file how to make a test measurement of a spea

4 years 7 months ago - 4 years 6 months ago #22363 by bee
By ear or by rta measurement.....

The answer for me is both, Both methods compliment the other. The human ear still being the best for sound quality. If it doesn’t sound right, then its not right. Our ear should always be the final judge on the overall sound, No matter how good the software or measuring equipment is. So why is there a need for measuring programmes.Many things can effect what we hear, illness, fatigue, poor acoustic memory and hearing deterioration due to age or prolonged loud music are just some of the main reasons.

By tuning a system totally relying on the ear, may not produce a consistent sound or quality of sound, and may being doing you system an injustice.
Like wise your rta measuring system could be wrong. This has happened to myself when i was using a measuring Mic that was miss reading due to a fault. I trusted my ears that something was wrong. It turned out that my calibrated microphone was damaged. Once i changed mic after trusting my ears, and re measured the issues became apparent and changes were made. But by tuning by rta measurement will uncover problems that the human ear cant or is not very good at detecting, These can be the problems that make a massive difference to your sound systems sound quality. For example one of your drivers or frequency range (cabs) are out of phase in your stack, You might be able to tell something is wrong at a certain listening position, but you may not be able to tell exactly what and were the issue is, but by doing an rta measurement reading would pinpoint that type of problem exactly and quickly.

The ear is perfect for most audio things like, balancing levels between separately amplified loudspeakers. But when used with a good rta measuring system can get your system sounding better quicker.

Just like the human ear there are many issues that effect the quality of your rta measurements, Mainly operator error..... The main ones for me are,

1) The flat RTA response misnomer
2) Improper measurement-mic placement, and
3) Attempted equalization of multiple-source or multiple-reflections contaminating your measurements.

I believe that 75% of all sound systems are equalized wrong due to these three errors, and this is why some will not agree and mistrust rta measurement geeks like me.

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4 years 7 months ago - 4 years 7 months ago #22364 by bee
So how do we Measure....

First of all measurements should be done at 1 watt at 1 meter, but sadly this is not very easy and most don't bother, even big brand manufacturers despite what it says on there spec sheets don't bother.

so what does this mean......

Well you only need to apply a voltage reading of 2.83v, this is harder than it seams as the impedance of a speaker changes with frequency, as will the wattage, so at any given frequency you will have much less or much more than 1 watt.

Now 2.83v is 1 watt into an 8ohm driver. If we base this on the standard impendence curve of any given 8ohm loud speaker you will clearly see that is around or close to 8 ohms, some times above sometimes below, but 8ohms will be the closest standard value. The same applies for 4ohm and 16ohm drivers. The 4 ohm, 8ohm and 16ohm tag often do not actually represent the actual impedance of the loudspeaker but the closest recognised value to that driver.

Best place to measure.....

The best place to do your measurements is in an open area, a field or a wide open space. It also does not have to be "in the middle of nowhere" but you will need to be able to recognize what reflections look like in a measurement and when to simply ignore then for the tasks like system alignment.
What you need equipment do you need......

To be able to do full rta measurements there is alot of equipment out there, some cheap some costing a few thousand and more. As this is a diy forum we will start with the cheaper end,

1. laptop running windows or mac
2. software there are a few free software options as well as the more expensive ones. A good free one is by Holm accoustics, www.holmacoustics.com/holmimpulse.php
this is a pc based programme.
3. a condenser measuring mic, this will need a phantom power supply, a budget one is the berry ecm8000, www.studiospares.com/Microphones/Mics-Co...icrophone_900033.htm
better mics will come with a calibrated file, but expect to pay £150 plus....
4. dedicated pro audio grade soundcard, with built in phanton power, these can be got from £100 up to £1000 plus, www.studiospares.com/Studio-Gear/Audio-I...rlett-2i2_389820.htm
5. Signal generator
6. voltmeter

I would recommend you do a calibration of your soundcard, this is were you connect the output to the input and take a reading, using the calibration feature within your software. This will smooth out any differences in your readings that may be an error of your sound card.
If you don't own a signal generator, find a WAV file of a 60Hz sine wave. I have a big collection on my website of free test tones available to download, www.elements-audio.com

Hook up your voltmeter to the output of an amplifier and turn up the mixer until you get a reading of 2.8v. Disconnect the meter and hook up the speaker to the amp. The choice of 60Hz is based on most common meters not having a wide frequency bandwidth, If you have a wider bandwidth, true RMS meter, use it. The recognised testing frequency is at 1khz

Placement of mic is critical, for all bass sub boxes. the cabinet should be placed on the ground, away from any walls or objects that may cause reflections. Place the mic 1 meter dead center of the cab.

Next step is to learn how to use your software.....

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4 years 7 months ago #22370 by Rog Mogale
Replied by Rog Mogale on topic how to make a test measurement of a spea
Hate to tell you this Bee, but there are more than a couple of mistakes in your method that make it completely inaccurate.

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4 years 7 months ago #22371 by bee
Please enlighten me Roger, there is very little written that goes indepth re this subject and a lot of mis guided info available. The last thing I want to do is mis guide people, and if im measuring wrong would help me out to....

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4 years 7 months ago #22374 by Rog Mogale
Replied by Rog Mogale on topic how to make a test measurement of a spea
I've just re-read your post Benjamin and its fine.

My mistake.

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4 years 7 months ago #22376 by bee

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4 years 7 months ago #22378 by Rog Mogale
Replied by Rog Mogale on topic how to make a test measurement of a spea
Apart from changing my name to Roger, yes.

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4 years 7 months ago #22384 by mykey-
Replied by mykey- on topic how to make a test measurement of a spea
You forgot the 3rd one. The rattle of the balls. If your balls don't vibrate, scrap it

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4 years 7 months ago #22385 by mykey-
Replied by mykey- on topic how to make a test measurement of a spea
''Placement of mic is critical, for all bass sub boxes. the cabinet should be placed on the ground, away from any walls or objects that may cause reflections. Place the mic 1 meter dead center of the cab. ''

2 meters with mic touching the ground

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4 years 7 months ago #22387 by bee
yes should of said dead center on the floor.... why 2 meters mykey,

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