ECM8000 Microphone

[Twisted85]

Hi,

I just ordered SoundEasy for my next loudspeaker project and I was wondering if I should get calibrated ECM8000 mic?
At the moment I use ECM8000 with a calibration file which I downloaded from internet, but is this good enough? Should I get another mic with exactly right correction file and sell this one? How big differences are possible?

And where could I get calibrated ecm8000?

[peter_m]

See what he has to say about it:

http://zaphaudio.com/setup.html

[claudio]

Hi Twisted,
a calibration service is done here: http://www.content.ibf-acoustic.com/

Needing a calibrated mic or not is a matter of tollerance, needs. Said this, the generic ECM8000 calibration file is old, maybe now Behringer uses a new capsule, since thew WM60 is no more produced.
Moreover, getting a calibrated mic now doesn't mean that it will stay calibrated forever, unless it's a B&K or similar: that is you shoul calibrate it once a year.

[Dave Bullet]

The ECM8000 is supposedly reasonably flat (+/- 1dB) around where most people crossover in a 2 way (ie. between 2 - 3KHz). Therefore for uncorrected measurement and modeling, the uncalibrated ECM8000 should be fine.

Where the ECM8000 changes is the upper (12KHz+) and lower (say sub60HZ?) frequencies. What I did was measure a well known tweeter and compared the response with what others have measured.

I then found a few calibration files and chose the one that gave the most similar measurment with the known driver.

I would like to get mine calibrated, but no service I've found around here to do it.

Hope that helps.

Cheers,
David.

[Pano]

I'll have to agree with Dave Bullet and will go a step further.
Just how accurate do you need to be? For a home speaker builder, even an advanced one, this would seem to be flat enough through the midrange.

Do any of use think that we can really get in room bass measurements that are even close to as accurate as this mic? I doubt it.

The main question would be: "Do the mics match the published curves?" How much deviation is there from mic to mic? If it's close, I wouldn't worry much about it. Just take into account the small deviations published.

If you have an anechoic chamber along with tons of software and hardware to really measure right, you probably won't be buying this mic anyway, right?.

(Yes, I have one)

[Twisted85]

Thanks for your replies!

Just by looking at the corretion file(s) I have, the corrections between 200Hz-5KHz seems to be quite small. I have one file that came with TrueRTA and other that I downloaded from internet (which was recommended and I was told it was better) but there is one big difference. The one I downloaded separately doesn't have any phase correction. How accurate the phase correction should be?
For example: I'm planning to make a delay circuit for the tweeter to match the "depth" of the drivers and phase, how much possible difference it could make in the design if I use uncalibrated mic?
I am not an expert speaker builder and this is first time I will use more computer programs in the design process (soundeasy should arrive tomorrow), but I'd really like that the measurements would be accurate, so I can be sure that I have correct data to work with.
Does anyone have any experience comparing calibrated and uncalibrated microphones and does this make any noticeable difference?

At the page claudio linked there seems to be two calibrated mics, the other one is double the price. Any quality differences between these? The more expensive one looks exactly like ECM8000 but is more expensive even without calibration.
I bought some time ago a better soundcard, M-Audio FireWire 410 which has Phantom power for my Behringer mic, how does the less expensive choice "EMM-8 Bias supplied" mic work?

I'm also planning to make a similiar dipole testing baffle which is introduced at zaph's page. How large this should be? The bigger, the lower the data is accurate, right? I've been thinking something between 1,5 to 2meters.
What about the lower frequencys? What is the best or most convenient way to do this at home or yard? Or is this possible without a closed baffle?

[Dave Bullet]

I use Speaker Workshop for measurement - which uses actual measured phase as opposed to applying some sort of transform, ie. HBT.

In my case, I don't think mic phase matters. After all, if you are measuring 2 drivers with the same mic. If the same setup and mic are used, then it is the relative phase between drivers that counts.

Not sure why you want your own test baffle. If you intend to design crossovers for drivers you have selected looking at others (ie. Zaphs) or manufacturer measurements, it is best to measure drivers on the target baffle in the target enclosure.

You will then see the true effect of baffle step (in combination with the woofer you've selected) plus effects of baffle diffraction.

The size of the baffle will lower the baffle step frequency - true. However, with SpeakerWorkshop you need to gate measurements so you don't pick up room reflections which will colour the driver response. For example - to measure down to 100Hz with speaker workshop - you need a 10ms gate. This requires approx 3 meters clear in all directions (including floor and ceiling) - which in most measurement rooms is the limiting factor.

Therefore use a test baffle and enclosure if you are designing an actual crossover, or if you want to test drivers on a baffle board - be wary of room dimensions/ need for anechoic conditions.

Cheers,
David.

[Twisted85]

Originally posted by Dave Bullet
[B]Not sure why you want your own test baffle. If you intend to design crossovers for drivers you have selected looking at others (ie. Zaphs) or manufacturer measurements, it is best to measure drivers on the target baffle in the target enclosure.

My last speaker project was the first I designed by myself. I made a simple 2-way speaker with a waveguide.

http://koti.mbnet.fi/twisted-/kaapit1.jpg

I made measurements with ARTA and made changes by looking at the measurements and listening. I'm very satisfied with both the sound and the measurements.

Today I received a packet from partsexpress which included 4 Dayton RS180-8 drivers and SoundEasy (I also ordered the manual). I'm also going to buy Peerless HDS tweeters from local store and my next project will be 2,5-way floorstanding speakers, tweeters located between the mids.
I though that the best way would be to measure all the drivers in "infinite" baffle and make all the box/crossover simulations and design in SoundEasy, but is this false?
I was also planning that I could make my own comparisons between different drivers. I'm also into car audio, and I would also like to measure different drivers that are designed to work in a car and make comparisons.

How does Zaph make his low frequency measurements?
Here is a quote from his site: "Woofers however have to be done in two steps with close mic (1/4") and no gating, and spaced mic with gating. The gating varies depending on how close I can get the mic."
Advice would be appreciated here.

The size of the baffle will lower the baffle step frequency - true. However, with SpeakerWorkshop you need to gate measurements so you don't pick up room reflections which will colour the driver response. For example - to measure down to 100Hz with speaker workshop - you need a 10ms gate. This requires approx 3 meters clear in all directions (including floor and ceiling) - which in most measurement rooms is the limiting factor.

3meters would mean ~ 6meters from driver to surface and from surface to the mic, is this actually necessary with 10ms gate? (some explanation would be appreciated )

I don't understand why Zaph uses 4'x8' baffle, wouldn't 4x4 serve the same purpose?

I'd really like to everything go right from the beginning of this next project and really make all the measurements as good as I can. I don't even have any use for these speakers (or the 2-way speakers I made) I just want to learn more and more about building speakers

[claudio]

Originally posted by Twisted85

How does Zaph make his low frequency measurements?
Here is a quote from his site: "Woofers however have to be done in two steps with close mic (1/4") and no gating, and spaced mic with gating. The gating varies depending on how close I can get the mic."
Advice would be appreciated here.

It's called the near field measurement, which is spliced with the gated far field to obtain the total driver response.
For more infos on how to do it, check my home page, it's all written there. Doesn't matter I show it with Speaker Workshop, the procedure is the same, just the software is different.

[Twisted85]

Originally posted by claudio

It's called the near field measurement, which is spliced with the gated far field to obtain the total driver response.
For more infos on how to do it, check my home page, it's all written there. Doesn't matter I show it with Speaker Workshop, the procedure is the same, just the software is different.

I read about that from your homepage and from loudspeaker design cookbook.
So, even If I'd want to test 10" drivers I don't need a very big baffle. If I make a 1x1meter baffle, the bafflestep would be around 150Hz, right? And with 10" driver the upper limit with near field measurement would be around 450Hz. So I can then merge these two results?

How does near field measurement work with a driver that has phase plug?