Time to tune up your system for the new year

[Doc B.]

Shawn and I just did our first of the year system tune up. We had borrowed some of the components for demos the past few months, and installed a new preamp. So today we set up the measurement system and checked the room response. Whoa! Problems!

One thing we expected was that we needed to turn the woofers down a bit. We had been feeling that the new, flatter bass response we get with the 300B preamp prototype was telling us that we needed to back the bass off a couple of dB.  A quick tweak of the active crossovers solved that.

But what about that hole at 2kHz!! After a few seconds of head scratching we remembered that we had removed the active crossover from the tweeters last year and gotten very flat response as a reward. This had mistakenly been put back together in the original way when we reinstalled some cables that were borrowed for a demo.

Once we had these things straightened out we remeasured our speaker distance and put a fresh tape marker on the floor to mark the sweet spot, replacing the one that had disappeared sometime last fall.

The end result was the system getting really good, a bit better than I remember hearing it last time I dialed it in - most likely due to the rockin' new preamp.

I heartily suggest everyone take some time to recheck all their cable polarity, remeasure speaker and listening positions, tighten to those binding posts and generally clean up connections and cable dress to be ready for the new year's upcoming music!

[porcupunctis]

Doc, that's good advice.  Especially for those of us that tend to do a lot of experimenting throughout the year.  Like changing the batteries in your smoke alarm, its good to stop and look (hear) over the whole system now and then.

I would love to know the equipment and set-up you used to check things out.  Can you give us some details? 

I love experiments.

[Doc B.]

Oh, it's very exotic -we use an old Toshiba laptop running ETF and an ancient Extigy external sound card. When PJ is over we use his really nice B&K mic that is great for driver measurements, but the rest of the time I use a cheap Behringer mic that we have found to be close enough in response to the B&K to use for tuning our room. The trick with this setup is that I have verified its performance by running it side by side with Bob Hodas' far more sophisticated SIM system. So we know that we can pretty much rely on what we are seeing to be accurate.

I usually start with measurements at 1M and then move the mic to the listening position for the final tweaks.

[Grainger49]

On December 31 1999 I took the whole system apart.  Paula was working for IBM in Atlanta seeing that the Y2K bug didn't shut down your power grid, bank, etc. so I was on my own.

I cleaned every contact from the cartridge pins to the speaker banana jacks.  Tired and not wanting to see midnight I listened to music for a couple of hours and went to bed.  The power did not shut off.

Since that was 11 years ago, and many changes in my system, Doc's suggestion is more than timely for me.  Not today, I just returned home from a myelogram (they are no fun, and painful).  I'm not bending over till tomorrow.  But a great idea.

[porcupunctis]

Thanks Doc, I have a Berhinger measuring mic and I have RTA for generating tones on my laptop.  I also have a Behringer DEQ2496 that should tell me what the mic is hearing once I get through the manual.

I have a pretty small listening room so I think my best approach would be to place the mic where my head would normally be, then measure, record, adjust and repeat until everything is as flat as possible?

If I pass a 100hz tone through the system, could I optimize the phase of my subs by simply adjusting the phase until the volume was at it's peak?  This seems logical but I've learned knowing is better than guessing.

Thanks,

[Doc B.]

I haven't pursued this since I've been using ETF for a long time, but it might be worth looking into some FFT or MLS type software. Being able to see notches where phase flips are happening and the like can be very useful. I measure at 1M first to get a good handle on the mid/tweeter integration, as it seems a bit more difficult to get good HF response measurements back in the room where reflections can mess up the readings. Then we set the mic back to the listening position to get the woofers balanced with the rest of the system.

One of the more rewarding tweaks this year was to time align all the drivers for the listening position. I started by using ETF to estimate the distance between mic and driver for each driver and positioning the drivers to all read about the same. Each driver is in its own box so this is pretty easy. Then to fine tune it I put the mid and tweet out of phase and tweak their relative positions to give the deepest, most narrow notch I can get at the crossover frequency. Ditto the mid/woofer crossover. What I end up with is a "curved" stack of boxes each staggered about 1-1/2" relative to its neighbors. The final touch was to play with the toe in, which puts the intersection of the perpendiculars to the front baffles just about at the ears or slightly ahead of them. Paul Stubblebine usually likes that intersection to be about a foot behind his head for his system, so it is to some extent a matter of taste.

[Grainger49]

  .  .  .   If I pass a 100hz tone through the system, could I optimize the phase of my subs by simply adjusting the phase until the volume was at it's peak?  This seems logical but I've learned knowing is better than guessing.

Thanks,

Randall,

Peaking the bass will most likely give you peaky bass.  You might set it up where you are at a resonance between the speaker/room/listening position.  Bass is not easy to tune, get flat or get in phase.  Tuning with a pulse and looking at the result can show you the relative phase relationships.  Sorry I can't explain any better than that.

[porcupunctis]

Right, my intention was not simply to maximize the bass but to be certain that the phase of the subs (which are manifolds in the ceiling) and the main speakers were together.  Then I could turn the bass volume up or down using the volumes on the bass amps but the waves should still be "together" and not cancelling each other out.

I'm a firm believer in the idea that subs should not be heard when on but noticed when they are off.  I just want to add that little touch of extension there. 

[Grainger49]

Randall,

Then yes it will give you the best phase. 

[Yoder]

If one is using a computer for audio needs, or anything else for that matter, then it is also a good idea to blow out the internal fans and filters. This is especially true if there are cats in the house. I bumped my MBP up to 8 Gb of RAM and decided to clean it...the amount of hair inside blew me away. I found a similar situation in both of my minis, but am reluctant to pull the screen off of my iMac's. The MBP was definitely running hot prior to the cleaning, but all is well now.