Coordinating Construction Trades to Optimize Noise Control

Coordinating Construction Trades to Optimize Noise Control

By Harry Alter & Norman Varney

  You've spared no expense to make sure your state-of-the-art studio or home cinema is designed to offer the most realistic experience. Ceiling, walls, doors and floor systems have been designed to achieve a minimum STC (Sound Transmission Class) performance rating of 60 and IIC (Impact Isolation Class) of 55. HVAC ducts were designed to make sure ambient noise levels within the room are quiet to an NC (Noise Criteria) rating of 20. You've crossed your T's and dotted your I's, there's nothing left to do... Right?  Wrong! The fun is just about to begin because what happens in the field will determine whether all your hard design work will pay off.

  Planning to reduce potential field problems before they happen is your key to success. So what more do you plan for? First, plan for flanking noise and second, plan for the trades in the field to work as they usually work. That means that if you want the various trades in the field to work together and do what needs to be done, you must provide clear and concise information and instructions (both visually and verbally) to help them through what will probably be a new and atypical construction process for them. It is important that all the trades are on the same page and understand what the goal is. Express to them how important their skill and care is in accomplishing the goal. Ask them to review the scope of work in advance and to ask any questions or concerns ASAP. 

  A few examples of how field conditions can affect a room's final noise performance level:

1.  Poor caulking around the frame of an acoustical door, or along gaps at the floor plate can cut a high STC door or wall system in half.
2. If a high STC wall assembly is built over an OSB or plywood subfloor, the performance level of the wall will (as a result of flanking noise) typically never achieve an STC rating above 50.
3. The improper installation of plumbing lines through wall studs and ceiling joists can take the room's ambient noise level from a quiet NC 20 to a distracting NC 40.
4. The direction of floor joists relative to a partition wall beneath it will affect the amount of airborne and impact noise flanking through the floor assembly to adjacent rooms. 
5. Lined duct runs alone don't assure a quiet environment. Typical HVAC installations can be very noisy even with lined duct runs.
6. Using heavy floor toppings such as gypsum-concrete can dramatically increase the STC (airborne) performance of a floor system, but can dramatically decrease the IIC (impact; footfall) performance when not properly addressed for noise control.
7. The fanciest electrical system cannot deliver instantaneous and continuous current, and will be susceptible to noise, if there are any connections along the path that are not clean and tight.  

  It is attention to detail that you must rely on from each of the trades in order achieve the invested potential. Dynamic range and low-level resolution are only as good as the noise floor allows.  Give the construction trades good information and they can give you the desired results. 

Norman just posted a rant called "The Pros & Cons of the Music Business (Part II) Quality Content at http://ping.fm/gwpa7

Pros & Cons of the Music Business (Part II)

Pros & Cons of the Music Business (Part II)
Quality Content

Record companies say CD sales are down this year another 15%- down 50% since 2000.  I think there are two primary reasons for this; today's music to too cheap and CD's are too expensive. 

Cheap content and cheap quality 
Not considering rap ('cause it's not worth considering), you wouldn't believe how many pop recordings today are entirely, or almost entirely, "built" with programed samples, loops and plug-ins. They contain no interesting nuances, no personalities, no real life. The stuff pushed by the record companies today is of such simplicity it's insulting. It's no wonder most of the music produced today is discarded tomorrow. 

Today's big record companies are not like they were in the 60's. The lack of  talent, along with a structured environment that supports the growth and development of artists, are why we have such a homogenized top 50 offering today. I looked at Billboard's top 50 for the week and found 3 artists who I think have been making music for about 10 years, 42 we will likely not hear from again after two years, but most interesting is that there are 5 artists in the top 50 who have been making the charts since the 60's. What does that say about the record companies today and their commitment?

 The world population has more than doubled since 1960. No doubt there is more talent available today than there was in the 60's. With twice the talent, twice the consumers, and many times better means of distribution, what would be the reason for declined sales? The problem lies with the record company's desire to get in, get out, and move on. It's a "drive-through" mentality.  
 

People will eat fast-food, not for the enjoyment of the palette, but as a quick filler for the stomach. However, most would select filet mignon over hamburger when given the choice. There is more to it. More smells, flavors and textures, more intrigue and complexity. A bit more left brain fun. The general population would certainly develop more sophisticated tastes in music if given the opportunity, but for now, the record companies are in the fast-food business. They don't like risk and they don't have patience. They like repeating simple, proven recipes that include cliche's, which help to mask the cheapness, much like salt and sugar does for a Big Mac. Forget about interesting melodies, rhythms, harmonies, tones, not to mention humans expressing themselves with physical instruments.

Add to this the high cost of a CD (which may only have two songs that you really want). Why are they marked up so high when recording studio rates are the same as they were in the mid '80s (yet their overhead is certainly not) and they cost so little to manufacture? No wonder people prefer to download singles. It takes the place of 45's. CD's costs the consumer the same whether it was cheap to produce, or expensive. We have better quality, low cost electronic instruments that did not exist in the 60's. We also have an amazingly affordable digital recording medium available to the masses that have advantages over previous equipment that only companies could afford to purchase. This should result in some really great recordings, right? The problem now is lack of training in how to produce, record, mix and master. Where would The Beatles be if it weren't for the likes of George Martin and Geoff Emerick?


And what about the sound quality of the mediums? Well, it's worthy as a separate topic, but suffice to say, MP3 (1/10th the data of standard CD) heard through ear buds is not very inspiring. Yet this is common place among young people today, while they are multi-tasking!

Summary
Generally speaking, the quality of the song writing today is lower, the quality of talent is lower, and the quality of recording process is much lower. Many of the hits today don't even use musicians. Programed music saves a ton of money for the record companies, but at the expense of the soul of the music. We have high quality, extremely affordable digital technologies available to operators who are uneducated regarding best practices.

I believe that if consumers were offered real meat for the same cost as the junk food they are currently being fed, they would discover they like many other foods, which would boost CD sales. People tend to gravitate towards quality, and quality always outlives cheapness.

 

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.