CurtPalme.com Home Theater Forum

[perisoft]

I've been working on calibrating my audio system, with the help of a Radio shack digital SPL meter, RoomEQ, and a soundcard oscilloscope thing.

I've got six subs, most completely different from each other, behind my couch. So what I've been trying to do is set each one to its maximum clean volume with the amp driving it (they're all driven separately). To do that, I've been using the o-scope with a sine wave output at a few different frequencies, and finding the level where I don't get any visible distortion from 30hz up to about 100.

Thing is, I'm seeing that even at 30hz, it's very hard to get much clean sound out of them; at 25, forget about it. Even the 12" Pioneers driven with a pretty beefy sub amp start to fall over anywhere under 30.

So, the questions:

1) Where's the majority of power used in theater LFE channels? Do they use a ton of 20-30hz stuff, or do they roll it off?

2) Does the LFE channel roll off above 80hz as mixed, since that's the expected roll off of the audio system? Or are there 150hz components of the LFE that ought to get rolled off by the audio system? These subs can hold cleanly up to 200hz...

3) What's reference SPL for the LFE channel? For that matter, what's reference for the fronts/center/surrounds? I can't find this information ANYWHERE; the best I can do is to find that 'your DTS decoder should be set to 7' ( ) and information about the X-Curve (see next question)

4) The X-Curve... it specified LFE roll-off at the low end, and some roll-off at the high end; supposedly this is why home theaters sound 'too bright' - because they don't tend to use the x-curve high end roll-off. So does this mean the mix might specify a 25hz sine wave (or whatever) at 70db, but they really WANT it to be 65 because at 25hz (random example) the x-curve says there's a 5db roll-off?

Oy vay! These specs are all stacked six ways from sunday... THX roll-offs, mix volume, an x-curve added on to that, expected room responses, whether the blurays are mixed with the x-curve 'burned' in (all I can find is 'no... maybe'). Aaaahhhh!

[Curt Palme]

I think your first problem is 6 different subs. A couple could be out of phase with each other, and you've ended up with a wall of mud. Get one or two matched ones, get rid of the rest.

[Curt Palme]

I think your first problem is 6 different subs. A couple could be out of phase with each other, and you've ended up with a wall of mud. Get one or two matched ones, get rid of the rest.

[perisoft]

[ecrabb]

I agree with Curt. Six completely different subs is going to be really difficult to try to make work right together. Unless you've got a really high-performance mains setup, 2-3 subs should be adequate for matching SPL to the rest of the system. This is definitely one of those cases where more isn't necessarily better. Try just turning 3 of the subs off and working with the best 3 and see if you don't end up with something that sounds just as good or better than all 6.

As for extension, yes - there are plenty of movies with content way below 30hz. Some action movies have effects in the LFE channel at 10-15hz, and a few even below that. Check out this really cool AVS thread, Perisoft... They have waterfall frequency plots in lots of cool movies with awesome LFE:

http://www.avsforum.com/avs-vb/showthread.php?t=755493

The problem is subs aren't like horsepower, in that no matter how many subs you have, if all the subs' have no- or unusable output below 30hz, the entire system won't have any usable output below 30hz.

However, subs are like horsepower in that it doesn't cost much to do something mild/average, but it does cost some bucks to get high performance. The practical reality is that any old 15 year old 12" sub is good to the low-30hz ballpark. But, to get good, usable, in-room extension to <15hz at nice SPL's is going to cost $300-500 even if you DIY, and no 15-year old sub is going to get you there.

SC

[Curt Palme]

Hey, want another subwoofer? I've got this 220 volt powered Sony speaker that you can have..

[Curt Palme]

Hey, want another subwoofer? I've got this 220 volt powered Sony speaker that you can have..

[Curt Palme]

A bunch of this will be the room as well. Trying to get anything below say 40-50Hz an a typical HT room simply isn't going to happen. Why not get some Aura bass shakers from Parts Express? Cheap, and you'll get plenty of punch.

[Curt Palme]

A bunch of this will be the room as well. Trying to get anything below say 40-50Hz an a typical HT room simply isn't going to happen. Why not get some Aura bass shakers from Parts Express? Cheap, and you'll get plenty of punch.

[ecrabb]

[perisoft]

[Curt Palme]

I posted a link to the unit in the buy.sell section...

[Curt Palme]

I posted a link to the unit in the buy.sell section...

[perisoft]

[perisoft]

OK, I did have a miswire on one of the subs that was doing some phase canceling. After fixing that and adding my final sub, which went in the corner rather than behind the couch...



Maximum output *while retaining clean output on each sub*. This was checked with the scope individually.

That's full scale, with correctly calibrated radio shack meter. So, that doesn't seem so bad. The question is, what's it SUPPOSED to be... Unfortunately I don't have EQ detailed enough to distinguish 50 from 40 from 30hz, which is really what I need.

[garyfritz]

That chart says you're down about 25dB at 10Hz -- but 15dB at **2** Hz!? Or is that greeen line the phase, not the SPL? The chart says it's both but there's only one line so I'm guessing it's phase.

[greg_mitch]

[ecrabb]

[1031]

[garyfritz]

[1031]

[greg_mitch]

[greg_mitch]

[perisoft]