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SPL calibration confusion!


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31 replies to this topic

#1 of 32 brettecantwell

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Posted January 14 2013 - 06:05 PM

I recently got a hold of an old radio shack meter (realistic 42-3019) its an analog meter. I turned on my test tone in the AVR and the AVR manual says to set to 75db, So i am assuming the signal is -30dbfs That seems to work alright, but when i go and stick in my disney WOW disc and run the audio tones. It never really says what to set the db to, (says to pick between 78-85) and then set the sub 3db higher. The WOW disc tones are definitely louder so i suspected it might be a -20dbfs signal, so i set the volume to achieve 85 db and i found my volume ended up being a few ticks lower than when i set the speakers with my AVR tones (volume at 64 with AVR and then it was 61-62 with WOW disc) Doesnt at seem strange? Then when i jump to the sub test tone on the WOW disc the DB readings go way higher (like 95-100db) So to wrap it all up, my AVR tones set my sub at about 3.5 on the dial on the back of the sub Then i keep the same settings and the disney WOW disc shows that as reading at least 10db louder then what my AVR tones are giving me. The bass seems abought right now, if i dial the sub back with the disney disc the sub wont be loud enough i suspect. Just wondering if something is amiss or if i am missing something here?? Also, ive found alot of radio shack SPL correction value charts, but do i really need to use that for pink noise tones??? IIRC pink noise has alot of frequencies in the tone??

#2 of 32 Jim Mcc

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Posted January 14 2013 - 07:36 PM

From what I've read, I would trust the audio test tones on the WOW disc more than the receiver's test tones. I'm interested in what other people here say about this. Does the WOW disc have separate test tones for HD audio and Dolby Digital, etc?

#3 of 32 brettecantwell

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Posted January 15 2013 - 12:17 AM

I believe they are all dts hd master.

#4 of 32 Jason Charlton

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Posted January 15 2013 - 01:52 AM

Really, it's all relative.  The point of using an SPL meter to calibrate your speakers is to ensure that they all produce equal SPL at the primary listening position.  Once you get them calibrated to each other, the volume control of the receiver adjusts the gain uniformly across the board.


Setting the subwoofer level is the one speaker that is most set to personal taste - so the fact that you find it a bit more pleasing pumped up a bit is not unusual (or incorrect) at all.


If it sounds good to you, that's all that matters.  You've already done more to properly set up your system than at least 85-90% of the population out there, so sit back and enjoy it!


Are you new to the Home Theater Forum? Stop by the New Member Introductions area and introduce yourself! See you there!


#5 of 32 Robert_J

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Posted January 15 2013 - 10:01 AM

Yes, the correction numbers play a huge difference in calibration. For the sub, room interaction also plays a part. I'll be able to post more tomorrow.

#6 of 32 Robert_J

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Posted January 16 2013 - 07:39 AM

IIRC pink noise has alot of frequencies in the tone??

Yes they do but the loudest tone will register on the meter. For example, my last sub had an inductance peak of 14db at 55hz. When I set the levels, the sub was boomy as heck on music but sounded weak on movies. I went to the next step and measured the in-room response where I found the uneven sub response. I added a sub EQ to flatten the sub response to + or - 3db from 100 hz to 15 hz. If I were you, I would use the WOW disc to set levels and then adjust the sub up until it sounds good. Then go the next step and use my instructions in this post to measure the sub's in-room response. http://www.hometheat...er#post_3831487

#7 of 32 brettecantwell

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Posted January 16 2013 - 06:54 PM

can you dumb it down for me some more lol? sorry i'm still learning. Do i just need to rip some sine waves and play them and record the readings and lay out my peaks and valleys?? What do i need to be able to adjust individual frequencies??

#8 of 32 BraveHeart123

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Posted January 16 2013 - 10:08 PM

Do i just need to rip some sine waves and play them and record the readings and lay out my peaks and valleys??

Yes.

What do i need to be able to adjust individual frequencies??

Some external EQ system will be required to flatten the response. The cheapest is BFD 1124p. It is not actually for home use; but gets the job done for sub duties. I am also using the same. It's easy. There is an ample literature available on home theater shack on how to set filters on bfd. Great piece of equipment, by the way.

#9 of 32 Robert_J

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Posted January 17 2013 - 01:13 AM

1. Wsed a free piece of software called ToneGen to create .wav files of sine waves centered on each frequency measured in the PEQ spreadsheet. If you can set the level, set it at 0db. I made each file 7 seconds long. 2. Burn them to a disc. I put a 10 second pause between tracks to allow me to write down the SPL. I made track one the highest frequency (100hz or whatever it is). 3. Set up your SPL meter on a tripod at your listening position. It should be at ear level and pointed up at a 45 degree angle. 5. Play each tone and measure the SPL. I set the volume so that 40hz (or some tone close to that) measured 85db. As you go through the different frequencies, you may have to adjust the range setting on the meter. If you measure 20hz and it is below 80db, then you set the range down to the 75. 6. When done, enter the values into the spreadsheet. You will apply the correction values to the numbers by checking that option. 7. Look at the graph. A perfect graph should not vary more than 3db in either direction. In my case, I had a 14db peak at 55hz. Not good. 8. You can add virtual filters in the software to flatten the graph more. Once you get the simulated graph looking like you want, you can take the values from each filter and input them into a BFD. After step 6, you can attach the spreadsheet here where Faisal and I can tweak the filters for you if needed.

#10 of 32 brettecantwell

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Posted January 17 2013 - 02:12 AM

OK i played around some, I ripped a bunch of test tones (-30dbfs sine waves) I went from around 25hz to around 180 in 10 hz steps. I then set the volume to "reference" i think it is ( the same volume that produces 75 db pink noise in AVR test tone) I then ran each one and ran the tones. One problem i had is i set the crossover to 200hz ( I only have one stop crossover in reciever, cannot adjust each speaker) I notice even though i turned the crossover up, the mains still still started playing the tones as i went up in frequency... so i am not sure when the AVR started pulling bass from the sub and started pushing the mains, Is there any work around to this?? regardless here is the info i have. Hz is on left, RS meter reading in center and the corrected value on right (using internet correctionn tables) 25hz ..... 78db ..... 83db 30hz ... 83db .... 86db 40hz .... 88db .... 91db 50hz .... 89db .... 90.5db 60hz .... 80.5db .... 82db 70hz .... 78.5db .... 80db 80hz ..... 84.5db .... 86db 90hz .... 73.5db ..... 75db 100hz .... 80db ... 82db 110hz .... 87.5db .... 88db 120hz .... 83.5db ..... 84db 130hz ... 82.5db ..... 83db 140hz ..... 82.5db .... 83db 150hz .... 81db .... 81.5db 160hz ..... 81db .... 81.5db 170hz 77.5db .... 78db 180hz .... 83db .... 83.5db Like i said my AVR is a SR 313 entry level onkyo so it only has one bass crossover in my settings, i cannot adjust indivual channel crossovers. I could definitely hear the mains starting to push the tones but i'm not experienced enough to know when and how much and at what point, the crossover was set to 200 hz, i am assuming the AVR rolls off the sub and rolls on the mains rather than a hard cut off... i am assuming the low bass is all sub perhaps??? Either way here is at least some data, i guess have peaks in the 40-50 hz range??? maybe someone could help me interpret this data???

#11 of 32 Robert_J

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Posted January 17 2013 - 04:32 AM

You have a 16db variance between 90hz and 40hz. That's terrible. Try the free software I mentioned and make a disc matching the frequencies in PEQ. Go through the same process and see what the results are. The graph can better tell you visually how bad things are. Plus the software can easily simulate how much a BFD will help. The $100 I spent for mine was some of the best money I spent on the audio side of my home theater.

#12 of 32 schan1269

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Posted January 17 2013 - 04:39 AM

I think the first thing you need to do is find somewhere else to put your subwoofer...

#13 of 32 brettecantwell

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Posted January 17 2013 - 04:57 AM

Ok i can try moving it some, i am fairly limited to where i can move it ( on other side entertainment center) this setup in in my living room so i have furniture and tables to work around. What about the fact the mains start playing my test tones as the frequency raises??

#14 of 32 schan1269

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Posted January 17 2013 - 05:05 AM

AVR crossover is not a "brick wall"... It is a slope. I would fathom a guess that most AVR use a 12db/octave crossover. So...even "at 100hz"...the subwoofer is still doing a little bit by 150hz...And the mains start picking up by 80hz. If you have to, put your sub behind the seating area...or under a table. Your dip at 90hz suggests one hell of a room node...

#15 of 32 Robert_J

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Posted January 17 2013 - 09:52 AM

From Brett's PM:

hey i appreciate the feed back in my thread, but i seem to have gotten myself confused on how to use this spread sheet.... Where exactly do i get the frequency numbers (what tab) and how do i use this entire tool, sorry if i sound like a newb but its going over my head at this point...

The Measured Response Tab. The first column named Freq. The numbers you get on your SPL meter go into the 2nd column, Raw DB.

#16 of 32 Robert_J

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Posted January 17 2013 - 09:53 AM

What about the fact the mains start playing my test tones as the frequency raises??

If you can't turn them off, disconnect them. We are trying to find the sub's in-room response and don't need phase issues coming into play. Once the sub is playing as flat as possible, we can look into phase.

#17 of 32 BraveHeart123

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Posted January 17 2013 - 05:19 PM

First up, why do you want to cross your sub at 200Hz? If that's the crossover suggested by the AVR auto setup, then I assume you are using some bookshelf sats that rolloff at 200. In any case 200hz is way too high for the sub to cross, which will further trigger bass localization issues that are uglier to listen to than state IMO. In simple words your crossover point is way too high for the sub. Lower it if your speakers allow. I think there is something wrong in your auto setup routine that sets your crossover point this high or you didn't run it correctly. Even average satellite speakers offer -3dB point somewhere near 120Hz. If you still want to go with 200Hz crossover, you are pretty short of luck with PEQ spreadsheet. You can go as high as 112.5Hz (fine tuning engaged) in it to create filters. It cannot tame any peaks or valleys higher than that. The alternative is REW (Room EQ Wizard), which I and many other people use. The learning curve is steeper than that for the PEQ. But once you get the hang of it; it is very simple to use and you can very easily plot your in-room response in less than 10 seconds. I am not trying to complicate things for you, but just telling you the possibilities. In any case, as suggested by Robert, disconnect the mains and run the tones only with the subwoofer in the sound chain. Switch off any internal EQ so that you get an unaltered sub response. One very important thing.....You need fewer and wider filters. If you need more than max 4-5 filters to tame the response, change the sub location. The key is fewer and wider. Avoid narrow or notch filters. Once you get this out of your way, then engage your mains, put the AVR in 2-channel stereo mode. We can then adjust the phase but that comes in the next step.

#18 of 32 brettecantwell

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Posted January 18 2013 - 08:15 AM

Sorry. I didnt provide enough detail... I run my crossover at 80 hz.... The reason i set it to 200 was to get all the bass signals to come from the sub. i wasnt aware of a way to disable the mains and I didnt know just unplugging them would do the trick...... Even with the crossover at 200 I could hear bass starting to come from the mains at well before 200 Hz if I got real close to the mains

#19 of 32 brettecantwell

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Posted January 18 2013 - 08:25 AM

How do i make sure I'm getting a complete to the sub? My speaker config allows me to shut off center and mains and sub but only have large and small settings for fronts.... Im afraid even if i unplug mains the avr will still try to crossover even with just the sub

#20 of 32 schan1269

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Posted January 18 2013 - 09:16 AM

It doesn't make any difference with the subwoofer. I'm not sure "why you care" what the subwoofer does over 80hz. So, set your crossover at 80(unless the main speakers are tiny...then 120-150, whatever) and unhook the main speakers. This "issue"(which is a non issue) affects every single modern AVR made in the last 12 years. Even the "real ones"...




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