[Florian]

Hello

I just did the room mode calculator and those are my results. Since i have no clue i would like some info on what i can do to get rid of some unnecesary modes.

Thanks

[JLM]

The larger table shows all the resonance frequencies for each primary dimension of a retangular room (the frequencies that have sound waves of a length to correspond to the stated width, length, and height of the room).  As frequency of sound goes up the length of the sound wave goes down in direct proportion.  So the top line of numbers are the lowest frequencies that fit exactly the inputed primary room dimensions and would resonant in the room.  And the following lines represent multiples of those frequencies that would also resonant.  

The smaller chart to the right lists examples of primary room width, length, and height dimensional ratios that provide a good spread of resonant frequencies so as to avoid getting multiple reinforcements at any given frequency.  Note in this example that 120 Hz (+/- 1.1 dB) shows up in the third resonant of the width and fourth resonant of the height.  Ideally this is to be avoided.  The stated list of ratios should avoid as many of these examples as possible.

Across the bottom is a graphical representation of all the room resonances and you can see the coincidence at 120 Hz in the above example and another at 177 Hz and so on.

Down towards the bottom right is the ratio of the inputed room dimensions and the room volume based on the inputed room dimensions (which would give an idea of how much amp power/speaker efficiency would be needed to provide a given sound pressure level (volume).

[Ethan Winer]

Florian,

> i would like some info on what i can do to get rid of some unnecesary modes. <

You can't get rid of modes; you can only learn where they are and what effect they have. Most of what you're asking is explained in the web page that describes the program. But I acknowledge that someone unfamiliar with acoustics may have to read it a few times before it all sinks in.  

Note that you should enter the Length, Width, and Height into the correct fields, so the reported ratio can be compared to the list of recommended ratios displayed on the right.

Also, as explained on the ModeCalc description page, unless you are willing and able to move your walls or build new ones, the results of a mode calculation are academic. And no matter what frequencies are reported as resonating, you still need broadband absorption that works at all low frequencies.

--Ethan

[John Casler]

Florian,

> i would like some info on what i can do to get rid of some unnecesary modes. <

You can't get rid of modes; you can only learn where they are and what effect they have. Most of what you're asking is explained in the web page that describes the program. But I acknowledge that someone unfamiliar with acoustics may have to read it a few times before it all sinks in.  

Note that you should enter the Length, Width, and Height into the correct fields, so the reported ratio can be compar ...

Hi Ethan,

I have a question which I think might seem elementary, but is very pertinant.

I very seldom see rooms (unless a spare bedroom or such) that are "totally" enclosed.  Most family and livving rooms in modern houses tend to be "open" to other areas.

Obviously this will have an effect of the sonic structure and interaction.

How can one, calculate irregularly shaped, and open space rooms?

I have a feeling that Florian's measurments do not disclose an opening or two.  (I could be wrong) So how would he (or anyone who has them) enter these irregularities?

Is it as simple as measuring the "additional" spaces and summing them with the main space?

[Florian]

Thats what makes me wonder too, here is a picture of the back.

[warnerwh]

Florian:  The bottom line is you would have to take measurements of your own room as soon as you open up a wall in that room too many possibilities open up.  In the meantime there's a great measurement tool called your ears.  You've certainly got a nice start and a willingness to learn and get things done.  Ethan's site has alot of good reading as does Rives audio.  Well worth spending the time learning this stuff, especially with as high of quality of a system as you have.  
Putting together a truly excellent audio system takes time and the room is the most rewarding but also the most difficult.  That's what makes this hobby fun.

[Ethan Winer]

John and Florian,

> Most family and livving rooms in modern houses tend to be "open" to other areas. <

Yes, and this makes it all but impossible to predict the room's response. Though you can still predict first reflection points, of course.

With rooms like this the only way to know for sure is to measure using something like the ETF software. But as I explain on the ModeCalc description page, it almost doesn't matter what you calculate (or measure) because the solution is always the same: Broadband absorption that works to as low a frequency as possible. Whether the room has resonant peaks at 50, 70, 90, and 130 Hz, or 60, 80, 100, and 140 Hz, or whatever, in all cases absorption will improve the response and reduce ringing. In fact, the only times measuring matters at all are 1) if you plan to build tuned traps to target specific frequencies, and 2) to verify that your system is as flat as you'd hoped.

--Ethan

[zybar]

Doesn't measuring matter in regards to helping with the placement of the speakers and listener?  

I have learned two major things over the last year...

1.  Ethan is correct in that acoustic treatments are absolutely necessary in order to "hear" your gear properly.  

2.  Placement of the speakers/listeners is equally important.  By changing both, you can impact how the room is effecting your sound.  Please remember that you can't necessarily cancel the room effects by placement, it is more of an effort to "influence" them.

George

[ctviggen]

And if your room isn't exactly rectangular, you might not get the right results using the room calculator.  In my room, for instance, a room mode calculator (not Ethan's) comes up with 24.5 Hz as my first axial mode, but a measurement with ETF comes up with about 30 Hz.  Also, the room mode calculator doesn't tell you the magnitude of the peaks.  For me, the 30Hz peak is huge relative to other peaks.

[Ethan Winer]

Guys,

> Doesn't measuring matter in regards to helping with the placement of the speakers and listener? <

Yes, measuring can help with that too. Though in most cases measuring just gives people agita when they see how terrible their room really is.

> my room ... comes up with 24.5 Hz ... but a measurement with ETF comes up with about 30 Hz <

I recently discovered the same disparity. In the perfectly rectangular "lab" room at my factory, ETF reports the first measured mode about 20 percent too high. I am certain that ETF is correct because I've verified its results using static sine waves. So something else is going that is starting to make me believe that the way modes are calculated is suspect, or at least incomplete. I've been discussing this elsewhere with an acoustician, and so far he hasn't had an explanation either.

I wonder how many professional acousticians have actually measured a room to see how the modes compare with what's calculated? I'll guess very few!

--Ethan

[ctviggen]

Ethan,

It would be interesting to build a rectangular room, put nothing but speakers in it, then see how close theoretical and measured values are.  In my room, the room isn't rectangular.  I'm in a raised ranch, so two of the walls are built using the foundation for the bottom half of the wall and a stud-built portion for the top half of the wall.  This means that the foundation part (the bottom part) is about a foot away from the top part of the wall.  Two other walls are flat, but one of those walls goes outward by a foot or so.  I also have a fire place that takes up space.  So, it's even unclear as to what values I put in the calculator (I chose values for the bottom half of the room; values for the top half would be a little larger).  I also have a beam that splits the room perpendicular to the speakers and cuts about a foot out of the ceiling.  

For me, it's easier to look at real values than to look at calculated values, so I'm buying a calibrated mic and the ETF program.  I'll use these for various purposes, including matching my sub and main speakers and speaker placement.

[Ethan Winer]

Bob,

> It would be interesting to build a rectangular room, put nothing but speakers in it, then see how close theoretical and measured values are. <

That's exactly what our lab is: a perfect room with nothing in it but speakers (and a desk with computer). We can bring traps in on stands to test them, and we even have hooks on the ceiling to easily hang and remove panels there.

> For me, it's easier to look at real values than to look at calculated values, so I'm buying a calibrated mic and the ETF program. I'll use these for various purposes, including matching my sub and main speakers and speaker placement. <

Every acoustician I know agrees with that advice. They all say that no matter what you predict, you still need to measure afterward if you want to know for sure what you have.

--Ethan

[ctviggen]

Ethan,

Does your room measure differently from what is theorized?

[Ethan Winer]

Bob,

> Does your room measure differently from what is theorized? <

Yes, this is exactly what I'm saying. In my "lab" the first mode is for the 16'2" length, and it calculates to 34.95 Hz. But the first mode actually measured by ETF is at 41 Hz!

--Ethan

[ctviggen]

Hmmm...That's hard to explain, but that's very similar to my result, too.