PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Using realistic test signals to evaluate existing structures for low
frequency sound transmission from clubs, live music venues,
discos, and exercise facilities.
David WOOLWORTH1;
1

Roland, Woolworth & Associates, United States

ABSTRACTLow frequency sound used in entertainment (and sometimes exercise) facilities is difficult to reproduce instandard testing procedures for existing facilities such as ANSI E336 and ISO 16283-1, as the test cutoff
frequency is well above sounds generated in-situ for these facilities, and some methods or loudspeakers
cannot reproduce the sound level of low frequency that would be typical for everyday operation for thesefacilities This paper proposes using alternate test signals and methods that are appropriate to facility
programming that must be isolated from neighboring structures. It addresses “worst case” low frequency
source characterization, sound levels that incite vibration of finish materials that are transferred through thestructure, and metrics used to evaluate receiving spaces.
Keywords: Pulse, Low Frequency, Isolation

1. INTRODUCTION
The advent of inexpensive low frequency sound reproduction in loudspeakers for music since the1980’s has made low frequency sound sources ubiquitous and in turn has changed the way popular
music forms are recorded, mixed, and mastered to include more low frequency content. (1) This
content is being manipulated by artists to create new sounds, in some cases with the goal of being
louder or increasing the physical impact of the reproduction. This is especially prevalent in music
forms such as pop, urban, electronic dance music (EDM), country music, and heavy metal (2); thismusic appears in exercise facilities, dance clubs, and live music venues among other places. TheU.S. trend of mixed use lightweight and/or historical construction that combines these venues withresidences or nearby residences can result in unwanted low frequency sound.
Samples of sound measured in residences and residential areas affected by low frequency soundfrom clubs are shown in Figures 1 and 2. There is significant energy below 50Hz that must beconsidered. What is also of interest is the low frequency content of operational sound levels is 1525dB Leq above background sound levels.

2. TESTING AND TEST SIGNALS
2.1 Standards for Field Testing of Sound Transmission Loss
Two standards were examined for suitability to examine clubs for sound transmission inside thesame structure: First, ISO 16283-1:2014 Field measurement of sound insulation in buildings and ofbuilding elements Part 1: Airborne sound insulation (3), which assesses the third octave band
frequency range 50Hz to 5kHz, and second, ASTM E336-19 Standard Test Method for Measurementof Airborne Sound Attenuation between Rooms in Buildings (4), which addresses the minimum thirdoctave band frequency range 125Hz to 4000Hz. ISO 16283-1 utilizes spatial averaging to determine
transmission loss in the 50, 60, and 80 Hz bands. Conceivably one could measure down to 31Hz
using these methods, and report the results with the understanding that this is specific to theparticular measurement location; however, these test methods utilize white or pink noise as a noise
1dwoolworth@rwaconsultants.net

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source. The test loudspeaker's ability to run continuous broadband noise at high sound levels islimited, and at high sound levels can burn up loudspeakers, especially trying to reproduce lowfrequency broadband noise. As seen in Figures 1 and 2, low frequency is our main concern in regard
to clubs. So a test signal should be considered that mimics the part of the sound source that is themain complaint, that is primarily pulsing low frequency.

Figure 1: Third octave band measurements of Leq in a bedroom on 5th floor of condominium above anopen stairwell with club on 1st floor, Note the drop in level of 15dB when the club closes at 4:00am.

Figure 2: Outdoor measurements 29m (95ft) from a club in an apartment complex 12:00am versus ambientconditions.
2.2 Proposed Test Signal
Bass drops and the actual music played in the venue are useful sources that contain low
frequency pulse information; live music will have large variations between acts and requires some
additional thought to ensure the worst case is tested (see 2.4 Sound Level of the Test Source). The
proposed test signal is a bass drop (or multiple types of drops).

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2.3 What is a Bass Drop?
A bass drop is a bass drum type sound sample used in music for impact, or sometimes as a drumsound. It is sometimes referred to as “808” in reference to the bass drum sound of an early drummachine, the Roland TR-808, created by Ikutaro Kakehashi in 1980. This was initially used by theJapanese electronic music group Yellow Magic Orchestra, and was considered more of a toy, but
drum machines began to drive new forms of music such as hip hop, and eventually the bass drop
continued to evolve and be adapted for pop music, heavy metal, rap/urban music, and electronic
dance music (EDM). (5)The bass drops studied for this paper had a duration from ~200 msec to several seconds. Ingeneral, the sound consists of a band of low frequencies that drops pitch over time. For example, thedrop in Figure 3 (left) starts out roughly in the band of 63Hz to 200Hz and drops to 31Hz to 80Hz in
0.2 seconds; with this frequency and level drop in the main band, higher frequency information will
drop off in level as well. Bass drops are further manipulated by their composers using various
electronic effects; harmonics are added to ensure good reproduction in sound systems with low
frequency limitations.

Figure 3: Waterfall analysis of two bass drops. Left, a well ordered oscillating 3 second drop; Right, a 0.2
second drop with some electronic effects. In both cases, the signal shifts to lower frequency over time.
2.4 Sound Level of the Test Source
The sound level of the test source is important and can be approached in several ways: (a) if weare trying to determine the upper level to limit the sound source, the level can be varied until areceiver criteria is met (b) if we are trying to evaluate the sound isolation between a source and areceiver, it is good practice to use low frequency sound levels that you have measured in similarvenues. It is important to note that when field testing is performed, the sound levels that matchtypical levels can seem louder than normal, as you are going from ambient conditions to high soundlevels, without the aid of tympanic reflex and other acclimation. It is not unusual for the owner ormanager of a source venue to claim that they are never as loud as the test. The best point ofreference for the highest sound levels for clubs will be the end of the night or the end of shows; thesound level is typically the highest then (See Figure 1). Live music venues requires that a samplingof acts is performed, as there can be large variations in the musicians’ and engineers’ low frequency
sound levels.
Bass drop frequency content, frequency shift and sound level together will typically excite mostlightweight surfaces in the room into vibration, actuating structureborne noise. Thresholds for3421

airborne induced vibration of windows, walls, and floors with two field measurement samples areshown in Figure 4 for reference. It is important to keep in mind this airborne sound to structureborne
sound can become the major issue for sound transmission.

Figure 4: NASA thresholds of airborne sound levels producing perceived induced structural vibrations.
Rock-pop curve extracted from Larsen(6) and author’s field data, fitness is typical ambient conditions for afitness facility. Note that “spin” (in-place bicycle class) can exceed the fitness level significantly (up to10dB). Both typical field conditions can induce structureborne sound.
2.5 Sound Source and Testing
If a “house” sound system exists, it is the ideal source as it has the appropriate capacity and insitu conditions of structural connectivity. In the case where no sound system is in place, or it is alive music venue, it is appropriate to bring a subwoofer that can reproduce down to ~30Hz, or
whatever the planned system low frequency roll off is designed for. The stage should be checked
separately in live music venues to simulate bass, synthesizer, or DJ setups, as the stage may havedifferent structural connectivity than the house sound system. Regardless of the sound source, it is agood idea to bring isolation pads for subwoofers to examine any improvements by isolation, or toverify if structureborne sound is the main issue.
The test can utilize sound level meters or microphones in both the source and receiver positions(best), however it may be sufficient or necessary to sample some number of bass drops at the source
and then again at the receiver under stable or low noise ambient conditions. Vibration monitoring ishighly recommended. The interval, duration, and style of the bass drop (in some cases bass drumsample) can be set up to mimic an expected range of tempos if exposure is being considered; forinstance, exercise music typically ranges from 115 to 160 beats per minute.
2.6 Using the Results
The data from testing for low frequency sound and vibration transfer using bass drops is
especially useful in troubleshooting sound and vibration paths, determining required in-situ noise
reduction of a construction, informing noise control measures, and determining limits for low
frequency output of sound systems.

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3. ON EVALUATION OF RECEIVER THRESHOLDS
3.1 Threshold Limits for Receivers
The discussion for receiver low frequency thresholds is ongoing; a recent summary of methods
can be found in ICA 2016 proceedings (Caniato, et.al) (7), which includes Roberts (8)recommendation for 5dB penalty for an impulsive source (bass beat), and Jakobsen’s method (9) that
includes vibration monitoring (structureborne sound). This summary builds on earlier work from
Leventhal (10). DIN 45680 Measurement and assessment of low-frequency noise immissions in theneighborhood (11) also recommends nighttime limits for sound and vibration. In some cases testingneeds to be performed during the day, so it is important to take in to consideration background noiseand penalties for nighttime ambient conditions. Determination of receiver metrics and refinement ofmethods for testing is left to the reader; ultimately it is important to measure both sound andvibration due to the potential for direct transfer of vibration and airborne to structureborne sound in
addition to airborne sound.

4. SUMMARY
The “808” bass drop is an element of popular music that should be considered as a repeatable test
signal added to standard field sound isolation testing to examine each unique field condition formusic and entertainment that includes low frequency content. The value of the bass drop is that it
defines “worst case” for sound levels and band-density in the low frequency region of musicsources, making it useful in establishing limits for sound systems or defining isolation needed tomeet threshold limits. The bass drop is particularly effective in generating airborne to structureborne
sound, where white and pink noise test signals may not due to demands of continuous broadband
sound on the loudspeaker.
Since the bass drop is an evolving art, it is difficult to define a standard drop sound, and theconsultant needs to be vigilant of the “state of the art” in music production to determine areasonable test signal(s). It is also critical for those involved in testing to identify any new elements
in popular music that can create annoyance with unintended listeners and ensure that they include
similar signals in field testing regimen. Ultimately the test signals should reflect the content andsound levels of a typical source or potential source.

5. FUTURE WORK
Three areas are of interest for future work; (a) sound quality (i.e. sharpness, roughness) ofvarious bass drops and the potential for annoyance, (b) the creation of a library of genre or venue
based music samples for field testing, and (c) development of indoor to outdoor sound transmission
measurement method that addresses low frequencies of interest.

REFERENCES
1. Woolworth, David, “New Orleans Sound Ordinance and Soundscape; Evaluations andRecommendations,” City Council Resources, City of New Orleans, August 5, 2013.
2. Hasnain, Zainab, “How the Roland TR-808 revolutionized music” The Verge, April 3. 2017,https://www.theverge.com/2017/4/3/15162488/roland-tr-808-music-drum-machine-revolutionizedmusic.
3. ISO 16283-1:2014 Field measurement of sound insulation in buildings and of building elements Part 1:
Airborne sound insulation.
4. ASTM E336-19 Standard Test Method for Measurement of Airborne Sound Attenuation between Rooms
in Buildings.
5. “Roland TR-808” Wikipedia, https://en.wikipedia.org/wiki/Roland_TR-808.
6. Adelman-Larsen, Neils Werner, “Rock and Pop Venues: Acoustic and Architectural Design”, Springer,
New York, 2014.
7. Caniato, Bettarelllo, Fausti, et al. “Low frequency noise and disturbance assessment methods: A brief
literature overview and a new proposal,” POMA, 22 nd International Congress on Acoustics, Buenos
Aires, Argentina, September 2016.
8. Roberts. C., “Ecoaccess guideline for assessment of low frequency noise,” in Proceedings of3423

ACOUSTICS 2004, Gold Coast, Australia, November 2004.
9. Jakobsen, J. (2001): Danish guidlines on environmental low frequency noise, infrasound and vibration.
Jnl Low Freq Noise Vibn & Active Control 20, 141-148.
10. Leventhall H G. Low frequency noise and annoyance. Noise Health [serial online] 2004 [cited 2019 Jun9];6:59-72. Available from: http://www.noiseandhealth.org/text.asp?2004/6/23/59/31663 .
11. DIN 45680 – Measurement and evaluation of low-frequency noise immissions in the neightbourhood,
1997.

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1. Beranek LL. Criteria for noise and vibration in buildings and communities. In: Beranek LL, Ver IL,editors. Noise and Vibration Control Engineering - Principles and Applications. 2nd ed. New York,
USA: Wiley; 2006. p. 887-909.
7. Caniato, Bettarelllo, Fausti, et al. “Low frequency noise and disturbance assessment methods: A brief
literature overview and a new proposal,” POMA, 22 nd International Congress on Acoustics, Buenos
Aires, Argentina, September 2016.
8. Roberts. C., “Ecoaccess guideline for assessment of low frequency noise,” in Proceedings ofACOUSTICS 2004, Gold Coast, Australia, November 2004.
9. Jakobsen, J. (2001): Danish guidlines on environmental low frequency noise, infrasound and vibration.
Jnl Low Freq Noise Vibn & Active Control 20, 141-148.
10. Leventhall H G. Low frequency noise and annoyance. Noise Health [serial online] 2004 [cited 2019 Jun9];6:59-72. Available from: http://www.noiseandhealth.org/text.asp?2004/6/23/59/31663 .
11. DIN 45680 – Measurement and evaluation of low-frequency noise immissions in the neightbourhood,
1997.

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