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I have been assigned to improve the audio quality in a School auditorium. In specific, it is a common complaint that spoken text is difficult to understand. The room is large, with a high ceiling, and while it is excellent for chamber music it is in fact a challenge to understand spoken text.

This year, of course, everyone is wearing a mask. This exacerbates the issue. When speakers use the mic it seems only to project their muffled sound, louder.

Assuming that speakers are properly trained in holding the microphone close to their mouths, how can I maximize the intelligibility of their speech? Our PA system is older, low-tech, but it does have a rudimentary EQ. Are there certain frequencies that I should adjust to help?

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    Is this a music question?
    – Tim
    Oct 6, 2021 at 8:08
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    @Tim - it probably isn't, but it's not sound design either… & this stack is a lot busier than sound. If it were singers rather than speakers we'd all be fine about it.
    – Tetsujin
    Oct 6, 2021 at 8:45
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    You really need some curtains to hang on all the walls. The ceiling would be nice to damp out also, but much more difficult. Oct 6, 2021 at 13:35
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    I'd just like to remind everyone that the question is not "How do I improve the acoustics of the room." Unless nuggethead wants to ask that question separately, I think we should all assume we're not looking for acoustic treatments or the ideal speaker arrangement, but simply how to get the most out of the existing sound system. Oct 6, 2021 at 18:28
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    @AndyBonner Sometimes stackexchange is just one big XY problem. Seriously, though: While knowing the room size and surfaces could lead toward acoustic recommendations, it can also help a little bit with performer/microphone placement on the stage and EQ settings.
    – Theodore
    Oct 6, 2021 at 20:18

6 Answers 6

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I'm going to offer a non-technological suggestion. As several answers have already observed, you're fighting some impossibilities (not the least of which is "I have been assigned to improve the audio quality in a school auditorium," presumably without any significant budget, just the expectation that you can create acoustics by tweaking a few pots). I'm also going to assume that having speakers remove their masks is not an option for policy reasons, and that we're not addressing here how one might upgrade the room or system if the money or will existed.

Yes, you should mess with the EQ; you should do so anyway to find what works best for the space. But the idea that you can take a signal that's muffled by the mask and "clean it up" through EQ is like the familiar trope from sci-fi and police shows: The team views a blurry picture of the crime scene, the commander yells "Enhance," and suddenly... we can identify the face of the killer! It's laughable because you can't just create data that was never there.*

Instead, I'm going to suggest that you do as much as you can to improve the human element. This can be a learning opportunity about elocution and skills that are always important to public speaking and singing, whether amplified or not. This training is the best way to radically improve the intelligibility of presenters at any time, but all the more so with masks on. I've been trying to remember, for the last 1.5 years, to walk up to a counter and place my order more or less in the character of Capt. Jean-Luc Picard. ("Hello. I would like a small house blend, please. Black. Engage!") Depending on the age of the students, there's only so much you'll be able to teach them, but you can try.

If leadership can give you a moment to do so, gather all the people who will be speaking. Train them to slow down their speaking (maybe 50%-75% of normal rate, especially if they're given to blurting a memorized line). Yes, train them to get appropriately close to the mic (a matter of inches for most dynamic mics) but also to project well, so you're not left maxing out the slider and getting feedback while someone whispers. Teach them to fill their lungs and use their diaphragm. Most of all, with face masks, encourage them to hyper-enunciate all consonants, since these are what is lost. Without face masks you might have to couple that with a "popper-stopper," but these days everyone is basically wearing one right on their face.

* (Or at least, that was true for decades; maybe now AI could make it possible. But if it's revealing "the face of the killer," maybe now we've got Minority Report-style concerns...)

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    I like this answer except eating the mic. Being too close to most microphones hurts intelligibility, although it can help gain before feedback (until you’re really eating the mic and then it hurts gain before feedback again). Unfortunately, in a reverberant space, EQ can seriously hurt gain before feedback also. Oct 6, 2021 at 13:33
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    Makes sense, and disclaimer, I'm a performer parroting what I've heard from "sound guys," not an actual sound guy. Also on second thought, as long as it's a quiet stage with one speaker, there's way less concern about gain than a singer in front of a drum kit. But I've also seen those folks who take a vocal mic, hold it at waist level, and mumble, and then wonder why no one can hear them :) Oct 6, 2021 at 13:38
  • Excellent answer, especially the bit about "enhance!".
    – nuggethead
    Oct 6, 2021 at 14:26
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    The speaking rate recommendation is gold. People simply aren't accustomed to speaking in a reverberant space where the echo smears their syllables together. (It probably also conceals the errors of student chamber musicians).
    – Theodore
    Oct 6, 2021 at 15:53
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    Actually, enhancing a blurry image is in many cases possible: if the blur is due to being out of focus, deconvolution can be applied. The downside is that it increases noise, but this may be tolerable. For the mask-muffled sound it's similar; boosting the treble frequencies is similar to what deconvolution does. None of this requires machine learning techniques. The thing in film that's impossible is enhancing pixelated images – in that case the required information is not merely muffled but actually missing completely. Oct 6, 2021 at 17:44
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There are three things I'd recommend in terms of PA-settings that do usually make a significant improvement on intelligibility in excessively reverberant rooms:

  • Cut the bass. Like, properly. Many consoles have 80 Hz low-cut filters on each channel, definitely use those, but in addition don't hesitate to pull down a 100-150 Hz band as far as it goes, perhaps even remove as high as 300 Hz.
    It may be counterintuitive that removing parts of the sound improves understanding, but the thing is, these frequencies add almost nothing to text intelligibility, however they do push the speakers out of their comfort zone, overload the ears, warble around a lot in the room, and contribute to feedback problems. The bass frequencies are even more over-present through the masks.
  • Find resonance frequencies of the room and notch them out. This requires a parametric EQ or graphic with at least 31 bands. Even then it's unfortunately often not possible to get it completely right; such resonances tend to shift around strangely.
  • Apply some compression. Big part of the problem with understanding speech in echoey rooms is that the louder parts of the sounds (often P and T plosives as well as vowels that hit a room resonance) smear over everything else. A fast compressor can attenuate these sounds and thereby lets the rest of it have its needed share of the attention as well. Also, a compressor will just even out the overall volume level, which makes it easier for the ears to adjust.
    Unfortunately compression increases feedback sensitivity, so this cannot be done too strongly.
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  • This! I strongly suspect that the "rudimentary" board won't let the OP notch room frequencies, but it's such an important thing to do especially in a room with acoustic issues. Oct 6, 2021 at 18:33
  • In that order too, ideally. Compressing before the bass and mud-frequency cuts is ideal
    – element11
    Oct 6, 2021 at 20:06
  • We don't have a compressor, but I can try attenuating the bass somewhat.
    – nuggethead
    Oct 6, 2021 at 23:20
  • @nuggethead - compressors aren't expensive, and can deal with all the vox channels on the p.a. simultaneously.
    – Tim
    Oct 7, 2021 at 7:47
  • I think that plosives may already be largely muffled by a mask, perhaps so much that it produces the opposite problem (speech too muddy). Oct 7, 2021 at 12:35
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Two solutions for you which are either no-cost or ultra-low-cost. They just need a little of your time and effort.

Clean or renew the foam mic windshield

Foam windshield are often left in place over a mic for a long time without being cleaned or replaced. They naturally will get saliva on them, which collects over time (and breeds bugs too). I've seen plenty of dirty foam windshields which cut off enough high end and high mids to interfere with speech intelligibility - as well as being a health hazard too, of course. They're easy to clean, and they cost peanuts to replace.

@AndyBonner has reminded me that many mics have an extra foam insert behind the mesh screen. Unscrew the mesh screen, and remove and clean that foam too. Spritz the mesh with antibac while you're at it too. Or if it's bad, replace the mesh ball entirely - it's pretty cheap, and you don't need genuine Shure mesh balls.

Where are the speakers, which way are they pointing, and what's driving them?

For clarity, you want one set of speakers at the front, facing down the hall. Since you have no room treatment, you want the speakers mounted fairly high and angled downward by about 20-30 degrees, so that the sound all goes towards the audience and doesn't bounce off the walls and ceiling. Speakers typically give out sound to about 30 degrees up and 30 degrees down. If your speakers have a tilt socket or are adjustable, then do it. If not, speaker tilt adapters cost very little.

If you have more speakers, you want them halfway down the hall and facing along the hall towards the back wall. Again you need these pointing down at the audience. For best clarity, you want a loudspeaker management system which can put a delay on the signal for these speakers, delayed by 1ms per foot of distance between the two sets of speakers. This is how long it takes sound to travel that distance, so you don't get a strange echo. In a smaller hall you might get away with it, but if you've got a large room then this is basically essential. Look up the Haas Effect for how this works.

What you absolutely must not ever do is have a second set of speakers at the back of the hall facing forward. This guarantees an echo which destroys intelligibility. If this is the setup you have, then turn off the back speakers. Cut the wires if there is no other option! You'll find people will be able to hear way better, even if it's less loud for people at the back. And if you can move the back speakers, then put them halfway down the hall as above.

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  • I need another upvote to give this answer for offering a dirt cheap, 5-second improvement in the form of the windscreens. Even a mic with an internal windscreen behind a grill like the Shure SM58 can replace that (or maybe it's easier to replace the grill as well? Looks like < $10). Oct 7, 2021 at 15:17
  • @AndyBonner Thanks for the reminder about the foam inside the mesh ball. I've updated the answer to add that too.
    – Graham
    Oct 7, 2021 at 16:55
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This probably isn’t something that can be solved at the microphone end. The space is too reverberant. Probably there are just a couple of speakers trying to serve the whole room. It needs more, smaller speakers, closer to the audience. Or possibly a line array. Not cheap, I’m afraid.

Masks don't actually muffle the voice very much. They make it harder to communicate largely by removing the visual clues from mouth and face.

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A radio (wireless) mic will help, along with not using a mask, but a visor instead. The kind which fits over the top of the head with a swan neck to position the mic in front of the mouth (I used to wear mine resting on my neck).

Without knowing the speaker configuration, it's difficult, but in a lecture room/auditorium holding say, 250 people, there needs to be 6 or 8 speakers minimum, spread from back to front. Even a couple of flown speakers covering the centre of the room would help. None would need to be expensive - covering vocal range will do - and my mic cost something like £50 - I used it for many gigs.

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    As I understand it, a visor may help to deflect droplets — but it does very little to stop aerosols, which are now understood to be the main route of infection for COVID-19.
    – gidds
    Oct 6, 2021 at 21:23
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    @gidds - yes it's worried me or some time - those arrogant aerosols who walk round with either no masks, or their noses poking out..!
    – Tim
    Oct 6, 2021 at 22:44
  • Face Shields are out re:our covid protocols, but I'll see if I can get wireless mics with the goose/swan neck
    – nuggethead
    Oct 6, 2021 at 23:22
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I can only recommend that each speaker, in order, approach the lectern and remove their mask.

Ensuring, of course, that everyone else on the podium or stage is six feet away or more.

Supply alcohol wipes to smear over the common microphone in between designated speakers.

Any other solution (such as boosting the treble for the Mic Line) is just folly, and more or less a socially-acceptable band-aid.

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    Definitely not a possibility with our covid guidelines
    – nuggethead
    Oct 6, 2021 at 14:08
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    It really varies a lot around the world. In Montgomery County, MD we have a rule (effective August 5, 2021) exempting face masks: when a person is giving a speech or performing for broadcast or an audience, if no one in a location accessible to the public is within six feet of the speaker. However, it is not widely known within the county and every jurisdiction has a slightly (or dramatically) different set of rules. And the rules today could change tomorrow. Oct 8, 2021 at 1:09

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