SPL calibration confusion! (1 Viewer)

[BraveHeart123]

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

When we say "Mains", we are talking about Front Left and Front Right. Whatever the nomenclature, you cannot disable the Front Left and Front Right speakers. That is the bare minimum you can have in any system; hence the large and small setting for the mains. Get this thing right......no matter where you cross your mains with the sub; the xo frequncy will be played by sub and all the speakers coz of the slope on either side of the xo frequency. How much of that content is played in the speakers depends on the slope (6/12/18/24) dB or whatever. This all is there to seemlessly transfer bass frequencies from speakers to the sub or you would have bass localization problem. Think of the sub-speaker frequency transition as a relay track race where one runner hands over the batton to the next runner. The runner doesn't come to a stand still while handing the batton over to the next runner. Rather both runners are at reduced pace (equivilant of Crossover Frequency Slope) while the batton switches hands. Once the batton is handed over to the next runner only then the preceding runner slows down and moves off the track and other runner blasts off at full pace.

 

[brettecantwell]

Ok I was confused... I was thinking that even with the fronts unplugged that the avr would still try to roll off the sub and bring on the fronts even if no fronts were hooked up... If that isn't an issue i will just unplug them and get new data..

 

[schan1269]

Ok I was confused... I was thinking that even with the fronts unplugged that the avr would still try to roll off the sub and bring on the fronts even if no fronts were hooked up... If that isn't an issue i will just unplug them and get new data..

You missed the point completely from what BH said... Anyway, what ARE your front speakers? What is their -3? Whatever that -3 is is where you should put the crossover...then unhook the mains. Then we'll have an accurate "idea" of what you need to do with your subwoofer...in your room/situation.

 

[brettecantwell]

My speakers are sx fluances and a bic f12 sub. The freq response of the fronts are advertised down to 50 hz but the center and surrounds are rated to 80. I'm not sure if that's -3 as the speaker doesn't have it listed so I would have to actually measure to be sure. I kept the crossover at 80 hz because my avr has only one crossover setting so I can't adjust the fronts separate from the rest. My apologies... I understand what BH was saying but I'm still a newb so bear with me. So just to be extra sure... I need to unplug fronts... Set the crossover to the -3 of the fronts and record the freq response from the sub again...?

 

[schan1269]

What I would do...given the speakers...and sub. Set the crossover, first, at 50hz...unhook your fronts and measure the sub to 50hz(I'll explain the whole thing later...) After you've plotted to 50hz... Change the crossover and do it at 80hz. Still leaving the fronts unhooked. Check the plot for both 50hz and 80hz.(there will be some variance....trust me) What you "might end up doing" is going into your set-up and changing your crossover from 80hz(for movies) to 50hz(for two channel music). It should only take a few seconds to swap the crossover. And you'll be able to figure out the "best compromise" of subwoofer performance between 50hz and 80hz.

 

[BraveHeart123]

Ok I was confused... I was thinking that even with the fronts unplugged that the avr would still try to roll off the sub and bring on the fronts even if no fronts were hooked up... If that isn't an issue i will just unplug them and get new data..

You are right about the sub roll off even if all the speakers are unhooked. But this roll off is near the xo whatever you choose it to be. The avr applies that sub frequency curve, which is always sloping near the crossover point. That is purposely done in the AVRs for seemless blending or you would have serious peak in the crossover region if the subwoofer is in phase with the speakers or a serious dip if out of phase. Another point.....with your speakers setup I would cross my system at bare minimum 80Hz. It's always better to cross your speakers higher than their published -3dB spec for smooth blending. Keeping the crossover low e.g. 50 or 60 hz or even lower demands high current power supply from AVR or an external amp to push the speakers that low down the spectrum, which will cost $$$$. Dedicated powered subwoofers are there exactly for this purpose and are an efficient solution. They relieve the avr of extra burden on the internal amp if you route the power hungry spectrum (80Hz and below) to the sub. Also, avoid using different crossover frequency for mains, center, surrounds even if the AVR facilitates that. Reason..........your sub may be in phase at one crossover point and be completely out of phase at the other meaning your mains may be in phase and center and surrounds will be completely out of phase. I would suggest you plot both the graphs; one with 50hz crossover and another with 80hz. Um sure u will choose the 80hz one. Do not get bewildered with dips and peaks near crossover point (60-80) hz in the raw sub response. Now hook up the mains (Front Left and Front Right Only with 2-Channel Stereo Mode engaged) and plot the response again keeping the 80hz crossover. You would see the response near crossover region smoother than what it was in the raw response. This will be so because of the mains and sub working together and aiding eachother. BUT, you have to bring the sub in phase with the mains before you plot the combined FR. That will give you real life response and facilitate the use of fewer filters in BFD to tame the sub

 

[brettecantwell]

heres some info The tones were a -30dbfs sine wave and volume set to reference (reference= volume that produced 75 DB with pink noise with avr balance tone) HZ...........sub(50hzXO).............sub(80XO).............Fronts (both)..............Surrounds(both) 25..................78............................78.5 30.................82.5..........................83.5.......................72.5 40.................83.5..........................86...........................87 50.................80.5..........................85.5.......................85.5 60.................65.5..........................74..........................82.5..........................67.5 70..................................................73..........................88.............................74 80..................................................77.5.......................88.............................77 90................................................................................87.5..........................87.5 100................................................................................65............................67 110................................................................................85...........................72.5 120...............................................................................81.5.........................75.5 130...............................................................................84..............................74.5 140................................................................................85.5..........................85.5 I ran the surrounds and fronts with both speakers to see where there drop dbs I ran test with multiple speakers and crossover at 60hz was seemed to keep the bass the flattest and smoothest response. but its still not great i has a peak around 90db at 40-50 and has a drop at 70hz which produced 79.5 db.... if i raised the crossover the 40-50 peaks remained pretty much the same but the 70hz tone would drop as crossover went up (droppped to 74db at 80hz with 80hz XO) i still have a drop at around 100 hz also to about 78 but i cant do much about right now. so i guess i should just run the crossover at 60?? the fronts seem to put out some bass enough to work with it and the surrounds dont really seem to but i am not sure if it matter too much as the fronts get most of the action anyways i am suspecting the surrounds dont get as much lower bass as the fronts?? Its hard to be objective but listening to stereo music it "seems" to sound better with 60HZ XO, the lower bass notes seem to be coming from more front and center and less localized.

 

[schan1269]

How close is your sub to a "corner"? That drop at 60 is ridiculous...leading me to think it needs moved out of the corner. Can you put it in the middle of the back wall? Or middle of either side wall?

 

[brettecantwell]

Its about 3 feet from side wall and 6 inches from front wall. so its in the front right corner about 1/4 distance of room width. This setup is in main living area so i really have limited space and it opens up to the dining and kitchen area so there isnt really a back wall until u go about 25 or 30 ft back

 

[schan1269]

Well, "middle of your floor" might yield better results... 6" is too close. In my living room my M&K sits right next to the couch, under a table. 9 feet from the back wall and 11 feet from the side wall. It was put there, cause that is very close to "flat" for the room. It also helps the other speakers in the room are big. I have an Onkyo with multiple crossovers and the crossovers(with width) are sub 80/main 40/center 70/rear 40/wide 100.

 

[brettecantwell]

Can i just sit the sub in the seat and actually measure response with thr meter on the floor in various spots?

 

[schan1269]

Can i just sit the sub in the seat and actually measure response with thr meter on the floor in various spots?

That is called sub crawl.