Axiom Home Page Forums General Discussion Technical Questions SPL Meter

I am still trying to grasp this SPL thing, I wanted to try and setup the EP500 today and was reading about it on http://forum.blu-ray.com/showthread.php?t=38765 and it stated, Set the db range on the meter to “75" or “80".

How do I do that? I don't see an option on my SPL to set a range.

This is the SPL meter I am using https://www.instrumentchoice.com.au/store/index.php?_a=viewProd&productId=64

Any advice would be very welcome

I would imagine that instruction applies only to analog SPL meters, not digital.

Graeme, surely the meter came with a booklet of instructions? Just from the brief info shown on the site it would appear that there are only two ranges, 30-100dB and 60-130dB, but there would have to be a switch to choose between the two. The comment that you quote from the Blu-ray forum apparently refers to a RadioShack meter or similar which has a relatively narrow range of +/- 10dB around the set number, which is on a round dial marked in 10dB increments from 60-120dB(allowing measurements from about 50 to 130db by varying the range setting). If your meter can in fact measure from 30 to 100dB in one range without having to change some setting, then of course that's even better than having to make a setting that's within 10dB of the sound level to be measured.

75 to 80 dB is your target SPL; you generate a test tone from each speaker and adjust the level so that the SPL readout is 75-80 dB at the primary seating position. For an analog meter, "setting" at 75 means that when the needle is showing 0 dB, the SPL is 75. Typically, the SPL meter has higher accuracy right around the 0 point and decreasing accuracy as the needle moves farther into either side of 0. I don't think it matters for digital meters. Don't forget to set your meter to "C" weighting and "Slow" response. Also, most hand-held meters are not perfectly linear, especially for low frequencies (as are produced by your EP500), and will need to be corrected; so, be sure to look up correction factors established for your particular meter for various frequencies. If you have any other questions, just shoot away. We are here to help.

You sound as if everyone should know these things? I have absolutely no clue what so ever with this, I have never used one in my life and have never even seen a Radio Shack SPL let alone used one.
It's a little hard when you don't understand what you are reading. It may as well be in Japanese.

I'm trying to learn, but maybe I should be a lot more knowledgeable before I ask a question.

Thank you for the info.

You're fine Graeme, keep the questions coming.

If we feel like you're getting too smart on any one topic, we'll start responding in Japanese to keep it challenging.

Otherwise, fire away.

Jason

I finally figured it out. Johnk is audiobot!

an grammerbot, and spellingbot, and attorneybot, and clasicalbot, etc...

I apologize if my post sounds patronizing. It is in no way meant to be. Just trying to help...

A decibel (db) is a measure of sound. An SPL meter tells you how many decibels it's picking up. Turn it on and talk, it should respond. See here for examples of how loud certain things are.

So with that in mind, the point of calibrating a system is so that all of your speakers produce the same volume. The 'set your SPL meter to 70-80db' is specific only to those of us with the old-style radio shack meters that are so popular. They look like this:

See the dial? That sets the range that the needle would register. It's set to "120". If the needle is pointing to "0" then you're hearing 120db (loud!). If it's -2, you're hearing 118db. +4 = 124db. But again, none of that really matters to you because you've got a nice digital one.

Imagine a thermometer. In your mind, you can see that it measures from -20º to perhaps 45º C. Now imagine a thermometer with a little window that only shows you 10º at a time. It'd be up to you to move the little window to the proper range to get the reading. If it's about 25º outside, you'd move the window to view 20º - 30º. The instructions you're reading are for an SPL meter that requires a 'window'.

But with your digital one, you've still got a 'window', it's just bigger. As JohnK says, it looks like 30-100dB and 60-130dB. It actually doesn't matter which you use because either range will give you readings in the 70-90db range that is usually used to calibrate speakers.

What you're trying to do with the SPL meter is to get all of your speaker outputs calibrated to play at the same volume given the same input signal. If they're out-of-balance, surround sound effects aren't nearly as convincing and your system just won't sound as good as it can. If your right rear speaker is closer to your seating position than the left rear, you're going to want to decrease the output from the RR and/or increase it to the LR so that they sound the same. By using an SPL meter, you can precisely dial-in the amount of +/- that you need. It's no different with the subwoofer, except that there are more variables involved with sub loudness because your sub has it's own amp & level adjustments. In other words, a sub's output can be quite 'wrong' compared to the rest of your system.

If all of your other speakers are pumping out 80db worth of test tone at X% volume, then you're going to want your sub pumping out 80db too*. The SPL meter just gives you a highly accurate way of making these adjustments.

Good luck! I'm sure there will be many others along to offer their assistance. We're all happy to help.

*Some folks (myself included) like to run their sub a little 'hot'. Mine is set about 3-4db louder than the rest of my speakers. I just like it that way.

I've dealt with attorneys way too often and JohnK is very emblematic of the profession . A kindhearted attorney with truculence to boot . Wait, did I just say that all attorneys are kindhearted??

PS. John, I hope you don't take that the wrong way.

Well I better brush up on my Japanese then

I see. An everythingbot. Very rare, those.

PeterChenoweth, thank you for the detailed explanation.

So I need to run a test tone and raise the main volume of my receiver until I hit 75 db using the spl. The run the test tones for each speaker making sure they are all 75db.

I think I would have to have each speaker slightly different to each other as I am not in the center, Maybe I would have a difference of -2db for the speakers closest to me?

You adjust each speaker's level according to the reading on the meter, so yes, the nearest speakers to you will have lower settings than those farther away.

Yes. The level that you choose as your baseline isn't that important. The goal is that you equalize all of the speakers to that baseline. I think that most of use use 70, 75, or 80 db. Depends on what you're comfortable with.

Whatever tool you use, whether it's a test DVD or tone generation as a setup function of your receiver, the point is the same. You'll play a test tone through one speaker, perhaps the left front. Then you'll adjust the main volume control to hit a specific db*. Say 75db. Now you'll either go to the next test (on a DVD) or change the tone to the next speaker. Perhaps the center. Now you will NOT use volume knob, but you'll use whatever calibration function that your receiver has to adjust that specific channel level up or down. If it's reading 73db, add 2db of trim. 79db, subtract 4db. You get the idea. And you just do that for every channel in your system.

A sub (including the EP500) really isn't that much different. Your receiver should have a trim level for the sub as well. However, the sub is unique because it will have it's own level control because the sub has its own amp. Usually a knob on the back. There should be recommendations on where to start with the EP500's gain level in the EP500 manual. It's a bit of a balance between how much gain you want to add or subtract from the receiver's trim vs what the EP500's gain will be set to.

For example, if you set the receiver's sub trim level too low, you may send the EP500 too little of a signal to trigger its remote turn on.

*Some receivers, like my Pioneer Elite, automatically set the volume control to a specific point when I tell it I'm calibrating the speakers. In this case, I don't have a choice in what the baseline db reading is. I just match all of my speakers to whatever db is produced by the left-front speaker.

Graeme - just to reiterate, in theory, you want to calibrate the sound level from each speaker so that the SPL meter indicates the same volume for each speaker.

In actual practice, however, many listeners calibrate their center speaker 2-4 dB higher than the rest (i.e. turn it up until the SPL measures 77-79 dB if the rest of the speakers are at 75). This is done because it helps to more easily hear movie soundtrack dialogue. Additionally, as others have noted, some of us like to run our subs a bit louder than the rest as well (myself included). I calibrate my subs to +3 dB than the rest of the system (again, around 78 dB).

Experiment to see what you like. These are just guidelines, but they should get you close.

Jason

You know, considering that many of us run the center a few dBs hot, the sub a few dBs hot, and the surrounds a few dBs hot.... When I calibrate tomorrow, I think I'll just run the Mains a few dBs cool....

Thanks to all for the input, I plan on trying to set it up properly tomorrow when the wife is at work.

The thing that I will have trouble with is the EP500, I have set it up according to the manual that came with it but it does not blow me away. I am a little disappointed actually. But I will have to try and find the best place for it and then try tweaking it.

Graeme, are you familiar with the idea of a "sub crawl" ?

If not, it's an easy way to find a good location for your sub. Rather than moving it from place to place then running back to your seat to see how it sounds, you reverse the process - put the sub in your listening position, play a DVD or CD with a decently broad range of bass, then walk around the room until you find where the bass sounds best. Put the sub there.

Bonus points for crawling, since the sub will be on the ground. If your friends laugh at you, sit in your listening position and make THEM drag the subwoofer around the room.

Yep know all about that did it with my old sub although it ended up back in the same place.

This EP500 is a big bugger and I will be struggling just to get it to my seating position.

My main concern will be fine tuning it once it's in it's new home.

I've been wondering; if trying a sub crawl, does it matter which direction the sub is pointing?

The direction the sub points can affect in room response. I get a better overall response with my sub firing forward in its current position compared to firing into the center of the room.

What is it's current position?

For the most part the subs frequencies waves come out omnidirectional below 80hz or so, so in my opinion it does not matter much which way the driver is facing. Think of it this way, if you throw a pebble into a pond, watch the ripples expand out in all directions.

I could be wrong, but...

My understanding of sound is that all sound waves follow the "pebble in the pond" model, not just low frequencies. That is to say, they all emanate from a point, and travel spherically outward.

The difference is human ears. Human ears have trouble pinpointing sound generation points in the low frequency bands.

Graeme, you say you are not blown away and have set the sub up acorrding to the manual. Is the sub level matched to the speakers with pink noise playing? if so try adding a couple more db to the level for the sub, but the idea for the sub is to not be 'blown away' but it should just be filling in the lower end the speakers are not good at reproducing. You really shouldn't notice a sub is even on during music only during movies.

Currently it is on the right side of the room on the wall facing towards the front of the room. By turning it 90 degrees (shoulda paid attention to that thread) I significantly reduced the 70Hz null and somewhat reduced my ginormous 50somethingHz peak. I can't say it was a night and day audible difference, but it was definately measurable.

Fred - agreed, the direction makes a difference due to the way the sound reflects when facing different directions in your room (think of a rock in the pond that the ripples bounce off -> move the rock, the reflections come back from a different direction). [Can everyone keep up with my ueber-scientific explantions?)

With that said, I've never heard anything close to a night & day difference from changing the direction of the sub either, but when graphing the response of the sub facing forward versus sideways, there are differences.

It's worth trying a different direction if you're trying to find the most linear response in a given position, but it is unlikely to cause a huge difference.

Jason

Keep in mind that any difference may not be due to the direction that the driver is pointing, as such, but that the distance of the cone from room boundaries will vary because of this and may be the variable that's significant.

Correct John, the distance of the cone to the walls in the room is what affects the FR. So turning the sub would change those distances, no different than moving the sub along awall a foot and watching the change of FR.

Well I spent a few hours today fiddling, I have set everything up with the spl and have allowed 5db extra on the sub and 3 for the center. I didn't have anything really decent to play while I did the crawl but hope to get to that later.

I have some blue rays coming tomorrow, so I can test it out a bit better.

I only had some music to try and test it with today, but I noticed the bass sounds much better in the wife's chair than it does mine, which is only 2 ft away. I found that absolutely amazing.
I plan on doing a sub crawl tomorrow and will also try changing the way the sub faces.

As you're discovering and others have pointed out, sound waves are fickle things and small changes can produce big changes. Especially with the low frequencies that the sub produces. I bet an hour or two doing a 'sub crawl' would help out your situation.

In my den/theater room, if you stand up in front of the couch near the center of the room, the sub doesn't really even sound like it's working. Conversely, if you go stand right next to the rear wall, near a corner, you get an enormous amount of sub - far overpowering to the mains. But from our seats it's all balanced appropriately.

Go rent Master and Commander and play through the opening naval battle. Crank it up. If the pounding of the cannons doesn't knock your socks off, then something is wrong with your setup.

You beat me to it. Most two-channel music is probably not the best way to show off the power of the EP500. I'd be curious to know your impressions after watching/listening the battle screnes in Master and Commander. Also, I am not sure if it has been mentioned or not, but if you room is not large, I would set the sub setting to Full and see if you like it better.

You read my mind, I was thinking about it last night and remembered people here commenting about that movie. I have seen it before but figured I would get it out again to see how things sounded. The last time I watched it, it was just OK nothing to go wow about.

I have the sub set to flat at the moment and have tried it on full and half, but with nothing to really compare to I haven't noticed any change.

If you have not been shaken by the EP500 on that movie after proper calibration, then something is not right.

Stop fiddling and just take your wife's chair.

Jason

I did try to convince her that mu seat was a little softer, but she ain't budging

But, while she was at work I played some more and ended up connecting my old sub as well, it seems to have evened things out and the base is sounding much better.

I still have not had a chance to do the crawl, but as soon as Xmas is over I will try to get it done.

Speaking of Xmas ...

Have a safe and happy one everybody

Many people end up doing this on January 1st. Audiophiles or not. Intentional or not.