Another First Grapher Needs Help

[Tobester]

I ran my first graph yesterday. It has taken me many hours and $$$ just to get to that point. Now I have hit a few snags.

1. I have a big wide peak that is centered around 36 hz and rises 13 db above my 75db target. I also have several smaller peaks and dips. This is without the house curve. Find peaks is set from 20 to 200 hz. In the filter tasks panel I am not getting a peak table after measuring response. I have fooled around with manually putting some filters in place but wonder why I am not getting anything under the peaks table.

2. House curves? I have entered one and displayed it. It has an 8db rise from 80 to 30 hz. By what method do you get your response up to the level of the curve? You can't raise the target. Do you raise the trace offset?

3. I have a Revel B15. It has a 3 band equalizer. My inclination is to turn off it's equalization, set levels to zero, and work with Rew and the 1124p without mixing in the subs own equalization. Any thoughts.

I know it would help to let you see the graph but I can't. I did not save the measurements and I am away from home today. Just thought I would get a head start on my next session. Thanks.

Tom

Behringer 1124p
external usb live
Galaxy 140
Revel B15

[brucek]

In the filter tasks panel I am not getting a peak table after measuring response. I have fooled around with manually putting some filters in place but wonder why I am not getting anything under the peaks table.

You did press the Find Peaks button after the measurement? It doesn't do it automatically. Then you press Assign Filters. Then you press Optimize PK Gain & Q.

If you know this already, then the problem would be that REW isn't finding any peaks above the target line that it considers worthy. You may at this point simply raise the measured line using the trace offset button and try and Find Peaks again. Or you can lower the target with the thumbwheel, which accomplishes the same thing and Find Peaks again. REW may also not consider the peaks modal resonances, at which point you can enter your own filters to get the levels you want. Be sure to check the waterfalls after you're done.

By what method do you get your response up to the level of the curve? You can't raise the target. Do you raise the trace offset?

Same as above. But, remember that you'll have to raise the subwoofer amplifier level when you're done if you were aggressive with the cutting filters. Too much and you can run out of level or headroom.

My inclination is to turn off it's equalization

Depends on how good it is. If it allows parametric filters, I would give it a try without the BFD and see what it can do. Three filters may be enough......

brucek

[Tobester]

Tuesday I should be able to hook everything back up and have another go at it. Yes, I was clicking on the find peaks button button but was getting a message to the effect that my target might be too low. Now I am wondering if what was going on between 100 and 200 hz was polluting the results. I will just have to check that out and get back with you. I will also post a graph. Thanks for your help and hope you will chime back in later.

Tom

[Tobester]

It's been several days since my last post and a lot of trial and error. I tried everything a 75db with my input and output set at 1.0 and kept getting a message that my input was low so I upped to 80db. I am using sound blaster live external. Anyway here is my uncorrected graph.

uncorredted.jpg

So a set the following filters

HZ ______ DB ____ BW

35.76 ______ -13 ____ 11
27.28 ______ 5 ____ 9
20.25 ______ 6 ____ 6
80.25 ______ -5 ____ 24
327.8 ______ -12 ____ 120 For the 8db house Curve

And I get response like this.

correctedhc.jpg

My question here is am I being to aggressive at raising my low end at 27.28 and 20.25? This is a Revel B15 sub and should be giving good output down there but is that kind of boosting uncool?

Then I added my mains and get a hump at 50hz. So I add another filter to bring the sub level doown in that area.
48.5______ -3______ 9

It helps but now looks like this after adding +4.5db to my sub in the AV speaker levels and the mains added to the graph.

correctedhcfull.jpg

Should I get more aggresive with that 50 hz area to compensate for the mains? What is that dip at 72 all about? What else should I be concerned with?


Thanks

Tom

[Tobester]

Here is my uncorrected waterfall

uncorrectedhcwf.jpg

and corrected.

correctedhcwf.jpg

[brucek]

What is that dip at 72 all about?

Since the dip occured after adding the mains, it's likely the interaction of the sub and mains around the crossover frequency. You can likely correct the dip by adjusting the subs phase control and also your sub distance trim in your receiver. Adjust and remeasure until it's gone (if possible).

The rest looks pretty good. You forgot to say anything about whether you felt it sounded any better.

brucek

[Tobester]

I will comment on the way it sounds after some more listening switching back and forth from corrected and uncorrected. Initial impressions are favorable but I have been tweaking much more than listening.

In my next session I will follow your advise on correcting the 72hz dip.

I was really concerned about the low end boosting I did. Since you did not comment on it I will assume that is OK to do.

I was also concerned about the 50 hz bloat with the mains added that tended to override what my house curve was doing. I was thinking about using one of the hard knee house curves and see how that worked out. I guess most of that just comes down to what sounds better to me.

What can you tell me about the waterfalls? Are they ok too.

Thanks so much for your help. This forum is just too cool.

Tom

[Wayne A. Pflughaupt]

Hi Tom,

In my next session I will follow your advise on correcting the 72hz dip.

I have seen people equalize those phase problems out, although yours is probably too deep to do that. Hopefully you can adjust it out or at least minimize it by following brucek’s recommendations.

I was really concerned about the low end boosting I did. Since you did not comment on it I will assume that is OK to do.

There are differing opinions on that, but to me the main thing is if your sub can handle it or not. If not, you can try eliminating the 20 Hz filter (assuming you’re still using the same filters you discussed prreviously).

I was also concerned about the 50 hz bloat with the mains added that tended to override what my house curve was doing. I was thinking about using one of the hard knee house curves and see how that worked out. I guess most of that just comes down to what sounds better to me.

Not sure why you’re getting so much “action” all the down to ~45 Hz from your mains. Are they high passed? What crossover frequency are you using?

Yes, I’d certainly try a hard knee house curve – love mine - but I’d try listening to what you have first for a while. That will let you determine which house curve you like better.

You might also experiment with a lower shelving frequency than 30 Hz. I’ve moved mine down to ~27-28 Hz and like it a lot. Another Shackster, Ayreonaut, takes his all the way down to 20 Hz. Experimentation and listening evaluations are the key to find what suits your tastes and your room.

What can you tell me about the waterfalls? Are they ok too.

Looks good to me. They look better than mine, and mine were taking with the SPL level ~10 dB less than yours across the board!

Regards,
Wayne

[Tobester]

Good to hear from you Wayne. Neither changing the phase nor distance helped with the 72hz dip. Fooling around with either just accentuated the problem or caused others. What did help is I narrowed the filter at 80hz from 24 to 12. The dip is no longer there but now there is a less pominent dip at 62. I will tweak some more and upload another graph soon.

The 50 hz bloat with the mains is still there and increasing the filter at 48hz doesn't seem to help much. It only causes unwanted dips to each side. I am crossed over in the pre/pro at 80hz.

The next time I have some time to kill I will try a hard knee curve and lower the shelf.

Thanks for your input.

Tom

[Wayne A. Pflughaupt]

The 50 hz bloat with the mains is still there and increasing the filter at 48hz doesn't seem to help much. It only causes unwanted dips to each side.

I assume you meant decreasing the 48 Hz filter? If it’s causing dips on each side, try a tighter bandwidth.

Regards,
Wayne

[Tobester]

Yes, I meant decreasing. I will narrow down and try again.

I see numerous graphs of subs that follow the crossover curve and look good by themselves. But really, it is a good looking graph with the mains added that we are really shooting for itsn't it? Even if, as in my case, one has to put in a dip in the sub response to smooth out the integrated graph.

I listened to some music after my last effort. I really liked what I heard. It was a new cd so not very good for comparrison. I had heard some talk on the forum about Dianna Krall (?sp) so I picked one of hers up. Pure listening pleasure.

Tom

[brucek]

But really, it is a good looking graph with the mains added that we are really shooting for itsn't it?

We do a sub only and EQ first to ensure there are no unknown influences, then the mains are added and final tweaking is done. But yeah, it's the final sub+mains that matters.

brucek

[Tobester]

Understood.

After I get things ironed out and feeling satisfied with my efforts in the Den with the Revel I will move on the the Great Room and see if I can tame things in there. It is an accoustic monster with 20' ceilings and a wall of glass. I have twin Klipsch Thx Ultra subs in there and it should be interesting. I am also close to purchasing a new sub (right now thinking conquest) and I want to be ready to get the best out of it.

I am going to do some more tweaking and listening and report back with impressions, graphs and etc. Thanks much.

Tom