Acoustical Tuning

[nickaschm]

I'm currently a new live sound enginneer at our local auditorium. We have a sing TOA series speaker (ugh, mono) that takes a feed from our Mackie 1604 FOH console. We're running it though a TOA amp. The speaker just sounds horrible. I have to apply heavy 12khz shelving on each of the channels to get any highs out of the mix. Recently, I put on a well mixed recording and listened to it throughout the auditorium, with a flat eq from the board. As I moved away from the front center, where the speaker is located, the highs disappeared. The farther I moved away from the speaker, both back and left/right, it sounded more like mush. Obviously, this is a horrible speaker. We do have a graphic eq in our rack which is currently a mess. I would like to acoustically tune the room with a pink noise or sine wave generator and calculate for axial modes, but will the results be worth it? Thanks for your help.

[DAS]

I wish I had the time to tackle this properly (there are MANY issues here), but I just don't. The very short and thus incomplete version is:

In a large room it is not unusual for hi freq's to dissipate as you move back. Lows do not, generally. The result is mush in the rear. You need high frequency devices that can throw to the back seats. Boosting the eq can help, but you said the sound changes as you move back, so you will have to find a compromise to avoid cutting off the heads of those in the front row. Different acoustic treatment may help as well, but it's a waste without improving the speakers.

Tuning the eq with noise may help a little, but you're either going to be tuning for one spot (where you place the mic) or you're going to have to find some way to take an "average," which can be tricky.

You may be able to help yourself by simply taking a lot of the bass eq out of the speakers. If they aren't producing as much low end (which ends up as mud in the back of the room) the clarity may improve quite a bit. May not sound good, but it will be intelligible.

Sorry I don't have time to get into more detail.

[Justin]

I want to make sure that you said there is only one speaker there in the auditorium. If that is the case, and everything sounds downright terrible, chances are that maybe the speakers are old and have taken a lot of abuse over the years and the low frequency device may be rubbing inside the voice coil and not reproducing very well. When the driver rubs in the voice coil, it can't physically reproduce the sound the way that it's supposed to.

In addition, if you're not hearing much of the highs in general, the compression driver or high frequency driver might possibly be blown or close to it. Generally, if a system is pushed hard, the first driver to get damaged is the high frequency driver. If this is the case, then the only highs that you would be hearing would be those in the upper midrange where the cross over of the low frequency driver would leave off.

As DAS said earlier, there are many issues here. This is another possible solution. Hope this gives you some insight

[Dink]

Nick,

I agree with Justin & DAS. They both are correct. My recommendation is as follows:
1. Verify speaker integrity, inspect, clean out speaker basket and driver groove using double stick tape.
2. Possibly replace speaker driver unit with higher output driver.
3. Add a 18" Speaker Horn System. Made for high frequencies.
4. One speaker cannot do the job. Must have at least two speakers for high frequency and a pair for low frequency.
5. Add a crossover unit to system to direct the frequency.
6. Speaker placements. One speaker cannot support an auditorium of any size. Budget cuts?
7. Add side field speakers in the center of room to continue sound to rear of auditorium.
8. Size of room matters also. Rule of thumb: Add a pair of speakers on top of current speakers every 100' of sound distance.
9. Equalize the high frequencies first.
10. Power of Amplifier matters so you don't overdrive the speakers.
11. A Sonic Maximizer added in front of amplifier can enhance either high or low frequencies.
12. Adjust the input microphone level properly. Don't overdrive the input signal.
13. Verify the microphones used. SM 57 or 58 can help.
I realize my recommendations are a cost factor, however if you want an excellent sound system you need to invest the time and money to achieve this. Maintenance is vital to any sound system. I always inspect my system after each gig. The effort alone pays for itself.

I hope this will help you Nick.
Good Luck!

[Justin]

Another thing that I forgot to mention earlier is to get a good sine wave generator and slowly sweep through the frequencies and find out where exactly everything drops off at. If everything from about 1.5K and up are severly low in volume, then chances are the high frequency driver is going to be the main source of problems. Let me/us know how these tips are working out. Hope things are working out for you there!