Problem with a certain frequency in a mix translation

[Torchlight]

A strange problem has occurred in my studio where there never was a problem before. Let me start by saying that all of the mixes I have done in my studio have translated beautifully. Up until I did this particular mix of a solo Didjeridoo I never encountered this problem before. For some reason there is an overwhelming low (100 Hz or so) tone that translates to about 75% of the sound systems I play the mix on, but I barely hear this tone in the control room. I used a notch filter set to around 100 Hz (fairly narrow bandwidth) to remove most of the tone. It's funny because the two sets of monitors I use in the control room are EQ'd extremely "flat" at the mix position; thus I have never had a translation problem. I use Dynaudio BM 6As as my primary monitors and Tannoy Reveals as my secondary monitors. I will say that the further back I move from the mix position the more the 100 Hz tone becomes noticable. This is more evident on the Tannoys. I also realize that this has a lot to do with wavelength at low frequencies, and the distance that they need to develop.

I will admit that I had never recorded didjeridoo before so I took a guess at mic choice and placement. The mic that gave me the most problem with this overwhelming tone was the Sennheisser 421 that I placed at the bell of the instrument. Unfortunately I did not use any low rolloff when tracking. Mistakenly I thought the low overtones of the instrument would sound very nice. After listening to commercially available didjeridoo recordings I now realize that the essence of the instrument's sound comes from much furether up the frequency spectrum. Hey, live and learn, right.

Anyway, the next time I record the didjeridoo I will try a different approach. The real problem though is the translational thing. I just don't get it! And it of course sounds worst when the mix is played on a car stereo system. Theoretically I should be able to get all frequencies in a mix to translate well. This problem is keeping me up at night!

Any ideas about what is happening here?

Thanks,

Torchlight

[Naagzh]

The wavelength of a 100 Hz cycle is quite long (about 11 ft.), long enough so that is would pass your ears by before it would fully develop, especially if you're close to the monitors.

If your room has large parallel surfaces this far apart, it's possible a standing wave has developed (perhaps this is why you noticed more bass when you moved back?).

I suggest treating your room with bass traps, so that you get a decent "picture" of lower frequencies throughout your room. Use PTs signal generator to judge the difference.

But this is also a problem when recording bass amps. The player says "I like lots of low end" and dials down all the mids and highs, and then when he plays a higher note, you can't hear him at all in the mix. It was discussed recently here, but suffice it to say that a small boombox can't reproduce these low frequencies, only the overtones (which reside further up the spectrum). Nonetheless, we "hear" bass on boomboxes because our brains psychoactively fill in the fundamental tones, even though all we're hearing are overtones.

[Torchlight]

Thanks for the response Naagzh! In fact I have treated my room with bass traps, but I must still be getting a standing wave at 100 Hz or so between my treated parallel walls. I did not have the luxury of designing the shape and size of the control room becauses it's an existing room in the basement of my house. I did the best I could with Auralex treatment. For the most part my mixes translate very well. Maybe I will just have to do a distance check from now on when I suspect a 100 Hz problem.

Torchlight

[M.Brane]

Foam is ineffective at lower frequencies which is unfortunate since that's where most of the problems lie in a small room.

EQ cannot adequately compensate for room acoustic problems.

I often walk around the room or even into other rooms while checking for low frequency problems in my mixes.

[accession]

The wavelength of a 100 Hz cycle is quite long (about 11 ft.), long enough so that is would pass your ears by before it would fully develop, especially if you're close to the monitors.



I often see this concept mentioned, though I wonder how well it stacks up as a valid statement...

The speaker cone generates a complete wave motion, up to the crest of the wave, and down through the trough. This wave radiates outwards from the speaker. Therefore, no matter how far one is situated away from the speaker, the entire waveform (peak and trough) will pass by our ears, and therefore the bass will present itself whether we're 1 foot away, 11 feet away, or 111 feet away.

What does impact the degree of bass experienced by the listener, however, is the resonance of the room itself, and the positions about the room of maximum waveform excitation (or complete cancellation, and everything in between) due to the interference of the rebounding wave from (mostly) parallel surfaces.

Food for thought?

[accession]

For some reason there is an overwhelming low (100 Hz or so) tone that translates to about 75% of the sound systems I play the mix on, but I barely hear this tone in the control room.



Your experience (no bass in some areas, boomy bass in others) points to a standing wave forming around the 100Hz mark.

As I understand it, changing your monitoring postion and/or bass trapping is the only things that will help against these dead spots.

[narcoman]

yup - bass trapping with proper bass traps. Cant do it with foam (unless you have it REALLY thick). As for bass not developing - not true. Im 5 feet from my monitors and there is a fully balanced sound coming out of them. Of course, the room has been well set up though.... The 100-120hz boom thing - VERY common from un/poorly treated rooms. ...Id address that.

[Naagzh]

long enough so that is would pass your ears by before it would fully develop, especially if you're close to the monitors.



I'll stand corrected. Not sure why I said that; it doesn't make sense to me now. Maybe I was just repeating something I heard. Ah well, I'm here to learn, too.

[Torchlight]

Thanks for the feedback (no pun intended) everyone! In the past week I made a few changes. I hear what you are saying about the bass traps needing to be something better that foam and I have known that for a while. However, I just can't afford to do any serious bass trapping right now, and that can be expensive. I did find that my monitors (Dynaudio BM 6A) were not setup in a perfect equallateral triangle the way they should be with the mix position. To my surprise and disappointment, I mis-measured the first time I set them up. I corrected that, moving them a bit further away from the walls/corners and now they are in an equallateral triangle with the mix position. I then used an RTA to re-measure the freq. response of the monitors at the mix position. I did need to make a few adjustments and I am very happy to report that the freq. response is damn near flat from about 50Hz up to about 20 KHz. Of course, as always the RTA gets me in the ballpark, but then I rely on my ears and my trusted reference CDs when making the final adjstments. Anyway, I remixed the tracks that gave me some translational problems and now they translate much better. Another words what I hear in the control room is pretty much what I hear on other playback systems, including my somewhat boomy car. The boominess problem I heard before I EQ'd and repositioned the monitors is nowhere near what it was. I used to be able to moved back from the mix position a few feet and hear (and measure) a very noticable boost in about 80-100 Hz range. This is no longer all that apparent. I also did a few other mixes and they translated very well too.

I do have another question though. Does anyone out there use the Dynaudio BM 6As (not the BM 6A mk II, but the predecessor) in conjunction with a sub. I don't......yet. I actually find that the BM 6As represent low freq. very well. This is true when I look at the RTA measurements as well as listen to my trusted reference CDs. Plenty of tight bass! So, can someone please tell me what the sub would do for me other than help my monitoring system (BM6As) to extend its range down to 20 Hz or so?

Also if it helps here are my approximate control room dimensions: (16ft. long) X (11ft. wide) X (8ft. ceiling). Of course this is less than ideal, and I am well aware of the probable room mode problems I have going on. I do the best I can with the room I have.

Thanks,

Torchlight

[M.Brane]

Amazing what a bit of position tweaking will do eh?

Being on the east coast you should be able to find compressed fiberglass pretty easily, and at a decent price. Wrap the sheets with some muslin, and put 'em in the corners. Instant budget bass traps.

Out here on the left coast when you talk about compressed glass most just look at you funny. The few that do carry it charge accordingly.

[accession]

long enough so that is would pass your ears by before it would fully develop, especially if you're close to the monitors.



I'll stand corrected. Not sure why I said that; it doesn't make sense to me now. Maybe I was just repeating something I heard. Ah well, I'm here to learn, too.



Did you miss my post?

Scroll down to the tuning fork...

http://faraday.physics.utoronto.ca/IYearLab/Intros/StandingWaves/StandingWaves.html

...can you see that it doesn't matter how close or far you postion yourself away from the soundsource, the complete wave vibration will pass you, meaning you'll hear the full soundwave...

...expect where rebounding waves cancel/boost the incoming soundwaves due to room's resonances as I suspect you're experiencing.

Thoughts?