Monday 8 September 2014

Cinemas Sound Report

When the arts centre wanted to put cinemas beneath Ben Jonson House they were asked to include a sound monitoring system which would measure the impact of sound from the new cinemas upon residents.   The planning committee agreed, but though bureaucratic sleight of hand the arts centre ended up installing sound monitoring inside the auditoria only, which is a bit rubbish because as one person involved put it:  We don't live inside the cinemas.

We did get a commitment from the arts centre to let us have sound data from the monitoring system upon request, and we asked if we could have a sample.  Well, here is the sample we've been given.  It's not the data, just a print out of a screen shot:

Click to make me bigger

We have asked if we can have the raw data, and the arts centre are having a think about that.

In the meantime, we can have a look at this report.

The display shows measures broken down into 5 minute chunks.  The larger numbers on the upper left (LAEq (period), 63Hz Leq (period) ... etc) are for the current period and when that period ends the numbers drop down into the table below, which shows the figures for the last 8 periods.  The new numbers appear on the right and the oldest set is pushed off to the left.

The figures are either LAeq or LZeq, which are, in essence, averages of sound levels over time.  This kind of measure has come in for criticism when used to measure environmental noise nuisance, see here for example.  If I understand this correctly, a massive sound (explosion in a film) surrounded by silence would not register as a problem, because the split second sound would be effectively averaged over the time window of 5 minutes.  If there were sound problems, this would appear to be a pretty poor tool to help resolve it, but perhaps a great tool if you want to 'show' / pretend that there is no problem at all.

Having said all that, it's worth noting that there has not been, to my knowledge, a single complaint about sound leaking from the cinemas and bothering residents.

... but if there ever are problems, I'd rather have good measurement in place.

No comments :