Rational Acoustics

Kip Conner
August 26th, 2009, 11:13 AM
Thought I would share this tidbit of fun.

I recently purchased a pair of DynAudio BM6a's studio speakers for my home editing room space. This is where I take the Live ProTools recordings that I do for folks and clean them up for the mix engineer (if not me). Like any good rational boy or girl would do I immediately took them out of the box to what they were doing. I've heard them before and loved the sound of them. They come with 2 trim knobs on the back to accommodate the bi-amp glorious-ness. I put them under test and used the the trims to determine what might be the flattest response I could get. Easy, turn the highs all the way up the and low trim all the way down. Frequency and Phase response looked good and typical of a 2 way system.

When I got the second box into play I started with it the controls set for the heart of the sun, i mean, identical to the first box. Uh-oh. Not the same. Not even close. The LF driver was spot on, but the HF driver was consistently 2.5dB lower across the pass band. I couldn't turn it up because it was turned up already. I couldn't lower the other one without compromising it's flat response.

After going back and forth with the guys at TC Electronics (they were great btw) we tried various things to looks for the quick fix. They said that the trim knobs were there to allow folks like ourselves to compensate and get them exact.

They didn't want to believe that their product was behaving in the manner that I described. I really can't blame them since the majority of the people that call them to get something working don't understand the basic principles of signal flow. So, I had to prove to them that I was the minority.

What do you do? You send the squints at TC your Smaart plots to show them your issues. When they come back with more claims about measurements you them write them a quick one page essay on the topic and include a couple new Smaart plots to back up your claims. Without getting into the details and explanations what I wrote (we know the details) the final word is that I'm getting new speakers from TC Electronics.

I attached the simplified plots of my data to show them A.) Raw Comparison of the 2 Speakers and B.) My attempt (based on their suggestion) to replicate the the 2 speakers.

They did their best to keep me from exchanging these speakers, but you can't deny the data.