Setting levels for two subs - Page 9 - AVS Forum
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post #241 of 249 Old 06-28-2009, 05:32 PM
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Quote:
Originally Posted by sivadselim View Post

You guys need to do the calculations with a certain SPL as the target. Like 75dB, for example. Because that is what is important.

I disagree. In the real world, you typically have a room that you can only do minor modification to if any, and you have already purchased the subs whose ground plane output is already a pre-defined quantity. Unless Seaton talked you into buying the 12 pack of Terraform XL's, you are probably more concerned with what your MAX output capability is, at the seats. This will vary a bit by frequency, and will vary with sub placement.

Assuming the placement is done, you can either level match or gain match the subs. In the gain match approach, both hit their max output at all frequencies at the same time. This is also the max output you can get from your subs in their current location.

With the level match approach, one sub has to be turned down so its level matches the level of the other one at max. In this case the gain increase from running both subs at the same time will be 6 db, but since you turned one down, the 6 db is added to the lower max output, and the summed output will be lower than in the gain match approach.

Anyway, what I am saying is what matters is what you can get for max peaks under each approach. With decent subs turned down well below their limits (75 db for example) you will not notice any difference between the approaches because you should have gobs of headroom to spare (or you have two wimpy subs and you should give Mr. Seaton a call!)
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post #242 of 249 Old 06-28-2009, 09:42 PM
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Quote:
Originally Posted by m-fine416 View Post

With decent subs turned down well below their limits (75 db for example) you will not notice any difference between the approaches because you should have gobs of headroom................

In which case crudely gain-matching (simply setting their gain knobs identically) is probably the easiest route.

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post #243 of 249 Old 07-15-2009, 03:20 PM
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Wow, this thread was a bit of a train wreck! Entertaining, however. And very educational in the sense that I now know who not to take audio advice from!

Would anyone like to take a shot on how one could set the levels on two very different subwoofers? I'm in the process of upgrading (replacing) my sub, and was toying with the idea of adding the older, less capable, sub back into the mix. (With the idea that this might give me a more even FR, spatially speaking. Fill in the gaps, so to speak.)

Anywho, I'd be combining a 15" ported sub with a 10" sealed one. Definitely an odd couple. Level matching is largely out, since the little sub would run out of headroom much much sooner. Gain matching is also a bit problematic, since we're talking about different amps. I'm just a newb, but it seems like my choices are:
  1. Set the gain knob on both sub-amps to 7.5, and call it good. Hopefully this will result in both subs running out of headroom more-or-less simultaneously. (I don't plan on listening super loud, so I probably have some leeway.)
  2. Do a scary test where I have REW output some sort of test signal, and then turn up each sub until something bad happens. Note the respective gain levels and use them as the basis of my actual settings.

Hopefully there is a third way that I'm not thinking of.
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post #244 of 249 Old 07-15-2009, 03:43 PM
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Quote:
Originally Posted by DaveNagy View Post

Wow, this thread was a bit of a train wreck! Entertaining, however. And very educational in the sense that I now know who not to take audio advice from!

Would anyone like to take a shot on how one could set the levels on two very different subwoofers? I'm in the process of upgrading (replacing) my sub, and was toying with the idea of adding the older, less capable, sub back into the mix. (With the idea that this might give me a more even FR, spatially speaking. Fill in the gaps, so to speak.)

Anywho, I'd be combining a 15" ported sub with a 10" sealed one. Definitely an odd couple. Level matching is largely out, since the little sub would run out of headroom much much sooner. Gain matching is also a bit problematic, since we're talking about different amps. I'm just a newb, but it seems like my choices are:
  1. Set the gain knob on both sub-amps to 7.5, and call it good. Hopefully this will result in both subs running out of headroom more-or-less simultaneously. (I don't plan on listening super loud, so I probably have some leeway.)
  2. Do a scary test where I have REW output some sort of test signal, and then turn up each sub until something bad happens. Note the respective gain levels and use them as the basis of my actual settings.

Hopefully there is a third way that I'm not thinking of.

If it were me, I would do one of two things. I would either: a) not use the weaker sub, or; b) use the weaker sub as a mid-bass module, (you'll need an external crossover for b.)

Craig

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post #245 of 249 Old 07-15-2009, 08:38 PM
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I have one question regarding sub woofer level set up. Should I manually set the level at 0 db or the highest level and let the AVR calibrates the sub output along with other speakers' output?
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post #246 of 249 Old 07-15-2009, 09:46 PM
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So, I got this Dragon to the right of my couch, and a MFW in the corner to the left...I gain matched the subs, then level matched them with my rcvr control......man I turned both sub gains to just 10 oclock..with -4 output at lfe out...

Both subs are equidistant to seating position and are on back well next to rear surrounds.

Question is...when I rotate the phase adjust from 0 to 180 on the MFW I get a 6db gain increase...both subs at zero to begin..

Is this just a huge room node increase, or are they coupled and I should leave it there.

Its seems to me I got TONS of headroom now, I can play movies with dialogue in the 60dB range, with LFE events like in Knowing literally causing pain in my ears, yet nothing is getting out of control...

Amps are running cool, barely warm to the touch after extended heavy bass scenes...

I read where both subs should be at zero phase when symmetrically positioned...then why am I getting this boost?



What does everybody like for a sub eq these days for 2 subs?

I am no longer able to watch a movie. I am monitoring a video display with regards to chroma, brightness, contrast and correct pulldown.
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post #247 of 249 Old 07-16-2009, 03:24 PM
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Quote:
Originally Posted by craig john View Post

If it were me, I would do one of two things. I would either: a) not use the weaker sub, or; b) use the weaker sub as a mid-bass module, (you'll need an external crossover for b.)

Not using the smaller sub will certainly be my initial approach! But it's not like I have anything else to do with it. I figured it might be an interesting experiment, if nothing else.

The "good" sub will be EQ'd through a Behringer FBD Pro. That only uses up one of its two channels, so I could use the FBD to high-pass the smaller sub. I think the little sub naturally rolls off at about 25Hz. Should I consider "forcibly" rolling it off at, say, 35Hz instead? Higher?

I guess I'm a bit off topic now. My apologies. I'm still interested in level-setting advice.

(I'm still slogging through that giant "3 inexpensive subs" thread, BTW. That's what gave me this lame idea.)
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post #248 of 249 Old 07-16-2009, 05:19 PM
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Quote:
Originally Posted by theelviscerator View Post

So, I got this Dragon to the right of my couch, and a MFW in the corner to the left...I gain matched the subs, then level matched them with my rcvr control......man I turned both sub gains to just 10 oclock..with -4 output at lfe out...

Both subs are equidistant to seating position and are on back well next to rear surrounds.

Question is...when I rotate the phase adjust from 0 to 180 on the MFW I get a 6db gain increase...both subs at zero to begin..

Is this just a huge room node increase, or are they coupled and I should leave it there.

Its seems to me I got TONS of headroom now, I can play movies with dialogue in the 60dB range, with LFE events like in Knowing literally causing pain in my ears, yet nothing is getting out of control...

Amps are running cool, barely warm to the touch after extended heavy bass scenes...

I read where both subs should be at zero phase when symmetrically positioned...then why am I getting this boost?



What does everybody like for a sub eq these days for 2 subs?

Isn't the Dragon a sealed sub? If so that would explain why you're seeing what you are. Is it a 6dB gain across the board? If so where is your crossover set? I would guess you'd get a gain at some frequencies but phase cancellation in another portion. If you're luck the phase cancellation will occur outside the passband of the subs though, if that's the case then you're good to go (I have something similar going on mixing ported and sealed subs and am getting great results running the ported sub out of phase - but the ported sub's only running 60hz and down...).

As far as an EQ for two subs (if you're going to try to EQ them separately, a different conversation entirely) the Behringer Feedback Destroyer (BFD - DSP1124) is the favorite in the DIY forum, it's cheap (~$100), has 12 PEQ filters per channel, and can save up to 10 EQ presets (the FBQ2496 is also a popular option, it has more filters but doesn't allow you to save presets). The BFD works great but it can be a bit of a learning curve to get setup. If you have REW you can get a USB MIDI card and have REW transfer the EQ filters directly to the BFD which is sweet (I've been doing it by hand lately though, once I figured out how I realized it's easier than digging out the MIDI card and running the cable down the hall to the BFD).
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post #249 of 249 Old 07-16-2009, 08:35 PM
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All speakers set to 80 hz, Audyssy sets ALL my speakers to large btw.. lfe at 120 hz crossover, running just audyssy for eq......

the dragon and mfw have fairly similar FR actually...the corner loading helps the mfw to match the mid wall placed dragon pretty well though..

I thought the house was gonna cave in from knowing on blu ray...

I have a spare PC to set up REW on...but just havent had the time to learn it yet..

I am no longer able to watch a movie. I am monitoring a video display with regards to chroma, brightness, contrast and correct pulldown.
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