130-140hz problem

lee · Post by **lee** » Fri Jun 16, 2006 8:23 am

im curious if anyone can tell me if 130-140 hz are the frequencies that travel the fastest thru solids. you see, im always having problems with those freq when im tracking and mixing. i know its common to remove a little of those freqs from the bass to give room for the kick, but i always have to take a two-three dB spike out of the bass instruments (even the mid-range instruments) at those freqs. it occurred to me that that freq could be traveling thru my desk faster than the other freqs and end up making distortions in what im heaing.
its weird if this is the case because my speakers are on stands and they're not coming in contact with my desk.

any help will karmically rewarded.

thethingwiththestuff · Post by **thethingwiththestuff** » Fri Jun 16, 2006 9:04 am

no. i dont even know where to begin....

what is your room like? what is your setup like? when you say "desk", do you mean your console or your....table? some frequencies do "travel faster" than others - higher frequencies. when you cut these problem frequencies, are your mixes left sounding thin in other rooms?

Phiz · Post by **Phiz** » Fri Jun 16, 2006 9:40 am

thethingwiththestuff wrote:some frequencies do "travel faster" than others - higher frequencies.

They do? I was always taught that the speed of sound was constant for a given medium. Or is this some second or third order effect you are refering to? Please enlighten me.

Professor T · Post by **Professor T** » Fri Jun 16, 2006 9:57 am

I don't think some freqs travel faster than others, but they could be resonating with the natural freq of your desk (ala some bridges in WA) making them seem louder than they should be.

The obvious test is to take your desk out of the equation.

David French · Post by **David French** » Fri Jun 16, 2006 11:15 am

For just about any practical purpose, the speed of sound is not frequency dependent. I seriously doubt that this has anything to do with your desk. Perhaps you are experiencing the effect of room modes? If you didn't know, in all encosed spaces there are a set of frequencies that will resonate based on the dimensions of that space, adn this can add or subtract to the percieved SPL depending on location of source and reciever. What are the dimensions of your room? Do you have any acoustic treatment? The only way to be 100% sure is to perform acoustic measurement, and if you haev some kind of flat small diaphragm omni I'd be happy to help you out with this.

bpape · Post by **bpape** » Fri Jun 16, 2006 11:28 am

I'd agree. It's not going to travel any faster based on frequency. It is possible however that you have something in the room that is resonating at that range of frequencies. Or, as David is implying, it may simply be a room mode based on seating/monitor position coupled with room dimensions.

Bryan

vsr600 · Post by **vsr600** » Fri Jun 16, 2006 11:41 am

the phase speed isn't frequency dependent except when dispersion and absorption are dominant... then there is a correction to the phase speed which is dependent on the frequency (which I could look up if someone really wants to know)...
Anyway I don't think that's what's going on in your case.

vsr600 · Post by **vsr600** » Fri Jun 16, 2006 11:51 am

but even in dispersive materials (like solids) the propagation speed increases with the frequency so if you were having problems with certain frequencies reaching you first or easier it would be in the higher range...
you could just have your monitors too close too the wall... i dunno more info needed.

kayagum · Post by **kayagum** » Fri Jun 16, 2006 12:01 pm

What are the dimensions of your room?

I'm sure someone here can calculate your room modes pronto.

thethingwiththestuff · Post by **thethingwiththestuff** » Fri Jun 16, 2006 12:15 pm

Phiz wrote:
thethingwiththestuff wrote:some frequencies do "travel faster" than others - higher frequencies.
They do? I was always taught that the speed of sound was constant for a given medium. Or is this some second or third order effect you are refering to? Please enlighten me.

i'm sorry, i didnt write that very clearly, that's why i put it in quotes. i just meant that the wave form cycles repeat more quickly....you know, with greater frequency...not that they travel over distances faster.

sonixx · Post by **sonixx** » Fri Jun 16, 2006 4:55 pm

in a nut shell, you have a modal problem in your room. there's two ways to solve 1) EQ (least preferred) 2) treat the room.

check out R+D at www.acoustisoft.com... download and run the R+D demo and take a look at your room. download the documentation and read it several times.

I had a significant 104Hz problem at my mix location and bass would dissappear at other locations in the room. treating the room I now have very even bass densities thruoughout. treating the corners (traps), reflection points (absorption and diffusers) is a must.

Cyan421 · Post by **Cyan421** » Fri Jun 16, 2006 5:05 pm

WOW YES higher fequency waves travel faster. How many times have you seen a speaker built with the tweeter set back from the sub. Earthworks, KRK, B & W all have done this. They call it time coherent. The speed of sound also changes with temprature and humidity.

Lee, im sure you have a problem with your room, celing hight, wall dimentions, something like that. the quick and dirty was is the run tones and listen for which ones appear louder. but that also has to do with your speakers and ears so.......

vsr600 · Post by **vsr600** » Fri Jun 16, 2006 11:17 pm

lemme clarify,
speeds of sound don't vary much with frequency in air but in solids it does, but still not much. ?nly in very dispersive solids does it really matter. See Kinsler, Frey, Coppens, and Sanders' Fundamentals of Acoustics (page 212 for air and page 382-385 for walls, plates etc...)

rhythm ranch · Post by **rhythm ranch** » Sat Jun 17, 2006 7:49 am

Cyan421 wrote:WOW YES higher fequency waves travel faster. How many times have you seen a speaker built with the tweeter set back from the sub. Earthworks, KRK, B & W all have done this. They call it time coherent.

The tweeter is set back in these designs to align it with the the woofer. The idea is to have both high and low frequencies initiating in the same vertical plane at the same time to more closely maintain time/phase coherence.

ceilingcat84 · Post by **ceilingcat84** » Sun Jun 18, 2006 4:10 am

room mode calculator (needs excel 5 or later):

http://www.wsdg.com/dynamic.php5?id=res ... gy/roomode

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