Acoustic measurements: Tutorial on decibels, microphones

The decibel is widely misunderstood. Fortunately, stating the sensitivity of microphones in V/Pa (volts/pascal) is gaining popularity. Article demystifies acoustic measurements. See equation.

08/27/2008


The decibel is widely misunderstood. Its definition came from acoustic studies in the early 1900s and has been widely adopted by many disciplines, most notably electronics. Fortunately, stating the sensitivity of microphones in V/Pa (volts/pascal) is gaining popularity. A white paper written by Endevco engineer George A. Pender entitled “Microphone talk”
In the beginning was the Bel (named in honor of Alexander Graham Bell). The Bel was first defined in terms of acoustic power, but it can be generalized as the logarithm of the ratio of two quantities with the same units. Since logarithms are extraordinary compressors, the magnitude of the Bel was deemed inconvenient for typical acoustic calculations, so it was subdivided into 10 (deci) parts and abbreviated dB.
In acoustic research, the power level of sound was defined as 10 log 10 of measured sound power divided by reference sound power. Because it is more convenient to measure sound pressure than sound power, the pressure level of sound was defined as 10 log 10 of measured sound pressure squared divided by reference sound pressure squared. Since log 10 ( N 2)= 2 log 10 N , the sound pressure level (in dB) can be rewritten as 20 log 10 of measured sound pressure divided by reference sound pressure.
Fortunately, stating the sensitivity of microphones in V/Pa (volts/pascal) is gaining popularity. Since the output of any type of microphone is linear with pressure, the units of V/Pa fall out naturally. As an indication of the confusion still prevalent in defining microphone sensitivity, the Endevco model 2510 piezoelectric microphone has several numbers and units listed for sensitivity (the electrical output from piezoelectric microphones is commonly expressed in picocoulombs [pC], rather than volts).
Although sensitivity units of V/Pa (or pC/ssure. Since no one (to our knowledge) has yet marketed a microphone with such a high output, microphone sensitivities in dB are negative ( e.g ., -60 dB re 1V/Pa).
C.G. Masi , senior editor
Control Engineering
Register here and scroll down to select your choice of eNewsletters free.





No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2013 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
The true cost of lubrication: Three keys to consider when evaluating oils; Plant Engineering Lubrication Guide; 11 ways to protect bearing assets; Is lubrication part of your KPIs?
Contract maintenance: 5 ways to keep things humming while keeping an eye on costs; Pneumatic systems; Energy monitoring; The sixth 'S' is safety
Transport your data: Supply chain information critical to operational excellence; High-voltage faults; Portable cooling; Safety automation isn't automatic
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Plant Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Maintaining low data center PUE; Using eco mode in UPS systems; Commissioning electrical and power systems; Exploring dc power distribution alternatives
Synchronizing industrial Ethernet networks; Selecting protocol conversion gateways; Integrating HMIs with PLCs and PACs
Why manufacturers need to see energy in a different light: Current approaches to energy management yield quick savings, but leave plant managers searching for ways of improving on those early gains.

Annual Salary Survey

Participate in the 2013 Salary Survey

In a year when manufacturing continued to lead the economic rebound, it makes sense that plant manager bonuses rebounded. Plant Engineering’s annual Salary Survey shows both wages and bonuses rose in 2012 after a retreat the year before.

Average salary across all job titles for plant floor management rose 3.5% to $95,446, and bonus compensation jumped to $15,162, a 4.2% increase from the 2010 level and double the 2011 total, which showed a sharp drop in bonus.

2012 Salary Survey Analysis

2012 Salary Survey Results

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.