Case Studies

Cinema Acoustic Upgrade

High-end Cinema Extension

High-end Showroom Acoustic Re-design

Home Recording Studio

case studies

Law Office vs Community Theater Noise

Resonating Cinema Seats

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Cinema Acoustic Upgrade

Problem

 In this study of a home theater, with high-end two channel listening being a priority, we were asked to optimize the existing room for the audio presentation. We were also able to optimize it for the video presentation. The room initially had Kinetics acoustic treatments in the corners, as well as some limited bandwidth absorption at first order reflection points on the side and rear walls.

Before

Solution

First we optimized the speaker/listener locations, which made a great improvement for the client. We then moved the projector to optimize its throw distance for the existing screen, which was also positioned at a new height. The FRP system was installed on all four walls and about 75% of the ceiling. This was covered with a very dark blue and black, acoustically transparent fabric, allowing for a picture that pops and does not have reflection, color or “light-up” interferences. Voicing of the entire electro-acoustical system was also performed. Before voicing, the system was strained and could not play some passages without noticeable distortion. After voicing, the system could play reference levels without any signs of strain.

During

Result

Below are the modeling reverberation times estimate, and the actual reverberation time measurements. As can be seen depicted in the graphs below, the room sounds very natural and articulate due to the FRP system.

·  FRP is effective down to 63 Hz. and is only 2.5” deep

·  Controls room modes, first order reflections, reverberation times and

flutter echo in a linear, tunable fashion

·  Conceals with an acoustic stretch fabric system

·  Fitted on-site by professional installers

“We are truly enjoying the acoustic environment you have provided for our cinema/music listening room”.

After

Estimated Reverb Times

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Actual Reverb Times

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Reverberation is probably the most recognized characteristic of a room’s sound. Reverberation is the acoustic energy in the space that lingers on after the sound stimulus has been removed. Each room’s reverberation times at each frequency are as unique as a signature. Ideally, we want the reverberation times to decay at the same rate across the audible bandwidth, and within a time window of about 0.25 – 0.35 sec. This allows for neutral sound conditions. An exception is for frequencies

below about 100 Hz., where we need slightly longer decays in order for our brain to make sense of the difference between what our ears hear vs. what our eyes see. Lack of reverberation control results in masking of low-level details, loss in dynamic range, soundstage, timbre and articulation.


High-end Cinema Extension

Problem

In this case study of a high-end home cinema that is primarily used for critical 2 channel listening, there were some notable room resonance slurring from about 40-55 Hz. The original acoustic design filled the room with Tube Traps, which couldn’t quite tame the annoying low frequency anomaly. While characterizing the room, it was noted that the ambient noise floor was also troublesome from both the HVAC and projector.

Prior Acoustic Treatment

Solution

An onsite visit allowed actual characterizing of the room and system interactions. To address the bass problems, A/V RoomService recommended lengthening the room 18” in order to smooth out the coincident room modes. The new dimensions allowed for much better mode distribution as well. We also optimized the speaker/listener positions, and introduced our Frequency Response Panel (FRP) system. To address the noise floor problems, we took measurements of the HVAC system for modeling and made several recommendations to lower the noise of the system, which was a distraction whenever it turned on or off. We also moved the projector behind the new rear wall and built a noise rated port window (incorporating special optical glass panes for video color integrity) to eliminate the fan noise.

Prior Treatment Layout

Result

Below are actual before and after treatment results. As can be seen in the articulation graph below (fig. 1), the troublesome bass frequencies have been eliminated. Overall, bass response is now linear and fast to start and stop. The Noise Criteria graph (fig. 2) shows the improved drop in the noise floor, which indicates a > 5 dB SPL improvement in dynamic range for the room, which also means higher resolution in low-level details. Finally, the room now sounds very natural and articulate due to the FRP system, which attenuated all first order reflections by about 15 dB, smoothed out room modes by an additional 4.4 dB from 325 Hz. and down, and controlled reverberation times to an average RT-60 of 0.25 seconds from 260-3,740 Hz. (fig. 3). Voicing was included a second time when the client changed speakers in the system from Wilson Audio to Dynaudio.

Finished FRP System

Fig. 1 Bass slurring eliminated

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Fig. 2 HVAC noise floor lowered

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Fig. 3 Reverberation times controlled

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Reverberation is probably the most recognized characteristic of a room’s sound. Reverberation is the acoustic energy in the space that lingers on after the sound stimulus has been removed. Each room’s reverberation times at each frequency are as unique as a signature. Ideally, we want the reverberation times to decay at the same rate across the audible bandwidth, and within a time window of about 0.25 – 0.35 sec. This allows for neutral sound conditions. An exception is for frequencies

below about 100 Hz., where we need slightly longer decays in order for our brain to make sense of the difference between what our ears hear vs. what our eyes see. Lack of reverberation control results in masking of low-level details, loss in dynamic range, soundstage, timbre and articulation.


High-end Showroom Re-design

Problem

In this case study of a high-end dealer, the reverberation times were initially too short in the mid and high frequency range, due to an acoustical designer over absorbing only the front wall, with nearly 2’ of material and many Tectum panels mounted on the side walls. There was no low frequency absorption and no proper absorption of the first order reflections on the walls and ceiling. The walls were a combination of cement block on one side and dry wall on the other. This created a horizontal imbalance of full bandwidth reflections from too much mass on the left and front walls, and not enough support from mass, plus wall cavity resonances on the right wall. In addition, the speaker/listener locations were not optimum for the space, further resulting in non-linear bass response.

Prior to Acoustic Treatment

Prior to Acoustic Treatment

Solution

A/V RoomService was hired to make the room the best it could be under some physical constraints. We were able to perform many tests of the room to characterize it before modeling. We removed the existing acoustic treatments, other than some Tectum panels towards the rear of the room. We introduced a double layer of gypsum (furred out from the cement blocks on the left and front walls) with our RoomDamp2 constrained-layer damping compound in-between. This provided some low frequency absorption, reduced cavity resonances and provided horizontal symmetry to the audio scene. We then incorporated our Frequency Response Panel (FRP) system to the front wall, side walls and two areas of the ceiling, further controlling first order reflection points, room modes and reverberation times. In addition, we incorporated our metu CornerTraps in each rear corner. We also optimized the speaker/listener locations for soundstage and room mode interaction. Voicing was included.

FRP before fabric

Result

Below are the actual before and after treatment reverberation times. As can be seen in the graph below, the room now sounds very natural and articulate due to the FRP system. Note the before and after differences between the acoustically treated room vs. the untreated, as well as the additional improvement with the optimized speaker/listener positions.

· FRP is effective down to 63 Hz. and is only 2.5” deep

· Controls room modes, first order reflections, reverberation times and

flutter echo in a linear, tunable fashion

· Conceals with an acoustic stretch fabric system

· Fitted on-site by professional installers

“I have a guy here [all the way] from Pittsburgh who is also enthralled with the sound he’s hearing, as I am I”.

Finished FRP

Before and After Reverb Times

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Actual Reverb Times

(click to enlarge)

Reverberation is probably the most recognized characteristic of a room’s sound. Reverberation is the acoustic energy in the space that lingers on after the sound stimulus has been removed. Each room’s reverberation times at each frequency are as unique as a signature. Ideally, we want the reverberation times to decay at the same rate across the audible bandwidth, and within a time window of about 0.25 – 0.35 sec. This allows for neutral sound conditions. An exception is for frequencies

below about 100 Hz., where we need slightly longer decays in order for our brain to make sense of the difference between what our ears hear vs. what our eyes see. Lack of reverberation control results in masking of low-level details, loss in dynamic range, soundstage, timbre and articulation.


Home Recording Studio

Objective

In this case study of a home recording studio, we had many physical and budgetary constraints to deal with. Very important to a recording studio is to isolate noise from being recorded, as well as providing a room with neutral sound quality characteristics so that the recordings and mixes created sound good anywhere. A/V RoomService, Ltd. was to provide acoustical noise control and sound quality designs and recommendations for the shell, HVAC and electrical with drawings in accordance to the customer needs.

Observation

The client indicated that rather high levels are likely while recording or mixing in the home studio environment. It was also indicated that noise control for these high-energy sound levels to the rest of the home is extremely important, as is noise entering into the studio environment. There is living area above the studio, a garage common to one wall and three exterior walls. In addition, local codes required two door entrances and a small window.

One of the most critical design features associated with good wall, ceiling and floor noise & sound quality control is to not only to dissipate energy leaving or entering the space, but to control sound energy which is ultimately held within the room. Therefore, the recommended wall design, while providing excellent noise attenuation, is also designed to help control resonant energy and modes, which typically find their way back into to the recording/listening environment. As a result, a number of issues are looked at, including stud material, spacing, cavity depth, insulation type, air space, damping materials and surface treatments.

Solution

A/V RoomService provided information for the following:

  1. Optimum room dimensions based on the existing structure
  2. Two different resilient wall assemblies having an estimated STC performance between 56-63, incorporating broadband blocking, isolation, absorption and constraint layer damping.
  3. Information on how to construct the ceiling having an estimated STC performance of between 58-63, and an IIC rating of 53-58, incorporating broadband blocking, isolation, absorption and constraint layer damping.
  4. Recommendations for an affordable door system with appropriate sealing.
  5. Electrical recommendations to provide clean power with high instantaneous current, isolation, filtration against both line and field induced noise, and safety.
  6. HVAC recommendations for an ultra quiet system that included: a. Number of air exchanges per hour b. Air flow rates into room (cfm) c. Maximum air velocity (feet/minute) d. Recommended size and quantity of supply and exhaust diffusers e. Cross sectional open area of a single duct f. Total open area of air volume entering space (sq. inches) g. Design Recommendations: (i) Designated duct line layout for studio (ii) Ductwork material or treatment (iii) Minimum absorption coefficients (iv) Treatment of ducts
  7. Optimum speaker/listener locations to offer a large, solid soundstage, and yet avoid exasperating the known room modes.
  8. Calculate first order reflection points on each surface, for each speaker.
  9. Estimate room modes and room reverberation times.
  10. Recommend A/V RoomService metu broadband, affordable,

attractive acoustical treatments for first order reflection points, room modes and reverberation control.

Studio Front

Studio Rear

Result

It is hard to estimate low frequencies energies for such a small room and we were not able to perform onsite tests, however the room performs well according to the owner. We are confident that we provided the best “bang for the buck” considering the many constraints. In order to do this, we communicate the pros and cons of different options, make our recommendations based on the client/room profile, and allow the customer to make final decisions.

Room Layout

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Estimated Room Modes

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Estimated Reverberation Times

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“It was such a pleasure to work with Norm and Harry on the design on my new studio. The results have exceeded my expectations. Comparing my old room with the new is night and day. I immediately noticed improved imaging with individual instruments occupying specific places within the stereo spectrum instead of being generally panned to the right or left, improved tonal balance, and improved dynamics. In short, my mixes are translating better than ever and with less work. Awesome!

As construction began on the project, the “facts on the ground” made it necessary for Norm to adjust the room dimensions at the last minute when our contractor realized a structural beam prevented the HVAC ducting from being placed where original spec’ed. Norm was able to come up with a solution quickly – allowing our contractor to get back to work.


I highly recommend A/V RoomService.”.


Matt F. McCabe

Finley Sound




Law Office vs. Community Theater Noise

Scope

In this condensed case study of law office vs. community theater, A/V RoomService was requested to perform acoustic analysis for the purpose of defining noise transmission from the theater venue into the law office space as a result of complaints of noise disturbances by the law firm. We visited the site prior to testing in order to learn more about the structure and to interview individuals from both parties regarding the noise problem. It was discovered that there are two common walls being shared by the parties. After our initial investigation, it was determined that we would perform ASTM E-336 tests to evaluate the sound isolation partitions of the two common walls. We also plotted Noise Criteria Curves for the office space. All equipment was calibrated on-site prior to testing. It was also determined that we would conduct our tests after hours in order to avoid outside traffic noise and office personnel and equipment from corrupting our data.

case studies
Conclusions

Test 1: The Noise Isolation Class (NIC) ratings (NIC rating was calculated in accordance with ASTM 413) for this series of tests were conducted between the theater lobby (sound source side) and the adjacent office space (sound receiving side). The NIC results ranged from an NIC-57 to NIC-59 and included 7 microphone locations

in the office space. NIC ratings of this level are considered acceptable for typical noise levels generated between the theater lobby and adjacent office space. This range of NIC results would be estimated to translate to STC (Sound Transmission Loss) performance levels in the low to high 60’s. It should be noted that while NIC ratings of this level are considered adequate, they do not assure a sound proof environment. As noise levels increase there will always be a possibility that some level of noise transmission to the adjacent space can occur, especially in the low frequency range.

The noise reduction decibel levels for each microphone location indicated no serious decibel deficiencies over the frequency spectrum of 125 hertz to 4000. A general dip in noise reductions from approximately 250 hertz to 1000 hertz was noted, but is typically indicative of this type of construction. The NIC rating based on the average of all 7 receiving microphone locations achieved a NIC-58 (see graph 8) and agrees with the observations noted above. During our inspection of the basement, there was some evidence of noise transmission occurring via the floor joist, however this path did not appear to be significant.

Test 2: The average NIC value based on 6 microphone locations over the 1st and 2nd floors indicated a NIC value of 61. (See graph 15) Again, this performance level is considered to be at an acceptable level for this type of theater separation wall construction. Again, the projected STC levels for NIC ratings of this magnitude would be expected to achieve STC rating from the low to high 60’s. As was noted above, no wall is soundproof and will transmit noise through it relative to the noise levels and frequencies being generated on the opposite side. A wall of this performance level, as with the lobby wall, is expected to adequately attenuate most generated noise levels from the theater. However, there will be times when high level mid frequency noise and low frequency noise achieve a decibel level which will penetrate the wall and be heard in the business space. The principle to understand is that annoyance levels, while significantly reduced, cannot be eliminated. For example, a poor noise control wall may have an annoyance level of 75%, while a high performance wall construction only 10%. Both walls will have potential complaints, but the quieter wall will have overall fewer complaints.

Test 3: This test looked at the noise reduction levels associated with the double doors separating the main theater seating area from the lobby on the 2nd floor. No sound gaskets were noted on the doors and as a result achieved a NIC rating of 22. (See graph 16.) The noise reduction curve indicates significant reductions in the mid to high frequency range which would indicate that the lack of door seals are limiting the doors ability to reduce noise transmission. As a result noise levels from the main theater to the lobby would be expected to be elevated due to this condition.

Test 4: During our recording of noise in the adjacent office space, it was observed that intermittent noise was coming from the roof area. While the exact location and source of this noise could not be identified, a noise spectrum of the noise was taken when it was noticeably on and off. The comparison of these two spectrums indicate increase noise levels indicative of motor harmonics. This spectrum indicated increase ambient noise levels at 80 and 160 hertz as noted on graph 17. After a quick investigation, we did note that the new HVAC generators for the theater were mounted directly to the rooftop with no type of isolation system in place.

Graph 8 – Average noise reduction of microphone locations

Graph 15 – NIC Ref. Curve vs Noise Reduction Data

Graph 16 – NIC Ref. Curve vs Noise Reduction Data

Graph 17 – Ambient Noise Levels in 2nd Floor Law Offices

Recommendations

A/V RoomService provided information for the following:

1a) After studying the data gathered, as well as experiencing the environment personally, our first recommendation is to install an electronic noise masking system into the office space. The reasoning behind this simple solution is due to the quiet noise floor inside the office space (after business hours). With such a low ambient noise floor, small noise introductions become noticeable, where under normal office conditions they would not. It should be noted that it was necessary to conduct our test after hours in order to eliminate noise introduced from other than the source of concern under test, i.e.; the theater. During normal business hours traffic noise and office personal and equipment occupy the noise floor. We understand that sometimes office personnel might be working after hours. It is then that the noise floor would be so low as to notice small noise introductions. It is also after hours that the theater would be producing the majority of their high noise levels. We noticed while performing our tests for noise floor in the office space that you can hear yourself breathe, swallow or stomach making noise.


Noise Criterion Curves (NC) are a series of standard curves of octave-band sound spectra in a system for rating the noisiness of an indoor space; a measured octave-band spectrum is compared with this set of curves to determine the NC level in the space. The determiner is the highest NC curve tangent to the noise spectrum. The lower the number, the lower the noise floor. Expectable levels for executive offices are NC 25-30. The average ambient noise level of the office space next to the theater without the roof noise was NC-20 as indicated in graph 18. This equals an approximate A-weighted sound level of 23-28 dB. With the introduction of an electronic masking system to raise the ambient noise floor levels, small noise introductions would become unnoticeable.

1b) Along with the masking system it is recommended that door seals be installed to all doors in the theater including the bathroom doors which share the common wall with the offices. We noted significant levels of noise escaping from the theater through the double doors separating the theater and the second floor lobby.


1c) All AC receptacles, switches, HVAC grills and any other penetrations above and below the drop ceiling, both in the theater and the office space, must be sealed with acoustic caulk. We noticed in particular that the outlet on the west office wall common to the theater had audible noise as well as airflow passing through it.“We believe these are the correct recommendations based on our findings and are surly the most cost-effective and least corruptive solution to the problem.” A/V RoomService, Ltd.


2a) In addition to the above, should it become necessary, a secondary wall would be built, on the office side, where the common walls to theater and office space is located going up the stairs. This wall should extend from the roof joists above the drop ceiling down to the second floor and under the stairs of the first level. See attached wall construction material and installation recommendations.

2b) As above, applied to the common wall of the theater lobby/office hallway that runs north and south.

3) If the above is still unacceptable, it is due to low frequency noise vibrating the building structure. The only path left to treat is the floor of the office space. Installing a floating floor system would “break” the last physical connection to the theater, thus isolating it from the theater. See attached floor construction material and installation recommendations.

Graph 18 – Noise Criteria Curve


Resonating Cinema Seats

Problem

In this case study, we had no problem until the very end. We designed and built the cinema (mainly used for 2 channel listening) from scratch including floating riser, ceiling and walls, HVAC, electrical, acoustically rated door, Frequency Response Panel system, etc. The client is an ear, nose and throat surgeon who really enjoys music. This room, at the client’s request, was the first room of the new house to be completed. We performed onsite voicing and everything was going great and I was just about ready to pronounce the acoustic treatments and all calibrations completed. During voicing I had used a non-cinema chair to easily move about, but when I placed the custom made seat into position, there was a 90 Hz. “muddyness” in the playback!? Both the Doctor and I could hear it. I did not hear it a minute ago, nor did any of my measurements indicate it. Going on a hunch, I switched back to the chair, and the problem was gone. I moved the cinema seat back, and there it was again. What was really odd was that neither one of us could feel the vibration on our body, yet I was able to confirm that the seat resonated at about 90 Hz. What was happening was bone conduction resonating our skull and/or middle ear. The doctor, being a specialist of the ear, completely understood why the problem existed, but of course was very upset about its presence.

Recommendations

After taking apart the seats, we could see a spring system inside the cushions that was likely the culprit. Using a tone generator through the playback system, it did sing. It was actually the metal suspension bars held by the springs that resonated. After a run to the hardware store and experimenting with different materials, we found a winner. Cutting up pieces of commercial-grade rubber flooring mats, and placing them in-between the springs and against the metal suspension bars stopped the resonance. A cheap and easy fix!

Seat before Treatment

Seat after Treatment

Prep for FRP acoustic treatment

FRP before fabric

Finished FRP

Result

Below are the actual before and after treatment reverberation times. As can be seen in the graph below, the room now sounds very natural and articulate due to the FRP system. Note the huge before and after differences between the acoustically treated room vs. the untreated.

·  FRP is effective down to 63 Hz. and is only 2.5” deep

·  Controls room modes, first order reflections, reverberation times and flutter echo in a linear, tunable fashion

·  Conceals with an acoustic stretch fabric system

·  Fitted on-site by professional installers

Unique room reverberation time signature before FRP acoustic treatment

Controlled reverberation time signature after FRP acoustic treatment

Reverberation is probably the most recognized characteristic of a room’s sound and the most difficult to control. Reverberation is the acoustic energy in the space that lingers on after the sound stimulus has stopped. Each room’s reverberation times at each frequency are as unique as a signature. Ideally, we want the reverberation times to decay at the same rate across the audible bandwidth, and within a time window of about 0.25 – 0.40 sec. This allows for neutral sound conditions. An exception is for frequencies below about 125 Hz., where we need slightly longer decays in order for our brain to make sense of what our ears hear vs. what our eyes see. Lack of reverberation control results in masking of low-level details, loss in dynamic range, soundstage, timbre and articulation.