Help with interpreting impulse and ETC graphs - Home Theater Forum and Systems - HomeTheaterShack.com

Old 03-15-09, 09:53 PM Thread Starter
Shackster

Tor

Join Date: Feb 2009
Posts: 18
Help with interpreting impulse and ETC graphs

Hi all;
Based on the following two graphs, I have 3 questions. Please let me know what you think.
Attached is an Impulse graph followed by an ETC graph of a full-range speaker. The questions are: 1) Whether the -ve peak in the Impulse graph around 2.5 ms, which corresponds to the +ve peak in the ETC graph means that the impact of this reflection is to create a dip in the frquency response?
2) Can then one use the combo of Impulse and ETC to predict which reflection cause dips and which cause peaks?
3) Finally, can one estimate the frequency that is affected based on the data on these two graphs?
Here are the two graphs:

Thank you for taking the time.
Torzel is offline

Old 03-16-09, 07:57 AM
Elite Shackster
brucek

Join Date: Apr 2006
Posts: 7,514
Re: Help with interpreting impulse and ETC graphs

The impulse response contains all frequencies, so you can't be frequency specific, but the best plot to establish reflection points is the ETC (as you have shown in your second graph).

ETC shows the large direct pulse and then any reflections after that. Measuring the distance of the reflections from the main bang can be used to establish how much further the signal had to travel to reach the microphone. This knowledge allows you to determine where the reflection point might be. It could be a side wall, or a back wall, etc.

Use the REW measuring tool to tell you the distance. To use the tool simply place the cursor over the main pulse and hold down the Ctrl key and the right mouse button and drag to the pulse you want to measure. It will display the distance.

Here's an example of an ETC (showing the measure tool) where the extra distance the signal had to travel was 2.5 feet. This could be a back wall that was 1.25 feet away (2.5/2), or perhaps a side wall that required the signal to go an extra 2.5 feet to get to the mic. This would be a good spot to test treatment on to reduce the reflection.

ETC

brucek
brucek is offline
Old 03-16-09, 02:20 PM Thread Starter
Shackster

Tor

Join Date: Feb 2009
Posts: 18
Re: Help with interpreting impulse and ETC graphs

Thank you Brucek for your reply. I understand measuring the ETC peaks to obtain distance with the technique you have described. My point was that at exactly the same time-point, there is a negative deflection (negative decibels) on the Impulse graph. Does this negative deflection suggest that the impact would be a dip in the frequency response?
Thanks again.
Torzel is offline
Old 03-16-09, 08:02 PM
Banned!
SturmMD

Join Date: Dec 2008
Location: Minneapolis, Minnesota
Posts: 165
Re: Help with interpreting impulse and ETC graphs

I suppose if you use the extreme simplification of considering only the direct wave and 1 reflected wave arriving later there will be cancellation at frequencies where time delay is equivalent to to 180 degrees of phase. But in your case (2.5ms), the first frequency where this would occur is about 200Hz.
SturmMD is offline
Old 05-20-13, 04:16 PM
Senior Shackster

Join Date: Jan 2013
Location: London
Posts: 121
My System
Re: Help with interpreting impulse and ETC graphs

How do you get the measure tool? (OS-X)

Quote:
brucek wrote: View Post
The impulse response contains all frequencies, so you can't be frequency specific, but the best plot to establish reflection points is the ETC (as you have shown in your second graph).

ETC shows the large direct pulse and then any reflections after that. Measuring the distance of the reflections from the main bang can be used to establish how much further the signal had to travel to reach the microphone. This knowledge allows you to determine where the reflection point might be. It could be a side wall, or a back wall, etc.

Use the REW measuring tool to tell you the distance. To use the tool simply place the cursor over the main pulse and hold down the Ctrl key and the right mouse button and drag to the pulse you want to measure. It will display the distance.

Here's an example of an ETC (showing the measure tool) where the extra distance the signal had to travel was 2.5 feet. This could be a back wall that was 1.25 feet away (2.5/2), or perhaps a side wall that required the signal to go an extra 2.5 feet to get to the mic. This would be a good spot to test treatment on to reduce the reflection.

ETC
Attachment 13274

brucek
stevekale is offline
Old 05-20-13, 04:37 PM
REW Author

John

Join Date: Apr 2006
Location: UK
Posts: 6,306
Re: Help with interpreting impulse and ETC graphs

Quote:
stevekale wrote: View Post
How do you get the measure tool? (OS-X)
Same as Windows, Ctrl + right mouse button and drag.
JohnM is offline
Old 05-20-13, 04:40 PM
Senior Shackster

Join Date: Jan 2013
Location: London
Posts: 121
My System
Re: Help with interpreting impulse and ETC graphs

Thanks. I was using a Wacom tablet and pen and couldn't get it to work. When I use the old Wacom mouse it works.
stevekale is offline

 Bookmarks

 Tags graphs , impulse , interpreting

Message:
Options

## Register Now

Random Question
Random Question #2

User Name:
 PLEASE READ BELOW PRIOR TO ENTERING AN EMAIL ADDRESS! ATTENTION! YOU MUST ACTIVATE YOUR ACCOUNT!Activation requires you reply to an email we will send you after you register... if you do not reply to this email, you will not be able to view certain areas of the forum or certain images... nor will you be able download software. AN INVALID EMAIL ADDRESS WILL CAUSE YOUR ACCOUNT TO BE DELETED! See our banned email list here: Banned Email List We DO NOT respond to spamcop, boxtrapper and spamblocker emails... please add @hometheatershack DOT com to your whitelist prior to registering or you will get nowhere on your registration. Email Address:
OR

## Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.