Do I need a Galaxy CM-140

[gerhardwessels]

Hello Everyone,

This is my first post and I apologize beforehand if this topic has been dealt with already but what I have read regarding SPL meters thus far has left me confused .

I already own a Behringer ECM8000 mic, a Behringer Eurorack UB1202 preamp and a Behringer FBQ2496 feedback destroyer. Am I right in saying that I only an SPL meter to calibrate my setup to 75db for REW and that I can use the ECM8000/preamp combo to do actual measurement?

The thing is I live in South Africa and I cannot get a Galaxy CM-140 locally which means I'll have to import it from the States and with shipping, tax, duties etc. it will work out to quite a lot of money. I can however get an EXTECH 407727 SPL meter locally at a reasonable price. Hopefully it would get me close enough to the 75db level ?

If I want to setup a room curve, surely I only need a relative room response to see where the peaks/valleys are and set the EQ accordingly ? Do my levels have to be absolutely correct?

I would very much appreciate any advice.

Regards,

Gerhard

[gerhardwessels]

gerhardwessels wrote:

Hello Everyone,

This is my first post and I apologize beforehand if this topic has been dealt with already but what I have read regarding SPL meters thus far has left me confused .

I already own a Behringer ECM8000 mic, a Behringer Eurorack UB1202 preamp and a Behringer FBQ2496 feedback destroyer. Am I right in saying that I only an SPL meter to calibrate my setup to 75db for REW and that I can use the ECM8000/preamp combo to do actual measurement?

The thing is I live in South Africa and I cannot get a Galaxy CM-140 locally which means I'll have to import it from the States and with shipping, tax, duties etc. it will work out to quite a lot of money. I can however get an EXTECH 407727 SPL meter locally at a reasonable price. Hopefully it would get me close enough to the 75db level ?

If I want to setup a room curve, surely I only need a relative room response to see where the peaks/valleys are and set the EQ accordingly ? Do my levels have to be absolutely correct?

I would very much appreciate any advice.

Regards,

Gerhard

Anyone??

[Otto]

Hi Gerhard,

Yep, if you have the ECM8000 mic, a preamp and REW, all you're really going to use the meter for is to generally calibrate the input levels for the mic/pre combo.

I believe that your locally available SPL meter will get you close enough.

How do you calibrate the levels of each channel right now?

Good luck!

[gerhardwessels]

Hi Otto,

I'm not doing anything right now! I first want to get all the stuff I need - like SPL meters etc.

I'll be ordering an SPL meter today

[Vaughan100]

Hi there gerhardwessels,

Nice to see another fellow South African on the boards. I currently have the Radio Shack SPL meter which I imported and it wasn't expensive at all. Came up to R450.00. Does the job very well except for calibrating subwoofer levels.

I'm in the process of trying to get the Galaxy CM-140 but for some strange reason, I can't find a place that will ship internationally ! I've tried so many online shops and no one seems to ship it.

Do you know of anyone online that would ship ? Apparently it is a pretty substantial improvement over the Radioshack meter, especially for calibrating subwoofer levels.

Cheers.

--Regards,

[brucek]

Apparently it is a pretty substantial improvement over the Radioshack meter, especially for calibrating subwoofer levels

I don't really understand this statement.

Can you explain?

brucek

[Vaughan100]

The Galaxy CM-140 apparently tracks the C-Weight curve far more accurately compared to the Radioshack meters. And the levels on the Galaxy are accurate for the warble tone.

I'm surprised you didn't understand my statement above. It was you who told me that the Galaxy meter was far better than the Radioshack in the first place especially for setting subwoofer levels.

--Regards,

[brucek]

I'm surprised you didn't understand my statement above.

Most receiver test tones, and even REW's pink noise is band limited from 30Hz to 80Hz in an attempt to capture a representative level of a subwoofer.

From 30Hz to 80Hz, both the Galaxy meter and the RadioShack meters track a C-Weight curve almost perfectly.

Below are two charts showing the Galaxy versus a C-Weight curve and the RadioShack meter versus a C-Weight curve. Both are from 30Hz to 80Hz.

Galaxy versus a C-Weight curve



RadioShack meter versus a C-Weight curve


The Galaxy meter has a better low end response than the Radio Shack meters and more closely matches the C-Weight curve down to 10Hz. The Galaxy meter also has a far better and more consistent high frequency response in case you want to attempt full range testing. But for something as basic as setting a subwoofer level, both types of meters are identical.

brucek

[Vaughan100]

Now I don't understand. I PM'ed you and you flat out told me that the meter would be better for things like setting levels. Now you are saying that it's not better ?

If I set the Radioshack meter to read 75 dB's then it's actually reading 77-78 dB's or thereabout according to members here and on other forums. So if I go from that SPL meter to the Galaxy, there will be virtually no difference whatsoever ?

I don't get it.

--Regards,

[brucek]

So if I go from that SPL meter to the Galaxy, there will be virtually no difference whatsoever ?

Depends on the frequency. As I said above, from about 30Hz to 80Hz the Radio Shack and the Galaxy would be fairly close to the C-Weight curve.

Below that range, the Galaxy tracks better and more closely to the C-Weight than the Radio Shack. Likewise for full range measurements. I would recommend the Galaxy for that.

brucek

[Vaughan100]

I want the Galaxy for calibrating my subwoofer levels accurately. Nothing more. I want to know that 75 dB's is 75 db's and not 78 or 79 dB's; which the Radioshack is doing.

If you are telling me that the Galaxy SPL meter would have the same discrepancy in the readings then I'm not sure. I was told that the Galaxy meter would be consistent and accurate in it's readings. The Radioshack meter is not consistent and is not accurate in it's reading for the subwoofer warble tone.

If the Radioshack meter reads low for pink noise measurements (in AVR) I thought that the CM-140 would not read low. Hence be more accurate. Now I don't know what to think.

--Regards,

[brucek]

If the Radioshack meter reads low for pink noise measurements (in AVR) I thought that the CM-140 would not read low. Hence be more accurate. Now I don't know what to think.

They both read low at low frequencies (from flat), just as every C-Weight meter does. The calibration files we provide on our site will show you how much they read low from flat.

A C-Weighted meters response will track a C-Weight curve. The Radio Shack and Galaxy don't track it exactly, so we provide a cal file that's a bit more accurate. Over the 30Hz to 80 range, both those meters track the C-Weight curve quite well though.

Certainly a meter that tracks a C-Weight curve will read a 75dB signal differently at every frequency where the influence of the C-Weight filter is not zero. That's the way you want it because your ears hear differently at low frequencies. In fact they pretty much track a C-Weight curve over a range of about 85-140dBSPL. For levels between 55-85dBSPL you should actually use a B-Weight curve and for levels from 20-55dBSPL, you should use an A-Weight curve. That's simply how we hear.

Usually we ignore the other two curves and use a C-Weight curve since it mostly applies to the levels we use in home audio.

If you want to simply set levels, then set them all equal with the meter. The meter is doing the hearing compensation for you with its C-Weight curve. The result may not actually be flat, but it will sound like it to you... In REW we go to all the trouble to make the response flat, then we realize this sounds terrible, so we add a house curve. House curve indeed - it's simply adding back the compensation we need because of our poor hearing..............

brucek

[Vaughan100]

I find it difficult to calibrate my subwoofer level. If I shoot for 75 dB's (73 dB's) the meter is moving all over the place.

I was under the impression that only the Radioshack meter read low at low frequencies (the subwoofer warble tone). Now I'm hearing things differently. According to new information, there is no real point in getting a new SPL meter.

The Galaxy will read also 3 dB's low inbetween 30-80 hz (or whatever the frequencies are for the subwoofer tone). This is a disappointment. Had I not known this I would have purchased this meter thinking it would have done the job and wasted a lot of money.

I was recommended to get the meter especially because it DOES NOT read low inbetween frequencies that matter in that subwoofer test tone, which is what I need it for. Anyways, thank you for confirming that it's really just as useless as the Radioshack.

--Regards,

[brucek]

I was under the impression that only the Radioshack meter read low at low frequencies (the subwoofer warble tone). Now I'm hearing things differently. According to new information, there is no real point in getting a new SPL meter.

Well, I don't really think this is new information.

If I look through answers I gave you about the Galaxy and RS meter below it looks like the subjects been covered before.

Sometimes I have trouble getting my point across though.

---------------------------------------------------------

excepts of information already given

Vaughan100 wrote:

From Galaxy, do you know of any of their meters which have the correct calibration set out the box ? Can Galaxy calibrate their meters and is it expensive ?

The Galaxy meters are consistent between units and actually track the C-Weight curve quite accurately. The calibration file we supply on the site only tightens the meters to the C-Weight curve by a small amount. You can be confident in using the Galaxy right out of the box with its C-Weight.

And for the pink noise, would the accuracy of the Galaxy be much better than the Radioshack ? I guess I hate having to add this or add that to the readings. I want a meter which will give me precise readings.

The Galaxy tracks the C-Weight far closer than the Radio Shack meters.

---------------------------------------------------------

and here's another answer I gave you to your question about the Galaxy versus radioShack

Vaughan100,

The Radio Shack meters are reported to be inconsistent at higher frequencies between different units, but at lower frequencies they simply read low. To compensate for that, we provide a calibration file to result in a flat reading when using REW on our downloads page. You can download any of the .cal calibration files there and read them as text with Windows notepad to see the values that are added and at what frequencies.

If you played single frequency sine wave tones as opposed to pink noise, you could easily add the value shown in the cal file to know the accual reading. Pink noise produces a jumping needle reading in all meters, it's the nature of pink noise. It's a good method of reading the energy of a speaker over the range of the filtering of the pink noise, but as you say, if the meter reads low, then so will the readout.

The Galaxy CM-140 is the Galaxy we recommend using the cal file on our site. All meters need a calibration file. They will all read low at subwoofer frequencies. You can see that the Galaxy has a flatter response down low by examining its cal file with notepad. It's better down low than the Radio Shack meter, but still not perfect.

Every meter and mic will need a cal file with varying amounts of compensation required. You can't get away from it.

If you want to be accurate, use REW to set the levels. It's not really neccessary to be that accurate though. Just add a bit of level to the reading and see how it sounds.

brucek

---------------------------------------------------------

Vaughan100 wrote:

The Galaxy will read also 3 dB's low inbetween 30-80 hz (or whatever the frequencies are for the subwoofer tone). This is a disappointment. Had I not known this I would have purchased this meter thinking it would have done the job and wasted a lot of money.

I was recommended to get the meter especially because it DOES NOT read low inbetween frequencies that matter in that subwoofer test tone, which is what I need it for. Anyways, thank you for confirming that it's really just as useless as the Radioshack.

I don't know why you think it's a waste of money. It's a better overall meter than the Radio Shack. It has a better lower and high end response. It enjoys a better build quality. I think it's a bit extreme to class the Galaxy as useless because it tracks a C-Weight curve. I would think for someone who is setting up clients equipment that they would want a meter that's a bit more professional.

brucek

[Vaughan100]

Brucek, I apologize if I came across upset or irritated in my previous responses. I'm just confused now.

Your previous responses gave me the impression that the "low reading" in the range of the subwoofer warble tone would be a non-issue. Which would mean that I wouldn't have to worry about adding this or that to the overall figure.

I should have rephrased my statements because I did not mean to say that the Galaxy is useless compared to the Radioshack but that if it reads identically to the RS meter for setting up subwoofer levels then it is as useless as the RS meter.

For what I need, the Galaxy's improved LF (like below 20 hz) response would not be needed per se. It's the accuracy of reading pink noise from the subwoofer test tone that is what I need. I understand that pink noise will cause the RS needle to swing wildly. What I want is for the readings to be accurate.

I don't want to have to add +3 dB's to a 75 dB reading to get the results I want. I want accurate results. I know it seems like a real trouble and really a small issue, I simply don't want to worry about these things. I want a meter that will not read low for what I need it for.

I don't know why you think it's a waste of money. It's a better overall meter than the Radio Shack. It has a better lower and high end response.

But it reads identically to the RS meter down to what, 30 hz ?

I think it's a bit extreme to class the Galaxy as useless because it tracks a C-Weight curve. I would think for someone who is setting up clients equipment that they would want a meter that's a bit more professional.

But if it also reads low with subwoofer tone then how would it be beneficial ? If it reads the same as the RS meter in that specific range then I don't see the point. I calibrate levels for customers and I seek the most accurate meter for calibrating levels.

If the subwoofer warble tone contains frequencies from 40 hz to 80 hz then I don't see the point if both meters are similar performers. If I'm understanding things correctly, both meters will be identical in that regard and that is why I'm a little frustrated because I wanted a better meter.

--Regards,

[brucek]

Your previous responses gave me the impression that the "low reading" in the range of the subwoofer warble tone would be a non-issue. Which would mean that I wouldn't have to worry about adding this or that to the overall figure.

I should have rephrased my statements because I did not mean to say that the Galaxy is useless compared to the Radioshack but that if it reads identically to the RS meter for setting up subwoofer levels then it is as useless as the RS meter.

I suppose if you don't intend to ever use your SPL meter for anything but band limited test tones, the Radio Shack would be suffice. The Galaxy just seems like a natural progression into response testing by using it with REW. Especially someone who does it for a job. Simply level setting of speakers doesn't do much for overall sound quality. Any peaks in the bass response will skew the levels.

For what I need, the Galaxy's improved LF (like below 20 hz) response would not be needed per se. It's the accuracy of reading pink noise from the subwoofer test tone that is what I need. I understand that pink noise will cause the RS needle to swing wildly. What I want is for the readings to be accurate.

I don't want to have to add +3 dB's to a 75 dB reading to get the results I want. I want accurate results. I know it seems like a real trouble and really a small issue, I simply don't want to worry about these things. I want a meter that will not read low for what I need it for.

Pink noise will always cause an SPL meters needle to jump around somewhat, no matter if the unit is accurate or not. Even a flat reading meter would have a jumping needle with pink noise. It's the nature of signal. You have to average.

But if it also reads low with subwoofer tone then how would it be beneficial ? If it reads the same as the RS meter in that specific range then I don't see the point. I calibrate levels for customers and I seek the most accurate meter for calibrating levels.

When you say accurate, it may not sound the best though. That's the entire reason the C-Weight filter is placed at the input of a sound level meter. Sound level meters are designed to hear like you do, and not like a flat microphone hears. If you had a Flat reading meter instead of a C-Weight meter, and you calibrated a tone at 25Hz to be the same as a tone at 250Hz, then they wouldn't sound the same level to your ears. You'd think there was something wrong with the meter because the 25Hz sounds low. Then you have to add and subtract and all that sort of stuff people hate to do.

To solve that problem, someone decided to put a filter at the input of the flat SPL meter that hears just like you do. Then when you measure 75dB at 25Hz and 250Hz, they sound the same. No adding or subtracting.

So if you have a meter that tracks a C-Weight curve fairly accurate over your band limited test tone, why are you adding numbers to the results?

brucek

[Vaughan100]

Brucek, as far as I know, the standard Radio shack analog meter reads low in the band limited test tone for the subwoofer. If I hit 72-73 dB's then I'm actually hitting 75-76 dB's.

Now if the Galaxy will improve on that and give me the actual results without having to add additional figures to, then I will be interested. Remember, I'm only referring to the band limited test tone for the subwoofer. Not the entire low frequency range.

Will the Galaxy be better in that regard ?

--Regards,

[brucek]

as far as I know, the standard Radio shack analog meter reads low in the band limited test tone for the subwoofer

As I've mentioned numerous times, all C-Weight SPL meters read low in the band limited test tone for subwoofers. It's designed that way to better approximate the way we hear.

brucek

[Vaughan100]

Thank you for confirming for me that the Galaxy is not a step up in performance over the Radioshack for testing band limited test tones.

Thanks !

--Regards,

[Fincave]

Hi there, maybe I am missing something, my apologies in advance if this is the case. You are lookng for an SPL meter that is accurate so that you do not need to add or subtract to end up with the accurate reading. You will be able to find a calibrated and accurate microphone but it will be very expensive, as I understand it the Galaxy and the Radio Shack meter will both meet your needs even though they do not track all that accurately. The workaround would be to use the correction files available and REW, the values are then automatically calculated, you would not need to do any addition or subtracting yourself, REW will do it for you. For REW to work you would need the cables and a compatible sound card. IIRC you had problems with your sound card, I am using this sound card and it works for me with REW. I noticed that you are in South-Africa and so had a look at where it can be purchased, from Terratec's website I found the following vendor, they have stores in JHB and Durban. Not sure as to pricing in SA but I paid 55€ for mine and so I think it would probably be around R600 which would be substantially less than an accurate and calibrated microphone. Hope this helps!

[Vaughan100]

Fincave, thanks for the response ! I understand that REW will provide most accurate results. I think I probably will go and just get a better sound card and be done with it.

Only problem is that I calibrate for clients. I need to do level settings now. It seems like a headache to get REW up and running and getting all the necessary cabling and then making sure that everything is working properly to verify the results compared to using the RS meter or any SPL meter. For convenience, it just wins hands down.

And if REW is 3 dB's more accurate within the band limited tone then it's not really practical to go all out with that approach. It's just frustrating that the results I get are not really the *real* results. Some people have suggested that I use pink noise from a test disk like Avia or Video Essentials claiming that it's better than internal test tones in the AVR.

Do I think that's true ? Have no clue. I just wish I could have a meter that would post consistent results that were accurate and no additional adding or subtracting would be necessary. I see that does not exist.

--Regards,

[arttu]

Seems to me like this confusion centers around the question: To what should the meter be accurate for? Somekind of objective reality (nature) or human hearing?

When thinking about your clients Vaughan100 C-weighing will give you the chance to quickly set levels and do calibrations that are accurate for humans (that would be the client). If you instead provide them with calibration without weighing you will give them something that they can say is "objectively" right but it will not sound right for their ears. Bass will be too low.

[Vaughan100]

I try to calibrate to SMPTE standards and a lot of my clients want accuracy. They pay a lot of money for their equipment and they expect accurate results. They want to hear what the director heard or close enough.

Now I understand full well how films are mastered and the levels required for reference playback. I simply want to get the clients systems up to that standard as close as possible. I guess I am arguing over nothing because the SPL meter is accurate for the main speakers but it's the subwoofer level that I need to get right.

And I also understand that it's personal preference. But I personally like to set the levels accurately according to spec and then if the clients need or want a change from that standard they are most welcome.

It's just that I've also heard reports on various forums where people say "the Radioshack meter reads low with pink noise for the subwoofer, get a better meter", etc, etc. Better meter ? What better meter ? "They're all the same".

I mean, do all SPL meters read 3 dB's down with bandlimited test signals for the subwoofer ? Or do they vary ? Because as I understand from Brucek, both the Galaxy meter and the RS meter should be near identical. Unless I misinterpreted his statements.

--Regards,

[brucek]

I mean, do all SPL meters read 3 dB's down with bandlimited test signals for the subwoofer ? Or do they vary ? Because as I understand from Brucek, both the Galaxy meter and the RS meter should be near identical. Unless I misinterpreted his statements.

You didn't misinterpret. The RS meter is as good as any for basic setting of speaker level, including the sub.

If you want to add or subtract to remove the C-Weight influence, then that's perfectly valid.

But the notion that the setting the levels with an SPL meter results in an "accurate" system is pure folly I'm afraid.

Subwoofer frequencies are subject to room modes that can (and almost always) create large peaks that exist within that band limited range that is used to set subwoofer levels. That peak(s) increase the energy in the subwoofer band limited range many-fold, such that the "accurate" level becomes the level of the peak. Your clients who demand accuracy are now listening to what's known as 'single note bass'. Hardly accurate by anyones measure.

brucek

[Vaughan100]

Brucek wrote:

Your clients who demand accuracy are now listening to what's known as 'single note bass'. Hardly accurate by anyones measure.

And yet according to Dolby Labs documentation, the RS meter is the standard SPL meter used in the industry for setting levels. If it is so inaccurate then I wonder why industry spec supports the use of the RS meter. Strange.

Obviously when I calibrate for level I'm not taking frequency response into account because I'm not shooting for a flat response. I simply want to shoot for equal levels among speaker and subwoofer (taking irregular FR into account) and then vary from there for personal taste.

I assume that there is nothing more that I can do to improve on the accuracy of setting levels (without having a laptop at my disposal with several cables lying around).

So be it. If there is nothing more I can do then I'll accept that.

--Regards,