Email from an expert on use of column speakers in acoustically 'difficult' buildings such as church halls and village halls with hard surfaced ceilings. The writer, a scientist at dbaudio, originally emailed me because of a problem with his central heating system. We swapped advice in our respective fields!

In many folk dance venues sound quality is poor. Often the problem is a highly reverberant building - one with far too high a percentage of acoustically reflective surface and often with a domed or pitched roof. Church halls often fall into this category, as do a few village halls. After explaining the problems experienced at some folk dance events the following advice was offered.

Level at a gig is easy to specify. Just get an app that can measure Leq, e.g. SPL Pro by Studio Six Digital's " AudioTools".

Tell the engineer you want the event to run at an event LAeq of (say) 80 or 90dB. This specifies the volume for the whole event. If they can't measure LAeq, put your phone on the desk and tell them to keep within the limits.

This is common practice at large outdoor events where nuisance noise is part of the licence agreement.

All pro engineers at such events HAVE to mix to the LAeq meter.

Clarity in a reverberant environment is challenging. Clarity, in particular speech intelligibility, is a function of the direct sound to reverberant sound ratio. Given that it's hard to reduce the reverberant level in a church for one event, the only other option is a speaker with very high directivity. This sends direct sound to the listeners and minimises excitation of the reverberant environment, thus improving the direct to reverberant ratio.

Ideally, the speaker would do this over the whole bandwidth, but physics prevents this unfortunately and we have to accept greater excitation of the reverberant field at lower frequencies where the wavelength gets longer. In larger venues, a modern line array does this well but is beyond the budget of a folk dance event.

The next practical way to get high directivity is with a column, but there are many drawbacks to a conventional column, the main one being too much directivity in the mid band and side lobe generation.

d&b looked at the benefits and pitfalls of the column and went about engineering out as many of the problems as we could, the result was this:

The 4" drivers are passive cardioid and the HF is handled by what is basically a line array of small tweeters. If you learn to read the isobar plots on page 7 of the manual, you'll learn a great deal about speaker directivity.

Hope this helps.

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