150hz spike--acoustic treatment

[pietro79]

I often find I need to EQ sounds to remove a spike at around 150hz.. sometimes it's 160, sometimes 155, sometimes 148-ish...

the fact that it happens often makes me worry... it means a possibilty of a few things:

1. I'm consistently recording spikes through the combination of my recording techniques & equipment

2. I'm consistently playing back spikes with my system (including the less-than-ideal room I'm listening in)

3. My ears create spikes at 150hz! (no, because then EVERYTHING I'd ever hear in day to day life would be that way, and I wouldn't notice any differences)

It's probably a little bit of #1, but I'm quite sure it's mostly #2 because listening back on headphones, there's no jump in frequency that I'd call a spike... I mean, I can still hear a little something, but definitely not a spike

I should mention, this spike is present on things recorded from various locations (ie-not only things tracked in the same room I'm mixing), which further shows me that it's not #1 (my tracking)

Anyway, please download the following WAV (roughly 1.7MB)... It's the bass gtr soloed... playing a line in 4 beats per pitch...recorded in a church:

Download wav here (right click "save as" for PC, or control click "download linked file" for Mac)

the second group of 4 beats (the second pitch) is where I hear a ridiculous spike mostly around 150HZ-160HZ... It is very obvious... do you guys hear it? It seems like this overtone is present throughout the clip, and comes to the forefront when certain notes are played (when it vibrates in sympathy with the overtone, in other words)

If you guys can't hear this spike, that's good in a way, it means at least my tracking is good and I just need to improve my listing conditions... kind of nerve-wracking though that there's uncertainty to what I'm listening

----
How should I go about fixing this problem?

I'm in a mostly-bright attic. Wood floor, plaster and drywall walls...

About 15 feet long by 12 feet wide by 7.5 feet tall, with the slanted ceiling running lengthwise (see attached image below...this is simplified)

the audio monitors are a little close to the wall behind them. Could pull out a foot, but will that do much? (FYI: they're Yorkville YSM1P, with "normal" and 1/4 room switches enabled... that keeps the top end flat and attenuates -2db below 80hz)

I've tried decoupling them by putting them on four 1/2 inch sheets of blue foam (cut up from the foam mattress you sleep on for camping), but maybe this foam is too dense and doesn't do enough. What foam is best?

As for the walls, egg crate foam won't do anything for such a low frequency spike... I need some sort of bass trap... a resonating one, right? Any suggestions on where to find plans for building one? And would I build only one? And where would I place it?

Thanks for your help & patience

Sincerely
Pietro

[ez_willis]

The link is dead, which kind of sucks because I was curious to hear what you were talking about.

When I first got into recording my acoustic drums, I'd get the same brief spike. I thought it was a type of digital distortion or something, and I'd have to edit it out, which was somewhat time consuming and very annoying.

It ended up being that the overheads(one in particular) was above the vent hole on the bass drum and every once in awhile, when I kicked it hard enough, a poof of air would hit the capsule. It was almost inaudible, but it would fuck with my ear drums.

[pietro79]

Sorry forgot to say

(right click "save as" for PC, or control click "download linked file" for Mac)

Urg, I feel like I've posted something too specific for people to really asnwer on a forum... I am going to pick up the Master Handbook of Acoustics and hopefully figure out some ideas for constructing bass traps...

If I specifically have consistent problems with spikes @ around 150hz, I should be looking for absorbtion with a narrow band width, right? And I suppose certain types of absorbers and placements are more focussed than others... if anyone can put labels on these, please do! it'll guide me in my research

Well, I guess I'll post questions after having taken a look through the handbook

thank you

pietro

[pietro79]

Originally Posted by ez_willis

It ended up being that the overheads(one in particular) was above the vent hole on the bass drum and every once in awhile, when I kicked it hard enough, a poof of air would hit the capsule. It was almost inaudible, but it would fuck with my ear drums.

No, mine is definetly a resonance issue

[ez_willis]

Post this in the Studio Building and Display Forum. You might get a better response.

[SouthSIDE Glen]

Originally Posted by pietro79

the second group of 4 beats (the second pitch) is where I hear a ridiculous spike mostly around 150HZ-160HZ... It is very obvious... do you guys hear it?

Gave your clip a listen...

I don't hear anything untoward in the clip in either phones (Sony 7506) or nearfields (Mackie HR824). The reason it's more pronounced in the second bar is because ~150HZ is apparently the primary overtone for the note played in that measure.

Based on the fact that I don't hear anything out of the ordinary in that frequency range here, nor see anything untoward in a FFT analysis, I'd agree that you probably have a monitoring problem. If you want to verify that, try two things: first see if that "spike" appears to you if you play it back on other systems in other locations yourself, and second, move around your room while playing back the "problem" clip and see if that spike disappras and reappears at various locations within the room; the modes should be somewhat granular and the spike should not be evenly spread throughout the room.)

Check out the "studio building forum" on this BBS for a whole cauldron of good info on bass trapping. It is frequented by Ethan Winer of Real Traps fame, but he also provids plenty of DIY tips on such treatments as well.

HTH,

G.

[ez_willis]

Originally Posted by SouthSIDE Glen

If you want to verify that, try two things: first see if that "spike" appears to you if you play it back on other systems in other locations yourself, and second, move around your room while playing back the "problem" clip and see if that spike disappras and reappears at various locations within the room;

Couldn't he just put some headphones on?

[SouthSIDE Glen]

Originally Posted by ez_willis

Couldn't he just put some headphones on?

Unless I'm using a 4-digit pair of AKGs, trusting headphones alone alone for testing bass balance would be like trusting Snoop Dog alone with my sister. Well...maybe a little better than that...

G.

[PhiloBeddoe]

I would recommend running a frequency response analysis on your room. There are free test tones at:

http://www.realtraps.com/test-cd.htm

You will need an SPL meter, but these are inexpensive and good to have anyway.

It's kind of tedious to run the test, but it will tell you whether or not you have a monitoring issue. You probably do. My guess is that you also have other room modes that may be less noticable for whatever reason. It helps to know where they all are so you can avoid temptation to do too much 'corrective' eq at the mode frequencies.

I'm not knowledgeable enough to offer advice on treating your room. The studio build forum here and johnlsayers.com are good places to start.

[bennychico11]

http://www.hometheatershack.com/roomeq/