Filtered impulse response - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

Reply
 
Thread Tools
post #11 of 28 Old 02-26-15, 02:27 PM
Elite Shackster
 
Talley's Avatar
 
Join Date: Dec 2010
Location: Houston Tx
Posts: 1,295
Re: Filtered impulse response

this is way over my head.... i wish i knew what all this meant ha

Master Electrician

To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.

XPA-7 & Krell Showcase 7 | XMC-1 | SVS Ultra Tower system | HSU VTF-15H MK2 | BenQ W1070 | Jamestown 135"
Talley is offline  
Sponsored Links
Advertisement
 
post #12 of 28 Old 02-26-15, 05:40 PM Thread Starter
Shackster
 
geopango's Avatar
 
Join Date: Jun 2012
Posts: 41
Quote:
subterFUSE wrote: View Post
Just to be clear, we need to pick a crossover point first and then measure as above to determine the delay? Or should we get a ballpark delay, and then set crossover and fine tune the delay as above? My situation is a little different because it's a car, with listening position in the driver seat. So I need some large delays on the left midbass and the subwoofer in particular. Furthest speaker is my right compression horn under the passenger side dash.
The selection of the correct crossover point based on the most linear frequency response of the two drivers combined is paramount. Ensure that both drivers exhibit excellent linearity before and after the crossover point. This attention to spl will allow the best phase matching and well matched filtering after the pass band.
My bass and mid drivers are very flat between between 250 and 500 Hz. I've chosen 345hz as crossover point providing excellent linearity above and below the crossover point.
Cheers
geopango is offline  
post #13 of 28 Old 02-27-15, 08:33 AM
Shackster
 
Join Date: May 2014
Location: Charleston, SC
Posts: 98
Re: Filtered impulse response

When you say you took multiple measurements at .1ms increments, do you mean you measured... then adjusted the DSP delay for a driver by .1ms, and measured again, then repeat, etc..?
subterFUSE is offline  
 
post #14 of 28 Old 02-27-15, 07:52 PM Thread Starter
Shackster
 
geopango's Avatar
 
Join Date: Jun 2012
Posts: 41
Quote:
subterFUSE wrote: View Post
When you say you took multiple measurements at .1ms increments, do you mean you measured... then adjusted the DSP delay for a driver by .1ms, and measured again, then repeat, etc..?
You just keep measuring and changing the delay incrementally till the phase align at the crossover point. You can theoretically do this just once. You can make a copy of that measurement , nudge it into alignment in REW, then subtract the time difference between the two measurements. That delay amount can then be applied on your DSP. It works.
geopango is offline  
post #15 of 28 Old 03-10-15, 09:18 AM
Shackster
 
Join Date: May 2014
Location: Charleston, SC
Posts: 98
Re: Filtered impulse response

When we are trying to do this at a higher crossover point from the LP, and we get a phase chart that looks like this:





Is it OK to use the Unwrap Phase button to view it that way?
subterFUSE is offline  
post #16 of 28 Old 03-10-15, 06:40 PM Thread Starter
Shackster
 
geopango's Avatar
 
Join Date: Jun 2012
Posts: 41
Re: Filtered impulse response

You really have to zoom right into the crossover point and examine how the wrapped and unwrapped phase aligns. You can then apply filtered IR for each measurement approximately at the crossover point. In overlays, view the alignment of IR and adjust delay accordingly till the wave forms sit perfectly on top of each other .
Good luck.
geopango is offline  
post #17 of 28 Old 03-12-15, 08:36 AM
Shackster
 
Join Date: May 2014
Location: Charleston, SC
Posts: 98
Re: Filtered impulse response

So I definitely understand that the crossover point must be set first because that will affect the timing.

What about EQ? If there will be a lot of channel-independent EQ applied, should the EQ be done before or after using this approach to adjusting time alignment/phase?
subterFUSE is offline  
post #18 of 28 Old 03-12-15, 02:33 PM
Elite Shackster
 
Join Date: Mar 2009
Location: Arizona, USA
Posts: 1,562
My System
Re: Filtered impulse response

Quote:
subterFUSE wrote: View Post
When we are trying to do this at a higher crossover point from the LP, and we get a phase chart that looks like this:

Is it OK to use the Unwrap Phase button to view it that way?
No, that will not normally help. When the IR is shifted very far away from 0ms there is just too much phase rotation to read the chart. Any reflections in the chart causing phase rotations also make the phase unreadable when unwrapped. The best action is follow the advice in Post 6 when the chart looks like this.
jtalden is offline  
post #19 of 28 Old 03-12-15, 02:45 PM
Elite Shackster
 
Join Date: Mar 2009
Location: Arizona, USA
Posts: 1,562
My System
Re: Filtered impulse response

Quote:
subterFUSE wrote: View Post
So I definitely understand that the crossover point must be set first because that will affect the timing.

What about EQ? If there will be a lot of channel-independent EQ applied, should the EQ be done before or after using this approach to adjusting time alignment/phase?
For a new setup I would prefer to:
> Set the XO freq and filters
> Set the delay via; phase tracking, or maximum SPL in the XO range, or this new filtered IR method.
> EQ to the house curve.

That said, having at least rough EQ in place to the house curve makes it easier to set the delays as the IR and phase charts are a little cleaner. I just leave the any old EQ in place if I decide to change XO settings and delays. Then revisit the EQ settings as needed. There is nothing wrong with adjusting back and forth as needed to assure that the best combination has been found.
jtalden is offline  
post #20 of 28 Old 03-16-15, 07:45 AM
Shackster
 
Join Date: May 2014
Location: Charleston, SC
Posts: 98
Re: Filtered impulse response

First of all, thanks so much for all of the guidance. I am having a lot of fun learning about this subject, and have spent a fair amount of time testing things. Although I'm still not achieving good results using this method, I think my environment being a car is largely to blame. Unequal path lengths to the different speakers from the LP in the driver's seat definitely make time alignment and phasing tricky.

I do have more questions:

My subwoofer to Midbass Xover point is currently 90 Hz. I have tried using Filtered IR at both 80Hz and 100Hz. Is there a preference for which filter to use when the xover point is between 2 filters?

Same is true for my horns to midbass transition, which currently is at 900 Hz.
Do I use 800Hz, or 1000Hz filter?

I have noticed that using the filtered IR method for my time alignment has yielded some wildly different results than expected when I take rough measurements of the distance to each speaker with my measuring tape. I have also not yet achieved good results with getting the proper phasing using this method. While the phase charts look correct, my ears are certainly telling me otherwise. My results have been better setting things by ear with pink noise.
subterFUSE is offline  
Reply

Bookmarks

Tags
filtered , impulse , response

Quick Reply
Message:
Options

Register Now




PLEASE COMPLETE ALL REQUIRED FIELDS BELOW... THANKS!

REQUIRED FIELDS ON THIS PAGE
YOU MUST COMPLETE ALL OF THESE

Username
Password
Confirm Password
Email Address
Confirm Email Address
Random Question
Random Question #2




User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
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










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



Posting Rules  
You may post new threads
You may 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 is not allowed!
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 


For the best viewing experience please update your browser to Google Chrome