Conference Room Setup - Home Theater Forum and Systems -

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post #1 of 6 Old 12-27-11, 02:40 PM Thread Starter
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Conference Room Setup


We have several conference rooms in my company where Phones are frequently used. We have several models of Polycoms with both, built in mics and those with mics that are placed like 3 feet away from the receiver. Rooms are on average 12 feet x 9 feet with a low ceiling (about 10 feet).

We have verified that "listeners" on the other side experience very poor audio quality that includes some kind of echo that seems to originate in the rooms.

Because those rooms were not originally intended to be conference rooms, i think their acoustics are terrible for their current purpose. We want to purchase some acoustic panels to improve their acoustics; however, i wanted to do some initial research on room acoustics in an attempt to determine/optimize where those panels should go and how big should they be.

I have recently downloaded RAW and played a bit with it in my office. I have calibrated the card as explained in the manual and took some readings. I know i should be using an SPL meter but for the time being i was just using my built in microphone and external speakers.

my questions are:
  1. Is there a way of determining if the phone mic is picking up some kind of echo using "RAW"?
  2. How should a perfect conf room curve should look like?
  3. How do i determine if acoustic panels would help and where to place them?
  4. How do I measure the acoustics of these conf rooms using raw? I mean should i place the speakers where the Phone speakers are located facing outwards?


Last edited by davor.pavisic; 12-27-11 at 02:43 PM. Reason: forgot a question
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post #2 of 6 Old 12-28-11, 07:43 AM
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Re: Conference Room Setup

If you don't hear an echo when you talk in the rooms that is more likely to be a Polycom problem than an acoustic problem. If the rooms are unpleasant to talk in then acoustic treatment could help, you would likely do just as well to get hold of some panels, distribute them around one of the rooms and see how it helps clarity of conversation as get involved in a lot of measurement, in such small rooms the measurements will vary substantially from place to place and you need a solution that will work for all those seated in the room. If you go overboard with treatment and make the rooms very dead that also becomes uncomfortable for meetings and conversations, but if you start working with some panels in one room you can find out how many panels are helpful then distribute any extras in the other rooms.

If you are keen to make some measurements regardless, try placing a loudspeaker at one (or several) of the positions used to speak from and make measurements with the mic at other seating positions (head position) and where the Polycom mics are located. Look at the RT60 plots for the measurements - whilst RT60 in its strict acoustic sense is not valid in small spaces, it nonetheless gives some useful information about how lively or dead the space is. The ETC plot also helps see the extent to which reflections from surfaces degrade the sound. This link has some helpful tips:
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post #3 of 6 Old 12-28-11, 04:27 PM
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Re: Conference Room Setup

As John said, you don’t have an acoustics problem unless it’s unpleasant to have a normal conversation in the room (i.e. the room is “echoey”). Besides that, it would be unusual for rooms that small to have that kind of problem unless they were made of glass!

I expect that when you say the people on the other end hear “echo,” it’s really some kind of delay or ”doubling” of the original voice.

For instance, you mentioned “phone speakers.” Where are these in relation to the mic that’s being talked into, and what kind of signal are they generating?

If the voice of the person speaking into the mic is also being reproduced in the same room by speakers, then that’s your problem: The person’s mouth is inches from the mic, yet the mic is also picking up the sound of that person’s voice from the speakers, which presumably are some distance away from the mic. Sound travels at roughly one foot per millisecond, so it takes several milliseconds before the sound from the speaker reaches the mic. (You can easily calculate the amount of signal delay by measuring the distance the speaker(s) is from the mic.)

So, the person in the other room hears the voice of whoever is talking to them, and several milliseconds later, the sound of that voice as it’s picked up from the speaker. There’s the source of your “echo.”

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post #4 of 6 Old 12-29-11, 10:40 AM Thread Starter
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Re: Conference Room Setup

Thanks for the valuable replies. Some further clarifications:
  1. There is some level of disconfort when sustaining a norrmal conversation in the room; however, we humans tend to compensate and disregard this problem. It seems that over the phone the problem is even more noticeable.
  2. The polycoms we use are very good phones (Polycom SoundStation VTX 1000)... they do suppress speaker output when the mics are picking up voice...

So we think that we are going to put some panels in the room to see if they make any difference. Hence i want to measure the acoustics of the room before and after.

However I am not sure what I shoulid try. In one of the references you guys recomended it mentions to first go with Bass traps in the corners.

Second maybe some 3d difusers?

Should i first see what type of data i get when measuring the room and decide after?

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post #5 of 6 Old 12-29-11, 12:38 PM
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Re: Conference Room Setup

> I suspect the Polycom(s)' auto-magic "mix-minus" ( echo-cancellation ) codec is getting overwhelmed ( confused ) by too many non-minumum phase reflections coming from the ( very close ) walls . That discrimination circuit can only do so much before it allows echos to get passed on-wards down the telephone line .
> I would agree that you should treat the walls .

> Start with something like (12 or 14) 24"x48"x2" Auralex acoustic panels( or equivalent coverage from the smaller sizes ) .
> The flat panels are much more attractive though I feel the ramp-cut is slightly more effective at breaking up flutter echoes .

> (Temporally ) hang/lean the panels against the walls so the bottom of the panels are approx. the same height of the table .

> Call someone ( familiar with the old setup ) & ask if the echo is gone ( or at the very least is now acceptable, ) .
> Depending on their reaction , consider removing up to 4 panels ( likely 8, 24"x48" panels is a minimum in this size room ) .

> I typically glue Auralex panels to either foam-core or gator-board for portability usage .
> Try this glue first to check for adhesion .

> If it's not sufficient then try ( for a more positive grip ) ;

> Measuring with REW will only serve to confuse you and delay the inevitable / but if determined, then treat the room until the T20 or T30 values fall to @ .3 ms to .4ms, in the range from @ 300hz to 5000hz, using 1/3 octave filtering ( found within REWs', T60 window ) .
> ETC graphs ( more important than viewing T60,T30,T20 values ) should show a nice fairly controlled view with no errant spikes greater than minus 15db from the stimulus spike .
> Here's a great overview ( a landmark Doug Jones study ) as to how speaker response improves ( with much less frequency notching & comb-filtering ) when 2" Sonex is added into a room ( in specific areas ).
> It is definitely worth your while to educate yourself using this "peruse an Amazon Book" feature , to look at a few relevant pages.
> Study pages 186 to 188, to get an idea of how the foam suppresses echoes ( seen in the ETC readout as spikes & note how they are detrimental to the overall FR ) .
> Notice how the Frequency Response cleans up nicely at page 188 with the final application of Sonex acoustic foam / the corresponding smooth ETC is what you should aim to emulate ( to suppress flutter echos, etc. ) .

PS : If the problem is determined to be an electrical based malfunction of your Polycom units ( ie; the auto "mix-minus" circuit being disabled, as a for instance ) / then you can always use the above mentioned stuff at your home .

Last edited by EarlK; 12-30-11 at 07:13 AM.
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post #6 of 6 Old 12-29-11, 07:30 PM
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Re: Conference Room Setup

davor.pavisic wrote: View Post
  1. There is some level of disconfort when sustaining a norrmal conversation in the room;
What is the room like? Lots of glass? Tile floor? What is the ceiling made of?

In one of the references you guys recomended it mentions to first go with Bass traps in the corners:
Bass traps are more for long reverberation times (ringing) in the lower frequencies. Typically the problems you’re hearing are in the mid-to-upper frequencies . They’re bouncing around the room because they’re not decaying fast enough. I’m going to hazard a guess that you have hard surfaces everywhere - there isn’t much in the way of absorptive material.

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