First Look

[kjgarrison]

Here are a few of my first measurements. Nearfield wo EQ, Primary listening postion sub only w/wo EQ, and full range. EQ in this case is Audyssey MultiEQ XT, Denon 4308. TASCAM US144 USB soundcard, Behringer ECM8000 mic. DIY IB (2x18" Fi Audio, Line Array), Mains=PSB Synchrony Twos, room=regular large (~7000+ cu ft) family room with hardwood floor and lots of windows, seating distance=9 feet.

Near, subwoofer only, no EQ


Center of Primary Listening postion, subwoofer only, no EQ


Center of Primary Listening postion, subwoofer only, Full EQ (Audyssey)


Center of Primary Listening postion, full range, crossover 60Hz, Full EQ (Audyssey)


Thoughts? Recommendations? Do-overs?

[waldo563]

kjgarrison,

I am still pretty new at looking at REW output and will defer to others with more experience and knowledge than I have. But it looks like Audyssey is doing a pretty good job at least for the low range. I was wondering if you have tried moving your mains around to see what effect it has. Do you have any room treatments? Maybe that might help with your nulls at 55 and 75 Hz and what appears to be a dropoff above 500 Hz.
I hope this helps at least a little bit.

[brucek]

Thoughts? Recommendations? Do-overs?

You haven't calibrated your soundcard or used a calibration file for your microphone. These are necessary items required for accuracy.

The small floppy icon in the lower left corner of the REW chart will save your graph to an 800 wide jpg file. Much more convenient than posting the entire REW page.

brucek

[weverb]

WOW! A ~10dB boost at 6Hz. I know our IB set-ups can take some boost, but over 10dB that low. Can you even feel it? I wish my room would support that low of Hz.

[kjgarrison]

brucek wrote:

You haven't calibrated your soundcard or used a calibration file for your microphone. These are necessary items required for accuracy.

The small floppy icon in the lower left corner of the REW chart will save your graph to an 800 wide jpg file. Much more convenient than posting the entire REW page.

brucek

Why do you say no soundcard or mic cal? If it's because they don't show in the graph, then it's that I unchecked them so as not to clutter the display.

The measurements were taken on a laptop with a calibrated sound card and a mic calibration file as well. They were then copied to a USB thumb drive and taken to my desktop where from within REW "Open Measurement file" is chosen. Should it be "import measurement" instead of open measurement?

I must be missing a step with the bringing of the file to the desktop. I tried to copy the soundcard cal file from the laptop, but I do get the warning that no cal file is present when I open these files at the desktop pc. The mic cal file is also present in the desktop. The graphs look pretty much the same, but I haven't done a side-by-side viewing with the desktop and the laptop.

[brucek]

Why do you say no soundcard or mic cal? If it's because they don't show in the graph, then it's that I unchecked them so as not to clutter the display.

I say that because they're not just unchecked, they're grayed out. If they're loaded and working, then the text will not be grayed out.

But, since you transferred the mdats from another computer, that would explain why the cal files aren't loaded.

brucek

[kjgarrison]

brucek wrote:

I say that because they're not just unchecked, they're grayed out. If they're loaded and working, then the text will not be grayed out.

But, since you transferred the mdats from another computer, that would explain why the cal files aren't loaded.

brucek

Does this mean the results are not as they appear?

Where do I put the cal files so that they behave properly?

[brucek]

Does this mean the results are not as they appear?

They're fine since you've loaded an mdat file from a computer that you had the soundcard and meter cal files loaded properly.

Where do I put the cal files so that they behave properly?

They can be in any location in the filesystem, but must be loaded by REW and show in the loaded window after you've browsed and loaded them with the settings screen.

brucek

[kjgarrison]

Thank you, brucek. I got the cal files loaded and they are no longer grayed out (which you can't see with the new way to save you pointed out.)

Here is Primary Listening Position, no EQ, subwoofer only


Primary Listening Position, Audyssey EQ, Audyssey Dynamic EQ, subwoofer only


Primary Listening Position, Audyssey EQ, Audyssey Dynamic EQ, Full Range, crossover 60Hz


They look pretty much the same, so the question is what should I do to make the full range better? I could try to adjust the mains, but there isn't much room to change their placement (just inches and toe-in is about all.) I could also try to measure just one main at a time and see if it is one more than the other causing the nulls.

The sub's EQ'd response by itself doesn't show any dips of consequence. I don't have the sweeps of the mains alone to show you, but neither do they. So, it is an interaction between the sub and the mains. Interestingly (to me at least) the dip changes location with different crossovers.

Here the crossover is 100Hz. Just 0-200 sweep, but Audyssey, etc ON. Left the cal lines in to show you.


Is figuring out what treatments to apply is most likely the next step if minor tweaks of positioning of the mains doesn't help? The IB ain't goin' nowhere! Any guidance on treatments planning?

[weverb]

kjgarrison wrote:

They look pretty much the same, so the question is what should I do to make the full range better? I could try to adjust the mains, but there isn't much room to change their placement (just inches and toe-in is about all.) I could also try to measure just one main at a time and see if it is one more than the other causing the nulls.

Is figuring out what treatments to apply is most likely the next step if minor tweaks of positioning of the mains doesn't help? The IB ain't goin' nowhere! Any guidance on treatments planning?

You can start by measuring just one main and try moving the few inches/toe in. I am currently doing the same thing and it is making a difference.

The is an acoustics section here in the forms. Bryan (bpape) is willing to give you some very good suggestions. There are many other forums that can help a lot with acoustics. AVS has a good thread that is supported by some very big names in the acoustics industry.

[brucek]

So, it is an interaction between the sub and the mains.

Usually, interaction between the sub and mains is controlled by the subs phase control. The best method is to use REW's RTA feature and dynamically set the phase. (See here for RTA setup variables).

As weverb says, acoustics questions are best directed to the acoustics forum section...

brucek

[kjgarrison]

weverb wrote:

You can start by measuring just one main and try moving the few inches/toe in. I am currently doing the same thing and it is making a difference.

The is an acoustics section here in the forms. Bryan (bpape) is willing to give you some very good suggestions. There are many other forums that can help a lot with acoustics. AVS has a good thread that is supported by some very big names in the acoustics industry.

brucek wrote:

Usually, interaction between the sub and mains is controlled by the subs phase control. The best method is to use REW's RTA feature and dynamically set the phase. (See here for RTA setup variables).

As weverb says, acoustics questions are best directed to the acoustics forum section...

brucek

Thank you both.

I'll see what the acoustics peeps have to offer.

My sub doesn't have a phase control. It's just my AVR to the sub's amp (Behringer EP1500). Perhaps I need an additional component between the AVR and the sub amp to add phase control? Do the BFD products do this?

[brucek]

My sub doesn't have a phase control.

Use the receivers sub distance trim as a proxy for a phase control.

brucek

[kjgarrison]

I'm working on this sub distance thing, and I have a question specific to the use of REW.

Is it possible to ping a very, very brief and sharp spike of sound at, say 80Hz, and then be able to capture the playback coming simultaneously from the sub and the mains (using so-called "double bass") and see a difference of a few milliseconds or whatever it would be?

[brucek]

Is it possible to ping a very, very brief and sharp spike of sound at, say 80Hz, and then be able to capture the playback coming simultaneously from the sub and the mains (using so-called "double bass") and see a difference of a few milliseconds or whatever it would be?

Well, you can use the "Left Channel as Calibration Reference" advanced feature to establish a subs acoustic distance from the listening position, but the result won't really help you in getting a smooth crossover.

The best method of setting distance of a sub, is to initially set the distance using its actual ruler measurement and then with the RTA feature of REW (with sub and mains playing) use the subs phase control to obtain the smoothest response at the crossover. If the phase control is not variable, you would select the 0 or 180 position and then use the receivers distance trim of the sub to get the best crossover response.

brucek

[kjgarrison]

brucek wrote:

Well, you can use the "Left Channel as Calibration Reference" advanced feature to establish a subs acoustic distance from the listening position, but the result won't really help you in getting a smooth crossover.

The best method of setting distance of a sub, is to initially set the distance using its actual ruler measurement and then with the RTA feature of REW (with sub and mains playing) use the subs phase control to obtain the smoothest response at the crossover. If the phase control is not variable, you would select the 0 or 180 position and then use the receivers distance trim of the sub to get the best crossover response.

brucek

Thanks. I'm not really working on a problem at the crossover. I'm just trying to figure out if Audyssey is correct in setting my sub distance a couple of feet shorter than it's true measured distance. I have a theory that this is to compensate for the fact that my sub and mains are all in a straight line across the front soundstage with the sub centered in between. I don't have a proper semi-circle with sub, mains, and center all equidastant from LP1. This "distance" is of course derived from the time it takes for the sound to travel to LP1, but if the sub were the same distance from LP1 as the mains, it would be an additional foot or two farther away from 'actual'. So, by setting the 'distance' closer than actual, I'm thinking this creates a delay in the mains. It is well accepted that Audyssey sets the distance to the sub greater than actual to compensate for delays caused by processing in such things as BFD, etc.

There has to be something in REW that will let me see the effect on changing the sub's "distance" has on sound coming from a combination of mains and subwoofer. Maybe using the scope? A sine wave which would look sharp when the 'acoustic' distances are equal vs smeared when they are not?

Another way to test of course is to move the mains to the same distance as the sub, or even closer, and then see what 'distance' is assigned to the sub.

[brucek]

There has to be something in REW that will let me see the effect on changing the sub's "distance" has on sound coming from a combination of mains and subwoofer.

There is. It's a standard frequency response graph. The bandwidth of the mains and sub have the greatest additive effect at the crossover, and as such the effect of phase (distance) will have the greatest impact at that point.

A sine wave which would look sharp when the 'acoustic' distances are equal vs smeared when they are not?

That's not how sound work. The signals are simply additive.

Certainly the Audyssey will alter the subs distance trim to obtain the best crossover smoothness. It will almost never be set to the true measured distance.

brucek