Speakerplans.com Homepage
Forum Home Forum Home > General > Advanced Discussion
  New Posts New Posts RSS Feed - laser measurement of distortion
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

laser measurement of distortion

 Post Reply Post Reply Page  <12
Author
Message
odc04r View Drop Down
Old Croc
Old Croc
Avatar

Joined: 12 July 2006
Location: Sarfampton
Status: Offline
Points: 5483
Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 5:23pm
There are tons of scientific papers out there that describe using laser/accelerometer systems to either measure a drivers distortion or reduce it using a feedback loop. Quite interesting stuff. If you really wanted to have a go then I expect you could get the optics and test gear required for a few £k second hand and put together a little measurement rig. The easiest method by far is a tiny wireless accelerometer with fast data acquisition which I think I mentioned as the best solution the last time this came up. Dirt cheap, lots of data, only one PC needed to process it afterwards and does not need to be real time either. Only downside is a small added mass on the driver. I would definitely start here if I was serious about driver position sensing - or maybe a pressure sensor inside the enclosure. 

A complete system with integrated enclosure feedback wouldn't be worth the cost/benefit analysis in the real world where risk of failure is high, cost is high, users don't want the data produced, and the empirical end gig result is all that counts. As mentioned earlier, some highly specialised products (M-Force) are starting to use sensing in their enclosures but it is not going to reach the more amateur end user anytime soon.

As Elliot said, simple methods produce good results. Take more drivers than needed, do not run them outside of the region where Bl behaves linearly, much less distortion.

Back to Top
snowflake View Drop Down
Old Croc
Old Croc


Joined: 29 December 2004
Location: Bristol
Status: Offline
Points: 3118
Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 6:40pm
not all distortion comes from the cone - throat distortion, cabinet resonance etc
Back to Top
Elliot Thompson View Drop Down
Old Croc
Old Croc
Avatar

Joined: 02 April 2004
Location: United States
Status: Offline
Points: 5172
Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 7:12pm
Lets not forget the source material. Recording/Mastering engineers are flocking to plug-ins that offer some means of sound degradation to make their work sound less Digital and more Analogue. 

Spotty Frequency Response from speakers in which many try to rectify with heavy equalisation. It really doesn't make sense trying to achieve 16 kHz from a driver that is -20 dB @ 16 kHz but, many do it anyway.

Best Regards,


Edited by Elliot Thompson - 05 January 2016 at 7:16pm
Elliot Thompson
Back to Top
fede View Drop Down
Registered User
Registered User


Joined: 07 April 2013
Status: Offline
Points: 18
Post Options Post Options   Thanks (0) Thanks(0)   Quote fede Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2016 at 7:16pm
Ipal is awesome because it is for sub bass range only where the cone is like a piston.. This is the first condition.
Back to Top
70,s hero View Drop Down
Young Croc
Young Croc
Avatar

Joined: 14 December 2014
Location: bristol
Status: Offline
Points: 637
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 8:35pm
Originally posted by studio45 studio45 wrote:

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.

Yes, I am sure that he could design such a product, I see the laser being attached behind the cone within the enclosure as it only needs a point of reference, it would not interfere with the cone in any way or add mass. Obviously the accelerometer type system adds mass to the cone which sort of defeats the process marginally,the correction signal to any distortion has to be a greater magnitude to take account of the introduced mass.The frequencies are quite low though and so the cone travels at a slower speed in sub.

So IMO an ipal system is only suitable for sub as adding an accelerometer to a high/mid frequency driver would be very counter productive. Taking Power softs concept forward, I guess that if they are quite serious about sound and they are, then we may see a laser type control system in the future.

I am seeing the laser design fella some time over the next couple of weeks so I will ask him what he thinks about it all. If it all stacks up, then I may be interested in developing such a system and will be happy to get anyone else on board who is interested.

 

 

Top banana
Back to Top
mark_in_manc View Drop Down
Registered User
Registered User


Joined: 13 February 2016
Location: Manchester UK
Status: Offline
Points: 15
Post Options Post Options   Thanks (0) Thanks(0)   Quote mark_in_manc Quote  Post ReplyReply Direct Link To This Post Posted: 13 February 2016 at 8:20pm
I used to work in a lab which had a Polytec scanning laser interferometer.  They're very useful for looking at motion of structures where adding an accelerometer would mass-load things to an unacceptable degree - like cone modes (break-up), for example.  More on-topic, a cheaper and more simple, non-scanning system for looking at the non-linear volts-velocity relationship in drivers was introduced a few years ago by a German called Klippel - he's a nice guy and has published a large number of academic papers on driver non-linearities, which industry can now measure by buying his analyser :)


Back to Top
 Post Reply Post Reply Page  <12

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.06
Copyright ©2001-2023 Web Wiz Ltd.

This page was generated in 0.109 seconds.