Sandy: I’m so excited to chat with you both and learn more about what you do as audiovisual design experts. Our topic is commissioning. Brian, what is AV commissioning?
Brian: Commissioning is the last step in the overall design process for the AV design team. At this point, the project has already gone through several phases. We start with programing and needs assessment meetings with the user groups. Then, we continue with the design process, which involves the whole design team: architect, electrical and mechanical engineers, and other consultants. Following the design phases, we provide a set of detailed drawings and specifications, which are used to bid on the project by system integrators.
Eventually, the project is awarded to a contractor who will install the AV systems according to our designs and specifications. Everything that we have documented in the drawings and specifications is now owned by the AV contractor as part of their scope of work. During the Construction Administration phase, which follows bidding, we review the documentation provided by the AV contractor, and accept or reject their submittals, based on adherence to the design documents.
Liz: Essentially, the contractor submits shop drawings and bills of materials. A bill of materials is an equipment list, with quantities and other equipment related details. Only after we approve these submittals, they can order all the equipment, deliver it to the site, and install it.
Brian: Once the AV contractor has installed the systems according to our specifications, they test the equipment’s performance and provide test reports to us. They must make sure that the system is configured properly, and functions as designed. After we receive their test reports and review them, we are ready to visit the site and check everything out ourselves. That is our commissioning.
During this visit, we walk through the site with the contractor, verifying that everything has been installed and is operating as intended, according to our drawings and specifications.
A small section containing items from the AV Consultants punch-list commissioning report to the project owner.
For example, does the system have wired or wireless microphones, and is this consistent with the design intent? Is the microphone not only working, but is it working without making any electronic noise? If not, we have to make note of that inconsistency or misbehavior, and include it in our punch list. The punch list is basically a list of items that we uncover during this commissioning visit, and which the AV contractor will need to fix.
Sandy: What happens if a contractor can’t fix an issue, let’s say it is a malfunction of the equipment? Does it go back to the manufacturer?
Brian: Exactly. If there is a problem, the contractor will start by troubleshooting the piece of equipment, which may only require some reconfiguration, and verify that the actual hardware works properly. But if they determine that there is a problem with the product itself, then they have to get the manufacturer involved and obtain a replacement.
Liz: Through commissioning, we are making sure the AV contractor performed the installation of the systems according to the contract. And with this, we make sure that the Owner is happy and has the assurance that they were provided with the system we agreed upon at the beginning of the project. This is maybe the most important part for them, to be confident that they get what they paid for.
Sandy: During the commissioning process, do you count on equipment, such as sound level meters, or do you rely on your subjective observations and trained ear?
Liz: Actually, we do both.
In the photograph to the left, Liz is using a light meter, which is used to determine the brightness of a projector on the screen it is displaying on. This data presented can be used to make adjustments to the projector for optimal calibration for the space it is in.
The NTI TalkBox is an acoustic signal generator for speech intelligibility measurements.
It is used in the Technology Group to measure amplified speech intelligibility (STIPA) either by plugging the TalkBox into the sound system or by positioning the TalkBox in the typical “speaker” position and placing a microphone in front of it.
The TalkBox has a wide range of test signals consultants can use to test the sound system in a space which is used to measure the frequency response around the room. Listen below to one of the sounds it produces:
Sandy: As someone who is NOT an acoustician, or audiologist or AV designer, but who thinks that sound is a subjective experience, in the way color can be subjective to visual perception, I am curious…Do you walk around the site and listen and say, ‘hey, it sounds great to me’? Do you bring in other people, like the Owner or stakeholders, and ask for their opinions as well?
Brian: When it comes to sound, there is a scientific baseline that we can start with. For instance, what is the frequency response of the system? Is there too much low frequency? Is there too much high frequency, or anything in between? We use microphones and test equipment to check for that frequency response, to make sure that everything is aligned with industry standards and our expectations.
When it comes to the “color” of the sound, the sound spectrum, that is something that the house engineer can adjust. In the instance of a performance space, the mixing engineer can shape the sound as part of their creative process. But our job is to make sure that all the ingredients are there for them to make that “magic” happen.
Sandy: That’s really cool…sound as an experience of art, I love that.
Liz: However, listening may also take the lead, particularly with a more modest project, where there is no opportunity for extensive measurements. For instance, I worked on a project recently, a fitness studio at a K-12 school, where they did not have a mixing console because it would have been too expensive. I didn’t bring a sound level meter or any other measuring equipment, but I have a catalog of songs on my phone, that I’m very familiar with and know how they should sound. It is some basic musical reference material — pop, rock, jazz, and some classical.
Typically, I would play short segments of each genre, and if I hear something funny, I’ll play pink noise through the system with something as simple as an app on my phone that has a real-time frequency analyzer with a built-in noise generator. I use the app to confirm what I heard. I used this simplified method in that specific studio, and got a big surprise. The audio was muddy, but when standing under the subwoofers, there was no low frequency, or any sound coming from them. And what is happening at 2,000Hz? Pink noise and RTA confirmed a weird boost in the low octaves, which caused the muddiness and lack of mid frequency (like speech or vocals) spectrum. That’s a little ridiculous. The contractor was there, and I pointed this out to him, and we listened together. He climbed up into the ceiling box (where the equipment was mounted) and… the subs were not even hooked up! There was an impedance mismatch at the subwoofers, requiring further investigation by the AV contractor to correct. The tech who tuned the sound system must not have realized that and tried to compensate by boosting the low frequencies of the non-subwoofer speakers.
Sandy: Oh, good. And then once they connected them, you’re thinking, “yes, this is the way it should be,” right?
Liz: Indeed!
Brian: Yes, I have an example like that, too. An auditorium sound system included a center cluster of speakers, which is primarily there for speech reinforcement from the stage. We had stage left and right loudspeakers, for music playback. In addition, this room was set up for movie playback. So, we had a Blu-ray player in there, and there was even a surround sound processor. I remember trying to play a Blu ray disc during commissioning, listening to it, and telling myself something was not right. And this is the kind of thing where it’s important to have a trained listener in the space, as opposed to relying on a sound level meter alone, because a meter cannot pick up what human binaural hearing can.
I stood in the center of the room and thought that something was weird sounding. I turned my head, and it sounded better. I turned my head again and thought, “now it’s weird again!” It turns out that the loudspeakers were out of phase.
Liz: Which is basically a timing difference between two identical sound signals. We just talked about this in class this week. (Editor’s Note: Liz teaches acoustics at Berklee College of Music.)
Brian: If anybody went in there and tested each speaker individually, they wouldn’t have troubleshot that because each speaker was operating fine, on its own. In situations like this, the equalization can be okay, but when the speakers all interact with each other, that’s when you might start to hear things that are not set up properly.
Sandy: Then how does it happen that there is a timing difference?
Liz: If you go back to the idea of superposition of sound waves, when you add at a single location sound waves arriving from different loudspeakers, they either boost their energy at a certain points in space or cancel each other out, depending on their interaction with each other. And this is frequency specific. So, you can end up with a situation where certain sounds are louder than they should be just because of your spatial position relative to the sound system. Or, likewise, some frequencies could be missing. Some people refer to ‘180 degrees out of phase’, when the troughs of one wave match with the crests of the other, as being the only “out-of-phase” scenario, but that’s not quite true. Phase shifts can be more minute than that, and equally powerful in the way we experience the sound. And in that case, it is not only about a signal flip (one loudspeaker being out of phase with the other, in the stereo pair), but rather about the listener’s location relative to those loudspeakers. It’s about positionality.
Brian: Phase is something that, when you hear it and you know what it is, you can recognize it immediately. But trying to describe what it sounds like… I struggle with this. Liz, do you have an explanation?
Liz: Well, when something doesn’t sound right and you can’t figure out what it is, I advise my students to check the phase to rule that out since (at least in mixing audio) it’s a relatively easy fix. To give them an idea of what phase might sound like between a stereo pair of loudspeakers, I like to pick a higher frequency (shorter wavelengths) so they don’t have to get up and can just move their heads to hear the change. I’ll play a 1,000 or 2,000Hz tone through the sound system in the classroom and have my students just shift their heads a little bit and ask, do you hear the ‘in’ and ‘out’ of the sound? That’s phase. Beating, the dissonant phenomenon musicians should be familiar with as it’s helpful when trying to tune our instruments, is an oscillation of constructive interference (too much of a sound) and destructive interference (little or no sound) – the technical terms for the two phase issue extremes.
Brian: In a theater space, for example, there are usually left, center and right loudspeakers up above the stage. These are the primary speakers that do most of the heavy lifting for sound reinforcement. But—depending on the position of those speakers—we may need to include supplemental loudspeakers to support them. So we may include front “fill” loudspeakers, which are small speakers that go across the front of a stage.
Since the primary loudspeakers may project the sound above the heads of the audience in the first couple of rows, we would need to use those smaller loudspeakers, across the stage, to fill in that gap. Likewise, if the primary loudspeakers are up too high, we can combine their sound with those small speakers in a certain way (through level optimization and delay processing) to bring the sound image, or otherwise said, the listener’s sound localization, down closer to the stage area, rather than from up above.
It’s disconcerting when you are sitting in the audience and you’re seeing somebody speak in front of you but you hear their voice way above them. The person’s location doesn’t match with the sound location, right? So those front fills help adjust that sound image.
At the same time, the back few rows of audience seats may be too far for those primary loudspeakers to reach out to with sufficient loudness and quality. In that case, we might add speakers farther back into the house to support the main system. These are called delay loudspeakers.
Liz: In terms of commissioning, it is our responsibility to set the processing correctly on all those loudspeakers, so that the sound is natural overall. You don’t want to bring the audience members’ attention to one set of loudspeakers or another. You want everybody to think that the sound is coming from the stage, whether you are listening from the main floor, or from the balcony, from the front of the room or from the back. All this fine-tuning is done with a bit of test equipment, but it is our ears, our listening experience that becomes our most valuable asset. You can set the system up ‘according to the rules’ with all the knobs turned to their right position, but it will still need a little bit of art – a little ‘finesse’, the human component under the form of our trained binaural listening. <– Click to read more!
Model of loudspeaker coverage mapping. (For clarification, a 3dB difference is just noticeable, a 6dB difference is definitely noticeable, and a 10dB difference is considered a perceived doubling of loudness).
Brian: Often during commissioning, I sit in one of the balcony seats and listen to the sound system, and I then realize that the speaker above my head, which is supposed to be supporting the primary ones, is a little too loud or not quite time-aligned with the rest of the loudspeakers. I can hear a disconnect between the primary loudspeakers and the support loudspeakers. At this point, we work with the contractor to fine-tune the system, to achieve the appropriate localization at any point in the hall as coming from the stage.
Sandy: So AV system designers are the mixologists of the palette of sound?
Brian: In a way! We’ll use a combination of test equipment and our own experience to achieve the ultimate outcome for our designs.
Liz: And try our best to support the architect’s vision and the client or end-user’s needs, while acting as a referee between the design team and the AV system installer. It can be a bit of a tightrope act at times, but we thrive on those sorts of challenges. Because we’re sound nerds!
Brian: Often during commissioning, I sit in one of the balcony seats and listen to the sound system, and I then realize that the speaker above my head, which is supposed to be supporting the primary ones, is a little too loud or not quite time-aligned with the rest of the loudspeakers. I can hear a disconnect between the primary loudspeakers and the support loudspeakers. At this point, we work with the contractor to fine-tune the system, to achieve the appropriate localization at any point in the hall as coming from the stage.
Sandy: So AV system designers are the mixologists of the palette of sound?
Brian: In a way! We’ll use a combination of test equipment and our own experience to achieve the ultimate outcome for our designs.
Liz: And try our best to support the architect’s vision and the client or end-user’s needs, while acting as a referee between the design team and the AV system installer. It can be a bit of a tightrope act at times, but we thrive on those sorts of challenges. Because we’re sound nerds!