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Advices on First Crossover Design (VituixCAD2)
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Old 24th February 2019, 07:07 AM   #91
ScottG is offline ScottG  United States
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Originally Posted by MrZoltan View Post


When you speak of damping is it something more like that Acoust-X goo ?
Nope.
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Old 24th February 2019, 07:08 AM   #92
ScottG is offline ScottG  United States
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Tomorrow I pack my luggage's


-have a good trip!
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Old 24th February 2019, 07:14 AM   #93
ScottG is offline ScottG  United States
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-it's a nice looking driver, but it's going to require a LOT of volume (for it's lower freq. extension).. and it's not nearly as efficient nor is its mass comparable (for a give surface area).
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Old 24th February 2019, 10:40 PM   #94
MrZoltan is offline MrZoltan
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Originally Posted by ScottG View Post
..it's not exactly a "static" thing.

(Test) Baffle edges induce diffractive ringing depending on distance from the source. ..a 150 cm by 150 cm open panel is good enough down to about 550 Hz, driver centered without any acoustic absorption on the edge and at a distance of 1 meter. You can improve on that with a mineral wool surround (edges of baffle) of sufficient thickness (10 cm) - maybe 300 Hz. As you move closer to the driver, the quality improves a bit lower in freq.

In this respect (a baffle that size testing in that manner), is quite likely to be more of a limit than the room itself (and reflections) - assuming you have the driver away from points of reflection (..like floor and ceiling - say 4 feet from the driver center for each).

A 4 x 8 (foot) sheet is good to almost 400 Hz 1 meter without edge treatment.

Well, in the end I don't really understand the principle behind that setup for the measurement, but that is to be expected.


I have noted by searching online that often I find measurement done with the driver already placed in a cabinet, and the few I see where the measurement is done with a large front panel they don't write much about it.


Article : Speaker baffle design, diffraction and baffle step – Audio Judgement
In the linked article find some things my brain can process, I don't know if it's accurate.


By going with a to measure with a large front panel are we avoiding that the edge diffraction of the higher frequencies and back firing waves "pollute" the measurement ?
I was supposing with any panel size and edge type it was possible to interpret the frequency response and compensate the reading, but from what you write it seem it is not that simple.


The other problem I see if I get what you are writing right is that in practice my drivers will be placed at the center of that +-5x5 that mean it will effectively have the floor +-2.5 feet from center (You ask for 4 feet).


Would it not be possible to play with a front panel that is the size of the actual cabinet project, close the sides of it and use some absorbing material at the back to eliminate some of the back firing waves?
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Old 24th February 2019, 10:45 PM   #95
MrZoltan is offline MrZoltan
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Originally Posted by ScottG View Post
Note: this isn't an absolute requirement (..unless the driver has a small transformer like a ribbon), IF you have your protocol down (no high spl "spikes").

The cap depends on the Impedance of the driver. The lower the impedance, the larger the cap.

-you want a cap that's large enough to have almost no effect on the response you are measuring. It's a DC blocker for the tweeter. Say, 100 uf of cheap non-electrolytic cap for 8 ohms.

ex.

ERSE - PulseX

The part you say "if I respect the protocol" is the one I'm afraid

I have noticed that when I disconnect the USB connection from that UMC204HD interface it send a loud pop in the speakers, scary.


EDIT: I think I will practice my protocol with Boston Acoustics drivers I still have from before (Neo5t, 5.5lf, 6.5lf) and then go with the LS plan when I am familiar with the process

Last edited by MrZoltan; 24th February 2019 at 10:58 PM.
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Old 24th February 2019, 10:47 PM   #96
MrZoltan is offline MrZoltan
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-have a good trip!

Thanks Scott, I need it.
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Old 24th February 2019, 10:49 PM   #97
MrZoltan is offline MrZoltan
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Originally Posted by ScottG View Post
-it's a nice looking driver, but it's going to require a LOT of volume (for it's lower freq. extension).. and it's not nearly as efficient nor is its mass comparable (for a give surface area).

I was not suggesting to replace the AXP-08 but I found them nice for the price.
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Old 25th February 2019, 04:28 AM   #98
ScottG is offline ScottG  United States
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Originally Posted by MrZoltan View Post


..it seem it is not that simple.


The other problem I see if I get what you are writing right is that in practice my drivers will be placed at the center of that +-5x5 that mean it will effectively have the floor +-2.5 feet from center (You ask for 4 feet).


Would it not be possible to play with a front panel that is the size of the actual cabinet project, close the sides of it and use some absorbing material at the back to eliminate some of the back firing waves?


It's not that simple.. but it doesn't have to be particularly complicated either.

The "IEC" has several baffles for testing. (see the pic. below.)

Just remember that you are mostly interested in freq.s above 1 kHz.. for typical domestic (far-field) measurements.

BUT you want your windowing (reflection free zone) more than an octave below that if possible. (..windowing introduces artifacts to the measurement for an octave plus above it's freq..) So ideally you want your window to be lower than 500 Hz.



Yeah, you need to lift the test baffle off of the floor (stand) and have the driver almost equidistant from floor and ceiling. Alternatively you can stack pillows at the bottom of the floor. Or you could do a ground-plane measurement. (..you'll have to search for that.)



Measuring on a speaker cabinet already assumes the speaker is "the" shape: it takes a huge "chunk" out of the process of loudspeaker design within a modeling program. What happens if that's not the cabinet shape that you want for a really good design? ..or (particularly) the driver isn't placed in exactly the same position you want for a really good design? It's an ***-backwards way to design a loudspeaker.


Note: with the off-center position and measuring off-axis: measure off-axis toward the most distant point of the test baffle. Ex. in the pic. with the gentleman off to the right of the test baffle, you would move the mic./mic stand to the left of the board (using a protractor + ruler to get the right angle and distance from the driver being tested). This is for omni sources where you need only one group of angles out to 70 degrees (or so). HOWEVER for your little line tweeter you might want to test it again the same way/mic position but a second time with the tweeter rotated 90 degrees (on the test baffle) so that you measure the vertical response with the same amount of baffle. (..however there should be little practical difference with the measurement so high in freq..)

-btw, nothing says that the baffle need be made of wood. I've done it with small driver-mount area of wood and the rest of it with damped cardboard on a rear frame before.
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File Type: jpg IEC_baffle_anechoic.jpg (57.0 KB, 17 views)
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Old 25th February 2019, 04:34 AM   #99
ScottG is offline ScottG  United States
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I have noticed that when I disconnect the USB connection from that UMC204HD interface it send a loud pop in the speakers, scary.

..and:

FACE-PALM!


um.. yeah, lets not do that.
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