Radio Shack SPL 33-2055 for measurements

[DozerMayne]

I dont have a measurement microphone at the moment. Is it possible to use the Radio Shack SPL Meter model 33-2055 in place of the measurement microphone for the time being?
Just to become familiar with REW, until I get my measurement mic, and the recommended preamp.

I have all things set and ready for measurements. Using an Emu 1820M audio interface.

Thanks.

[thewire]

Just limit your measurements up to 2Khz or 3Khz. You may want to use a 45 degree angle in your room for doing measurements around 300Hz or higher, and then use it facing the ceiling for lower measurements. My RS Meter gets stuck sometimes and needs to be reset. Try not to get to excited if the battery gets low and you will be in good shape.

[salvasol]

First of all ...Welcome to the forum

DozerMayne wrote:

I
Is it possible to use the Radio Shack SPL Meter model 33-2055 in place of the measurement microphone for the time being?.

Yes, that's what most of us use, is good up to 3KHz ...

[DozerMayne]

Alrighty, thanks alot. Im off to reading and studying the forums, and the REW manual.

[brucek]

Read and become familiar with the REW HELP files and the REW Cabling and Connections Basics.

Also note the REW information Index and the Download Page.

brucek

[DozerMayne]

I am basically just measuring from my mix position.
I have:
2) Rokit KRK RP5's
1)Rokit KRK RP10S Sub

The RP5's are connected to the back of the RP10S Sub via XLR to take advantage of the internal
80Hz hipass filter network in the sub.

Another thing:
I see that the XENYX 802 mixer is recommended as the preamp to use for the ECM8000.

But I could just use my Emu1820M mic input right?
But here is the thing. My Emu1820M phantom power supply went out a while back, so I had do purchase an external phantom
power supply(ART Phantom II Dual Phantom Power Supply). So I run my mics through the external phantom power supply, into the mic input
for use of the preamp. Not sure how that would effect measurements.

Photo of Emu1820M and External Phantom Power Supply


Photo of External Power Supply


Notice the 2) 9Volt batteries. Well, I have yet to find a 600mA AC power supply that doesn't induce noise.
The DC 9Volt power supply is a better choice anyway, more constant.

Oh and a bit of information about Emu 1820M and other similar audio interfaces mic inputs on the front of the AudioDock.
The input into the microphone preamp on the front of the Audiodock allows you to use either(from the same input):
XLR connection for "Mic Level" input(+20dB to +55dB Gain)
1/4" "Line Level" input(-10dB to +25dB Gain)

From the manual:
Link to Manual/Goto Page 20

The front panel mono Mic/Line inputs A & B can be used as balanced microphone
inputs, hi-Z guitar pickup inputs, or line level inputs. The Neutrik combination jack
accepts microphones using a standard XLR connector or line level/hi-Z inputs using a
1/4 inch TRS/TS connector.

So Im guessing if I had the ECM8000, connected to my external ART Phantom Power Source,
then from the phantom power source, using a short XLR to 1/4" TRS cable coming from my external Phantom Power source to the
line level input on the front of the Emu1820M. Then that would be just fine. Because Im not tapping into the "Mic Level" preamp, as shown in
the Emu1820M manual.

[brucek]

So Im guessing if I had the ECM8000, connected to my external ART Phantom Power Source,
then from the phantom power source, using a short XLR to 1/4" TRS cable coming from my external Phantom Power source to the
line level input on the front of the Emu1820M. Then that would be just fine.

Fine, but the 1/4" TRS plug engages the line level input (as opposed to a mic level input with an XLR connector). The phantom supply is no problem as it simply powers the mic, but the level is still at mic level. You need to use the EMU mic preamp (use an XLR connection) to bring the level to line..

brucek

[delphiplasma]

Hi,

You say not to use this meter above 2-3khz. However, I've been making readings above that and manually adjusting the error to the graph that is plotted in the instruction documents. Does such a calibration file exist to correct the frequencies above 2khz?

Thanks

[brucek]

However, I've been making readings above that and manually adjusting the error to the graph that is plotted in the instruction documents. Does such a calibration file exist to correct the frequencies above 2khz?

No, since the RS meters are quite variable among the different models above 3KHz. No one is saying you can't use it above that, but it can't be considered accurate when using a generic cal file.

See this article about RS meters. Many have observed marked differences between units of the same model.
If you want a decent SPL meter to use full range, get a Galaxy CM-140 and use our generic file....

brucek

[delphiplasma]

Thanks, BruceK.

Very useful information. I've studied the AudioXpress document.

I have to say that the findings for the old RS meter frequency response match the response as provided in the manufacturer’s documentation. As the article in the AudioXpress mentions, the old RS meter does meet the +-3db specs between 32 Hz-10 kHz. There is the obvious rise in frequency response above 2 kHz peaking to approx 5db at around 6 kHz. Now there may be slight variations in meter frequency response, depending on the manufactures tolerances. However, I feel that the frequency anomalies above 2 kHz are mainly characteristics of the microphone itself, which would be fairly consistent within the specified model range.

Now I have got a very accurate Mic and pre-amp set-up, which will give me some idea of the errors inherent within the RS meter.

I mainly use the RS meter as a quick check, as it is much easier to lug around and connect up. As previously stated, I feel that a calibration file could be produced to improve the meter readings, if not make it 100% accurate above frequencies of 2 kHz.

Someone is bound to prove all this wrong? Please feel free.

Thanks for the reply

[brucek]

I do think you can develop you own file for the higher frequencies as long as you have a calibrated mic to compare against.

But to create a generic one that others can use, it's a bit tough. When we developed the three files we use for the three different models, we came across a problem where it appeared they switched mic elements for the different models that didn't align with the model change. This makes it tough to offer a decent cal file for everyone to use.

So, I'll stick by my recommendation to limit the upper range to 3KHz for most people.

brucek

[adrian_veerapas]

Does the Radio Shack SPL 33-2055 work down to 20hz ? (taking into account the correction values)

[brucek]

Yes.....

[Keith Shaw]

brucek wrote:

See this article about RS meters. Many have observed marked differences between units of the same model.

Thanks for the interesting link. Do we believe that the largest differences, unit to unit, are probably in the sub-bass range (when discussing the 10 - 200 Hz region)? It seems reasonable given the amount of compensation needed for flat response, but I wonder if there's good data.

Keith

[brucek]

Do we believe that the largest differences, unit to unit, are probably in the sub-bass range (when discussing the 10 - 200 Hz region)

The variations between units appears to be at higher frequencies. The 15Hz to 200Hz is quite stable in the units that we tested (small sample of 4 or 5 - I can't remember). I wouldn't use the RS meter below 15Hz though, as noise becomes an overwhelming factor (as you have correctly identified in the larger compensations needed).

brucek

[hybris]

If I understand the comments in this thread and the linked article correctly, each individual SPL meter does at least deliver a consistent (if not correct) frequency response up to about 10khz? (I made some quick tests and mine seemed not to drop off dramatically in sensitivity until abuot 10khz.

I'm about to add some acoustic panel/absorbents in my listening room, and intended to use the radioshack to measure the differences before/after. This should work fairly well up to 10khz?

[brucek]

I'm about to add some acoustic panel/absorbents in my listening room, and intended to use the radioshack to measure the differences before/after. This should work fairly well up to 10khz?

Yes, all this discussion about the meter is related to its absolute readings, not its relative readings. It can be used at any frequency when you are concerned about a before and after.

brucek