Need help with ETF and feedback into system... (1 Viewer)

[Craig Chase]

BruceD, I TRIED the manners approach with you. We will settle this one way or another. Either as friends, or not... I TRIED the friendly approach.

The ETF says ALMOST ANY SOUND CARD WILL YIELD NEARLY PERFECT RESULTS. That is a quote. I learned differently. I purchased my computer system in March, 2004, and according to the ETF help file, it was EVERYTHING needed for NEAR PERFECT results.

I also learned the even after calibrating MY Radio Shack, it was terrible below 200 Hz.

I told Mr. Dahl what I, through experience, thought.

The ironic part is this, I really think that you, with FIVE years experience, DO know more than I do about ETF.

ALL you had to do was suggest help, and NICELY let me know you were experienced.

You won't see me challenging Edward J M on measuring a subwoofer, and you won't see him attack me about his superior measurements....

I would STILL welcome working with you to learn more, but YOU will have to decide that I am not some pariah as you suggested.

In other words, if you want to try a new start, I am all for it.

If not, we both lose...

 

[BruceD]

I'll bite and agree a new start is worthwhile

The key to getting any mic/mic-preamp setup to work for low frequencies is making sure a mic-calibration file is loaded and making sure the ETF windowing (gate time) is set for >200ms. Otherwise you won't get accurate results for bass frequencies under 200Hz (just like you indicated). There are generic mic-calibration files available for the RS SPL meter. I think ETF used to have it on their website.

IIRC, the Behringer mic needs a mic-preamp to work with ETF, one that provides phantom power. This is why the RS SPL meter is still useful, as it provides mic and preamp together.

I agree a professionally calibrated mic with a mic-preamp (and calibration file loaded into ETF) allows for greater accuracy but, IIRC the RS-SPL meter is rated at +-3dB 32-10k Hz.

Also, the 3D waterfall chart is very useful for identifying obvious peak modal bass frequencies (those with persistance times that are too long) i.e the boomy bass frequencies.

 

[Craig Chase]

No Biting...

The ETF software is very involved...

1. Yes, The Behringer will still require a phantom power supply... so even if I send it, Paul cannot use it.

2. With the gating that open, (>200ms), the measured bass response will have the room effect in it, IIRC... but there really is no way around that. But since David is listening in his room, not a bad thing.

Dave, When you think of room boundries, and there effect on sound, sound travels about 1.13 feet every millisecond. If the nearest boundry (as in the floor) is 2.26 feet, all sound outside 2 milliseconds will have room effect. For bass, you cannot measure anything below about 250 Hz with a 2 millisecond window.

A 250 Hz signal has a wavelength is 4.52 feet long (1130/250) ... and a 1/2 wavelength will determine how long the gating window is... in this case 2.26 feet... or two milliseconds...

Thus... the ETF software can give you quasi anechoic response from 200/300 Hz and up, depending on distance of speaker (actual drivers) to nearest boundary...

SO... Once BruceD gets you to achieving acceptable performance, YOU get to figure out what you want to do...

The ETF software WILL give accurate in room responses below 200 Hz...

BruceD... Thoughts ?

 

[BruceD]

Since Dave has Martin-Logan electrostatic speakers, I'm not sure how low his frequency response extends. I don't know if he also has a sub.

I'm guessing Dave wants to measure in-room response, ETF's forte. ETF has a separate low frequency graph designed for 20-200Hz in-room frequency response.

Regardless of the actual frequency you want to capture, you want the in-room response of your speaker setup because that's what you actually hear in the listening position.

You want to identify those frequency anomolies/reflections that cause less than ideal listening experiences and correct for them with - speaker positions, listener positions, big furniture, rugs, acoustic wall treatments, bass traps, parametric EQ, etc.

Measuring a speaker in close to free space doesn't tell you how it will sound in your room in your listening position.

 

[Craig Chase]

I am chuckling here... I tried to point that out to a LOT of people in the past... You are right, of course, used right, ETF OR TrueRTA can be a BIG help in making the room better...

ETF is actually more powerful... TrueRTA is simpler...

 

[dave alan]

BruceD and Craig,

I'm glad to see a fresh start here.

I've read mostly every post the two of you fellas have written over the past couple of years and I always have respected both of you and come away with good info.

I've always thought that software maker's claims that the inadequacies of the mic and sound card can be nuetralized by calibration files is a bit misleading.

Also, a free space, or half space ground plane graph, when overlaid with an in-room graph can reveal a lot regarding the room's influence, when using a RTA.

Just my opinion.

The bottom line is that both ETF and TrueRTA are very affordable and great tools for us enthusiasts.

Discussions amongst us users of those tools in a public forum helps everyone to get the best use from them.


...just appreciating another great thread with info I'm interested in...

Dave

 

[Craig Chase]

Dave, Well said, As usual...

And yes, Bruce is VERY knowledgible, and an asset to the community.

 

[BruceD]

Shedding light on the mysteries for good sound is what we all want to do.

I find the knowledge and opinions of Dave and Craig to advance this forums understanding of these topics. Let's keep exploring all those corners with enthusiasm

 

[Dave Dahl]

Hi all,

I've only a minute before work. It turns out the feedback was due to an improper mixing setting (thanks Edward).

Later tonight (maybe tomorrow) I'll let everybody interested know what the results are.

-Dave

 

[Craig Chase]

Dave - Look forward to hearing about your results...

 

[Edward J M]

Cool. One would intuitively think that "Line-In" is the logical and correct choice, but that is not the case; "Wave" is the correct input to have running.

 

[Edward J M]

The reason I use a better sound card is primarily for THD work. The noise floor is much lower, and the card can take a higher input level before distorting. And even though TrueRTA and ETF both correct for the sound card's FR, I found that the new sound card had a more consistent response (particularly in the 10-20 Hz bandwidth) to multiple TrueRTA Quick Sweeps than did the original cheapie OEM sound card.

According to the calibrator Kim Girardin, my particular ECM8000 was damn flat right out of the box. I think the largest correction factor was about 2.5 dB (down) at 10 Hz. Nearly all of the CFs from 15-18,000 were 1.5 dB or smaller. If the ECM8000 has any failings, it certainly isn't its FR. Usually the more expensive mics can take a higher SPL before distorting. I doubt the ECM8000 is good for 140 dB or anything like that.

The standard FR correction factors for the c-weighted RS meter are of limited usefulness if you are going to do any serious FR work. The standard RS CFs are a combination of the theoretical correction factor for the C-weighted filter, AND additional correction for the inherent meter inaccuracies. I suppose if you are going to spend the time to get your RS meter professionally calibrated to obtain its actual CFs, you might as well buy a decent mic (and get IT calibrated), and use that instead. I?ve also read the RS meter tends to send a hot signal to the sound card line input, which can cause overload.

Only the very finest SPL meters have an unweighted option (it just disables the C-weighted filter), and even then, you still don't know the unweighted CFs for that particular mic and it would still require professional calibration.

My advice is to buy a decent unweighted measurement mic, get it professionally calibrated (don't use any generic calibration files), and input the actual CFs for THAT specific mic into the software. It's the only way to be sure you are getting the true FR.

Also, checking the FR of your mic pre-amp (if required for phantom power) isn't a bad idea; preamps CAN have FR anomalies, but they generally aren't large. I measured the FR of my UB1002 phantom power source by looping TrueRTA through it via the XLR mic input and Main Out (you can buy adapters fittings from RS that converts from XLR to TRS to 1/8"). The UB1002 was literally a flat line from 10-25,000 Hz. I think it might have deviated less than 0.25 dB. That's a darn nice mic pre-amp for the money, and dead quiet too. It CAN be overloaded, though (just like any mic preamp) with too much gain on the input side, so experimentation with the windows mixer, and the preamp line gain controls is definitely in order.

I see ETF in my near future, if for nothing more than the capability to measure group delay and impulse response. I'll be checking in with you guys for advice as I get it up and running.

Regards,

Ed

 

[Dave Dahl]

Hello,

Sorry about the delay in posting. Real life has a way of happening.

After first running the ETF software (without the feedback) I was shocked to discover that I have almost a perfectly flat frequency response below 200Hz. Of course, I was wrong. It took me a little while to understand what the slices were for. What an eye opener. I know understand where the boominess I perceived is coming from. There is a spot at about 40HZ where the 20, 40, and 60ms slices come together to from a big hump. At its peak it is 15dB above the 20ms slice (which I figure to be about 3 times as loud). Room interaction at its finest.

Fortunately I own a BFD Pro, with which I tried to tame the unwanted frequencies. Interesting enough I could not reduce the reflections enough. When I tried to use brute force and lower the offending frequencies by 48dB the graph changed a bit yet the subwoofer basically stopped producing sound. Tomorrow I will have to judiciously use the BFD Pro and target 43Hz more precisely.

-Dave

On a side note, the ETF software seems very cool. It will take some time before I understand all its features.

 

[Craig Chase]

Dave... ETF will make you scratch your head... think through it, and make decisions.

Right now... moving the subwoofer will help.

 

[Dave Dahl]

Craig,

Of course you're right in that I should be moving the subwoofer around before any electronic correction.

Keeping in mind that my goal is a flat frequency response what should the graph look like when it's done? For the sake of this discussion I will use four slices. Should the slices be at equal volume throughout between 20Hz and 200Hz or should I have a layered effect where the earliest slice (20) be the loudest while the others fall in volume at a constant rate?

Thanks!

Dave

 

[Craig Chase]

Dave - You are using the M/L Ascents... what subwoofer do you have, and where is it being crossed over ?

 

[Dave Dahl]

I am using a Velodyne FSX12 servo controled subwoofer. It is crossed over inside the receiver (B&K AVR507) at 80Hz.

-Dave

 

[Craig Chase]

Nice system ... Have you tried to get the flattest response with room location yet ?

Also .. once you do that, what will you be using to get the electronic correction ?

I would recommend you work on the subwoofer only, and not the M/L's ...

 

[Craig Chase]

Dave - Once you have gotten the flattest response, THEN you might look at some curves that you personally enjoy... but the first objective should be a flat to the deepest bass your system can achieve response...

 

[BruceD]

Dave,

If I read that correctly, you are not measuring low frequency room response accurately. 20, 40, and 60ms time slices are too short to accurately capture low frequency room reflections.

As I said in an earlier thread, you need to measure the 20Hz-200Hz low frequency response with a time slice >200ms in order to properly capture and identify modal room peaks i.e. boomy bass.

Hope that helps.