Question about ultrasound

[Brian Gaff]

If you amplitude modulated a 40Khz ultrasonic sound that you could obviously
not hear with audio, could you hear it?
I was thinking it might be a good way to beam audio.
Brian

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[Jim Lesurf[_2_]]

In article >, Brian Gaff
> wrote:
> If you amplitude modulated a 40Khz ultrasonic sound that you could
> obviously not hear with audio, could you hear it? I was thinking it
> might be a good way to beam audio. Brian

Yes, people have indeed reported modulation high power level ultrasound to
'project' audible sounds. Works by being so loud as to function via
nonlinearity. So best avoided! Bad for the ears and for quality.

Jim

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[Phil Allison[_3_]]

Brian Gaff wrote:

-------------------
>
> If you amplitude modulated a 40Khz ultrasonic sound that you could obviously
> not hear with audio, could you hear it?
>

** Yes, but with many conditions and limitations. It's a fringe idea looking for an application that others methods cannot do better.


> I was thinking it might be a good way to beam audio.

** Really ?

A very effective way to "beam audio" is to frequency modulate pulsed, Infra-Red light from an array of LEDs. Perfectly possible cover an entire hall or auditorium this way, or use a much narrower beam if desired.

Listeners wear lightweight, battery powered headphones fitted with a sensitive IR detector, FM demodulator and audio amplifier. Sennheiser made and still make systems like this intended for "assisted hearing" or language translation for audience members.

I once got a box of about 30 IR headsets plus master transmitters dropped on me from a local Theatre & Performing Arts centre for their 5 yearly service and battery change. NiCd button cells have a limited life when left on continuous charge and most showed signs of corrosion too.

The carrier frequency used in the late 1980s was about 40kHz ( so ultrasonic ?) and audio modulation was extracted by a common IC found in FM tuners. Sound quality was good with only a slight background hiss.

The "line of sight" only nature of IR audio systems is actually a big plus in such environments.



..... Phil

[Andy Burns[_6_]]

Phil Allison wrote:

> Listeners wear lightweight, battery powered headphones fitted with a
> sensitive IR detector, FM demodulator and audio amplifier. Sennheiser
> made and still make systems like this intended for "assisted hearing" or
> language translation for audience members.

Probably quite annoying if the audience is watching a 3D film using LCD
shutter glasses though ...

[Phil Allison[_3_]]

Andy Burns a smug prick who thinks he is smarter than everyone wrote:

--------------------------------------------------------------------
>
>
> > Listeners wear lightweight, battery powered headphones fitted with a
> > sensitive IR detector, FM demodulator and audio amplifier. Sennheiser
> > made and still make systems like this intended for "assisted hearing" or
> > language translation for audience members.
>
> Probably quite annoying if the audience is watching a 3D film using LCD
> shutter glasses though ...
>

** Who said IR phones were useful in cinemas ?

My post specifically mentioned halls, auditoriums and live theatre productions - where they cater mainly older members of the audience who may find themselves seated near the back and unable to follow dialogue.



..... Phil

[Brian Gaff]

Oh I know about those as they are used for audio description in cinemas and
theatres. I was thinking more of exhibitions where an exhibit has a button
to press to hear a description, but if there are a lot of these the sound
when used normally is spilling over to other exhibits and hence makes it
hard to detect the one you want.
However if it has to be so loud as to make ears go into clipping even
though you cannot hear the actual frequency then its a non starter.
Brian

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"Phil Allison" > wrote in message
...
Brian Gaff wrote:

-------------------
>
> If you amplitude modulated a 40Khz ultrasonic sound that you could
> obviously
> not hear with audio, could you hear it?
>

** Yes, but with many conditions and limitations. It's a fringe idea looking
for an application that others methods cannot do better.


> I was thinking it might be a good way to beam audio.

** Really ?

A very effective way to "beam audio" is to frequency modulate pulsed,
Infra-Red light from an array of LEDs. Perfectly possible cover an entire
hall or auditorium this way, or use a much narrower beam if desired.

Listeners wear lightweight, battery powered headphones fitted with a
sensitive IR detector, FM demodulator and audio amplifier. Sennheiser made
and still make systems like this intended for "assisted hearing" or language
translation for audience members.

I once got a box of about 30 IR headsets plus master transmitters dropped on
me from a local Theatre & Performing Arts centre for their 5 yearly service
and battery change. NiCd button cells have a limited life when left on
continuous charge and most showed signs of corrosion too.

The carrier frequency used in the late 1980s was about 40kHz ( so ultrasonic
?) and audio modulation was extracted by a common IC found in FM tuners.
Sound quality was good with only a slight background hiss.

The "line of sight" only nature of IR audio systems is actually a big plus
in such environments.



..... Phil

[Brian Gaff]

The whole point of my idea was that no equipment is needed by the user. its
well known that these devices need to be recharged and ones in cinemas are
often not working etc, so from my point of view, if you could beam it to the
person then it might be easier. Brian

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"Phil Allison" > wrote in message
...
> Andy Burns a smug prick who thinks he is smarter than everyone wrote:
>
> --------------------------------------------------------------------
>>
>>
>> > Listeners wear lightweight, battery powered headphones fitted with a
>> > sensitive IR detector, FM demodulator and audio amplifier. Sennheiser
>> > made and still make systems like this intended for "assisted hearing"
>> > or
>> > language translation for audience members.
>>
>> Probably quite annoying if the audience is watching a 3D film using LCD
>> shutter glasses though ...
>>
>
> ** Who said IR phones were useful in cinemas ?
>
> My post specifically mentioned halls, auditoriums and live theatre
> productions - where they cater mainly older members of the audience who
> may find themselves seated near the back and unable to follow dialogue.
>
>
>
> .... Phil

[Phil Allison[_3_]]

Brian Gaff wrote:

-----------------

> The whole point of my idea
> was that no equipment is needed by the user.


** Your idea ???


So the user has no control the sound nor can turn it off.

Damn silly idea if you ask me.



> its
> well known that these devices need to be recharged and ones in cinemas are
> often not working etc,


** Then ask for one that works.


> so from my point of view, if you could beam it to the
> person then it might be easier. Brian


** You really do have some wacky expectations.



...... Phil

[Phil Allison[_3_]]

Brian Gaff wrote:

----------------------
>
> Oh I know about those as they are used for audio description in cinemas and
> theatres. I was thinking more of exhibitions where an exhibit has a button
> to press to hear a description, but if there are a lot of these the sound
> when used normally is spilling over to other exhibits and hence makes it
> hard to detect the one you want.
>
>

** IR headphones can do that job, just define the IR energy to a marked area near the exhibit and illuminate from above.


...... Phil

[Graham.[_4_]]

>Brian Gaff wrote:
>
>-------------------
>>
>> If you amplitude modulated a 40Khz ultrasonic sound that you could obviously
>> not hear with audio, could you hear it?
>>
>
>** Yes, but with many conditions and limitations. It's a fringe idea looking for an application that others methods cannot do better.
>
>
>> I was thinking it might be a good way to beam audio.
>
>** Really ?
>
>A very effective way to "beam audio" is to frequency modulate pulsed, Infra-Red light from an array of LEDs. Perfectly possible cover an entire hall or auditorium this way, or use a much narrower beam if desired.
>
>Listeners wear lightweight, battery powered headphones fitted with a sensitive IR detector, FM demodulator and audio amplifier. Sennheiser made and still make systems like this intended for "assisted hearing" or language translation for audience members.
>
>I once got a box of about 30 IR headsets plus master transmitters dropped on me from a local Theatre & Performing Arts centre for their 5 yearly service and battery change. NiCd button cells have a limited life when left on continuous charge and most showed signs of corrosion too.
>
>The carrier frequency used in the late 1980s was about 40kHz ( so ultrasonic ?) and audio modulation was extracted by a common IC found in FM tuners. Sound quality was good with only a slight background hiss.
>
>The "line of sight" only nature of IR audio systems is actually a big plus in such environments.
>
>
>
>.... Phil
>

Well there's got to be something better than the baseband inductive
loops that are the standard in the UK.
--

Graham.
%Profound_observation%

[Trevor Wilson]

On 30/01/2018 12:39 AM, Graham. wrote:
>> Brian Gaff wrote:
>>
>> -------------------
>>>
>>> If you amplitude modulated a 40Khz ultrasonic sound that you could obviously
>>> not hear with audio, could you hear it?
>>>
>>
>> ** Yes, but with many conditions and limitations. It's a fringe idea looking for an application that others methods cannot do better.
>>
>>
>>> I was thinking it might be a good way to beam audio.
>>
>> ** Really ?
>>
>> A very effective way to "beam audio" is to frequency modulate pulsed, Infra-Red light from an array of LEDs. Perfectly possible cover an entire hall or auditorium this way, or use a much narrower beam if desired.
>>
>> Listeners wear lightweight, battery powered headphones fitted with a sensitive IR detector, FM demodulator and audio amplifier. Sennheiser made and still make systems like this intended for "assisted hearing" or language translation for audience members.
>>
>> I once got a box of about 30 IR headsets plus master transmitters dropped on me from a local Theatre & Performing Arts centre for their 5 yearly service and battery change. NiCd button cells have a limited life when left on continuous charge and most showed signs of corrosion too.
>>
>> The carrier frequency used in the late 1980s was about 40kHz ( so ultrasonic ?) and audio modulation was extracted by a common IC found in FM tuners. Sound quality was good with only a slight background hiss.
>>
>> The "line of sight" only nature of IR audio systems is actually a big plus in such environments.
>>
>>
>>
>> .... Phil
>>
>
> Well there's got to be something better than the baseband inductive
> loops that are the standard in the UK.
>

**Such loops are standard the world over and have been for decades.

--
Trevor Wilson
www.rageaudio.com.au

[Phil Allison[_3_]]

Graham.

---------


> >
> >A very effective way to "beam audio" is to frequency modulate pulsed, Infra-Red light from an array of LEDs. Perfectly possible cover an entire hall or auditorium this way, or use a much narrower beam if desired.
> >
> >Listeners wear lightweight, battery powered headphones fitted with a sensitive IR detector, FM demodulator and audio amplifier. Sennheiser made and still make systems like this intended for "assisted hearing" or language translation for audience members.
> >
> >I once got a box of about 30 IR headsets plus master transmitters dropped on me from a local Theatre & Performing Arts centre for their 5 yearly service and battery change. NiCd button cells have a limited life when left on continuous charge and most showed signs of corrosion too.
> >
> >The carrier frequency used in the late 1980s was about 40kHz ( so ultrasonic ?) and audio modulation was extracted by a common IC found in FM tuners. Sound quality was good with only a slight background hiss.
> >
> >The "line of sight" only nature of IR audio systems is actually a big plus in such environments.
> >
> >
> >
> >.... Phil
> >
>
>
> Well there's got to be something better than the baseband inductive
> loops that are the standard in the UK.
>

** Inductive loops systems all appear to be intended for use with hearing aids equipped with inductive pick-ups - so users need to be wearing one.

I note that it is now possible to buy inductive receivers and use them with standard mini headphones - however results are nothing wonderful and vary with the relative orientations the receiver and loop.

It seems the big advantage of loop systems is they are the cheapest option.


..... Phil

[Don Pearce[_3_]]

On Mon, 29 Jan 2018 17:31:09 -0800 (PST), Phil Allison
> wrote:

>Graham.
>
>---------
>
>
>> >
>> >A very effective way to "beam audio" is to frequency modulate pulsed, Infra-Red light from an array of LEDs. Perfectly possible cover an entire hall or auditorium this way, or use a much narrower beam if desired.
>> >
>> >Listeners wear lightweight, battery powered headphones fitted with a sensitive IR detector, FM demodulator and audio amplifier. Sennheiser made and still make systems like this intended for "assisted hearing" or language translation for audience members.
>> >
>> >I once got a box of about 30 IR headsets plus master transmitters dropped on me from a local Theatre & Performing Arts centre for their 5 yearly service and battery change. NiCd button cells have a limited life when left on continuous charge and most showed signs of corrosion too.
>> >
>> >The carrier frequency used in the late 1980s was about 40kHz ( so ultrasonic ?) and audio modulation was extracted by a common IC found in FM tuners. Sound quality was good with only a slight background hiss.
>> >
>> >The "line of sight" only nature of IR audio systems is actually a big plus in such environments.
>> >
>> >
>> >
>> >.... Phil
>> >
>>
>>
>> Well there's got to be something better than the baseband inductive
>> loops that are the standard in the UK.
>>
>
>** Inductive loops systems all appear to be intended for use with hearing aids equipped with inductive pick-ups - so users need to be wearing one.
>
>I note that it is now possible to buy inductive receivers and use them with standard mini headphones - however results are nothing wonderful and vary with the relative orientations the receiver and loop.
>
>It seems the big advantage of loop systems is they are the cheapest option.
>
>
The real reason they became popular was because they function like a
transformer rather than a receiver/ transmitter. The field strength
within the loop is more or less constant wherever you stand, and
outside it the signal drops away rapidly. That lets you implement
virtually private circuits - for bank checkouts and the like. And as
you say, they are also really cheap to set up - just a moderately
powerful audio amp and you are done.

d

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[Phil Allison[_3_]]

Don Pearce wrote:

----------------


> >
> >It seems the big advantage of loop systems is they are the cheapest option.
> >
> >
> The real reason they became popular was because they function like a
> transformer rather than a receiver/ transmitter. The field strength
> within the loop is more or less constant wherever you stand, and
> outside it the signal drops away rapidly. That lets you implement
> virtually private circuits - for bank checkouts and the like.
> And as you say, they are also really cheap to set up - just a moderately
> powerful audio amp and you are done.
>
>

** Except when that "moderately powerful audio amp" objects to driving a copper wire loop. Even using 1 sq.mm wire involves a loop 220 metres long to achieve a safe resistance value of 4 ohms. I've seen a 2 ohm loop connected to one channel of a 2 x 300W amplifier to cover a private cinema - the amp did not last long.

Standard practice is to use a "constant current" amplifier and a signal limiter to prevent accidental overdriving of the amp. Band limiting the audio is a good idea too, from say 250Hz to 10kHz.

Oh yes, if a group using electric guitars wants to perform in the space, turn the loop amp of.


..... Phil