Axiom Home Page Forums General Discussion Advice from Axiom Owners BFD - Opinions on My Latest Graph Plot

Here is my plot from the re-eq session tonight. Is this about what everyone calls a "house curve"? Any thoughts from all the experts?. Anyone see anything they think I should change about my curve?

All of my Axioms are blending wonderfully with my twins!!

Updated pic links at the bottom of my post..

Thanks guys..
Rick



TV with Axioms
http://www.stampcometal.com/files/axioms.jpg

Dual SVS 20-39 PC+
http://www.stampcometal.com/files/dualsubs.jpg

Back Left and Rear Back QS8's
http://www.stampcometal.com/files/surrounds.jpg

Rick, I haven't a clue about subwoofer mojo, but I sure do love that entertainment center. A+ home theater in my opinion.

Rick,

First some questions:
Where do you have your crossover set?
Did you play your test tones with only your subs on, or with the subs and mains?
What SPL did you use as reference?

It'll be easier to analyze your graph with these answers.

Rick, as long as the blue line isn't after, you're doing great! Peter raises interesting questions, and I assume that you ran the sub alone. It would help to understand the before peaks if you'd give the room dimensions and the sub position.

Peter and John,

My crossover is set at 80 and the tones were run with my sub and all of my speakers turned on, even the suurounds. I was under the impression that it was correct to have them all on since the plot would determine how they all interacted with the sub. Please correct me if I am misunderstanding this concept.

Regarding the SPL: Since I had such initial high peaks I started with the 16hz tone registering at 70 on my meter. I had read about how hard it is on the voice coils if you run the tones too loud so I was afraid to push it too high. Is there a right or wrong number to start with regarding this as well?

All in all I like how it turned out and what I hear now but I don't want to be staisfied with that if it can even be better!

All constructive help and insight is appreciated.

Thanks guys..
Rick

PS John..yes the pink line is what my final target was and not the blue..Room size is 20x20 with a vaulted ceiling of 8-13 feet and if you looked at the pics the TV is directly across from the blue couch. So the subs are to the left of the main listening area in the corner.

Thanks for the extra details, Rick.

If all your speakers were playing during your measurements, then I see a problem. It is very strange that the right side of the graph (from 80Hz upward) dips so low. Ideally, it should be at the same average level as everything to the left of 80 Hz. This would indicate a problem with your speaker calibration, and not your subs, however.

Your adjusted sub response is very good, so I'd leave that alone, but I'd suggest recalibrating your Axioms to bring them up to the same level (about 85 dB) as your subs.

Peter,

Thanks for your thoughts. After I re-eq'ed my subs I did re-run my calibration levels using my DVE disc to readjust the SPL for my subs. Using DVE I calibrate at 75db on my mains and surrounds and 85db on the subs.

I see your point about the curve should stay higher at the end but how would I get this to change?

I am confused now(but I stay that way most of the time..LOL) I only have one more filter I can use on my BFD and doubt that only one would fix that but most of all they speak against using a filter to add gain, especially since it would be such a large increase.

Note Dennis's graph here..
http://www.axiomaudio.com/boards/showflat.php?Cat=&Board=HT&Number=90033&page=1&view=collapsed&sb=5&o=0&fpart=

Is his big dropoff due to only calibrating using the sub and not using the rest of his speakers or do you know?

Any more info for the confused would be apreciated..

Rick

Do you folks mind if I chime and ask a dumb question? Didn't think so .

Anyway, regarding the graph and in laymans terms, what are you looking at and what should it look like. I suppose in otherwords, what is the graph telling you?
Thanks and excuse my ignorance.

BrotherBob,

The more the merrier!!LOL

If you note my graph...the blue plotted line is the uncorrected SPL (or db) level at each given frequency when that specific tone is played. Note the ups and downs. That means that certain frequencies are played louder (i.e. 28hz & 63hz) or softer (i.e. 100hz) at the same master volume setting . What one wants to accomplish is to have all of the frequencies play at the same level (db)so across the board everything is balanced.

Using the BFD's (Behringer Feedback Destroyer)parametric EQ feature you apply filters at a set frequency to increase or decrease that frequency. It has a total of 12 filters than can be used.

Some users have stated a slight downward slope (the pink line)from the lower frequency to the higher frequencies works well for them. They call this a "house curve". Some try to target a complete straight pink line.

Here is the setup guide for the BFD. It explains it in detail.

http://www.snapbug.ws/bfd.htm

Hope this helps..
Rick

Sure does, thanks Rick.

Rick, those peaks in the blue line(I was kidding about whether it was the after result, of course)are about what would be expected from your room dimensions. Both the 20 foot length and width would lead to modes in the high 20s(1130 feet per second/40 feet~28)and the peak in the low 60s area would correspond to about a 9 foot floor to ceiling mode(1130/18)which may be about where the subs are located.

Yes, I certainly interpreted Dennis's curve to be that of his subs alone, but Peter or someone else who was present can clarify that. The reason why I thought yours was also that of the subs alone was that I was interpreting the gentle slope over about 90Hz as being simply the natural rolloff of those subs. I don't follow this "house curve" concept and don't understand why the speakers should be at a lower level.

John,

Man you are spot on with the ceiling to floor heights where the subs are at - due to the slope of the ceiling vault it's about an average of 9 feet as you stated.

In reply to:

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I don't follow this "house curve" concept and don't understand why the speakers should be at a lower level.

---

In your opinion would you target a more level line rather than the slope that I have now and throw out the house curve idea?

Since I am in the "know enough to be dangerous catagory" do you think the drastic dropoff at the end could possibly be a phase related issue of the subs with my Axioms?

Thanks for your thoughts and input..
Rick

John and Rick,

The reason Dennis's curve drops off steeply at around 100Hz is that there are no more data points after that. The test disc we used maxed out at 98Hz.

The front L & R channels were active during the sub calibration. This allowed us to adjust the critical range between approx 65 - 95 Hz where the M80s and subs overlap.

Rick, if you calibrate your subs at 85dB, you should do the same with your other speakers.

In reply to:

---

Rick, if you calibrate your subs at 85dB, you should do the same with your other speakers.

---

Peter,

Since I use DVE to calibrate with isn't it my understanding that the LFE track on that disc is off? Thus the reason for the 75db for the mains and 85db for the sub?

Thanks..
Rick

That has been my experience, but maybe I've just been taken in by the intarweb hype.

We may be having a miscommunication here. When you calibrate all speakers, you should strive to do so at the same dB level. To ensure this is what you're doing, pick a level on your receiver or pre-amp's volume dial that brings the mains close to 85 or 75 dB -- the number you pick is up to you. Once you find that level, don't touch the volume knob until you're done calibrating ALL the speakers.

What this accomplishes is ensuring that your subs and speakers are of similar loudness whether you're playing them softly or loudly.

Since you have a 10dB difference in your sub vs. speaker calibrations, your subs sound (on average) 2.5 times as loud as your speakers. This is bad news from an accuracy perspective.

Not really. There is a (possible, but very likely) bug on the DVE disk where the sub test tone is 10 db lower than the test tone for the other speakers. Therefore, those of us saddled with this disc calibrate the sub 10 db hotter than the rest of the speakers. Sounds good to me!

Ahhhh. I see what you're saying. But that still doesn't explain why the SPL levels are sliding down as the Hz increase.

No, it doesn't, does it... Guess I should actually read the rest of the posts instead of skimming....

Peter,

Kcarlile explains it like I had meant for you to understand about the 10db low LFE test tone on the DVE disc. I thought most everyone knew about that fault in DVE.

Don't tell me I have stumped the experts?...LOL

Now that you have pointed out the drastic drop after the crossover it's got me concerned now as I know it shouldn't drop off like that but stay much higher up. I am loosing db's after the 80hz crossover point and that's not good!!

I think with my Onkyo 601 it will let me turn off my surrounds and center and re-plot with just my mains and the sub or should it be just the sub only?... I have heard that both methods are correct..I am soooo confused now....LOL

Thanks again guys for the continued ideas..
Rick

re: mains plus sub vs. sub only -- there is no "right". Sub only is the most useful generally because everything you see relates to the sub (placement, EQ, level setting etc..) so you can get everything dialled in more quickly.

At the crossover region, graphing with sub + mains starts to be useful as (a) an "end to end check" on calibration, (b) confirmation that phase is optimal, but it's more of a final check than something you would use when you are tweaking EQ and placement.

Make any sense ?

EDIT -- the rolloff after 80 Hz looks OK to me, almost exactly the 24dB/octave you would expect from the receiver's bass management system.

MORE EDIT -- just noticed you had mains running as well. Hmm, that's not right. Either the sub level is WAY too high relative to the mains or something I don't understand is going on ;(

Rick, yes you shouldn't be getting that slope-off above 90Hz when the mains are also operating. The only context in which I've heard the "housecurve" idea discussed which made any sense to me was when it was suggested that the very lowest frequencies, say below 40Hz, be sloped up a bit to compensate for the lower sensitivity of the ear at those frequencies. I don't think that even that is necessary, but in any case it isn't your situation. DVE and the other setup discs have some good features, but it isn't necessary to use them for the basic volume balancing calibration, which the receiver's built-in test tones handle well. Just in case the slope above 90Hz resulted in some way(other than that 10dB difference)from the use of DVE, why not run a calibration using the receiver test tones?

John and bridgman,

Thanks to you both for your input. I will try the sub only method to see how my plot compares to what I have now. I really guess the final decision would be if I like what I hear and the wife and I agree so far that it really sounds good where it is now but I can't explain to her that "tweakers disease" that most of us have..LOL

I will also try John's idea and use the Onkyo's internal tones to set my levels and see how it compares to the DVE tone settings.

I feel like I am worrying much about nothing to be honest but just want to make sure I can get my system set to the best it can be.

Thanks to all for hanging in there with me!!
Rick