I Want to Have My Cake & Eat it Too!

In Uncategorizedby tfwm

It happened to me again last week. I was at a church trying to voice their ailing loudspeaker system in an effort to make it sound at least as good as it could. We’re in the process of designing a replacement sound system for them, but I don’t like to walk out and let any system sound as bad as that one did.

I tried my best. I used every trick that I know, and several thousands of dollars worth of test gear to help me sort it out, and still left unrequited. That virtually never happens to me, so I was frustrated.

Ultimately, what stood between me and a decent sounding loudspeaker system was a cheap …’er… inexpensive, one-third octave equalizer. In order to make even a small change in the frequency response of the system I had to pull the EQ control down to something like -12! In other words, adjusting the EQ slider to -12 dB at, e.g., 1 kHz, resulted in about a 3 dB change in the output.

Now, there are anomalies that can show up in the frequency response of a loudspeaker system that are not created in the frequency domain. Ultimately what that means is that you can’t fix it with an equalizer – it has to be resolved by some other approach or tactic, like moving a loudspeaker in the time domain either physically or electronically. But I was able to rule that out in this particular case. This was just a poorly designed equalizer that didn’t do what it promised on the silkscreen.

As I mentioned, this isn’t the only time that this has happened to me. I was on a similar trip to another church last year. Our contact at the church told us about how one of the members of his tech team had spent hours making small adjustments to the system equalizer just using his ears. They had achieved a setting on the one-third-octave equalizer that they were happy with. But when I listened to it, I decided that we could at least get it to sound better than that. So I grabbed my test gear and set out to improve on things. And I found myself following a similar track where it didn’t seem to matter what I did to the EQ – it just didn’t show up as a corresponding move on the TEF display.

I was intrigued enough to stop for a moment and try connecting the equalizer unit directly to the TEF. In other words, I would make a purely electronic measurement to evaluate the response of the equalizer at various frequencies.

My suspicions paid off. Want to see the results? I made individual measurement sweeps at a variety of frequencies and then overlaid those curves on one graph. Indeed, one had to push or pull those graphic sliders substantially before the curve would even begin to move in response. I’m used to working with very good equalizers. When you tweak a good EQ and measure its response, you’ll find very close agreement between what the EQ unit is saying it’s doing and what you measure in response.

These measurements were made with the 1/3 octave equalizer connected directly to an electro-acoustic analyzer called the TEF (www.gold-line.com). The test signal is fed to the equalizer’s input, and the output of the equalizer is connected to the line level input of the TEF.

One would expect that adjusting the controls based on the markings on the front of the unit would yield close to that effect in the acoustic output of the loudspeaker. In other words, if we pull a graphic slider down -4 dB at 500 Hz, we would expect to see a corresponding drop of 4 dB at 500 Hz in the measured output of the loudspeaker. However, as we can see here, the unit does not live up to its silkscreen even when connected directly to the analyzer.

The black, relatively flat line is the response of the unit with all controls set for flat, in effect with the unit bypassed. The overall level drops by about 1 dB when the unit is put into circuit. The EQ settings we adjusted here were all made with the 5 kHz slider. A separate TEF sweep was made at -3 dB, -6 dB, -9dB, -12 dB, as well as at +3 dB, +6 dB, +9 dB and +12 dB.

Even a casual scan of these graphs shows that the equalizer doesn’t even begin to achieve those results. To ensure that we didn’t just have a problem with one frequency slider, we took similar measurements at other frequencies, and even with a second unit of the same model. Similar results were found in all tests that we did.

These measurements were made under the same conditions as those in the last graph, this time with a center frequency of 200 Hz. Similar results were achieved. Note that the equalizer makes little impact on the signal itself until the slider is pushed beyond the +/- 9 dB positions. Basically, one has to push the slider all the way up, or all the way down in its travel, in order to affect an aural change to the signal.

Cherry Frosting
I realize that it’s tempting to believe the promise of the cut sheets, but you really need to keep your wits about you when you go to buy the next widget for your church’s sound, video or lighting system. The old adage that “you get what you pay for” is still true. Despite our best efforts to be good stewards of the money we’ve been given to spend, sometimes the best thing to do is hold onto that money and wait until we have enough to buy the better unit.

To the untrained eye or inexperienced user, a mic stand is just a mic stand. But did you realize that a cheap mic stand can change the sound character of your mix? Okay, you probably think that I’ve really gone off the deep end now, but realize this. A cheap mic stand is made from very lightweight metal parts. When sound from the instruments gets loud enough, it can start to vibrate the stage platform. Those vibrations can easily transmit to the mic stand. If that mic stand is made from lightweight metal, those vibrations will transmit right up to the microphone. And if the microphone itself has poor handling noise characteristics, the vibrations will be amplified by the microphone and heard over the sound system and on tape recordings as a nasty coloration to the sound.

I know that may seem far-fetched, but it happens every day in thousands of churches that are wondering why on earth their sound is so bad. Investing in a better quality mic stand from the start will save you years of grief.

Investing in a higher quality anything will save you years of grief on those items as well. For example, it may seem as though any sound mixing console will do. But consoles do have a sound character of their own, and the better-sounding consoles can typically sell for a higher cost. Higher priced consoles typically provide more routing flexibility as well, allowing the sound team to provide multiple mixes for various needs, like multiple monitor mixes, tape recording feeds, sends to the foyer, the nursery, and so on. It’s easy to choose a console based on the number of inputs. Many churches neglect to sort out how many individual outputs they need from their console.

Lower priced microphones may not live up to your expectations. They may exhibit poor off-axis coloration, or poor handling noise. Their frequency response on-axis may be acceptable, but what they do to sounds arriving from off-axis may be a huge problem that you’re not even aware of.

Look Beyond the Gleam
We could have similar discussions over the choice of cassette decks, CD players, headphones, video projectors, projection screens, wireless mics, intercom systems, even mic cables and speaker cables. A friend of ours used to work at a major theme park, and one of the departments there was having huge problems with RF reception on their wireless mic systems. The techs in charge of that area had tried everything they could think of to resolve the problems with no success. Instead of calling in our friend, Chris, to take a look at it first, they ultimately decided that the proper solution was to invest about $200,000 (literally) to replace a key component of the system that they thought was causing the problem.

The department placed the order for that unit, but were still experiencing problems. They happened to call Chris over to take a look at the problem to see if any temporary solutions could be found. Chris took one look at it and realized the problem was that they were using the wrong type of coax cable for the interface. The fix was simple, involving making a couple of new coax cables with the right kind of wire. With the new cables in place, the problems totally disappeared. Unfortunately, it was a $200k mistake because they couldn’t stop the order.

One way to keep from wasting those dollars is to do your homework. That may mean perusing the internet or polling our ChurchSoundcheck discussion group for user reports on the unit you’re wanting to buy. It may even mean asking the store to let you try the unit for a weekend with no obligation simply to confirm that the thing actually does what you want it to do. This is especially true of wireless microphone systems.

If you can relate to some of these stories, please be encouraged in the fact that you’re not alone. This kind of thing is far more common than you may realize. Do all you can to keep your wits about you, and don’t be so quick to jump into a purchase until you’ve done your homework.