Could someone explain what a "bass null" is?

M

MDS

Audioholic Spartan
If you were talking about a null in the context of frequency response it would be a point where the amplitude of a specific frequency drops to zero; ie the speaker couldn't reproduce it all.
 
Sheep

Sheep

Audioholic Warlord
MDS said:
If you were talking about a null in the context of frequency response it would be a point where the amplitude of a specific frequency drops to zero; ie the speaker couldn't reproduce it all.
I think he's referring to cancellation in a room.

SheepStar
 
M

MDS

Audioholic Spartan
I didn't think about room cancellation but my generic definition holds there as well. If two soundwaves destructively interfere, the amplitude drops appreciably.
 
Guiria

Guiria

Senior Audioholic
This is how I understand it.

If two or more soundwaves of the same frequency collide at the peak of each soundwave then that frequency is amplified (room gain, increased db). If the waves collide at the trough of the soundwave then you get a cancellation effect (decrease in db) or a "null" in your frequency response.

This exact thing is why room acoustics play a large part in improving the linear frequency response of sound in your listening environment.

If you're interested in some more info read this sticky in the room acoustics section of audioholics forum.

http://forums.audioholics.com/forums/showthread.php?t=8119
 
HP666

HP666

Enthusiast
I have a large room, 27 X 12.5 X 7. My seating area is right in the middle facing one of the long walls where my TV/stereo is; the upper wall if looking at the sketch from above. I was told that my seating was in the "bass null" by someone who saw a sketch of my room. My Sub will be in the upper right hand corner of the room.
 
Jack Hammer

Jack Hammer

Audioholic Field Marshall
HP666 said:
I have a large room, 27 X 12.5 X 7. My seating area is right in the middle facing one of the long walls where my TV/stereo is; the upper wall if looking at the sketch from above. I was told that my seating was in the "bass null" by someone who saw a sketch of my room. My Sub will be in the upper right hand corner of the room.
In essence, sound moves in sonic "waves". Lower frequency (bass) waves are spread out further (think more distance between crests of waves) than higher frequencies are. Now picture a wave, ~~~~~, a null is a point where that wave's "hill' or 'valley' is going over/under you. The result is you hear less of that sound. Meaning if you walk closer to your subwoofer the bass will seem to increase, but when you go back to the null the bass will seem to disappear.

Hopefully that description wasn't too far off or confusing.

Read this article on subwoofer location, Crawling for Bass.

Good Luck
Jack
 
N

Nuglets

Full Audioholic
Jack Hammer said:
In essence, sound moves in sonic "waves". Lower frequency (bass) waves are spread out further (think more distance between crests of waves) than higher frequencies are. Now picture a wave, ~~~~~, a null is a point where that wave's "hill' or 'valley' is going over/under you. The result is you hear less of that sound. Meaning if you walk closer to your subwoofer the bass will seem to increase, but when you go back to the null the bass will seem to disappear.

Hopefully that description wasn't too far off or confusing.

Read this article on subwoofer location, Crawling for Bass.

Good Luck
Jack
I don't know if you can describe it quite like that...For one, sound is a compression wave so you can't quite picture it like a wave going above or below you...Maybe I'm not understanding you correctly but your description seems to be a ways off. I'm assuming that he's asking us about room acoustics causing nulls. A better description would be a place where the sound wave's collide kind of like what Guria said. It goes more like this though: If a crest is occurring at the same place as another crest or a trough with a trough then you will get constructive interference and the amplitude will increase. If however a crest and a trough come together you will get destructive interference resulting in lower amplitude(null).

The reason you get this interference is because the sound you hear isn't necessarily coming directly from the speaker, much of it is reflected off the walls and depending on the size, shape, material and many other factor's of the room the sound wave's will interact in many different ways.
 
j_garcia

j_garcia

Audioholic Jedi
Yep, what Nuglets said. When it comes to low bass, it isn't just most, but more or less all of the bass that is reflected because a single wave for 20Hz is longer than the average room. A null is when you happen to sit at a point in the room where a particular frequency or range of frequencies cancel eachother out to some extent, and it can be quite audible. Looking at a sketch, it is basically impossible to tell if you will be in a null, however sitting in the exact center of the room is generally not a good idea, particularly in a square or nearly square length room.
 
mtrycrafts

mtrycrafts

Audioholic Slumlord
MDS said:
I didn't think about room cancellation but my generic definition holds there as well. If two soundwaves destructively interfere, the amplitude drops appreciably.

When you are in the wrong room mode where a frequency is at minimal level, that is not a destructive interference, is it? It's just a null position.
 
M

MDS

Audioholic Spartan
mtrycrafts said:
When you are in the wrong room mode where a frequency is at minimal level, that is not a destructive interference, is it? It's just a null position.
Where the amplitude of a given frequency is minimal, then no that probably doesn't qualify as a null. What I was getting at was nicely captured by j_garcia in his response above: 'A null is when you happen to sit at a point in the room where a particular frequency or range of frequencies cancel eachother out to some extent, and it can be quite audible.'

By my definition that is destructive interference. Total destructive interference would be when two exact waves, 180 degrees out of phase, collide. The result will be a total null - as in silence. I don't know if that could happen in a room unless the sound reflects more than once and two different reflections happen to collide.
 
N

Nuglets

Full Audioholic
I'm not that familiar with room acoustics and room modes but I think room modes are a caused by wave interference...I'm not really sure though...:confused:
 
j_garcia

j_garcia

Audioholic Jedi
I know this first hand because I had a big null in my previous room because the room layout dictated that I sit close to the center, which made for some cancellation issues with my PB-10 at around 80Hz. The effect was considerably reduced when I swtiched to my current sub, but there was still a little bit of a dip.
 
Jack Hammer

Jack Hammer

Audioholic Field Marshall
I might be even further off...

... It wasn't a perfect description. I was trying to explain it in an uncomplicated (simple) way to give him the general idea. Maybe I should have said something like, "a null is an acoustic dead spot for a given frequency. Try moving your subwoofer." :)

I don't really have a deep enough understanding of acoustical theory yet to explain some of the things I've begun to grasp. I just remember how confused I was when I first read about it. The more I read, the more confused I got. Especially when people started posting back and forth about different aspects.

I used to think a speaker would sound equally well regardless of how it was placed...:eek:



Jack
 
D

dbpolk

Enthusiast
Like waves in the water

Think of it as waves in the water. When two waves meet sometimes they combine to make a larger wave (amplitude). Somethimes they combine to cancel each other out. The sound waves behave in exactly the same way. How they behave and react to the environment is very hard to predict. Same with sound. Way to many variables.
 

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