PSA: Check yer monitors now and again

[Bob Womack]

We are fairly regular at checking our monitor for frequency response shifts. They do happen as your monitors age. We've got some pretty impressive testing gear but really, you can do the basics with a Radio Shack SPL meter and a tone series/pink noise CD. I've been working on a project with a custom score where the scoring composer has a nasty habit of spreading the melody instruments outboard and not balancing them up. I've got pretty sophisticated energy-metering hardware (a DK "jellyfish" Meter) and a similar plug-in (iZotope Insight) so I am able to balance things up but when I got a balance on the meters I was still being aurally "steered" to one side by a midrange hump in the speaker on that side. I've been switching to the alternates to compare for a couple of days so it was time to work them over again.

The main system is a pair of Urei 813c monitors, soffit-mounted, EQ'd with Clarke Technik room EQs and powered by David Haffler Trans-Nova power amps. The system works for 8-12 hours a day recording and mixing.

We ran pink noise through each side and mapped it via a direct feed from the board and a calibrated instrumentation mic in the engineer's position. We took the signals into software on a Microsoft Surface then overlaid the plots.

What did we find? The phase response of the system was really good. But on frequency response and gain there were issues to sort. The high-end on the left had sagged a little bit but when I exercised the crossover pot it snapped right back. The response at the crossover point had drifted a little as well. We also verified the midrange hump on that side and a little tweeter drift on the other side and took steps with the crossovers and EQ to bring them back in.

We've also got an amp gain issue we'll have to sort out. We've got several of these Haffler amps in house so we'll throw a known good amp into the slot and have the engineers take a look at the amp.

The results were a much more comfortable and balanced array and a smoother sound stage. It is really important that you not be fighting your monitors or being fooled by them so pay attention to them and check 'em out regularly.

Bob

[muscmp]

as usual bob, very interesting.

i have none of that testing gear and wouldn't know where to find it. certainly not at rat shack anymore.

play music!

[Bob Womack]

Well, let's fix you up.

AMAZON SOUND LEVEL METERS

Cheaper, probably not as precise, APPLE iOS APP

TEST TONES FROM THE INTERNET

Bob

[runamuck]

I just calibrated my monitors with pink noise a few days ago. During the time pink noise was running through, a friend moved a mic stand across one of the monitors. I'm not sure what to call it - comb filtering or phasing, maybe - but the change in pink noise sound was amazing and I could hear it move spatially.

[cotten]

Bob, I find your job both fascinating and a bit intimidating, since I know so little about it. This means I appreciate your posts about it more than most people, I suspect.

cotten

[Bob Womack]

Hehehe... That's kind of you, John.

Bob

[RayCJ]

Originally Posted by Bob Womack

Well, let's fix you up.

AMAZON SOUND LEVEL METERS

Cheaper, probably not as precise, APPLE iOS APP

TEST TONES FROM THE INTERNET

Bob

Thanks Bob...


Ray

[muscmp]

Originally Posted by Bob Womack

Well, let's fix you up.

AMAZON SOUND LEVEL METERS

Cheaper, probably not as precise, APPLE iOS APP

TEST TONES FROM THE INTERNET

Bob

great! thanks bob!!!

quite a variety in the pricing. any recommendations?

play music!

[Bob Womack]

I bought the old RS meter with the LCD display for myself and it seemed to do fine. I think there was a +/- 1db variance from an expensive one we used here. For the cheap bucks it cost that was fine with me. You can find those on eBay. They were the cheapo standard in the industry for years.

Bob

[muscmp]

Originally Posted by Bob Womack

I bought the old RS meter with the LCD display for myself and it seemed to do fine. I think there was a +/- 1db variance from an expensive one we used here. For the cheap bucks it cost that was fine with me. You can find those on eBay. They were the cheapo standard in the industry for years.

Bob

thanks again, i'll check it out.

play music!

[Bob Womack]

Glad to help!

Bob

[Bob Womack]

Postscript:

We scheduled some downtime today and traced the monitor circuits from the console to the speakers. I used my little Radio Shack Sound Level Meter (now only available on eBay) in the final stages to check the output, and sure enough, the right side of David Haffler Trans Nova amp on the mains had lower output and was exhibiting some non-linear frequency response as well. It became clear when we put up tone, cross patched between channels, and observed the effects on level. We switched off to a known-good amp and all was well... except the all the drift we'd corrected for was in the amp, not the speaker or crossover!

That meant we had to pull out the real time analyzer gear and true up the monitor frequency response again, but that's kind of fun when you know that the result will be smooth, comfortable monitors.

So, the problematic amp is back in the shop being worked on and I've got my nice listening situation back. Huzzah for my friend and engineer Joe who helped me sort the mess!

Bob