HDMI vs Analog for dual sub alignment and EQ

[cbredesen]

Hi forum, thank you all a WHOLE LOT for REW and this community. I'm diving down the rabbit hole of bass management to optimize my 2 Hsu ULS-15 Mk2's which I think can do a lot better. I have the UMIK-1 and miniDSP and I'll be spending time next week doing All The Things.

My question is: if I'm really only focused on bass management, is there an advantage to doing measurements using HDMI, and thus all my speakers? Must I turn off all the non-sub speakers to do the bass alignment & EQ? In my Yamaha receiver, that's a bit of a pain but doable. I thought it would be super simple to just hit the miniDSP with analog and create a well aligned and EQ's virtual sub from there, and then connect that back to my receiver output (I'm using both outputs now but I'd of course just use one after the miniDSP is in place) and then complete YPAO + tweaks after that.

What might I be missing or not thinking of here? I've already quickly done a measurement with HDMI and saw quite a few nulls so I am very excited to improve my sound!

 

[cbredesen]

I guess a related question is: let's say I do a 10-200Hz sweep and my mains are crossed at 80hz - that would mean I'm getting some bass from my mains (JBL 580s) in the graph. I should be avoid that when I am doing Sub alignment right? Again, using analog would just make this not a thing from the get-go, since I could go straight into the miniDSP input from REW.

 

[John Mulcahy]

Sure, nothing wrong with using analog connections.

 

[JStewart]

My question is: if I'm really only focused on bass management, is there an advantage to doing measurements using HDMI, and thus all my speakers? Must I turn off all the non-sub speakers to do the bass alignment & EQ? In my Yamaha receiver, that's a bit of a pain but doable.

You didn't mention what mic you're using. If it's a USB mic then HDMI may be a better choice so that you can use a REW Acoustic Timing reference with your measurements. A timing reference will be desirable to see the effects of changes to the timing between the subs for "alignment" purposes.

Use the AVR LFE channel for your subs and their measurements.
For the acoustic timing reference channel using a speaker with a tweeter is required. Set whichever speaker you want to use to "Large" in the AVR so no part of the timing signal at all can be routed to the sub LFE channel and pollute your sub measurement.
Easy peasy.

 

[JStewart]

I should mention with the method above you'll be limited by the Low Pass Filter (usually 120Hz) on the LFE channel in the AVR (Yamaha). If you want to measure the subs beyond that....

Set the fronts to large.
Connect miniDSP to the left channel and the subs to the miniDSP (naturally).
Use the right channel for your acoustic timing reference.

Of course power is always off to all components including sub amps when connections are being changed. But you probably know this already

A little more effort but analog will work too.

 

[cbredesen]

You didn't mention what mic you're using. If it's a USB mic then HDMI may be a better choice so that you can use a REW Acoustic Timing reference with your measurements. A timing reference will be desirable to see the effects of changes to the timing between the subs for "alignment" purposes.

Thanks for the reply. I'm using a UMIK-1. Most of the information I've consumed has been pretty manual and I'm not sure I've gotten to the more automated alignment between subs and along with the mains.

I'm going to re-read your advice a couple times so it gels with what I've already read. So much to learn!

 

[JStewart]

Thanks for the reply. I'm using a UMIK-1. Most of the information I've consumed has been pretty manual and I'm not sure I've gotten to the more automated alignment between subs and along with the mains.

I'm going to re-read your advice a couple times so it gels with what I've already read. So much to learn!

A timing reference is needed if you want to use REW‘s tools, such as the Alignment Tool found in the All SPL window, to see what happens to combined output of two sources when changing delays. It is needed because the measurement system latency is not consistent. i.e. the time from button press to sound will not always be the same. It’ll be useful regardless of alignment method.

Here is an alignment tool example (in this case subs to mains but could just as easily be sub to sub):

MiniDSP Sub Setup

Currently have have Audyssey turned off and have changed the distance measurements (laser measure) Since you didn't mention the subs specifically I'll add that even with only 1 sub the actual physical distance setting is not likely to be the correct one. Of course with 3 subs a physical...

www.avnirvana.com

 

[cbredesen]

OK forum, got some time to play with this. I'm using macOS and the analog output to the miniDSP to manage 2x Hsu ULS-15 Mk2 subs. The room is very open and there is no acoustic treatment of any kind. The subs are about 5" from the wall at 1/4 and 3/4 positioning along the same wall as the screen. Here are the measurements.

Subs 1 and 2

Sub 1+2 along with the aligned sum (they are understandably almost identical)

Same as above (aligned sum highlighted) with +1, +2, +3ms delay

As you can see there is no configuration that improves the situation. The 78Hz null doesn't get much better and then I add one or more elsewhere. Am I out of luck with correction here? I guess the next step is to try different room positions? Any advice on open-room tuning? I realize it's not ideal ... or do I just need more subs, haha.

 

[cbredesen]

OK here's another data point. Hsu has EQ1/EQ2 settings and "Q" value for managing EQ which I don't fully understand. From their FAQ (sorry I can't link it because I can't yet):

Generally the auto EQ in receivers are getting better and better, and it's usually beneficial to use them. One general guideline for using the auto EQ for the subwoofer - set the subwoofer for the lowest extension and flattest response so the EQ compensates for the room acoustics alone. e.g. with our VTF series subwoofer, set the subwoofer to one port open, EQ1, and Q=0.7. This is the flattest response mode. The EQ will then correct for the room effects. After EQ, you can select other operating modes for the subwoofer - two ports open, EQ2, Q=0.3, etc.

So I changed to EQ2 and moved the Q knob all the way to 0.7. Here are three measurements labeled

The highlighted curve is EQ1 Q=0.3 (I think that's the min). The other two deviate from that and are the recommended settings when using correction. The nulls are about in the same spot but there's a lot less boost from 15-50 or so. This looks easier to PEQ but maybe I'll just be losing too much output?

Still learning...

 

[John Mulcahy]

Can you attach the mdat files for your measurements?

Hsu are trying to avoid you EQ'ing away the boost which comes from changing the subwoofer Q setting, hence their recommendation to use the Q=0.7 setting for EQ purposes, which has a nominally flat response. Any peaks that then need to be removed are coming from the room, so after you deal with them you can use the sub's Q adjustment to tune to taste.

 

[cbredesen]

Can you attach the mdat files for your measurements?

Hsu are trying to avoid you EQ'ing away the boost which comes from changing the subwoofer Q setting, hence their recommendation to use the Q=0.7 setting for EQ purposes, which has a nominally flat response. Any peaks that then need to be removed are coming from the room, so after you deal with them you can use the sub's Q adjustment to tune to taste.

Thanks for the context on the Hsu settings. I've always had them at EQ1 Q=0.3 because I felt I got the most punch out of it but the result when measured is very peaky so I see what you're saying.

At this point I guess I need to consider moving subs around? WDYT about the ~80 and ~100 low spots?

 

[cbredesen]

If I delay sub 1 by around 2ms, I can greatly reduce the low spot at 80hz but I deepen the one at ~95. How big an issue is this? The videos I've watched always say to delay the second sub but I guess that's arbitrary?

 

[John Mulcahy]

You could delay either sub depending on what gives a preferable response. It is best to also measure or calculate the effect of the subs + main speakers, especially if you are looking at features past the planned crossover frequency.