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Advice on directional speakers


pete10uk

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I’ve been asked to look at installing some directional speakers in an art gallery.

 

I’ve seen the plastic domes before but I don’t think that is what they are after. They have mentioned sound shower or an alternative, ’ve no experience of these, any advice or recommendations?

 

Thanks

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By their very nature all speakers are more or less directional. Maybe a clearer brief from the gallery as to what they want to achieve?

 

Point taken, what they want to achieve is a person stood looking at piece can hear audio which no one else can. Given that this is a gallery which is quiet, I know personally this can't really be fully achieved, but in the art world this seems to be a thing!

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I've only experience the sound domes. With low levels and a bit of carpet on the floor (handily doubles as 'stand here' signage) you can achieve some impressive separation.

 

The effect from a dome is quite spooky.

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I did once see (At PLASA show) some flat speakers -looked like a sheet of polyboard with a magnet on the back- which were really highly directional but a distinctly NON hifi sound. They gave a sound beam comparable to a pin spot or ACL. Talk to PLASA?
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I've been asked to look at installing some directional speakers in an art gallery.

 

I've seen the plastic domes before but I don't think that is what they are after. They have mentioned sound shower or an alternative, 've no experience of these, any advice or recommendations?

 

Thanks

 

There's a few approaches to this, either using an array or panel to achieve directivity or using ultrasonic transducers to blast out high level ultrasound that gets demodulated "in mid air".

Both can effective, but users of the old style analogue hearing aids found that the ultrasonic device would swamp the aid's front end and produce painfully loud artefacts in the audible band. Fortunately, digital aids tend not to suffer the same fate.

Spotphonics and Holosonics (Bryson's link) are two names that come to mind.

 

However, the dome type covers work with standard technology and don't deafen animals...

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Was it these? https://www.holosonics.com/products

 

We've used them on a project recently. I assume they have UK distributor too.

 

The product I saw seems to be a precursor to these. Definitely a R&D job not a production job, but apparently very similar. They seemed to be suitable for putting a picture on and framing to make a picture that spoke.

 

I suspect that increasing size narrowed the beam.

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I was looking for something to do just this sort of job nearly twenty two years ago for a projected museum oral history project. Nothing like the devices Simon mentions were available then or if they were I didn't find them. But there were solutions of a kind which all had one thing in common - they were all incredibly expensive. A brief look at some of the ideas above seem to indicate nothing has changed, it's always a give away when the, very few, suppliers are cagey about retail prices. Where these were available they seemed to start at £500 for a small flat panel and £600 for the pendant version.I could see that easily turning into say £800 per installation. Seems a lot of money when a label could do the job for 3/6.
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The product I saw seems to be a precursor to these. Definitely a R&D job not a production job, but apparently very similar. They seemed to be suitable for putting a picture on and framing to make a picture that spoke.

I suspect that increasing size narrowed the beam.

 

That rather sounds like a Distributed Mode Loudspeaker.... One of their attributes is the ability to excite pretty much any suitable surface, so the device could be made as a picture, plastered into a wall or made into a whiteboard.

 

However, the dispersion characteristics are completely different from the Holosonics panel (where the directivity pretty much is down to the dispersion of the ultrasonic transducers - i.e. narrow). Instead, the DML is dispersive, generating a plane wave with diffuse radiation. It is also bipolar with summative rear radiation, exhibits linear loss of sound intensity with distance (for as long as the panel is acoustically "large") and can reproduce over ~ 8 octaves without a crossover. Interestingly, rather than being subject to the pistonic behaviour of traditional loudspeakers, the DML has the opposite behaviour of increasing dispersion with increasing frequency. This makes it really good for such applications as ceiling speakers (usually as a drop in ceiling tile) as it reverses the annoying tendency of traditional speakers to only sound full range immediately beneath them, and to lose HF as the listener walks away and goes off axis (thus losing speech intelligibility).

 

DMLs can project some distance, but I wouldn't say that they are highly directional, so not much use to our OP.

 

There was another highly directional panel in addition to the ultrasonic array approach, which I think was based on some form of capacitive drive, perhaps in a Bessel array? I'll try and find it...

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