Reckoning the "boldness co-efficient" of this title statement, I am expecting a generous backlash, lol. But, truth is what we seek! Don't take my word for it, use your own brain, just let me help you... ;) Let's first understand the concept and reason behind using a vocal shield. Curved vocal shields were introduced as a quick solution to address sound reflections in vocal recordings originating from room boundaries. However, their design and material composition may work contrary to their intended purpose. In this article, we will delve into the acoustic properties of vocal shields and explore why they may not be suitable for achieving transparent recordings.
WHY?
The reasons are simple, however, we would instead take a gaze at the design factors of the product, which is simply self-explanatory: 1) Rigid and Reflective Frame:
Vocal shields often feature frames made from rigid and hard materials, such as plastic or metal. Unfortunately, these materials are strong sound reflectors, which means that instead of attenuating sound reflections, they bounce sound waves back into the recording space, potentially causing interference and coloration. (Please note, not all of the sound is bounced back. There are frequencies that get diffracted, transmitted beyond the shield, and some might as well get absorbed. The ones which get reflected off depend on the size and mass of the reflective object. Usually, in the case of vocal shields, it is midrange. 2)Thin Foam Absorption:
To absorb sound, vocal shields incorporate foam as an absorptive material. However, the thin layer of foam used in these shields may not effectively absorb frequencies within the fundamental vocal range due to inherent material qualities. You might ask why. Well, it is a topic of its own, and not in the scope of this article. However, we already have a rather long one elaborating all that the so-called "Acoustic Foam" has to offer! (you may call it a rant, it sounds like it, lmao): As a result, while higher frequencies may be absorbed, lower frequencies essential for a well-balanced vocal recording are left untouched. To a not-so-trained ear, this creates an illusion of a tight, reflection-free sound, but in reality, it is just a tonally uneven recording, which potentially has no observable reflections in the higher range, but fully mudded up in the lower and the mid-range. 3) Size and incident surface area:
The size of vocal shields is another aspect that warrants consideration. While they serve to create a barrier between the vocalist and room boundaries? the dimensions of these shields may not always be sufficient to provide complete sound transmission blockage. As a consequence, sound reflections can still occur despite the presence of the shield, reducing its overall efficacy in achieving transparent recordings.
Even if we assume that not much sound would leak outside the surface area of this shield (Which is not the case), the surface area of this shield allows low-frequency sound to simply diffract around it. with the biggest footprint being the horizontal dimension, which is usually around 1-1.5 ft, everything below 700Hz gets simply diffracted. Even if we assume for the foam to absorb a few dBs, it won't do anything below 400-500Hz. 4) Concave shape:
The concave shape of vocal shields can inadvertently lead to the direct targeting of reflected sound (from the frame) directly back at the microphone. This phenomenon occurs as the curved surface focuses the reflected sound waves, causing them to converge at the dead center, where the microphone is placed supposedly. Hence, potentially interfere with the original recording. As a result, the recorded vocals might exhibit undesired coloration and unnatural timbre.
A CLEVER DESIGN NONETHELESS?
Well, I'm not here to defame this shield. All we chase is physics! Purely intended to find the right info, the right solution! So, If you notice, there is a very clever element to this design, which doesn't come forward. The designers do get a little credit for this clever design; Part of the original vocal soundwaves which do not directly interact with the shield, but rather go in a different direction get reflected back from some wall. Now, a very small percentage of it has the potential to be incident on the back of this vocal shield. This percentage of sound, most of it is prevented from entering that shielded zone back! Here, all of the material properties of this shield that we have been criticizing come together to keep that reflected sound away from the "supposed" reflection-free zone! The steel frame reflects back the incident sound. The additional foam helps in absorbing at least a minimal amount if not a lot which might leak through, the concave surface (Which now becomes convex for the now incident sound) redirects these soundwaves to reflect in different directions much further away, and also the curved surface allows for some edge diffraction, which minimally diffuses the reflected sound further helping in reducing the energy intensity. We didn't talk about the size here, did we? Because that is what just simply Fs this up. (Sorry, I can't find a better word). All the forces of this shield, trying to shield the zone from the room reflections, and the size allows for every and all kinds of leaks. This small incident surface just doesn't allow any isolation. Even for the sound which falls directly on the external surface, only the mids and highs get reflected away. Frequencies below 700Hz again take the support of diffraction, wraps around the shield, and come through the microphone, via a second reflection from the back wall for sure, if not directly!
This apparently clever design is often mispresented by many sellers as an acoustically isolating shield, which magically creates a sound barrier. But that is just pure crap. Please use your wits and don't just believe they know their stuff. So far, there's been no magical advancement in the world of acoustics. The problems are the same as they were decades ago, and solutions stay the same as well. What has changed? The number of people selling snake oil! (uh, positively) (in stats, not effect. Written language is often tough, lmao!)
AN ACTUAL GOOD USE
Well, before this rant comes to an end, we actually do have to share a very peculiar benefit this vocal shield provides. No, honestly. No games this time :P Despite the inherent limitations mentioned above, the concave design of vocal shields offers certain advantages when used strategically. Precise construction and placement of the shield can lead to phase-coherent reflections reaching the microphone. In specific applications, this phenomenon can be advantageous for acoustically reinforcing the texture of the voice within a narrow bandwidth. By leveraging this characteristic, engineers can achieve a boost around certain frequencies where the vocalist may naturally sound weak, effectively achieving a reinforced vocal texture that might be challenging to achieve using other methods. This can often be useful for recording voice-centric projects such as podcasts and narrations. I don't think it is a good idea for music. Since every other sound is designed around everything, vocals included, tampering with vocal texture acoustically can potentially damage the entire song. As a creative experiment, this phenomenon can also be used to actually attenuate some specific frequencies which the room might be boosting. These frequencies are usually in the low end, where this shield cannot work - neither as an absorber nor as a reflector. (It just is invisible to low-frequency sound, as if they just pass through), but in case there are some relatively high-frequency peaks introduced by some acoustic distortion (rare to happen), some experimental placements, and re-iterations can help acoustically attenuate those frequencies if the shield reflects back those certain frequencies at the mic, which could interfere destructively in phase with the rest of the signal. Tough job, but fun for sure! To simplify, it's just like how Digital Room Correction EQ softwares work! They attenuate the level of frequencies in the original sound of speakers, those frequencies which are boosted by your room, which creates an illusion of a balanced signal to your ears. (We are coming up with a detailed blog on it. Till then, you can just take my word for it - Room correction Digital EQ does more harm than good! You hear one thing but you render something else.) However, the actual result would not be harmful, unlike the room correction softwares. What you record is not illusion, but acoustic sound. What you hear is just what you render!
VERDICT
In summary, vocal shields may not be ideal for transparent recordings due to their reflective frames, thin foam absorption, limited size, and converging shape. However, when used with careful consideration and precise calculations, the concave design of vocal shields can be advantageous in reinforcing specific vocal textures. As with any acoustic treatment, it is crucial to understand the strengths and limitations of vocal shields to make informed decisions about their application in recording environments.
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