OK, I've got another philosophical question.

I have a Denon 3805 that has an auto-calibration feature using an available Denon mic, or, according to Denon, you can use another mic if you wish. I don¡¦t understand how that can be? Doesn¡¦t the calibration need a mic that has a ¡§known¡¨ frequency response?

If the Denon-supplied mic is down -4db at 38Hz, the receiver could automatically ¡§add¡¨ 4db to it¡¦s readings at 38Hz to make up for the mics¡¦ lack of ruler-flat response. But if a user can supply their own mic, doesn¡¦t ANY sense of a reference disappear from the get-go? How could the receiver adjust itself to the readings from a listener¡¦s position if the readings themselves are not from a calibrated, adjusted source?

OK, I¡¦ve wondered about that since buying the receiver a couple of months ago, even though I know many say that the auto-calibration doesn¡¦t sound that good anyway¡K (Ummm, maybe this is WHY?). Here¡¦s how this ties into something current and Axiom-oriented:

I have a test DVD, but have wondered about a good set of test-tones to manually plot my listening room. Recently, it occurred to me that I don¡¦t really need to find a test disc, I can make my own with the tone generators in several audio editing software packages I have. So, yesterday I started to meticulously create 15-second test tones at mostly 1/3 octave intervals, individually for Left and Right, except for the bass region, for which I have also added ¡§less than 1/3 octave¡¨ tones starting at 16Hz and in stereo to boot. My thought is that these will work well for me to plot my subwoofer, mains, and both together through the various combinations available. I¡¦ll hook up my QS8s and VP-150 as ¡§mains¡¨ to run the tones through them as well.

By the way, I do disc duplication/printing here at my business, so if someone wants a disc of the tones, PM me. I can run off hundreds pretty easily, though if I start getting THAT many requests I might have to charge a dollar (or a beer) for shipping and packaging. No, I don¡¦t look at it as a profit maker, but it really could get ridiculous if I receive two hundred requests! ƒº

Anyway, on to the second part of the question:
I have the Radio Shack sound level meter in a box somewhere¡K I musta bought it 20 years ago. But just like the Denon situation above, how do I know that IT is accurate? I know the RS meters are widely used, but is that because of accuracy or inexpensiveness and convenience? Does IT adjust for anomalies in its built-in mic?

Here¡¦s why I ask: A good part of video production is audio production. Towards that end, I have a nice selection of mics, including a Rode large-diaphragm studio mic with an ART tube mic preamp that I use in a voiceover soundbooth. I¡¦m not saying that the combination is inherently flatter than the RS meter¡¦s mic¡K in fact, the ¡§warmth¡¨ from the tubes and mic might actually lean them towards being decidedly ¡§unflat¡¨.

But if that $30 Radio Shack meter with it¡¦s $5 mic is NOT being adjusted for by the meter, might it not be better to use some much, much higher quality electronics to obtain my readings?

BTW, I¡¦m not really this anal with most things in life! I just think it¡¦s an interesting hypothetical discussion on a widely-used ¡§test instrument¡¨ and practice, and, yes, when all is said and done, I would LOVE to spend a weekend afternoon tweaking and measuring my home theater!

What Say Ye, Oh Mighty Axiomites? How Hath Ye Measured?

I have found that when correcting for frequency response one should take into consideration the speakers inherit response. Assuming you like how your Axioms sound, flatteinig their response can take away from their magic. I once tried flatening the frequency response of my m60s with a Pioneer Elite and found that I liked how the m60s were tuned without any correction. A lot of people like using correction and also listen to their speakers set to small with a sub, both of which I feel change the m60s character for the worse. It is all getting to complicated, crossovers in front of crossovers, and equalizing for lack of proper room treatment. I guess, in the end whatever sounds best to you. Have fun.

Hi Mark,

Your thoughts on the Denon's auto-calibration circuitry are exactly why I tell Axiom buyers not to use it. To do careful room measurements, you'd need a lab-calibrated B&K measurement mic that would cost thousands. That is exactly the type of microphone that is used to measure frequency response of a loudspeaker in an anechoic chamber at the National Research Council in Ottawa, where initial Axiom prototypes are measured.
Anyway, the Radio Shack SPL meter is reasonably accurate--within a few dB--when I compared readings to a professional B&K device at the NRC and an expensive meter we have in Axiom's listening room. But if you want precision--and you do if you are measuring or attempting to alter frequency response in a room or in an anechoic chamber--you ain't gonna get it from the RS meter, or from the microphones supplied or sold by Denon or other manufacturers for their auto-EQ circuits.

Regards,

Hi Alan:
Thanks for the response! I wasn't sure if no one was interested in the topic or if no one had any answers!

Since you compared the RS to the B&K, do you remember how the bass region compared? My guess is that this is where the RS was the furthest off from "flat", and yet the bass region is primarily the reason why I started putting together the test tones and wondering about all this in the first place.

I saw a post on the Behringer Feedback Destroyer Pro as used as a parametric EQ and I thought it would be really great if I could map out the subs' interaction with my room and be able to correct some peaks and standing waves to tighten up the bass!

Mark,

I have a Behringer Feedback unit coming in on Wednesday to "tame" my SVS 20-30 PC+. I will report in when I get it all hooked up and adjusted and let you know my thoughts about it..

Rick

Thanks Rick-
I look forward to it!

Mark, note that although the RS meter isn't of course perfectly accurate, the reason that it's "off" in the low bass is intentional. The C weighted curve is intended to approximately compensate for the Fletcher-Munson effect which makes bass sounds at the same level seem quieter than midrange sounds. So, the meter reads several dB lower than the actual level to reflect the response of the ear. Boosting the sub level to compensate would result in a response in the bass which would be closer to being audibly flat, although it can't be adjusted perfectly, of course.

JohnK is correct about the C-Weighting curve not being flat... But I disagree about adjusting it to C-Weighting flat.

That should not be done if you want an accurate system because you would end up with non-flat frequency response where your deep bass overpowers the rest of the music.

Well produced music is designed to be heard on a neutral system, not a system that compensates for the inadequacies of the human ear. Use this to compensate for the meter in the bass region. I do this when I calibrate my system and it has never failed me. By the way, if you want a good program to generate test sweeps in, out of, and independent in phase, look here.

In the end, audio is such a subjective field. Do what sounds best to you! I know that I used to be a bass-head before and a flat frequency response used to sound "FLAT" to me. Now if I listen to boomy bass, I almost feel disgusted by it.

DJ:
Thanks for the SVS Link... that's EXACTLY what I've been thinking! I'm gonna print it out! I had never spent much time on the SVS site to stumble across it!

I agree that when all is said and done, it's really about what sound each person prefers. But I also know that, as boomy as my bass is with my current speakers, and the limitations I have in my room and with sub placement, I'd really like to get a handle on some of those issues when I'm setting up my Axioms.

And, as long as I'm doing it for the sub, might as well do it all the way around!

That is pretty much in-line with my philosophy, but apparently, many disagree with me.

Does this read correctly to everyone?

When I read it, there are many "symbols" among the text... certainly not the way it was written. Is anyone else seeing the same thing? I'm wondering if it's actually in my original post, or if it's the way Explorer is interpreting it now....

I compose my posts in Word if they're longer than a paragraph and then paste it over. Is there something I'm missing?

Sorry about this question being in this particular forum, but it obviously makes more sense to keep it within this thread...

I was wondering about that. Your initial post has weird punctuation, but the current post works fine. Hmm... I hate troubleshooting this sort of thing if I'm not in front of the machine!

Try saving the Word file as .txt, see if it looks right there, then try pasting it in. This would at least give us some info. What OS are you using?

OK, I figured it out. It's Word's smart quotes. It changes regular apostrophies and quote makrs into ones that curl into or out of the surrounding text. `` as opposed to '' (a very rough approximation). If you turn off smart quotes in Auto Correct, that should fix it.

Cool!

Thanks- I wasn't even looking for help, just curious if others saw it the same way! It probably just makes sense to save as a .txt to ensure nothing carries over.

I have a lame keyboard that needs to be taken out and shot. I end up missing a pretty high percentage of characters, yet have no problems on any of my other keyboards. It makes spell check and therefore Word a necessity!

Thanks again!

No problem. Probably easier just to turn off smart quotes, though.