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ETF question


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6 replies to this topic

#1 of 7 JamesDB

JamesDB

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Posted February 23 2005 - 02:50 PM

I have been trying to get ETF to return fairly consistent reading for the sub in my living room. I notice when I take two consecutive readings, there can be as much as 6-10 dB change in some of the peaks and dips when FFTing into frequency vs dB.

1. Can the MLS in ETF give better results?

2. Additionally I notice differences between the sweep reading and MLS (gate time 200ms). Which one should be trusted?

3. I also notice peak frequency motion in their location

4. Lastly, when aligning the impulse initially during calibration, I have three distinct peaks, for sound card, system and system + soundcard. Which two do I need to allign up? I am thinking its system and soundcard.

How consistent and reproducible have your readings been?

Any thoughts or suggestions?

James

#2 of 7 JamesDB

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Posted February 24 2005 - 07:22 AM

No takers for some answers ETF experts?

I just got TrueRTA so I am going to try to compare the results I am getting.

#3 of 7 Ilkka R

Ilkka R

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Posted February 24 2005 - 07:37 AM

I suggest that for setting and measuring a subwoofer you use TrueRTA. I've used both programs and I kinda like TrueRTA more. ETF is of course much more advanced program and it has tons of different options, but they can be little bit hard to learn.

1: Compared to what?
2: I use MLS/low frequency
3: How much did the peak(s) move? (Hz)
4: Not sure what you mean, but system+soundcard is the measurement that microphone gives, so that is your real impulse response.

With TrueRTA I've done tons of measurements and they are very reproducible, less than +/-1dB differences. With ETF I've only done few, so I can't tell for sure.

What microphone you are using?

#4 of 7 Kevin C Brown

Kevin C Brown

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Posted February 24 2005 - 12:32 PM

James- I use ETF.

You are using the specific low freq test? I sometimes get "better" results by using the full range test, but just looking at the low freq range. (Low freq test only goes up to 160 Hz or so. I like looking to 200 Hz.)

I don't use the sweep. Just the pink noise tests.

Gating: a gate time of 0ms is the initial sound. If you gate to something like 200ms or more, you are picking up the nodes of the room too. Both are important, but a lot of people think that you should just look at a gated response for eq'ing the sub, for example.

For example, with a discrete test tone disc, the RS meter, and manually plotting points, the gate is something like a few seconds, plenty of time for any nodes to build up.

My results also move around a bit too. I'm not sure about 6-10 dB though. Maybe 3-5 dB.

I should look at TrueRTA someday though too... Posted Image
If it's not worth waiting until the last minute to do, then it's not worth doing.

KevinVision 7.1 ...

#5 of 7 Tim Holyoke

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Posted February 24 2005 - 02:35 PM

Major League Soccer? Exchange Traded Funds? I thought this was a home theater forum Posted Image ?

What are MLS and ETF?

#6 of 7 Kevin C Brown

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Posted February 24 2005 - 06:21 PM

http://www.etfacoustic.com/
If it's not worth waiting until the last minute to do, then it's not worth doing.

KevinVision 7.1 ...

#7 of 7 JamesDB

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Posted February 25 2005 - 07:10 AM

Key Kevin,

Too bad we don't live a bit closer, I'd ask you to come over and look at my room and readings. Maybe you'd have better insight than me.

I looked at the TrueRTA response (1/24th octave, and it seemed to be more stable. I see some corresponding data between the MLS and the RTA reading I took using the two programs. But I noticed another problem. I think I have gremlins in my system today. When I make parametric changes on my DEQ2496 my readings don't change. I am crossed over at 80Hz so maybe my paradigms 60s are still hitting too hard at the 50Hz room mode where I was trying to attenuate my curve 8 dB on just the sub. (There is another problem I see, but it's a discussion for another day and that is that the room behaves differently at difference initial volumes. This is where I should dynamically EQ the room but arghhh... this is too nightmarish since I can't even get it right at 1 level hahah))

Getting back to ETF. My couch where I am taking my measurements is pressed up to the back wall (my room is only 10ft to speakers) Is it possible that some of the strange ETF changing responses are caused by that? (There are also windows behind the couch) I run the near real time MLS (sub mode) and its amazing how much it changes. I'm thinking of trying a difference mic location.

I was going to mic an eq that falls between 0ms gate and 240ms gate since it should give me a fair balance between quick base transients and rumbling buildups.

Ilkka or anyone else

As for my initial question 4, I have three impulse peaks appearing. First a System peak, then System + Soundcard centered on 0ms, then Soundcard. The instructions tell you to make sure somehow they are aligned. When I do the +1 move impulse thing, I have both the System and the System + Soundcard peaks that move together. So I can either center the System+Soundcard over the Soundcard impulse or the System impulse over the SoundCard impulse or just leave the whole thing alone. Which one should be over the Soundcard impulse?

Thanks for all the help,

James