Anechoic type workbench?

[Randy Bassinga]

Looking to try my hand at making a speaker driver through mostly trial and error. I think a good test environment will help greatly. I am thinking along the lines of a folding screen covered in some sort of foam that can be deployed around the test area, or a fabric tent. What do you guys use?

 

[AllenB]

Open space is preferred.

 

[Randy Bassinga]

I live in a very windy area with a lot of bird life. Have been looking for good spaces but a bit problematic with multiple runs and also things like power supply and such.

 

[jan.didden]

Depends on what you mean by trial and error.
If you mean trial - measure - modify, with modern software you don't really need an anechoic environment.
If you mean trial - listen - modify you definitely do not want an anechoic environment.
See - just solved your problem and saved you money ;-)

And as noted above, open space should be ample in Australia!

Jan

 

[AllenB]

What I'm saying is that a filter screen won't do what you're asking. It will present a reflection.

Many people try things like setting pillows and quilts around the speaker and microphone, but this limits the reflection free space. It would be better to go without and find the walls in your measurements and gate them out.

 

[Randy Bassinga]

If you mean trial - measure - modify, with modern software

This one. Trying my hand at a coaxial driver, I thought I should try to eliminate reflections to capture only driver emissions through iterations and work towards a flat response without any sort of boundary effects contaminating the results. It will be good is my concern is a non issue but with my limited current understanding of things, I fail to see how that would be the case

Plenty of open spaces, its finding quiet ones in average 20 knot winds that presents the difficulty

 

[stv]

Either gated measurements and listening in the middle of your workshop far from any reflective surfaces or maybe something like this:
https://www.iac-nordic.com/products/acoustics-department/anechoic-chambers/small-anechoic-chamber

 

[jan.didden]

Yes. Gated and swept measurements like with REW or Acourate are the way to go imo.
They wont give useful results below 60Hz, but an anechoic room for below 100Hz is HUGE and not realistic either.

Jan

 

[Randy Bassinga]

Good to know guys, thanks

My room walls are 40mm XPS/alloy composite, so free from any resonance that can induced by the audible frequency range. Do the walls and furniture warrant any acoustic treatment to help with in room testing?

 

[stv]

acoustic treatment to help with in room testing

it will help for listening.
for measurements it does not matter:

• for low frequencies the treatment would need to be HUGE (damping material thickness similar to 1/4 wavelength)
• for higher frequencies you can perfectly use gated measurements. no need for treatment.

 

[stv]

They wont give useful results below 60Hz, but an anechoic room for below 100Hz is HUGE and not realistic either.

even for a gated measurement down to 60 Hz the first reflective surface must be around 3 m distant from the measurement setup. that is also bigger than most domestic rooms allow!

EDIT: ground plane measurement could be feasible, though!

 

[Randy Bassinga]

Trying to take all this in. Would a two part indoor and outdoor testing provide more accurate results? I'll see about making a recording outside in an open space and then filter it down until all wind noise is gone, maybe then I can measure clean down to below 40hz. Not sure how I would manage the height above ground thing

@stv .... assume that I am starting from absolute zero knowledge of correct testing procedures. I have to search up the terms that you guys are using so I can keep up with the conversation

 

[Randy Bassinga]

http://www.mh-audio.nl/Acoustics/Groundplane.html

Is this about right?

 

[aslepekis]

Looking to try my hand at making a speaker driver through mostly trial and error. I think a good test environment will help greatly. I am thinking along the lines of a folding screen covered in some sort of foam that can be deployed around the test area, or a fabric tent. What do you guys use?

Perhaps a Tetrahedral Test Chamber? It has the downside of only providing axial measurements (which may not be a problem for what you are looking to do), but it should provide highly repeatable data as well as some isolation from external noise.

 

[stv]

Is this about right?

I assume so, yes!
But usually you don't need groundplane measurements (unless you need distorsion numbers and high resolution spl).
You can take the nearfield response, apply baffle step correction and splice it to farfield.

Or you rely on simulations for the low end and just use gated measurements for the rest. Keep in mind that gating not only sets a lower frequency limit but also the frequency resolution, which will be low at the lower frequency limit.

 

[Randy Bassinga]

Looks like a groundplane measurement can also help minimise wind noises as opposed to lifting the speaker up in the wind. I am using a desktop PC and have installed ARTA and have a Bheringer calibrated mic as well as a Yamaha MG12UX as audio interface. See my issue regarding portable test rig?

Ideas for equipment to set up for groundplane? Looks like I would need to replace everything but the mic

 

[stv]

usually you don't need groundplane measurements

I repeat:
Start with what you have and indoors. It may be just enough for you.
You said you are not experienced yet, so i strongly suggest you make small steps!
Download REW and try using it!

 

[Randy Bassinga]

Cool man, I should be good for some startup stuff then. There is one field where we go to fly RC. This place might work in the lee of the treeline. has both grass and bitumen options there. I'll try to install on an old netbook and get a 2/2 card that can power on from USB. Do the iPad guys have any tools for measurements?