Expert advice needed on subwoofer delay and also connections

[marked sound]

I have decided to go with 2 subs that apparently have a fair bit of delay due to all of the processing they do. (KEF KC92).

Someone recommended to use the miniDSP 2x4 HD, as it not only does room correction, but also has adjustments for speaker delay.

However, the miniDSP 2x4 HD does not have XLR ins and outs, only RCA. More money miniDSP units have XLR hookups but, I would also be paying for extra things that I don't need or want such as a DAC and or streamer. (I have a separate DAC / streamer I already wish to buy).

My questions are as follows.

#1. Up to how many milliseconds is an acceptable delay for a sub before I would really start to notice?
#2. How much of a sound compromise would I experience using RCA over XLR
#3. Would the benefits of using the miniDSP and delay adjustments, with the RCA connections, outweigh the benefits of XLR connections?
#4. Is there another product like miniDSP 2x4 HD you could recommend that has XLR connections, and room correction / timing only, and not too much other stuff, and doesn't cost a fortune?

Thanks for your help.

 

[RayDunzl]

If this is correct the existing delay should be inconsequential at sub frequencies.

Processing delay of the KEF KC62

It’s hard to say. For now, I’m leaving that value at 0.5ms and focus attention to the other settings (crossover frequencies and types). Also, there’s no way to make RoomPerfect sound good to my ear, it’s always like to have a loudness mode on instead of removing exceed of bass.

community.roonlabs.com

You could even eliminate that delay by moving the sub toward you by about 5 inches.

 

[marked sound]

If this is correct the existing delay should be inconsequential at sub frequencies.

Processing delay of the KEF KC62

It’s hard to say. For now, I’m leaving that value at 0.5ms and focus attention to the other settings (crossover frequencies and types). Also, there’s no way to make RoomPerfect sound good to my ear, it’s always like to have a loudness mode on instead of removing exceed of bass.

community.roonlabs.com

View attachment 411131

You could even eliminate that delay by moving the sub toward you by about 5 inches.

Thank you very much for your input! While I know a little about HiFi audio, this more in depth stuff is a little above my head for now. One person indicated in their testing on youtube that they noticed a delay of 6-7 milliseconds. This is why I asked. I still question how much i'd notice of 6-7 milliseconds. But the guy seemed to think it was a big deal.

Thanks

 

[RayDunzl]

Something to think about:

Here's a track split into two frequency ranges...

The top represents the motion of the main speaker and the bottom is what the sub would be doing with an 80Hz crossover.

At the top is the timing, by millisecond.

 

[marked sound]

Something to think about:

Here's a track split into two frequency ranges...

The top represents the motion of the main speaker and the bottom is what the sub would be doing with an 80Hz crossover.

At the top is the timing, by millisecond.

View attachment 411156

Forgive me but I am not understanding what you are trying to show me and the point you are making.

 

[RayDunzl]

Forgive me but I am not understanding what you are trying to show me and the point you are making.

Subs are slow... A little delay isn't going to be noticed as mistiming.

 

[DaveBoswell]

I have decided to go with 2 subs that apparently have a fair bit of delay due to all of the processing they do. (KEF KC92).

Someone recommended to use the miniDSP 2x4 HD, as it not only does room correction, but also has adjustments for speaker delay.

However, the miniDSP 2x4 HD does not have XLR ins and outs, only RCA. More money miniDSP units have XLR hookups but, I would also be paying for extra things that I don't need or want such as a DAC and or streamer. (I have a separate DAC / streamer I already wish to buy).

My questions are as follows.

#1. Up to how many milliseconds is an acceptable delay for a sub before I would really start to notice?
#2. How much of a sound compromise would I experience using RCA over XLR
#3. Would the benefits of using the miniDSP and delay adjustments, with the RCA connections, outweigh the benefits of XLR connections?
#4. Is there another product like miniDSP 2x4 HD you could recommend that has XLR connections, and room correction / timing only, and not too much other stuff, and doesn't cost a fortune?

Thanks for your help.

My 2 cents:

- any speaker, and subs in particular, don't introduce a single "delay" number, but they introduce a varying amount of delay at different frequencies (this is called "group delay")
- some delay is from electronics, but most is from normal characteristics of amp + speaker + port physical configuration - GD can be seen with a REW plots (for example my sealed subs have 8ms delay at 80Hz, and 26ms delay at 30Hz)
- group delay is normal and generally accepted to be non audible as long as it is below 1 or 1.5 cycles, which most subs are fine at, especially sealed subs (1 cycle at 80Hz is 12.5ms, and 1 cycle at 30Hz is 33ms - the 0.5ms electronic delay is no concern at all)
- the delay that does matter is making sure that the delay in the subs and the delay in the main speakers is about the same at and nearby the cross over frequency of typically about 80Hz - misalignment of the delay here by 1 or 2 ms can result in significant cancellations of the sub+speaker sound waves altering the in room frequency response
- good news is you can easily align the delays at the cross over by manually adjusting the sub-woofer distance in your AVR or Processor - each additional 1ft (0.3m) of distance added to the subwoofer distance adds about 1ms of delay to the main speakers or vice versa. It's pretty common to need to add somewhere between 3 to 6ft (or more if poorly behaved sub+dsp) of additional corrective distance to the subwoofer to compensate for variance in group delay + electronic delay but it is easily done without a MiniDSP or other tools. Search for "sub distance tweak" for methodology
- there is no sound fidelity issue with RCA over XLR - the reason for using XLR is to reduce/eliminate the likelihood of hum being created in subs from a ground loop - I use RCA to XLR adapters in my setup with a miniDSP and am lucky to have no ground loop issues, and most others are as well. If you don't hear ground loop hum, RCA will sound just as good as XLR
- the MiniDSP Flex has an option of Balanced connectors (basically phono plugs for microphones) that can be used with adapters to XLR cables, but agreed it is significantly more expensive and had unnecessary features not worth paying for.

 

[marked sound]

Subs are slow... A little delay isn't going to be noticed as mistiming.

Got it. Thanks!

 

[marked sound]

My 2 cents:

- any speaker, and subs in particular, don't introduce a single "delay" number, but they introduce a varying amount of delay at different frequencies (this is called "group delay")
- some delay is from electronics, but most is from normal characteristics of amp + speaker + port physical configuration - GD can be seen with a REW plots (for example my sealed subs have 8ms delay at 80Hz, and 26ms delay at 30Hz)
- group delay is normal and generally accepted to be non audible as long as it is below 1 or 1.5 cycles, which most subs are fine at, especially sealed subs (1 cycle at 80Hz is 12.5ms, and 1 cycle at 30Hz is 33ms - the 0.5ms electronic delay is no concern at all)
- the delay that does matter is making sure that the delay in the subs and the delay in the main speakers is about the same at and nearby the cross over frequency of typically about 80Hz - misalignment of the delay here by 1 or 2 ms can result in significant cancellations of the sub+speaker sound waves altering the in room frequency response
- good news is you can easily align the delays at the cross over by manually adjusting the sub-woofer distance in your AVR or Processor - each additional 1ft (0.3m) of distance added to the subwoofer distance adds about 1ms of delay to the main speakers or vice versa. It's pretty common to need to add somewhere between 3 to 6ft (or more if poorly behaved sub+dsp) of additional corrective distance to the subwoofer to compensate for variance in group delay + electronic delay but it is easily done without a MiniDSP or other tools. Search for "sub distance tweak" for methodology
- there is no sound fidelity issue with RCA over XLR - the reason for using XLR is to reduce/eliminate the likelihood of hum being created in subs from a ground loop - I use RCA to XLR adapters in my setup with a miniDSP and am lucky to have no ground loop issues, and most others are as well. If you don't hear ground loop hum, RCA will sound just as good as XLR
- the MiniDSP Flex has an option of Balanced connectors (basically phono plugs for microphones) that can be used with adapters to XLR cables, but agreed it is significantly more expensive and had unnecessary features not worth paying for.

I plan on having 2 subs of the same kind. One will be in the corner next to one of my tower speakers. which will be the same wall as my amp. The other sub will be oposite corner of the room. My space is 12 foot long. My towers will be approx 18-24 inches from the front wall and the towers are approx a foot deep, so at most my rear sub will only be like 8 ft from the front towers. It's just I am spending a fair bit of money building my system, so I want to do it right.

Thanks for the input!

 

[RayDunzl]

I plan on having 2 subs of the same kind. One will be in the corner next to one of my tower speakers. which will be the same wall as my amp. The other sub will be oposite corner of the room. My space is 12 foot long. My towers will be approx 18-24 inches from the front wall and the towers are approx a foot deep, so at most my rear sub will only be like 8 ft from the front towers. It's just I am spending a fair bit of money building my system, so I want to do it right.

My room has an open left rear corner.

So, bass from the left speaker can travel ten more feet before bouncing off the wall "behind" me than on the right side.

The left and right measure similarly, without major problem.

But when both speaker play the test tone, a deep hole in the response occurs around 48Hz.

The waves cancel at the listening position, and can be measured to be 180 degrees out of phase.


Left, Right and Both speakers playing a test tone (mono), unsmoothed.

The waves at the listening position, centered around 48Hz, from left and right speakers, go 180 degrees out of phase around 48hz.

Left and Right speaker phase

The measured hole can be filled by playing around with delay.


I don't notice this hole with music. didn't know it was there until measured.

I don't measure this problem with music when the bass is "stereo". If the bass is mono, the hole shows up in measurement, but doesn't seem to be heard.



Some track with stereo bass.

Red - peak in-room response
Black - ignore, it is an instant reading.

Result? I don't worry about it.

Good luck with your room.

 

[marked sound]

My room has an open left rear corner.

So, bass from the left speaker can travel ten more feet before bouncing off the wall "behind" me than on the right side.

The left and right measure similarly, without major problem.

But when both speaker play the test tone, a deep hole in the response occurs around 48Hz.

The waves cancel at the listening position, and can be measured to be 180 degrees out of phase.


Left, Right and Both speakers playing a test tone (mono), unsmoothed.

View attachment 411362

The waves at the listening position, centered around 48Hz, from left and right speakers, go 180 degrees out of phase around 48hz.

Left and Right speaker phase

View attachment 411363

The measured hole can be filled by playing around with delay.


I don't notice this hole with music. didn't know it was there until measured.

I don't measure this problem with music when the bass is "stereo". If the bass is mono, the hole shows up in measurement, but doesn't seem to be heard.



Some track with stereo bass.

Red - peak in-room response
Black - ignore, it is an instant reading.

View attachment 411364

Result? I don't worry about it.

Good luck with your room.

Thanks!