Measuring reverb time without any tools?

[Ivan Beaver]

Re: Measuring reverb time without any tools?

Jason,

The critical bit is that by using a good measurement tool you can measure below the noise floor, which is critical to getting a real RT60 in many rooms. With your ears, you're just guessing. This type of measurement is easy to do wrong.

The thing that many people "miss" is that to get a TRUE RT60-the sound has to be able to decay 60dB and you be able to measure it.

So if you say 60dB +6dB for peaks and you have a noise floor of 50dB, then the system has to be able to do 116dB (preferably louder) at the measurement location. And you have to run it that loud to do the measurement.

That is quite a task for a lot of installed systems-especially those in rooms in which you are actually trying to measure the RT60- or need to.

 

[Brad Weber]

Re: Measuring reverb time without any tools?

Somebody got sued over an RT60? Now you got us curious. Depending on details, I might have bet on a hand clapper with good ears who knows acoustics over someone with much less experience but with a calibrated instrument. What was the issue being litigated?

The situation was apparently that the party selling and installing an audio system for a venue told the venue that for the system to deliver the results they wanted the venue needed to also address the room acoustics. The venue did not address the acoustics but then subsequently refused to accept and pay for the audio system as it did not perform "as expected", arguing that they felt the room acoustics were acceptable and not a factor. One of parties involved in the install came to us to ask what would be involved in a proper analysis of the room. We generally avoided such work and did not get directly involved, but the party that had contacted us later reported back to us what had transpired.

I would accept an experienced individual's subjective opinion, however I do have to question being able to testify to a specific numerical RT60 value based on having a student clap their hands while you walked around the room. Or how qualified and experienced in room acoustics one is simply by being a physics professor. That was my first introduction into "expert witness" testimony and it supported what I later heard from an attorney that you can find what appears to those who are not experts themselves to be an eminently qualified expert that will support just about any view or perspective you want and there are people that do that for a living.

Some years later I ran into another situation relating to community noise where a commercial property owner was being asked to either make extreme changes or purchase a neighboring residential property due to noise from their facility. It turned out this resulted from a 'nuisance and annoyance' noise code and a report from a university professor that was hired by the homeowner. We were asked by the commercial property owner to review the report and confirm the findings. We quickly found that the report and the measurements in it were very questionable. After verifying the inaccuracy of the field measurements, which were not even close, and some further research we were eventually able to find out that apparently the site measurements were made and the report prepared by students without the direct involvement of the professor, they just put their name on the report the students had prepared. I won't go into the ethics of a professor at a State university putting their name on work they did not perform or oversee or of their using unpaid students to perform work for which the professor was paid through their private independent consulting practice, but since the report appeared to come from someone highly qualified people, including local government officials, had simply assumed it to be accurate even when all one had to do was walk on site to immediately know it was not.

 

[John Roberts]

Re: Measuring reverb time without any tools?

Sounds like a "failure to communicate"... The installer may have advised the client that they needed to deal with room acoustics, but the client did not hear or believe. I don't see an easy answer other than putting that into writing up front.

If it is going to be part of a contract, it needs to be a proper (well defined and repeatable) measurement.

JR