Axiom Home Page Forums General Discussion Home Theater Avia Disc & Sub-Woofer Calibration...

This is reference to the first Avia calibration disc.

In Chapter 7 (Subwoofer Calibration) the disc goes through a series of alternating high and low frequency pink noises from left main to sub, center to sub, right main to sub and so on until all speakers have gone through this pink noise process. Whenever I do this the sub is reading my pre-setting of 75/75db for the mains but 61/75 and 60/75db for the center and surrounds. The disc instructions says to calibrate the sub with either the receiver or the sub's amp so that you'll get the same db reading on the sub throughout all of the speakers but this can't be done, if I calibrate the sub to 75/75 db with the center and surrounds the sub goes through the roof whenever the mains are played. Am I missing something here?

In the past I've always calibrated all speakers using pink noise and set all db's the same.

Speakers to set to small, sub (EP600) is set to -7 db on the receiver and the crossovers are as follows, mains (80s) to 60, center (VP150&100) and surrounds (QS8s) to 100.

Wasn't there something about the calibrations being off on the Avis discs?

I really can't remember Jay, do you believe it may be a fault with the Avia calibrating disc?

I've never understood that part of the Avia disk either. I try and calibrate it to my mains then eventually give in to the temptation to adjust it myself anyways.

Also, I don't have the adjustment table for my particular SPL Meter's inaccuracy for LFE. I have seen downloadable tables for the Radio Shack meter but that is a bit of a Holy Grail device here in Canada considering we haven't had a Radio Shack in many years since they pulled out and got replaced by "The Source".

Same here.

I usually calibrate the subwoofer to my left main and just skip the subwoofer calibration for the other speakers. My thinking was the additional test sweeps for the other channels was if you were say running stereo, tri, quad etc… subwoofers you could calibrate each speaker + subwoofer pair individually. Never read that anywhere but it was the only thing I could figure it would be useful for.

Murph, if you are interested, you can get the Radio Shack SPL meter through Sonicboomaudio.

I will have to look around to see where I read the avia disc is out of whack.

I could be wrong and without going back to the disc I thought it stated the calibration process was for a single sub system. Like you Grunt, it seems to me like that particular calibration process could be designed for a multi-sub system.

While we're wallowing around in calibration, I'd like to ask a stupid question.

The RS analog meter has ranges for 60, 70, 80 db, right? And on the meter itself, we see 0db as the midpoint, right? So, isn't a reading of 0 on the 70db scale, well, 70db? If so, why do we try to calibrate to 75 instead of 70 or 80?

I dunno Tom, I have a digital meter. I believe the apparently broke Avia disc also states to calibrate above 70db, so I just calibrate our stuff to 75.

That's how I read it, Tom. If I'm misreading it, then I'm listening to stuff substantially louder than I thought...

I think the 75 db might be the standard to allow for headroom of various speaker sensitivities in a system and still achieve the 85db movie standard.

I guess you could clibrate to 70 while using the disc and then to 75 when using the pink noise from the receiver, as the receivers output is set at 75db. The biggest thing is maintain the same speaker levels all around.

Just to be clear I was thinking it would be good for speaker + subwoofer pairs where each pair is hooked up to it’s own channel L/main, R/main etc… otherwise I can’t see any use for them in a single or multi-sub system running off the subwoofer line out.

Clearly how they tell you to use those other test tones is very confusing.

Good question Rick, and sorry I could not answer your question last night. I may try my new AviaII disc but I admit, I was confused by the calibration for each speaker.

Rick,

That alternating test between sub and channel is for setting your crossover point. Or, at least that's what I use it for. Play with it some and you'll changing your crossover (at the channel level) will change the spl db reading on the meter.

Thanks Mike, Randy and I were talking on the phone last night and actually touched upon whether it was for setting the crossover or not, I assumed that normally the crossover would be set by the freq. response of each speaker in the manufacturer's specs? My center and surround crossovers were both set to 100 whenever I did the quick calibration with the 10+db difference between the mains, centers and surrounds.

What do you have your centers and surrounds crossovers set on?



Grunt thanks for the explanation, I'm getting old ... you'll have to bear with me.

Tom, it really isn't very crucial and the more important point is to get all the speakers equal in level, regardless of what SPL level is used for the calibration. Be that as it may, most(all?)receiver test tones are set 30dB below the maximum level of 105dB that movies are supposed to be recorded at, so if you adjust the levels to 75dB, then the movie sound(not applicable to music discs, which have no established standard level)would be played at the designated "reference level" when the receiver volume control was at 0 or whatever number was used during calibration. Of course, few listeners find that using the "reference level" for movies is acceptable for long-term listening in the home and use a a level 10dB or more lower.

Rick,

My twin M22 centers is set to 60, the QS8 surrounds are set to 100 and the M3 S-Backs are set to 90. Mains are set large.

I played with this function quite a bit. It really does make a difference in LFE / Low bass DB levels by changing crossover points. This is largly ignored because most receivers restrict you to a global crossover point for all channels.

Tell me about it Mike, my 2805 is a global setting, sucks.

That's one of the issues I have with the H/K Mike, although it does allow separate crossover adjustments for all speakers it only does this in increments of 20hz ... 40, 60, 80 and etc., that is why I had the surrounds and center crossover at 100. I did change the crossover for the center and surrounds to 80 last evening but I haven't really noticed much of a difference in my minimal amount of time with the system since then.

Mike just curious, why did you go with the 'large' setting for your mains?

Oh no, I can see it already... here comes the Mains = Large, Sub = LFE + Mains versus Mains = Small, Sub = LFE + Mains discussion again.

I believe the reasons I've seen stated in the past for running the M80s on large versus small is b/c people have a hard time mentally cutting out all of the low end from the M80s since they're such highly capable full range towers. (I too have this mental hurdle that I can't get over and run them on large with the subs set to LFE + Mains)

Jason

I must have missed that particular thread Jason, I've always valued Mike's insight and knew he would have had a good reason for it.

LOL - I'm not sure if Mike said it or if it was someone else. I'm happy to put words in his mouth though.

I'm pretty used to people putting words in my mouth. I enjoy hearing about what I say. (joys of living in a small town)

I have tried the M80’s set to small at differing crossover points and set to large as I have them now. I prefer them set to large with LFE + Mains. My “preference” could be nothing more than perception or some other pseudo psychological rational. I am OK with knowing that though and am sticking with running them large. Until someone can come up with a sound and compelling reason to not run the M80’s at large, I will continue to do so. I have plenty of power (350 WPC / 4 ohm or so), so that’s not a consideration.

I do not think folks give the M80’s the credit they deserve in regards to low end bass. Most just default to the position that their sub does better because that’s what subs are designed to do. I’d encourage anyone running a set of 80’s to run them without the sub and throw in a known, hard hitting CD with some good kick drums. Crank it up and then just crawl around the perimeter of your room. I guarantee you will be impressed. Sooner or later you will find a spot in our room where the bass from these speakers floors you. (then you can call Randy and talk about bass traps)

PS: Rick - not real sure why you are screwing with anything. My set up still does not sound as good as you had your's a couple years back when I dropped by.

I have found my M80s set to large and LFE+ gives me a boomy bass, but I know this is due to the dual corner loading I have, as the M80s are against one corner and the sub in the corner to the side of them.

How come Jason didn't get sent to his room?

Mike, I'm totally with you philosophically on this deal. I think many people too easily accept the notion of simply not using the extended bass capabilities of full-range speakers. If your amp has adequate headroom, I see no reason why the 40-80Hz bass from a subwoofer would somehow be "better" than the 40-80Hz bass from your M80's.

The same principle applies even in my weird room with the M60's. I have tried running them "small", but much prefer the response running them full range with the appropriately REW/BFD-tuned sub.

I do run My M80s at 60hz and sometimes 40, but even at 40 it starts to get boomy. I guess if calibrated with 40 hz settings the boominess may go away, oh great, I have talked myself into even more tweaking . I finally have my old XP box back together and running so I will be experimenting with REW in the near future.

It's a domino effect Mike, whenever our power goes out the H/K resets the channel adjust mode so that all speakers default back to 0db + or - gain while all other settings (crossovers, distance and etc.) keeps whatever I previously set. (weird, huh?) The power went out a week or so back and I dusted off the Avia disc and SPL meter to re-check the speaker adjust gain and thought I'd re-check the subwoofer calibration but whenever I couldn't understand the calibration process I brought the question up here, and whenever you mentioned that you had your mains set to large ... well, you know the rest of the story.

I did write down and store the speaker adjust settings this time though.

It's the roll-off. Although the M80 may be capable of producing a 40Hz tone, it will produce it 6db quieter than a 100Hz tone. The EP500 however would not have this limitation.

The bass response for the M80s are +/- 3db @ 34HZ, so how would it be down 6db @ 40HZ?

Just look at the M80 graph... It's -6db at 40hz from 100Hz.

+/-3db means it can be 6db off the peak... which it is.

Sorry to multiple post...

And, the EP500 is almost flat as a board down to 20 Hz (and 10db higher to start with, which can be attenuated with the gain knob). That's why you need a sub to extend to the low frequencies.

The +/- 3db does mean it can be off either +3db or - 3db which is a 6db swing but not down 6db at 34hz.

It can mean -6db off the high point, wherever that point is.

Hey, here's the graph, you tell me your interpretation.

http://www.axiomaudio.com/gallery_m80ti_diagram.html

The graph does not lie nor does Steve. Many manufacturers quote their specs this way.

A quote from Alan's article.

A simple claim of frequency response that cites two frequency extremes unqualified by a dB specification (e.g., frequency response: 34 Hz - 22 kHz) is meaningless and useless. It may mean that although the speaker responds at 34 Hz--the cone moves a bit, perhaps--nothing will be audible because the speaker's response at 34 Hz is at -30 dB and inaudible! On the other hand, if Axiom states that the M80’s frequency response is 34 Hz - 22 kHz +/-3 dB, this indicates that every tone that emerges from the M80 will be within 3 dB of any other over that entire frequency range.

Alans article

Well, that is either misquoted, or untrue, or both. The tolerance is +/-3db, not +/-1.5db. To be +/-3b is a 6db swing. Axiom's graph shows the evidence.

As Steve comments, if a speaker was 6dB down from a high point at a particular frequency, that frequency would still fall within a +/- 3dB spec, which encompasses a 6dB "window".

Wid,

I read Alan's article. You did not misquote it. Alan is incorrect in his statement.

I am sincerely sorry for having invited discord. My intent was not to create controversy over analysis of the M80 response curves. By using "60-80Hz" instead of "40-80Hz" in my example, I suppose all of this could have been avoided while still conveying the core issue.

For the sake of discussion, let's assume that a large front speaker (like M60 or M80) is capable of producing FLAT response down to 60Hz. Let's also assume that you have a big, honkin' amplifier so that the notion of relieving the amp of the 60-80Hz load is moot.

Other than enabling more amp headroom, are there ANY benefits of crossing over the mains at 80Hz rather than 60Hz?

Intuitively, I would think you would want the mains to play as low as they are capable of as long as you could provide adequate current.

The only reason is the placement of the main speakers. For example, until I piled up a whole bunch of boxes of paperback books in a corner of my room, even setting the M80 at 80hz was problematic (terrible booms). Now that I lessened one of my "corner problems", I can go down to 50hz with only a small range of boomy notes (noticeable mainly with pipe organ) near 40hz. Setting the xover at 60hz provides a very good bass distribution accross the whole room, better than at 80hz. A lot of these choices depends on placement.

The M80s alone have really good bass. Before I received by new HT unit, which forced me to put the M80s much closer to corners, the bass was astonishing, even for the 2 months I waited to buy my EP500.

I'm sure Alan will be along to confirm who is truely incorrect.

Hitting on Eric's comment, I think maybe the reason I've lucked out and our room sounded decent from jumpstreet (re: Mike's question regarding why screw with anything) is that I set the speakers up according to the Rives suggestion of the 1/5th room placement, in other words I have my 80s set 5' off of the front wall in a 25' long room. Whenever I had them fairly tight to the wall they sounded a bit boomy but after they were moved way back the bass seemed to have tightened up quite a bit, which makes me believe that room and room placement makes a huge difference ... probably more so than is given credit for at times.

Which also makes me believe that there can be no one set procedure for setting these systems up due to the numerous room layouts these speakers are going in, comes back to that personal preference thing I suppose.

BTW, for *my* particular room and taste I did set the 80's back to a small setting and the crossover back to 60 after trying the large and LFE setting on our AVR for a day.

<slaps forehead> The Room! Of course!

Eric and Rick, thank you!