posted freq response of my room

[bantam]

im trying to decide how to treat my 17x9x8 room with drop (A frame looking) ceilings,

here is the response from pink noise using a rat shack spl meter

http://home.bellsouth.net/p/s/community ... thumbs&ck=

any ideas?

i know the 100-200 hz problem is my biggest!

[OneZero]

Can you tell me how you do this? What kind of software is that?

[vsr600]

are you sure you didn't just measure the frequency response of the radio shack SPL meter?

[bantam]

ok i sent pink noise from my emu 1820m out to my monitors. (you can do this with their patchmix software) so now i have 83db of staticy shit coming out of my speakers. then i use the radio shack spl meter as a microphone (it has an omni in it) and attach a cable to its line out. then i patch the line out into my daw and put the waves pzm mono freq meter on that channels live input and screen shot it.

in essence it should be flat , where its not flat (like the boost at 100Hz means that the room is amplifying these frequencies) i think...


the spl meter mic is supposed to be close to flat but the net has some correction tables for certain freq.

[vsr600]

I seriously doubt that spl meter is flat over the frequency range you show.
Try this to at least get an idea of the frequency response of your speaker and your spl meter: Put the spl meter pointing directly at the center of your speaker and see what kind of response you get....

[Randy]

I seriously doubt that spl meter is flat over the frequency range you show.
Try this to at least get an idea of the frequency response of your speaker and your spl meter: Put the spl meter pointing directly at the center of your speaker and see what kind of response you get....

I agree, you are kind of going down the rabbit hole with this. First you have to determine how flat your signal is all the way from converter, to mixer, to amplifier and then to speaker. Then you have to find out where the non linearities exist in the chain from measurement mic to preamp to converter.

Once you have those charted out, you then can take measurements in the room and do your figuring from there. I have seen a room being "pinked" before, and it was not an exact science by any means. It was just a way to find out where the big problem spots existed. The guy had an RTA and moved the measurement mic all around the room and took notes on a layout to see where frequencies were hitting peaks and valleys. That gave some clues on where to put diffusers and traps. They put up some blankets and moved some furniture and saw if it had the desired effect.

So, all this said, I wouldn't worry too much about the actual curve that you see, I would take it all around the room and get an idea of where the curve changes. For all we know, your room could be acoustically perfect and your equipment has all those bumps.

[philbo]

Yeah - - I'd try remeasuring using an omni mic, preferably a SDC.

The RS meter mics are definitely NOT flat. In fact they're pretty horrible.
________
DESPERATE HOUSEWIVES DICUSSION

[vsr600]

I seriously doubt that spl meter is flat over the frequency range you show.
Try this to at least get an idea of the frequency response of your speaker and your spl meter: Put the spl meter pointing directly at the center of your speaker and see what kind of response you get....

I agree, you are kind of going down the rabbit hole with this. First you have to determine how flat your signal is all the way from converter, to mixer, to amplifier and then to speaker. Then you have to find out where the non linearities exist in the chain from measurement mic to preamp to converter.

Once you have those charted out, you then can take measurements in the room and do your figuring from there. I have seen a room being "pinked" before, and it was not an exact science by any means. It was just a way to find out where the big problem spots existed. The guy had an RTA and moved the measurement mic all around the room and took notes on a layout to see where frequencies were hitting peaks and valleys. That gave some clues on where to put diffusers and traps. They put up some blankets and moved some furniture and saw if it had the desired effect.

So, all this said, I wouldn't worry too much about the actual curve that you see, I would take it all around the room and get an idea of where the curve changes. For all we know, your room could be acoustically perfect and your equipment has all those bumps.

exactly.
If you REALLY want to do it right you need a $6000 mic (B&K probably), a $2000 calibration pistonphone (also B&K), an anechoic chamber for the calibration, an extremely quiet and linear preamp (B&K), and a $20,000 signal analizer (HP).
So instead of all that, don't trust whatever graphs you get. Just use them to get a general idea and look for trends. For example in that graph you posted, if you really believe that peak is real around 100Hz do a swept sine around that frequency. I.e. send a sine wave out starting at 50Hz and ending at 200Hz stepping up in steps of say 5Hz every couple of seconds and listen for ringing in the room. Sometimes your ears are the best measurement devices.

[bantam]

thanks great ideas.

i came across this - made me consider the rat shack in the first place, seems like you guys don't think its very accurate

http://www.digital-recordings.com/audiocd/radio.htm

they are trying to sell test cds to people who probably can't afford b&k....

[Ethan Winer]

busch,

> here is the response from pink noise using a rat shack spl meter <

The image is too small to see the vertical scale so I can't tell if the response is great or if it stinks. How many dB is each vertical division?

It almost doesn't matter what you measure because the solution is always the same for a room like this: Broadband absorption that works well to as low a frequency as possible.

As for the Radio Shack SPL meter, those are fine up to about 800 Hz. Above that the accuracy falls off. But the major problems in small rooms are usually below 300 or 400 Hz anyway, and the RS meter is fine for that.

--Ethan