REW for Measuring Acoustical Distances

[TomW16]

REW is a tremendously powerful and beneficial software that made me confident enough to purchase a Rotel RSP-1576 processor, which does not have Dirac. (The Mk II version has Dirac but I have the original version).

My question is around the acoustical distance from a reference speaker capability in REW. I am using that feature to set the distances (i.e. delays) for each of my home theater speakers in the processor (7.2.0 for now but will add Atmos speakers in the coming weeks). The processor allows for setting speaker distances to a 0.25 foot resolution. My challenge is that I am not able to adjust the speaker distances for a few speakers that result in a <0.25 ft acoustical delay with my reference speaker. I am wondering if this is a problem with my measuring process/setup or potentially a lack of resolution within the processor. Below is my measuring process (noting that the microphone is in the primary listening position and not moved throughout all measurements):

I set all speaker distances to 1 foot (minimum allowed) in the processor to minimize any delays. The following were the acoustical distances referenced to my center channel:

Front Left: 0.05’
Front Right: 0.05’
Center: 0’
Surround Right: -4.74’
Center Back Right: -1.78’
Center Back Left: -1.71’
Surround Left: -4.55’
Subwoofer: 14.75’

Since the subwoofer is the furthest away acoustically, I used that as the speaker to base all distances off of:

Front Left: 14.75’
Front Right: 14.75’
Center: 14.75’
Surround Right: 19.5’
Center Back Right: 16.5’
Center Back Left: 16.5’
Surround Left: 19.5’
Subwoofer: 1’ (no adjustment)

When I re-remeasured with the above distances entered into the processor, only the following channels had acoustical differences that appeared to require further adjusting within the processor:

Center back right: @16.5’= 0.45’ acoustical distance delta (ADD), @16’=-0.68’ ADD, @16.25’=0.45’ADD, @15.75’=-0.7’ADD

Center back left: @16.5’=0.52’ acoustical distance delta (ADD), @16’=-0.61’ADD, @16.25’=0.52’ADD, @15.75’=-0.61’ADD

Surround right: @19.5’=-0.26 acoustical distance delta (ADD), @19.75’=0.87’ADD, @19.25’=-0.26’ADD, @19.0’=-0.26’ADD

I am not sure if I am doing something incorrectly or if the processor has insufficient resolution to get within 0.25 foot acoustical difference with the reference channel.

I appreciate your expertise and let me know if I can provide any additional information.

Kind regards,
Tom

 

[John Mulcahy]

A tape measure is probably the most reliable way to get distance figures for speaker setup, though the subwoofer typically needs more work such as using the alignment tool.

 

[TomW16]

Thank you John. I can easily use a tape measure to enter the physical speaker distances but was hoping to validate those measurements with the acoustical reference through REW but that is where I was running into difficulty. I was not sure if REW is the wrong tool for the job or if my processor did not have fine enough resolution to get within 0.25 feet.

I will read up on the alignment tool.

Thanks!

Tom