Speaker Boundary Interference Response. (SBIR) A topic that I am guessing most of you never heard of. And that is exactly why we are covering it. Before talking about the phenomenon in discussion, I'd like to shed a little light on the cause of its disappearance from popular culture. SBIR is not a rare or newly discovered thing that not many know about. It has been existing for decades, and would exist everywhere there is a speaker and a room boundary, hence, every studio! So why has nobody ever talked about this? Because while there are so many reputable companies building studios, (and highly professional engineers working in those studios), as it seems, not much has been put into consideration except for the agenda of making quick money! (HARSH TRUTH) SBIR is currently one of the "insider topics" because over time, newcomers ignored to delve under the surface, and the history was forgotten (okay, that was a little too much, lol). And these tight corners are where we emerge. Hold tight! As a DIY studio builder or a professional designer, comprehending SBIR is essential for creating acoustically superior listening environments. In this article, we will explore what SBIR is, its significance in studio design, and practical strategies to mitigate its effects.
What is Speaker Boundary Interference Response (SBIR)?
SBIR, or Speaker Boundary Interference Response, refers to the complex interaction between sound waves emitted by studio monitors and the nearest largest surface, i.e. front wall of the room in which they are placed. When sound waves from a speaker encounter the front wall, trouble happens.
To fully understand this, we need to understand the way a speaker works, and how sound propagates before delving further into SBIR;
So far, we visualize sound coming in a beam form from a speaker, in a linear route. Well, this linearity starts broadening up as we move down the frequency spectrum, and it just loses it all at about 130Hz.
In simpler words, a speaker starts radiating sound in a broader span in lower frequencies, and in the bass range, it effectively radiates everywhere around it like in a sphere, even behind the speaker, as if the woofer is present on all sides at all points!
Now, does it make sense, how the sound might get reflected off the front wall? And for the major part, we are looking at Low Frequency problems here. So while it sounds like the range of problems is limited in the low-frequency range only, please bear in mind that this range is the nasty one! It's not a child's play to control the BASS!
Why Does SBIR Matter in Studio Design?
For studio builders and designers, SBIR is a critical consideration because it directly impacts the accuracy of sound reproduction. In a studio, the ability to monitor audio accurately is paramount. SBIR-induced frequency response irregularities can lead to misleading audio information, making it challenging to make precise mixing and recording decisions.
SBIR can result in dips or peaks in specific frequency ranges, leading to an unbalanced mix. Accurate sound reproduction ensures that the mix translates well to various playback systems.
If you don't understand how and why, this passage is for you: Simple enough - the sound in the low range, which radiates everywhere, strikes first on the first wall (the nearest boundary), and the distance to the front wall and back to the listener is so small, that the sound probably couldn't even interact with the rest of the boundaries before the front wall reflection has already reached to listener's ears almost with the direct sound. Overlapping of two signals (one direct and one reflected) in such a short timeframe is bound to produce unpredictable but significant distortion to the sound, hence affecting monitoring and critical listening.
So, what's the solution?
Eradicate the interaction of the sound with the front wall. And some popular solutions include - 1) Moving speakers away from the front wall 2) Deadening the front wall with heavy absorption. But the key to understanding here is - Is SBIR the only problem to address in a studio? That's where things start to complicate. Changing the speaker's location would result in changing the listening position to a point that might not be the right location in the room. Even if not, I don't see how this is solving the problem, how further can you get the speakers anyway? Bass will still spread and it will still reflect! In the second case (Deadening the front wall with absorption), the solution seems like a no-brainer. And it is! You simply prevent the sound from reflecting - easy. But as you guessed, I am going to show a problem here as well - a tad later!
Ironically, you see a lot of hard front walls in many studios, especially in traditional control rooms, GrayVee's DRS Rooms, Hidley's NE rooms, and Northward's FTB rooms. Well, these are all complicated design approaches to properly address all the countless problems associated with room acoustics, including the SBIR. (The hard front walls we build in our DRS rooms are not just plain walls. The wall system is a complex composition of speaker soffits, pressure bass traps, diffraction, and redirection geometrical devices. Making them look like a simple wall is a work of art that we find pride in!)
So coming back to it, why not porous absorption on the front wall?
Well, I don't know a lot of people who'd like to live in a really dead room for a good few hours of the day! Full range absorption on all the walls - NIGHTMARE! The unnaturally dead environment can make you go mad in minutes if not seconds! Don't believe me, search about people visiting anechoic chambers!
The question arises - What is the correct solution?
(EDIT: )
Since only low-frequency energy is being reflected off the front wall (unlike other surfaces, where sound interacts in full range), we can limit our absorption to only tuned bass trapping in the front wall. Not much need for porous absorption there. We can leave some hard surfaces there to act as a natural psychoacoustic cue for the engineer's brain to stay neutral, and not go under the stress of being in an unnatural space.
If this was a little too much for you to digest, don't worry. Over the course of the next few months, we have a list of blogs scheduled on psychoacoustics and how humans react to sound and different sonic environments. Psychoacoustics is a big, big part of the basis of our DRS design. And, one of the causes which sets us apart from the competition. When all the room measurements read near perfect, and the artists in the room don't get creeped out by the usual pressure-deadening vibe of traditional studios, it marks the success of a true DRS build for us!
Well, this was how we manage the issues of SBIR along with making sure to address all the other aspects of the space, but what about you?
(EDIT CLOSE)
What are solutions for you as a home studio owner who can't go this complex route just yet?
Quite a few! But, this blog limits us to wait for next week to finally get the right solutions to manage the SBIR in a room!
This blog was just a technical overview of SBIR, and in actual practical environments of a small home studio, there's quite a different way to look at it, which we will discuss in next week's release!
Till then, if you want to get a step ahead, and find the solutions, get researching on the following:
1. Monitor Placement and choice: Right size, right field of range, and right placement.
(Something aroun 6 inches- 1.5 ft has been observed as a good starting point in small stereo monitoring spaces)
2. Isolation and Decoupling
3. Bass trapping
4. Room Shape and Dimensions: Design studios with consideration of room shape and dimensions. Avoid overly cubic or symmetrical spaces, as they can enhance SBIR effects.
Conclusion:
In the world of studio design and construction, managing Speaker Boundary Interference Response is vital for creating acoustically superior environments. By understanding SBIR's impact on sound accuracy and implementing the right strategies, you can ensure that your studio provides an ideal platform for musicians and audio engineers to create, record, and mix audio with the utmost precision. Achieving optimal sound quality is not just a goal; it's the foundation of successful studio design.
Comments