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Larson Davis System 824, Training Manual

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Larson Davis System 824 Training Manual Download Page 49

3/22/01

Environmental Measurements

2-17

The measurement period is from 12:00 midnight to 12:00
midnight each day. 

Explanation of L

dn

 and CNEL

L

dn

 and CNEL are similar to a 24 hour Leq except the night-

time hours are weighted.

The L

dn 

adds 10 dB to the Leq’s measured during the hours

of 10:00 PM to 7:00 AM.

CNEL is similar to L

dn 

except that 5 dB is added to the mea-

surement levels between 7:00 PM and 10:00 PM and 10 dB
are added between 10:00 PM to 7:00 AM.

These measurements are used because people tend to be
more sensitive to noise during the nighttime and early morn-
ing hours.

Hourly Statistics

For each hour the Daily History logs the following:

•

Hourly Leq 

•

Background Leq 

•

Hourly Excd Leq

Use the

arrow keys to step

between the two Daily displays.

Summary of Contents for System 824

Page 1: ...System 824 Training Manual Larson Davis Inc 1681 West 820 North Provo UT 84601 USA Phone 801 375 0177 FAX 801 375 0182 www LarsonDavis com I824 02 Rev C...

Page 2: ...ity or fitness for a particular pur pose This documentation is subject to change without notice and should not be construed as a com mitment or representation by Larson Davis Inc This publication may...

Page 3: ...Some Buttons 1 7 SSA Measurements 1 8 Time History 1 8 Interval History 1 10 Broadband Measurements 1 11 Lets Go For a Test Drive 1 13 SLM 1 13 RTA 1 13 Intervals 1 13 Time History 1 13 Ln 1 13 Resett...

Page 4: ...ecial advanced feature 2 7 Time synchronization 2 7 Exceedance History 2 8 Exceedance Time History 2 10 Setting the parameters for an Exceedance History 2 11 Excd Enable Yes 2 12 Min Duration 000 2 12...

Page 5: ...T60 Defined 3 1 How does my 824 measure an RT60 3 2 Taking an RT60 Measurement 3 3 Exciting the Room 3 3 Setting up the 824 for an RT60 measurement 3 3 RT60 A and RT60 B Setups 3 3 Advanced RT60 Measu...

Page 6: ...824 Training Manual vi...

Page 7: ...r it a getting started guide as you get to know your 824 What you will Learn This manual is best used accompanied with the instrument and 824 Reference Manual You will be guided through a step by step...

Page 8: ...ay that was established before it was powered off in its previous session The On Off key can also be used to check the battery power as well as verify the on off status of the display s backlight Pres...

Page 9: ...xit the PWR screen An Acoustic Chameleon Even if you didn t purchase some of the options demo versions are pro vided of all of the optional virtual instruments The 824 is a quick change artist and can...

Page 10: ...ce history daily history Ln percentiles statistical data exposure and dual SLM current and overall Real time analyzer High speed spectral data gathering of up to 400 spectra per second using Autostore...

Page 11: ...ure ment setup you have selected The PRINT key is used to estab lish the settings required to communi cate with an external serial printer and to select the type of report to print The TOOLS key is us...

Page 12: ...will clear and a new measurement can be acquired The PAUSE key suspends a measure ment Pressing the pause key again will allow the measurement to con tinue Pressing the pause key when the 824 is stop...

Page 13: ...When modifying a setting the left and right arrow keys select a character or digit to modify The up and down arrow keys will modity the parameter Check key The check key is used to select an option o...

Page 14: ...ta versus time The time history is valuable at detecting what might be the offending noise source s Below is a level versus time graph showing several Time History periods The graph is divided into ei...

Page 15: ...ax Slow dBC Lmax Slow dBA Lmax Impl dBF Lmax Impl dBC Lmax Impl dBA Lmin Fast dBF The lowest instantaneous SPL during the period Lmin Fast dBC Lmin Fast dBA Lmin Slow dBF Lmin Slow dBC Lmin Slow dBA L...

Page 16: ...nterval 1 Interval 2 Interval 3 Interval 4 1 sec to 99 hrs 1 sec to 99 hrs 1 sec to 99 hrs 1 sec to 99 hrs Metric Explanation of Metric Leq dB w selected weighting Short Leq average of all energy duri...

Page 17: ...rics are recorded Metric Explanation of Metric Six Ln values broadband The level that the instantaneous SPL was over for n of the time Six spectral Lns Six spectral Lns whose frequency band levels wer...

Page 18: ...s SPL during the measurement Lmin dBC Lmin dBA SEL dBF Sound exposure level during the measurement Leq 10 Log T where T is in seconds SEL dBC SEL dBA Peak dBF The largest peak level achieved during th...

Page 19: ...rrow to enter into the SSA settings menu For an explanation of any of these settings please see chapter 7 of the 824 Reference Manual You will notice that you have alot of choice concerning the setup...

Page 20: ...enable the Lns statistical data For this measurement we will only record SLM RTA broadband data over the run time of the instrument Step 5 Once you have completed configuring the 824 back out of the t...

Page 21: ...4 19 01 824 Quick Start 1 15 Settings Menu and Submenus...

Page 22: ...1 16 824Training Manual 4 19 01 Settings Menu and Submenus continued...

Page 23: ...e 824 Reference Manual Taking a Measurement Step 10 Press the RUN STOP key to start taking a mea surement Let the instrument run for about a minute then press the RUN STOP key again to stop the measur...

Page 24: ...neously RTA Data To view the RTA data press the VIEW key and back out to the main VIEW menu by pressing the left arrow key Highlight RTA from the VIEW menu and press the right arrow Highlight RTA Live...

Page 25: ...e VIEW menu From the VIEW menu you can view the data that is impor tant to you Download Data Using 824 Utility Software Using the 824 Utility software allows you to download the data files stored in t...

Page 26: ...omputer Refer to chapter 9 of the 824 Reference manual if you need help getting to this point Step 1 Run the 824 Utility software by clicking on the icon on your desktop Step 2 Connect the 824 to your...

Page 27: ...or all of the same type of measurement Let s select the first measurement for download LM RTA The file will automati cally be named using the date the measurement was taken on You have the option of...

Page 28: ...ports To get the data into a form that we can look at we need to translate it To translate the data click on the translate win dow button on the tool bar The translate window is shown below To look at...

Page 29: ...readsheet select File and then Export Data or View Data in a Spread sheet The report will be printed in the format you see on the screen For some reports such as the Time History report you may need t...

Page 30: ...raining Manual 4 19 01 Shows values for each filter for Leq spectra Max spectra and Min spectra 6 Ln statistical values over the run time of the 824 showing the distribu tion of the SPL exceeded n of...

Page 31: ...Start 1 25 Time History Report The Time History report shows each time history sample selected for the time history period For each time history period you can record up to 37 data parameters as expl...

Page 32: ...e Interval report shows the data for each interval period See page 1 10 for explanation of data parameters for interval history That s the basics Now you can move on to some more pow erful measuring a...

Page 33: ...lity of life It can cause annoyance hearing loss stress and loss of sleep The num ber of noise sources are increasing on a daily basis For those involved in measuring analyzing and processing of envir...

Page 34: ...ajor projects usually require an environmental impact study roadways new plants mines etc May require permanent noise monitoring system Industrial noise Industrial noise may come from machinery such a...

Page 35: ...tc Firearms small arms ranges Why Measure Community Noise Community noise is measured for a lot of reasons but mostly because someone is being annoyed by some noise source Here are some other reasons...

Page 36: ...OG instrument has the following histories Time History Interval History Excd History Daily History In addition to the Histories the LOG instrument measures the following Current Overall levels Six Ln...

Page 37: ...me History Period 3 Time history period 4 Time history period 5 Time history period 6 Time history period 7 Time history period 8 SPL Fast dBF SPL Impl dBC Lmax Slow dBA Lmin Slow dBF Peak dBC SPL Fas...

Page 38: ...nter val History This statistical history provides a number of parameters calculated over a period of time that can be set from 1 second to over 99 hours Below is a level versus time graph showing fou...

Page 39: ...ws each inter val record for example to begin at the start of each new hour of the day Syncing can be done to the following incre ments of time 1 minute 5 minutes 10 minutes 15 minutes 20 minutes 30 m...

Page 40: ...y The Exceedance History is a special history of events which go over a set threshold For each exceedance history the fol lowing are recorded Duration Leq Lmax SEL Peak I Peak II Time and date of occu...

Page 41: ...look at what constitutes an exceedance Below is a detail of one of the peaks shown in the previous graph Level dB Level versus Time Graph Total time of measurement Exceedances Time SPL Excd Level 1 S...

Page 42: ...t ended The Leq and SEL are calculated over this period The Lmax is the largest instantaneous SPL achieved during this period Exceedance Time History A time history of the exceedance can be recorded a...

Page 43: ...commended that you get familiar with the type of events you would like to capture Remember that the data recorded in the Exceedance history are Duration Leq Lmax SEL Peak I Peak II time and date of oc...

Page 44: ...aining Manual 3 22 01 Triggering SPL Excd Lvl 1 70 SPL Excd Lvl 2 90 Pk 1 105 Pk 2 Excd Lvl 100 Hysteresis 2 Excd Enable Yes Min Duration 000 Excd Time Hist Yes T H Period 032 Excd Trigger Level Excd...

Page 45: ...3 22 01 Environmental Measurements 2 13 Exceedance History Triggering Menus Trigger Menu Exceedance History Menu...

Page 46: ...70 dB to trigger an exceedance Allow the meter to run for several seconds after triggering the exceedance in order for the level to drop below the hysteresis level Press the RUN STOP key to stop the m...

Page 47: ...and SEL of the highest event to raise and lower 10 dB in SPL It is used to capture single events such as a vehicle or aircraft passby or other event noises such as blasts or gas jetting noise as requ...

Page 48: ...By under the Excd Trigger setting The data for the PassBy function can be stored manually To access this display press the VIEW V key scroll down to PassBy and press the Check c key For the passby mea...

Page 49: ...hours of 10 00 PM to 7 00 AM CNEL is similar to Ldn except that 5 dB is added to the mea surement levels between 7 00 PM and 10 00 PM and 10 dB are added between 10 00 PM to 7 00 AM These measurement...

Page 50: ...change of the hour Since most events are rather short in duration the hour is extended until the exceedance ends up to 30 seconds If after 30 seconds the exceedance has not ended the exceedance is spl...

Page 51: ...ed between 10 00 PM to 7 00 AM These measurements are used because people tend to be more sensitive to noise during the nighttime and early morn ing hours Background Leq Background Leq can be consider...

Page 52: ...2 20 824 Training Manual 3 22 01...

Page 53: ...easurements are used to determine the sound absorption characteristics of a room This is also known as the reverberation time or the decay time The reverberation time in a room at a given frequency is...

Page 54: ...e records show each time slice 2 5mS as the sound is decaying in the room The ByTime display of the 824 shows each of the 1 3 octave frequencies over time The following diagram shows the level versus...

Page 55: ...60 measurement For an RT60 measurement use the RTA instrument of the 824 Step 1 To select the RTA instrument press the SETUP key Use the up and down arrow keys and high light either RT60 A or RT60 B a...

Page 56: ...3 4 824 Training Manual 3 22 01 RT60 A Settings Menu and Submenus...

Page 57: ...test will be free of interference Caution Wear hearing protection when generating noise levels of 90 dB or more Remember that levels will be greater near the noise source Make sure you can energize t...

Page 58: ...he Trigger Status display will show these four states sequentially as the measurement is taken Stop Ready Armed Triggered NOTE Triggering is performed on one frequency band or Flat as selected by the...

Page 59: ...int Due to the differing geometries and acoustic characteristics of some rooms a perfectly linear decay curve may not always be obtained Using the left land right rarrow keys a custom start point can...

Page 60: ...or a certain amount of time Level is equal to or greater then or less then a preset level for a certain amount of time Logic In line changes Logic In line changes Logic In line changes A preset amount...

Page 61: ...erage data does not take any additional memory Each additional measurement will be averaged insitu with the first The END condition must be TIME or SAMPLES so that the records are all identical length...

Page 62: ...suring may have a shorter or longer reverberation time than the 3 seconds selected in the End menu If the reverberation time is much shorter it is not necessary to store additional unneeded samples wh...

Page 63: ...e record to the next Pressing the Check key will put you in the Autostore check menu From the Autostore check menu you can view the ByTime spectra and ByTime graph each frequency over time NOTE If an...

Page 64: ...3 12 824 Training Manual 3 22 01...

Page 65: ...rts 1 23 D Daily History 2 16 date of occurrence 2 11 Download Data 1 19 duration 2 10 E End Time 3 10 Environmental Noise 2 1 Excd Leq 2 19 Excd Time 2 12 Excd Trigger 2 12 Exceedance History 2 8 Exc...

Page 66: ...ng Data 1 18 Recreational noise 2 3 Reports 1 23 Resetting Data 1 17 Road traffic 2 1 RT60 Defined 3 1 RTA Data 1 18 S screen contrast 1 3 Short Leq 1 10 simple measurement 1 13 SLM Data 1 17 slope 3...

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