September 14, 2009

The Room Wizard Of Oz.

A typical Room Wizard EQ menu operating on screen.

Do you know how much of your room's sonic signature you're hearing thru your hifi every time you turn it on to play some music? Some say as much as 40% of what you're hearing thru your hifi system is influenced by your room's sonic signature! Every room, based on their L x W X H layout, volume of air in cubic capacity and choice of furnishings will leave their sonic thumb print on to your hifi's reproduced sound.If the above is true, then your room's sonic signature could potentially make or break your hifi system's sound, irregardless of price. So how do we deal with it?

I personally know almost too many audiophiles whom spend large fortunes of $$$ on cables to try and correct their system's sonic capabilities to what they want. They mostly feel that cables can cure every audiophile ills. I hate to break this to you, if you're one of those guys! Cables cannot make sick system sound good. Cables are like vitamin supplements, if you've a good, healthy system, then spending some $$$ on the right quality cables can enhance the sonic performance some what. If you've got room acoustic problems, your hifi system will never be able to perform to their full potential, because the room is interfering too much in to the sound!

Now I've also seen in some cases, where the room's sonic signature can be used to aid a given hifi system's performance. Think of your room factor in aviation terms, just like an aircraft(your hifi system). If your aircraft is always flying against a head wind(your room), it will ultimately fly slower then it's full top speed capabilities, the flight would also be rather turbulent, burn up more fuel in the process and will delay arrival to your destination(sonic nirvana?) some what too. Then imagine if your aircraft is flying with the assistance of a tail wind? Not only would it fly faster, smoother, use less fuel doing so but will probably arrive to your destination just a little bit sooner too! Isn't that nice?

Now, do you know why pilots do pre-flight plans just 3 hours prior to take off? It is so that they have an understanding of the latest en route weather developments, calculate their fuel requirements for the journey based on weather, air traffic and load factors. Lastly, also figure out alternative routes and identify possible emergency places to land in case if the worst should happen. For the pilots, all the information is available to them from various sources like meteorological dept, radar read outs, maps and aircraft manual.

But the typical audiophile has little or no access to such information. Some highly experienced ones can probably hesitate a close educated guess, but how do you confirm what's right or wrong, and what's good or bad for your hifi system?
The mic been set up for measurement.
When it come to room acoustics, at least in the Malaysian and Singapore hifi scene that I know of, Joamonte stands as one the most experience person to talk to. I know he is Singaporean and our political differences between governments does not quite allow us to sing praises of each other. But this is hifi we are talking about, and others may disagree with me, only because if they know some else better! Well if you do, please do me a favour and introduce that person to me. I am always eager to learn from another expert source.

Quite recently Joamonte visited me and asked if I like my room acoustics to be measured by him. While I already have a pretty good idea about my room sonics, I'd love to confirm my hunches too. So Joamonte set up his rig in my room for measurement.
Joamonte busy at work, note the amount of equipment he has to lug around!
He uses a mic powered by microphone pre amp, set it up in my usual sweet spot to pick up the variable frequency sine sweep generated by a laptop computer loaded with a software called the "Room Wizard EQ", which you can download from http://www.hometheatershack.com/roomeq for free. The sweep signal generated from the laptop computer is looped in to one of my pre amp inputs. Adjusted for normal listening volumes, Joamonte starts by scanning for room ambiance to get a base line of the room's noise floor. Once that's obtained, he then uses to frequency sine sweep to measure the in room response. The system would generate 3 charts of the room almost instantly after the final test tone is over. Now the easy part is over, as most of us with a bit of money can invest in the hardware required to do the job and the free software is icing on the cake.
Doing the frequency sine sweep for analysis.
The though part is actually interpreting the results as shown from the charts generated, then armed with his past experience Joamonte can tell you a lot about your room from the 3 charts. He can tell you about the noise floor, room mode's frequency and it's peak decibel, the room's decay response time and the room's dynamic range(this is important as your hifi system's dynamic range would be cap by the room's!).

Joamonte explaining what all the charts mean to me.
The following charts are results of my room's measurement.


From this frequency response chart, it's very obvious that there's a major room mode at 48Hz peaking 20dbs above the average response. Joamonte recommends that I fix the room mode, because once the 48Hz peak is fixed, the next immediate dip at 100Hz will level up to ensure a flatter response curve. There's also a gentle roll of once past 2.5kHz which is at high mids frequencies onwards, considering most of my plastered brick walls are bare with some diffuser treatment, it's o.k. not to do anything about it. The good part is that my room response is relative flat at the mids. It is also noted that the best sweet spot with the least room mode is actually 6 inches further up front from my present sweet spot. That means pushing my listening couch further in to the room by six inches. I did try that position for a while, but that means listening to the speakers at nearly near field position. I did found that the bass had tightened up and became more linear, but I had lost some sound stage depth by then. I reverted to my original couch placement.


The above is a waterfall chart which tells me about my room's decaying time, which measured 0.5 milliseconds. According to Joamonte, that's pretty good. A fast room decay time means there's minimum note smearing, i.e. that a musical note could stop before another one starts. Too long a decaying time means certain notes hang around the room for too long, polluting the next note as it starts, causing ill defined imaging properties amongst many other perceived ills and could even contributed to harshness in worst case scenario.



This chart tells you about my room's dynamic range. Which Joamonte says at 50db for a small room measuring 12 x 10 x 9.8(L x W x H), is reasonably good. I've observed that some rooms have much less dynamic range, when I followed him on a few other measuring jobs. The impulse chart works on the assumption that if one listen to music at peak 100dbs, minus the room's noise floor at 50dbs, that leaves your with about 50dbs of dynamic range. However, the interpretation of the impulse chart is not as simple. Most hifi system would struggle to reproduce un clipped music at 100dbs peak. In fact 95 dbs is a more commonly attainable peak music level. Joamonte has describe in detail to me, but he's the pro, I am the bro, so I can only understand that much.

Now that I know my room's biggest issue, I worked towards to fixing it. But sometimes, music is just not as simple as graphs or charts dictate. I've tried a few methods to reduce the 48Hz room mode with some success.I managed to reduce the room mode peak by as much as 8dbs. However, I've found the flatter frequency response chart to sound a little dull, perhaps due to less bass volume perceived! Maybe I am the sort whom likes my music rich. I eventually settled for a small reduction of the room mode peak by 5dbs, which to me is a fair compromise. It did not take too much bass volume away, whilst gently tightening up note to note articulation on instruments such as Cello and Double bass. However, the dreaded Fret less bass is still somewhat fat and poorly controlled though that too, has seen some small margin of improvement. That small flaw, I could live with.

Remember that an audio system's performance is about the least compromise of all the audio properties that it is required to perform. This way the end result will be a system that has less noticeable flaws, and will likely result in very even handed overall performance.

I choose to do things the hard way, by exploring the possibilities(read DIY) myself. Joamonte can always come up with a series of professional solution which you can subscribe to for a fee.

For those interested to know more about their room's sonic signature and possible remedies if required, do leave your e-mail contact on the comments section. I'll pass them to Joamonte for him to contact you.

I wish to thank Joamonte again for his time and advice regarding my room. He is indeed if I may call him that, "The Room Wizard Of Oz!"

7 comments:

Rabin said...

I heard about someone who had his room measured and later professed that it had no apparent major faults. Listening to the system however told a totally different story. We all agreed that the lower end was just not right.
I sometimes wish it was as simple as that i.e get a near flat lower end response and your system will sound good but music is just not a series of tones and a room will react differently to a series of frequencies at the same time as compared to single tones one at a time.
I could be wrong but were you even aware of that peak as I sure did not detect anything like that when I last listened to your system.
Measurements aside its how your system sounds with the music you listen to and unless there is something that's glaringly obvious its best left alone.
With regards to RT, I have long known that based on my limited exposure to concert hall reverb my own room could be better i.e is longer. I also however realised that the reverb varies with music e.g full orchestra is the longest while chamber is shorter and light or fast music music even shorter.
Listen to Cheah's room and you will realise its "tuned" (by his wall of LPs) for rock with really very short reverb.
If I ever get an empty room I would love to have Joamonte panels and hopefully he will have something up his sleve to able to change the reverb time like they do in concert halls like move the ceiling, panels etc.

Big E said...

Rabin,

When I first re-started hifi a few years ago in the room, Winnie the Pooh(remember him?), had told me that based on his calculation of my room size, he'd hazard a guess that my room's major room mode would fall some where between 40-60Hz. He was pretty spot on, and well ahead of my time!

Back then, I did not take him too seriously. But as I went on my hifi journey, the room boom in the bass area would always come back to haunt me!

The Audio Physic Spark is "the perfect fit" for my room size wise. This is only because this dinky pair of speakers doesn't put out a lot of bass, and will need that major room mode to help along.

Put in any bigger speakers and the room mode will come back to haunt me again like an old friend! He!He!

When you last heard my system, I had already known about the problem, but I've fixed it to a point that it doesn't much anymore except for a few unfortunate songs. I believe every system has a few of those nemesis.

Hence you did not heard anything that bother you. Like I said a near flat frequency room response is no gurrantee to good sound in it self. Just like what I experienced when I tried and successfully bring down my room mode peak by some 8dbs. I was happier with 5dbs down as a compromise.

I will say it again that there's no hard and fast rule that a near flat room response will sound good. But I feel it is a good starting point to have never the less. You may then bend your room acoustics some what and make it work for your system, not against it.

Victor said...

I was sitting next to joamonte when he measured the room, don't know if i have being a 'tube trap'(u can see my hand pointing at the lcd screen) Hah, hah, hah!!! Anyway, I tended to agree with Rabin about how a room will react to a series of musical tones(or notes) and its harmonics, it's very different from a reaction(or feedback) with just a sweeping test tone! I had a friend showed me an analyser with a screen that depicts all the related tones and related harmonics of a musical combination of notes/tones when a piece/track was played. The graphical presentation (in real time) sure looked very/extremely ugly(in my opinion is not flat and varies up and down by alot!)!!! I've heard rooms measure flat but sounded not friendly to the ears. Most of the time we may overlooked the amplifier and speaker combination, its potent effect, its shortcomings and its limitation (if any at all)in any given room.

Joamonte said...

hi all,

Just to share my personal opinion , a room that measure flat(not easy, a +/- 6dB below 120Hz is good enough to me) and don't sound good ,to me its either the equipment matching or capability problem.....there are nothing wrong with getting a response, particular bass region , as flat as possible if we able to do it..

In a perfect situation, room acoustic treatment is suppose just to allow the equipment to reveal what it able to produce without adding salt or pepper, so a good matching system should sound good, a bad matched or lower quality system will sound not as impressive or even sound bad sometime....

Take Big E system for example, I don't know what method he use to reduce the 48hz peak (0dB flat? Wow...! how you did it, brother?), but if he done it correctly , what he hearing is the actual bass performance of his speaker capability...now what happen if he change to a speaker that able to produce down to 20Hz? will it sound better than now or sound worse?


Big E brother, the 3rd graph is not the graph that show the dynamic range of the system I show you that day, its the reverberation time(RT) of the room, the graph indicate how much time it take to decay a 20 dB (T20) from 50hz to 10Khz in 1/3 dB averaging.

The graph the I use to compare compare the dynamic range room is the ETC (energy time curve) , to be exact, that graph is used to compare the S/N ratio of different room only, the quiet the room , the more lower level signal can be hear, thus given the same listening/measured volume at 2 different room, the one with lower ambiance level will have better "Dynamic range" .

.....but,to really talk dynamic range of a system we would need to compare how loud a system able to play without distortion too..... I explain the ETC graph in in that way ("Dynamic range") so that it is more easy for you to understand , but I feel that I would need clarified it, make it more clearly if to write it down into paper...

I will find the ETC graph to post here later, to show what am I talking about..


Cheer!
Joamonte

Joamonte said...

Opps! Big E...I think a am a co*k eye , you mention you bring the peak down 8dB , not make its 0dB flat , I mis-read it...not enough sleep recently , sorry...LOL!

Joamonte

Eddie said...

Joamonte,

You are very skillful very professional, I also believe we must measure our room to play hifi properly,Sifu Felix what do you think?

Big E said...

Hi! Joamonte,

Thanks for the updated impulse chart. I've modified my post to suit today.

You're a big help.