I'd like to pull your brains on subwoofer calibration.
 
I installed a subwoofer (ADAM Sub 7) a while ago in my studio, following the traditional recommendations on placement (somewhat off-center, same distance as satellites, etc.) and I did the "crawl around and listen" thing. I'm actually quite happy with what the system sounds like and how mixes turn out. It nicely clears out the lower mid range when switching from 2.0 to 2.1 while not changing the level of the lower end.
 
Anyway, the voices in my head keep telling me that there should be more to it than crawl around and be happy. So, I'd like to do some proper acoustic measurements like I did for the rest of the studio, but can't find much useful literature telling me what to expect and what to aim for in the calibration process.
 
I wonder if any of you guys can point me somewhere for further reading, provide some insight in your own calibration efforts or maybe even share some measurement plots of a properly calibrated system???
 
Cheers.
 
Rob
 

Aside from speaker placement and bass trapping, really all you can do beyond that is to fiddle with the crossover frequency.


Even though a subwoofer only has to handle an octave or two, it's very hard to design a box that's truly flat over that span when you're talking low (< 60Hz) frequencies. You can't do much about the low end of its range, but you can decide where to set the crossover for the upper end. 

You'll find that there is some upper frequency where the sub starts to wimp out. On a quality unit like yours that might be well over 100Hz, but on my cheaper M-Audio sub it's around 70Hz. Since my main speakers are reliable to about 46Hz, I let them handle as much of the low end as they're capable of, and set the crossover to around 55Hz. This yields a flatter response than when I previously had the crossover set to 70Hz.

Hi bitflipper,

Your advice is spot on, as always

I did a number of measurements (using REW) this morning and it turned out that regarding subwoofer placement and sub level the calibration by ear gave pretty much the best obtainable settings; so the "ear calibration thing" actually works quite well. SPL meter actually showed only about half a dB difference between satellites and subwoofer. 

Nevertheless, from your recommendations I could get a somewhat flatter response by lowering the crossover frequency from the recommended 85 Hz to about 80 Hz. Biggest impact, however, had the phase inversion switch on the sub, which basically ironed out the dip at the cross-over.

Interestingly, subwoofer placement doesn't seem to have much of an impact at all in my control room; this may sound strange at first, but in the past year I put several months of work into design, construction, bass trapping and building a RFZ. So it's good to see REW plots confirming a pretty flat response across the bass range.

BTW, this re-design and major construction effort was triggered by a discussion I had with you and Bristol_Jonesey on this forum about 1 1/2 years ago; the subject back then was ARC and the outcome was about 25K spent rebuilding the studio with proper acoustical measures in place. Unfortunately I don't have the website online yet (I have that done by a pro) but once it's online I'll PM you to get a glance to see where some simple discussion on this forum lead to ...

ARC I bought and used meanwhile in the poorly treated old mixing environment. It has served me well ... and since I already own ARC, I think I should give it a try in the new control room to see if it'll be the cherries on the cake or just empty calories ...

Cheers, mate.

I'm jealous. I'm still trying to scrape up cash to complete the treatments here after moving into a larger room. 

Last summer I converted a garage into an office/studio. I took a big chance on a wacky design of my own invention, using pegboard for the entire ceiling topped with thick insulation bats. The idea was to employ the attic space as a bass trap and hopefully tame the projected 70Hz resonance that I'd previously calculated. To my relief, it worked. I still have a measurable 70Hz resonance but it's 3db instead of 30!

I also tested a theory I'd come up with that the optimum location for a subwoofer is where none of the distances between speaker and room boundaries (walls, ceiling) is a whole multiple of one another. My sub is 4' from the nearest wall, 5' from the next-nearest wall, 11' from the next-nearest, 19' from the furthest wall, 9.5' from the (acoustically-transparent) ceiling and 11' from the actual roof. 

So for the most part, the distances are not exact multiples. And it seems to have worked out just fine. Was it because of my brilliant theory, or just luck - I don't know.

bitflipper


Aside from speaker placement and bass trapping, really all you can do beyond that is to fiddle with the crossover frequency.


Even though a subwoofer only has to handle an octave or two, it's very hard to design a box that's truly flat over that span when you're talking low (< 60Hz) frequencies. You can't do much about the low end of its range, but you can decide where to set the crossover for the upper end. 

You'll find that there is some upper frequency where the sub starts to wimp out. On a quality unit like yours that might be well over 100Hz, but on my cheaper M-Audio sub it's around 70Hz. Since my main speakers are reliable to about 46Hz, I let them handle as much of the low end as they're capable of, and set the crossover to around 55Hz. This yields a flatter response than when I previously had the crossover set to 70Hz.

I discovered the same thing with my BM5a's. Much better to leave them flat. I was getting really screwy mixes when I tried to let the sub handle everything below 80hz.
 
Regards,
Dan
 

A good start might be to visit this article here from the Bob Katz website:

http://www.digido.com/art...atz/14-subwoofers.html

It is not about fiddling and hoping you are going to get things right. It is about taking on a calibration approach to what it is you are doing.

Oh sure, go and get scientific on us, Jeff. We all know that trial-and-error is the approved method of Famous Professionals the world over. I read it on Gearslutz so it must be true.

Make an ARC  mesuerement , then use it to crorrect what can be crorrected in real world like eq's on monotiors , treatement , paceement ad cross over freq between  sub and satellites ...then aftre 2/3 meseuremnt (full seuquence) if you can't do no more tweaks , let arc do its job and it does it well with a sub

Adamp P11A +Sub 8 here : epic combo .....
Gen 8020 + Sub 8 ...

ARC won't compensate for antinodes, unfortunately.

Zo, I have the same monitors as you (P11A), but I couldn't afford the matching sub. That would indeed be an epic combo. 

One last observation...most peoples' mixes would probably improve if they just shut the subwoofer off and HPF'd everything at 50Hz. :)

Bitflipper , you would be surprised how the P11A sound via the sub cutoff , as they don't have to handle lows no more, the details i get in mids a re way better that without sub , plus you gain in longevity as the monitors never been pushed hard ...i can get loud when needed without any stress or distortion....

EDIT : i'm using this for my sub and it's night and day !!  

http://www.sweetwater.com/store/detail/GRAMMA/

you also have this  :

http://www.sweetwater.com/store/detail/SubDudeHD/

and this (going to try those for moniors also

http://www.sweetwater.com/store/detail/ISOL8R200/