Tuning with .WAV files and Timing Reference.......is there any procedures

[Newfiestang50]

Not inferring from the mdat. I don’t have a REW capable machine at the house this weekend.

When looking at the routing photo you posted the thought occurred to me. My reasoning for reducing the left and right mains input to each sub was because a full left signal and a full right signal are added together and sent to each sub, so each sub will be twice as loud as a main (electrically speaking as the sub’s amplifier volume adjustment comes after). The 2nd reason is because I don’t know what the result in the digital realm is when the left and right signals are combined for each sub.

Ahh got it, yes that makes sense.

Hopefully someone else can provide clarity.

By the way, was this the specific warning you saw or something different?
View attachment 67836
If it was you can find more info in REW help

Making Measurements

Yes the message was like that but also had 11.3% distortion listed i think. Ill do another sub sweep to confirm.

 

[Newfiestang50]

Here is the mdat of subs and mins after trying my hand at time align and EQing the subs. Here are the settings i used for the EQ and house curve. Subs to mains not time aligned in this mdat.

 

[JStewart]

My reasoning for reducing the left and right mains input to each sub was because a full left signal and a full right signal are added together and sent to each sub, so each sub will be twice as loud as a main (electrically speaking as the sub’s amplifier volume adjustment comes after). The 2nd reason is because I don’t know what the result in the digital realm is when the left and right signals are combined for each sub.

Ahh got it, yes that makes sense.

I submitted this question to miniDSP.

 

[jtalden]

The 26.24 ms delay you selected for the front sub results in the front sub now trailing the rear sub by about 9 ms. That setting does provide relatively favorable SPL smoothness through the bass range compared to most all other settings. I would have recommended a delay of 17.35 ms which would have aligned 2 subs in time. The noticeable effect is that it provides a little more SPL support <20 Hz and >100 Hz. The resulting SPL smoothness through the 20 - 100 Hz normal sub working range is similar however, so the EQ burden there is about the same. I would not expect that there would be a significant difference between them regarding sound quality, however this type of difference may be noticeable. You may prefer one or the other. Below is the SPL difference between them prior to EQ and my working mdat.

 

[Newfiestang50]

The 26.24 ms delay you selected for the front sub results in the front sub now trailing the rear sub by about 9 ms. That setting does provide relatively favorable SPL smoothness through the bass range compared to most all other settings. I would have recommended a delay of 17.35 ms which would have aligned 2 subs in time. The noticeable effect is that it provides a little more SPL support <20 Hz and >100 Hz. The resulting SPL smoothness through the 20 - 100 Hz normal sub working range is similar however, so the EQ burden there is about the same. I would not expect that there would be a significant difference between them regarding sound quality, however this type of difference may be noticeable. You may prefer one or the other. Below is the SPL difference between them prior to EQ and my working mdat.

View attachment 67860

So why would my running copy of REW give a different delay then yours using the same mdat file.

 

[jtalden]

The REW Alignment Tool was created to assist in aligning sub to main XOs. It can also often work well for sub to sub alignment, but I haven't personally used it for that very often. In this case I started with it but got a wide variation of delays. I tried different several different cursor frequencies, smoothing, and FDW settings using both phase alignment and IR alignment, with no clear consistency. The more room effects in the range the more difficult it is to determine the best setting.
I always confirm the relative IR positions after adjustment to assure the favorable setting was found. In this case none of the suggested setting provided good IR alignment, so I measured the delay manually using your measured front and rear IRs as shown below.

I was measuring about 17.4 to 17.6 ms this way. After setting that delay in the Alignment Tool I then used the adjustment slider to find a favorable SPL near that setting. Below is the resulting IR alignment when using the final 17.35 ms setting. I only chose to deviate a very small amount from ideal IR overlap position.

Edit - corrected chart.

 

[JStewart]

When looking at the routing photo you posted the thought occurred to me. My reasoning for reducing the left and right mains input to each sub was because a full left signal and a full right signal are added together and sent to each sub, so each sub will be twice as loud as a main (electrically speaking as the sub’s amplifier volume adjustment comes after). The 2nd reason is because I don’t know what the result in the digital realm is when the left and right signals are combined for each sub.

Hopefully someone else can provide clarity.

I submitted this question to the always helpful and responsive folks at miniDSP and aft a quick back and forth to clarify the question they provided this answer:

Hi John,

Thanks for your message and we know your concern now. Indeed you are correct if 2 identical signal adding together , you may reduce -6dB in master volume to prevent clipping. But the tricky point is you are setting this for listening to music , it is a non periodic signal and non mono tone signal.

You can apply to -6dB on outputs after mixing and ensure no any clipping .( the RMS meter we captured was feeding 0dBFS sine wave to 2 inputs )

My summary: if you want to be 100% sure there is no digital clipping caused by this configuration, no matter how unlikely from a music signal, then reduce the gain of an output derived from 2 inputs by 6dB.

 

[Newfiestang50]

I submitted this question to the always helpful and responsive folks at miniDSP and aft a quick back and forth to clarify the question they provided this answer:

Hi John,

Thanks for your message and we know your concern now. Indeed you are correct if 2 identical signal adding together , you may reduce -6dB in master volume to prevent clipping. But the tricky point is you are setting this for listening to music , it is a non periodic signal and non mono tone signal.

You can apply to -6dB on outputs after mixing and ensure no any clipping .( the RMS meter we captured was feeding 0dBFS sine wave to 2 inputs )

View attachment 67934

My summary: if you want to be 100% sure there is no digital clipping caused by this configuration, no matter how unlikely from a music signal, then reduce the gain of an output derived from 2 inputs by 6dB.

Ok thanks for checking on this for me. I will reduce by 6db and redo the sweeps when i get time. This do indeed make sense.

 

[JStewart]

Ok thanks for checking on this for me. I will reduce by 6db and redo the sweeps when i get time. This do indeed make sense.

There’s no need to redo any measurements because of this. Your measurements were made with sweeps recorded at a lower level. -12dBFS is REW default, I believe.
If you want peace of mind just enter the -6dB gain for each sub.

What will change is the level of the subs relative to the level of the mains.