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# could a speaker damage a laser?

#### maxkillz

##### New member
k-shell said:
well that sounds like:

A. your desk is built like a drum or
B. that is one loud speaker!
it's a 15 year old solid oak desk and yes it does get quite loud, if you know how loud certain things are in DB levels this speaker puts out about ~140db when I close my door and crank it up as far as it can go before it starts to distort

#### k-shell

##### New member
Ok so here’s my scientific analysis:

You have built a transducer mechanism that incorporates 5 primary functions.

the acoustic generator (speaker) produces shockwaves at controllable frequencies (function 1) which are imposing upon an object (your desk) that resonates at specific frequency harmonics.
this creates kinetic energy in the resonating object and causes it to move back and forth (function 2).
you also have objects that do not resonate at the same frequencies of the desk, but because they are in contact with it and held down to it by the force of gravity the kinetic energy is conducted through the smaller objects (function 3).
This is a dynamic process, as the primary resonating object (desk) is flexing which throws the smaller object (laser) up into the air. this is a form of storing kinetic energy. (function 4)
As the smaller object falls back to earth from the pull of gravity it hits the larger object and releases its kinetic energy instantly causing a much higher shock due to instant deceleration as opposed to the initial gradual acceleration of when it was thrown up (function 5) this shock will propogate through the laser and if the force is either strong enough or goes through something the right way, it could break or misalign something.

So no, your speaker will not damage your laser, but what you have built is a mechanism that transduces the acoustic energy from your speaker into kinetic energy that results in making the laser bounce on the table...

#### maxkillz

##### New member
wow thats a big explanation. maybe a solid structure transfers more energy? i have hard wood floors and I can feel the subs vibration through my feet even when it's at such low frequencies I can't hear it that may also transfer more energy to my desk

#### k-shell

##### New member
maxkillz said:
wow thats a big explanation. maybe a solid structure transfers more energy? i have hard wood floors and I can feel the subs vibration through my feet even when it's at such low frequencies I can't hear it that may also transfer more energy to my desk
The more solid the two objects are, the faster they will decelerate when they hit each other. but typicaly the more solid something is the more it resists vibration (well let me paraphrase that) something with a hollow cavity will vibrate more than something that is solid of the same mass. A desk is not very solid in many aspects.

Larger objects resonate at lower frequencies (larger wave lengths), this translates into how much they will flex (and how fast). You wouldn’t expect a skyscraper to resonate at the same frequency as a church bell. Inversely, you wouldn’t expect a church bell to flex as much as a skyscraper...

If your desk where bigger the flex would be larger, but slower. Maybe slow enough that objects sitting on the desk would not have enough speed to overcome the force of gravity...

But the primary harmonic would change and a larger desk would resonate at a lower frequency.

Oh and as for your floor. its either your are feeling the sub conducting through it, because it sitting on it or you are feeling either a 3rd 4th 5th or so on harmonic. beleive me, if you hit the primary harmonic of your house, you know you hit the primary harmonic of the house! ;D

Try this just so you can understand what a primary harmonic is:

Wet your thumb slightly and let it dry a little, put all five figures on a large piece of drywall (like in a stair well) and face your thumb in the direction you're walking. Now start walking and slide your hand across the wall, while doing this try to make your thumb skip, if you do it right it will start to bounce at the primary harmonic of the drywall. Once it’s started vibrating you can push harder or go faster, you will notice the pitch will never change but the amplitude will get higher!

Don’t Do This While People Are Sleeping!

#### PyroEric

##### New member
Low frequency high decibel sound can crumble masonry, loosen screws, and vibrations carried by load bearing beams can gradually loosen nails some range away from the sound source. You might want to worry more about what its doing to the house than the laser.

With intense sound in the 40 htz range you can literally bring buildings down. 7.5 htz can be lethal.

I would guess that most lasers are not made to survive strong vibration, though as long as you have it on a piece of folded cloth or something so it doesnt physically hop across your desk it should be fine. The instantaneous shock of it hitting a hard surface even from a short distance could be bad.

#### maxkillz

##### New member
when I bring it down to a hz level so low I can't hear it anymore everything still rattles and the floor shakes the lowest i can hear is about ~15hz the sub seems to peak in the mid to low 20's though it's still very strong all the way up to 45hz. at 33hz with 80% volume it's putting out 115db, i can hear something happening to my walls and floor when I bring the frequency down and crank up the volume, can't tell what it is but the house was built in 1927 and has iron pipes thats just so you know how old everything is in here :-/

#### Cyparagon

##### Well-known member
No. it is virtually impossible to damage a laser with any audio transducer. You'd have to be looking for ways to do it, and even then it would prove to be a challenge.

#### PyroEric

##### New member
Sound is a pressure wave, when its at low enough frequencies and high enough dB's the energy of the moving air is very easily converted into motion of other objects. The sound might not damage the laser directly, but if the sound causes the desk to vibrate, and the laser vibrates across the desk, it might cause some damage over the long term.

I'd still be more worried about what the vibrations are doing to your house. When the floor vibrates, it means that the boards are moving up and down, only a little bit, but they are still moving. The beams in the house would be doing the same thing.

Each time they move every nail is slowly loosening, every screw slowly unscrewing. Most people dont realize its happening until they see the effects of even higher dB levels.

High dB sound also has very bad physical effects other than just causing you to go deaf.

Certain frequencies are worse than others, some will make you feel sick, some will make you feel high, and some will cause your body to have a massive biological reaction where your cells release chemicals that are responsible for cleaning up old dead cells, basically dissolving them, except on such a level that your good healthy cells start to get dissolved too until you fall over dead.

Even if the exposure is not at one of the key frequencies, your body basically vibrates with the sound, causing all kinds of problems, loss of energy and appetite, and feeling like you need to sleep a lot.

I work with things that produce sustained sound up to around 200 dB, at that level there is no such thing as hearing protection, even if you wear 32 dB ear plugs and 34 dB artillery gunner ear muffs the sound absorbed by your body and transmitted to your ears is around 140 dB.

If you jump, for the moment you are in the air you dont hear the sound your body is absorbing from the vibrating ground, also if you open your mouth things get louder, the tubes that run to the inner ear to equalize pressure transmit the sound directly to the inner ear.