AV RoomService just sent out our Acoustic Tips Newsletter Vol.6 Issue 3.

Check out my Re-issue Review of The Band's "Music From Big Pink" at http://ping.fm/deHY5

Pros & Cons of the Music Business (Part I)

Lacking Credit Information

  One of my favorite pass-times has been visiting record stores to see what new discovery might be waiting for me there. I would pour over the jacket credits of unfamiliar contenders looking for familiar, creditable contributors. I might recognize the producer, engineer, studio musicians, etc. If my curiosity matched my confidence and available cash, I'd buy it, take it home, listen to it and learn what and who I did or did not like about it. This would inevitably lead me back to the record store with an expanded appetite for more. A snowball effect.

  Gone are those days. Our search for music now is via the internet. Sure, we can check out short, low-res samples if we find something, but how do we find something in the first place? Who produced it? Who recorded it? Who even plays on it?  Those artists deserve credit and if I saw it, I'd be more inclined to buy it (or not). This lack of credit information has cut my risk-taking down to almost zero.

   The online shopping experience is lacking and overwhelming. And posting reviews by end-users with opinions that are all over the place is a waste. How do you go about finding something new? These days I tend to rely on my friends who I can gauge, and who can gauge me. I'll check out Pandora Radio, etc. to try to find new artists that match my tastes, and this technique has certainly opened a few doors, but it is very inefficient compared to rifling through record bins checking credits.

   I find it incredible that in this age of instant electronic information, the whining record companies are missing out on such a huge sales opportunity. Why are we forced to play a white elephant game? Intrigue me by telling me what is in the package. Give me some background. Get me involved in the music and the artist. Tell me about the recording venue, the approach, the equipment, the instruments, etc. Teach me so that I may become a connoisseur and share it with my friends. Include anecdotal information like; "this song incorporates the new...", or "Steve Gadd was called in to record the incredible drum part for the title track "Aja" and laid it down in one take, without a rehearsal". Create some "buzz". Information is going to be the first step towards enticing me to purchase new music and currently the record industry is lacking this key component.

Symmetrical vs. Non-symmetrical Layouts

“Symmetrical vs. Non-symmetrical Layouts”

Audio has been a serious part of my life for more than 40 years. Having said that, never in my experience has the notion of non-symmetry in audio layout been regarded as a good thing. However, I see it being done frequently these days. Open most any magazine about home theater and you'll see pictures of layouts without a seat centered between the speakers. Where is "the money seat"?  Sadly, there can only be one designated location where all the speakers can converge at the same space, at the same time, and at the same amplitude. To have two seats flank the spot where all the magic lives means a large investment is not paying off to its full potential. Sure, you can adjust levels and delays electronically to any location, but it will still be severely skewed acoustically between left and right if it is not centered in the room. The design hierarchy must be: set-up, calibration, acoustics, and equipment. Even a stereo boom box can't be perceived as stereo unless your head is oriented correctly in front of it.

I have also been seeing dedicated listening rooms where the both the speaker and listener positions are deliberately positioned off-center of the side walls. This is very odd! Why would someone design such a layout? It turns out that the idea is to avoid the width axial room modes. Sounds like a great idea until you realize that even with a relatively small theater width of 16 feet, the f1 axial mode cancellation is 35.3Hz., which means:

a) This frequency is the fifth note up from the bottom of a piano, so except for keyboards, it is not likely that a soundtrack will play 35.3Hz. long enough to cause much of a standing wave issue. 

b) This wave is 32 feet long.  You may ask how far off-center you'll have to move to be out of the cancelled wave? You'll have to shift about 3' to gain only about 5dB. And what about f2, which is a crest at 70Hz. and f3, which is another trough at 105Hz.? And what about the length and height axial modes? Well, room modes are most everywhere, and as you move out of one, you likely move into another. In addition, they become more plentiful as you move towards a boundary.

c) If we also move the speakers, aren't we likely to exasperate the room modes? Yes. 

d) If we move ourselves and the speakers closer to one side, aren't we likely to perceive a difference in low frequency pressure between right and left? Yes, and also hear differences in timbre, spatial ques, imaging, etc. all due to boundary effects. If we were to measure the same signal being fed from both L and R speakers at the skewed listening position, they would be very different. And no, a digital signal processor ain't gonna fix it.

It is true that we want to avoid placing ourselves and the speakers in areas that will exacerbate room modes. It is also true that in an enclosed space, we must make many compromises. The best choice for speaker/listener positions are to avoid the fundamental height and length modes and sacrifice the width. This has to do with human perception and the fact that by design, we are much more sensitive to the horizontal plane than we are to the median or lateral planes. I'll sacrifice a few rare low frequency irregularities for constant linear mid and high frequency tonal balance, and accurate soundstage and imaging any day.

Lastly, a rectangular room is more predictable and easier to treat acoustically because of symmetry. Irregularly shaped rooms are difficult to computer model, and difficult to control acoustically. Symmetry in audio is always a good thing.

Reissue Review of Fleetwood Mac "Tusk" at http://ping.fm/xCusX

How Important are Doors in Cinema Design?

"How Important are Doors in Home Cinema Design?"

By Harry Alter

An example: Your client has requested that his new home theater not disturb the rest of the household during viewing. The walls to the theater are designed to achieve an impressive Sound Transmission Class (STC) performance rating of 65. The entrance door to the theater is solid oak with full perimeter gasketing. Everything should be great, but it isn't...you've got a problem, a BIG PROBLEM. Your client can hear every word coming from the cinema while he's in the study a couple of doors down the hall. What happened?

Many things can determine the overall performance of a theater, and doors are a common problem. Many people think that by increasing the wall's performance, it will overcome any inadequacy of the door. Not true. In fact, you could continue to increase the wall's STC performance far beyond its acoustical rating and it would have no effect on the outcome. A standard solid oak door with perimeter seals has an STC rating of 25. As a result, the overall composite wall performance on this example is now only a STC-34. That's the same as a regular 2x4 stud wall with no insulation. An expensive theater just became more expensive to fix.

AV RoomService provides full service noise control design recommendations to not only increase the cinema's performance, but to assure every aspect of you client's noise control concerns are addressed early in the deign stages...not later.

Sound Quality & Room Modeling

What is room modeling and why is it important to sound quality you ask? A/V RoomService provides modeling for door & window systems, projector silencers, fabrics, risers, etc. but in this edition we'll cover; room dimensions, speaker/listener locations, 1st order reflections, screen size & location, reverberation control, HVAC, wall, ceiling and floor systems. This is a huge topic, so we'll only look at each of these in brief to answer what they are and why they're so important.

Room Dimensions
AVRS uses our own proprietary software program to look at five criteria to determine optimum low frequency mode distribution and how they relate to human perception. These dimensions are based on available space, noise control issues and budgetary constraints. The results are linear bass response and knowledge of what and where standing waves will live in the room so that they can be addressed with acoustic treatments.

Speaker/listener Locations
Once the room dimensions have been determined, we use another proprietary software program to determine optimal speaker and listener locations. This program again takes into account room modes for linear bass response, boundary effects for tonal purity and geometry for a large, solid, holographic sound field.

First Order Reflections
Once the room dimensions and speaker/listener locations are known, first order reflections can be calculated for each speaker on each surface. Acoustic treatments will be needed at these locations to absorb or diffuse these reflections that would otherwise distort spatial cues and tonality.

Screen Size & Location
After determining the optimum location of the speakers and listeners, it is possible to determine the best location for the screen so that the picture and sound is cohesive. Once this is determined, screen size can be calculated for viewing distance acuity. This information will help determine projector model and screen type.

Reverberation Control
Another AVRS proprietary program is used to plug in the noise reduction co-efficients of all construction materials and furnishings that make up the room. We then start adding needed acoustic treatments for wave acoustics (low frequencies) and ray acoustics (1st order reflections) to see what is needed to control the reverberation window across the audible range to between 0.25 and 0.35. The result is a fast, articulate and natural sounding room.

A few notes:
AVRS has a compendium of tens of thousands of noise reduction co-efficients, many of which are exclusively our own, such as; book cases, sofas, perforated screens, etc.

We look at reverberation times across the entire audible spectrum. Typically a single reverberation time is given for a room, which is meaningless. We find most rooms that have been acoustically treated without engineering to be too dead in the mid and upper frequencies and too live in the low frequencies. Such rooms are usually over treated with a single type of treatment that absorbs mid and high frequencies only.

The Frequency Response Panel system (FRP) incorporates seven panels to address specific bandwidths for absorption, reflection and diffusion, is effective down to 63 Hz. and is layout engineered for panel type, location and quantity. The FRP system is the only system to allow such control over such a wide bandwidth. In addition, a stretch fabric system covers the entire treated area, masking any visible hint of acoustic panels in the room.

HVAC
Have you ever been immersed in a movie only to be suddenly pulled back to reality because the HVAC turns on or off? Using proven formulas, AVRS can engineer air exchange volumes, air velocity, air flow rates, duct size & type, number & location of bends, number, size & location of registers, plenum silencers, damper locations, and Btu for an HVAC system designed to be comfortable and silent.

Wall, Ceiling & Floor Systems
In order to experience full dynamics and low level resolution, the shell of the cinema must well isolated from outside noises. In addition, the cinema must not be a noise polluter to those not in it. What a waste it is to invest in a home theater that cannot be used when the kids are in bed. AVRS models shell systems to meet the physical and budgetary constraints while incorporating a proper balance of mass/spring for good isolation and sound quality. Too much or too little mass and the room becomes slow and boomy. Engineered shell systems mean fast and articulate low end, high resolution and wide dynamic response without distractions to or from the outside.

I hope that this post has helped you to better understand the importance of room acoustics and its role in the end experience.