Help designing a muffler box for my amp!

[paulspencer]

I want to build a muffler box for my Behringer Europower EP2500 amp to cut down the fan noise. No, I don't want to put it in another room (want to see clipping light and need to be in the room to turn it on). No, I'm not opening it up and messing with the warranty! This needs to be in the room and not involve any mods to the room.

The basic idea is to have an inlet and outlet tunnel designed like a muffler so that the noise of the fan is muffled and reduced in level so its not annoying on quiet parts of movies.

Now this is what I'm looking for help with:

* suggestions, advice, help with designing this to reduce fan noise - I want to tune it like a helmholz resonator, it seems the fan noise is mainly from 200 Hz - 2 kHz (from looking at my RTA)

* links to sources of info on how to design this thing

Thanks

[wintermute]

If you want to get adventurous you could try building a noise cancellation circuit for it

In theory at least, all you need to do is sample the noise and amplify it and play it back exactly out of phase. The waves then cancel each other out.

here is a link to a project for headphones, not sure if it could be adapted to use a small amp and speaker positioned in the right spot.

http://www.headwize.com/projects/noise_prj.htm

I know that they use this sort of technology in planes, and I beleive in some cars.

Tony.

[paulspencer]

Interesting idea, thanks Tony. I imagine it would be a matter of getting a cheap and simple amp and pream with a fullrange driver with a reasonably flat response in the midrange at least, a mic and putting it on top of the amp. It would be more compact than the box idea of mine. Or maybe I could even include it in my muffler box which could then be smaller. Hmmmmm ...

[neutron7]

Here are a few other ideas in order easy to hard-

but they involve modding it.

maybe you could complain that you got a noisy fan and want them to fix it

1:
since it is Behringer they probably used a cheapo fan, maybe you can even drop in a relacement from "pabst", "silencer", "panaflo" or similar less noisy fan that works just as well and is quieter anyways without doing any mods at all except replacing the fan with a better unit. <could probably be done without them noticing on warranty, but its your risk!>

2:
I do not know what size fan it uses, but say it you have an 80mm fan at 12 volts you can put a 120mm fan and turn it at 7 volts, and it will do the same job and run much quieter

3:
modify it with a bigger heatsink and take the fan completely off. (usually the heatsink would have to be about 4 times surface area to run passive, assuming a LOT of things there though) you will need to be carefull with this.



can be used with 1 and 2

build or buy (pc modding places have things like this)
a circuit that gradually speeds up the fan according to the temperature sensed on the heatsink. dont get one that just turns on and off at a certain temp. it is really annoying and noticeable, you need one that = g r a d u a l l y = turns the fan speed up as the temperature gets warrmer. probably most of the time it will be at its lowest setting unless you are listening loud for a extended time.



.

[wintermute]

Hi Paul,

I just thought of something else..... this will depend entirely on the directionality of the fan noise. I'm thinking that maybe the noise is exiting at the back and reflecting off your back wall. if this is the case you could try getting some sound deadening foam like this http://www1.jaycar.com.au/productVie...=&SUBCATID=645

or this http://www1.jaycar.com.au/productVie...=&SUBCATID=645

and simply place it between the behringer and the wall, might save a lot of hassle

I'd say you are on the right track with the sound cancelation.... not something I've tried, but thought it was an interesting idea

Tony.

[motherone]

I'm with the fan replacement idea. Computers have been pushing the 80mm fans to become ever so much quieter. If you know the type of fan and voltage, you can probably replace it with something that runs quiter (multi-ball-bearing).

Is the fan temperature controlled? Or does it always run at full speed?

[paulspencer]

The fan is an 80mm fan and it is variable speed temperature controlled, however I think it runs faster than it needs to. I'm not willing to touch it due to warranty issues. Outside warranty I might consider it.

[simon5]

There's lower speed 120mm fans with same CFM, but yeah, still the warranty problem...