So today we’re going to talk about a subject that kind of drives us crazy:  acoustical doors.

In our experience over the years, we’ve designed a lot of projects. We’ve worked on many projects that called for the use of acoustical doors. Quite often, acoustical doors don’t work properly in the field. The ones that we specify are magnetically sealed, and they tend to work quite well. The ones that are compression sealed, however, do not.  

Most recently I was asked by an architect to do some testing on a project that we did not design. There was a compression sealed door substituted for a magnetically sealed door. It was testing at NIC 38 but it was supposed to be a NIC 50. Why was that? Well, the door simply could not get enough compression to seal the seals.

The results in this instance were so poor because they were using a card swipe access system that would not allow that amount of compression. So, the customer was paying for 50 and getting 38, which is a dramatic loss. 10 Points is twice as loud……

And in this particular example, it was a vocal isolation booth in broadcast, so it was a big deal. What they needed to do was change the seals out to magnetic, which can be done in the field. It is an added cost and obviously contractors would be involved.  Since it was not our project, we have no idea what they finally decided to do about it.

Why Mag Sealed Doors?

So, what I want to talk about is why magnetically sealed doors are used.

Our first example is your refrigerator. Your refrigerator has a mag sealed door on it because you want to keep the cold in and keep the heat out.  Acoustics are the same thing. A magnetic sealed doorframe, like a refrigerator door, reaches out and grabs and the refrigerator frame, and that keeps the door closed.

In the case of a door that is used by the public, it must meet ADA* requirements. The door must have the proper opening effort to meet ADA. There are some magnetically sealed acoustical doors that do and there are some that do not.  *ADA: Americans with Disabilities Act of 1990

When you get beyond about STC 45, you must go to a double magnetic seal. Most of those will not meet ADA requirements and would then require something like a motorized operator to open the door to meet ADA.  If you want high performance doors, you are going to be using double or triple magnetic seal doors and they are not going to meet ADA. Good as they may be acoustically, they are not always usable.

We’ve had some clients who have chosen to go with compression seals because of the opening force, but they are often 10 dB or more lower than their rating because they don’t compress.

We show you something in this video (starting at about 3:00 on the meter) as we look at a door online and kind of walk through how it is assembled and the type of performance that you can expect out of it, if it is properly installed.

 

 

Our base spec is always centered around IAC Acoustics because of our experience with them in the past. (A picture is worth 1000 words, right? Well, In the video above you will see this and other examples and we explain them.)  This door is an STC 43 but we have had field performance from this door closer to 47. Now they won’t rate it that way because they are very conservative, but we have had many of these in the field for quite a while and that has been what we have observed. Not only have these acoustic doors performed higher than the official rating, but they have also continued to perform that way as time goes on.  

So, why do they perform so well?  First of all, they are built completely assembled with hardware delivered. So, the contractor can simply set the door in place to the threshold and the walls and it is done. No one has to put assemble  hardware in the field.

This door also uses a cam-lift hinge system. So, the door rises up in the air as it is opened so that it lets a yield pad compression seal at the bottom expand and then it compresses as it drops. You’ve got the magnetic seal around the perimeter which really is a very high performing seal.

Double Magnetic Seal Doors

Now let’s talk about situations where you need something beyond. In these cases you will be getting into a double magnetic seal door.

Again, it is kind of like your refrigerator. When you go to pull it open with a single magnetic seal, most people can open it, no problem.

If you had a double magnetic seal, and then added to that a cam lift hinge raising and lowering the door, you might not be able to get your refrigerator open. You have probably seen small children who cannot open the refrigerator, even with a single magnetic seal.

Double or even triple magnetic seal doors are used in higher performance music spaces such as recording studios giving them up to way beyond 51 with a triple magnetic seal. The doors also weight 300 Lbs Plus.

Now, the reason I think they go with the double seals is when you get into these thicker heavy doors, you’ve got issues with potentially leaks around the seals themselves, possibly due to the doors. The second seal would be there to close that up. I am not really sure why they cannot do that with a single seal with a really heavy door, but everything above 51 tends to be double magnetic seal. Then the really high-performance doors tend to be triples.

A word to the wise, if you really want a compression seal door to work, be prepared to have to lean on it with your body weight to close it. (also not ADA compliant)  And then all of the tension when you do that is at the latch set. If your latch is the tension point for the door, it’s not holding it evenly around the perimeter. So you’re not necessarily going to get a compression seal that holds at the perimeter when all of your tension is at a latch set, which is where the mag seals come into place. The door is not being pressured to make it work.

In our opinion, mag seals are the only thing you can trust. Everything else we’ve tested has been sketchy at best. We have tested many doors over the years, we’ve had one or two with compression seals that came anywhere close to their spec. It just happened to be a very perfect, pristine installation and there is no guarantee that they’re going to stay that way. 

Do take a couple of minutes to watch our video.  It includes further explanation concerning the compression vs. mag sealed door decision and you will see why acoustic doors DRIVE ME CRAZY!  

We hope this post and video help you avoid a disappointing result (and the frustrating and often costly need to make corrections after) as you create a sound-isolated space.

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Let’s talk about microphone techniques.  I work with a lot of singers. When I work with them, I am always surprised the little they seem to know about how microphones work or that they have a part in getting a successful sound in a live environment.

So, I made a video called Microphones 101 to teach how the new (and not-so-new) microphones work and how to get the best sound in a live venue.  *Watch the full video here:

https://www.youtube.com/watch?v=UCFeVznYFNE&t=15s

The first mic we will look at is a kind of beat up Sennheiser wireless. It’s a G1 series wireless with a condenser head. This mic has its own particular group of things that go on with it.

So, this mic has some good and bad characteristics depending on what you’re looking for. When you have no EQ applied to it, you’ll notice there’s some serious sibilance* in this microphone and a fair amount of low frequency handling noise.

DEFINITION: sibilance = a hissing sound

1. The first thing a singer should be aware of is whether the mic they are using is making noise when they move it around.

2. And the second thing the need to know is where do they hold the mic when they are singing.

This seems to be a problem for some singers. One of the events that I work at regularly involves 8 singers, all of whom are quite animated on stage. They move around a lot. They do a lot of things and, as a result, the positioning of their microphones is very inconsistent. Microphones are designed to be used at about a two to four inch working distance in front of the capsule. (i.e. their mouths should be no more than 4 inches away from the mic.)

If you take that mic and tilt it, as some people do, to a 90-degree angle, you’ll find that there is a relatively large shift in the response of the mic. Some wind noises change frequency to very low frequencies.

This image shows frequency spectrum where you can see the different frequencies being affected with lows and highs. If you don’t know that, then you are probably not a sound guy, you are probably a singer. The important thing to remember is that the position of the mic is a big deal.

The other thing with the microphone is that gain is related to the position. So, if I hold the mic just 2 inches from my mouth and then I double that working distance, I just went from 2 inches to 4 inches. That movement will cause a huge drop in level, with an attendant change in frequency response. This is what is known as “proximity effect.”

Proximity Effect

Most microphones exhibit proximity effect to some degree, some more than others. Condensers like the 865 head have a lot of proximity. And if you get really close to the capsule, it gets really kind of crazy. Then, if you get extra close to the capsule along with moving it at funny angles, it gets even weirder.

So, when mixing one of the first things we do with condensers is we typically roll off the really low frequencies by putting a low-cut filter on them. And then, once that is done, we start looking at other things as getting rid of sibilance that is on the microphone. Now the singer has a microphone that is a little more neutral, but if they back off the mic, they are gone. In actuality, when the gain drops down to 20 DB below everybody else, it’s a problem.

What I like to do, and not everybody agrees with this, is make it where if they get too far away from the mic, it turns them off. In other words, the gate just turned them off.

Why?  Well, when you have 8 singers on stage and you are trying to blend their voices (I deal with this regularly) they are getting so far away from the mic that effectively their voices disappear. You would think that the fact that they no longer hear themselves in the monitors would signal to them that something is wrong. But typically, they ignore it. So, the sound engineer has a singer who is not cognizant of what is going on. At that point, I would rather have their mic off, than having it pick up random noise from other things on stage. It is a matter of preserving the overall good of the audience’ experience.

To recap:  working distance is very important and performers need to be aware that, if the working distance is not reasonable, they will not only have tone problems, they will have an, “I left the mix” problem.

Working distance is the first thing to look at. The second is a consistent use of the microphone. One of the more fashionable mic handling styles with some singers, first popularized by rap stars, is cupping the hand over the microphone.

Cupping your hand over a microphone does a number of things.

1. It changes the frequency response.
2. It changes the gain.
3. It changes a lot of things.

As you watch the video, you will notice the big boost around a hundred, two hundred, 1K 2K, and  that it gets kind of nasally sounding. Part of that depends on how far you cup your hand. This technique can go from several stages of partial covering till the mic is almost completely covered.

If I wanted to fix these things, I could. If the singer wanted to use the mic the same way all night, I could kick in a compressor to level out the gain problems I’m running into because of all of this. But if that singer suddenly decides to go back to holding the mic normally again, everything changes. Those abrupt changes just do not work well for those of us who care about the overall mix. This is just one example of the problems that happen with singers on stage who inconsistently handle the microphone, not to mention handling noise that also goes on. Add to it that you have eight singers all doing this, you have a lot of unpredictable modifications in the mix.

So avoid the gain changes that occur with microphone working distance. If you are going to be moving around a lot, learn to move your body with your head, which means you cannot have your head going in different directions than your microphone.

Handling a microphone is like playing an instrument.

It is kind of like playing an instrument. If you’re a guitar player, your fingers are supposed to be on the strings when you are playing chords. So you really have to work on this. Many singers seem to, at least the ones I get to work with, ignore all of this. And then they wonder why there are no altos. There are no tenors. There’s no, this there’s no that. The other ones that I really don’t like for other reasons, when I turn this compress around, before I do, this are the ones who eat the microphone.

Now in this particular situation, the gain of the mic is already too high to get away with this. So, I’m clipping the input. Now I’m just backing off that. And then I’m using the compressor and I’ll have to use some makeup gain to get back the gain I’m reducing. But when you get really, really close to one of these microphones, I will have to turn the EQ back on to try to fix the stuff that’s happening by being really, really close to this microphone.

So, there’s a lot that goes on with the 865 p microphone when you get really close to it. So, you end up with a curve that looks pretty bizarre when you get really up there. That sibilance peak, while it’s still there it is less prevalent, and you get all of this low, mid frequency energy going on. The way you fix it is that is you use the mic properly.

So, this is one style of microphone. Let’s talk about one that is radically different. And if you have singers who, for example, like to cup their hands over the mic, is a better choice.

It is a Beyer TCX 58, which is their kind of version of an SM 58. This mic with EQ off is very neutral sounding. Now, if I were to cup my hand over the microphone, there is nowhere near the dramatic effect you get with the condensers, which is one of my contentions. A lot of times people will walk in and they’re used to doing something with the mic they used to use. Then the sound company shows up with a different kind of microphone and hands it to the same artist and they decide to do what they always do. And they don’t realize that they’ve gone from that to this.

And this is now a significant problem. Now you’ll notice also that this Beyer TCX 58 mic, although it has a lot of proximity effect when you get really close to it, it doesn’t have nearly as much. So, the shift with gain is not as hard to manage. If you wanted to work it out with a compressor, you can actually get the compressor to manage the gain a lot better with this microphone.

So you get on this mic and then when you back away from it, it turns you back up. So you can get some things that aren’t nearly as dramatic as you get with proximity effect on a different microphone. The other thing with this one is if you do wanna put in a low cut filter, it solves the low frequency problem pretty much entirely.

Singers => Learn Your Hardware

So, I guess what was trying to get across in this short video is that singers really need to learn their hardware.

They need to learn what works, what doesn’t work. They need to learn how to follow themselves around. And if they’re really singing, dancing type folks, they either have to go to a headset or they have to do something else. But when you’re dealing with handheld microphones, you have a responsibility to make sure you’re rendering properly. And, if you don’t, the sound guy can’t deal with that with eight people.

“Hey, where did I go?“

So wondering why you disappear in the mix is something you shouldn’t be doing, which is why I do this thing where, if you get away too far, in my world I just turn you off. And when you have a bunch of singers on stage and you’re gating them all heavily like that, there is obviously band noise on stage, You have to gate it within that realm to get that to work. But what turning some voices off prevents is picking up a lot of distant noise that you really don’t want in your mix.

So, gating is one good way to solve that problem. And I’ve noticed the singers, at least the ones that I have worked with, they often don’t even know that they left the mix, which shows that they’re really not paying attention …but that’s a whole nother story. And we can talk about that, maybe, some other time.

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I wanted to do a video about the most difficult thing about soundproofing a home studio. We could call it “What’s That Noise?”  So, what’s the big deal about that? Well, oddly enough, this story starts on the roof of an apartment building. If that sounds weird, check out our “Kokomo Hum” video; then you will understand what I’m talking about.

The most challenging part with a home studio is low frequency control. You can get isolation for vocals and that type of thing somewhat easily. However, when you have base drum, bass guitar, any low frequency sounds that you don’t want seeping into the rest of the house — or low frequency noises from upstairs that you don’t want filtering into your studio (which you may not hear with your headset mic) — there is the challenge!  

For the backstory, listen to The Kokomo Hum.

You will notice in the soundproofing video that I am wearing headphones. Computer speakers typically do not pick up the elusive low frequency sounds that we are featuring so, when watching the video, you should put on a set of good headphones or in-ears to be able to hear the type of low frequencies.

Next, and unrelated to that, we were called to come to an apartment building. Residents were complaining about a humming noise that was occurring in several apartments in the same complex. It was a 3-story apartment building with dozens and dozens of apartments that were not hearing this noise. For those residents who were hearing it, though, the noise was annoying and impossible for them to track down.

So, we were called in to solve the mystery and tell them how to get it to stop. (You will want to go over to our soundproofing video now, wearing headphones, to get a much better perspective on this.)

 

And just so you know, we actually are going to get to why this has something to do with soundproofing a home studio and many other things. So, we arrived at the apartments where the hum was occurring, and we took a look at the roof above them. It was lined with air conditioning units — dozens and dozens and dozens of them. And they were all mounted the same way. They were mounted to a rail, sitting on another rail, sitting on a roof. They are just air conditioning units like you may have outside of your house. Now the ones outside of your house don’t do this into your house or you would probably leave your home.

So we discovered the air conditioning units were how the noise was getting there. The next step was to find what was causing it in the first place.  So when went into the apartments that were having the noise problem, we definitely heard the noise.

We went up on the roof and, when you’re walking around the roof you don’t really hear it, but you feel it in your feet. When you would get your ear up really close to one of these air conditioning units — really, really close – you could hear the noise.  When you would get your head down lower towards the bottom, it would go away. On the roof, you could hear it and feel it in the floor. Now what we got into is that we found that the units were mounted on rubber vibration isolators. They have a high enough deflection that typically 48 Hertz wave, which is what we were hearing, would be damped by them.

However, the problem was that they had them sitting on rubber vibration isolators. That seems pretty good, other than they could fall off the rail, which is a whole nother issue. The problem turned out to be this simple. They fastened them to the rail with an angle bracket that tied them to the rail.

So a single screw in four places on each unit was enough to put the unwanted low frequency noise into the apartment downstairs. We disconnected it from the rail and the result in the apartment downstairs was:  no noticeable noise.

When it comes to doing home studios, the likely challenge will be => vibration.

Note:  if you’re listening carefully to the video on good headphones, you can hear that it’s still there, but we had a 24 DB drop in level by simply disconnecting four screws. The takeaway is that when you get into doing home studios the challenge you are most likely to face is vibration.

When you try to do vibration isolation, no matter how you go about it, there are a lot of challenges. The first challenge is physical contact. If your walls are tied to your joists in the basement, you are going to have some issues. In this apartment scenario, there was other stuff going on that was kind of unusual and not easily understood. The entire roof here had many air conditioning units. They were all over the place. But there was only one apartment in the building that had the noise interference going on.  

So the question then is why, and it has to do with deflection and flexibility of the roof system. So, it was just the magic of math that in a particular spot up there in the roof, you ended up with this situation where all the right things came together, causing this frequency to show up in that apartment. And it was a little bit in the hallway outside it, but the neighboring apartments weren’t getting it. When we turned on all these other units, this was the unit that was for the apartment we were working on. When we turned on the other ones, it hardly changed at all. Uh, the other ones could activate it.

However, it didn’t matter which one on the rail did it. It was just this thing where this one place was a problem. So when people talk to us about designing a home studio with isolation or any kind of isolation, the challenge is always, how do you prevent isolation vibrant from occurring?

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