Axiom Home Page Forums General Discussion Advice from Axiom Owners Advice on Freq. Resp. (Wide Photo!!)

Mark, when you are getting your readings, do you have the meter at your primary listening location? Or is it as pictured in the image? I ask because you may find that you get some notable differences as you move the meter throughout the room. I would think that the curves might look quite different if you set the SPL meter up on your couch for example.

Edit: Actually like mwc said (except without the sub), I think the curves I would be most concerned about if it were my setup, would be the curves taken with the SPL meter in my primary listening location and both M60s running.

Scrolled my way through, Mark. Another illustration of harsh audio realities: some worry about relatively insignificant things like players, amps and wire, while even with good recordings and flat(anechoically)speakers it's the listening room that makes most of the difference. Your graphs are a little bumpier than some I've seen, but nothing unusual. Are you going to run another set with 3805 equalization to note any differences?

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Have you tried to plot a graph with both speakers + sub? The sub might help smooth out some of the low frequencies.

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Mike:
No, I don't. I wasn't kidding when I said that I probably have 30 graphs, but I haven't done both R & L at the same time. I have done both M60s individually, with and without the sub & with receiver set to small and large in several positions.

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I do have some diy room treatments plus lots of plushy stuff in the room.

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At this point, I really wish I had an acoustically "dead" room. I really think that the problem is more small size, square size (especially!) and limited placement options.

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when you are getting your readings, do you have the meter at your primary listening location? Or is it as pictured in the image?

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Andrew:
Actually, this was the only test where I placed the meter in anything other than the "sweet spot"! This was more of an experiment to see what differences would be read in moving the M60 variable distances from the wall. In this one case only, I placed the meter there to hopefully "take the room out" of the readings a bit. Didn't work!

The other readings I've taken of all the speakers show similarly wide swings, though at different places.

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Actually like mwc said (except without the sub), I think the curves I would be most concerned about if it were my setup, would be the curves taken with the SPL meter in my primary listening location and both M60s running.

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I honestly would not have thought that a reading with both M60s running would have been that beneficial. As mentioned above, I did meter them separately and put them on the same graph (their irregularities were somewhat consistent). I would have thought that metering them together would not really accomplish much (in my room anyway) as the speakers are not "centered" within a wall in the room and I would think that they could "smooth each other out", but that doesn't really help me when you have an acoustic guitar on left and a different one on right… does it?

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Are you going to run another set with 3805 equalization to note any differences?

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John:
I didn't for that one particular test because, as mentioned above, it wasn't being metered from my primary listening position. With the other ones I've done, yes, I've re-metered after some EQ and re-plotted on the same graph for "before and after". There's a little difference, but nothing significant as far as the charts go and just tonight I've done some listening with the EQ Off and on my custom setting, and it's close, but I think I just prefer it "off".

Like I said, I can't really make very significant changes via EQ as the Denon 3805, while offering full parametric capability with it's "auto" function, actually isn't that flexible in manual mode. You have fixed center frequencies and no "Q" adjustments, so you're always fudging it a bit!

First comment -- wow, that's a lot of testing

I haven't plotted response as carefully as you but I remember getting readings with almost 20dB swings. Your room might be a bit worse but not much worse.

Other random comments :

How big is the room ? I'm guessing one dimension is about 11 feet ?

Sorry if I missed this, but was the graph you posted with the meter as shown in the picture or in the sweet spot ?

Was the blanket positioned to intercept the first reflection off the walls to your listening position or was it really close to the speaker ?

Have you had a chance to convert the peak & valley frequencies to distances and go looking for those distances ? I was just working the numbers in my head during a particularly dull meeting today and if I didn't screw up you're looking for 4-1/2 foot and 11 foot distances, either wall to wall or front of speaker to wall.

IMO you definitely did the right thing measuring the speakers independently. You can average the readings and plot what you would get with both speakers turned on, but you can't separate the plots if you measure together.

Now I can see your chart.

And I'm sorry to say that is f*ed up. Wow. I have hardwood floors + rug, too, but I've never seen freq. resp. like that in all of my testing.

Dude.

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wow, that's a lot of testing

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Yeah, it is. I'm a "detail" person anyway, but this whole thing's gotten away from me. Once I started testing and seeing results like this, I keep going back with different options to try. Along the lines of what John said, I don't "tweak" my systems once they're set up. I won't explore different cables, etc… but these swings sure seem big and they're certainly and directly affecting the sound.

It's funny…. I mentioned in my original post that I am happy with my Axioms. If I'm happy with them now, how ecstatic could I be if I could tame this room a little? Further, sometimes I think "Well, John likes his Axioms, and Ray likes his Axioms, and Peter and Jack and Tom, yadda, yadda yadda…. BUT….. what if Tom "settled" on his sound and because of his room, isn't getting ANYwhere near the quality that Ray is getting? Since we each hear differently, and we're not hearing each others' systems, how do we know? How do I know that it couldn't just "come together" and I wouldn't love my Axioms 3X as much with a little tweaking?

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How big is the room ? I'm guessing one dimension is about 11 feet ?

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The room is 13' square, with an 8.5' foot ceiling.

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was the graph you posted with the meter as shown in the picture or in the sweet spot ?

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That particular graph was metered as shown in the photo… NOT in the sweetspot as all my others' were…

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Was the blanket positioned to intercept the first reflection off the walls to your listening position or was it really close to the speaker ?

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It was placed to diffuse that first reflection off both the floor and the wall….to that particular meter position.

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Have you had a chance to convert the peak & valley frequencies to distances and go looking for those distances ?

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No, I haven't. I don't know how to do this. Can you recommend an article? I come across "acoustics" articles pretty often, but not ones that explain the hard math and how to do the calculations….

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you definitely did the right thing measuring the speakers independently. You can average the readings and plot what you would get with both speakers turned on, but you can't separate the plots if you measure together.

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Good point; thanks. Yes, to me, the most important plot I've got is the one with the M60s metered independently, with the sub on, charted on the same graph. I can read them independently, or see the very obvious similar characteristics between them.

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I'm sorry to say that is f*ed up. Wow. I have hardwood floors + rug, too, but I've never seen freq. resp. like that in all of my testing.

Dude.

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Gee, now I'm depressed. Wait till you see how drunk I get at your Superbowl party!

OK, I've thought it over and worked through the issues several times. I believe your only option is to package all of your HT equipment in it's original boxes and send it to me as fast as you can! I'll perform an audio exorcism and return it to you. This sometimes takes several years, so be patient. Now, where is that packing tape?

While I recover from that spew, let me ask you something. If you had never started down th epath of reducing the audio to lines, squiggles and charts, would you have just enjoyed the audio? I mean, how does it really SOUND to you? Don't get me wrong, science and technology are good things, but why go looking for stuff to fret over if the speakers sound OK to you? STEP AWAY FROM THE METER WHILE YOU ARE STILL ABLE!

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how does it really SOUND to you? Don't get me wrong, science and technology are good things, but why go looking for stuff to fret over if the speakers sound OK to you?

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If I have to be completely honest, I'm happy. But not thrilled. And many of you are thrilled with your Axioms....so I wonder if I'm missing something.

The biggest variable between my system and others' is the room. I'm really not obsessing over this, I just want to be as constantly amazed and blown away with my sound as I am with my DLPs' picture everytime I turn that on.

I just think there's more there, and if I could tame the Wild Jungle Room I think I could be happier... and stop all this "setup" stuff that I've been working on for the last couple of months, and just get down to enjoying music and movies. I miss it. The "setting up" isn't fun after this long a time...

>>Can you recommend an article? I come across "acoustics" articles pretty often, but not ones that explain the hard math and how to do the calculations….

I'll look for something good. I learned what little I know from a Philips / DeForest "build your own speakers" book about 30 years ago which had a couple of really good chapters on room acoustics. I have not seen anything as comprehensive yet accessible since.

Here's what I remember. Speed of sound is about 1130 feet per second. For any given frequency, the wavelength is <speed of sound> / <frequency>. If the round-trip distance between the walls is 1 wavelength, or a multiple, you get a peak. If the round trip distance between the walls is 1/2 wavelength, or 3/2, or 5/2 etc..., you get a null (valley).

Let's look at your 13' dimension, or 26' round trip bouncing back and forth between the walls. One wavelength round trip gives you a peak -- 1130/26 is 43 Hz (43 hz signal has a 26 foot wavelength), so you should expect peaks at 43, 86, 129, 172 etc.

One-half wavelength (3/2, 5/2 etc..) gives you a null. If 26 feet is a half wavelength, then 52 feet is a full wavelength, corresponding to 22 hz. You should get nulls at 22 (1/2 wavelength), 66 (3/2), 110 (5/2), 154 (7/2).

OK, let's look at the chart. Yep, peaks around 43 and 86, and a hole around 66 Hz. Things rarely work out so cleanly, unless you have a square room

We need to do the same calculations for the 8.5 foot dimension but the 13 foot dimension will dominate since your room is square. The same concept can also be applied in a bunch of other ways as JohnK reminded me -- eg. if your speaker is 4 feet from a wall, or 8 feet round trip, you will get peaks at 141, 282, 423... and nulls at 70, 210, 350...

Even worse, if you have a reflection off wall, ceiling, floor then you're going to get peaks and nulls at frequencies where the difference in direct & reflecting path lengths is one or 1/2 wavelength.

Makes you want to just cower in the middle of the room with a big drink and good headphones, doesn't it ? The good news is that you only have to worry about a the lowest frequencies since at higher frequencies there are so many multiples that they all start to cancel each other out.

I have never played with bass traps, but from what reading I have done they sound like the best solution. Bass traps are basically custom-crafted big, flat boxes which absorb low frequencies to damp out the response peaks resulting from room modes. In theory they should be able to have some effect on the nulls (aka nodes) but nobody ever seems to talk about that.

Here's a first link to get you started. Google on "bass traps" and have fun. EQ will also work but with the drawbacks already mentioned -- you can't eq out a null, only a peak, and you need different eq for different locations in the room. Bass traps (in theory) treat the whole room.

http://www.realtraps.com/art_tuning.htm

Go get that drink now