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Discussion Starter · #1 ·
Shortly after getting my AVM-20, I went out and bought the trusty RS analog SPL meter. I used it to set the levels of all of my speakers, including the subwoofer.


Every time I changed a parameter, I recalibrated and made sure that all channels were at the same level. This produced pretty good results with movies, although I found that the surrounds didn't seem quite as prominent as I expected them to be. I chalked this up to my surrounds being dipoles and the physical characteristics of my room working against me.


So, a few weeks ago, I read an article about bass management and decided to change my mains to be "small" in the AVM-20 and cross them over at 60 Hz. My mains are Paradigm Studio 100s, so their bass performance is quite capable. I set them up as small, ran the test tones and recalibrated. I made only some very minor adjustments (less than 2 dB).


A few days later, I started listening to CDs on my system. ... and I hated every CD I listened to. As I listened to CD after CD, I thought "these are simply *horribly* recorded. They are nearly unlistenable." After I got to the 4th or 5th CD, I put two and two together and checked the configuration of my speakers. I had forgotten about having changed my mains to be "small". I adjusted the configuration to large mains and listened to another CD. Low and behold, I had *great* sound again! The missing bass, that was making every recording sound thin was back in spades. The fatiguing, beatless, lifeless sound I was getting was the sole result of not nearly enough bass in the reproduction.


I was puzzled by this, as I carefully calibrated the subwoofer levels with the AVM-20 internal test tones and the RS SPL meter. This made me wonder about DVD movie sound as well. After all, even with mains set to large, the level of the subwoofer controls the level of the ".1" bass channel.


So, I changed the mains back to small, put in a CD with fairly intense bass that I am *very* familiar with and started adjusting the sub level. I did this, not from the "levels" menu, but from the subwoofer "tweak" button. I adjusted it to +7 dB and did some listening. That was a little bass heavy. Back down to +6 dB provided a much closer to "real bass" level. Music now sounded fairly well balanced, compared to the mains being set to large.


So, on to movies. I played a variety of bass heavy scenes, including the opening sequences of AOTC. The bass is now pretty impressive; much more than I've heard from my system in the past. This is no surprise of course; I'm sending four times the power to the sub compared to what I've been sending it for months.


I'm left with a dilema though. I *know* how music should sound. I've listened to countless "stereo" systems over the years and I have a very good feel for tonal balance among other traits. So, I'm pretty confident that my settings of the subwoofer are approximately correct for music. For movies though, I don't have a great frame of reference. The vast majority of information below 60 Hz in movies is special effects. It's much harder for me personally to calibrate, by ear, to the sound of gunfire, or simulated explosions, than it is to calibrate with timpani, kick drum, bass guitar, and other "known" instruments.


I'm left with some nagging questions: Why is the SPL meter calibrated configuration so obviously wrong for stereo recordings? This effect isn't subtle; It's *glaringly* obvious. Does the AVM-20 have some different behavior with stereo sources than with 5.1 sources? I.E., is the SPL meter based calibration reasonably accurate with 5.1 channel sources, but way off for 2 channel sources? Is my SPL meter simply broken? Is the AVM-20's bass management broken in some way?


Any insight into this will be greatly appreciated.


Thanks for reading.


Brian.
 

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It sounds like the level of the subwoofer is too low. I own the Anthem AVM-20, Paradigm Studio 60s, and a Servo-15. Instead of calibrating the sub with an SPL meter, I use Sound & Vision's HT Tune-up disc and set the level "by ear" with their alternating front/sub test. I find this sets the sub about 8-10dB hot according to the SPL meter. This should give you very satifactory results.
 

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Discussion Starter · #3 ·
I may try this with VE, or with the internal test tones.


In the mean time, I've done some more listening and I think my sub definitely needs to be moved to get a better frequency response.


Thanks for the input.


Brian.
 

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Wow, I had a very similar experience. I have an AVM 20, Active 40s and a Servo-15. To calibrate my sub I connect both analog and digital outputs from my DVD player to the AVM 20. On the analog input I set the AVM 20 to bypass bass management. I play a CD that's got a lot of bass. I switch between the analog and digital inputs and adjust the level of the sub to match the bass output when the Active 40s are feed a full range signal. Like levind, this usually ends up 8 to 10 dB above the other speakers.
 

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the radioshack meter is very inaccurate at low bass levels. I don't have a link handy, but there have been many posts in the past listing what to add/subtract from the meter's reading at various freq's to get the actual SPL. The effect is exaggerated at the extremes of high/low, but the lows are the worst, especially below 40Hz.
 

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Discussion Starter · #6 ·
Jake,


I've read about the corrections necessary for the RS meter. I kind of mentally averaged them over the 0 to 80 Hz range, and they come out to only a little higher than 0 dB. In other words, when you are taking a reading from your sub and the sub is being sent pink noise, the SPL read by the RS meter is pretty close to accurate. If anything, you might need to add a few dB to the reading for it to be accurate.


My problem is sort of the opposite. The sub sounds too low, even though the meter says it is right on.


Through doing more listening, I think I've determined that I'm missing some band of bass in the sub. It seems to have very little output from 45 or so Hz, up to crossover. This may be due to the way the sub interacts with my mains, or it may be an acoustic (placement) problem.


I'm going to try to measure the frequency response, in room, using either test tones and the meter (and the correction table of course), or a computer program like ETF. I'll be working on this over the next few days.


I'll report back what I find. In the mean time, if anyone has a good procedure for getting best flat, in room response from a subwoofer with mains, I'm very interested in hearing it.


Brian.
 

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From what you describe, ti sounds like the sub level "matches" the other speaker levels in general, but due to room resonances and nulls does not have flat response. It seems likely that the freqs below 45Hz are very high and are actually the ones driving the meter. You are on the right track with a detailed frequency response test as that will give you a curve allowing you to see what you need to correct. If you search this forum for terms like "subwoofer placement" and "tuning", you should get a wealth of information. An internet search engine will return many helpful tips as well.
 
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