Very low frequencies (WinISD vs. laser measurement) - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 17 Old 11-19-2013, 09:47 AM - Thread Starter
Advanced Member
 
FoLLgoTT's Avatar
 
Join Date: Apr 2001
Location: Hannover, Germany
Posts: 513
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 82
I stumbled on an increase of cone excursion in the very low frequencies of WinISD. It strongly depends on the parameter Ql which describes the box' leakage. The lower Ql the higher the increase.



I wanted to know if this is correct and took a measurement with my laser (Baumer OADM 20l6441/S14F) directly from the moving cone using REW. The subwoofer was a Peerless XXLS12 in closed box of 150 l. Soundcard and power amplifier were calibrated.



The measurement clearly doesn't show this increase. Simulation is only always as acourate as its parameter settings. smile.gif
LTD02, popalock, Nuno C and 5 others like this.

Nils
 

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
FoLLgoTT is offline  
Sponsored Links
Advertisement
 
post #2 of 17 Old 11-19-2013, 10:05 AM
Senior Member
 
splotten's Avatar
 
Join Date: May 2009
Posts: 434
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 67 Post(s)
Liked: 45
UNIBOX does the same thing. The lower you set Ql the more excursion in the very low bass.
How do you know which Ql to input in the simulator?
splotten is offline  
post #3 of 17 Old 11-19-2013, 10:21 AM
Advanced Member
 
nfraso's Avatar
 
Join Date: May 2013
Posts: 578
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 165
Pretty nifty measurement/tool there.

Unibox uses three presets: Minor Leaks, Minimal Leaks, No Leaks. These correspond to a Ql of 20, 30, and 50 respectively.

WinISD defaulted to a Ql of 10 for me- that's seems like a pretty leaky assumption!

Sounds like if you know your box will/has no leaks, go with a Ql of 50 for better simulation.

Also, right next to Ql is Qa, or the Absorption factor. Give this article a run over for comparisons: http://www.data-bass.com/data?page=content&id=79

WinISD defaults to 100 for me. Unibox has four presets: Heavy Fill, Walls Covered, Minimal Fill, No Fill. These correspond to a Qa of 5, 20, 80, 120.

So WinISD's default assumption is a pretty leaky box with minimal to little fill. tongue.gif

Here's the difference between default WinISD parameters, and Heavy Fill (Qa of 5) with No Leaks (Ql of 50) for a SI-18 in 4cf with 1000w:

LTD02, popalock and MemX like this.
nfraso is offline  
post #4 of 17 Old 11-19-2013, 01:53 PM
AVS Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 20,509
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 201 Post(s)
Liked: 153
That's odd.

I guess if it's leaky enough it's essentially unbaffled and should approach the excursion with a very large Vb

Noah
noah katz is offline  
post #5 of 17 Old 11-19-2013, 10:07 PM - Thread Starter
Advanced Member
 
FoLLgoTT's Avatar
 
Join Date: Apr 2001
Location: Hannover, Germany
Posts: 513
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 82
Quote:
Originally Posted by nfraso View Post

Pretty nifty measurement/tool there.

Yes, I used the setting as described in ARTA application Note 7. ARTA has the ability to measure THD over excursion ("Klippel light"). I bought the laser and a low THD microphone (Audix TM-1) to do this.


Quote:
Sounds like if you know your box will/has no leaks, go with a Ql of 50 for better simulation.

I think so. I only use a high Ql now like Unibox is suggesting it. It seems to be more real.
LTD02 and popalock like this.

Nils
 

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
FoLLgoTT is offline  
post #6 of 17 Old 11-19-2013, 10:20 PM
Advanced Member
 
MBentz's Avatar
 
Join Date: Jun 2006
Location: Chicago
Posts: 945
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 20 Post(s)
Liked: 41
So if you intentionally make the box leaky, do you see the predicted behavior?

Where did you purchase the laser? That's a real neat test setup.

-Mike Bentz
~It's all about compromise~
MBentz is offline  
post #7 of 17 Old 11-19-2013, 11:56 PM - Thread Starter
Advanced Member
 
FoLLgoTT's Avatar
 
Join Date: Apr 2001
Location: Hannover, Germany
Posts: 513
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 82
Quote:
Originally Posted by MBentz View Post

So if you intentionally make the box leaky, do you see the predicted behavior?

No, but I can do it when I have time. Since the box was bassreflex originally I just have to remove the cover of the hole and measure again.
Quote:
Where did you purchase the laser? That's a real neat test setup.

I had luck and found a used exemplar on ebay for 150 €. A new one costs about 900 €. I don't know if there are other cheaper distance sensors that work for this case. The Baumer can measure +/- 20 mm and its response time allows an upper frequency of 550 Hz. For many subwoofer this is enough (but not for the very high excursion ones, of course).

Nils
 

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
FoLLgoTT is offline  
post #8 of 17 Old 11-20-2013, 08:09 AM
AVS Special Member
 
Ricci's Avatar
 
Join Date: Mar 2007
Location: Louisville KY
Posts: 5,094
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 14 Post(s)
Liked: 204
Nice setup FoLLgoTT...You got a great deal on the laser. (Poor mans Klippel is still expensive. )


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
Ricci is offline  
post #9 of 17 Old 11-20-2013, 09:42 AM
AVS Special Member
 
lilmike's Avatar
 
Join Date: Dec 2009
Location: Pacific Northwest
Posts: 2,193
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 18 Post(s)
Liked: 86
Now that is cool. I had no idea that ARTA could do this.

Time to learn what I can do with the things I have...

Hornresp Tutorials (By amateurs, for amateurs!)


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
lilmike is offline  
post #10 of 17 Old 11-20-2013, 11:58 PM - Thread Starter
Advanced Member
 
FoLLgoTT's Avatar
 
Join Date: Apr 2001
Location: Hannover, Germany
Posts: 513
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 82
Quote:
Originally Posted by lilmike View Post

Now that is cool. I had no idea that ARTA could do this.

ARTA is still one of the best measurement tools if you want to develop a loudspeaker. REW's focus is much more on room acoustics. Both tools have its strength.

@all
So here comes the laser measurement with a small leakage. I loose three of the screws that hold the plank covering the bassreflex hole I used originally. So it was not a big leakage. The driver's cone still came out slowly when I pushed it in. This usually is a sign for a small leakage.



As you can see the simulation with WinISD was correct! Only the default value for Ql is completely useless for closed boxes. smile.gif

LTD02 likes this.

Nils
 

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
FoLLgoTT is offline  
post #11 of 17 Old 11-21-2013, 03:43 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 16,457
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 347 Post(s)
Liked: 1025
nice work.

2db increase of spl is something on the order of magnitude of 30% increase in cone motion, no?

Listen. It's All Good.
LTD02 is online now  
post #12 of 17 Old 11-21-2013, 04:27 PM
Advanced Member
 
nfraso's Avatar
 
Join Date: May 2013
Posts: 578
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 165
I believe that's a direct graph from the laser in REW, so the curves represent excursion. I'm not sure how you'd use the Y-axis though other than for comparison.
nfraso is offline  
post #13 of 17 Old 11-21-2013, 05:16 PM
AVS Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 20,509
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 201 Post(s)
Liked: 153
I'd be a little leery of using the port, as the Helmholz resonator behavior could confuse leakage effects

Noah
noah katz is offline  
post #14 of 17 Old 11-21-2013, 10:56 PM - Thread Starter
Advanced Member
 
FoLLgoTT's Avatar
 
Join Date: Apr 2001
Location: Hannover, Germany
Posts: 513
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 82
Quote:
Originally Posted by noah katz View Post

I'd be a little leery of using the port, as the Helmholz resonator behavior could confuse leakage effects

There was just the hole left. I removed the tube long time ago. No reason to be leery. smile.gif
Quote:
Originally Posted by nfraso View Post

I believe that's a direct graph from the laser in REW, so the curves represent excursion. I'm not sure how you'd use the Y-axis though other than for comparison.

Yes we just can compare the shapes of the curves. And we have to consider that REW shows voltage in dB. WinISD shows excursion lineary. The laser's output voltage is linear, too. So if the whole chain is calibrated we could calculate the absolute excursion from REW's SPL. But I would rather buy an oscilloscope and connect the laser to it, because it can display DC displacement. A soundcard with its high pass can't do this.
popalock likes this.

Nils
 

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
FoLLgoTT is offline  
post #15 of 17 Old 11-23-2013, 04:33 AM
AVS Special Member
 
Martycool007's Avatar
 
Join Date: Jun 2011
Posts: 3,560
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 199 Post(s)
Liked: 154
Quote:
Originally Posted by FoLLgoTT View Post

There was just the hole left. I removed the tube long time ago. No reason to be leery. smile.gif
Yes we just can compare the shapes of the curves. And we have to consider that REW shows voltage in dB. WinISD shows excursion lineary. The laser's output voltage is linear, too. So if the whole chain is calibrated we could calculate the absolute excursion from REW's SPL. But I would rather buy an oscilloscope and connect the laser to it, because it can display DC displacement. A soundcard with its high pass can't do this.

I would love to see some discussion on how to properly calibrate the down-stream components. I am just getting my feet wet with regards to measurements, but I would love to have the knowledge & ability to calibrate all of the components in my audio system.
Martycool007 is offline  
post #16 of 17 Old 11-28-2013, 11:51 PM
Member
 
Nuno C's Avatar
 
Join Date: Dec 2009
Posts: 60
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Liked: 12
Great post. Thumbs Up for sure.
Nuno C is offline  
post #17 of 17 Old 11-29-2013, 12:16 AM - Thread Starter
Advanced Member
 
FoLLgoTT's Avatar
 
Join Date: Apr 2001
Location: Hannover, Germany
Posts: 513
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 82
Thank you. smile.gif

I converted the measurement data to a linear representation. So it can be directly compared to WinISD or Unibox.





Now in lnear representation I can see a slight raise of excursion in the lowest frequency. Apparently the test subwoofer was not as airtight as I thought first.
popalock likes this.

Nils
 

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
FoLLgoTT is offline  
Reply DIY Speakers and Subs

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off