How to measure speaker response with True audio RTA.

[Forte_II]

I am looking for tips on getting the most accurate measurements possible with my test setup.
What are the best settings?
What is the best mic position?
What is the best SPL for testing?
etc...etc...
Here is what I have:
Naty CM100 reference measurement mic. Anyone got a mic correction file for this?
Behringer 1002 mixer.
1/3 octive EQ
CD player
Active X- over
Amps.
Comp with True Audio RTA level 2 installed. Will get level 3 or 4 on payday.
Thanks.

[Forte_II]

Well, No one use TA RTA? What do you all use for speaker testing? For both distortion and freq. response?

[moniker]

Mic position depends on what you are measuring. If you are measuring a speaker, then 1 meter on axis is a common location. If you are measuring a driver, then you might do a Jon "very nearfield" test at 1/4 inch from the cone at various parts of the cone. If you are measuring what you will hear in your room then the mic might be placed at the listening position.

Problem is, if you are measuring a speaker, you cannot get good results from RTA in a room, unless it is anechoic or unless you are outside with no reflecting surfaces within any reasonable audio wavelength. You might be able to do nearfield measurements but normal driver measurements at 1 meter will not be too good either. You can do listening position measurements but will really be measuring the total room+speaker system. So it depends what you want to do to determine if RTA will do the job.

Best SPL depends on what you want to measure. If you want to measure distortion you must slowly increase amplitude from a low level and increase until you understand the distortion profile vs amplitude. I do not think RTA is the tool for that though. If you want to measure frequency response. A nominal amplitude above the ambient noise level should be ok. Try about 90db SPL. That should not overdrive the speakers and not hurt your ears too badly (always wear ear protection).

As for settings, if you want a measurement of approximately what the ear will hear you might try 1/3 octave bands (or smoothing). But if you want to see what is really happening and want to pinpoint the frequencies that may be causing problems, then go to the finest resolution you have, 1/24 octave or better (no smoothing if possible).

So you see, as usual, it depends. I suggest you go to the Mission Accomplished page and look at the thread on software available for this hobby. Go to each web site and read their manuals and examples. This should give you a good start to help you make up your own mind as to what to do.

I have RTA level 4. I also have ARTA full license. There is no comparison between the two.

ARTA is way better for all sort of speaker and room measurements. But it will cost you some time to understand what you are doing with it and it will cost a bit more too.

You can upgrade your RTA for about $65 or get the full ARTA for $118. To me it is a no-brainer because ARTA does so much more than RTA. But first go to the ARTA site and read the manual that you can d/l from there. Here is the URL: http://www.fesb.hr/~mateljan/arta/ The manual is clear and very instructive. It is a learning treasure.

ARTA will also let you d/l a free version. I don't remember the limitations but if you d/l it you can see it work and get a feel for it.

I am sure others will make their own suggestions, but be sure to look ARTA over.

[Forte_II]

Thanks, I grabbed all the manuals for ARTA. I am designing my own speakers and want to measure FR, SPL, THD and any other relavent info. I am assuming I want to do this Near field in a neutral (as I can make it) enviroment.
I am just getting into this and learning all I can. I appreaciate any and all help.
Thanks again.
Randy

[moniker]

This forum is long and deep. Unlike some audio forums, many of the posters here are real experts in speaker measurement and design.

I know it is a daunting task, but do the best you can to read at least all the posts in the Mission Accomplished section. There you will get an insight into some measurement methods and the tools to get them done.

Also there are some books available that will give you further insight. I think the Speaker Builder's Cookbook may have a section on speaker measurement in it, but check it out before you buy it.

And don't forget to read every bit of the Linkwitz Lab site: http://www.linkwitzlab.com/. Even if you never plan to build a dipole design, that site has a lot of the basic information and excel worksheets that help you to understand and build "normal" speakers.

Also go to: http://www.audua.com/. There you will find a free measurement and speaker design package. Lots of people use it. I have never been able to work my way through its style. It is not structured the way I think. But it might work for you. Also its manuals and jigs are very instructive regarding what you might want to do with it (or other programs) for measuring and designing speakers. It will be a very educational read.

Speaker building is a very intersting and rewarding journey that can keep you entertained for many years. And the beautiful thing is that your creations will sing to you. Can't hardly beat that!

Good luck with it.

[Forte_II]

I am blind (i use a screenreader) and all the pics of graphs and going through the website line by line is tedious. Think of it this way: You read the web like a CD, you can jump straight to the point you want like skipping to the 10th song on a cd. I have to read the web like an old tape player: start at the top and fast forward to the point I want, line buy line. If you remember trying to find the beginning of a song (article or post) half way through a cassette (webpage), forward then back then forward again. the web is like that with a screenreader. So it is not that I am lazy I am just trying to save myself some time. :P
Thanks for the links, I have read the Linkwitz site it is a great resource. I am off to the finished projects sticky for more info.
Randy

[Landroval]

These could be of help:

Zaph's setup with SoundEasy:

http://www.zaphaudio.com/setup.html

Roman's setup for Speaker Workshop:

http://www.rjbaudio.com/Audiofiles/SWsetupProcedure.html

[moniker]

Many years ago when I was in law school (it was BC - before computers), there was a fellow in the class ahead of me who was blind. He used a reading machine in which a book could be placed and the machine would optically view a page line by line, word by word, letter by letter. The result would be back projected on to a screen like a modern rear projector tv with letters about 6" tall. It worked something like a microfilm reader. He would put his face up against the screen and it seemed to me that he would read letter by letter.

Cleary, this was a tedious and slow process. I could never understand how he was able to keep up with all the reading necessary for law school. But he did and he graduated in his class.

Does your reader do the same sort of thing?

Keep up the good work. :T

[Forte_II]

Hi, Landroval, Thanks that was the kind of info I was hoping for.

Hey moniker, I used one of those before I lost all useable vision. Now I use Jaws. It is a voice synth. that talks to me. Like Stephen hawkins' computer does. Much better than the poor guy you described above. But still has its quirks and limitations.
Well anyway I built a set of sealed MTM's 0.47cu^3 useing Vifa PL14 5.5" woofers and Vifa XT27TG ring radiator tweeters. They are bi amped useing active x-over. I like the sound of them alot but I want to measure them and see what can be improved. Then build passive x-overs for them. Then I will design a bass bin as a stand for them and use active x-overs between the Woofers and Mid/tweter section.
Any Ideas for the bass bins? I am all over the place with this part of the design. 2 small (6.5": or 7") woofers or a single larger 8", 10" or 12" woofer. Maybe Sub crossed at 80Hz. I just can't make up my mind.