Shady Grove Teaches Us The Importance of Distance When Measuring Sound

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A very important concept that’s usually missing from people’s understanding of measuring sound is the necessity to include the distance from the source that the measurement was taken. There is no single sound pressure level (SPL, what people usually mean when they say “decibels” or “decibel level”) for any given sound source; SPL varies considerably with distance.

In this video about the shut-down of Shady Grove, you can see David Scott taking measurements of various sound sources in an effort to put “70 decibels” into perspective.

Without holding his sound level meter in a meaningful location, his measurements are just about worthless. “Our truck exhaust pushed near 80” he says, while holding the meter 3 feet from the tail pipe. If he were to move away another 3 feet from that tailpipe, his sound level meter would read 74 dBA. 6 feet more and it would read 68 dBA. (In general, a doubling of distance from the source means a decrease of 6 dB).

This is why the Austin noise ordinance needs to be changed to be based on sound levels at the receiver, not at the source. Limiting a restaurant with live music to 70 dBA “at the property line” does not take into account the distance from the stage to the nearest sound sensitive receptor, nor does it take into account any noise barriers, such as hills or other buildings, that would help to decrease sound where it is not wanted.

An outside music venue located thousands of feet away from the nearest residence should be able to have much louder music than a venue located across the street from an apartment building. Currently, the ordinance makes no distinction between the two.

An outside music venue with an enclosed stage and sound walls protecting the nearest neighbors should be able to have louder music than a venue with an open stage. Again, the noise ordinance as it stands makes no distinction.

To illustrate the importance of the position of the receiver relative to the source, I’ve used Shady Grove as an example and done some very simple calculations to show how sound pressure levels driven by the same source can be very different depending on distance. The only factor I’ve taken into account here is distance; I’ve neglected any ground effects, atmospheric effects, shielding from buildings, background noise, or diffraction from trees. Including additional effects in the calculations would cause the SPLs to vary even more.

Sound Levels vs Distance

At Shady Grove, the stage is only about 14 feet from the property line. Even though the property line is next to a busy street and the nearest residences are some 150 feet away, sound levels at the stage must be kept low in order to maintain the limit at a point only 14 feet away.

But, by simply moving the stage away from the property line an additional 45 feet (2 doublings of distance), Shady Grove would suddenly be able to turn the music up by 12 dB while still maintaining the property line limits. As a result, the SPL at Meghan Lane would be 9 dB higher.

If the ordinance were receiver based rather than source based, outdoor venues would have a measurable incentive to design their facility with the goal of keeping SPLs at nearby properties within the applicable limits. Sound barriers and speaker directionality could be used to the maximum benefit of the venue and the surrounding community.

Another consideration is that, under the current system, someone can call in a noise complaint from anywhere, regardless of what the noise level at their home is. Since the limits are set only for the property line of the source, the distance between the source and the receiver is irrelevant, as is the actual measurable SPL at the location of the complainant. This is not a fair arrangement.

For Your Convenience: The Austin Noise Ordinance

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I’ve added a set of pages that have what I believe to be the entirety of sections dealing with noise limits from the City of Austin Code of Ordinances. You can access them through the link at the top right of the page.

The Title pages contain entire chapters and sections, copied straight from the code. The summary page contains my best interpretations of each of the line items found throughout the code that deal with noise level limits.

I will try to keep this as updated and accurate as possible with the aim of providing a quicker, easier reference than searching through the full Code of Ordinances.

Take a look at the summary page and I think you’ll agree that our noise ordinance is needlessly complicated. Also, if there’s something I’m missing, please point it out so I can add it. I literally assembled these pages by searching the Code for the terms “decibel” and “noise.” I could very well have missed something.

Getting Up to Speed – Relevant Reading

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Here is a collection of interesting articles and blog entries that can help catch you up on Austin noise issues if you’re just tuning in.

From Austin Contrarian

July 28, 2009 – Stacking the deck

July 12, 2009 – Shady Grove needs a parking variance

June 18, 2009 – Update and clarification on the music ordinance

June 18, 2009 – No finish line

June 16, 2009 – Restaurants and cocktail lounges and the noise ordinance

From Austinella’s Austin

June 22, 2009 – APD vs Music: More to the story

From M1EK’s Bake-Sale of Bile

June 17, 2009 – Connecting some dots

June 16, 2009 – Laura Morrison’s innocent act

June 12, 2009 – Who’s been complaining about the music?

March 16, 2009 – It’s not the condo dwellers complaining about the music

From Austinist

June 12, 2009 – Zombie Noise Ordinance Claims Second Victim

From The Statesman

June 15, 2009 – Council to consider resolution to extend outdoor music permits

April 20, 2009 – Practical solutions to music scene problems: #1 in a series

April 14, 2009 – Freddie’s Place permanently cancels live music performances

From Burnt Orange Report

June 12, 2009 – Unplugged at the Grove Shut Down Due to Noise Complaint

Review of the Live Music Task Force Overview and Recommendations from an Acoustician’s Point of View

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I should have started this blog one year earlier, as the LMTF presented their findings and recommendations back in November. Nevertheless, it can’t do any harm to share my thoughts on the Live Music Task Force Report.

From an acoustics standpoint, the most important section in the report is Sound Enforcement & Control Subcommittee Recommendations. Some of the writing in this section shows a true disconnect from actual, acoustical science. Let’s examine:

1. CITY STAFF POSITION. Creation of a staff (or contract) position within the MD responsible for managing outdoor live music sound control and attenuation.

a. Structure. The individual selected to fill the position should report to the newly created Music Department and should, ostensibly, possess substantial experience and expertise in live music engineering, acoustics, and sound attenuation.

b. Responsibilities:

i. Train and qualify sound engineers working at Austin’s outdoor live music venues;

ii. Work with outdoor venues and neighborhoods to explore ways to attenuate sound;

iii. Establish and implement “sound engineer certification program” which will teach and certify sound engineers employed by outdoor music venues;

At outdoor venues that have had acoustical engineers develop noise control, there is usually a microphone at a strategic location in the venue measuring the sound level, which is displayed on a small readout near the mixer. There is a number written next to that readout representing the maximum allowable sound level and anyone operating the board knows that the number on the readout should not exceed the written number. This does not require special training or qualification.

Assuming the physical orientation of the venue does not change and the microphone has been put into a reasonable location, the relationship between sound levels at the microphone and sound levels at the neighbor’s will not change. An acoustical engineer can spend a few hours determining what the sound level at the microphone should be to prevent excessive sound at the neighbor’s property, and that number is written next to the display. No full time personnel is needed; no special trainers are needed. Just a small contract with an acoustical consultant.

iv. Explore the most appropriate ways to measure music frequencies (as opposed to the current method of measuring decibel levels).

I am very happy to see the LMTF recognizing the difference between music and other noise sources, and understanding that there can be better ways to measure and quantify the loudness of music. However, the language here is cringe inducing. The term “decibel level” has, unfortunately, worked its way into the vernacular. It’s a term that is meaningless without being defined. The term “music frequencies” is also pretty bad.

The most appropriate way to measure “music frequencies,” or any other kind of sound, is with a sound level meter. Modern sound level meters all measure sound divided into frequencies or added into single number metrics such as A-weighted decibels (dBA). dBA is what people generally mean when they say “decibel level.”

There’s no shame in not understanding acoustics. It’s a complicated science and the terminology specific to acoustics doesn’t really come up in daily life. What is unacceptable is producing official documents based on incorrect or nonexistent principles.

2. SOUND ENGINEERS AT OUTDOOR LMVs. Recommend amending the appropriate ordinances to require all outdoor LMVs offering live, outdoor amplified music to utilize (i.e. hire or otherwise arrange for the services of) a city-approved sound engineer. The MD should determine, based on the size of the venue, the PA system, and other relevant factors including residential complaint history, what the standards for sound engineers should be. On a case-by-case basis, the MD may determine that this requirement may be waived. The ordinance should include penalties that require venues to stop music performances if certified engineers are not on site during performances of amplified music at venues where they are required.

Acoustical engineers are already professionally trained, qualified, and equipped to analyze a music venue based on size and sound equipment. We have at least three acoustical engineering firms in Austin. Simple technology that is easily purchased and installed by the right people can perform the same duties as the Sound Engineers proposed by the LMTF. There is no reason to hire and train full time people to accomplish tasks which can be performed as-needed by consultants.

3. CONSTRUCTION STANDARDS, INCENTIVES & BEST PRACTICES.

a. Recommend appropriate City departments and Austin Energy jointly explore and develop construction methods that reduce and improve sound attenuation at outdoor venues.

b. Recommend the City require all future Central Business District (CBD) commercial venues to adhere to enhanced construction methods that include improving acoustical insulation and soundproofing.

These are great ideas and, if implemented, would put Austin in the position of setting a good example. With the new Comprehensive City Plan in the beginning stages, we have an excellent opportunity to incorporate construction standards related to noise into the long-term planning of the city. I support these recommendations 100%.

c. Recommend adding sound control to the density bonus list to entice developers in the CBD to construct in a manner that better insulates residential projects from nearby venues.

Another good idea.

Noise control is most beneficial and cost effective when it is done proactively. Proper building construction and simple space planning are the best ways to control noise. In architectural acoustics there is a rule of thumb that states costs to fix a noise problem are 10 times what costs would have been to prevent it.

California has “Title 24” for multi-family housing projects. Part of Title 24 declares that any new multi-family building needs to be analyzed for sound exposure and be constructed to ensure appropriate indoor noise levels. This is not a new idea, but it is a good one and could fit quite nicely into the comprehensive city plan.

d . Recommend requiring future CBD residential projects to notify all tenants, before execution of lease or sale or property, of all the nearby live music venues and ask tenants to sign an acknowledgement of the nearby venues and to acknowledge that live music might be heard within a residence given their proximity.

This I can take or leave. Perhaps, rather than notify prospective tenants of specific venues, they should be made aware of what kind of district they’ll be living in in terms of the noise ordinance. That way there’s flexibility for venues coming and going during a tenants stay.

Still, though, it sounds like this is asking new tenants to sign away their right to a reasonably quiet home environment. Perhaps this stems from the common misconception that most noise complaints are generated by the people moving into the downtown condos. “Those damn Californians who are ruining Austin.” Everything I’ve read points to single family homes in Zilker and Bouldin occupied by long-time Austin residents as the true culprits. But that’s starting to get pretty far off topic.

Sections 5 and 6 are about modifying the complaint process and starting a database to accumulate and analyze the characteristics of noise complaints over long periods of time. These are good ideas, if implemented properly.

The next important section is about non-live music:

7. PROHIBITION OF AUDIBLE NON-LIVE MUSIC. Recommend the City amend appropriate ordinances to prohibit outdoor non-live music (i.e. prerecorded music, radios, television, etc.) from being audible to a single family residential property, including penalties for violation. The MD should establish a definition for non-live music, and in the interest of respecting their contribution to the live music community, include DJs within the definition of live music. Also, non-live music must conform to existing sound ordinances that regulate sound audible to residences.

Sadly, more bad acoustics shows up here. The term “audible” should be used with great caution in legal documents. “Audible” is very subjective, and inaudibility can, for certain sounds, be impossible to attain. The human ear is an amazing machine; people can hear, recognize, and understand sounds which are actually below ambient noise levels. What’s audible to a person is not the same as what’s audible to a sound level meter.

Also, I take offense at the protection this paragraph offers to single family residential property, as if dwellers of multiple family properties are not entitled to the same protections. What’s is the reasoning for this?

The remainder of the report concerns politics and financing, which is beyond the scope of austinnoise.org (for the time being).

In summary, the LMTF was clearly well-meaning and came up with some good ideas. My hope is that experts in acoustics are consulted before any changes or decisions are implemented. I would also hope that, in the future, any task forces or advisory committees take the time to educate themselves on the concepts they’re using to make decisions. A decision made based on bad information is likely to be a bad decision.

Things that are wrong with the Austin Noise Ordinance

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Despite undergoing frequent revision due to changing political pressures, the Austin Noise Ordinance is still poorly written. The very fundamental aspects of the ordinance are flawed, written by people attempting to adopt portions of ordinances from other jurisdictions without totally understanding the differences in terms which sound similar but are actually quite different. Here’s what’s wrong.

It Uses the Wrong Property Line
Measured levels at a property line are very commonly used in noise ordinances, and it makes sense to do so. But Austin’s Noise Ordinance has a very serious flaw: it refers to the wrong property line.

Typically, the property line of the complainant is what matters. Noise ordinances say you (the noise maker, or “source”) are not allowed to cause noise levels to exceed a certain level on my (the one hearing the noise, or “receiver’s”) property. This is logical and wholly compatible with the concept of noise enforcement being complaint driven.

Austin’s Ordinance, however, puts limits on levels as measured on the source’s property line. This implies that the effects of identical noises generated at 100′ and 1000′ are the same. This is illogical and unfair to noise generators who put effort into locating themselves away from residences or other noise-sensitive locations. As I see it, this is the biggest flaw in the Ordinance as it stands today.

I’ve listed the relevant sections from the Ordinance below. Amusingly, the only part of the ordinance that refers to the affected property line is for mobile food establishments.

Guidance for Noise Enforcement is Spread Throughout the Code of Ordinances
There are bits of regulation for sound in various sections of the code of ordinances. The actual noise section primarily deals with permitting and has very little in the way of explanation of permitted noise levels.

The sections of the ordinance that are most often used to enforce noise complaints come from zoning, rather than the actual noise section. Recently this was brought into public view when the levels specified in the restaurant zoning section were used against Freddy’s on South First.

It is inefficient and illogical to have different, sometimes contradictory, noise standards spread throughout the code of ordinances. All enumeration and explanation of noise limits should be kept in a single section, referenced by other sections when appropriate. This will promote better understanding of the limits and homogeneity, and also prevent future “gotcha” uses of limits which are hiding in other sections.

All Sound Sources Are Treated The Same
With a few exceptions, all sound sources are treated equally. Since the ordinance (like most ordinances) relies on A-weighted decibels, this results in a flawed system.

Music and construction noise are very different types of sounds, and should be treated as such by the Ordinance. Music is very tonal in nature and is very recognizable to humans. This makes it more perceptible and, sometimes, more annoying than other types of sound. It also has a lot of low frequency content, which is more or less ignored by A-weighting. dBA is a not an appropriate metric for for music.

The ordinance should include modifications to general limits which account for tonal, rhythmic, and impulsive characteristics of sounds. Alternatively, the ordinance could have limits for individual frequency bands, rather than the A-weighted spectrum.

Here are the relevant sections from the Austin Code of Ordinances

§ 9-2-4 RESTRICTION ON DECIBEL LEVEL.

A person may not operate sound equipment at a business that produces sound:

(1) in excess of 85 decibels between 10:00 a.m. and 2:00 a.m., as measured at the property line of the business; or

(2) is audible at the property line of the business between 2:00 a.m. and 10:00 a.m.

Source: 1992 Code Section 10-5-4; Ord. 031023-13; Ord. 031211-11.

§ 9-2-5 RESTRICTION ON USE OF SOUND EQUIPMENT IN A RESIDENTIAL AREA.

(A) This section applies to property zoned as residential under Section 25-2-32(B) (Zoning Districts and Map Codes).

(B) A person may not use sound equipment that produces sound audible beyond the property line of a residence in a residential area between 10:00 p.m. and 10:00 a.m.

(C) A person may not use sound equipment audible beyond the property line of a residence in a residential area that produces sound in excess of 75 decibels.

Source: 1992 Code Section 10-5-5; Ord. 031023-13; Ord. 031211-11.

§ 25-2-583 COMMERCIAL RECREATION (CR) DISTRICT REGULATIONS.

(A) This section applies in a commercial recreation (CR) district.

…

(K) The noise level of live music may not exceed 70 decibels, measured at the property line.

Source: Section 13-2-660; Ord. 990225-70; Ord. 031211-11; Ord. 20090521-017.

§ 25-2-648 PLANNED DEVELOPMENT AREA (PDA) PERFORMANCE STANDARDS.

(A) This section applies to a planned development area agreement or zoning district. The requirements of this section supersede conflicting provisions of a planned development area agreement or ordinance, if any.

(B) A planned area development may not produce a dangerous or objectionable element, as described in this section or a City administrative rule.

…

(E) A dangerous or objectionable element may not exceed the limits prescribed by this subsection.

(1) Except for noise from a transportation facility or construction work, noise may not exceed 55 decibels LAN during daylight hours and 45 decibels LAN during night time hours.

…

Source: Section 13-2-269; Ord. 990225-70; Ord. 000309-39; Ord. 031211-11.

§ 25-2-808 RESTAURANTS AND COCKTAIL LOUNGES.

…

(3) Live entertainment is permitted if the amplified sound does not exceed 70 decibels, measured at the property line of the licensed premises. In this paragraph, “premises” has the meaning ascribed to it in the Texas Alcoholic Beverage Code.

Source: Section 13-2-263; Ord. 990225-70; Ord. 031211-11.

§ 25-2-812 MOBILE FOOD ESTABLISHMENTS.

…

(D) The noise level of mechanical equipment or outside sound equipment used in association with a mobile food establishment may not exceed 70 decibels when measured at the property line that is across the street from or abutting a residential use.

…

Source: Ord. 20060928-020; Ord. 20080131-134.

§ 25-3-86 COMPATIBILITY STANDARDS [FOR TRADITIONAL NEIGHBORHOOD DISTRICTS]

…

(B) The noise level of mechanical equipment may not exceed 70 decibels at the property line.

Source: Section 13-9-56; Ord. 990225-70; Ord. 031211-11.

What Is A Decibel?

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The first goal of this site is to provide (hopefully) good explanations of acoustical concepts in a community noise. In this post I will try to explain the most basic concepts of measuring sound, since that is where people typically go wrong. A good grasp of the following terms are vitally important to being able to discuss noise in a meaningful way.

Admittedly, these definitions tend to have more detail than necessary. You don’t need to understand every little bit of what is written below to be able to discuss acoustics intelligently. If you only have the time or patience to learn one term, please read about A-weighted decibels (dBA).

Sound
Pages and pages could be written about what sound is, but the thing you really need to understand is that sound is, at its most basic level, a change in air pressure. A very, very small change in air pressure that fluctuates with time. That is why sound is measured in Pascals, the same units used to measure water pressure or atmospheric pressure.

Decibel
This might be the most important yet least understood concept in acoustics. A decibel is a ratio. It’s a numerical tool that comes in handy when measuring things that don’t act in a linear way. Sound, earthquakes and electrical signals are all items that it is useful to use decibels to describe. Although it appears to be used that way, it is not a unit of loudness.

Decibels are used in acoustics in a variety of ways, leading to further confusion among people trying to understand it. The most common uses are measurements of sound power and sound pressure. In talking about community noise, sound pressure is what we are most concerned with. You might see the term SPL, which stands for Sound Pressure Level. Decibels of sound pressure are calculated by dividing the absolute sound pressure at a location by a universal reference quantity (20 micro-Pascals, it turns out), taking the log of that, and then multiplying the resulting quantity by 20. Like this:

“Lp” is just shorthand for Level – Pressure, which is equivalent to SPL.

Frequency
This is where people tend to start getting glassy looks in their eyes when they’re trying to wrap their heads around acoustics in one sitting. But it’s very, very important, so it’s worth the effort to try to understand it.

Sound is a vibration in air. Vibrations happen in frequencies. Frequency describes how many times per unit of time a vibrating object goes back and forth. The most common unit used for frequencies is Hertz. 1 Hertz just means “one time per second.” So if you have a sound with a frequency of 100 Hz, the air pressure is changing 100 times every second.

Sound is very rarely only a single frequency. “A sound” is usually vibrating at a whole bunch of frequencies. How much of each frequency determines what something “sounds like.” Sounds with lots of low frequencies are low and rumbly. Sounds with lots of high frequencies are hissy.

Each of the frequencies of a sound is completely independent. So, in a sense, a sound that you hear is really many individual sounds put together. When acoustical engineers do their work, they typically divide a sound up into groups of frequencies called bands. The most common bands are octave and 1/3-octave. You’ve probably seen bands like these on your stereo’s equalizer. An equalizer is a device that adjusts the volume of each frequency band independently.

While treating frequencies individually is the most accurate way of talking about acoustics, it’s not very convenient. This brings us to our next term…

A-weighted Decibels (dBA)
When people who are discussing community noise say “decibels” or “dB,” chances are what they really mean is dBA. A-weighted decibels is a convenient way of adding up all the frequencies in a sound into a single number. The vast majority of noise ordinances and enivronmental acoustical criteria use dBA.

The way dBA is calculated is by first weighting individual frequency bands based on their relative audibility to humans. Then each of the weighted bands are added up into a single number which approximately describes the total loudness of that sound to people.

dBA places high importance on higher frequencies and low emphasis on lower frequencies. It is possible to make significant changes to the low frequency content of a sound without having much, if any, effect on the overall dBA level.

There are plenty of worthy guides on the internet that can teach you the basics of acoustics that probably do a better job than this post. If you have a very real interest in acoustics and noise, I recommend spending some time acquainting yourself with the concepts of sound and its measurement. If anyone reading this has any favorite websites, please let me know and I’ll link to them.

What is the purpose of Austin Noise (.org)?

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I created Austin Noise .org to act as a center for discussion specific to noise in Austin. It’s a topic of discussion that is more relevant here than in most other cities due to our rapid expansion and identity as a premier live music location. Following articles and discussions about the noise ordinance, community noise, and the now-in-development comprehensive city plan I have noticed that few, if any, of the people involved have a good grasp of the basic concepts involved in creating and using noise regulations.

There is nothing shameful about not truly understanding what “decibel” means. Acoustics is a complicated science with a lot of similar sounding yet importantly different concepts. Hiring an acoustical consultant can be expensive because developing a good understanding of acoustics as it relates to communities takes years. And so the first and most important goal of this website is to attempt to provide informative, meaningful explanations of acoustical concepts and their relationship with the real world.

The second objective of this site is to generate good ideas that can be used in Austin noise regulation. Austin has a unique set of circumstances and, accordingly, deserves a unique noise ordinance and city plan. Rather than the patchwork set of misapplied limits and rules in our current ordinance, a new, meaningful, objective, and scientifically correct ordinance should be developed. A noise element should be added to the new city plan. I believe that Austin is a leader in community development and our approach to noise control should not be an exception.

So who am I? My day job is consulting in acoustics, noise, and vibration. My specialty is environmental noise. I’ve worked as an acoustical consultant in three states: Colorado, California, and Texas. Practicing in these states has exposed me to a variety of approaches to noise control in a fair and realistic way. Undoubtedly, some ways are better than others.

This site is not meant to solely serve as my soap box. My hope is to generate discussion and solicit honest review, questions, new ideas, and corrections from anyone who has interest in the Austin noise landscape. I will try to technically configure the site in a way that makes this as easy as possible.

So here we go… Austin Noise .org has begun.