Hi everyone. I'm curious about how folks have their subs calibrated relative to the rest of their speakers. I've SPL matched my LFM-2 to the rest of my speakers using the 990 test tones and consequently found the bass a little lacking in movies.

The purist in me says leave it flat to stay as true as possible to what the director and sound engineer intended. The hedonist says to kick it up a few notches because... well, it just sounds better.

So, in your system, do you like your sub flat or hot for movies? For extra credit, how about music?

For movies, I've got it flat (especially with the SMS-1 in the mix). For music, I run the sub a couple dB cool.

I initially let my receiver set the level using it's auto setup. It set the sub at -4db so I guess the sub's gain was too high. I tweaked the LFE trim in the receiver to 0db, so relative to the receiver it is now 4db hot. I can adjust the level on the fly via the remote in case the bass level seems too low/high.

If it sounds good to you, set it where you like it!

This my theory when setting up subs. Use your ears to get it where you like it. If you need a reference level, the best sweep I've found is the subwoofer sweep on any THX certified disc. It sweeps down from 200hz to like 20hz (I think)and you can really hear if your subwoofer is set right by how clean the transfer is from your mains to your sub. You can also hear room nodes very nicely. Those are the parts where the volume goes up and down for no other apparent reason. Very educational for your system...

So, with a meter, you watch the spls as the sweep moves down. If the spls change as you pass the crossover frequency, you need to make a adjustment. Is this correct?

No meter needed. Just use your ears. If you hear a large volume change when the subs kick in, they're probably set too high. I suppose you could do it with a meter but your ears should work just fine.

Your just looking to get the smoothest sweep possible from end to end. Unless you have your room tuned, however, you're going to hear some bumps. Just try to make it as smooth as your current system allows.

The other "by ear" bass check for subwoofers is playing a CD containing either acoustic piano or acoustic bass. Listen closely to the bass lines and see if you can hear your crossover point as the bass line goes from higher to lower. Again, if the change to your subwoofers is too much, take a little level off of them. This also relates to what Gonk mentioned where his bass levels are different for movies and music. You're probably going to want more "boom" in your movies than in your music. It's really all about what makes you smile.

I tried Jason's suggestion to use the sub calibration in the THX optimizer. Sure enough, my "flat" calibration resulted in the sub being audibly quite a bit lower when doing the frequency sweep - by about 8dB.

Anyway, after the new adjustment...I listened to some bassy scenes in a couple different movies, and the bass is definitely no longer lacking - in fact, it may be a bit much for my taste. I suspect I'll have to compensate for music now too. We'll see. Thanks for the advice, Jason.

Anyway, this is interesting since it suggests that the 990's internal test tones are not so useful for sub calibration... seems like a sweep tone ala the THX optimizer would preferable to the pink noise approach...

This isn't terribly surprising. RTA's and level meters have a lot of trouble with bass frequencies. It requires a lot more processing for those devices to accurately gauge bass performance. For instance if you look at the Galaxy Audio meters , you will notice that the CM130 is half the price of the CM140. But the CM130 is only rated down to 125hz, where as the 140 is rated down to 31.5hz.

Also the human ear can easily be fooled while listening to pink noise going from speaker to speaker, and suddenly to the sub. So a sweep works better since you are continuously listening as the tone changes pitch.

Now since I don't own a 990, and am not familiar with its programming, I can't state whether or not Outlaw dedicated a bunch of processing to that feature to ensure truly accurate bass setup. But it is possible they did, and in that case mic placement and sub placement issues could have caused the mis-alignment in your system. Moving the mic or sub just a small amount (a foot or so) could cause it to end up in a peak or cancellation node within your room.

With regard to SPL meters what is the best value today? I have the Ratshack meter, which I have heard was bought by ATI, and recoginize the errors of my ways. I would like something that will be more accurate at levels down to 5 Hz.

just because something is set at a reference level or calibrated by a machine to be flat, doesnt mean it will be the way you prefer something to sound. we have hearing loss, personal taste, etc. i recommend using reference settings as a "reference" of where to start rather than the perfect setting for everyone. no one is going to tell me how i like to listen to my movies or music. also you will have to adjust settings sometimes because all media is not normalized in sound or in sound quality. one dvd might sound great, but another needs more volume in certain ranges, etc. make yourself happy rather than let references or standards rule your listening habits.

The problem with meters is that they only take a measurement in one spot. With bass issues, you can move the meter a few inches one way or the other and get a different reading. I think the best meter today is to get a laptop with a measurement microphone and use a spectrum analysis program. This way you can compare different results to get the best average level for your room.

As for the Ratshack meter, I remember reading about a chart that will adjust the curve to make its readings more accurate in the bass range. Here's a link:

http://www.svsound.com/questions-faqs-rscomp.cfm

Thanks, Jason J. I have heard about this conversion table before, but could never find it. One question though -- if one uses the speaker calibration test tones in the 990 or some other receiver/processor for setting levels, what is the effective frequency for determining the correction of the meter's response for the sub level?

Me too. I use the 2 channel offset to "cool" it down by 6dB for 2channel listening and leave it at 0dB for movies.

Perhaps the original poster has a placement issue? With "boomy" movies, my LFM-1 literally rattles the walls at anything close to reference levels.

Cheers,

To add to the chaos .... I prefer throwing the Video Essential disk in the DVD player and use the test tones on the disk. This way i am testing the entire audio path.
I have found a difference between the dvd player and the 990 test tones (up to a couple of dbs).

Jason J,
Thanks for the chart. good stuff.

When using low frequency pink noise to level match a sub, should placement matter?

Depending on its position in the room, the sub may sound more or less loud to a meter at the same gain setting. However, once the sub gain (or trim) is adjusted to compensate, so that the meter indicates the loudness of the sub is the same as the rest of the speakers in the room, you'd end up with more or less the same result regardless of where the sub was placed. Wouldn't you?

To be clear, I do understand that placement does matter for a sub, just not how it matters when level matching relative to other speakers with pink noise and an SPL meter.

I have used the Velodyne SMS-1 parametric equalizer and found that moving the mike (pickup) around does make a significant difference in the readings. I am sure that an SPL meter is even less sensitive. When it comes down to the nitty gritty I think Curegeorg is right, it's best to use the end results in determining what sounds right via the ear. The mechanical method, although we all want to get it as close as possible, is a second guess in comparison with the EAR, opps, I mean END results.

Yes. Even though multiple frequencies are being played at even levels, when your room interaction is added to the mix some might be much higher and/or lower than others. Most people, except in the extremest of situations, will not be able to hear enough of a difference between those levels at individual frequency bands. With that much extra energy (or possibly not enough depending on cancellation/enhancement) the meter is going to misread as it will detect a lot of energy, even though much of it is at specific bands instead of even across the board.

Now if you had an RTA (real time analyzer) which would be able to show you the amount of sound pressure at different bands, you could potentially compensate for those issues, or even have a visual guide to moving the sub around until you find the spot with least problems. Most people do not have that capability as stand alone units that would have any reasonable bass accuracy are very expensive (>$1000), and easily available software solutions are not terribly accurate either, and depend heavily on the mic and other hardware hooked into your machine.

As attested to in other parts of the forum, getting the sound right in any room has just as much to do with room interaction as it does with the reproduction equipment – a little spent on room treatment can go a long way.

With mid and high frequencies, there can be reflections and multiple signal paths in a room that detract from the accuracy and intelligibility of the sound. For the lower frequencies, there are the added troubles of room resonances and standing waves in different places that result, depending on frequency, in near nulls or huge boosts in sound pressure level.

Without room treatment, what’s a poor person to do? Even on a small budget, an SPL meter is a worthwhile investment. Some reputable free versions of software can allow you to generate tones. While sine waves have disadvantages in some ways, they can be very helpful in others. One can set up steady tones or slow sweeps through the subwoofer range and watch the SPL meter as one moves the meter horizontally and vertically from listening point to listening point. (Aside: I’m not one that says, “if I have consistent levels in the middle of the room 3.5 feet above the floor, I have the best sound in this room.”) Moving the subwoofer a foot at a time, then 6 inches at a time, then 3, 2 or 1 inch at a time and watching the meter at various low frequencies as one moves the meter through the same listening positions over and over again can help a person determine which subwoofer location presents the least variance in overall level. Likely one can reduce wide variances, but it is unlikely that anyone can achieve, without additional treatment, a near flat response in multiple seating positions. Go for reduced variance in the more likely listening positions.

Once you have found the best compromise position for a subwoofer, the level setting(s) for your subwoofer will probably need some adjustment once again. Whether automated or by manual means, placing the meter’s microphone, or the auto EQ microphone, at a point of least variance, and in the most likely listening positions, is best. Some auto EQ equipment will allow the user to obtain ‘readings’ at more than one point and then make adjustments to tame the worst of any variances. If your budget and significant other allow, room treatment would be the next step.

If one expects perfection, they are likely in for disappointment. On the other hand, one can obtain meaningful improvement by reigning in nulls and peaks with the methods they have at hand.

BB4TB, how do you know if your room treatments are working? I am asking form the point of view of - this is something I have never done, have no experience with and am a little confused as to what to buy, how to use it affectly, that sort of thing. I mean, can you start out small work your way up seeing/hearing results along the way. Can you really hear the difference by hanging some foam on the wall or in the corners? How do you know you have a problem to begin with? How does a guy sitting in a 5.1 room with an SPL meter in hand figure out he has room treatment problems?

Let's face it, I can sneak another component into the rack, but this is re-decorating, by God.

To know what has changed in a room following any changes, we’re back to some testing, either by some analysis software (for a more complete picture) or at least the ol’ RS SPL meter.

For subwoofer placement and low frequency room treatment, using some free tone generating software, one could run a slow sweep from about 20Hz to 80 Hz and get a rough idea of where any ‘booming’ or ‘missing’ frequencies might be. Then pick some individual steady test tones in the problem ranges and get an idea of where some of the trouble spots are by walking through the room watching the SPL meter rise and fall. Try an adjustment of placement or treatment and then repeat the testing to see if the response at the trouble frequencies has become more even as one moves the meter around the room.

If you’re not sure what the benefits of a treatment will be, do you have something already around the house that could be used temporarily to simulate the real thing?

A good while back someone in this forum was having issues with a center speaker on top of a projection television and was unsure if the resulting visual interference was magnetic, electronic or a physical interconnection. For the sake of diagnosis I suggested folding a bath towel and placing under the speaker so that vibration from the speaker would not be easily transferred to the television. That solved the problem, so this particular Outlaw ordered something designed for the purpose and better looking than a folded bath towel.

To experiment with bass traps, try one or more mattresses from a single bed standing upright and gently leaning against a chair such that the mattress is almost diagonally in the corner, with a few inches gap on either side so that some sound can get around the mattress. Drape a soft blanket over the front and back of the mattress and chair.

To experiment with damping higher frequency reflections, try beach towels hanging like folded drapes in certain places along the walls, perhaps using the ‘mirror’ technique to determine trial locations.

Yes, mattresses and towels are not the best compared to products designed for the purpose, but if you note some positive improvement with mattresses, blankets and towels, then obtaining the correct treatments should only be better. I think there was a positive experience related by one or more Outlaws in a forum topic called something like 'DIY Room Treatments.'

And, yes, I’m sorry to say that the kind of treatments that will reduce reflections and standing waves will have to be introduced into the environment, potentially disturbing the current arrangement of furniture or 'redecorating.' If that is going to cause WW3 in your household, then do what you can with some adjustments to placement and let peace prevail.

Hey MeanGene, good to here from you again. You know even doing the bare minimum of treatment for your room can make some pretty cool improvements in your sound. I experimented with just the basic level of room treatment a few years ago in a rental house and got some pretty positive results.

Anyway, There is a lot to cover on this topic and Ethan Winer does a great job at it. Far better than I could ever do. Here is a link to his site with tons of good information on this issue.

http://www.ethanwiner.com/acoustics.html

E'pin Sen Ob,
What a smookin' site.
Thanks.

Cool tmdlp, glad you liked it. Ethan Winer has a lot of sound advice. I only wish I knew half of what he knows.