Interesting sub calibration I did (1 Viewer)

[Patrick Nevin]

This past weekend I got to play with my system a little bit. I had all of the speakers calibrated to the AVIA DVD and wanted to see if there was any difference with the internal receiver test tones. With the receiver at 00, the left, center, and right channels were great. The rear channels were a bit off. Then the sub channel came on. The sub was a few dB’s higher so I made that level with the main speakers at 85 dB. After the calibration, the bass had more range than before. It seemed like the AVIA disk calibration was is using lower bass frequencies to for sub calibration. While I was listening to some bass heavy music on Saturday, the music was awesome and I could hear and fell all of the frequencies played. I have not tried movies with that setting but want to soon. It seemed that the AVIA subwoofer tone played lower frequencies making every bass scene I watch shake everything (which is fine with me) but I wanted more bass range.

 

[Vaughan Odendaal]

I don't think I understand you. Do you mean that after using Avia's test tones, the bass on program material sounds deeper ? How is that possible ?

And you calibrated your subwoofer to 85 dB's ? Apparently, if you want your subwoofer to be at the same level as all the other channels, you must calibrate an additional 4 dB's higher given the insensitivity of the meter.

Dolby Labs and THX's Tom Holminson recommend the same thing. I found out about this not so long ago. I always thought that if the sub was to be set accurately, it would be 72 dB with normal reciever test tones, and with Avia, 82 dB.

--Sincerely,

 

[Patrick Nevin]

Vaughan,

Calibrating the sub's spl with AVIA made the lower frequencies higher then the higher frequencies even when I had it set at 82 dB. I then re-calibrated using the internal test tones and that made the bass sound a lot better. I have been emailing Jim from SVS because i was getting better bass standing up than sitting in my sweet spot. He told me to have the overall volume at 85 db and do sine waves from 15-100 Hz in the standing and sitting positions to see the frequency response. When I am done I am going to send the excel sheet of the db's at different frequencies sitting & standing to him and pics of my room so he can tell me where to put the sub. I have to email him back so I will ask him if the sub should be set at 80 db to be level with the rest of the speakers.

 

[Charles J P]

One thing to remember is that Avia sends a bandwidth limited signal to your main left and right and lets it pass through your receivers crossover and to your sub. If you turn your sub off and run the Avia sub test tone, you should get SOME sound out of your main speakers (actually, it might be that it sends it out of the matching speaker like in Avia your sub test tones are like Left/Sub, Center/Sub etc.) Any way, try it and I think that instead of sending a signal out your LFE channel it just plays like 80dB crossed over pink noise. Because of that, depending on the slope of your crossover you can get a "boost" from your mains when calibrating with Avia. If you DO that means your sub is actually calibrated too low. Now contrast that with most receiver test tones that send the signal out the LFE channel instead. I hope I'm right on all this but I thought this was the explanation from the guy that wrote Avia.

 

[Charles J P]

From the Avia wesite (ovation multimedia)

When I use Avia’s subwoofer audio tests, why I don’t get any output from my subwoofer?

One must realize that LFE and low bass content are NOT one and the same thing. The subwoofer portion of the tests was intentionally placed in the main channels rather than only in the LFE. This allows more complete evaluation of how the sub integrates into overall bass reproduction.

In detail:

1. A great deal of low frequency sound is present in the main channels as well as the optional LFE channel. Not all low bass sound in the main channels is duplicated in the LFE. It is even possible to have no LFE and still have low bass in the sound mix.

2. The subwoofer in a system is optimized for low bass output. It should extend deeper than the main speakers, otherwise there is very little reason to have a subwoofer.

3. The main speakers in a system are rarely as capable as the subwoofer in reproducing low bass. Low bass content in the main channels can be routed to either the main speaker or the subwoofer. This is done be selecting "large" or "small" speaker size. Since most main speakers can still benefit from the subwoofer helping on the very low bass, it is usually best to set speaker size to "small" and let the bass management system route low bass to the sub.

From the above, you should begin to understand why it is important for subwoofer setup tests to account for low bass content of the main channels.

If the subwoofer test tone is recorded on the LFE, the test would not test handling of low bass content in the main channels. The test would produce subwoofer output no matter what size one chose for the speakers, but the test would be useless for the more important low bass content of the main channels. Hence, the AVIA subwoofer tests are recorded on the main channels rather than just the discrete LFE.

Getting no subwoofer output from AVIA is not a bug in the audio section. Many people don't fully comprehend the important distinction between getting overall bass management optimized vs calibrating only the LFE so they choose suboptimal speaker size settings. If one sets all speakers to "large," bc bass management fails to route any low bass content from the main channels to the sub. Hence, nothing comes out of the subwoofer if one does so. You can set your system up that way, but you give up the low bass in those five other channels. At the very least, set your front channel to "small."

How many center speakers are out there which extend as deep and loud as a sub?

Once you have at least one main channel set to route low bass to the sub, you can use the AVIA subwoofer tests for that channel and get better distribution of bass between your main speakers and subwoofer.

What about the LFE level? That is preset at the factory relative to the other channels so setting the other channels for correct bass reproduction should also set the LFE correctly. In truth, there aren't a lot of machines that let you fine tune LFE level independent of subwoofer level anyway.

 

[Vaughan Odendaal]

Patrick, what I was responding to was the apparent quality difference you had between using your recievers test tones compared to Avia.

I was thinking about buying Avia but I'm not so sure anymore. Isn't it a hassle to use ?

Charles, what do you think about the whole "4 dB's over the main channels for sub calibration" thing ? For accuracy, I mean. How do you have your sub calibrated ?

--Sincerely,

 

[Charles J P]

Vaughn, I think you have the concept right but the reality wrong. The Radio Shack SPL meter that everyone uses is LESS sensitive down low. That means if you play a low tone and it reads 80dB it might ACTUALLY be 84dB. So if you are calibrating your sub "hot" related to your mains, and thus calibrate your mains to 85 and sub to 87 or mains to 82 and sub to 85, you are actually calibrating your sub WAY hot by the insensitivity of the meter. For this reason, I usually calibrate my sub flat relative to my mains which means in reality it will be a couple dB hot. This is a preference thing.

 

[Patrick Nevin]

Hey Guys,

I guess I prefer how the sub sounds when calibrated using the internal test tones. I was watching a clip from T3 & the Incredibles. I like how I could feel the upper bass more than it was before. I could feel the upper bass of the guns at the beginning of the Incredibles & I could also flee the punches that Dash was throwing at a guy just before his glider crashed into the mountain. As for the glider crashing into the mountain i could feel that and the bass felt alot tighter and quicker. Jim emailed me back I he said if i want the sub lever with all of the other speakers, lower the volume 2-3 dB. I am going to do 2 dB. Once the frequencies have been plotted , the pics of my room sent to him & tells me where to place the sub. I am going to set my reference volume back to 75 dB, because 85 dB is just too loud.

 

[Charles J P]

You should always do what sounds best. I was just trying to account for the differences you hear. If your main speakers have a peak (or the room has a peak) slightly above the crossover point, you will get more output with the test tones on Avia than the internal ones. Therefore you end up setting your sub lower. Then when you play back actual material, it lacks impact. I'm not saying Avia is wrong, you might be a little hot by calibrating the way you did and that might just be your preference. Any way, one of the problems with not EQing your sub is that you are really calibrating to the highest room induced peak. Because we're talking about a test tone covering a bandwidth and not a single frequency, if you have a 10dB peak at 40hz, THAT'S what your SPL meter is going to pick up and except for that ONE frequency (and the surrounding area) your sub is going to be 10dB too LOW. Calibration is better than none, but getting your sub to sound its best requires EQing understanding of acoustics, room treatments (ideally) etc.

 

[Vaughan Odendaal]

Then why does Dolby labs support the idea that a 4 dB increase over and above the main channels for an equal response reading ?

Tom Holminson from THX recommends the same thing. The sub channel does not work the same way compared to the other main channels. I used to think the way you do Charles, but after reading a few articles, I found out that I was wrong.

Take a look at AVS forum in the theory section. There you will find a thread dealing with this topic as well.

--Sincerely,

 

[Charles J P]

I believe there is a "boost" built into the sub channel. This is why the Dolby "reference" is cited as 105dB peaks for the 5 channels and 115dB peaks for the .1 channel. This is built into the encoded track or the processor specs (I forget which one) and is not something the user is to apply during calibration). I have never heard the 4dB thing. Do you have a source you can provide?

 

[Vaughan Odendaal]

Yes I do have a source. First, I'll point you to this thread:

http://www.avsforum.com/avs-vb/showthread.php?t=640252

Two sources:

http://www.grammy.com/PDFs/Recording...rs/5_1_Rec.pdf

And the Dolby professional guidelines. I'm sorry, I can't link the PDF file at the moment. If you do a search on Dolby guidelines for music or home theater, you should get the file.

It's relatively big. Also, several forum members in the aforementioned thread have said that Tom Holminson from THX also recommends the same 4 dB increase over the mains for HT/hifi use.

--Sincerely,

 

[dave alan]

Patrick,

It sounds like a simple case of running the sub hot vs running the sub closer to the level of the satellites.

Many like the sub calibrated hot, but it results in a bloated low end relative to the higher frequencies. Some prefer the higher level of the subwoofer frequencies calling the distorted frequency response a 'house curve' which they say makes the overall response better as humans are less sensitive to lower frequencies (see Fletcher Munsen curve).

I prefer the overall FR to be as flat as possible and, apparently, you do also. The flatter response allows you to hear the upper bass freqs because the lower bass freqs are not masking them by being relatively too loud

Vaughn,

His name is Tomlinson Holman, or, of late, Tom Holman.

I believe that Charles is correct when saying that the RS meter will give a reading that is lower than actual SPL. One should calibrate the sub 2 dB lower than the satellites when using the RS meter to level all channels, which will result in a closer-to-flat response.

I don't know where the 'add 4 dB' thought you mentioned came from, but it's probably in relation to something else like when listening at lower levels. Using a receiver's pink noise tones and the RS meter and adding 4 dB to the SW level will result in a 6 dB or more hot setting of the sub.

As I said, some prefer this type of calibration, but IMO, it's a distorted FR with a bottom heavy sound at louder levels.

Bosso

 

[Patrick Nevin]

Dave,

When I did the avia sub calibration I set it at 82 and it still sounded bloated. With the internal test tones that did not happen.

 

[Vaughan Odendaal]

Dave, there was no need to be condescending. I knew who the man was but the way in which you corrected me was a bit snobbish I think.

I am following what the authorities are suggesting. Dolby Lab's and Tom Holman both agree with this 4 dB increase over the mains for an accurate calibration.

There is nothing more that I can say about this. It is what it is. Have you read the PDF file I cited ? Or the THX thread in the link ?

--Sincerely,

 

[Brian_cyberbri]

Did calibrating with your receiver's test tones result in a different level for the sub? The receiver's tone may be using different frequencies than Avia. And/or, the receiver's tones are from the LFE signal only, not run through your receiver's bass management setup like Avia. Try turning the crossover in your receiver as high as it will go (ie 150Hz or 200Hz) if it's adjustable, and re-do the Avia tones.

I know that in my case with my HK, the internal tones of my receiver are about 3-4dB off from Avia (and DVE), which uses -27 Dialnorm. Dialnorm tells the receiver to lower the volume (4dB for -27), while the receiver tones are not adjusted like this. DD soundtracks use Dialnorm (usually dropping volume by -4), which is why DTS soundtracks (that don't use it) sound louder.

Case in point - I had been using Avia to calibrate my speakers and sub to 85dB and 82dB or so with my Master Volume at 0. However, running the internal test tones of the receiver, at MV=0 the level was 78dB (maybe .5dB higher). I discovered that this is because Avia and DVE use -27 Dialnorm like most DD soundtracks. So I used my receiver's internal tones to calibrate MV0 as 75dB. But my receiver doesn't have a tone for the sub, so I used Avia (which was reading 82dB (probably about .5dB higher than that), and calibrated the sub at that level to 79-80dB or so.

Once I did that, MV=0 gives me 75dB with the internal test tones, and 82dB with Avia (+/- .5dB), and -10 on my dial gives me 65dB with the receiver's tones, and 72dB with Avia.

 

[Patrick Nevin]

Brian,

I know the sub level was a little higher using avia tone compaired to the receiver tone. I did a waterfall chart using the avia disk wit the left channel and there was not consistency with the frequency on that channel. I haven't checked the receiver test tone yet but will do that soon. I like the sound much better and I can't wait till I can check the frequency response levels when I sit and stand because of the 2 db increase in bass while standing.

 

[Brian_cyberbri]

The Avia tones fluctuate a lot so you can try to get an average reading/number. Say you have a 6dB hump at 55-60Hz, but a 4dB dip at 70Hz. If the tone was only around 70Hz, you'd end up calibrating too hot, or too low if the tone was only at 55-60Hz. So the tones do jump around a lot to try and give a better picture of the level. (helps to use Slow weighting)

What you can do is download test tones for individual frequencies and either play them off a computer or burn them to a CD. Then you can find a pre-made Excel sheet on the web somewhere and plot the frequency response. I talk about how I did that with my Acoustech H100 here.

 

[timNGY]

Patrick,

Since you stated you are using receiver's internal test tones, shouldn't you be calibrating to 75dB? I think only AVIA test tones is calibrated to 85dB.

 

[Brian_cyberbri]

Yes, you calibrate to 85dB with Avia, or 75dB with the test tones. They will both yield the same volume (except for the 3-4dB offset for Avia/DVE because of the Dialnorm -27 setting).

Ie., on my receiver I was calibrating with Avia so that Master Volume 0 = 85dB. Now I have calibrated with MV 0 = 75dB with the internal tones, which is about 3-3.5dB louder than Avia because of Avia's use of Dialnorm. So by using Avia, 0=85dB with Avia and 78-78.5dB with internal tones. Using the internal tones, 0=75dB, and 82dB or so with Avia.