What frequencies to use for ETC measurement?

gremmy · 16th March 2010

Hi guys,

I took a look at an old ETC graph for my room that involved a bass frequency sweep, from 20hz to 200hz, and it occured to me that this probably isn't the best way to measure ETC since those lower frequencies are generally very difficult to absorb at first reflections.

To measure ETC, is it more reasonable to do a sweep of 1000hz to 20000hz? My goal is to create an RFZ, and then to see if I can do some interesting things with the Haas effect. But I'm never going to absorb reflections at 30hz.

PaulP · 16th March 2010

There is no frequency involved with the ETC, it's just an impulse. In large
halls they can use gun shots. I don't know how the impulse is produced when
using monitors, there's got to be some frequency involved for sound to be
produced, but there's no sweep.

There isn't enough time for it. For example, in an ETC graph a 6ms side wall
reflection is a single wavelength of 166 hz from the moment of impulse.

Lupo is the one to give you a real explanation.

Paul P

SAC · 16th March 2010

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gremmy · 17th March 2010

I'm using REW. In REW, I can generate an ETC on any "measurement." So, if I do a sweep from 20hz to 200hz, I can then go to the ETC tab and click the "generate ETC" button and the pic will generate. Based on what you guys are telling me, REW is allowing me to do something which is not entirely useful... Heck, I don't know.

As far as not limiting the frequency of the impulse, I'm not concerned with reflections that may or may not be happening at deep sub frequencies, as there's nothing I can do about them anyway. I've got a concrete wall on the other side of one of my stick-frame walls, with dirt on the other side of the concrete wall.. I'm pretty sure I've got reflections coming back into the room off that wall that are fairly deep. But what I really want to know is the effectiveness of the RFZ in frequencies where I can actually hope to make a difference.

SAC · 17th March 2010

klpjkl

16th March 2010	#1
gremmy Gear nut Join Date: Jan 2010 Posts: 107 Thread Starter	What frequencies to use for ETC measurement? Hi guys, I took a look at an old ETC graph for my room that involved a bass frequency sweep, from 20hz to 200hz, and it occured to me that this probably isn't the best way to measure ETC since those lower frequencies are generally very difficult to absorb at first reflections. To measure ETC, is it more reasonable to do a sweep of 1000hz to 20000hz? My goal is to create an RFZ, and then to see if I can do some interesting things with the Haas effect. But I'm never going to absorb reflections at 30hz.

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16th March 2010	#2
PaulP Lives for gear Join Date: Sep 2009 Posts: 1,196	There is no frequency involved with the ETC, it's just an impulse. In large halls they can use gun shots. I don't know how the impulse is produced when using monitors, there's got to be some frequency involved for sound to be produced, but there's no sweep. There isn't enough time for it. For example, in an ETC graph a 6ms side wall reflection is a single wavelength of 166 hz from the moment of impulse. Lupo is the one to give you a real explanation. Paul P

16th March 2010	#3
SAC Registered User Join Date: Dec 2009 Posts: 2,622	kkjl kl

17th March 2010	#4
gremmy Gear nut Join Date: Jan 2010 Posts: 107 Thread Starter	I'm using REW. In REW, I can generate an ETC on any "measurement." So, if I do a sweep from 20hz to 200hz, I can then go to the ETC tab and click the "generate ETC" button and the pic will generate. Based on what you guys are telling me, REW is allowing me to do something which is not entirely useful... Heck, I don't know. As far as not limiting the frequency of the impulse, I'm not concerned with reflections that may or may not be happening at deep sub frequencies, as there's nothing I can do about them anyway. I've got a concrete wall on the other side of one of my stick-frame walls, with dirt on the other side of the concrete wall.. I'm pretty sure I've got reflections coming back into the room off that wall that are fairly deep. But what I really want to know is the effectiveness of the RFZ in frequencies where I can actually hope to make a difference.