Hello Camplo
You ever hear of analysis paralysis?? If I were you I would be bolting on your driver to the horn and figuring out the center of gravity of your horns and driver and building a sled you can move back and forth and easily adjust any tilt as required. I would also limit the PEQ points to a minimum. You can think this stuff out to the cows come how but sooner or latter you have to bite the bullet and execute your design.
Rob 🙂
You probably have nothing to worry about at 10% distortion levels.
The oscilloscope could tell you something, but you'd need to learn how to interpret what it can tell you.
I've mentioned using the CEA-2010 test many times already, it will make the low frequency limits of your horn/driver obvious, not only in the measurements, but audibly.
I'd suggest first working with your 15" to get the procedure down, then progress to the AXI-2050.
The horn should be angled down to point it's center axis at the test mic, so the (beamy) upper harmonics read correctly.
Grass will attenuate the upper harmonics a bit, placing plywood or other smooth hard surface in the two meters of ground between the mouth and mic would minimize that slight reduction.
https://brentbutterworth.com/cta-2010-manual
Art
Looking at matching bass (horn) solutions, there are many options, but few candidates for a true 2 way.
I believe Camplo has already been working on a PPSL-like solution, which should be good up to about 300 Hz.
Personally I like this one much better - especially in MMTMM configuration 🙂
The low-end extension is unfortunately limited to 70 Hz, which is of course perfect for midbass.
Considering portability, I would choose a modular solution myself.
A 4x15 cab with Tractrix mouthpieces (like the Klangfilm Euronor) could be a combination providing extension to below 40 Hz, a handful dB's of gain and directivity to match Camplo's mid/high horn, which can then be mounted coaxially in the horn mouth.
Alternatively, the same 4x15 cab can be used separately with the horn on top, or... you split the cab into 2 (2x 2x15), which can then also be used in MTM configuration.
I believe Camplo has already been working on a PPSL-like solution, which should be good up to about 300 Hz.
Personally I like this one much better - especially in MMTMM configuration 🙂
The low-end extension is unfortunately limited to 70 Hz, which is of course perfect for midbass.
Considering portability, I would choose a modular solution myself.
A 4x15 cab with Tractrix mouthpieces (like the Klangfilm Euronor) could be a combination providing extension to below 40 Hz, a handful dB's of gain and directivity to match Camplo's mid/high horn, which can then be mounted coaxially in the horn mouth.
Alternatively, the same 4x15 cab can be used separately with the horn on top, or... you split the cab into 2 (2x 2x15), which can then also be used in MTM configuration.
As Robh3606 rightly pointed out elsewhere, YT videos are generally unsuitable for providing a realistic impression of a loudspeaker system in a particular room. This video is therefore only illustrative of a rather large mid horn (which in this case is loaded by 2!! WE 555 substitutes) with direct radiating low section.
At this point why not a waveguide???
Well what the heck! Where did I get the notion? Is 7-10% thd expectation at xmax strictly a dynamic driver type rule of thumb or is it not even consistently true? The thresholds of the CEA2010 burst are based around distortion values once again. This seems like a good way to set dynamic limits for a driver but not for finding xmax or xlim. Am I correct?
No, it doesn't need it, but I bet a horn loaded woofer will match the overall signature of your e-Trak horns much better. Especially as you've perceived the (positive) effects of horn loading down to the low midrange.
This 50 Hz mid bass horn is theoretically sub-optimal, because it's too short and the mouth is undersized. In addition, it is crossed 1st order at 250 Hz 🤔
Despite this, the system has received numerous positive reviews and the bass reproduction is sufficient for most owners (about 40 Hz in room).
What if you'd enlarge this horn by 25-50%?
This 50 Hz mid bass horn is theoretically sub-optimal, because it's too short and the mouth is undersized. In addition, it is crossed 1st order at 250 Hz 🤔
Despite this, the system has received numerous positive reviews and the bass reproduction is sufficient for most owners (about 40 Hz in room).
What if you'd enlarge this horn by 25-50%?
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The CEA-2010 “pass” limits are a metric for comparing usable output based on objectionable distortion components, not for finding mechanical Xmax or Xlim measurements.
The distortion generated when a driver reaches Xlim will likely be above the CEA-2010 “pass” limits, or the more stringent CEA-2010A thresholds of -25 dB for the 4th and 5th harmonics, -35 dB for the 6th, 7th and 8th harmonics, and -45 dB for 9th and higher harmonics.
The AES2-1984 (r2003) defines Xmax for Low Frequency drivers as:
“Voice-coil peak displacement at which the “linearity” of the motor deviates by 10%, Xmax. Linearity may be measured by percent distortion of the input current or by percent deviation of displacement versus input current. Manufacturer shall state method used. The measurement shall be made in free air at Fs.”
Few manufacturers appear to use that definition, most derive Xmax as a linear mathematical value derived from various calculations based on voice coil vs gap height. Regardless of Xmax derivation, the distortion produced in free air at Fs won’t inform what distortion products occur at other frequencies and loading due to cabinet design.
If listed, a high frequency driver’s “Xmax” is probably the diaphragm to phase plug spacing, equivalent to Xlim, Xmech, Xdamage in a loudspeaker. Unlike a loudspeaker, the HF driver motor may be linear over the diaphragm’s entire range of excursion.
Art
Although a waveguide is not comparable to a real (mid) bass horn, it should offer some advantages over direct radiation (directivity, slight increase in efficiency).
JWC has designed an 1/4 space Tractrix successor to his 70Hz Tractrix midbass horn.
It is a dual 12" design that already goes down to 40 Hz in the ported version.
A dual 15" version should improve things further.
I would go for the ported version, but closed may be preferable if additional subs are used.
Front ported:
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CEA-2010A Traditional
(1M peak) (2M RMS)
40-63 Hz average 135.5 dB 126.5 dB
63 Hz 135.2 dB 126.2 dB
50 Hz 136.0 dB 127.0 dB
40 Hz 135.4 dB 126.4 dB
20-31.5 Hz average 130.5 dB 121.5 dB
31.5 Hz 133.6 dB 124.6 dB
25 Hz 131.4 dB 122.4 dB
20 Hz 123.7 dB 114.7 dB
200hz won, mainly because it seems the woofer involves the room more but 200hz seems to be that particular point in the spectrum that is the veil to localization in this room, for the midwoofer... There seems to be a transition at 200hz to where as if I move the point up or lessen the slope, theres, like, a veil lifted off of the midwoofer saying.....here I am, where as a steeper filter at 200hz on the mid-woofer disappears within the presence of the horn.
I will have to take this with a grain salt just incase all these ideas go out the window once in a more permanent position. This is just what I perceive in this present case.
Please don't be mad at me lol! Soooo in the nearfield whats going on? My guess is that nearfield suggest, being within the influence of heavy direct energy and if I use the inverse square law I will be exercising conservative views, by using 12" measurements that are within nearfield?
Using the Hulk movie as a template of potential true peak dynamic slope combined with the ideas of equal loudness.... it seems I'd only need ~110db at 1meter at 200hz...with at least a 200hz 2nd order XO I believe this is possible, in contingency with the above question....Also consider that 200hz will be another -3db in use of the XO taking even more load off.
So because I know that I don't know....I will go outside, voice, and check at 1m.
I moved the microphone over about 17" horizontal and the ripple did not "move"...
I think I am all set for a 200hz 12db or 48dbt XO with regards of headroom... I believe I only need about 110-108db capability for headroom, at 200hz and I have that and then some I think.... Heres another outside measurement at 1m with voicing and 200hz 48db bessel. Not much, changes at, 200hz, between 48db and 12db slope, so either seem to fly. Below is 48db bessel at 200hz.
I don't know why I perceive this to be such a chore ....call me lazy... and then after I get everything back inside I remember that I did not take any off axis measurements...oommggggggg.
I have no idea what measurements you are comparing but the diffractive ripple in a measurement has to move if the distances involved are changed.
Most likely what I am describing is not the same thing you are.
Camplo, label your charts, maybe I could then tell what the traces are. In the above, the response is quite different in the frequency extremes, if they were measured in the far field, they would be nearly identical, if they were both on-axis.
I'll get back to you on that...supposed to rain soon. But yes...
I pretty much disregarded the 12" measurement and you inspired me to take the horn back outside and take 1meter measurements... Outside, I voiced the speaker and then I used the CEA2010 tone burst to test frequencies in the cross band for distortion, -4.5db on the gain sounded about right to me, as in, I shouldn't go higher this sounds distorted enough, then I ran a sweep as you can see in the last measurement.
is there some other information you wanted? The horn is on my deck, facing the sky.
Not trying to ruin the measurement party, but the outcome won't be fundamentally different from what I predicted based on the measurement data of the eTrak 300 by K+T. The horn is a physically fixed item and the limits of the Axi 2050 are also known.
The last plot roughly reaffirms these predictions: 200 Hz = lowest limit, 300 Hz = reasonable lower limit.
You could measure until hell freezes over, but you only change the observation points and/or the conditions, obviously not the physics of the DUT.
The last plot roughly reaffirms these predictions: 200 Hz = lowest limit, 300 Hz = reasonable lower limit.
You could measure until hell freezes over, but you only change the observation points and/or the conditions, obviously not the physics of the DUT.
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