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  1. #11
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    Noise cancellation for your refrigeration units

    Quote Originally Posted by epoch1970 View Post
    Of course, noise cancellation would be great... There are refrigeration units, quite loud and they produce what I think is stationary noise.
    Hi!

    Cancelling the noise of your refrigeration units may not be as easy as you think - how many independent units are there?

    Each one will switch its compressor (i.e. the refrigeration pump) on & off thermostatically according to the temperature inside the unit & therefore even though the noise made by each compressor may be "static" in nature, the aggregate noise generated by them all will vary as individual units switch on & off independently of one another - none of them should be on all of the time: if this is not the case then you don't have adequate refrigeration capacity.

    You'd have to "close mike" each unit separately & insert a reversed phase signal from each through a mixing unit into your audio signal - & even then you'll only be able to achieve one "dead zone" in which the sound is cancelled. You would probably end up with greater "compressor" noise in other areas where the introduced cancellation signal itself was actually louder than the noise there from the refrigeration units themselves...

    How loud are these things anyway?

    Dave

  2. #12
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    Quote Originally Posted by Golden Earring View Post
    Cancelling the noise of your refrigeration units may not be as easy as you think - how many independent units are there?... How loud are these things anyway?

    These are commercial refrigeration units similar to these: https://upload.wikimedia.org/wikiped...lregal_USA.jpg
    There is an area with about 15 linear meters of them, shaped like an L. They have doors, I think we are talking of 4 or 5 devices overall.
    Facing the angle of the L, there is a freezer unit. It's not huge but this one is a noisy b****. But hey, even in an organic foodstore I guess you can feel entitled to a frozen TV dinner.
    First impression, I would say the "L" group + freezer are more or less running constantly.

    Then in another area there are 2 units of similar shape, these have no doors (only a curtain drawn after hours) and are used for vegetables. I'd say they are set to a higher temperature and work less hard, although the lack of doors must have an effect. They are anyway in a noisy area, near the entry/exit doors at street level.

    I only measured the ambient noise level once, with an iPhone... I did not expect to have to disclose my findings here Anyways, there was little public in the store, and the quietest place measured at ~34 dB. In the "L" group, 1m away from the freezer I measured ~46 dB. Facing the 2 doorless units, I read a bit less noise, except when doors where opened to the street.
    Near the doors, I measured up to 55 dB. Anyone rolling a shopping cart in there makes ambient noise spike to well over 50dB.

    So it's all relative, inaccurate, and that's only one measurement I took. But a difference of more than 10dB between the constantly quiet and noisy places seemed significant to me.

    You'd have to "close mike" each unit separately & insert a reversed phase signal from each through a mixing unit into your audio signal - & even then you'll only be able to achieve one "dead zone" in which the sound is cancelled. You would probably end up with greater "compressor" noise in other areas where the introduced cancellation signal itself was actually louder than the noise there from the refrigeration units themselves...
    Yes I can see the can of worms. But perhaps if the units are indeed working more or less constantly, a mild noise reduction could be achieved?
    3 SB 3 • Libratone Loop, Zipp Mini • iPeng (iPhone + iPad) • LMS 7.9 (linux) with plugins: CD Player, WaveInput, Triode's BBC iPlayer by bpa • IRBlaster by Gwendesign (Felix) • Server Power Control by Gordon Harris • Smart Mix, Music Walk With Me, What Was That Tune? by Michael Herger • PowerSave by Jason Holtzapple • Song Info, Song Lyrics by Erland Isaksson • AirPlay Bridge by philippe_44 • WeatherTime by Martin Rehfeld • Auto Dim Display, SaverSwitcher, ContextMenu by Peter Watkins.

  3. #13
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    Practical solutions

    Quote Originally Posted by epoch1970 View Post
    I only measured the ambient noise level once, with an iPhone... I did not expect to have to disclose my findings here Anyways, there was little public in the store, and the quietest place measured at ~34 dB. In the "L" group, 1m away from the freezer I measured ~46 dB. Facing the 2 doorless units, I read a bit less noise, except when doors where opened to the street.
    Near the doors, I measured up to 55 dB. Anyone rolling a shopping cart in there makes ambient noise spike to well over 50dB.

    So it's all relative, inaccurate, and that's only one measurement I took. But a difference of more than 10dB between the constantly quiet and noisy places seemed significant to me.


    Yes I can see the can of worms. But perhaps if the units are indeed working more or less constantly, a mild noise reduction could be achieved?
    How many loudspeakers do you have in the store? Are they all supplied by the same amplifier?

    I would suggest the following relatively inexpensive approach:

    1. Apply any practical soundproofing techniques to the refrigeration units themselves, in particular making sure that their noise is not being amplified by resonances in the floor or by the units touching one another. You need to ensure that the compressor units themselves do not overheat, so unfortunately you can't simply wrap them up with soundproofing material - however adding some sound deadening panels (of the type used in cars to improve the sound of in-door speakers) to the inside of the casing of the refrigeration units may have some effect for relatively little cost.

    2. Use separate amplification for each speaker zone so that you can set the volume relative to the residual ambient noise in that particular area. Amps are cheap these days too!

    3. Follow the earlier suggestion of reducing the dynamic range of the music programme material so that the music level itself remains more or less constant in each zone.

    This is likely to work out cheaper than any alternative approach & I suspect that it would prove to be just as effective.

    Good luck!

    Dave

  4. #14
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    Quote Originally Posted by Golden Earring View Post
    How many loudspeakers do you have in the store? Are they all supplied by the same amplifier?

    I would suggest the following relatively inexpensive approach...
    The plan was for 5 amps (PCP with Pi3 + Justboom amp HAT) in dual mono, for 10 speakers. For the moment there are 3 installed, maybe the count will stop at 4.
    They are configured independently regarding volume and equalization (different speaker types...)
    I am looking into compression, not sure yet how much heavy-handed it should be...

    I'm not sure there is much that can be done with the refrigerators themselves. If the compressor has to be pushed to castrating levels then perhaps...

    Thanks again!
    3 SB 3 • Libratone Loop, Zipp Mini • iPeng (iPhone + iPad) • LMS 7.9 (linux) with plugins: CD Player, WaveInput, Triode's BBC iPlayer by bpa • IRBlaster by Gwendesign (Felix) • Server Power Control by Gordon Harris • Smart Mix, Music Walk With Me, What Was That Tune? by Michael Herger • PowerSave by Jason Holtzapple • Song Info, Song Lyrics by Erland Isaksson • AirPlay Bridge by philippe_44 • WeatherTime by Martin Rehfeld • Auto Dim Display, SaverSwitcher, ContextMenu by Peter Watkins.

  5. #15
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    Compression of musical material & copyright considerations

    Quote Originally Posted by epoch1970 View Post
    I am looking into compression, not sure yet how much heavy-handed it should be...
    Have you considered using a low bitrate internet radio station as a compressed music source?

    They're obviously less than CD quality, but should be fine for background music & they already use quite sophisticated (& expensive!) electronic compression systems to reduce the volume changes in their broadcasts: it could save you the trouble if you can find a suitable station...

    BTW, in the UK you're supposed to get licences from the Performing Rights Society (who handle royalties for composers & publishers) AND a Public Performance Licence (royalties for playing the music recordings themselves in public) if you are going to play recorded music in a shop, or indeed pretty much anywhere else that a 3rd party can hear it, & there are fines for non-compliance with this. It applies whether you play CD's, digital music files or any form of radio broadcast or stream. I imagine that similar laws apply in other countries. Thankfully the licence fees are not that high for small retail premises.

    Dave

  6. #16
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    Quote Originally Posted by Golden Earring View Post
    Have you considered using a low bitrate internet radio station as a compressed music source?
    ...
    BTW, in the UK you're supposed to get licences from the Performing Rights Society (who handle royalties for composers & publishers) AND a Public Performance Licence (royalties for playing the music recordings themselves in public)
    The shop owners insisted on playing their own playlist. No radio for them. LMS with all its automation, virtual libraries, etc. proved invaluable.

    Of course in France we have a tax for that. I think SACEM is the equivalent of the MCPS and SPRE is the equivalent of PRS.
    I don't believe SACEM (the collector) is investigating the blockchain or any of that What you pay is a flat tax sized against your average number of employees during the year. Which music plays, audience size are irrelevant...
    3 SB 3 • Libratone Loop, Zipp Mini • iPeng (iPhone + iPad) • LMS 7.9 (linux) with plugins: CD Player, WaveInput, Triode's BBC iPlayer by bpa • IRBlaster by Gwendesign (Felix) • Server Power Control by Gordon Harris • Smart Mix, Music Walk With Me, What Was That Tune? by Michael Herger • PowerSave by Jason Holtzapple • Song Info, Song Lyrics by Erland Isaksson • AirPlay Bridge by philippe_44 • WeatherTime by Martin Rehfeld • Auto Dim Display, SaverSwitcher, ContextMenu by Peter Watkins.

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