Time alignment vs. frequency response: Is the battle real?

[seedragon]

I believe I am having to make a trade-off in my system's performance and would like your input on whether it's a real trade-off or if I can have my cake and eat it too.

System: Revel F208 L/R, C208 center, M105 SL/SR, dual PSA 15V ported subs, Denon X4400, UMIK-1 and REW.
Room: ~4,000 cu ft largely rectangular.
Subwoofer placement: SW1 is behind MLP on the midpoint of the left wall. SW2 is in front of the MLP in the front corner against the right wall. Not ideal, but it's what the room allows.

Here's the situation: When I let Audyssey calibrate my two subs separately (using the Sub 1 and Sub 2 outputs), I get excellent imaging of low-frequency content (kick drums), but terrible frequency response (massive peak at 40hz then falls off rapidly below that).

When I level-match and set the delays of the subs manually to achieve as smooth an FR from 20-150hz as I can, then use a Y-splitter to make Audyssey treat them as one subwoofer, I get much better frequency response, but the imaging of low-end content is noticeably worse. In fact, I perceive an unevenness to the bass between my left and right sides (probably physical rather than auditory).

It seems that when I try to optimize for imaging at low frequencies, I compromise in-room frequency response. When I optimize for frequency response, I compromise the time alignment of the low frequencies. Changing the crossover from 40hz to 60hz to 80hz makes a difference, but seems to slide between one side of the compromise to the other.

What I think is going on is that when Audyssey can calibrate the subs independently, it can time align and level match them, but it makes no adjustments for frequency response; it simply aligns them and doesn't check how they behave in room when played together. When I manually match them and adjust delay to get a better frequency response via room averaging, I'm unable to time-align them.

Is this a real trade-off?

If so, what can I do to solve both problems?

 

[LTig]

I don't think the FR of a subwoofer has any influence on imaging as long as it is lowpassed (as it should). Must be some other side effect of Audissey.

 

[seedragon]

I don't think the FR of a subwoofer has any influence on imaging as long as it is lowpassed (as it should). Must be some other side effect of Audissey.

If the crossover is set to 60hz or 80hz, and it's a 2nd order crossover, the subs will play content that is localizable if I'm not mistaken. When that content is not time-aligned, the effect is definitely audible.

 

[JustJones]

Can you adjust delay after running Audyssey? If you set it before you run it as if it's 1 sub not sure how it would know to set the delay right but I'm not familiar with that program

 

[Spenav]

Your experience mirrors mine. Audyssey seems to do better if it sees only one sub. I am not sure why. I have four in my system but presenting them to Audyssey as one sub always measured and sounded better. I still wasn’t happy when I look at the time domain response in REW. Adjusting the time domain always seems to mess up the frequency domain response. Then I discovered a little box by DSPeaker that finally solved my problem in both realms and sounded like it too. You still let Audyssey do the final set up. Do a search on DSPeaker antimode 8033. Good luck.

 

[flyzipper]

One thing that stands out as potentially problematic in your description is the only device that can be used for delay and EQ is the Denon, but then you're using a Y cable to connect your subs (meaning they can't be independently time aligned with each other, only relative to your other speakers). That's not an issue if they're both the same distance from your listening position, but an issue if they're not.

I don't use Audyssey, but my experience using YPAO on Yamaha requires:

- time align the subwoofers, and then run REW to calculate EQ filters (delay set independently on each output channel using a MiniDSP 2x4HD, and EQ filters applied to the single input channel)
- present the subs to the AVR as a single device (connect the MiniDSP to the AVR sub-out).
- run the AVR's calibration
- make a note of the calculated distance (delay) for the subwoofer (it won't equal the tape measure distance in my case because the MiniDSP is introducing its own delay).
- throw out every setting changed by YPAO
- manually set speaker distances with a tape measure (use the subwoofer distance calculated by YPAO)
- manually set speaker levels with REW
- no EQ applied by the AVR (subs are already EQ'd by the MiniDSP, and that's all)
- run some tests with REW to ensure everything looks properly integrated (bass follows the curve you wanted in REW, and no dips at the AVR crossover point)
- listen to the result and see if it sounds as you wish

If I had your X4400 (looks like it has independent sub-outs), I'd ensure the subs are connected independently, measure them with REW and use the EQ filters recommended by it (these need to be applied equally to both subwoofers), then manually apply those in the X4400, set speaker distances and levels manually, and be done.

I've used Multi Sub Optimizer to determine EQ filters for each subwoofer independently, but prefer using REW and applying a single set of filters to the time-aligned subs.

 

[seedragon]

Can you adjust delay after running Audyssey? If you set it before you run it as if it's 1 sub not sure how it would know to set the delay right but I'm not familiar with that program

Yes, that's what I used to do but found that messed with the EQ that Audyssey had already done. You're right that can't know how to set the delay after making them into one sub--that's the problem =\

 

[seedragon]

Your experience mirrors mine. Audyssey seems to do better if it sees only one sub. I am not sure why. I have four in my system but presenting them to Audyssey as one sub always measured and sounded better. I still wasn’t happy when I look at the time domain response in REW. Adjusting the time domain always seems to mess up the frequency domain response. Then I discovered a little box by DSPeaker that finally solved my problem in both realms and sounded like it too. You still let Audyssey do the final set up. Do a search on DSPeaker antimode 8033. Good luck.

I checked out the Anti-Mode, but it doesn't seem to work with multiple subs. Are you using one Anti-Mode for each of your subs?

 

[617]

A low frequency sound wave by definition has a long wavelength, meaning the distance between high pressure areas is relatively large. It will also having a long period, meaning the amount of time between waves is comparatively long. In a normal indoor space, in the amount of time it takes for a low frequency sound to manifest, the distance it will have traveled is often larger than the room it is bouncing around in. The specific pattern of cancellation and augmentation is frequency and space dependent, meaning it will have a different amplitude at each point in space for each frequency.

Since the sound waves are larger than the room, and since the periods are so long, the sound waves will bounce around the room before they even get established as cyclic signals. This is (one reason) why low frequency sounds aren't really localized indoors; they don't exist as a focused wave of sound coming towards you, they are a chaotically forming field coming from all directions at once, changing with frequency.

You seem like you've read up on bass management a bit, so you may have some understanding of this. However, the consequences of this situation are that:
1. Bass management is best done with multiple sources measured at many places in space around the listening position. Audyssey tries to do this but its implementation is not exactly state of the art
2. The steady state response of your bass is all that matters, indeed it is all that really exists in a small space.
3. Time and frequency domains are really the same thing, and you should focus on the frequency response graphs since they show you what you hear.
4. What you should be looking for is smooth frequency response at a bunch of points in space.
5. If you want great bass response with multiple subs I doubt Audyssey is going to do the job. I won't speak on other products but manual EQ with a minidsp is probably the best solution for you.

Bass management is hard and many audiophiles prefer lackluster bass to weird or distracting bass, but the rewards are worth the effort.

 

[Spenav]

The Antimode 8033 can handle up to 4 subs
http://www.dspeaker.com/en/technology/anti-mode-technology/anti-mode-connection-examples.shtml
it does everything for you. Read the manual on line and see if it is for you. You should be able to find one on eBay. Really easy to setup And it works.

 

[Spenav]

By the way mine is set up a little differently. I have the two front subs in series going to one output and the two back ones in series going to the second output.

 

[617]

By the way mine is set up a little differently. I have the two front subs in series going to one output and the two back ones in series going to the second output.

How many locations does the antimode measure?

 

[Spenav]

You can choose one or multiple.

 

[Bullwinkle J Moose]

Factoid of the day:

A Single Sub is always the best solution!

 

[seedragon]

Factoid of the day:

A Single Sub is always the best solution!

How do your seat-to-seat measurements look with a single sub?

 

[Spenav]

Factoid of the day:

A Single Sub is always the best solution!

Well, Dr Earl Geddes and Dr Sean Olive, two of the foremost experts on the subject would respectfully disagree with you. They did their PhD dissertations on this very subject. But maybe you have the facts and ample knowledge to back up your factoid. Please do tell us.

 

[Bullwinkle J Moose]

How do your seat-to-seat measurements look with a single sub?

FANTASTIC!

Far better than 2 subs

In fact, it's not just the Sub that should be a single speaker

ALL mono information can only be properly reproduced from a single speaker to avoid muddy midbass, frequency cancellations and reinforcements at various frequencies and create a sweet-spot that covers the entire room

I'm not saying you should listen to a singe speaker, but properly decoded stereo information is actually 3 separate channels
LEFT - MONO - RIGHT

By avoiding the reproduction of mono in 2 (or more) locations, you will hear tighter midbass with more impact

An EQ should never be used for a pair of subwoofers, because on good quality subs, the drivers ARE reproducing bass information correctly

It is the nodes and anti-nodes caused by reproducing the same information in 2 separate locations that you are trying to EQ

The sound IS there, but you simply cannot hear it and an EQ cannot give it back to you

But it CAN blow your drivers!

ENJOY!

 

[Bullwinkle J Moose]

Well, Dr Earl Geddes and Dr Sean Olive, two of the foremost experts on the subject would respectfully disagree with you. They did their PhD dissertations on this very subject. But maybe you have the facts and ample knowledge to back up your factoid. Please do tell us.

I am the only one with the facts!

They certainly don't sound like experts now do they

 

[Spenav]

I am the only one with the facts!

They certainly don't sound like experts now do they

Obviously you have strong opinions but very little facts. The problem is not the bass driver but rather the room itself. Below 200 Hz or so, the room is very dominant. The additional subs are to reduce the effects of the modes in the room. Please read up on the subject. The information is readily available.

 

[flyzipper]

Please read up on the subject

... and actually measure the behaviour of a single sub in your room, at your listening position, and various other locations. It becomes very obvious very quickly once you see the frequency response graph staring you in the face.