I have some questions regarding using an SPL meter for setting all speakers to equal sound pressure level. I have read that you should set all speakers to 75db and the sub to 85db. Is this correct? Also I can achieve this but when I am listening to a movie, my volume level will alter this, will it not? Lastly, on the subject of volume control....My receiver shows all negative db readings. A positive db reading would likley blow all of the speakers since it gets louder the closer I get to 00. A setting of -25 is usually pretty good for most DVDs. Am I working the amp harder than I should be? Would it be smarter to bump up the db's on the individual speakers?

Hi Thinkly
I would never have the sub 10db higher than the rest. That would mean that your sub is going to be 10db louder than the rest of your speakers. Your speakers should all be equal. It is not important to have them all read 75 or 65 or 120 just that they are all equal on the SPL.

Volume will infact alter the db readings, but you are not setting your speakers to one specific db level. What you are doing is balancing them so that sound from your listening area is equal from all speakers so sound from one speaker is not over/under powered.

The fact that your receiver only shows in -db is just the way your receiver shows your volume level. Personally I don't like this way of showing volume level. If your receiver is THX cert. than it may be showing the amount of dbs that you are below THX level which I believe is 115db.

I would set my SPL to slow response to by the way...much easier to use that way...Tony

Thinkly,
First, let me suggest that you use a calibration DVD to set up you audio (and video). The two that are probably the most popular are Avia and Video Essentials. Since a movie's sound varies both in volume and frequency almost continuously from frame to frame, it would be difficult to calibrate your speakers' output that way. You need a consistent sound source to set the output(using the SPL meter). That is the express purpose of these two DVDs.

I own and have used Video Essentials. It provides very complete instructions on the DVD. After the first time through it, the instructions are relatively tedious. It calibrates the speaker output to 75dB. The Avia DVD calibrates the speaker output to 85dB. I have never used the Avia DVD but understand that it is much more complete for both audio and video.

With respect to setting the subwoofer +10dB above the other speakers, I have read a number of posts that suggest doing that. If you have a good sub, +10 dB is probably a bit much. In fact, the Radio Shack SPL meter is supposed to register low in the subwoofer frequency range so by setting it to equal SPL levels, the subwoofer is already set higher than the other speakers. My suggestion is do whatever you think sounds best for your system (and only you can determine that; trust your ears). The reference level is just that; reference. You will then know how different you are from the reference level.

With respect to THX reference level, or any other reference level, most people rarely drive their systems to the reference level. Most subwoofers will not even produce reference level output period.

Check out the following websites:
www.hometheaterforum.com; www.hometheaterspot.com; www.avs.com; or search on "video essentials" or "avia" to find out more about calibration.

Hope this info helps.

The reference level is just that;

I know you just mad that probably as simple as possible but I still don't quite get it. Can you try and simplify further what you mean by reference level? I calibrated all of my speakers to have an even 75 db output? What is reference level in regard to this? I do plan to pick up a test CD, probably the Avia. I guess the biggest thing I don't comprehend is the difference between achieving 75 db by virtue of rasing the volume control knob or by attaining it by virtue of raising the db setting on each individual speaker. In other words, I could conceivably achieve 75 db output by having my volume control set to 0db on each speaker and having the volume set to -10 db. (pretty darned high on my receiver) Or I could achieve 75 db by having each individual speaker set to +10 db and having the volume control set lower,say at -45 db. (volume barely turned up) Which is the better way to go? It seems like presently where I have most of my speakers at around 2-5 db+ I have to adjust the volume control all the way up to around -25 while watching a movie. Seems like I might damage the amp. I have to hold the volume up knob for about 5 whole seconds to achieve a suitable volume level. What am I missing here? Again, presently I have set all of my present levels to 75db using the analog RAdio Shack meter and the pink noise generated from the test mode on my receiver. The meter was place at listening position.

Think, if I may.....

The 75db reference level is high because a movie theater is a large volume of space, and has a fair amount of absorption going on, especially when the seats are all filled in with people.

The 'reference' way to set the levels is (although the markings on a volume control really are arbitrary) to set the receiver's volume control to "0" db, and use the individual channel level controls to set each to the 75db level, and, unless you think it's too overpowering, the bass to 85db.

Now, when your volume is set to -20db, the level is (somewhere near) -20db, 'referenced' to the THX standard. Decibels are a relative term. Sounds are so many db louder or softer than another sound. 0db is supposed to be the threshold of hearing (who's?), and 100db is supposed to be the threshold of pain (again, who's?).

Actually, the original term was the 'bel', named after Alexander Graham Bell, but was divided by 10 because instrumentation improved, and the bel was found to be too coarse a scale.

Again, remember that home theater is supposed to mimic the movie theater experience, and the professional terms and references can be too much for many people, their rooms, and their equipment.

Try the settings I've described here, and let us know if you find your equipment seems up to the task, and maybe even easier to set to comfortable levels. Don't forget to make sure the levels are once again matched if you change anything that might affect volume levels, such as tone settings, equipment, furniture, seating positions, and/or equipment connections.

In my theater, the 0db level is as loud as I care to hear, and I like it loud. Of course, the overall level will vary movie to movie, because the engineering and the material itself varies. There are no absolutes.

Larry

This message was edited by Larry Fine on 11/30/01 19:34.11.

Larry,
As Always, Great info. Before I go any further in incorporating your advice, let me tell you that my receiver set to +0 db may be the "threshold for pain." At -00 db there is no volume. It is as low as it can go. I can only take it to around -23db and it is WAY loud and also almost at the end of the spectrum. I won't try it any further for fear of damage. I suspect that 00 db on my Kenwood VR507 receiver is the Maximum volume level. Why are my volume readings all in a negative value. Obviously as you have stated these volume "markings" must be arbitrary. I just wonder what the Kenwood is referring to when the have everything marked in negative dbs. They must have had something in mind? I also wonder if by using the test tone generated by my receiver, if adjusting the bolume control effects the dbs of the test tone or not? Does it when using a test CD such as the Avia?

Think, the negative numbers mean that the volume is so many db below the reference level, which again, is largely arbitrary, as Kenwood obviously has no idea what the signal level of a source or the efficiency of a speaker will be.

I meant the +0db (max), not the -00db (min). If you adjust your channel levels to the point where you can (barely) reach +0db with the main volume knob, you will find that you have a greater "resolution", or range of useable volume knob rotation.

Why have to try to pick a suitable volume from a small portion of the range of knob rotation? Use the full range. You might even find you have less background noise.

Larry

I didn't read the whole post so pardon me if my info is slightly rehashed...

There is such a phenomenon called the fletcher-munson curve in human hearing. It basically states that human hearing isn't logrithmic in its ability to hear low frequency sounds. So, your subwoofer setting is dependant upon the overal level of the system.

At low levels, it could mean as much as 20db boost and around 85 db, no boost what-so-ever. That's what the loudness button on your stereo is taking into condsideration. There is a company who makes a compensator for this called Radio Desing Labs..I've always wanted to try to incorporate this into an HT somehow, but never have had the time, opportunity, or money.

Just my 2 cents.

Matt is correct. The human hearing is less sensitive to bass (and to a lesser degree, treble) at lower volume. Years ago, the 'loudness contour' compensation gradually increased the bass as the volume was lowered, and in fact there was not always a loudness switch. However, these days, it's often a fixed boost, and must be manually defeated when not required/desired.

Ever wonder why the music sounds better, and not just louder, at high volume? It's because the apparent frequency response is flatter. Keep in mind, it's your hearing that makes the extremes seem to drop off as the sound gets softer; it's actually as flat as ever.

The actual "proper" volume for any given music (or other sound, like action soundtracks) is whatever is lifelike. I've read that most people don't realize how loud live music is. I'm not just talking about rock concerts, either. Even jazz, symphony, etc.

I once read that a test is to crinkle a crisp dollar bill a few inches from your ear the next time you are at a live performance, and then see how loud your system has to be playing to make the same bill sound the same, i.e., the relative loudness.

I remember being at concerts where you had to yell to hear your OWN voice. Ever have your system that loud? What? Huh? What did you say?

(*_*)

Larry

Think,

The "trick" is to set all the speakers to the same level, at the point where the listening experience is comfortable to you!

The THX Ultra reference standard calls for all speakers except the subwoofer to "standardize" at 85db, with the ability to "surge" an additional 20db to a peak of 105db. Because human perception of low freqencies is usually that they sound "softer" than they actually are, the THX Ultra standard calls for the subwoofer to run 10db louder than the others (95db, peaks as high as 115db). This is the volume level at which the original movie studio engineers calibrated the channel balances when mixing the soundtrack, and therefore the point at which THX "promises" you will hear the sound just as the engineers intended.

However... This level is also usually louder than is comfortable in most home theaters. I know it is in mine! So here's the tricky part. If you blindly followed instructions and calibrated everything to 85db, but then turned down the overall volume because it's too loud, guess what? You disrupt the channel balances because it's no longer at "reference" level: the center channel dialog may get overwhelmed by the L and R main sounds, the surrounds may be muddy or out of balance, etc.

Instead, find the point at which the overall volume is what you like, and make that your personal "reference" level! A good range for many home theaters is about 10db less, so many authorities will recommend standardizing on 75db. In fact, the Avia disc does just that (explains the 85db reference level and then suggests you'll probably want to standardize lower). But that should be your start point. Play with the volume from there until you find your personal level (for me it turned out to be 77db) and standardize on that. This means that the original soundtrack channel balances will be correct, at the level you find comfortable. Even though it's no longer "THX spec," it should sound great.

Personally, I ignored the volume control display entirely. When I set the standard levels, I set the master volume until the first test tone (Main Left, if you cared) was at my preferred volume without adjusting the individual channel level off "0" Then I adjusted the other channel levels "+" or "-" as necessary. Only after that did I note the volume display setting, so I can return to the "reference" level as needd. So now, if I want to go louder or softer I just turn the knob... Now that I've read Larry's post, I may rethink that philosophy :)

Side note: Bear in mind that anytime you adjust the volume above or below your reference level, you inadvertently change the channel balances to some degree. Personaly, I've never gotten far enough away from 77db to tell the difference without an SPL meter. For example, up around 81db my left back surround drops 1db below the rest, but my ears don't notice.

-Bruce

i just wish i could get hold of an SPL meter. Ive been phoning a number in England every chance i get but its always bloody engaged.

oh well best get off the net so i can phone again.

uuhm

John, if you cover all costs, I'd be happy to buy one here, and send it to you. Always happy to help a fellow enthusiast.

Larry

THanks everyone. I think I am starting to get it. First of all as far as my understanding of reference level. Apparently reference level is basically just the level at which all of your speakers are set to an even number of decibels. In the Dolby example it is generally 75db. On my system this is too loud. So I compromised and set it at 70db. The volume level was at -30db when I did this so I will call -30db my reference level. If I want to be assured that my outputs are as they were when they were calibrated then my volume MUST be at reference level. (In my case, currently -30 db) To account for variances in DVD's I conclude that this would have to be adjusted every time I watch a different DVD or make any alterations to my system whatsoever. Please correct whatever is wrong about my perceptions so far. Ok now another question. On the Radio Shack SPL meter it is set to slow and is placed on 'C'. The instructions say that C is the proper weighting for setting up a room. It also says that A is the proper weighting for testing sound level in a room. The major difference appears to be that is C the meter responds mostly uniformly all the way from 32-10,000 hz. The A range is supposed to be more sensitive in the frequencies 500-10,000 hz . When you all say that 75 db may not be comfortable to listen to, you are saying that listening to a DVD where all of the channels have been calibrated to 75db may be uncomfortable to listen to. In fact the "sound level" in the room may measure way higher than that even if each channel were individually calibrated to 75 db? What uselful information can be gathered from an SPL meter while listening to a DVD? I don't have the Avia or Video essentials CD yet, so once I do maybe some of this will clear up for me. I am just wanting to know if while listening to a normal DVD, like The Matrix for example, the SPL meter can tell anything except for sound level?

Think, the only reason, or for that matter, the only way to adjust for every disc would be if every disc had its own level-check noise track. The meter "hears" the actual loudness, like your ears do, so a given perceived level will read the same on the meter, regardless of the actual volume setting.

The SPL meter is useless during a program, unless you just want to see how loud a given soundtrack plays at a given volume-knob setting, because every movie is engineered at its own average and peak loudness levels.

I still suggest, if your equipment has the range needed, is to reset the levels so your meter reads 70db (or 75) with the volume knob set to +0 instead of -30. This will give you an expanded range of settings. With a typical rotation of 7 o'clock to 5 o'clock, why limit the useful range to 7 to 12 or 1. The max useful loudness should be reached around 3 o'clock.

I can set mine to +0, but it's hard to stay in the room, but then, with a total continuous power capability of 2200 watts, it should be. Of course, it again depends on the recorded level on a particular disc; with some, I can't get to +0, and with others, I can get to +10.

Actually, with my amps rated at eight ohms, but my speakers rated at six, the wattage should be a little bit higher.

Larry

This message was edited by Larry Fine on 12/01/01 23:00.03.

Me again. Another useful point: At least, with separate preamps and amps, the higher you can set the preamp for a given sound level, the lower the gain (if adjustable) needs to be set on the amps' inputs. This will give a lower noise level.

That's because the higher the voltage coming out of the preamp, the greater the signal-to-noise ratio (the background noise level is generally constant, and does not vary with the volume setting), and any noise picked up along the interconnect is reduced by the amount the amps' input level is reduced.

That's why car stereos are going to higher drive levels. (typically 4 or 5 v. instead of the usual 1 or 2 as found in home audio); the higher voltage reduces induced noise. That's also why speaker-level lines are less susceptible to noise pickup.

Larry

This message was edited by Larry Fine on 12/01/01 23:53.23.