)1 41 54 19 59
E-mail : patrice.congard@anagramme.fr
Articles by Patrice Congard in French that explain step-by-step the conception, design, construction and selection of components for the auditorium :
Un Home Theater de A à Z PRO Partie 1 : La construction d'un auditorium show-room Un Home Theater de A à Z PRO Partie 2 : Comment choisir et Bien aménager la pièce Un Home Theater de A à Z PRO Partie 3 : L'étude acoustique d'un auditorium show-room Un Home Theater de A à Z PRO Partie 4 : Les achats Un Home Theater de A à Z PRO Partie 5 : Conception, réalisation et installation d'un ensemble d'enceintes acoustiques Un Home Theater de A à Z GENERAL Partie 1 : Introduction Un Home Theater de A à Z GENERAL Partie 2 : Comment choisir et Bien aménager la pièce Un Home Theater de A à Z GENERAL Partie 3 : Le câblage Un Home Theater de A à Z GENERAL Partie 4 : L'équipement Un Home Theater de A à Z GENERAL Partie 5 : Les enceintes acoustiquesFor a humoristic learning experience (Home Theater doesn't work - how to make it work) :
-Pourquoi le Home Cinema ça ne marche pas Partie 1 -Pourquoi le Home Cinema ça ne marche pas Partie 2 -Pourquoi le Home Cinema ça ne marche pas Partie 3 -Pourquoi le Home Cinema ça ne marche pas Partie 4 -Pourquoi le Home Cinema ça ne marche pas Partie 5 -Pourquoi le Home Cinema ça ne marche pas Partie 6 -Pourquoi le Home Cinema ça ne marche pas Partie 7