My 2x DIY Scan-Speak Revelator 32W subs build

[concorde1]

@concorde1 I would have a look at what I'm getting in-room in the listening room now before doing too much. Your nearfield measurement seems to have -6dB at 29hz and -10dB at 20hz already which is not too bad.

Hi again sigbergaudio (and all others)

My interconnects finally arrived.

Here is my new Equalizer APO config (L and R are the 2 subs ; C and LFE are the 2 speakers) (Recall: using 8 channel Topping DM7 in 7.1 configuration)

Special trick in REW I figured out - might help someone! - I had to select "EXCL" version of Topping DAC in REW preferences, in order to access individual channels. When I wanted to measure ALL channels simultaneously, I had to select the "Topping DAC" option without EXCL and use L+R

Strangely, while the subs are about equidistant from my listening position, the right one apparently needed a significantly longer delay. (See config above)

Here's full system with all delays and full-range EQ applied (no bass boost though).

Note the 2x subs have a different volume control than the 2x speakers -- so I can turn the bass up further safely.

The subs are just placed without thought in front of each speaker.
Again, I did find it suspicious that the R sub needed much longer delay than L sub - maybe causing this 40Hz deficiency . . . ?

Any suggestions to improve freq response? Thanks.

 

[sigbergaudio]

How did you determine that one needed longer delay? I would also suggest measuring them independently to identify any differences, and through this potentially help you place them in the best place(s) in the room.

 

[Flaesh]

First, measure and compare both subwoofers.

 

[concorde1]

How did you determine that one needed longer delay?

I used left speaker as acoustic reference in REW, and measured the respective impulse responses of right speaker, left sub, and right sub.

Then I calculated the difference (right speaker subtract left speaker, and so on).

I'm wondering if the difference in impulse measurements could be due the great deficiency of the left sub measurement relative to right sub, throwing off the result.

Here are independent measurements from listening position, of the 2 subs with no EQ and no delay (left is red, right is green).

EDIT:

My room dimensions: 13 ft * 15 ft * 11 ft (l*w*h) - or ~2200 ft³

 

[concorde1]

I've been experimenting with different settings in REW and EQ APO for a while now, and now going nuts with it.

The results have been strange - including the speaker bandwidth part of the measurements being much less smooth than before I used this complicated setup.

I'm going to take a break from this and I'll see if I get anywhere next time.

In the meantime though, does the Eq APO config below look logical?

Also an observation in REW is, where I have dips in response, the distortion also peaks between 5-15% (even for the loudspeaker range > 80Hz)

 

[sigbergaudio]

I'd suggest to remove the delay from both subs.

Also, when sharing REW measurements, if you adjust the Y-axis to 45-105dB and the X-axis to 20-200hz, it will be much easier to read.

At the moment it looks like the left sub should ideally be placed somewhere else.

Higher distortion in the dips is just a measurement anomaly. Since the level is much lower, the distortion will be higher. In the same way you will see the distortion is lower where you have peaks, as you get "free" energy from the room without increasing distortion.

 

[Ktacos]

Also an observation in REW is, where I have dips in response, the distortion also peaks between 5-15% (even for the loudspeaker range > 80Hz)

Could be a few things, could be something wrong on a technical level, or its just typical low frequency distortion results in a room. Pretty tough to get low frequency distortion results that are accurate in a home, lots of random noises our ears kind of filter out that add to distortion, mic handling noise, vibrations bleeding into the mic stand, cars outside, lawnmowers, etc... Sharing .mdat can be helpful.

In the meantime though, does the Eq APO config below look logical?

I'm not sure what's going on visually with the first copy task but you generally don't need more than one copy in a config. The first one can route everything. What are the 0.5 notations doing? Just a nitpick that might help declutter.

I would say your EQ approach isn't the best, these broad EQ's and linkwitz transforms aren't going to get you anywhere. You need to measure and use REW's EQ function to flatten things out. Ideally you'll want each speaker and sub to have it's own EQ config generated by REW. As is you have L+R main speakers paired sharing the same filters.

I'm wondering if the difference in impulse measurements could be due the great deficiency of the left sub measurement relative to right sub, throwing off the result.

IR and FR go hand in hand, pretty much the same thing from a different point of view, so if one shows an issue the other will as well. FR can show you an amplitude dip and IR can show how far away from the source the thing that caused the dip is.

 

[concorde1]

Yes shortly after I posted that I realised about the two copy functions - I have combined them to one copy function for simplicity. But good spotting.

The 0.5 notations are taking 0.5L and 0.5R and copying them to both L and R ; this is how I get combined mono.

The L and R to C and LFE are so the speakers actually get signal.

Those EQ's above are just the crossover and the safety 19Hz high pass.

I have been using full range EQ from REW -- applied to ALL of: L R C LFE. it's not shown there as it was pointless doing EQ when one of my subs is 40hz deficient.

-

I've been moving the left sub all round the room and it hasn't helped. But I know both subs are functioning fine - because I have seen the bass deficiency move to different regions instead of 30-40 Hz, indicating it's the room. I think my listening position could be problematic too. However . . .

I happen to be moving to a different room soon, fingers crossed this room's easier for bass management.

I'll post back when I've done more experimentation in this new room!

 

[concorde1]

Happy new year. Well after hours of experimentation (in a different room) I have results that sound great to me. A little aside in code text here that might help someone in future...:

When separate L, R, C, LFE channels were required, I had been using EXCL mode on my DAC in REW output options.

This seemed to mean the DSP wasn't being applied for the measurements.

A better trick I figured out was to go back to the standard mode, where only options are L, R, or L+R (where L+R is actually all 8 channels), then to measure this "L+R" twice at 20-100Hz with my EQ APO set to respectively reduce gain of each sub by 20dB. That way I could measure each sub independently while still keeping the crossover applied. I could then safely (I think) proceed to use alignment tool to find the delay on one sub relative to other to best align phase.

Or I suppose I could have just unplugged one sub each time.

So the subs actually produced an excess of bass in bottom octave (red trace in SPL graph). Although, my subs seem unable to produce much output below 24Hz. (A low shelf of +5dB seems to have no effect on SPL in this region.)

Big dip at 122Hz (I presume floor-ceiling distance causes this null (122Hz -> 2.8metres which is probably about right).

THD seems excellent, at least at this SPL.

Potential for improvement:

I did not time- or phase- align speakers with subs at all, because I couldn't figure out how. I only phase-aligned the two subs with each other as per REW Alignment Tool.

.mdat is attached in case anyone particularly eager would like to inform me where I inevitably went wrong with something I'm unaware of

EDIT: by the way I made a "crossover" by using HPF on speakers at 60Hz and LPF on subs at 80Hz.