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laser measurement of distortion

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Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 70,s hero Quote  Post ReplyReply Direct Link To This Post Topic: laser measurement of distortion
    Posted: 04 January 2016 at 8:19pm
I met a client yesterday who manuafacturers laser measuring equipment, in the conversation the inevitable subject came up. He said that it would be quite simple to design a laser to measure cone movement. 

This could be compared to the input signal to ascertain distortion, it could then lead to a corrective digital system to minimise distortion. I know about the accelerometers etc but this seems to be an interesting way to get reliable feedback from equipment.

He seemed quite interested and asked about the frequency requirements, I said about 30k as although we only hear to about 16k, it seems fashionable to oversample, it may be that there are high frequency signals in this range that are unwanted within the signal approaching DC in terms of what the load sees.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 04 January 2016 at 10:56pm
Pretty sure you've just described the IPAL platform and therefore also part of M Force platform.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote King George Quote  Post ReplyReply Direct Link To This Post Posted: 04 January 2016 at 11:10pm
AFAIK IPAL relies on a traditional pressure sensor not a laser... but yes, you just described IPAL.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Teunos Quote  Post ReplyReply Direct Link To This Post Posted: 04 January 2016 at 11:23pm
Its now a new idea, it has just never been widely implemented. Philips did it decades ago with their motional feedback. Great impulse responses on those cabs, although the use was very limited to strict small low-power hifi cabs, they made some great cabinets.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 04 January 2016 at 11:29pm
Laser measurements are commonly used by driver manufacturers to look at cone motion.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 70,s hero Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 10:20am
yer but, IPAL is only a sub system, sub systems are mostly distortion, they can get away with an acclerometer as the frequencies are very low, I am taking about a full range system.

Just about all speakers enclosures are designed to give a maximum performace and it is a tricky ask sometimes. I am asking the question.... why would you not control the cone at source as opposed to relying on loads of air.... well in combination with the enclosure.

At present we have a whole array of SMS settings designed to get the best out of our cabs. By deriving accurate response data  from the cone a simple data set would select the enclosure parameters based on a sweep or two. The information could then be used as previously discussed to practically eliminate distortion within the system.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hvedstrup Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 11:22am
Once i i got the Coda Audio 4x18" SC8 sub demonstrated. The funny thing is that i moved insane amounts of air, but the lack og distortion made is sound like "less".

It seems that a certain amount of distortion on subs is desirable. 


 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fede Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 1:07pm
You can fix cone movement if you are in the piston range only..and also if you implemented this in digital domain you must have a very very fast processor.. No easy
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fede Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 1:14pm
Originally posted by Hvedstrup Hvedstrup wrote:

Once i i got the Coda Audio 4x18" SC8 sub demonstrated. The funny thing is that i moved insane amounts of air, but the lack og distortion made is sound like "less".

It seems that a certain amount of distortion on subs is desirable. 


Oh yes and this has a name: Missing fundamental

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 70,s hero Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 3:27pm
Originally posted by fede fede wrote:

Originally posted by Hvedstrup Hvedstrup wrote:

Once i i got the Coda Audio 4x18" SC8 sub demonstrated. The funny thing is that i moved insane amounts of air, but the lack og distortion made is sound like "less".

It seems that a certain amount of distortion on subs is desirable. 


Oh yes and this has a name: Missing fundamental

Federico

Quite a few posts on here are about sound quality be it driver or enclosure specs, as we know,the perception of loudness is derived from the amount of distortion that a system produces. Systems driven to a level where they produce listener fatigue are IMO ok if you roll that way but I prefer a reasonably defined sound. As you say, driving subs relatively hard does produce that feel/punch ... whatever... sound that people like, it would be good to get that without distortion. In the same way, both mid and high would benefit from less distortion in P.A. systems or at least some of them.

I see no reason why this can not be done with current technology
 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 4:02pm

This does not require current technology. It requires common sense.

 

The majority of providers do not carry enough equipment to cover the area properly. This is precisely the reason they present a lot of distortion for they are overloading their system.

 

As the old saying goes “There is strength in numbers.” When you have more than enough amplifiers and speakers to cover area with ample amounts of headroom, you will have all the volume you need with very little distortion.

 

Best Regards,

Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 4:16pm
So your man could make a laser widget that attaches to the driver chassis somewhere. not requiring to be aimed at the cone from outside, no? Because something like that would be *much* easier to retrofit to existing drivers than any kind of accelerometer. I've been tilting at that myself, but quite discouraged by the problems of mounting the sensor somewhere it receives the relevant information, without potentially interfering with cone movement or cosmetically damaging driver cone.
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