Why is 100hz to 80hz so hard to deal with?

[Ryan Silva]

In my control room I have always known there to be a little cancellation going on, around 100 to 80hz. So I always check my lows on headphones to make sure (well kindda sure). Anyway, I just installed 8 24"x6"x6" corner fills in the corners behind my monitors. I thought it was a good start with 8, however I expected to get more in the future.

After the installation was done, I checked it with a measurement mic one speaker at a time and holy hell!!!

Everything below 25hz was down about 75% Great, right?

Secondly, it increased energy in 160-120hz and from 65-40hz but left a big valley in 100-80hz Very weird to me....

Could it be that I needed bass traps, but not for my trouble with 100-80hz?

Any help would be nice

[bpape]

That area may be seating and speaker placement related so less affected by the bass absorbers.

[Professor]

I'm going to guess that you might have issues with those frequencies because of your room shape and dimensions.
The wavelength for 80Hz is about 14 feet while 100Hz lands around 11' 4". If you have dimensions close to those, or perhaps in multiples, then you're going to have trouble in that range.
You may find that the response levels out if you move 3-4 feet forward, back, left, right, or even up or down depending on which walls could be creating the standing waves.
Of course, there's also no particular guarantee that the dip isn't just the result of the monitors. Maybe they're not quite as flat as you think. What kind are they?

-Jeremy

[Ethan Winer]

Ryan,

> I just installed 8 24"x6"x6" corner fills in the corners behind my monitors. <

What's a corner fill - foam? What brand and model?

> Everything below 25hz was down about 75% <

I don't know of any bass trap only 6 inches wide that has any affect at all at 25 Hz let alone lower. A better explanation is that your measuring microphone was not in the exact same place for both tests.

> Could it be that I needed bass traps, but not for my trouble with 100-80hz? <

All small rooms benefit from as much bass trapping as possible. Especially in the range from about 80 to 300 Hz.

--Ethan

[Ryan Silva]

Thanks Guys.

1. To answer the question of my monitors, they are Event Studio Precision 6's.

2. My room is 20ft by 9ft. Control area being on a short wall.

3. I will explain my testing setup: First I created a Pink Noise using 'Wav Lab' put a 'Behringer ecm 800' test mic through a 'Trident s20' at listening position. Then I recorded one speaker at a time. I then ran the recorded tracks through 'Wavelab's' 3d analyzer, and what I saw was what I mentioned before.

4. I never moved the mic, or changed settings. My monitors are about 1.5 feet away from my wall, which may account for the drastic difference in 40hz and below. I do not know the brand of these 'Bass Traps' I got them (8) for $44 on eBay with no documentation. They resemble 'Auralux's Corner Fills'

5. I am reading these measurements as they are, and I'm sure that Ethan knows a lot more than I about such things.

6. I can hear a difference in the sub-lows, but does it correlate to what I'm looking at from 'Wavelab'? I couldn?t say for sure.

Thanks

[bpape]

OK. I missed the 6" part - Ethan is absolutely correct. You'll need a lot more surface area - especially in a 20+' long room where you'll have at least 10-11 axial length modes under 300Hz.

You've given room dimensions and speaker position but not seating location - that is probably the most critical thing.

Bryan

[Ethan Winer]

Ryan,

> I recorded one speaker at a time. <

Even more important is to record both speakers playing the same thing in mono at the same time. With most pop music, bass instruments are usually panned to the center, so a low frequency analysis should emulate that.

> I do not know the brand of these 'Bass Traps' I got them (8) for $44 on eBay with no documentation. They resemble 'Auralux's Corner Fills' <

"Resemble" is the key word. Sad to say but you were probably cheated. Foam By Mail is a popular eBay seller of bogus acoustic foam. They took the data from Auralex, changed it slightly, and call it their own. But the foam they sell is nowhere near as good as Auralex. If that's what you got you should return it if it's not too late.

Even genuine Auralex LENRD corner foam, which work okay, is not as good as other commerical bass traps, or even DIY panels you can make yourself using 4 inch thick rigid fiberglass.

--Ethan

[snuffinthepunk]

what about your *gasp* ceiling??? I dunno...you might be getting standing waves between the console and ceiling, which would explain the frequencies coming back if you move away from the listening position. I know a lot of people either have a sloped ceiling or traps above the console/listening position for that reason. Sneaky sneaky. I fear you are understimating the sneakiness. If the wavelength of 80 Hz is roughly 14 feet, and you have 10 foot ceilings, and the console is rougly 3 feet above the ground...that leaves roughly 7 feet between the console and the ceiling...half the wavelength, which could of course bounce up to complete and leave a mess in the area blah blah yeah. Hopefully that'll help, I'm certainly no expert but it is a factor. Cheers mate.

J

[Ryan Silva]

Ryan,

> I recorded one speaker at a time. <

Even more important is to record both speakers playing the same thing in mono at the same time. With most pop music, bass instruments are usually panned to the center, so a low frequency analysis should emulate that.

> I do not know the brand of these 'Bass Traps' I got them (8) for $44 on eBay with no documentation. They resemble 'Auralux's Corner Fills' <

"Resemble" is the key word. Sad to say but you were probably cheated. Foam By Mail is a popular eBay seller of bogus acoustic foam. They took the data from Auralex, changed it slightly, and call it their own. But the foam they sell is nowhere near as good as Auralex. If that's what you got you should return it if it's not too late.

Even genuine Auralex LENRD corner foam, which work okay, is not as good as other commerical bass traps, or even DIY panels you can make yourself using 4 inch thick rigid fiberglass.

--Ethan

Thanks Ethan, I have tested in the way you are describing, but then I had someone tell me to do one speaker at a time. The results were more or less the same.

On the subject of the legitimately of my 'eBay foam corner fills' I was not aware of this being a rampant scam, so thank you on that. However, the rating of this seller was very good, and it still had some of those 'Auralux' removable tabs on the back. They certainly were installed before somewhere else. I somehow find it hard to believe that someone would take the time to distress foam to make it look like it was in a studio for a lousy $44.

Please check out the page, let me know if it looks fishy to you.

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... %3AIT&rd=1

Besides, they?re working pretty well; all I need is more of them.

Thanks

[Ethan Winer]

Ryan,

> I had someone tell me to do one speaker at a time. The results were more or less the same. <

If you got similar results with each speaker alone versus with both, that's a good thing!

> the rating of this seller was very good <

Foam By Mail's rating is good too, surely because the people who buy from them have no idea they've even been scammed! I mean, if you put that stuff in a room the sound will surely change. Just not as it should. But in your case it appears to be a legitimate person simply selling off some used goods.

--Ethan