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PA problem in super boomy room

jumblemind

jumblemind

I also answer to Bryan
Aug 27, 2011
2,981
1,293
Knoxville
#1
We play a charity gig every year that involves letting the organizers and guest speaker use our PA. Unfortunately, the room is a giant glassed-in pavillion with a concrete floor, and the acoustics are terrible. It's not a huge deal when we are singing while playing, but trying to understand someone who is talking into the mic is really difficult. Each year the crowd seems to get more impatient with the situation, to the point that last year the guest speaker gave up on the mic altogether and simply yelled his speech. He happened to be a college basketball coach, so he projected pretty well on his own; but this year will be someone else, and I'd rather do what I can to minimize the issue and prevent the crowd yelling "we can't understand you, fix the sound!" again.

Our PA setup is a 200w powered mixer type combo into two JBL speakers (horn + 12" woofer in each, I believe) that are set up on pole stands. We also run a few wedges for monitors. Is there anything physical I can do, or is there a specific EQ I should try? Maybe just boost the mids and cut the lows and highs?
 
#3
The problem lies in not having a loudspeaker that is made for the application. Room "hang time" as I like to call it, is a physical acoustic issue that cannot be resolved with the "right" loudspeaker, but It can also be helped with the right loudspeaker.

Most traditional boxes HF horn pattern coverage is typically only good to around 1k at best before it's coverage pattern goes " omnidirectional" and the pattern of the horn is no longer effective. There are boxes made with a lower directional coverage capabilities such as the Electro Voice EVH series. Due to it being a horn loaded design, and hence a much lager than normal cabinet, it retains its pattern coverage all the way down to 400hz. This means when the horn is supposed to have a 90 degree by 60 degree horn pattern, it retains a true 90x60 pattern all the way down to 400hz, while your cabinets are holding pattern to no better than 1k. This is enormous when asking for clean clear human voice reproduction. But this is a huge box. It takes a bigger bucket to control pattern, and the only type of box that can provide such pattern coverage at such a low frequency requires a bigger cabinet.

But as the laws of physics were handed down by the good (insert deity of choice), and seeing that your respective (insert deity) has not repealed said laws of physics....the space you played in needs acoustics treatment to be controllable in the lower frequencies. The more low frequency energy you create in a room like that, the more you generate reflections. These reflections will muddy the intelligibility of the music and the spoken word/human voice. Typically these are speaker cabinets used by professional integrators/contractors. You won't see a tour outfit dragging cabinets like the EVH around due to size and truck packing reasons. But Danley, JBL, and EAW make cabinets aimed at this market. But you will never find them in a mail order catalog.

And the wives tales about just pounding the room and overdriving it with power to cut through is complete and utter BS. Doesn't really happen.
 
#5
The problem is that the offending frequencies can be totally different depending on where a sample is taken.

If lots and lots of money is available, one trick that works well is to have multiple, small, limited-dispersion, limited-throw sound sources located around the room, but running at a low enough volume that a) they don't interfere with each other, and b) there is little to no reflection because by the time a boundary is reached the volume is low enough not to cause any meaningful damage.

One sound source -- no matter how well-architected -- just won't get it done in the room described.
 
#6
Where are you positioning the speakers, and how much flexibility is there to move them around? If the main cause of the lack of intelligibility is from room mode resonance, you might be able to reduce the mode reinforcement by adjusting the positions of the speakers with respect to the room dimensions. If the cause isn't frequency related but just a long natural reverb, then you have to either reduce the volume (as the previous poster suggested) or find a way to absorb more of the reflections. Since this is a temporary installation, you might look into either some sort of wall hangers like curtains. Another possibility would be temporary room-divider-like partitions with sound absorbing materials. If the ceiling/roof of the pavillion isn't also glass or particularly decorative, it would also help if the owner of the venue would hang some sound absorbing panels around from the rafters.
 
#7
Vertical pattern performance really matters in keeping spoken voice clear in a reflective room, as Keith said.

One thing that can work is to put the mains as close to the ceiling as posible to get some control on that reflection. Another approach that works well is a zoned approach. In that method, you use speakers set at FOH, and an additional pair midway back. For some reverberant spaces you may need several pairs. The other thing about this approach is you run each pair at lower volume than you'd run a single pair as FOH. Getting the delay right is fun.

I've been in a number of European venues (Cathedrals) that had wonderful spoken voice clarity. They all were outfitted with small line array columns set up in the zone format. What they did was keep the energy right where the ears are and reduced reflections through tight pattern and by low volume operation. One of the venues I've spoken at uses a two zone system - the room is horrible - but spoken voice is very clear.
 
#10
Jumble the worst thing you can do is turn up the PA or try to EQ the hell out of something. The problem is the acoustics. There isn't much you can fix. Hang a large curtain or drape to absorb some of the reflection in the room. And Absolutely no reverb on spoken word. Hope this helps.
 
#11
Speech un-intelligibility, in your case, is probably due to reflected sound having more energy at the listeners ear than the direct sound from the speakers. Without treating the room or buying a line-array system Your best bet to improve with what you have is:
1) keep the speakers as close to the crowed as possible.
2) Angle you speakers DOWN AT THE PEOPLE. pay attention to the dispersion angle of your speakers. I'd bet most of you acoustic energy is shooting over the heads and bouncing of the ceiling and walls before making it around to the people. there are angle adapters available for speaker stands to help with this.
3) Turn down the volume - less volume into the room will decrease the reflected energy.
4) Frequency range critical to speech intelligibility are between 400 and 5k boosting these won't help much but cutting other may.

this is a big deal when designing installed systems for large venues and big churches. there's a lot in the net about it and a lot of AES papers as well.

Other suggestions are good as well if you have $ to invest. a better PA would help. more, distributed speakers with each at a lower volume would fix it as well.
 
#12
Also helpful (some already mentioned):
Find some way to roll off a bunch of low end. For speech, you don't need much below 250Hz for most people (people with a low voice are an exception), and big rooms (i.e. gyms) are often very energetic around 200-250Hz.
Get as much soft stuff on the walls and such as possible. Putting curtains and other baffling in the room, particularly at the ends, will help a lot. Even miscellaneous stuff such as tables, chairs, etc, helps break up the hard boundaries of the room.

Consider a single cluster arrangement. Speaker separation may be working against you.

As
 
#13
Coach all speakers beforehand to lip the mic and talk loudly.
They usually forget after a minute or two, but it's worth a try.

Turn off the stage monitors--which can cause newbs to speak quietly--or better yet point them at the audience and crank them up.

And I agree with Hactar--if you can stack your speakers vertically or put them right next to each other it will reduce reflections and enhance efficiency.

Cutting lows will improve clarity and give you more available power, and you really want to make sure there's a lot of energy in the 5-10k range so consonants are clearly heard.
Give the speaker your very best mic, and consider renting/borrowing a condenser vocal mic.
A compressor at 4:1 or so with the attack turned clockwise a bit to allow consonants through might help, too.

I've used all of the above tricks, especially at weddings during the speeches, and you often have to combine several to get decent results.

Good Luck!
 

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