# Using minidsp2x4hd with REW



## sunnyc06 (May 17, 2012)

Looking for some help. I have Marantz 8802a, two Sunfire amps, Goldenear one.r for fronts, Goldenear two for rear, supersat 50’s for surrounds, HTR 7000’s for ceiling, and two HSU subs. Since Goldenear speakers have their own powered subs, I effectively have six subs running from the two sub outs from my Marantz via Y splitters. This works great but I have a standing wave at a low frequency. I have bass traps for all corners and acoustic panels on all walls. I am considering minidsp 2x4hd with REW to manage the subs. Here is my question: how do I connect the minidsp to Marantz? Do I use just one sub out from Marantz or do I connect the minidsp to both sub outs? Minidsp has two inputs and four outputs. Do I need two minidsp’s or just one to do the job? I have the minidsp mike and REW installed on my computer and have done a test that shows my room needs some correction. I am new to this so please be specific with any help you may offer.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Just connect the miniDSP to the Marantz’s sub output, and use all the splitters you’re currently using to get signal to the various subs.

Regards,
Wayne


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## sunnyc06 (May 17, 2012)

So, you are saying to use just one of the Marantz sub outs?. If I do this do I tell the Marantz I have just one subwoofer?


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## cineburk (May 2, 2010)

I'm not Wayne, but yes, just use the one output and set your Marantz to use a single sub.

But why are you considering trying to use a MiniDSP? The Audyssey processing in the Marantz is pretty dang good, and you'll have to spend a lot of time tweaking a MiniDSP to get it to sound as good (let alone better) than Audyssey.

Here's how Audyssey described their Sub EQ HT process:

*Sub EQ HT is a method we came up with to deal with multiple subs. If you only have one sub then it's not in use. The idea is to first measure each sub separately, then apply delay and level settings so that the two subs are now time and level aligned. Then we ping them once more as "one" sub to derive the room correction filter.*

If you're determined to use an external solution, I would highly recommend checking out an Anti-Mode processor instead of the MiniDSP. You'll save yourself a lot of time and probably get better results.

At the very least, get a UMIK mic and use REW to take measurements so you can see what is happening in your room before and after the Audyssey processing.


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## AustinJerry (Apr 2, 2010)

I have compared connecting the subs to both outputs on the 8802a and allowing Audyssey to time align the subs, and using one sub output to the 2x4 and using the 2x4 to time align the subs. Either approach produces essentially the same results.

Your real challenge is how to integrate the low frequency drivers in your mains with the two subs. Your mains placement is dictated by producing the best soundstage, so the subs in the mains are likely not in the optimal placement for smoothest bass response. This is one of the issues with using mains with inbuilt low frequency drivers. I am not sure the 2x4HD will solve this issue.


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## perceval (Oct 17, 2012)

If you can't play with sub placement so much, have you tried flipping the phase on one of your subs?

Flipping the phase on one sub will cancel the standing wave, and fill in any other nulls you have.

Give that a try before investing some more money.


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## cineburk (May 2, 2010)

perceval said:


> If you can't play with sub placement so much, have you tried flipping the phase on one of your subs?
> 
> Flipping the phase on one sub will cancel the standing wave, and fill in any other nulls you have.
> 
> Give that a try before investing some more money.


Even if that were to work (assuming the null is created by one sub cancelling the other and not a room mode), it would only create nulls at other frequencies. The only way for it to work perfectly is if one sub is perfectly matched to the other sub, placed perfectly to match the first sub, and time delayed to cancel the positive energy of the first sub, like in a double bass array.

Sunnyc06, can you upload your REW file with the measurements you've taken so far, and a sketch of the room and speaker locations?


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## perceval (Oct 17, 2012)

The null is a room mode. The spike as well. Of course, why would we think otherwise?
How easy it is to dismiss an idea without even thinking about it, or dare I say, trying it!

By having two subs (or more), it often excites the same room modes, especially if subs are placed in symmetry with the room's design.

Having one of the subs fire in an inverse phase often cancels the nulls and peaks.

Not just my idea, it is also mentioned when using "The Swarm" sub system.

http://www.audiokinesis.com/the-swarm-subwoofer-system-1.html

Taken from the 3rd paragraph:



> The Swarm is unusually user-adjustable to deal with problematic rooms. One or more of the subwoofer modules can be converted to a low-Q sealed box by plugging the port, and *many users report improved in-room bass smoothness from inverting the polarity of one of the subs, further decorrelating the in-room bass energy. Decorrelation of bass energy is desirable if the goal is smooth bass, and it should be, because smooth bass = fast bass;* it is primarily peaks in the bass region that make the bass sound slow, boomy, and otherwise unnatural, and poor speaker/room interaction causes those peaks.


I have myself tried it, even though my subs were asymmetrically placed in my room, and it fixed a huge null and the booming I had in certain section of my room.
Tried it, and kept it.


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## cineburk (May 2, 2010)

perceval said:


> I have myself tried it, even though my subs were asymmetrically placed in my room, and it fixed a huge null and the booming I had in certain section of my room.
> Tried it, and kept it.


Did you measure it, or do it by ear? And did you measure the effect at other frequencies and listening positions? Do you have before and after measurements you could share?

Obviously, you can cancel a wave at one location and frequency with an inverted wave of equal intensity. But two subs in a room are going to have a lot more interactions than one frequency at one location (unless, as I mentioned before, they are placed and calibrated with the precision of something like a double-bass array which is designed for full cancellation of _all _ bass frequencies after the initial wave).

This being the REW forum, I would suggest there's a better way to make sure the phase on your subs is set correctly in a multi-sub setup. I've attached some examples from when I recently set up an SVS SB-2000 and HSU VTF5-MK3 (as part of a four-sub system) I time delayed the HSU to match the SVS, and you can see phase graph and impulse response to showing how things look at the main listening position.

The red trace is the SVS.

The blue trace is the HSU with 180° shift.

The green trace is the HSU with 0° shift.

I've unwrapped the phase on the phase graph, and you can see which one is most in phase with the SVS.

On the impulse response, you can see which one is aligned with the SVS.

This is the first time I tried this with REW, so obviously someone can correct me if I did it wrong or am drawing the wrong conclusions. But it seems pretty clear to me.

Certainly, there are nulls and variances across the listening area. But even if shifting the HSU 180° helped with a peak or null, do you see how it would cause other problems?

Solve peaks and nulls by focusing on placement, EQ, and additional subs. Use phase to make sure all the speakers are pressurizing the room at the same time.


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## perceval (Oct 17, 2012)

Yes, of course I measured with REW.

My room always had a nasty spike, followed by a deep null.
Adding 2 or more subs in the room asymmetrically didn't work. What did work was when I flipped the phase on one sub.
The FR cleaned up to be almost completely flat, but most importantly, it cleaned up all the built energy that was happening at the spike.
It was easily seen in the Spectrograph window.

My REW files are buried somewhere in my computer... I'll try to dig them up.


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## sunnyc06 (May 17, 2012)

Fixed the standing wave problem by moving one of the Hsu subs and changing the phase on both Hsu subs.
If you want to find out just how good your system is, get the BLU-RAY “ Hans Zimmerman - Live in Prague”. It has Dolby Atmos.


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## cineburk (May 2, 2010)

sunnyc06 said:


> Fixed the standing wave problem by moving one of the Hsu subs and changing the phase on both Hsu subs.
> If you want to find out just how good your system is, get the BLU-RAY “ Hans Zimmerman - Live in Prague”. It has Dolby Atmos.


Good to hear. Are you using the Audyssey calibration in your receiver? Do you have any measurements?


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