Are these the correct things to buy for SPL measurements?

[JonW]

Now that I’ve got speakers for a 5.1 system, I need to start taking SPL measurements and get each speaker at the same output level. Rather than just an SPL meter, maybe I should get a microphone setup, for future flexibility. From reading around, I gather these are the things I need:

-The Behringer ECM8000 Microphone:

http://www.behringer.com/ECM8000/index.cfm?lang=ENG

-The M-Audio Mobilepre USB:

http://www.m-audio.com/products/en_us/MobilePreUSB-main.html

-Room EQ Wizard software:

http://www.hometheatershack.com/roomeq/

Am I missing anything or is this everything?

Also, does anyone have any experience with Room EQ Wizard and a Mac? That’s all I’ve got.

Thanks.

-Jon

[---k---]

You forgot the Dell Laptop. :B

You should just write a couple of those in your next grant proposal and be done with it.

[soho54]

You will still need an SPL meter if you want calibrated graphs. Without it the graphs are only relative to one another.

[JonW]

You will still need an SPL meter if you want calibrated graphs. Without it the graphs are only relative to one another.

Really? So... ummm... what do you mean by calibrated graphs? Obviously, I've never done this before. Won't he mic + amp + REW tell me the output level (at a given frequency)? What does the SPL meter add?

You forgot the Dell Laptop. :B

You should just write a couple of those in your next grant proposal and be done with it.

:P You'd be surpised how restrictive these federal grants are. We cannot use them to buy things we really need like paper or pens. Seriously. Just forget about computers.

[Jack Gilvey]

Really? So... ummm... what do you mean by calibrated graphs? Obviously, I've never done this before. Won't he mic + amp + REW tell me the output level (at a given frequency)? What does the SPL meter add?

An absolute reference with which to calibrate the program.

[JonW]

An absolute reference with which to calibrate the program.

Thanks. OK, that raises 2 questions:

-The SPL meter is calibrated but the microphone is not?

-Does it matter if the microphone is calibrated, when all I want to do (for now) is get each speaker to the same level? (Or measure the room response in various configurations.)

[Licinius]

No it doesn't, unless you want to know the exact spl you're puttin' out. Otherwise if you just want your speakers levels set right and to graph the response (ie. to look at the picture, not so much the number), no worries. But after all that stuff, whats an spl meter anyways? =)

[soho54]

Really? So... ummm... what do you mean by calibrated graphs? Obviously, I've never done this before. Won't he mic + amp + REW tell me the output level (at a given frequency)? What does the SPL meter add?

REW will work without the SPL meter, but the SPL it graphs will be meaningless. The curve will be correct from freq to freq, but the SPL column could be way high or way low.

The SPL meter is calibrated but the microphone is not?

As far as the SPL mic and the microphone is concerned neither are calibrated, out of the box.

-Does it matter if the microphone is calibrated, when all I want to do (for now) is get each speaker to the same level? (Or measure the room response in various configurations.)

No, but for this use an SPL meter might be a better replacement for the microphone at this point. If you aren't after super accurate measurements use the SPL meter to setup the levels, and also use it as the mic/calibrator in the REW setup, for calibrated measurements so you can compare to others graphs. Later if you want better gear for say speaker xover designing just add the ECM mic in the SPL mics position, and you are good to go. :T

The calibration we are talking about is the REW calibration. This is just my opinion though. I get a lot more milage out of my RatShack SPL meter than my measurement mic.

[chasw98]

Jon:
Go get one of these . It's $44.99. I would also advise you to go to a music store and buy a mic stand for the ECM8000 (a cheap $20 one will do the trick). It will save lots of hassle in positioning. AND if you really want the cats meow, go get a cheap photography tripod to mount the SPL meter on. I paid $10 for mine and it works well. You really do need the SPL meter. And don't forget to pick up a mic cord while you're at it. Call me with any questions.

Chuck

I guess you don't want to hear about MIDI control with REW right now, huh?

[ThomasW]

Gee I must have missed the boat since in 40+yrs of speaker building I've never owned or used a handheld SPL meter ..

I second Chas98's recommendation regarding something like a tripod, but instead recommend a short boom mic stand. These too are cheap, as low as $25 or so with careful shopping. The boom allows accurate placement of the mic...... :T

[JonW]

Thanks, folks. I've already got a photo tripod. A mic stand is easy topick up. I see the benefits of the SPL meter, but no sense in buying it if it'll be redundant later.

In comparing mt recently built speakers to my commercial speakers (sorry for all the debate on that) it would be neat to see if the output levels vs. frequency are different. Would be neat, but really not needed.

Gee I must have missed the boat since in 40+yrs of speaker building I've never owned or used a handheld SPL meter ..

So would you recommend just getting the ECM8000, Mobilepre, and REW? Or something in addition to or instead of?

[Jack Gilvey]

In comparing mt recently built speakers to my commercial speakers (sorry for all the debate on that) it would be neat to see if the output levels vs. frequency are different.

You can do a FR measurement without the meter, but you can't determine absolute level at a given frequency. Even then, you'd want to determine THD to get any useful info.

[ThomasW]

So would you recommend just getting the ECM8000, Mobilepre, and REW?

That's what I use these days, but I also have software programs like TrueRTA and others that provide SPL measurements. The ECM8000 is far more accurate than the RS SPL meter. So I spend the money on software instead of the meter. It's less convenient than using a SPL meter, but 'good' SPL meters aren't $50. So anything done with a RS meter is just an educated guess as well.

[JonW]

You can do a FR measurement without the meter, but you can't determine absolute level at a given frequency. Even then, you'd want to determine THD to get any useful info.

Presumably, thought, things are consistant enough that you can compare things well enough to get good relative leveles, just not get absolute levels. Seems OK to me unless I'm missing something? How do you get THD?

[JonW]

That's what I use these days, but I also have software programs

Thanks Thomas. Sorry if it seems every one of my posts opens up a can of worms. It's not my intent. Really. :W

Between the ECM8000 and the Mobilepre (and my laptop) is there anything else I'd need, like cables? I can't see any mention of the ECM8000 having a cable. So that would be a regular XLR cable to buy as well?

My software options are limited for a Mac. REW looks like it should work, but nope on TrueRTA.

[Jack Gilvey]

Presumably, thought, things are consistant enough that you can compare things well enough to get good relative leveles, just not get absolute levels. Seems OK to me unless I'm missing something?

Right, no need for absolute levels to get a picture of frequency response. All FR is relative levels, although such sweeps at progressively higher levels give a good indication of dynamic compression beginning in the bass.

How do you get THD?

Haven't messed with REW much, but in TrueRTA it's a manual calculation based on the level of measured harmonics. PITA.

[soho54]

I think we are dancing around here.

If you just want to set your HT speaker levels- SPL meter
If you want to set levels and mess around with REW a little- SPL meter
If you want to build your own speakers- dedicated mic
If you just want to equalize your HT speaker levels without knowing the real SPL levels- dedicated mic

If you don't calibrate the software to a known SPL how can you use it to setup HT levels?
I'm missing something I guess.

[---k---]

Jon,
The picture will become clearer after Saturday. I have most of the gear you are talking about and can show you how it works. I have the ECM8000, RS Meter, RoomEQ, ETF5, but not the Mobilepre (Which I wish I did have).

[ThomasW]

JonW,

In this situation Macs mess things up, where they usually make life easier.

If you're running a Dual-Core or an emulation program try run the Windows version of REQW, it's less flaky than the Apple java version...

If you can't or don't want to run windows programs consider Fuzzmeasure Pro. Since you're a teacher (prof) you qualify for the education discount.

This will do more than what REQW and TrueRTA combined will do. Hint you can test your crossovers, subwoofer and everything else. And since there's a 14 day free trial period, what's not to like.....

Wait on the RS meter until you play with Fuzzmeasure. If after the trial period you find it too complicated, buy the meter and use REQW.

[Dennis H]

Thomas didn't mention it but his DEQ2496 includes among its functions a 1/6 octave RTA and a very accurate SPL meter. Plug the Behringer mic in the back and you're good to go -- no fuss, no muss, no computer required. If you're considering an EQ for your sub, the DEQ2496 is almost a no-brainer.

Thomas's DEQ page (under construction)

[chasw98]

Gee I must have missed the boat since in 40+yrs of speaker building I've never owned or used a handheld SPL meter ..

I second Chas98's recommendation regarding something like a tripod, but instead recommend a short boom mic stand. These too are cheap, as low as $25 or so with careful shopping. The boom allows accurate placement of the mic...... :T

Obiwan catches the Padiwan on another slip up. I am assuming you are referring to an SLM instead of an SPL meter :Z ;x(
As far as a tripod, in JonW's case his soon to be RS meter is threaded for a photography style tripod as opposed to a mic stand thread. (Although I suppose adapters are available).

And I can't beleive you have never used a Bruel & Kjaer handheld????? Personally, I was very comfortable with my Ivie IE30 and a Tektronix 100 Mhz hanging off the attached IE15 for SLM work. :T

[ThomasW]

Oh sure now you'll really confuse everyone....... :rofl:

No, I've never owned a hand held meter ....

I've always had access to either an actual hardware based RTA, or in recent years computer based testing software.

Back just after Edison created the lightbulb, we had a B&K 4133 interfaced by a HP mic preamp to a White Instruments RTA. Things like that were CUBIC money long ago. When the White finally died, I bought an AudioControl RTA and Jon bought an early version of Clio that operated in DOS.

Now we look back at this stuff and wonder how anything we build sounded good, probably dumb luck...

[JonW]

Hey Guys-

Thanks again for all the help.

That Fuzzmeasure Pro program looks pretty slick. Maybe I’ll try that with the mic and Mobilepre and see how things go. Although Chuck is still angling for the RS SPL meter.

JI guess you don't want to hear about MIDI control with REW right now, huh?

I remember back when was I was a kid and playing a little music with friends- guitars and synthesizers- MIDI was this really new, fascinating thing. Wow- use a computer to control an instrument! Heck, computers were new. Much easier to use than that abacus.

[chasw98]

Back just after Edison created the lightbulb, we had a B&K 4133 interfaced by a HP mic preamp to a White Instruments RTA. Things like that were CUBIC money long ago.
Now we look back at this stuff and wonder how anything we build sounded good, probably dumb luck...

The guy that owned the company I worked for in Carbondale had a White RTA. I think we had the only RTA between Denver and Grand Junction. Yes, it was an incredible amount of bucks back then!

An early version in DOS! Come on, now I feel like the dinosaur. I wrote my own RT60 calculation program in basic on an RS level 2 with 16K of ram, cassette for hard drive, and TV for a monitor! But it was better than using my HP scientific calculator and spending 8 hours to come up with 1 scenario for a room.

[JonMarsh]

Yeah, the new version of Fuzzmeausure Pro 2.0 is pretty nice, I'm playing with it on my PB17, may put it on my MB Pro also.

It doesn't exactly rival Praxis, but you can do a heck of a lot with it, especially considering the price.

[ThomasW]

An early version in DOS! Come on, now I feel like the dinosaur. I wrote my own RT60 calculation program in basic on an RS level 2 with 16K of ram, cassette for hard drive, and TV for a monitor! But it was better than using my HP scientific calculator and spending 8 hours to come up with 1 scenario for a room.

Jon's the numbers guy. Before we got White Jon did all the design work with the ever reliable HP scientific calculator. Our ears were our 'calibrated' test instruments ....:roflmao:

When TI introduced it's first "Pro" PC we both bought in. That assisted Jon quite a bit, and left me wondering why I just spent $5000 ..... :thud:

[---k---]

Thomas didn't mention it but his DEQ2496 includes among its functions a 1/6 octave RTA and a very accurate SPL meter. Plug the Behringer mic in the back and you're good to go -- no fuss, no muss, no computer required. If you're considering an EQ for your sub, the DEQ2496 is almost a no-brainer.

Hey Jon, I got one of those too!

[chasw98]

Jon's the numbers guy. Before we got White Jon did all the design work with the ever reliable HP scientific calculator. Our ears were our 'calibrated' test instruments ....:roflmao:

When TI introduced it's first "Pro" PC we both bought in. That assisted Jon quite a bit, and left me wondering why I just spent $5000 ..... :thud:

Hmmmm..... seems our roots have some commonality I can remember getting a Commodore VIC 20 later on. We should sit down some day at the old folks home for retired sound dudes and reminisce :T

PS - Have we taken over and ruined this thread yet? Sorry ;x(

[JonW]

PS - Have we taken over and ruined this thread yet? Sorry ;x(

You guys haven’t yet told us what you used to record and reproduce the sounds of dinosaurs…
:P

[Evil Twin]

It was similar to Edison waxed cylinders, but using solidified tar pitch, as wax hadn't been invented yet.

[Dennis H]

Geez, don't you guys watch the Flintstones?

[chasw98]

It was similar to Edison waxed cylinders, but using solidified tar pitch, as wax hadn't been invented yet.

I preferred these for getting the maximum L/R separation from tin cylinders.



I averaged 7 db separation with 22 db S/N ratio. SOTA for my day sonnyboy :rofl:

In case you wonderd why I used tin, it is because Evil Twin was light years ahead using the "BLACK" substance.
I quote:
"By 1902 the brown wax cylinder was eclipsed by the molded black wax cylinder, which was actually made of a soap compound. They were much more ‘hi-fi’ than brown wax cylinders and usually lasted longer. A typical recording on a black wax cylinder was about 2 minutes"

Sigh.......... even then I wasn't as "Audiophile" as those guys...........

[JonP]

I might be a bit off base here, but how about taking that $40 or so for the SPL meter and spending it by sending the mic to Kim Girardin and getting an actual calibration file for it?

I would think that with the cal file, one MIGHT be able to extract accurate SPL readings using the mic and various softwares? Then again, it might be too clunky for practical use? Possibly such a cal file would only be relative, not absolute data?

I guess it boils down to what your usage would be, as was explained earlier. It's always good to get the mic cal'ed anyway, to have accurate relative measurments when you're doing speaker work....

[ThomasW]

I've read that Kim G. won't calibrate RS meters.

One could do their own meter calibration by comparing it to a calibrated mic.

[Brian Bunge]

Thomas,

I think he's saying to spend $40 to get your mic cal'd instead of spending the $40 or so on the SPL meter.

[ThomasW]

Oops my bad, dyslexia strikes again.... :cry:

[JonW]

Not to hijack the hijack or anything, but a little more clarification for the slow ones here...

No, I've never owned a hand held meter ....

So then do you have your mic calibrated or something?

I gather that what I should buy is still:
-ECM8000 microphone
-Mobilepre
-The Fuzzmeasure software

And that will do everything I need except provide for a calibration. Which can be accomplished with an SPL meter (sounds easiest?). Or buy a calibrated mic or send a mic out for calibration. Do I have all this correct?

[soho54]

JonP

I would think that with the cal file, one MIGHT be able to extract accurate SPL readings using the mic and various softwares? Then again, it might be too clunky for practical use? Possibly such a cal file would only be relative, not absolute data?

I think there is some miscommunication here. Let's say you were trying to calibrate you HT to an 85db reference level. You take a measurement mic and hook it up to a computer with REW, TrueRTA, or whatever. You play a -20db tone from say the Avia DVD. REW registers 90db. Is this correct? No, because the software is not calibrated. It has nothing to do with mic calibration. What happens when you change the recording level in REW, without touching the AVR volume? The programs posted SPL level changes.

This is why you need something to tell you the SPL in the room. You then raise or lower the REW levels until it matches what the SPL meter says. Once this is done you can set the levels with REW. If this is what you intend to do.

Any graph made with uncalibrated software is exactly the same as the calibrated one, with the exception of the SLP variable. That is the only difference. The graphs will look exactly the same except for the numbers on the side.

With that said if setting your HT up to a known level is not your cup of tea, you can skip the SPL meter all together. :T

[WillyD]

Soho - Could he not still set the levels of the speakers relative to each other, using the mic, mobilepre, and whatever program he ends up with?

I understand what you're saying, but I don't see the point "setting the HT up to a known level" as long as the speakers' individual levels are correct, relative to say, the fronts.

Does that make any sense?

[soho54]

Could he not still set the levels of the speakers relative to each other, using the mic, mobilepre, and whatever program he ends up with?

That's why I added the last sentence.

I understand what you're saying, but I don't see the point "setting the HT up to a known level" as long as the speakers' individual levels are correct, relative to say, the fronts.

It's part of the whole "reference" deal. Theaters are supposed to be setup up at an 85db nominal level, and soundtracks are recorded for this level. This defines spoken word (dialogue), and the max SPL levels of the film. That’s what the dialnorm in DD tracks is all about. Some people are into it, some aren't. :B

[WillyD]

That's why I added the last sentence.
:B

:banghead:

:B

[ThomasW]

Not to hijack the hijack or anything, but a little more clarification for the slow ones here...

Killjoy... :B

So then do you have your mic calibrated or something?

Here's the deal. When ECM8000s burst on the scene, Jon and I bought 3. We compared them to his $5000 B&K 4133. In his words "the differences weren't worth worrying about...Above 10kHz they're rolled off a bit, but who EQ's up there anyway? And the bottom end isn't quite as flat".

Kim G uses a 4133 for his calibrations. Now I don't know if his capsule is as good as one Jon owns...there are different versions of the mic-capsule. The one Jon has is the most $pendy around.

So that's the long way of telling you no my ECM8000 isn't calibrated, and it's not something I'm concerned about.

I gather that what I should buy is still:
-ECM8000 microphone
-Mobilepre
-The Fuzzmeasure software

Yep that's it

And that will do everything I need except provide for a calibration. Which can be accomplished with an SPL meter (sounds easiest?). Or buy a calibrated mic or send a mic out for calibration. Do I have all this correct?

At this point some clarification is in order. Room EQ Wiz, uses a meter to set the program default SPL. I'm not sure why that's the case, because the meter isn't as accurate as the mic. So it's using a less accurate device to set the standard for the more accurate device....go figure?

With other software programs they just use the mic and tell you the SPL it's measuring...

PS regarding mic calibration. Real calibrations run $250 and up. The frequency response of a mic changes with temp, barametric pressure, altitude and other variables. So even if one pays Kim G the $40, the file he makes is only accurate for ambient conditions when he makes the cal file. Ship it by air to a different altitude and weather conditions and the performance changes....

[---k---]

I don't think the computer has anyway of knowing what input level from the mic is 75db. That is why you keep bumping the volume on your receiver until the meter reads 75. Then you tell the computer that the sig it is getting at that point is 75db. You could probably skip this step, but then your measurements would all be a +/- from a reference level that isn't necessarily 75db - which doesn't really matter, but is nice.

[JonW]

Thomas- perfect. It's all clear now. :T
I'll just buy the software, mic, and Mobilepre and be set. Oh, and an XLR cable for between the mic and the Mobilepre- I think that should be everything.

Yeah, I thought the RS SPL meter wasn't so accurate and it was confusing me that it was needed for calibrations.

The Fuzzmeasure software runs on the very latest Mac OS. So I've first got to buy that and update my creaky, old laptop. And then buy the mic, etc.

[soho54]

Room EQ Wiz, uses a meter to set the program default SPL for the mic. I'm not sure why that's the case, because the meter isn't as accurate as the mic. So it's using a less accurate device to set the standard for the more accurate device....go figure?

All programs are this way. It can only work this way.

TrueRTA setup:

TrueRTA has an option to calibrate the absolute SPL level. Play for example 100Hz or higher sine wave (but below 500 Hz) and check the reading on your meter. You can play the tone using the built-in generator or you can use a cd/dvd. Have the program measuring all the time (GO button down) and enter Audio I/O / SPL Calibration menu and enter the SPL reading. Now the program is calibrated and it's showing absolute SPL's (=real).