Do bass frequencies build up over time in a room?

We recently moved back out to the garage for practice and dress rehearsals. I'm once again using my 4 b1's instead of 2. HOLY COW I forgot how much bass there was....

Anyway, at first I seem to low in the mix on bass so I turned it up. It was fine for a couple of songs. Then it seem to progressivly get more bassy and louder on the bass guitar.

When I turned it down to where I felt I was too low in the mix earlier, it was again balanced in the mix.

Do, bass frequencies somehow build up in a room because of acoustic and building materials?

Hi Ric,

I am pretty sure that sound (bass or otherwise) dissipates pretty quickly in most rooms. In all but the largest spaces, we are probably talking milliseconds or maybe seconds at most. Any of that energy that does not bounce back at you almost immediately is probably passing through the walls and out to the neighbours. Anything that is stopped in the building materials is probably being converted to heat. Albeit not much.

Maybe you are experiencing ear fatigue. For me, it seems that when exposed to loud volumes I stop hearing the intricate details of the mids and highs, and the lows seem to dominate.

Does that fit with what you are experiencing?

Hi Ric,

Sometimes where you are in a room will dictate how much bass you hear.

In my basement room it (bass response) seems to change every two steps or so.

I "think" this is caused by "standing waves", certain frequencies (wave lengths) are cancelled in places because of reflections.

Try placing the B1's right against a wall.

O..

quote:

Do bass frequencies build up over time in a room?

Yes.

You can think of a room like a leaky bottle under a faucet.

This is true for all frequencies, including bass.

The amount of water coming out of the faucet is analogous to the sound level coming out of the source (say a bass guitar amp or and L1 system) and the number of holes of a certain diameter in the bottle is analogous to the amount of sound that's absorbed by the room plus what's transmitted out of it.

(Note that rooms are different at different frequencies, and so are the sources. So to be complete you need to think about a different faucet setting and different number of bottle holes for each frequency.)

What happens when you first turn on the faucet(source)? The bottle (room) begins to fill with water (sound level) and starts leaking (being absorbed and transmitted through the room surfaces) until it reaches equilibrium: the level stops changing so long as the source is not changing. If you suddenly shut off the faucet, the level declines until all the water has leaked out.

The more holes in the bottle (of a certain diameter) the faster the water will reach equilibrium and the faster it will drain when the water is shut off. Conversely, if you reduce the number of holes, the water takes longer to reach equilibrium and longer to drain out when the water's shut off.

In general, bass frequency bottles tend to be less leaky and so bass tends to build up more slowly when a source is turned on and take longer to decay when the bass source is turned off.

This buildup and decay time is directly related to what is called Reverberation Time -- defined as the time it takes a sound source that has been on for a long time (long enough for the leve to have reached equilibrium) to fall by 60 decibels when the source is suddenly turned off. Reverb Times for bass frequencies can typically be more than twice the times for midrange and higher frequencies.

I hope this is of some help.

With best regards,

Ken

Good analogy, Ken!

quote:

Originally posted by Ken-at-Bose:
...Reverb Times for bass frequencies can typically be more than twice the times for midrange and higher frequencies...

Keep in mind that the construction of the room and the materials on the room surfaces can sometimes reverse this "rule of thumb".

When the mid-to-higher frequencies have longer Reverb Times than the lower frequencies, a room can sound very "noisy" with just 3 people talking.

Take note of the table of "absorption by materials" near the bottom of this page. You'll see that drapes and carpet act just the opposite of glass windows and wood.

So, if you like the frequency balance when you rehearse in a carpeted room with lots of drapes and acoustical ceiling tile, but then you walk in to perform in a room with lots of un-curtained large glass windows and wood paneling over stone walls -- you'll likely want to consider dialing back the mid- and high frequencies from your previous EQ settings.

Hi Ken,

Does the build-up of sound you described (neat description) account for Ric's experience over several songs?

quote:

Quoting Ric

Anyway, at first I seem to low in the mix on bass so I turned it up. It was fine for a couple of songs. Then it seem to progressively get more bassy and louder on the bass guitar.

When I turned it down to where I felt I was too low in the mix earlier, it was again balanced in the mix.

Do, bass frequencies somehow build up in a room because of acoustic and building materials?

I would have thought that what you are describing below is happening in milliseconds to say several seconds in a very large space.

quote:

Quoting Ken-at-Bose

This buildup and decay time is directly related to what is called Reverberation Time -- defined as the time it takes a sound source that has been on for a long time (long enough for the leve to have reached equilibrium) to fall by 60 decibels when the source is suddenly turned off. Reverb Times for bass frequencies can typically be more than twice the times for midrange and higher frequencies.

I think the 'fatigue factor' is at play over the duration of several songs.

I've heard low frequency resonance 'accumulate' in a room which took 10-20 seconds to build up to 'saturation' -- but never anything on the order of minutes. This was caused by low-frequency feedback between a mic and speakers, where the 'low speed build up' was simply because the feedback loop was right at the "threshold".

Keep in mind this is in my 2 car garage converted to a practice space. The walls are 7/8 drywall. The only wall that doesn't have dry wall is the one opposite us, which is the garage door, which is metal. The floor is painted cement with a short carpet over it.

We recently changed our play position. We used to face from one side to the other. Now we face the garage door with out stuff planted opposite it along the wall. We've found that the sound doesn't escape from the garage much this way, and we havn't had sound complaints from neighbors for quite a while.

I've also notice that certain notes on my bass really seem to be boomy and loud, but only in the garage.. Is that's what's known as a ,"bass node?" within a room.

We had our masters at 11:30. And the channels appropriate for the mix we wanted.

quote:

Originally posted by Ric:
...I've also notice that certain notes on my bass really seem to be boomy and loud, but only in the garage.. Is that's what's known as a ,"bass node?" ...

Yep! Especially since garages tend to be fairly "square" (if not cubic!).

If you look at this article, you can probably predict which notes (frequencies) will be boomy, too. (Your ears actually are telling you the note(s), of course!)

Do you have a T1? If so, you could use the ParaEQ to notch down the worst of the boominess (and save as a 'garage' scene!).

quote:

Does the build-up of sound you described (neat description) account for Ric's experience over several songs? I would have thought that what you are describing below is happening in milliseconds to say several seconds in a very large space.

Does anyone remember the character Rosanne Rosanna-danna from Saturday Night Live?

Well, if you do, then you'll know what I mean when I say...

Never mind!

ST is right. My answer is true for fractions of seconds, and up to a few seconds, not the time it takes to play several songs.

Sorry.

Never mind.

Ric, I can't think of anything in the acoustics of the room that would build up bass energy over a long time.

Ken

quote:

Originally posted by Dan Cornett:

quote:

Originally posted by Ric:
...I've also notice that certain notes on my bass really seem to be boomy and loud, but only in the garage.. Is that's what's known as a ,"bass node?" ...

Yep! Especially since garages tend to be fairly "square" (if not cubic!).

If you look at this article, you can probably predict which notes (frequencies) will be boomy, too. (Your ears actually are telling you the note(s), of course!)

Do you have a T1? If so, you could use the ParaEQ to notch down the worst of the boominess (and save as a 'garage' scene!).

This must be what is happening. We start with a song that is open E To B on my first string..no problems there. Then the next couple of songs hover around G on the third fret of my bass. I think I'm hitting some bass nodes around G & A.

Usually the B on the E string is very boomy. That is the note I used to test combo amps since it has resonance that can make some combos rattle. Rattles drive me nuts.

Hello, dctommy

We have a new discussion for your question. Please see:
Boomy feedback: a bass frequency on the A string of bass guitar

Thank you.