Dual Sub Frequency Response (Rythmik L12)

[CoolHandDuke]

At the request of my wife, I recently ordered a pair of Rhythmik L12s to ideally replace one Hsu VTF-2 Mk5. She wanted the white finish and smaller form factor. I figured what I'd lose in sub bass (from the larger ported design), I'd gain in more even room response.

That is not happening for me. I independently measured the best locations for the subs using REW. The response of 1 sub between my mains looks really good considering no EQ. As soon as I add in the second sub, I see a big null from 60-80hz. Doesn't seem to matter where I put it.

This is frustrating. Every resource I read talks about the advantage of multiple sub woofers, but my response is better with one. I understand that dual may be better for more positions in the room, but I don't want to sacrifice the even response at my listening position.

I've attached my measurements. 1 with front placed sub, 1 with the other on the left, and the last shows overlay between single sub measurement and both run together (60-80 null very apparent).

I also played with phase delay of the one sub, but it seemed to make no difference. I'm not sure if I'm missing something here, but disappointed so far. I ensured Audyssey is off, crossover to max, but set to full extension.

Any advice or explanation is welcome.

 

[Kal Rubinson]

I had a similar occurrence with a pair of subs. One just to the right of mid-front wall was pretty smooth and adding another on the left side wall was disruptive. Adding a third at the rear right corner helped only a little. OTOH, using a pair of subs on the front wall was good with little added deviations but adding that third one to this pair was very effective in smoothing out the whole bass response.

My point is that merely adding more at random or for pure convenience is unlikely to be optimum and experimentation is necessary.

 

[CoolHandDuke]

I had a similar occurrence with a pair of subs. One just to the right of mid-front wall was pretty smooth and adding another on the left side wall was disruptive. Adding a third at the rear right corner helped only a little. OTOH, using a pair of subs on the front wall was good with little added deviations but adding that third one to this pair was very effective in smoothing out the whole bass response.

My point is that merely adding more at random or for pure convenience is unlikely to be optimum and experimentation is necessary.

Thank you. Perhaps my understanding of how multiple subs would work was flawed. I wasn't expecting perfection, but I did not expect to have more issues. It was a stretch to get the wife to okay the dual subs (even smaller sealed ones). So my options are either figure out a solution with this pair or go back to the one larger Hsu that at least provides a linear response at the MLP.

 

[Jdunk54nl]

Do you have the phase response for the subs? Did you take Measurement sine sweeps, if so you should.

Click the overlays and pull up both of their phases and post that picture.

I can tell right now, you have a definite phase issue though, you are barely getting any gain by using both subs compared to just one and that huge dip. Your dual sub setup should have an spl higher pretty much across the board (unless you are doing volume changes when you add the second).


If you have the ability to do a loop back, try this program. Open Sound Meter
It will be able to measure phase in real time as you adjust the sub phase control.

If you don't, after you take the measurment sweeps, click on All SPL and click the gear icon. In there click alignment tools and choose sub 1 and sub 2 (from being measured separately) and align their phase using that.

 

[Pdxwayne]

What if you cross both subs at 50 Hz? Based on the graph, second subs makes improvement between 20 to 50 Hz....

 

[CoolHandDuke]

Do you have the phase response for the subs? Did you take Measurement sine sweeps, if so you should.

Click the overlays and pull up both of their phases and post that picture.

I can tell right now, you have a definite phase issue though, you are barely getting any gain by using both subs compared to just one and that huge dip. Your dual sub setup should have an spl higher pretty much across the board (unless you are doing volume changes when you add the second).


If you have the ability to do a loop back, try this program. Open Sound Meter
It will be able to measure phase in real time as you adjust the sub phase control.

If you don't, after you take the measurment sweeps, click on All SPL and click the gear icon. In there click alignment tools and choose sub 1 and sub 2 (from being measured separately) and align their phase using that.

It was late when taking measurements so I can't recall if I lowered the volume when measuring the summed subs. I think I found the tool you were referencing. I played with the theoretical phase adjustment of the further sub and moved it so the averaged response looked best (about 5.5mS of delay). Is this correct? REW is new to me. I'm mostly capable of taking measurements. I haven't used many of the other features.

 

[Jdunk54nl]

Ya, if you look at the phase post delay, you can see how far off it is (90, 180, etc.). If you have T/A ability that can adjust the time part of it, but an actual phase control would be better. Time only does some funny things with different frequencies.

The top window bold black line is what the summed response should look like. So you can play with the delay and see what sums the best.

 

[CoolHandDuke]

Ya, if you look at the phase post delay, you can see how far off it is (90, 180, etc.). If you have T/A ability that can adjust the time part of it, but an actual phase control would be better. Time only does some funny things with different frequencies.

The top window bold black line is what the summed response should look like. So you can play with the delay and see what sums the best.

Thankfully the Rythmiks have infinite variable phase, so I think I have the ability to play with it that way.

 

[Jdunk54nl]

Thankfully the Rythmiks have infinite variable phase, so I think I have the ability to play with it that way.

Ya, if it works right, it may or may not. People put "phase" on many things but it doesn't actually mean phase. With subwoofers it is easier as they are big wavelengths and easy to adjust to get them in phase as you see in your previous post.

Either way if you put your delays to 0 on that previous picture you posted and look at like 50hz (choose whatever frequency you want. The y-axis tells you the degree in phase. Look at one sub result and see what it is at, look at the other and see what it is at. Say one is at 160 degrees and the other is at like 45 degrees. You would then need to adjust one of them by 115 degrees to match. If you have phase, just adjust it by 115.
If you want to calculate the time delay you can use this formula:
Change in phase / 360 degrees / Frequency *1000 for ms. So for our example of 115 degrees at 50hz we would have 115 / 360 degrees / 50hz *1000 = 6.38ms delay needed.

 

[Jdunk54nl]

Also, I did notice you do not have a timing reference for REW, either acoustical or loopback. That may cause issues. I never tried it without one so am unsure of how well it will work.

 

[CoolHandDuke]

Ya, if it works right, it may or may not. People put "phase" on many things but it doesn't actually mean phase. With subwoofers it is easier as they are big wavelengths and easy to adjust to get them in phase as you see in your previous post.

Either way if you put your delays to 0 on that previous picture you posted and look at like 50hz (choose whatever frequency you want. The y-axis tells you the degree in phase. Look at one sub result and see what it is at, look at the other and see what it is at. Say one is at 160 degrees and the other is at like 45 degrees. You would then need to adjust one of them by 115 degrees to match. If you have phase, just adjust it by 115.
If you want to calculate the time delay you can use this formula:
Change in phase / 360 degrees / Frequency *1000 for ms. So for our example of 115 degrees at 50hz we would have 115 / 360 degrees / 50hz *1000 = 6.38ms delay needed.

I see. With any luck the Rhythmik has actual phase ability. Had to leave the house for a bit, but I'll keep working when I get home and update.

 

[CoolHandDuke]

Also, I did notice you do not have a timing reference for REW, either acoustical or loopback. That may cause issues. I never tried it without one so am unsure of how well it will work.

I'm not familiar with that tool. How do I set that up?

 

[Jdunk54nl]

What microphone are you using?

 

[CoolHandDuke]

What microphone are you using?

UMIK-1.

 

[Jdunk54nl]

Ok. So you are going to have to do an acoustic timing reference.

First go to preferences and the analysis tab and clikc the checkbox for adjust clock with acoustic ref.

When you click measurement it is in there, Subs are hard to use as timing references. I usually set the output to my farthest speaker away as the timing reference.

 

[CoolHandDuke]

Ok. So you are going to have to do an acoustic timing reference.

First go to preferences and the analysis tab and clikc the checkbox for adjust clock with acoustic ref.
View attachment 110757

When you click measurement it is in there, Subs are hard to use as timing references. I usually set the output to my farthest speaker away as the timing reference.
View attachment 110756

In my case I only have the 2 mains. I suppose I'm a bit lost. Will I need to measure the subs responses along with one of the speakers to get an accurate time?

 

[Jdunk54nl]

What is your interface here? I know for me when I connect I can control which speaker plays via my computer (macbook built in or asio4all driver for windows). But that depends on your interface. Most AVR's allow for this.

 

[CoolHandDuke]

What is your interface here? I know for me when I connect I can control which speaker plays via my computer (macbook built in or asio4all driver for windows). But that depends on your interface. Most AVR's allow for this.

Denon 3700. I just got it.

 

[Jdunk54nl]

Denon 3700. I just got it.

Mac or windows computer?

Either way connect via HDmi and on Mac go to audio midi to set up for multi channel, windows download asio4all and Google instructions on how to set rew up for that

 

[CoolHandDuke]

Mac or windows computer?

Either way connect via HDmi and on Mac go to audio midi to set up for multi channel, windows download asio4all and Google instructions on how to set rew up for that

Ok. I got this setup. What I'm noticing is adjusting the phase on the sub doesn't seem to make a difference. However, if I manually change the distance on Denon, it is smoothing out the response. My question: if I dial it in thru trial and error using Denon distance, won't running Audyssey revert distance back to its own measurements and my EQ will be off?