Room Analysis Primer

[DanDan]

How does that sound look?

Room Analysis Software of decent quality has become very affordable. This has led to many attempting to use it to evaluate their studio or other listening room. The immediate results can be confusing and disappointing. To get the best from any tool, some skill and understanding is essential. This is intended as a simple primer on how to do it, and how to view it.

What to expect.
No miracles! It is unlikely that you will get beautifully flat frequency response curves. I find that Software is best at showing changes rather than evaluating a static situation. It excels at comparative jobs, such as finding the best speaker and listener positions by trial and measurement. Frequency response is the most common and easily understood graph, but there are other, perhaps more powerful ones. In most rooms, there will be particular frequencies or bands of frequencies which ring on longer than their neighbours. This causes particular notes or tones to stick out, blurring music or speech. This behaviour can be seen very graphically on a Waterfall plot. These graphs have three Axes:
Horizontal is Frequency, in this case restricted to 20- 600Hz.
Vertical is Sound Level.
The third axis describes time starting from zero at the back. Consider the spectrum at 0 as the instant when the noise is suddenly turned off. The ‘slices’ coming towards the viewer are spectra taken at later instants. An ideal room would have very even decay, longer at low frequencies, gradually shortening towards the highs.

Example Waterfall plot moved to Room Analysis Primer V2.

Given time and experimentation, one learns how to interpret these different ways of visualising the room sound. Changes however, can always be immediately seen and appreciated.

The Microphone.
You may well have a suitable mic in your closet already. A multi-pattern condenser switched to omni will work fine. The frequency response bumps of say an 87 or 414 are tiny compared to the 30dB anomalies we find in real rooms. Measurement mics are omnidirectional Small Diaphragm Condensers. These are optimised to have a very flat frequency response, unfortunately this is often at the expense of very poor noise figures. I recommend spending a little more on an omni SDC which is also quiet enough for recording. DPA and EarthWorks spring to mind here. I have found the DPA 4060 lavalier omni to be the single most useful microphone in my studo. Most Sound Level Meters have an AC OUT socket. This socket has a pre-amplified line level output from the SLM’s inbuilt microphone. This output is useable for comparitive measurements. You could even borrow/hire a perfectly flat mic and use the software to generate a calibration curve to correct this output to flat. The RadioShack SLM is popular historically, but there are many options these days with similar low prices. I use an Az one with a very large display. I strongly recommend picking up an SLM. You will discover all sorts of uses for them, plus they are fun and eductational.

Measurement and Evaluation Tools.
ETF5 is a very affordable PC program which most directly addresses our needs. FuzzMeasure Pro is a similar product for the Mac. There are many other analysis tools, from free to extremely expensive. I strongly encourage supporting the very reasonably priced professional offerings mentioned here. I use several tools and helpers simultaneously to achieve a holistic evaluation of the room.
Here are some that I find invaluable.
A CD of reference Tracks. I bring mine with me everywhere.
LabMeter, a Mac Frequency meter from rustykat.com
A Tape Measure with a spreadsheet Room Mode calculator such as this one http://www.bobgolds.com/Mode/RoomModes.htm
The free MiniRator and Test tones at RealTraps - Home
The SoundCheck CDs by Alan Parsons.
The Signal Generator plug-in in your DAW or even better a real one.
Oneself- the body can generate tones of varied pitch and duration. Uniquely this human tone generator can move about the room, tuning in to, and stimulating hot spots. Humming barking or grunting at varied pitches can provoke the booms honks and rings, plus identify exactly where they are. Labmeter will show the frequency. You might want to be alone when doing this!
A sound absorbent panel, temporarily held in place by a friend or mic stand, can nuke these problems, also showing exactly where to put treatment.
Lastly, a caveat; some software graphs allows clicking on, say a peak, to identify it’s frequency. These seemingly exact frequencies are not always correct.
I wouldn’t use them to create a Room Eq. for instance.

How to do it.
I am assuming a rectangular room, with speakers at the narrow front wall. Identify the zones at 3/8 (38%) of room length from the front wall and ditto from the back wall. These zones mathematically have the best balance of room modes and should sound best. Another rule of thumb suggests there is little Bass at the room centre. These are useful, often correct, guidelines, however Measurement always trumps Theory. Using masking tape, label the floor at all significant listening spots, e.g. Engineers seat, Producers seat, Couch. Use descriptive names and numbers for your chosen spots. My software uses one speaker at a time during Measurement sweeps, so I use names like, L38FC (Left Speaker Front Centre), L38BL (Left Speaker Back Left) and so on. Establish your own system and stick to it. 8 or so spots seems appropriate in a small room. Mount the Microphone or SLM on a stand or tripod. Seated ear height is good. If you use a Mixing Desk and like to prowl around, then use standing ear height. Mix and match heights if you like, but do remember to use fully descriptive labels. I tie a thread with a small weight to the microphone. The dangling weight over the marked floor spot guarantees repeatable location and height.
I point the mic directly at the tweeter. 45 degrees upward is more usual Stateside. Whichever you chose, do keep it consistent.
A human body close to the mic causes strong midrange anomalies. So stay at least a metre away from the mic. The software generates very loud noises. Wear earplugs or closed headphones. Start at low volume, try a couple of measurements, increasing the volume until you feel the room is well driven. Watch out for overload lights on active speakers, particularly at high frequencies. If you have an SLM I recommend 85-90dB SPL with Slow and C weightings. Label each measurement and move on.


How to view it.
Don’t panic! The curves almost always look awful. Frequency response graphs shows scary peaks and dips. Waterfall plots will often show one very low extremely long decay accompanied by a confusing array of peaks and dips up through the spectrum. Let’s take a real world example. This room is from hell. It has mostly concrete surfaces, it is asymmetrical, and worst of all it has alcoves. It is a tuned indoor swimming pool.

Attached FR graph moved to Room Analysis Primer V2

The Green Before curve shows the room with elementary treatment; the Red After curve is with much more considered treatment, of considerable quantity and quality. We did the lot; four corners, alcove corners, ceiling cloud, RFZ. Sadly, the After curve has a very similar shape to the Before. Disappointing. Let’s look closer, with focus on the one big issue; the musical crucial 100 Hz zone. Here we find a 6dB improvement. Now, consider if you were to eq a full mix with such a broad 6dB boost….. This is a big and welcome change. A poll of 7 professional sound engineers was done in this room. All aspects averaged, it scored 9 out of 10. Before it was a 6. Perhaps the curves don’t do justice to the great sound and the great change. The Frequency plot does deliver some clear and solid advice though: Review the speaker positions. Be careful of Bass decisions in the 100Hz zone. Try listening at spots in the room where the graph is flattest. Use top quality headphones to help judge Kick and Bass relationships.

The Waterfall plot told another story. On a cursory glance the After again looked very similar to Before in shape, just generally shorter. Octave Reverb Time Measurements varied a lot with position, some were zero. I am somewhat doubtful as to the accuracy or validity of such Reverb Time measurements in small rooms. Again I would only use them for comparisons. In this roomt he Before Waterfall showed a 1.3 Second long boom at 37Hz. After, it was reduced to 0.7 S. Sonically, this changed a Kick drum from a chest massage to a nice ‘subby’ thump. Note there is almost no sign of this huge anomaly in the averaged Frequency response graph.


Conclusions.
FM and ETF will not tell you simply what is wrong, or how to treat your room, or where to put what. They can however bestow great certainty when making comparative choices. There is a wealth of knowledge at John Sayers Productions, RealTraps - Home, GIK Acoustics., studiotips - tips on studio design, acoustics, and wiring, and here. There is simple clear advice as to where to put treatment and why. All the advice agrees on the basics; Broadband or Bass Traps in the corners, a Ceiling Cloud, Side Reflection points. This is not voodoo and it doesn’t change from room to room. Treat the Room first, then use Software to make comparitive choices- best speaker position, best seating positions, best speaker eq settings, etc. Room Treatment will yield spectacular results, absolutely no doubt. The use of Measurements to decide on Positional and other tweaks is the Icing on the cake, not the Dough.

Dan FitzGerald AMIOA

Sound Sound - Homepage

[madtheory]

That's great Dan, well written.

I've noticed that the Ethan Winer/ Realtraps example plots almost all exhibit a dip around 200Hz. Any idea as to the reason? I do see in his videos that he's often standing near the mics, but 200 is not mid, and he's probably presenting the show, not doing the actual measurement!

[Jam]

Thanks Dan

That's really useful.

James

[DanDan]

Y'all. Here's a quote from the Bruel and Kjaer primer on Measuring Sound. I am sure they won't mind. By the way, a booklet worth reading over and over again, IMHO.
"When measuring noise, precautions should be taken to
keep the sound level meter and operator from interfering
with the measurement. Not only can the instrument
body and operator's presence block sound coming from
a given direction, but they can cause reflections that
may cause measurement errors. You may never have
thought of your body as a sound reflector, but experiments
have shown that at frequencies of around 400 Hz,
reflections from a person may cause errors of up to
6 dB when measuring less than one meter from the person"


Perhaps Ethan will have a reason for that 200Hz commonality? I reckon US rooms would in general be much bigger than Irish ones.

DD

[Ethan Winer]

Originally Posted by Tomás Mulcahy

TI've noticed that the Ethan Winer/ Realtraps example plots almost all exhibit a dip around 200Hz. Any idea as to the reason?

Most of the graphs on our site were done in either the 16 by 11.5 foot "lab" room in our factory, or my partner's 16 by 10.5 foot control room. A few were done in my 25 by 16 foot living room, and some in my larger studio. So it's more a matter of using only a few rooms than anything else.

--Ethan

[jayfrigo]

I'm going to leave this up on sticky for a little while. Thanks for the effort in compiling this, Dan.

I would offer an opinion, however, that the microphone choice is somewhat more important than the article suggests. I understand that for DIY use, a calibrated test mic is not necessary, though I would stop short of using a laptop mic or a Shure SM57. One needs to attain at least a minimum threshold for an appropriate mic. Ethan's roundup of affordable measurement mics is worth looking at for this. Even a decent, small-diaphragm condensor that one might typically use for drum overheads will work better than a 57. A laptop mic typically lacks what I would consider the minimum necessary extension and uniformity of frequency response to illuminate important parts of the spectrum, and is attached to a laptop presumably, which is going to cause some interference on it's own.

[DanDan]

Hi Jay, thanks. I hope the primer helps people get started and prevents the common initial disappointments. Others have had similar thoughts on my microphone paragraph, so I will rewrite it shortly to make it clearer.
In a comparitive test of say listening position, everything except the position remains the same during the before and after measurements. In this context I am happy to use almost any old mic. Incidentally I have found many laptop mics to be remarkably good.
On the other hand I am playing down 'absolute' measurements.
The graphs are difficult to interpret. I have repeatedly seen appalling looking graphs in great sounding rooms, and occasionally vice versa. One often has to change something to prove the cause of some anomaly. It is deep and not for the beginner.
For absolute meaurement I use a Bruel and Kjaer mic certified within 0.5dB from earthquake to bats. I also use a DPA 4091. The HF boost grille can be temporarily replaced by it's foam pop filter. In this state (DPA approved in phone conversations) it is for our purposes, flat. When not taking measurements it is the single most useful recording microphone I have. I am trying to gently steer away from measurement mics, which are too noisy for recording work and thus IMHO not a good purchase.
Best Regards, Dan

[Ethan Winer]

Originally Posted by jayfrigo

Ethan's roundup of affordable measurement mics is worth looking at for this.

Just for completeness, here's that link:

Comparison of Ten Measuring Microphones

--Ethan

[jayfrigo]

Originally Posted by DanDan

For absolute meaurement I use a Bruel and Kjaer mic certified within 0.5dB from earthquake to bats.

As much as B&K measurement mics are the closest thing to a standard out there (and excellent), mine is mostly retired now in favor of ACO Pacific (AcoPacific - Acoustics Equipment). Anyway, this overly nerdy talk of esoteric measurement mics is just going to put the larger audience to sleep, so I'll stop now!

[run, megalodon]

Originally Posted by DanDan

A poll of 7 professional sound engineers was done in this room. All aspects averaged, it scored 9 out of 10. Before it was a 6. Perhaps the curves don’t do justice to the great sound and the great change.

Originally Posted by DanDan

I have repeatedly seen appalling looking graphs in great sounding rooms, and occasionally vice versa.

Could we talk a little more about this phenomenon, or could someone perhaps point me towards some info (a book, web page, or whatever) on it? These quotes really surprised me when I read them, and it seems somewhat counter-intuitive. Should I really believe that a room as skewed as the one in DanDan's first post would function so well (9/10) as a performance and control room?

[DanDan]

Hi Run, I am glad my point comes across. I did pick a strong example to illustrate it. I also wanted to warn people to expect ugly graphs, and not to take them too seriously.
Regarding the 9/10 - Perhaps these guys are all used to working in much worse rooms? Some aspects of the sound in this room are very spectacular, e.g. imaging/stereo. This may be obscuring the bass problem. One of guys is a Mastering Engineer. He spent some with Dave Collins at his Mastering facility. Strangely my friend said he remembered the sound quality there and that my room was on a par. I have worked in many studios as a freelance engineer. I had terrible difficulty getting mixes to sound 'the same' in the outside world. This room here translates perfectly, first mix attempt often accepted.
All of this is strange, I am well aware. My article is not simply what it says in the title. Part of the subplot is ' and why one should not take measurements, or any single analysis technique too literally, instead take a range of viewpoints using different techniques to achieve a realistic, holistic, evaluation'
Happy New Year, DD

[Hybrid]

Originally Posted by DanDan

How does that sound look?
The Microphone.
You may well have a suitable mic in your closet already. A multi-pattern condenser switched to omni will work fine. The frequency response bumps of say an 87 or 414 are tiny compared to the 30dB anomalies we find in real rooms. Measurement mics are omnidirectional Small Diaphragm Condensers.

A lot of good information here Dan!
I just wanted to mention that a real omni mic really is required.
A switched mic is nothing more than two cardiod mics (a velocity type of mic even if it's switched) and they will have a different diffuse field response than a real omni mic (works on pressure principle). A real omni mic can be had for $50 (Behringer ECM8000). Like you say the response linearity isn't really that critical for room acoustics measurements and noise floor isn't really critical either unless you want to do critical noise measurements but the real benefit with the real omnis is the small body, smaller diaphragm with minimal intereference as well as a much better bass response.

Best,
H

[DanDan]

Thanks for the comments hybrid. Some others share your view, lucky for Behringer and others selling these faux measurement mics. I am afraid I can't go along with your statement however. To illustrate differences, any mic will work. The variations between high quality mics in a studio closet are tens if not hundreds of times smaller than the acoustic variations we are trying to measure or view. A fully scientific measurement requires equipment and expertise at entirely another level.

DD

[Hokut]

Hi,
I posted this question elswhere on these forums but I have deleted it from there and added it here, I think this is a more appropriate place? Hopefully otherwise I'll move it away no problem

I have been reading the other threads here about room analsysis, the primer here, etc... and checked other sites for info on room analysis in general, including Real Traps and Real Traps page on MICs tests

I have a small room 3m x 3m x 2.3m (high); yes it sadly is square

I have installed and calibrated the KRK ERGO which when used does remove boominess from the room. I already have foam panels on the 4 walls, a foam cloud and bass traps in the corners. All done based on listening etc.. no analysis yet

Now I would like to use something like FuzzMeasurePro3 to measure the response in my room for eventual adjustments

This is my kit
Intel MAC Desktop
Adam A7s
Adam Sub 8
KRK ERGO used as a Firewire Interface

In terms of MICs I have
Rode M3
Measuring Mic that comes with the ERGO
TubePre Presonus (XLR/Jack)

1) Is there a free alternative to FuzzMeasurePro 3? (That works on a MAC)

2) Which MIC should I use if any will do the job, the Rode M3 or the MIC that comes with the ERGO?

3) Shall I use the RodeM3/ErgoMic and plug it in straight into the ERGO Jack-Input
or shall I send the MIC to the TubePre then from the Tube Pre to the ERGO input? (would this colour the analsysis?)
Or other option?

I did read around what I could find including the FuzzMeasure FAQ/Forum, but I guess what I don't know is if I can use the MIC that come with the ERGO and if I can just plug it in the analogue input of the ERGO or if I MUST use a pre amp

Any help appreciated,
Thanks you
Hokut

[DanDan]

FM3 is a fine program. The Room Eq Wizard is a free alternative. I found REW quite flaky and unstable on the Mac. Why not try the demo of FM?
I can't get into specifics about a particular interface and how to persuade it to connect to FM and all of that. However, between FM3 and the Audio/Midi control panel in the Mac you should be able to get it working.
I guess the ERGO mic should be suitable. Use a preamp or not exactly the same as when using the ERGO for room Eq or whatever it does.
Your room is small and square. Difficult. Your corner bass traps need to be really powerful. Take a look at Studiotips Superchunks.

Good luck, DD

[Hokut]

Thank you DanDan

Yes, dodgy room . I was asking about connecting the MIC with/without pre amp becaue the ERGO MIC during calibration goes into a dedicated calibration input connection which I assume does not take the signal into the MAC, ERGO calibration is inside the ERGO Box... uses MAC just for the GUI.

I'll try FM3 demo, see if I can get it all to work.

Thanks

[DanDan]

You will have to try it to find out. A preamp is not harmful in any case.
DD

[Hokut]

Yes, hopefully this weekend I can try it all out. Ta

[Warren Beck]

thank you for putting this here. Very helpful.

[DanDan]

Cheers Warren.
DD

[CaptPicard]

DanDan.
Thank you for writing this article, very revealing, helpful, and practical. I specially like the fact that I can use the mikes I have, avoiding me to invest in some piece of equipment that is not used that often like a reference mic. I cannot see why a good old C414 (the XLS, not the voice corrected XLII) cannot be of any help doing some first room measurements.

A little idea crossed my mind here, it would be great to place one of my monitors in open air with the C414 in front of it, switched to Omni of course, and create a flat-response-reference for calibration (canceling out the gear influences on the frequency spectrum) in this measurement software? I could not find that specific but rather crucial function in FuzzMeasure... Anyway, just a loud thought, this procedure could be straight forward - I just do not see it yet.
CP

[DanDan]

Thank you Captain! That idea of calibrating both mic and speaker together is clever. I believe you will find what you need at FuzzMeasure/Window/Microphone Calibration. It may be elsewhere in your FM. I am on V2 as I still use Tiger.
While the idea is good in itself, I believe FM and others are best used for comparisons. e.g. move a speaker and measure to see if there is an improvement. Your idea is heading towards a fully calibrated absolute measurement of the room. This is something I discourage. But if you do wish to do that, and are going to all that trouble, why not go all the way and borrow a flat omni?
Some more important points have come up over time, in discussions with Ethan and others. I have an intention of revising the primer to include those, if Jules is interested.
In short.
Cover your listening area with individual measurements and use the averaging functions to sum it up.
For Modal measurements drive both speakers.
For Frequency response drive only one speaker.
DD

[CaptPicard]

Thanks again for the summary, smashing!
You are reading my mind, I was thinking about borrowing/hiring a measurement mic when I am further down the road with the room here, when going for that extra notch.

I asked SuperMegaUltraGroovy in the meantime, and they mentioned 2 methods me:
- Frequency-domain combination (might provide a better result)
- Export the response as an FRD file, and then import it using the microphone calibration feature (recommended procedure)

I am dying to test both of these soon, but have to install it on my second Mac first to see if this works. The demo license already run out. Not going to happen tonight.

[HDJK]

First, thanks for the excellent write-up thumbsup

I followed your link to determine room modes (http://www.bobgolds.com/Mode/RoomModes.htm) and frankly I could not understand the result:

Frequency hz Spacing % Wavelength 1/2 Wavelength 1/4 Wavelength p q r Mode
36.5 9.44 4.72 2.36 1 0 0 Axial
37.7 3.1 9.14 4.57 2.28 0 1 0 Axial
52.5 28.1 6.56 3.28 1.64 1 1 0 Tangential
53.3 1.5 6.46 3.23 1.62 0 0 1 Axial
64.6 17.4 5.33 2.67 1.33 1 0 1 Tangential
65.3 1 5.27 2.64 1.32 0 1 1 Tangential
73.0 10.5 4.72 2.36 1.18 2 0 0 Axial
74.8 2.4 4.6 2.3 1.15 1 1 1 Oblique
75.4 0.7 4.57 2.28 1.14 0 2 0 Axial
82.1 8.1 4.2 2.1 1.05 2 1 0 Tangential
83.7 1.9 4.11 2.06 1.03 1 2 0 Tangential
90.4 7.4 3.81 1.9 0.95 2 0 1 Tangential
92.3 2 3.73 1.87 0.93 0 2 1 Tangential
97.9 5.7 3.52 1.76 0.88 2 1 1 Oblique
99.3 1.4 3.47 1.73 0.87 1 2 1 Oblique
104.9 5.3 3.28 1.64 0.82 2 2 0 Tangential
106.6 1.5 3.23 1.62 0.81 0 0 2 Axial
109.5 2.6 3.15 1.57 0.79 3 0 0 Axial
112.7 2.8 3.06 1.53 0.76 1 0 2 Tangential
113.0 0.2 3.05 1.52 0.76 0 3 0 Axial
113.1 0 3.05 1.52 0.76 0 1 2 Tangential
115.8 2.3 2.97 1.49 0.74 3 1 0 Tangential
117.7 1.6 2.93 1.46 0.73 2 2 1 Oblique
118.8 0.9 2.9 1.45 0.72 1 1 2 Oblique
118.8 0 2.9 1.45 0.72 1 3 0 Tangential
121.8 2.4 2.83 1.41 0.71 3 0 1 Tangential
125.0 2.5 2.76 1.38 0.69 0 3 1 Tangential
127.4 1.8 2.7 1.35 0.68 3 1 1 Oblique
129.2 1.3 2.67 1.33 0.67 2 0 2 Tangential
130.2 0.7 2.65 1.32 0.66 1 3 1 Oblique
130.6 0.3 2.64 1.32 0.66 0 2 2 Tangential
132.9 1.7 2.59 1.3 0.65 3 2 0 Tangential
134.6 1.2 2.56 1.28 0.64 2 1 2 Oblique
134.6 0 2.56 1.28 0.64 2 3 0 Tangential
135.6 0.7 2.54 1.27 0.64 1 2 2 Oblique
143.2 5.3 2.41 1.2 0.6 3 2 1 Oblique
144.7 1 2.38 1.19 0.6 2 3 1 Oblique
145.9 0.8 2.36 1.18 0.59 4 0 0 Axial
149.6 2.4 2.3 1.15 0.58 2 2 2 Oblique
150.7 0.7 2.29 1.14 0.57 0 4 0 Axial
150.7 0 2.29 1.14 0.57 4 1 0 Tangential
152.8 1.3 2.25 1.13 0.56 3 0 2 Tangential
155.1 1.4 2.22 1.11 0.56 1 4 0 Tangential
155.4 0.1 2.22 1.11 0.55 0 3 2 Tangential
155.4 0 2.22 1.11 0.55 4 0 1 Tangential
157.4 1.2 2.19 1.09 0.55 3 1 2 Oblique
157.4 0 2.19 1.09 0.55 3 3 0 Tangential
159.6 1.3 2.16 1.08 0.54 1 3 2 Oblique
159.9 0.1 2.15 1.08 0.54 0 0 3 Axial
159.9 0 2.15 1.08 0.54 0 4 1 Tangential
159.9 0 2.15 1.08 0.54 4 1 1 Oblique
164.0 2.4 2.1 1.05 0.53 1 4 1 Oblique
164.1 0 2.1 1.05 0.52 1 0 3 Tangential
164.3 0.1 2.1 1.05 0.52 0 1 3 Tangential
164.3 0 2.1 1.05 0.52 4 2 0 Tangential
166.1 1 2.07 1.04 0.52 3 3 1 Oblique
167.5 0.8 2.06 1.03 0.51 2 4 0 Tangential
168.3 0.4 2.05 1.02 0.51 1 1 3 Oblique
170.4 1.2 2.02 1.01 0.51 3 2 2 Oblique
171.7 0.7 2.01 1 0.5 2 3 2 Oblique
172.7 0.5 1.99 1 0.5 4 2 1 Oblique
175.7 1.7 1.96 0.98 0.49 2 4 1 Oblique
175.8 0 1.96 0.98 0.49 2 0 3 Tangential
176.8 0.5 1.95 0.97 0.49 0 2 3 Tangential
179.8 1.6 1.92 0.96 0.48 2 1 3 Oblique
180.5 0.3 1.91 0.95 0.48 1 2 3 Oblique
180.7 0.1 1.91 0.95 0.48 4 0 2 Tangential
182.4 0.9 1.89 0.94 0.47 5 0 0 Axial
184.6 1.1 1.87 0.93 0.47 0 4 2 Tangential
184.6 0 1.87 0.93 0.47 4 1 2 Oblique
184.6 0 1.87 0.93 0.47 4 3 0 Tangential
186.3 0.9 1.85 0.92 0.46 3 4 0 Tangential
186.3 0 1.85 0.92 0.46 5 1 0 Tangential
188.2 1 1.83 0.92 0.46 1 4 2 Oblique
188.4 0.1 1.83 0.91 0.46 0 5 0 Axial


Computed Information:
Room Dimensions: Length=4.72 m, Width=4.57 m, Height=3.23 m
Room Ratio: 1 : 1.41 : 1.46
R. Walker BBC 1996:
- 1.1w / h < l / h < ((4.5w / h) - 4): Fail
- l < 3h & w < 3h: Pass
- no integer multiple within 5%: Fail (ratio3 = ratio2 * 1)
Nearest Known Ratio:
- "3) L. W. Sepmeyer: 1965" 1 : 1.28 : 1.54
RT60 (IEC/AEC N 12-A standard): 246 ms
- ±50ms from 200Hz to 3.5kHz = 196 to 296ms
- ±100ms above 3.5kHz = 146 to 346ms
- <+300ms at 63hz = 546ms
- 300<RT60<600ms
RT60 (ITU/EBU Control Room Recommended): 220 ms
- ±50ms from 200Hz to 4kHz = 170 to 270ms
- <+300ms at 63hz = 520ms
- 200<RT60<400ms
Absorbtion to achieve ITU RT60: 545 sabins
Volume: 69 m^3
Surface Area Total: 100 m^2
Surface Area Floor: 21 m^2
Surface Area Ceiling+Floor: 42 m^2
Surface Area Front Wall: 14 m^2
Surface Area Front and Rear Wall: 28 m^2
Surface Area Left Wall: 15 m^2
Surface Area Left and Right Wall: 30 m^2
Surface Area 4 Walls: 58 m^2
Surface Area 4 Walls + floor: 79 m^2
(sabins - front wall - carpet) / Left+Right+Rear wall: 35 %
(sabins - front wall) / Left+Right+Rear wall: 83 %
Schroeder Fc: 106hz
Frequency Regions:
- No modal boost: 1hz to 36hz
- Room Modes dominate: 36hz to 106hz
- Diffraction and Diffusion dominate: 106hz to 424hz
- Specular reflections and ray accoustics prevail: 424hz to 20000hz
Count (36.4-189hz) : Axials=13, Tangentials=55, Obliques=75
Count (36.4-100hz) : Axials=5, Tangentials=7, Obliques=3
Critical Distance (direct = reverberant field): 4.60m

Does this tell me anything about how to properly treat it or where to place the speakers (5.1) or where to sit? Or is this just nice to know and measuring is the only way to determine all of the above?

Thanks

[DanDan]

There is an underlying text in my Sticky. i.e. these measurements are difficult to interpret, and are best used as part of the overall jigsaw puzzle. A mode calculation just another part of the jigsaw. The question, 'where do I put my speakers and where do I sit to get the best compromise in my particular room' is a big ask. To fully answer that I suggest that we need to use all the tools mentioned working together holistically.

Pragmatic decisions will determine approximately where the gear goes in the room.
This will result in a range of possible locations for speakers and listener. The Room Mode calculator can show you some very dangerous spots to avoid. For instance it may describe an axial mode with a null expect around that 38% spot. A sine wave at or near the predicted mode's frequency will make this null audible, confirming the prediction. You will find the frequency is slightly different to the calculation. Two heads are better than one. Now that you are sure of the problem area, you can move speakers or/and listener back or forward. Measurement software will then confirm the best compromise. Note that the height of the speakers is just as important. They can be shifted out of a trouble spot by a height change, perhaps an inversion. Slightly up and angled downward can sometimes get out of the vertical null, plus help avoid comb filtering from the bounce off your console. Conversely you might want to place the woofer exactly in the null if there is another dimension equal to the height. It ain't easy!
DD

[HDJK]

^^ I thought so. But I'm really new to calculating room modes and such. Can you make anything of the data above? Where are those dangerous spots I need to avoid?

[DanDan]

Bob has uses a colour coding system to indicate trouble. Trouble comes in various forms, so I think has made an attempt to amalgamate them. Read his instructions. To be honest I don't fully understand it. e.g. I don't know what the green negative means. I think we can assume that Red is not good! Isolated frequencies or groups or clusters of adjacent modes are obviously dangerous. Axial are usually much stronger then the others. There is a more pictorial mode calculator which I found helpful. It shows trouble and it's locations visually. hunecke.de | Room Eigenmodes Calculator Unless you are prepared to go all the way I wouldn't bother with any of this stuff. Treat your room in the basic standard manner. Corner traps, RFZ and so on. Ethan and Glenn's sites have this. If you have Fuzz or REW, tweak your final positions by measurement and comparison. Don't forget the height.

DD

[HDJK]

Well, Bob's instructions are not really instructing the un-knowing. I checked out the other link and by the looks of it, there is a problem everywhere

I already contacted Glenn from GIK to get the basics in room treatment. I guess I'll just move everything into the room, setup according to ITU for 5.1 and start measuring.

Thanks

[DanDan]

I suggest you do the treatment first, then put your gear in.
The basics are at RealTraps and GIK. They will apply to your room.
Treatment really works, just stick to the basics, no 'creativity' !
DD

[Seamus TM]

Originally Posted by DanDan

Bob has uses a colour coding system to indicate trouble. Trouble comes in various forms, so I think has made an attempt to amalgamate them. Read his instructions. To be honest I don't fully understand it. e.g. I don't know what the green negative means. I think we can assume that Red is not good! Isolated frequencies or groups or clusters of adjacent modes are obviously dangerous. Axial are usually much stronger then the others. There is a more pictorial mode calculator which I found helpful. It shows trouble and it's locations visually. hunecke.de | Room Eigenmodes Calculator Unless you are prepared to go all the way I wouldn't bother with any of this stuff. Treat your room in the basic standard manner. Corner traps, RFZ and so on. Ethan and Glenn's sites have this. If you have Fuzz or REW, tweak your final positions by measurement and comparison. Don't forget the height.

DD

Hey,

I had a question about that Room Eigenmodes Calc.
Could you just tell me if my logic is correct?

So, the calc shows areas of high pressure.
Your basic porous absorbers are velocity-based.
Tuned absorbers are more pressure based.
Therefore, the areas of high pressure would be good spots for tuned absorbers, but not porous absorbers?

I understand that all of these calculators are theoretical and assume 100% reflective boundaries, but is my logic flawed in general about this?

Thanks,
Seamus