Disappearing BASS

[XenosoniK]

hello, all. I have a problem. My bass disappears in the sweetspot of my setup. I am listening with Behringer Truth 2031As set about 6 feet apart and angled to form a triangle. Due to space restrictions, they are pretty close to the wall, but not butted up against it.

The problem is, I can hear the lower frequencies in different parts of the the room, mostly closer to the walls and (of course) the corner. But, of all the places for it to disappear, bass vanishes in the sweet spot.

I guess my question is, will bass traps help with this? I know bass traps are used to smooth out the bass response by attenuating the peaks but will it also alleviate the problem of disappearing bass?

Thanks.

[sabianq]

yea, your getting frequency cancellation from standing waves.

if you isolate the offending frequency, you can make a trap to sit in your corner of the room or diffusers to place on the opposite wall of the monitor.

place these on the other side of the wall.



whoops sorry, wrong site.

Just kidding, you should get a tone generator and sweep the freq until the you get the cancellation, write down that freq, then build a bass trap that targets that frequency.

[dcwave]

If you are in the typical square room plan on bass traps in all four wall corners, and all four wall and cieling corners, then add two more in the middle of each wall They you ca start working on the problem you have with the high end and flutter echo because you'll hear it.

[XenosoniK]

quite a setback. both in terms of time and finances. i had just put a whole bunch of 2" wedge foam on my walls to help with the flutter echo, which is not completely gone in all parts of the room, just my listening position. i've always wanted to make bass traps but man, living in an apartment makes it difficult to do any kind of woodwork.

hmmm...

would relocating my speakers fix the problem, at least for the listening position?

[oretez]

maybe . . .

but for down and dirty trap you might try some rolls (left rolled, two stacked one on the other per location) of home insulation (you can make them prettier by draping with some type of fabric)

[howie15]

Sabian,

If I see that correctly as a Rattl' Trap that's damn funny.

Howie J

[sabianq]

Somehow I figured you, Howie, being from St Paul, would appreciate my "wet" attempt at humor.

My Grandpa use to take me Bass fishing a lot when I was just a young lad living in Wisconsin, we used lures similar to the one pictured above.

and yea, I think it actually is a Rattl' trap.

[dcwave]

OT thread hijack -
sabiang - where at in Wisconsin - I lived in Cedarburg and Theinsville and spent a lot of summers in my youth at Port Washington.

[sabianq]

Hey dc,
I was born just outside of Milwaukee then my parents took me to Eau Claire where I lived until I was 3. Then every Summer or so until I was like 15 I would go back and visit my Grandparents who lived in Mondovi and Eau Claire.

I still visit my grandma in Mondovi every couple of years.

But in essence, my family is a Gun totin', Bass fishin', bunch of cheese heads.

I still haven't been to Port Washington, but I have heard of the place and from what I have heard, the destination seems quite nice.

[dcwave]

Wow - small world indeed - I was born in Milwaukee - most of my family is a bunch of cheese heads all the way from north to south, although the older relatives, the dinosaurs they are, have migrated to Florida and Vegas to escape the winters.

[Juan]

If you do some refrence monitoring you can figure out if the bass is even there. I bet some other monitors will help. The new self tunning monitors might be the best solution.

[XenosoniK]

Well. I used a tone generator and yes, the bass does reach down there in other parts of the room, but in the sweet spot, the bass vanishes from around 135Hz and down.

Since bass is omnidirectional, are there any specific places other than the corners that i should put bass traps? i'd hate to have to put it on the flat surfaces of the wall because i've already installed 2" foam to deal with the reflections.

and will putting it in the corners have a dramatic effect or am i only gonna get a dB or two? once i find free RTA software, i can give you guys some specific numbers.

thanks again for all your help.

[Juan]

Using traps for the most part helps to not have to much bass bouncing around. This will create a mushiness or a not very defined bass sound.
It seems that you are getting as was mentioned before a standing wave. And the way to deal with a standing wave phisicaly is to pin point it and break it up. What I have always done is imagined it, visualize the dang thing and break the paralell reflections with a material that is simpathetic to the bass frequencies you suspect.

[sabianq]

Originally Posted by Juan

visualize the dang thing and break the paralell[sic] reflections with a material that is simpathetic[sic] to the bass frequencies you suspect.

YES! Exactly! You are correct, our brains have the ability to visualize the way sound interacts with a space, I have always done that by understanding how long audio waves are and to get that, it helps to know that 100 Hz is roughly 11 feet.

there are only a few ways that sound interacts with its surroundings
this is true for waves in liquid (waves), solid (seismic), gas, and space-time (light and gravity)

now ironically, the same math that describes these waves works all waves whether it is mechanical (molecules shifting with the pressure waves interacting them) or whether they are Electromagnetic (radio, heat, light, microwave, x ray, gamma and gravitational) to conclude that the velocity of the waves are directly related to the elasticity and density of the medium they pass through. ( i think that the speed of electromagnetic energy is directly related to the density of space-time since the density of our universe is constant all over then the speed of light is also constant, and that explains the light speed speed limit. one way to prove that is to see if light traveled faster in the past when the universe was young, small and hot.)

Just my personal observation, it might not (most likely) correct.



but in this example we will be talking about mechanical waves through air (sound)
To reiterate, sound interacts with its surroundings by either:



Adsorption
works by absorbing the sound wave and turning it into heat the amount of loss is a function of density.
there is actually a name for how much audio energy a piece of absorption material can absorb or how efficient the material is.

Absorption is measured in Sabines after W.C. Sabine. He was considered by "a whole lot of people" to be the father of modern acoustics. He worked on all sorts of **** related to room acoustics, if you are interested in acoustics, you should read his works, actually if you want to get into it professionally, his works should be required.

anyway,
an absorption rating of 1.0 indicates 1 square foot of total absorption. if you have a rating less than one, then it is less than total. imagine 1 being 100% absorption and .5 being 50% absorption.
sometimes an absorption can be more than one with new materials and new fabrication process but any number way more than one should be suspect.

there is an interesting side note with the use of resonators for acoustic absorption, the Helmholtz Resonator with perforations is a very old acoustic treatment, probably the first. Romans made them using big clay pots filled with ashes. the wind would blow across them and make tones.

you can use the same principal for acoustic treatment by building floors or panels on springs and types of rubber mat, you can counter act the pressure wave and bring it to a halt.



there is diffusion:

a special form of reflection, you break up the wave by creating an obstacle with a complicated geometry that reflects or scatters the wave.
Like frosted glass on a light, sound waves scatter when they hit something with multiple angles for reflection.
one of the absolutely simplest diffuser is a sheet of ply wood bent into a slight bow shape on your wall.

a quadratic diffuser was devised by a guy named Manfred Schroeder. He built a field of wood pegs that resemble a city scape with many skyscrapers.

the blocks are placed in a mathematical organization defined by (well depth factor=the modulo of a prime number and a whole number.

look up "quadratic residue sequences" to a better idea of this.



then there is refraction,

sound can be bent by temperature differences in the atmosphere.
if you set up your sound system mid day, and the show starts at sun down, the sound will change when the air temp gets colder, the velocity changes.
refraction is usually associated with light but sound does the same thing when it hits temperature gradients. the sound will bend toward the cooler air.
This is a big weird problem that can have whole books written on it.

needless to say, the acoustics of your room can be changed by taking the uniformity out of it.

you can make big bass trap diffusers that have the same dimension as the sound waves that are causing problems.
you can do any of these to stop your resonance issue.
but you need to stop the reflection of the wave on itself.
so you can use absorption and/or diffusion sounds like you already have absorption on your walls so you can implement diffusion

an easy diffuser is a big tall cylinder made of the biggest concrete tube you can find at home depot, cutting one to 7 feet and one to 5 feet, stuffing them full tightly packed news paper and covered with a berber carpet. place them in the corners and that should work.

[vulcan_dc]

Originally Posted by sabianq

( i think that the speed of electromagnetic energy is directly related to the density of space-time since the density of our universe is constant all over then the speed of light is also constant, and that explains the light speed speed limit. one way to prove that is to see if light traveled faster in the past when the universe was young, small and hot.)

LOL ... this thread went totally off topic..... sorry Xeno...

http://archives.cnn.com/2000/TECH/sp...d.of.light.ap/

should clear things up... FTL is possible right now, why an early universe!!... there is no speed limit.....