claudio said:
Ok, thanks.
I understood that it needs another type of preamplifier?
http://www.content.ibf-acoustic.com/catalog/product_info.php?cPath=26_27&products_id=29
I played with SoundEasy for few hours and came up with this:
http://koti.mbnet.fi/twisted-/baffle2.jpg
The driver is located so that the distance from the driver to the baffle edges differs from each side (55/70/85/100cm).
A bigger baffle would be a problem to move and this size of baffle was what I pretty much initially had in mind.
What do you think?
http://koti.mbnet.fi/twisted-/baffle2.jpg
The driver is located so that the distance from the driver to the baffle edges differs from each side (55/70/85/100cm).
A bigger baffle would be a problem to move and this size of baffle was what I pretty much initially had in mind.
What do you think?
I contacted the ibf Akustik about the microphones and here's a part of the response:
The EMM-8 itself cannot be supplied from Phantom power. A special "active" adapter is necessary that downconverts the Phantom power to the EMM-8 Bias power requirements.
Any comments/suggestions about the baffle?
The EMM-8 itself cannot be supplied from Phantom power. A special "active" adapter is necessary that downconverts the Phantom power to the EMM-8 Bias power requirements.
Any comments/suggestions about the baffle?
Twisted85 said:
Download datasheet for EMM8 from here:
http://www.content.ibf-acoustic.com...id=28&osCsid=8bf3f83b6aefd56af63a91e629170eeb
On the 3rd page of PDF they have a schemo for power supply for this mic. It is just basically an ordinary electret mic setup. Make an adapter to the XLR input and you are set.
It is unclear if you already have ECM8000. If you do I would not bother getting a new stuff.
For any practical measurements it will be quite sufficient, unless you are a perfection freak who likes a real party and has an anechoic chamber, or willing to go out to the desert and place all that stuff about 40 feet above the ground. In that case get already something like B&K 4133/4134 or Gefell MK202/221 if you have some dough to spare.
Hi Brandon.
Thanks for posting the FR graph. It looks like a lot of others I've seen around the web.
That bump at the top seems typical of condenser mics. Nice to know it's there and how big. You're right that it would lead you to think the top end is too bright when it might not be.
Good to know!
Thanks for posting the FR graph. It looks like a lot of others I've seen around the web.
That bump at the top seems typical of condenser mics. Nice to know it's there and how big. You're right that it would lead you to think the top end is too bright when it might not be.
Good to know!
I got the additional step-by-step guide yesterday and I've been just reading it before I have a possibility to make the actual measurements. (I need to make the probes and the baffle)
I was reading the instructions about the nearfield measurements which brought a question to my mind.
The manual says:
6) Reposition the mic so that it is on the axis of the driver but in then plane of the baffle.
Ok, I have a little issue translating/understanding this sentence but this means the mic is at the same depth as the baffle surface, right? The acoustic distance is also adviced to be set at 0.
I thought that the point was to get the mic as close as possible to the driver cone in a nearfield measurement?
If I want to measure a 6,5" driver which diameter is for example 12cm, the maximum distance is 0,055*12 which is 0,66cm, righ? If the mic is at the depth of the baffle, this is too far away?
And if the mic is closer to the driver, the acoustic distance should be negative, right? (if the acoustic distance equals to the baffle surface with all drivers)
Could someone explain this to me
I was reading the instructions about the nearfield measurements which brought a question to my mind.
The manual says:
6) Reposition the mic so that it is on the axis of the driver but in then plane of the baffle.
Ok, I have a little issue translating/understanding this sentence but this means the mic is at the same depth as the baffle surface, right? The acoustic distance is also adviced to be set at 0.
I thought that the point was to get the mic as close as possible to the driver cone in a nearfield measurement?
If I want to measure a 6,5" driver which diameter is for example 12cm, the maximum distance is 0,055*12 which is 0,66cm, righ? If the mic is at the depth of the baffle, this is too far away?
And if the mic is closer to the driver, the acoustic distance should be negative, right? (if the acoustic distance equals to the baffle surface with all drivers)
Could someone explain this to me
panomaniac said:
Not necessarily. That actually is a topic which can potentially create a lot of confusion.
The main problem is how the measurements were done, where the distance from the sound source to the mic, as well as a type of sound field are absolutely crucial.
All measurement microphones designed to give FLAT response in a CERTAIN FIELD (which can be pressure, free, or diffused one) where the high FR corrected according to that specific field. Should you measure the response of the mic in a different field the graphs will be totally off.
For example, if you take B&K 4134 which is flat to 40KHz in a pressure field mic and start measuring signal in a free field there would be a HUGE bump on the top.
On the other hand, if you take B&K 4133 (ruler flat in a free field up to 40KHz) and put it into a pressure field there would be a fall in high FR starting as early as around 2KHz.
Looking at the posted ECM8000 graphs, to me it actually seems more like a mic with a flat FR corrected for a diffused field, but used to measure in a free field.
Hopefully it helps.
Best, M
Marik said:
My knowledge in electonics is quite limited, so I need to ask more info about this.
Does my M-Audio FW410 supply Bias voltage to the Mic inputs? (couldn't find any info about this from the manual)
If I just make an adapter with a resistor and a capasitor like presented at this page should it work?
(referring to the Powering two wire electret capsule from soundcard bias voltage output title)
Marik said:
Well kinda, sorta.
But you do well to mention it. A tricky subject of which most people are not aware. And I'm not too sharp on it.
Yes, I see what you mean. The high end bump does look like the response that would happen because of the physical presence of the mic capsule.
The important thing to know, and Behringer does not tell us, is how was the mic designed to be used? It would seem that the ECM8000 was designed for room measurement, thus for diffuse field. If we are using it for speaker measurement, that's free field (or should be).
So if the ECM8000 is pointed directly at the source - the loudspeaker, it may exhibit that top end bump, because it was not EQ'd for use on axis.
Sooooo.... what should we do? Point the mic directly at the speaker and use a correction file that compensates for the HF bump? Or turn the mic ~ 90 degs. for diffuse field and assume it's flat at the top?
What's your take on it Mark?
panomaniac said:
Well, my point was that the speakers will not necessarily sound bright, if measured with this mic.
If we know there is this bump in free field in a microphone characteristic and if we have the same bump while measuring the driver in exactly the same free field, then the driver will be flat. That is not the concern.
The important issue is HOW and in WHICH CONDITIONS that bump in the mic characteristics was measured first thing, as that will determine bump's size and shape. Here the most we are interested in precise distance to the mic and amount of reverberant information reaching the capsule. Many people underestimate how much of the "room sound" a small diaphragm omni can pick even at very short distances and if the measurements were done in a living room the error can be quite significant no matter how well the room is damped.
Moreover, for example, reverberation of my living room is very different from yours and results will be completely different, so there is nothing to talk about any "scintific approach".
Since not all the folks here have an access to anechoic chamber and acoustical treatment of the room can be quite expensive (and impractical, esp. if your wife is not that diyhearted
), the practical way to do it right and have good repetative results is to make measurements outside in the field (of course, no buildings around), with very strict distance between driver and mic, and mounting the driver/mic structure at the certain height from the ground (the higher the better ).Best, M
P.S. BTW, the diffuse field mics should be turned about 70-80 degrees in a free field for flat response. Your 90 degree example was for pressure ones. But as I said above, we are not really concerned with that.
P.S.S It makes perfect sense that the ECM8000 is a duffuse field mic, as it is intended for use with room EQs.
Thanks Marik,
So bottom line is that the ECM8000 is designed for a diffuse field (we assume). Using it for direct on axis measurements of loudspeakers will result in a HF bump of the type posted here and elswhere on the Web.
So what to do? Either turn the mic 70-80 degrees to the source or use a mic compensation file to correct for the HF bump. Sound right?
Using the mic for room correction it can be assumed flat, at least from about 30Hz up.
BTW, I remember a Radio Shack SPL meter I bought years ago said to turn it 90 degs to the source if measuring speakers. I don't think the present meters say that.
So bottom line is that the ECM8000 is designed for a diffuse field (we assume). Using it for direct on axis measurements of loudspeakers will result in a HF bump of the type posted here and elswhere on the Web.
So what to do? Either turn the mic 70-80 degrees to the source or use a mic compensation file to correct for the HF bump. Sound right?
Using the mic for room correction it can be assumed flat, at least from about 30Hz up.
BTW, I remember a Radio Shack SPL meter I bought years ago said to turn it 90 degs to the source if measuring speakers. I don't think the present meters say that.
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