Room dynamics

drifterman_ · Post by **drifterman_** » Fri Apr 04, 2008 3:26 am

I'm currently using Alesis Pro Linear 720 monitors. I'm happy with them. Except for a few issues which have only really come to my attention recently. After asking around on MSN and googling a bit I thought i'd start a topic here as well.

When i'm sitting infront of my monitors the sound is fine, the Sub isn't amazingly clear but its audible and relativley detailed.

However when I stand up and walk behind my monitors it is much louder than at the front.

The monitors are on my desk which is facing a wall, the wall is slightly indented from the rest of the wall in the room. Is the sub sound getting caught here? What can I do to stop this and make the sub equal throught the room, or at least the same volume as the front? Egg boxes? Speaker stands? Speaker isolators?

Any tips or suggestions appreciated....

psyphon · Post by **psyphon** » Fri Apr 04, 2008 9:40 am

This is all to do with standing waves.

Each frequency has a different wavelength. Low freq's have longer waves, higher freq's have shorter waves.

When a soundwave comes out the speaker, depending on its length, it will bounce back (reverberate) off multiple surfaces in your room and begin to travel back on itself.

When this happens the peaks and troughs of the soundwave will collide with each other and either cancel out (sound quieter) or reinforce (sound louder). This is why any sound will appear louder or quieter when you move around the room. This is called a standing wave.

To reduce this problem will be a big task unless you're willing to spend money and time sorting it. You'll have to work out the different absorption levels of the ceiling, floor and walls of your room, then you can work out what frequencies will be causing standing waves,

After doing this you work out which materials, etc will be best to absorb the frequencies you're have problems with.

A cheap and simple way would be to get some drops of a heavy felt like material and enclose where you sit with these drapes. They should absorb a lot but wont solve the problem totally.

Also you could try here: http://www.dolphinmusic.co.uk/page/shop ... 83e8a088ca
to give you an idea of types of sound absorption materials you can use although these are expensive, but you'll probably find it a lot cheaper elsewhere.

Hope this is of some help?

kato! · Post by **kato!** » Fri Apr 04, 2008 10:19 am

psyphon wrote:This is all to do with standing waves.

Each frequency has a different wavelength. Low freq's have longer waves, higher freq's have shorter waves.

When a soundwave comes out the speaker, depending on its length, it will bounce back (reverberate) off multiple surfaces in your room and begin to travel back on itself.

When this happens the peaks and troughs of the soundwave will collide with each other and either cancel out (sound quieter) or reinforce (sound louder). This is why any sound will appear louder or quieter when you move around the room. This is called a standing wave.

To reduce this problem will be a big task unless you're willing to spend money and time sorting it. You'll have to work out the different absorption levels of the ceiling, floor and walls of your room, then you can work out what frequencies will be causing standing waves,

After doing this you work out which materials, etc will be best to absorb the frequencies you're have problems with.

A cheap and simple way would be to get some drops of a heavy felt like material and enclose where you sit with these drapes. They should absorb a lot but wont solve the problem totally.

Also you could try here: http://www.dolphinmusic.co.uk/page/shop ... 83e8a088ca
to give you an idea of types of sound absorption materials you can use although these are expensive, but you'll probably find it a lot cheaper elsewhere.

Hope this is of some help?

Bloody hell psyphon is on the money again with this reply!!
As mentioned you have a problem with standing waves, very common problem and it can be difficult to solve, especially if your new to acoustics as there are quite alot of calculations that are required to get it right.

Here's a very simple solution however.

This requires you to emoty the room first of all of all your equipment.

You also need another person for this.

Get that person to stand two or three metres away from you whilst holding one of your monitors, to help keep your distance, tie a string between you and the speaker, or use the power chord.

Get your friend to slowly circle around you, whilst you are in the centre of the room.

Now listen to where the bottom end sounds fullest, you will notice a big difference in frequencies from dif parts of the room.

Listen for where you get the fullest sound.

You should find several spots, mark them.

Get your friend to then put the speaker in each of these spots, the winning position will be where the speaker sounds the closest at the greater distance, with a solid round sound.

__________ · Post by **__________** » Fri Apr 04, 2008 1:14 pm

top marks! i'm gonna be stealing some of that to put in a college assignment on standing waves. i have major acoustic problems when i use my monitors as the room is far from ideal. me monitors are next to a big cupboard which amplifies the bass and makes it sound really muddy - makes it really really hard to get a good mix in the low frequencies. also both my speakers are right next to eachother which can't help.

if you have the space/money/time, do what psyphon says and take this shit seriously!

Sub Shifter · Post by **Sub Shifter** » Fri Apr 04, 2008 2:16 pm

Great thread thanks for the tips

psyphon · Post by **psyphon** » Sat Apr 05, 2008 1:48 am

Over this weekend, I'll try and get some more info posted up.

Check back in soon...

drifterman_ · Post by **drifterman_** » Sat Apr 05, 2008 3:32 pm

Thanks for the help Psy and Kato, really appreciate it.

setspeed · Post by **setspeed** » Sat Apr 05, 2008 4:03 pm

^^ kato's reply is good

it's not just standing waves though, it's room modes (or resonant frequencies). these tend to be at the low end of the spectrum, and are mroe noticeable when you, or the speakers, are close to the wall (try going into the corner, so you're close to 2 walls), and see how it's bassier.

the upshot is that you need to move the speakers 2 or 3 feet away from the wall if possible. also try to keep them out of a bay window or anything like that.

but mainly its a case of learning your set up. in my current room my speakers are only about 4 inches away from the wall, about 2ft apart from each other, and in the middle of a shelf stack with wood panelling above, below and either side, but over the last month or 3 i have figured it out and am now starting to produce some releasable quality mixdowns. so don't fret! it's always possible!

(nb. the egg boxes thing is an urban myth so don't bother with that

)

Littlefoot · Post by **Littlefoot** » Sat Apr 05, 2008 4:48 pm

ez drifts.

I treated me room with some miscut acoustic foam. Sometimes people on ebay who manufacture acoustic foam cut their stuff in funny/wrong dimensions and sell em off cheap on ebay. This wont really effect the sound, it just means my room has odd shaped rectancles all over the wall.

The different i made (8 spaced out around my room on the walls, one behind my speakers) is instantly noticable, as my room has a high pitched flutter echo which created a false sense of reverb when making tracks.

you can also get kits of different shaped tiles, and also bass traps (important for bass heavy music mixing!) that are worth looking into, but are over 100 quid each

psyphon · Post by **psyphon** » Sat Apr 05, 2008 5:34 pm

setspeed wrote:

it's not just standing waves though, it's room modes (or resonant frequencies). )

You'll find that room modes are a direct result of standing waves.

Room dynamics

Room dynamics

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