CLIO Clinic

[Zilch]

To those producing and using plots... are you doing some sort of spatial averaging that each other understands...?

No, it's primarily simple on-axis. Off-axis is done and shown separately for beamwidth and DI. We each settle upon those approaches which confer the highest personal level of comfort in the quality of the result.

To me, spatial averaging is dubious, difficult to interpret, and certainly much more difficult to accomplish and reproduce. If someone's reporting spatially averaged curves, I expect them to say so, as my assumption is not. I don't want to adjust frequency response for power response, either; the result is artificial. If something's anomalous, find it, figure it out, fix it.

With respect to curve smoothing, low resolution better reveals the big trends requiring adjustment. That's what's most audible, but I rarely show those here. At the other extreme, highest resolutions charactize more the quality of the test environment and methodology than the information of interest. It's a compromise.

Same with windowing. I think we pay attention to the scales, methods, and resolutions of what others post here, because we're familiar with the tradeoffs from our own experience.

As for "getting it right," I find the multiple driver/horn studies essential. It's important to work with a "typical" when doing filter fine tuning, then verify with multiples for confidence in the outcome. That also gives me the data to match pairs for systems, and a baseline for comparison to unknowns.

[And finds my defectives.... ]

[grumpy]

Zilch,

1) thanks for diverting my H9800 hijack... it needed divertin'.

2) helps to know what we're looking at. Thanks for pointing out the CLIO clinic thread
and taking the time to respond.

-grumpy

[Mr. Widget]

To those producing and using plots... are you doing some sort of spatial averaging that each other understands...?

When I get some free time I'll try to do some spatially averaged measurements... I'd like to replicate John Atkinson's measuring techniques so that I can get a better personal understanding of how his Stereophile plots represent what I actually hear. Among other things, he always measures at 50" away from the speaker and centered on the tweeter's axis... I have found that this is not always the most revealing set up, correlating to what we hear,... especially with some of the large horn based systems that are common here, but quite rare in "Audio Land" in general.

But as Zilch mentions, taking a simple on axis measurement is far less trouble.


Widget

[Robh3606]

When I get some free time I'll try to do some spatially averaged measurements...

Yes I would like to as well. All my stuff hase been on axis and I want to take a L20T3 and do a complete 360 degree test sweep using 10 degree increments. Even then it's a daunting 36 measurements. One of these days

Rob

[Robh3606]

Hello Zilch

How big is that Lab

I have the same issue with 7 1/2 ceilings in my basement. Go in close with the MLS and use Sine too. The advantage with Sine is it's quick and it only excites the range you decide to sweep. You sweep above your primary modes, drop something on the floor to help minimize reflections, and measure in close. You should be able to get as low as I am with these horns. Once I get below about 500Hz all hell breaks loose unless I am on top, 1/2"-1" off the driver I am measuring. How is the horn set-up?? Mine are on top of the 4344's and flush with the side. They are seeing 1/2 a baffle. Here's my basic set-up as you can see no big deal.

Rob

[Robh3606]

I was able to get these measurements on my 2122's going in close to the driver. The MLS is not windowed. Moved the 4344 into the middle of the room as far away as I could get it from the walls. Had the microphone about 2-6" off the dustcap.

Rob

[Mr. Widget]

Hey Rob,

For near field measurements you really don't need a great amount of space between the system and other objects in the room... I typically take them at 0.25" from the dustcap surface and at this location there is virtually no room or reflective information compared to the direct info. The curve you get will be slightly tilted up on the bottom...

For horns, if I am only measuring a single horn over it's entire spectrum, I typically take my measurements at 4-5 feet from the floor with 5-6 feet to the ceiling and an on axis mic distance of 1 meter. Under these conditions I can get a ~9msec. window before my first reflections. I'd guess my lower usable measurement frequency is around 300Hz.

I don't think you should measure the horns at 6", but I suppose, we could do some comparisons between 6", 12", and 1m curves and see what happens.


Here is an old plot of the Klipsch K-400 with KV-55... I wanted to get it's low end response which is supposed to be good to below 400Hz when mounted on a baffle... this measurement was taken with the horn mounted on the La Scala baffle with the mic on axis at 1m.

Widget

[Mr. Widget]

Your equipment rack seems unfortunately placed for the cleanest measurements, (maybe you could rotate your horn away from it 15º or so?) and I see another issue too. I used to take my measurements on a pedestal not unlike yours... now I place Sonex on the front surface of the pedestal... it does influence the response.

That said, what are we measuring? I mean... typically our horns will not be free floating in space, they will be on a baffle so a simulation of the actual baffle is probably the best way to get a better idea of what the final result will be... however, in Zilch's case where he is exploring for the sake of exploring, I think he should carve out some space upstairs in his house where he could get some really long time windows and use a pile of Sonex. As for the low frequency ringing in his posts on that other thread???? I am kinda curious about that. They seem strange to me.


Widget

[Zilch]

The brain freeze I'm having is that Rob seems to be suggesting windowing is unnecessary; just use sinusoidal or unwindowed MLS nearfield. Well, I'm gonna have to read the book again, apparently.

I can typically get 5+ ms in my space with thick bats of high-density (R-21, doubled) fiberglass on the floor to kill that reflection. I don't know why I was getting the ringing on 2370 horns. What I did tonight with Altec 811B looks much better, even though I didn't raise it up to the mid height of the room:

http://audioheritage.org/vbulletin/s...257#post156257

If I'm doing critical measurements, I raise the DUT up and wheel stuff out of the room to reduce the clutter. As more projects accumulate, I'm running out of space for that even, tho....

[Robh3606]

The brain freeze I'm having is that Rob seems to be suggesting windowing is unnecessary; just use sinusoidal or unwindowed MLS nearfield. Well, I'm gonna have to read the book again, apparently.

Hello Zilch

You don't have brain freeze. By me not windowing I am running the risk of my measurement being corupted by the room response. When I do window I get the same curve just less resolution. When I do a measurement set I run MLS and SINE. I use the two different measurement types to get the different information in each and to see if the set up is good. If I get almost identicle measurements I am confident they are valid for that measurement set-up. That's the key though. If I you use the same set-up and get repeatable measurements using 2 different measurement methods you have a valid set-up but the measurements are only valid for that set-up. There may be anomalies introduced into the measurement by the set-up. Attached are the impulse file and the effect of windowing on the response. The windows are at 6, 9, and 15 Miliseconds. The top curve is the raw MLS measurement with 1/12 octave smoothing. You can clearly see the resolution getting progressively more washed out below 1KHz. Almost looks like what happens when you change over from 1/12 to 1/3 smoothing. The basic curve remains but the detail and resolution get lost.

Hello Widget

That set-up may look odd but it works well for what I am using it for. I get repeatable measurements and changes are easy to see. That's what I am looking for with this set-up. That said any measurements I get are only good for that set-up. If I was using it to evaluate that actual horns low frequency performance it most definately would be baffled. I usually try to measure horns futher out as well however I will change distances to see what works and look for spectrum tilts when I get close. On the next run of diaphram measurements I will change the measuring distance to see what the effects are and post them here.


Rob

[Robh3606]

Bump

What's going on?? We want to try to resolve this or should I let this die??

Rob

[Zilch]

I'll try to resolve some of it in doing the Valencia fix testing. A bunch of drivers/configurations are on the docket here....

[Mr. Widget]

What's going on?? We want to try to resolve this or should I let this die??

I'm confused... what are we dropping or proceeding with?


...and that last plot of yours... The notes are garbled. What are you showing us?


Widget

[Mr. Widget]

To be blunt, he's a genius. Unfortunately he couldn't design an actual fully functional loudspeaker system that sounded reasonably good to save his own life.

In my opinion that isn't a unique situation...

As for the idea of outdoor measurements... I wish I had a quiet yard. Both Zilch and I are too near major freeways... actually the same one... I am about 1 block away from the West Coast terminus of Interstate 80 and Zilch is just about 10 miles away.


Widget

[Robh3606]

I'm confused... what are we dropping or proceeding with?


...and that last plot of yours... The notes are garbled. What are you showing us?

The discussion just kind of died. What am I showing you?? Did you read the post?? Just what the effects are with various windowing times. Just want to see if we were going to see if we could figure out what the ringing was. I have seen ringing on Sine measurements from reflections off nearby objects. Move the object it went away as an example.

Get it out on a stool in the back yard at least 3 feet off the ground and start measuring.

I don't think the neighbors will like that at 3AM. I have two major roads less that 1/4 mile away plus overhead airport traffic depending on the runways used. Outdoors sure would be nice!!

Rob