[Cathan]

Hi everyone. It's been a while, but I finally managed to complete my theater and am now on the last stage of sound equalization.

Quick background I started the room a couple of years ago. Bryan Pape designed the treatment plan, I pretty much did the rest. I'll post a quick couple of photos and then start with the REW stuff. If folks want more details, just let me know.

Okay so now the REW fun.

I custom built a massive IB sub chamber (for sound isolation purposes) to contain the back wave for the four 18" Fi drivers. The subs can not be moved, so it was a bit of a gamble and guess work in how they would perform. Here is my sub only measurement chart. I think I did it correct. I also included Bruce's house curve as a reference point.

While I do have a pretty sharp dip at 100 Hz, overall I'm thinking that it looks pretty good. And while I had a BFD waiting in the wings, I don't think I actually need it. BTW, my IB subs seems to remain pretty flat all the way to 8 Hz.

And here is the full spectrum chart. I used the 1/3 smoothing setting.

There is a bit of a dip at 100 Hz, but I don't think there is much I can do about that. And it looks like I need to play with my speaker levels to bring the main speakers up closer in line with the subs. I actually already have my receiver bass setting at -15 db and the mains at around +5 db.

One issue i can into while taking this measurement is that I really had to increase the volume on my receiver so to get my mains level checked at close to 75db. That cause the subs to run way too loud. I assume the fix is to continue to increase the levels for the mains? Would reducing the gain setting on the sub amp help reduce the spread between the db values the the sub and the mains produce?

 

[laser188139]

That is a very attractive room. Congratulations, Michael.

... Would reducing the gain setting on the sub amp help reduce the spread between the db values the the sub and the mains produce?

Yes.

Bill

 

[Cathan]

That is a very attractive room. Congratulations, Michael.



Yes.

Bill

Thanks, Bill. As a follow-up, I assume I really want to get the stuff above cross over point closer to 72db while keeping the sub where it's at, right? When I take that chart, should I calibrate the REW levels using the main speaker pink noise signal, or the sub signal? I used the main speaker signal.

 

[laser188139]

Since you ask, I used the Audyssey calibration in my receiver to set all the levels at 75dB, then used the SPL meter to verify all the levels were correct. So I was quite puzzled for a while to see a 3dB higher level at the sub than the fronts: REW would measure my fronts at 75dB and the sub at 78dB+. Eventually I figured out this was destructive interference from the mono signal sent to both fronts together.

The lesson I learned was that the charts should appear flat if you measure just one front at a time with your sub. If you have set these individually using the receiver's 75dB test tones, these should appear flat when you compare the band limited range of the mains, typically 500Hz-2000Hz to the center of the sub range, 30Hz-80Hz. If the mains appear flat with the sub, examined individually, then if you measure them together with the sub the sub level will appear about 3dB high, just as mine did. Your sub may appear a little higher than this from your house curve, of course.

Bill

 

[Cathan]

I think you may have lost me Bill. In order for my chart to look as follows, I had to increase the reciever's level to +11. That puts the volume at around 82 when playing the audyssey calibration file. My sub is at level -15 which I read the volume as around 80db. When I run ReW setting the receiver volume so that I get 75 db when using the speaker level check I get the following chart.

So long as my end results produce the above, do the levels really matter that much as long as they are proportionally level with each other?

 

[Wayne A. Pflughaupt]

Here is my sub only measurement chart. I think I did it correct. I also included Bruce's house curve as a reference point.

And here is the full spectrum chart. I used the 1/3 smoothing setting.

Hi Michael,

Your sub-only chart looks fine. However, when the mains are introduced, it appears they are “blowing out” the house curve. It looks like way too much bass from them is getting past the crossover. Notice in the second chart that the bass is no longer tracking the house curve Target, but is virtually flat out to 70 Hz.

Also – don’t know if you have any way to accomplish EQ with the main channels, but your 700-1500 Hz range is a bit exaggerated and most likely could use a few dB of attenuation.

One issue i can into while taking this measurement is that I really had to increase the volume on my receiver so to get my mains level checked at close to 75db. That cause the subs to run way too loud. I assume the fix is to continue to increase the levels for the mains? Would reducing the gain setting on the sub amp help reduce the spread between the db values the the sub and the mains produce?

Either way – increasing the mains level or reducing the sub level is fine. That’s primarily for measuring, however; I typically make my final sub level adjustment by ear.

Regards,
Wayne

 

[laser188139]

From what I'm seeing, I think your levels look fine. But I'm just guessing what it should like with the house curve.

What I was trying to say, though, is that it is easier to judge the level looking at one main at a time. Plug the computer output into the left channel aux input of the receiver, generate the REW graph, and look at the left front relative to the sub. Then plug into the right channel aux input of the receiver, generate the REW graph, and look at the right front relative to the sub.

Let me try to illustrate with some of my graphs. Here is a graph of the mains together, measured with the sub:

If you look at this, the sub appears elevated relative to the mains. Every part of the sub curve appears above the 75dB target. What gives? I might be tempted to lower the sub trim level. Yet I know they measure equal with the SPL meter when I use the receiver test tones on the speakers individually.

Now look at the curve of just the left front with the sub.

Here the sub peaks do indeed appear level with the main peaks, with a lowered level around 2kHz and at the top end of the main from the Audyssey Reference curve. By not measuring the two mains together, I avoid a testing anomaly that appears when sending the identical signal to two stereo front speakers simultaneously. (When you feed a monaural signal to the two channels, you get +6dB of gain where they are added electrically in the sub, and only +3dB of gain from the two front speakers due to interference. Thus, the 3dB difference.)

When I measure the right front with the sub, the peak levels now appear even here, too:

As I said at the top, taking into account your house curve, yours appear fine.

Bill

 

[Cathan]

Hi Michael,

Your sub-only chart looks fine. However, when the mains are introduced, it appears they are “blowing out” the house curve. It looks like way too much bass from them is getting past the crossover. Notice in the second chart that the bass is no longer tracking the house curve Target, but is virtually flat out to 70 Hz.

Also – don’t know if you have any way to accomplish EQ with the main channels, but your 700-1500 Hz range is a bit exaggerated and most likely could use a few dB of attenuation.

Either way – increasing the mains level or reducing the sub level is fine. That’s primarily for measuring, however; I typically make my final sub level adjustment by ear.

Regards,
Wayne

Thanks, Wayne.

I've let Audyssey handle the equalization to this point. I assume it is doing something.

Think adjusting the crossover point for the mains from 80 Hz to 100 Hz help?

Bill - I'll try running the sweeps one front speaker at a time this weekend. I can see why folks can get caught up with endlessly tinkering with this stuff.

 

[Cathan]

I just realized that I didn't check to make sure that my mains weren't set at full. I recall Audssey screwing with the setting the first time I can the setup. Just making a note here so I remember to check for it when I get home.