Something stirs in the Undergrowth

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chris661
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#2116 Re: Something stirs in the Undergrowth

Post by chris661 »

Measurements are difficult. Room reflections mean some frequencies will cancel out perfectly at a steady-state. Move the mic 3" and a whole new set of peaks and dips appear.
Try putting the mic within 1 foot of the ribbon, and see what you get.

Our ears are good at filtering out reflections and "uncorrelated" stuff. Mics are terrible at it.

Remember that adding the cap would shove the slope frequency up an octave. If you're running a first-order crossover, then you're looking for a 6dB difference below the rolloff point... IF the ribbon doesn't have anything of it's own going on. If the ribbon is rolling off acoustically at 18dB/octave below 4kHz (to pull numbers out of the air), waving a 6dB/octave slope around isn't going to change much.

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#2117 Re: Something stirs in the Undergrowth

Post by ed »

chris661 wrote: Tue Sep 05, 2017 11:37 am
Try putting the mic within 1 foot of the ribbon, and see what you get.
?

I have never moved the mic or the dut in all measurements I have taken. except 45 degress off axis at 1m.
I always thought that looking back through historic measurements I would never be comparing apples with apples if I had moved anything. I have turntable control which I've never used. I always thought keep all distances the same and all angles repeatable.

imo madness lies in that direction.

diet: bit of misinformation there, looking through notes I see that sometimes I've used a chair to get quad ESLs to listening height and off the ground...only exception I can find
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#2118 Re: Something stirs in the Undergrowth

Post by chris661 »

Close-micing improves the SNR hugely. If Mark's measuring at the listening position, he's measuring the room at a steady state, reflections and all. Trying to optimise a crossover with all those reflections going on would be a nightmare. I wouldn't even attempt it.

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#2119 Re: Something stirs in the Undergrowth

Post by ed »

I wouldn't advocate near field measurement for aligning any filter, let alone xover tuning. I accept near field measurement might be used to overcome the effect of low frequenct standing waves..it can wipe out diffraction and room effect, but that isn't what Mark is trying to achieve, if I'm understanding what Mark is trying to achieve.

Keele has written extensively on close micing...it's not for xover comparisons.

I maybe spouting complete bollox but I would stick with 1m measurements for comparison. The other issue is that of using a test CD in this set-up. I can't see why the generator is not being used.
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#2120 Re: Something stirs in the Undergrowth

Post by IslandPink »

Ok I more or less agree with Ed here. I can't measure the ribbon at 1 foot away, because the two midrange drivers are 8 inches and 12 inches away , and I'm trying to level-up the FR in the range 4kHz to 10kHz . I'd need to be at least a meter away.
OK maybe I should take a few measurements a few inches apart and average the results - I guess I assumed that since we are talking frequencies much above the room nulls/peaks in lower midrange, that this would be OK. I know this is not true for single tones even in the high treble from experience using the RadioShack with discrete frequencies.
However the bigger problem is that I just don't trust the data I'm seeing at all, because of the test I did adding ( in parallel) the 2.7uF cap to the high-pass on the tweeter. The curve I captured then was identical to previous, the level of the noise on the curve. There should definitely have been extra output in the 2kHz to 6kHz region , and there was nothing. However the ears certainly noticed a difference.
I didn't understand your explanation (Chris) of this bit and why you thought it wouldn't do as I just described. Bear in mind there is already a 3.9uF series cap ( and a choke first to ground, for a transitional 2nd-order ) to the tweeter.
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#2121 Re: Something stirs in the Undergrowth

Post by ed »

well as I see it, or to be more precise, the way I'd do it....

measure the speaker at 1 metre....MLS
measure the drivers from exactly the same position one at a time MLS

you should see the filter slopes for each driver and be able to see where the sums occur quite easily..

it should be easy to see the product of adjustments at this point....

I would lend you my Clio set up but for the fact that you're miles away and I've only just got it back from Simon...and I'm gearing up to do some measurements on the Walsh and radialstrahlers.

Notwithstanding the drawbacks of audiotester, you should be able to see the individual driver MLS plots and the effect of the crossovers fairly accurately if you use the generator. Whichever system I use I always calibrate the amp for 2.83v at 0.775v output. I can't remember exactly the procedure with audiotester but from memory there is a closed loop calibration and it should be possible to feed in the calibration figure of your mic.

Apologies if there is an email I haven't read yet, I'm not in the office at the mo.
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#2122 Re: Something stirs in the Undergrowth

Post by chris661 »

The problem with even measuring 1m out (which might be too close for some speakers) is that you're at a distance where room effects can easily mess up your measurements. Is the peak at 60Hz because the port is tuned incorrectly, because the room has a big peak there, or both?

Near-field measurements, while introducing their own problems, mean you can see exactly what the driver (and only the driver) is doing. You can check the out-of-band rolloff to see if it's where you want it to be.

It's another compromise. When Mark said he didn't spot any difference when modifying the crossover, my suspicion is simply that the room's own frequency response (for that speaker and that mic position) is having a much greater effect than altering the crossover a little. In order to get all that noise out of the way and see what's REALLY going on there, I'd still recommend nearfield measurements to check that the crossover is behaving as it ought to be.

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#2123 Re: Something stirs in the Undergrowth

Post by IslandPink »

chris661 wrote: Fri Sep 08, 2017 4:41 pm The problem with even measuring 1m out (which might be too close for some speakers) is that you're at a distance where room effects can easily mess up your measurements. Is the peak at 60Hz because the port is tuned incorrectly, because the room has a big peak there, or both?

Near-field measurements, while introducing their own problems, mean you can see exactly what the driver (and only the driver) is doing. You can check the out-of-band rolloff to see if it's where you want it to be.
Yes but at frequencies like this ( 5kHz or so ) with one of the drivers a cone, it's a vector sum of their outputs you'll hear & measure at 1m - not a scalar sum. So how do you combine the near-field measurements meaningfully ?

I have advice from Ed off-line which I'm mulling over ( equipment ) re. MLS . Otherwise I think the safest approach is to use my ears - after all, the only variables I have are one capacitor and the tweeter level. Basically it's almost there anyway, in terms of tuning.
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#2124 Re: Something stirs in the Undergrowth

Post by chris661 »

Mark, all I was trying to do is offer a way of getting your measurement system to show up what your alterations are actually doing. I strongly suspect they're being swamped by room effects, and moving the mic in closer will improve the SNR so that you can see what's actually going on with each driver.
We all agree close-micing has it's own set of problems. When you report that you've changed something but the measurements show no difference, it's time to take a look at the measurement method and see if there's a way of improving it.
IslandPink wrote: Sun Sep 03, 2017 8:37 pm Been trying to test the OB to finalise the tweeter high-pass today - without much success. Dunno if Ed is around, if so, Audiotester is producing perplexing results. I seem to get a frequency curve from the white noise ( from CD ) signal I feed the system - and it changes ever so slightly with different captures - so I believe I'm receiving some data which IS being processed - however the FR looks awfully choppy in the 1k to 10k regions, several +/-5dB peaks/dips. Not really expected from the drivers I'm using and the quality of the sound. The FR rolls off around 15kHz which might mean the new soundcard on this PC is 14-bit ? I have the 24-bit one I acquired a while back, which I saved from the old PC , haven't tried to fit this.
All I really want to do is check the area around 5 to 8kHz to set level and high-pass point. Having clip-leaded a 2.7uF cap across the 3.9uF I have on the tweeter and seen nothing at all happen to the frequency curve, this is where I started to lose heart.
I will just have to use my ears if I can't make headway on this.
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#2125 Re: Something stirs in the Undergrowth

Post by IslandPink »

Sorry Chris - I will make some more steps on this - eg. loading up AudioTester onto the laptop, thanks for your advice. As you say - simplify the measurement to confirm if changes are being seen. Been a bit 'messy' around here with some things going on the background that are taking up my spare time.
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#2126 Re: Something stirs in the Undergrowth

Post by IslandPink »

Not much practical happening, but this was very interesting recently, from Romy ( ps. Khorn = Klipschorn ) :

"I very much do not mind to try the biggest Khorn bass section with my setup. I am trying to figure out how to do it with buying the damn thing…

I need to say that the best midbass I hear in my life was from Khorn, well not from Khorn itself but from Vitavox CN-191, which was UK replica of Khorn. It was back in 2001-2002, if I am not mistaken. David Karmeli from Damoka Audio brought to Vegas a par of vintage Germans Klangfilms that made everybody pee with steam. I never had any warm feeling about David’s Klangfilms, however David also brought to Vegas a pair of Vitavox CN-191 with 151 drivers. He did not show the Vitavox and there was no room for them, so he dumped then it a corner of some kind of secondary room and did not even connect them. One day, at evening, when the Morons are gone he decided to plug them in. I was hanging around and did not care too much what he was doing, and he was doing something for a while and the Vitavox sound like shit. Then David informed us that he confused the polarity of the speakers and now it “should be better”. The sound suddenly turned to “holly shit” status. All of the sudden the speakers went alive and it was absolutely stunning. There was problems that I would comment in that sound BUT the midbass was truly beyond believe. Exactly after that events I went and bought a few very same drivers as I did feel that it was absolutely the best midbass I even heard. They were driven by Lamms ML2.0 I need to note that I heard CN-191 in a few other settings, including the very same David’s Vitavox CN-191. Any other time they sound like shit. I think David was bringing the same CN-191 during consecutive years into different rooms with pretty much unsuccessful results. In THAT Las Vegas however, in THAT very lucky room, the stars were aligned and it was truly midbass firework. So, taking about the corner loading idea I do have a kind spot in my hard and the hope that I with the same drivers will be able to get the same sound. How will it work in context of my specific corners/ room I have no idea.
"
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#2127 Re: Something stirs in the Undergrowth

Post by IslandPink »

Sorry not much to report here - still ill with something not fully diagnosed - though the list of things it isn't is quite long.
Still also waiting for the quartet of FX120 drivers from the dealer in France - will email them later this week to check on current prognosis.

Meanwhile here's a nice pic of Paul Klipsch a few years ago with a transparent demo model of the Klipschorn.
Klipsch_Plexi.jpg
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#2128 Re: Something stirs in the Undergrowth

Post by ed »

I was lucky enough to hear a pair in the mid 80s courtesy of a friend in Devon. I remember being awestruck at the time but I can't for the life of me remember what they sounded like...I do remember he was on a Nick Drake crusade so it was endless repeating of 5 leaves, nearly put me off ND, but didn't thankfully ..historic yardsticks are like smoke...
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#2129 Re: Something stirs in the Undergrowth

Post by IslandPink »

Thanks Ed. It's interesting that although the K-horns have some complaints on forums, it's usually the upper-mid horn or the tweeters that get the most flak. On paper you'd think the bass horn would have more shortcomings, but it seems pretty successful.
Another nice shot of the transparent one half way down this page :
https://positive-feedback.com/show-repo ... mage-2017/
Shows a sort of triangular splitter in front of the cone, rather like the phase plug used in the Vitavox 'Thunderbolt' which I would think is also present in the Vox Olympians.
Ps. Vitavox did a version ( licensed, I think ) of the Klipschorn called the CN191 which used their drivers, ie. K15/40 and the S2 compression driver - it's supposed to sound significantly better than the K-horn.
http://website.lineone.net/~empson/191Manual_part1.html
http://website.lineone.net/~empson/191Manual_part2.html
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#2130 Re: Something stirs in the Undergrowth

Post by Toppsy »

IslandPink wrote: Tue Oct 24, 2017 6:14 pm
Still also waiting for the quartet of FX120 drivers from the dealer in France - will email them later this week to check on current prognosis.
Mark,
I'm not at all surprised you are still awaiting the drivers. From what Scott has told me, Fostex are not making any new FX120 drivers, and haven't for quite some time now, and have no current plans to make any new units in the future. He says that Fostex are simply running down current stock of the parts they have to assemble drivers on an as-and-when basis they get an order placed by their distributers for them. Once the current stock of parts is gone, that's it, no more new drivers. So it's highly unlikely any the advertisers of these drivers will have them in stock and so the wait for them coming direct from Japan after Fostex have made up the units.
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