PA Top with AMT

Moritz Bachmann

New member
Nov 7, 2019
12
1
3
24
Austria
So although we are still busy with our subs we were able to do some measurements outdoor. As we were interrupted twice by sudden rain, we couldn´t test all we would like to. Also, as this is our first speaker design, we don´t know what REALLY matters in the measurements to aligning those three sound sources in a box into a well balanced loudspeaker. Anyone who knows good guidelines or papers to start designing the speaker, in terms of correct crossover settings, phase alignment and so on?
I downloaded xsim today and watched some tutorials, but i couldn´t find one for activ crossovers. What programs do you use (in combination with REW)?
attached are the measurement, mic was 1,5m off the ground, 2m from speaker, not normalized (we had no Voltmeter with us)
What do you think of them, the 2nd order LR at 650 Hz (we had a cll with Mundorf and they affirmed that the AMT will handle this crossover Frequency without problems up to 130dB+
We also tried things like mixing different slopes (36dB LR on low frequencies, 48dB LR for the high frequencies), i think I was misunderstanding a paper about MTM designs.... nevertheless it did work surprisingly good, which was the reason why we tested some EQ points with this setting.
What do you think about the 3 almost identical peaks in the IR for the 12dB LR measurement? Is this an evidence for no correct time/ Phase alignment?


PS: the new ordered Speakers show through a very rush "free space, speaker in hand" the same near field-behavior andas the following measurements doesn´t show any of them, we are fine with that)
 

Attachments

Stef Smits

Freshman
Apr 4, 2017
65
13
8
A few questions/points:

-Is your goal to build a passive XO for the box? If yes, getting such slopes will take a lot of components.. And looking at the current design, you don't have much space. So try getting them right with less.
-Using the correct DSP settings (active XO), you need to measure and try different settings. Knowledge is key, and there are topics to be found on the net regarding time and phase allignment. REW does have a disadvantage here, because you have to sweep every time to see what your results are. SMAART or similar would have an advantage here.
-For what purposes do you want to use that cab? If PA, the 650 Hz crossover is probably to low for the AMT.
 

Moritz Bachmann

New member
Nov 7, 2019
12
1
3
24
Austria
The XO will be active, I was using a dbx venue 360 until now, but a BSS Soundweb BLU 160 is on the way to replace it.

I will spend a lot of time to test different settings, XO and PEQ for sure, but still I don´t know which steps to go through to align the chassis correct, or how to tell from the Phase where and how to determine which XO (slope) COULD fit... I know there are no real rules to find the perfet XO, but my problems start earlier. How to measure and set the delay between the speakers, do I measure HF and LF without XO first to see their full response and try XO settings acording those measurements. Or do I have to make the first measurements after setting a "blind shot" XO?
I don´t want you to answere all of this, it would be just cool to find articles or videos about that stuff. Especially for REW i can find room acustic measurements tutorials only (well, it is a room equalizing program, obviusly)

The cab shall be for PA, but high sound quality is more important than a high SPL for us, so we defenitely don´t need 140dB. Let´s consider 100-150 Peoply, and it´s also ok if the last row doesnt´t have the full impact experience.
Also, we tried a 700Hz crossover, which doesn´t seem to have that much disadvantegs over th 650Hz.
 

Max Warasila

Graduate
Feb 20, 2013
1,170
53
48
Richmond, VA
Hello,

I am also making a 10" cabinet this summer. I think your issue last time your made measurements was definitely having to do with box reflections. I'd start with fiberglass insulation on the walls, just to see if you can get the higher order stuff to go away. Always my go-to for aggressive damping and reduction of reflections. Sometimes I've gotten decent results from 1.5" + of solid acoustic foam (the old d&b special!), but in my experience the insulation was much cheaper and made things easier due to it's "big stick" nature.

For measurement, I think it's really important to understand that your options are either to hoist the cabinet to 4-5 m and test at 1-2 m or do a mix of 2 m ground plane measurements for the LF (< 4 kHz) and 1 mgated IR measurements for the HF (> 1kHz). Testing Loudspeakers by Joseph D'Appolito is an excellent reference on the subject. I'd try and do raw driver measurements for each passband at 15 or 30 degree intervals to get a feel for what the box is doing, and how things will combine off axis. You can then use these to find the relative phase angle throughout your crossover (for your design, I'd probably choose at least 800 Hz because of the limitations of the AMT). If you're not interested in the polars (which I think you should be, personally) the best bet will be to simply use a gated IR measurement of each driver on axis at 2 m to find the Δt. The increased distance here is important because it reduces the error incurred from the vertical distance off axis of the 10" drivers.

I personally use ARTA for measurement - but that's just because I'm a cheapo! It's an excellent tool if you know what you're doing, though, and it's more than capable of matching the power of systems many times it's price with the right know how.