the science of sound systems?

Subject: the science of sound systems?
From: leeneia
Date: 11 Apr 11 - 08:55 AM

Where can I get some science (book or site) on the proper use of sound amplification systems? How to do it right, how to avoid feedback, etc

Our church (age 60 - 80) merged with a younger congregation (30 - 50), and to them it's inconceivable that a person would speak in a large building without a microphone. Never mind that we have done it successfully for years.

The pastor is so over-amplified that she sounds tinny. The speaker hums constantly. Two times her voice has hurt me - seriously over the threshold of pain. I protested that (much to their shock) and they did lower the volume from actually painful to merely disturbing.

The pastor uses a lapel mic. The reader uses a mic that's mounted on the pulpit.

Yesterday I understood everything, but another person said she understood nothing. I suspect it's so loud that sounds are echoing.   (This other person is not a native speaker, so it's harder for her to decipher our language. She's not deaf or anything.)

I need a reliable source of info on using a sound system. They aren't going to listen to a mere me. I need a book written by a white male with show-biz credentials so they'll be impressed.

I've tried the net and the library already. I'm probably not using the right search terms.

Any suggestions?

Subject: RE: the science of sound systems?
From: Jack Campin
Date: 11 Apr 11 - 09:09 AM

I have a little book called "Basic Live Sound" by Paul White that covers a lot of the technical stuff. Nothing about speaker placement for large weird-shaped rooms, though.

I have heard said that if you want to see an example of really good large-scale PA, watch "Triumph of the Will". The Nuremberg Rallies got it spot-on, using only 1930s technology.

Subject: RE: the science of sound systems?
From: pdq
Date: 11 Apr 11 - 09:19 AM

Making a PA system sound good and work correctly is a matter of common sense and practical experience.

Hard to put that type of stuff in a book.

Hum is often from ground loops, but can come from a defective power amp. Take the amp out of the system and listen to it under controlled conditions. If it hums by itself, fix or replace it.

Subject: RE: the science of sound systems?
From: GUEST,Ted
Date: 11 Apr 11 - 10:25 AM

I get a lot of use from "Ultimate Live Sound Operator's handbook" by Bill Gibson. As well as being well written by an experienced pro, the accompanying DVD has useful examples. It's listed on Amazon

Subject: RE: the science of sound systems?
From: The Fooles Troupe
Date: 11 Apr 11 - 10:29 AM

This is so complex people study it for years and still don't get it 'right' for every situation.

Your hum can come from an amp that has problems, or long runs of mic cables of the wrong type, or faulty cables. You can even get hum picked up by the speaker leads, that then gets fed back into the amp.

In a building like a church, it was designed for a longer reverberation rate - 'echo time', i.e. it is assumed that you will speak slightly slower, so that the sound is not 'eating itself', but the echoes of one syllable die out before the next one hits. Throwing speakers into that situation can actually make things more inaudible. Ever been to a large showgrounds where you can hear the ring speakers sound arrive one after another? If you have just one lot of speaker (or one each side that same distance away), you can have one set of problems, having several rows of speakers long the side makes another nightmare, like the showgrounds I mentioned.

I know of no simple book that can help, sorry. You didn't say who 'set up the sound system'. If it was some rock group sound guy roadie self taught expert, just shoot yourself now, it'll be easier. :-0 The only thing they know is More Watts Man! It sounds like this happened if your ears hurt!

"The pastor is so over-amplified that she sounds tinny" - the sound is not balanced across the spectrum - tinny usually means that the higher frequencies are being over boosted.

'Avoiding feedback' - basically, you have to stop too much of the output getting back into the input. That is a black art in itself... :-) But the higher the output, the more chance of reflected sound from the speakers bouncing back to the mics, it doesn't really matter that the sound can be delayed, that in itself doesn't stop feedback. The 'howl' will usually be at a particular narrow frequency range - so a trick is to add a circuit that cuts out that frequency range, and that can stop the squeal. The hum, however is at about mains frequency, but has 'overtones' - 'harmonics', and they can be a nuisance.

I'm sorry to say this, but as a relatively inexperienced person, you may eventually end up with two choices, having to get a 'real professional' and a fat cheque nook, or the older people may just stop turning up.

Acoustical Engineering is the area of knowledge, but if you search on that, you will probably find lots of very advanced stuff that will probably not understand.

Subject: RE: the science of sound systems?
From: leeneia
Date: 11 Apr 11 - 11:07 AM

Thanks, Jack and Ted, for the names of books and authors.

Thanks, F'troupe for the observations. For example, that's a good tip about speaking more slowly.

I'm sure no rock-group roadie was involved. What we have here are well-meaning amateurs.

The first day of amplification, a man set an amp on the floor, then walked up to it, grabbed a dial, and turned it all the way to the right, thus unleashing a howl of high-pitched feedback. Honest to God, it was something a little kid would do. "I wonder what happens if I spin this?"

Fortunately, that amp is gone, replaced by the speakers mounted on the church walls years ago. Now when we're supposed to be playing the prelude to calm people and focus them, guys are scooting around saying "Testing one! two!" over and over. I feel like a Cub Scout troupe has invaded my church.

The tradtition of my church has always been that the time before the service is for prayer and contemplation. I now realize that the prelude is also a signal that T is about zero, and everybody should get in place.

But I'm just venting. It's so nice to have the Mudcat, where people understand what I'm talking about. I'm going to look for those two books.

Subject: RE: the science of sound systems?
From: Andy Jackson
Date: 11 Apr 11 - 11:24 AM

What a dilemma, I wont confuse by putting my four penn'orth in. But, I am moved to say that it looks like some people seem to have forgotten what the church and the service are there for.
Any sound checks, one two one two, should and could be done in an empty church. We are talking sound reinforcement here so any change in acoustic when the congregation fill the pews, as I hope they do, is not really significant.
Whoops my two penn'rth slipped out there!
A delicate situation though, I hope you find a peaceful solution.

Subject: RE: the science of sound systems?
From: pdq
Date: 11 Apr 11 - 12:11 PM

A sound system installed in the walls and/or ceiling may be anything from full range 8" speakers to 15" coaxial ones.

They will do well for background music but are seldom articulate enough for lectures or sermons.

That is best done with one or two medium column speaker systems placed near the podium and adjusted to match the voice of the person speaking.

The installed system also spreads the sound around in all directions which may invite the feedback mentioned.

A separate PA system near the podium can direct the sound foreward and away from the microphone, reducing the chance of feedback.

Also, a good quality mike helps a lot, since the quality of the sound is only as good as the microphone.

Subject: RE: the science of sound systems?
From: leeneia
Date: 11 Apr 11 - 12:49 PM

thanks for the info. pdq.

A church I used to belong to ordered a new sound system. Included were two extremely impressive-looking speakers, about 10 or 12 feet high but very slim in profile. Once installed, they have very little impact on the appearance of the church. I believe they came from Norway.

That sound system does an excellent job, but I'm sure we don't have the money for something like that.

Interesting note: close to the scheduled arrival date, the church was told there would be a delay. It turned out that ATF was suspicious of the long, thin wooden shipping crates from Norway with many, many screws. The speakers weren't sent on their way until it was verified that they were not guided missiles or something.

Question - if a mic is adjusted for a speaker and the speaker gets very intense and talks an octave or a fifth higher, how much higher is the energy load on a listener's ear?

Subject: RE: the science of sound systems?
From: pdq
Date: 11 Apr 11 - 01:03 PM

The entire question does not register to me, sorry 'bout that...

If the voice you hear through the speakers sounds distorted, it will be harmonics from what is called "clipping" and may sound higher pitched than the fundamenal. Solid state amps clip very hard and will do so with the smallest amount of overdriving.

Tube PA amps are better, some are they are very forgiving about clipping and also have tons of "headroom".

I have made column speakers with four cheap 8" "stiff cone" speakers per box, all material ripped from a 4' X 8' sheet of 3/4" plywood.

Subject: RE: the science of sound systems?
From: GUEST,highlandman at work
Date: 11 Apr 11 - 03:54 PM

Hey, leeneia-
Sorry to hear about your woes. The church I used to attend, though smallish, had wonderful acoustics and we never ever needed reinforcement for the speaker or the musicians. But that aside...
There's lots of good technical advice upthread, and good sources. But what you may need more is the human factors stuff, so I'll toss out a few thoughts in no particular order.

If you can't talk 'em out of the PA, then...

(1) make a habit of referring to it as "sound reinforcement" rather than amplification, and you may achieve a subtle mind-shift in the desired direction.

(2) try to have one single person assigned to getting the sound right (hopefully a competent one with some common sense and not a rock roadie), and -- important -- try to arrange to FORBID anybody from helping. I'm only half kidding on this. Too many cooks...

(3) consider the differing auditory needs of various ages of folks in the congregation. The more, er, experienced folks may have high frequency loss which makes discerning the consonants in speech difficult. Amplifying the mids is exactly the wrong thing to do for these listeners, it makes it louder but much less intelligible.

(4) IMO you need TONS of headroom in a sound reinforcement application. You want gobs of fidelity and not so much sound pressure. If you have to have the master volume past around 3, you may need a bigger amp.

(5) Speaker clarity is a black art. All the headroom and EQ in the book won't fix a cheap, muddy speaker. I happen to like Peaveys and JBLs, don't think much of Behringers and absolutely despise Kustoms for this trait. Sorry, 4 & 5 were techie and not human factors. Back to topic:

(6) Final comment is on mic use. Lapel mics if they are good quality solve the problem of the speaker constantly getting too near and too far. Fixed lectern mics are too often of the vocalist type which have very touchy response -- okay when used by someone with the experience to subtly modulate their distance from the mic according to what they are putting out. Most people do exactly the wrong thing and swallow the mic when they want to get loud.

Hope this helps. I also hope you can hold the line on the prelude time. The congregation needs time and the appropriate environment to shift from 'getting there' to 'being there.' Make the sound checkers start earlier.
Cheers
-Glenn

BTW always make the sound checks in an empty room, but then pay attention to the result when the congregants fill it up -- it will be different. Make the appropriate compensation next time. -G

Subject: RE: the science of sound systems?
From: leeneia
Date: 11 Apr 11 - 06:11 PM

Hello, highlandman. Thanks for the info.

What do you mean by 'amplifying the mids?

And headroom? The ceiling's probably 40 feet high, but I don't think that's what you mean.

Subject: RE: the science of sound systems?
From: Richard Bridge
Date: 11 Apr 11 - 06:15 PM

Distortion comes from many sources. It may be a cheap mic overloading, it may be the input of a cheap amp overloading, it may the the output stage of an underpowered amp overloading (that, and only that, will be "clipping") it may be inadequate speakers (or speaker cabinets). To avoid most of these things - turn it down.

Mics can be picky. So long as there is enough headroom to TURN IT DOWN a pair of the "old standard" SM58s - a "cardioid" microphone angled in towards the middle of the lectern plus a soundman with hands and ears should be able to create a reasonable simulacrum of the human voice. The SM58 itself is almost impossible to overload.

Churches have lots of natural echo. This is what gives music in churches a wonderful sound (sometimes).

To reduce echo, turn it down, point the speakers towards the middle of the rear of the room, and put curtains on the back wall.

Speakers are vital. No matter what you put into a system you will only get out what you can get out. Peaveys are the Dr Dre of loudspeakers - (ask a young person who listens to MobO (Music of Black Origin) about Dr Dre. Big thud at about 60 Hz, (low-ish, out of range for human voice) and scratch at about 8,000 Hz (will make "S" sounds splashy). Don't go there for spoken word.

15 inch drive cone drive units will sound chesty on spoken word. Many compression drivers will sound scratchy on spoken word.

I'd suggest something not too loud, 12" main drivers, and maybe even hifi tweeters.

I normally amplify rock and metal. I like it loud and have been heard to say "If it's too loud you're too old" - I'm 62 - but loud and proud is not what you need here.

Subject: RE: the science of sound systems?
From: leeneia
Date: 12 Apr 11 - 10:17 AM

Thanks, Richard.

Re: "If it's too loud, you're too old."

Does that mean if it's too loud, your hearing is too good?

My mother had a hearing test at about age 75. She had never worked outside the home (much) and we never played music very loud at home. At the end of her test, the physician called in an assistant-in-training and said, "This is Mrs. Jones. Mrs. Jones has the best hearing of any person I have ever tested in my entire career."

And she was 75!

I inherited that hearing. Amateur soundmen who have deafened themselves can cause me terrible pain with sounds that don't even bother them.

Subject: RE: the science of sound systems?
From: GUEST,Chris P
Date: 12 Apr 11 - 02:35 PM

Here's a very good site explaining the basics of PA, in humanspeak. It includes a couple of book recommendations :-
http://www.astralsound.com/basics.htm

Subject: RE: the science of sound systems?
From: GUEST,highlandman at work
Date: 12 Apr 11 - 02:57 PM

Leeneia-
Amplifying the mids = midrange frequencies. That's the "presence" part of the audio spectrum. It makes the overall sound seem louder, but because speech is highly dependent on the high frequencies for intelligibility, it doesn't make it more understandable. Often less, even while being uncomfortably loud.

As per Richard B, "headroom" is a catch-all term for having more power capability at every stage of the process than you plan to use. Running out of headroom at any point - in the mic, in the preamps, in the power amps, or in the speakers - results in distortion and nastiness. Distortion doesn't have to be complete fuzz and clippage to make the sound unpleasant. Competent sound people can detect it at levels most people would not recognize, except to be vaguely dissatisfied with the quality of the sound.

The SM58 is a very forgiving mic, but even though you can't overload it, the proximity effect can still bite you. Any mic is more sensitive the closer you get, particularly at the low "boom and thump" frequencies, and the difference between 1 inch and 2 inches is huge compared to the difference between 8 inches and 9 inches. Setting the mic level high enough so that the speaker (the human one, not the paper cone one) can comfortably stay some distance away from it allows them to move around more naturally without accidentally getting too close. I know this sounds like the opposite of the "turn it down" advice, but if you've played around with a mic you know what I mean. Higher level, more distance, more forgiving of position.

Richard, I won't argue with you about Peaveys, except to say that IMO the newer neodymium types don't seem have the flaws you refer to. My main PA speakers are 2-year-old 12" Peavs and they do have excellent clarity, not thuddy at all and the various frequency ranges don't seem to get mixed up and overload each other. (As long as you stay well below the published power rating, as with most speakers. Headroom again.)

Auditory damage usually takes out our upper frequencies, which is where we detect distortion. Clumsy, half-deaf soundmen will tend to crank up the highs so it sounds right to them (and probably to half their listeners as well, these days). Interestingly, there is an electronic contraption called an "audio exciter," which introduces subtle distortion only in the highest frequencies. The explanation of why it is thought to improve the sound in some circumstances I will leave for another day. It's commonly used on lead vocals in pop recordings. I hate the sound of it, myself.

Cheers
-Glenn

Subject: RE: the science of sound systems?
From: leeneia
Date: 12 Apr 11 - 04:19 PM

Thanks for the site, Chris. It's interesting but does tend to assume everyone knows the subject already.

Highlandman, that's very interesting about high tones being important for intelligibility. Our new pastor is a soprano, and I'm sure her high tones are higher than most people's. When they turn up the volume, they are merely strengthening the low tones of words like 'of' and muffling everything else up high. I think.

Subject: RE: the science of sound systems?
From: GUEST,highlandman at work
Date: 12 Apr 11 - 04:58 PM

I think I got this chart from another thread on Mudcat, I'll recycle it here. An interactive chart of various frequencies and instruments and where they are on the spectrum, including human voices. Includes lots and lots of information on what the effects of the different frequency ranges are.
frequency range chart
-Glenn

Subject: RE: the science of sound systems?
From: JohnInKansas
Date: 12 Apr 11 - 05:13 PM

Unless it's a very large church, the proper solution is to obtain a very large amplifier (box size, not necessarily power) and at least a couple of enormous speakers, and place them prominently where they can be seen by everyone.

It may help if they're ugly.

The amplifier must be modified by opening the box and disconnecting the power lead (inside the box) so that NO POWER can ever be supplied to anything connected to it.

Next you need a small voltmeter mounted conspicuously on the amplifier, and a small (micropower) "random sinewave generator" to connect to the voltmeter so that the needle will move around a bit.

Tell everyone it was very expensive, and sit back to wait for them to congratulate you on your technical accomplishment and how much better the sound is.

(Every guy over 40 knows that the best cure for the "hot flashes" is to disconnect the thermostat.)

Of course I'm kidding. ... ... ... maybe.

John

Subject: RE: the science of sound systems?
From: Richard Bridge
Date: 12 Apr 11 - 05:17 PM

Curiously, despite my having paid my way through my law degree working as a mobile DJ, and having mucked about with bands ever opportunity I got, people still say to me "Wow, did you really just hear that?"

About 10 years ago my now late wife accused me of going deaf - I think I might have been tuning the whine out - and insisted I went for hearing tests. Medway Maritime Hospital said "Your hearing is normal". I said, "Do you mean normal for my age" - and they said, "No, normal".

Maybe Peaveys have improved. They HAVE to sound better than those awful Mackie 12" powered units that everybody think are the mutt's nuts!

I did suggest with SM58s putting them either side of the lectern, crossed. This should minimise proximity effect because it will be hard for the pastor to get too close. Omnis would avoid that problem - but would substitute oscillatory feedback.

Subject: RE: the science of sound systems?
From: The Fooles Troupe
Date: 12 Apr 11 - 06:11 PM

Taking how many nowadays seem to be swallowing the mics, I have often wondered about osculatory effects...

Subject: RE: the science of sound systems?
From: Gurney
Date: 13 Apr 11 - 01:19 AM

Yup. I wouldn't put my mouth on anything that contains electrishitty.

More on topic, PDQ touched on it right up top. Make sure everything is connected to the same wall-socket, unless you know what you are doing.
I fell for that one.

Subject: RE: the science of sound systems?
From: leeneia
Date: 13 Apr 11 - 09:11 AM

John, I love your idea of the speakers without any power.

This is a church which was served by a succession of retired ministers, each of whom had his regular Sunday. Many of them were over 80. They would stand at the front of the pews and deliver sermons to all of us, including people 80 and 90. In three years, I never heard a complaint that they couldn't be heard.

Now the new people mount the antique pulpit (relict of the 17th Century) and bellow at us.

Subject: RE: the science of sound systems?
From: treewind
Date: 13 Apr 11 - 03:25 PM

The Yamaha Sound Reinforcement Manual is an excellent introduction and technical reference.

Sound reinforcement in a reverberant space like a church is a nightmare. It's typically done badly "to save money", and sometime done again properly, at which point the money spent on the first system has been wasted. Unless you are lucky you need someone with a lot of knowledge and experience to get it right.

This is a church which was served by a succession of retired ministers, each of whom had his regular Sunday. Many of them were over 80. They would stand at the front of the pews and deliver sermons to all of us, including people 80 and 90. In three years, I never heard a complaint that they couldn't be heard.

Really, that's your entirely practical, tried-and-tested answer!

If the church is very reverberant, sound absorbing material, correctly chosen and applied, may be what you need more than clever electronics.

Subject: RE: the science of sound systems?
From: bruceCMR
Date: 13 Apr 11 - 03:26 PM

There's an article by Jim Brown, one of the most respected people in sound system design, called "Why Churches Buy Three Sound Systems, and How You Can Buy Only One".

You can find it at http://www.audiosystemsgroup.com/3Times.pdf

Read it and learn :-)

The basic story is that the "first" system is designed by the building architect rather than a specialist. Aesthetic finishes are more important than functionality. Components are chosen from catalogues without looking at the whole system. It's not seen as a fundamental part of the building, so corners are cut. It's built to a tight budget.

A couple of years later, when they realise the deficiencies, a "local expert" offers to "improve" things. Often someone that has a band, or a disco, and so "knows about these things". So they build something that's a bit like a big disco...

And then eventually, they get a pro in and do the job properly. An independent acoustic consultant who will specify and design the system, without being tied to any particular supplier. Who has done "church installs" before, and can provide reference sites. Who will manage the tender process and supervise the installation. And who will stake their reputation on "getting it right".

http://www.audiosystemsgroup.com/3Times.pdf

Subject: RE: the science of sound systems?
From: treewind
Date: 13 Apr 11 - 03:37 PM

"Why Churches Buy Three Sound Systems"
That's the one I was thinking of!

Subject: RE: the science of sound systems?
From: GUEST,glueman
Date: 13 Apr 11 - 05:30 PM

A friend of mine bought a sound system from an old rude boy, a unit constructed in 1968. It'll make yer nose bleed.

Subject: RE: the science of sound systems?
From: Joe Offer
Date: 13 Apr 11 - 05:41 PM

"Why churches buy three sound systems"? Boy, isn't that the truth!

Our church is on sound system #2. The first was a single cluster of speakers, high above the altar, designed and installed by Muzak. That, teamed with a choir area with two pillars blocking the choir's view of the congregation, made for impossible sound.

Now we're on the fifth year of installation of our second sound system. The pastor met some guy who used to work for Bill Graham's outfit. You know the type - the tech-geek roadie, the only one around the band who wasn't stoned. Really likes music and can do good work, but never can seem to get the job done. He's using a Mackey mixer and four of those powered speakers that go up on tripod poles. The sound actually isn't bad, but the mixer is in the open and surrounded by piles of wires for people to step on, and somebody is always changing the adjustments.

There has to be a better way. I wonder how long it will take to get our third system....


My previous church had maybe 20 speakers in upside-down Kentucky Fried Chicken buckets, suspended above the congregation. The buckets were painted brown, but you could see the Colonel and the red-and-white stripes through the brown on a sunny day. Then we had a professional sound company install a system for $20,000, but half the speakers worked only half the time, and the sound company field rep was a jerk. That was our third system, I think - and it was worthless, too.

-Joe-

Subject: RE: the science of sound systems?
From: Richard Bridge
Date: 13 Apr 11 - 05:51 PM

Those 12" powered Mackies sound like a bucket of gravel.

Subject: RE: the science of sound systems?
From: The Fooles Troupe
Date: 14 Apr 11 - 08:38 AM

Well, I reckon I could get you a bunch of shipping containers real cheap after Easter ...

Subject: RE: the science of sound systems?
From: s&r
Date: 14 Apr 11 - 08:53 AM

There are some good examples of the problems inherent in church acoustics
here

Subject: RE: the science of sound systems?
From: leeneia
Date: 14 Apr 11 - 09:50 AM

Thanks for the additional info, Bruce and Treewind.

Joe, that's a riot about the Kentucky-Fried containers.

"the mixer is in the open and surrounded by piles of wires for people to step on"

That's bad for two reasons. One is the tripping hazard. The other is that piles of wire can cause feedback. My husband used to work backstage in theatre, and he tells me that one of the basic rules of sound is 'no coils of wire.'

Subject: RE: the science of sound systems?
From: treewind
Date: 14 Apr 11 - 10:15 AM

"piles of wire can cause feedback."
Not in the usual loudspeaker-to-mic feedback sense, they can't.

If you run mic cables alongside stage lighting power cables you can get interference in the form of buzzing noises as you operate the light dimmers. Maybe that's what your husband is thinking of.

Subject: RE: the science of sound systems?
From: leeneia
Date: 14 Apr 11 - 12:34 PM

maybe. Maybe he was referring to buzzing or humming. Imagine the complexity as the current in one coil sets up a magnetic field which induces current in the next, which then...

I used to get a hum in my stereo because a speaker cable crossed a wire to a rheostat at a right angle.

I have a friend who's an electrician. He told me once that he was wiring a McMansion that had electricity, phones, stereo and intercoms. He had to work hard to make sure that no lines crossed.

Subject: RE: the science of sound systems?
From: GUEST,highlandman at work
Date: 14 Apr 11 - 05:34 PM

>....good examples of the problems inherent in church acoustics

Which brings up something I've been thinking vaguely about since leeneia started the thread: the appropriateness of repertoire to the acoustics (read, architecture).
You wouldn't think of seriously performing brass ensemble music on a piano, or harp music on a concertina (yes I know there are exceptions). But people charge blithely ahead trying to perform fast, busy music in the sorts of grave, reverberant spaces that gave birth to Gregorian chant, and vice versa. No sound engineer can fix that mis-match.
How much should we allow architecture to drive our selection of repertoire?
(Now, having committed severe thread creep, I contritely retire....)
-Glenn

Subject: RE: the science of sound systems?
From: The Fooles Troupe
Date: 14 Apr 11 - 07:16 PM

Actually that is not creep, but highly significant. If you speak too fast, you also have problems. Chant works fine.

Subject: RE: the science of sound systems?
From: treewind
Date: 15 Apr 11 - 05:41 AM

"Imagine the complexity as the current in one coil sets up a magnetic field which induces current in the next, which then..."

In theory, yes. In practice, a proper mic cable (two core shielded, balanced input at the amplifier) will not pick up enough even from an unshielded speaker cable to cause that type of feedback.
In a speaker cable, there are two internal wires carrying equal and opposite currents so there isn't the big magnetic field you imply by it being coiled up.

Triac-dimmed lighting, on the other hand, creates quite high frequency transients which leak out (and in) more easily. And GSM cellphones radiate a 200Hz buzz that gets in everywhere.

But this is all minor detail - acoustics are the #1 problem in a church.

Subject: RE: the science of sound systems?
From: Dan Schatz
Date: 15 Apr 11 - 03:31 PM

This article came in today's e-mail. I thought it might be helpful to post here.

Dan