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Multi-Way Conventional loudspeakers with crossovers

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Old 12th September 2017, 06:52 PM   #14681
gedlee is offline gedlee  United States
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Originally Posted by ra7 View Post
Yes, if the timing is grossly out of sync, then yes, it is audible. I've had it happen to me a few times because the FIR correction produces different delays for my subs and mains, and you have to get them somewhat aligned, otherwise it sounds odd. However, these are gross errors, on the order of 10s and 100s of milliseconds. But the delays or phase warps produced by crossovers are so minimal that they are unlikely to be audible.

I read that note you linked from Troels. Seems to me like he is expressing his subjective opinions on the different on- and off-axis frequency responses produced by different orders of crossover. The conclusion I do not agree with. It is not that one crossover order is preferable over another because of its so called "timing" benefits. But that different crossover orders produce different frequency responses and those are audible. How two drivers combine depend upon their inherent responses, relative position on the baffle with respect to the listening position, crossover point, order, and type. At the end of the day, its not the crossover order but the on- and off-axis response that matters. When we express subjective opinions, we are simply responding to the FR. Nothing more, nothing less. Now, I'm sure I'll be run out of the room with this notion, but it's been well established by folks much smarter than me, and who've spent their entire lives researching this topic.
RA7

I would tend to agree with you nearly 100%, with one caveat.

Years ago I believed that all studies of phase showed it to be virtually inaudible and I saw nothing in the theory of hearing that would allow for phase detection (the ear is mostly an energy detection system and phase is lost.) However a paper by Greisinger some years back showed me how the phase between harmonics of a complex signal would affect the amplitude of the signal on the cochlea and that this could affect detection and audibility. That said, the major results on phase still showed it to be inaudible, but now I could see how the physics of audibility might happen.

It seems to me that given a system with significant amounts of diffraction would swamp out the signal phase and hence it would not be detectable on such a system. But a highly developed set of loudspeaker with very small amounts of diffraction placed in a room where the diffraction around the speakers has been minimized and the phase could possibly be detected.

I have never witnessed this to be the case, but some reputable people have. Almost without except they report it as a fairly minimal effect, implying that so many other aberrations often present could mask it.

That's where my opinion now stands - theoretically possible, but undetectable for the most part on most system.
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Old 13th September 2017, 06:44 PM   #14682
docali is online now docali  Germany
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Default Radian investigatins

Just did some further investigation of the 745neo driver.

With the back cover open it showed no damping material at all in the back chamber. Would some thin damping foam help to damp inner chamber resonances? 5mm should work and would left some space towards the diaphragm.

What is very interesting that the the back cover has a small hole which allows some ventilation of the chamber.

Measured also the impedance of the driver lying flat on the table with it's opening as suggested here in the thread (diphragm in a very small closed box). Sorry, but I find this method absolutely useless. The impedance curve is completely different from the two shown before (free air and CD horn). The highest peak looks deformed and is shifted to about double the free air peak and not so high. There are several other higher frequency peaks. All in all it shows no similarity to the former curves. The free air curve remains my favorit as reference.
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Old 14th September 2017, 12:37 AM   #14683
gedlee is offline gedlee  United States
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Measured also the impedance of the driver lying flat on the table with it's opening as suggested here in the thread (diphragm in a very small closed box). Sorry, but I find this method absolutely useless. The impedance curve is completely different from the two shown before (free air and CD horn).
Of course it's "different", it has to be different. Just because you don't know how to use the data does not mean that it is "useless".
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Old 14th September 2017, 06:32 AM   #14684
docali is online now docali  Germany
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Originally Posted by gedlee View Post
Of course it's "different", it has to be different. Just because you don't know how to use the data does not mean that it is "useless".
IT is nice that you let us know that you most probably know how to use it but do not tell. This is not the sense of an official forum.

I assume that we need to know the inner volume the driver is working on while it is terminated by the table?
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Old 14th September 2017, 02:27 PM   #14685
Kindhornman is offline Kindhornman  United States
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Docali,
like testing a compression driver face down on a table there is also a test for cone drivers where you block any movement of the cone and measure the blocked impedance. The tests you use have a lot to do with the type of impedance curve you are looking for. You may want the free air, horn mounted or even a terminated tube for a compression driver test of acoustical impedance but someone can be looking at acoustical impedance changes and another person needs to know the ac impedance of the voice-coil. I think that was what Earl was alluding to.
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Old 14th September 2017, 05:36 PM   #14686
gedlee is offline gedlee  United States
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Correct, what you do with the data depends on what you are looking for. Face down nulls out virtually all acoustic effects, which is highly desirable if one is trying to determine some of its mechanical parameters.

One could mathematically determine the parameter content of the blocked impedance, but I just took a simpler route. I had a computer model of a compression driver and I would simply fit the models impedance curve to the measured one. Since you know that only mechanical parameters are significant you only need to manipulate the mechanical ones (and the Bl). Then fit the impedance to the open throat case and maybe an open back case and you have all the parameters that one needs in a model. This is an iterative process but once you get a fit in all two or three cases you can be sure that the parameters that you have are the correct set.

As anyone who deals with compression drivers knows it is very difficult to determine things like moving mass, compliance, Bl, etc. My techniques works, but there may be others. But they are certainly not "useless".
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Old 15th September 2017, 12:39 AM   #14687
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Anyone have recommendations on what exhibitors to visit at this year's Rocky Mountain Audio Fest?
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Old 15th September 2017, 02:04 AM   #14688
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Anyone have recommendations on what exhibitors to visit at this year's Rocky Mountain Audio Fest?
My approach is to keep going to rooms, looking for something that seems both novel and nonridiculous, listen to those if I can. Then when I get good and tired of doing that, I just hang around and talk to people. Nothing really targeted to listen for, though I'd like to hear maybe the Grimm speakers.
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Old 15th September 2017, 03:59 PM   #14689
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Originally Posted by gedlee View Post
Correct, what you do with the data depends on what you are looking for. Face down nulls out virtually all acoustic effects, which is highly desirable if one is trying to determine some of its mechanical parameters.

One could mathematically determine the parameter content of the blocked impedance, but I just took a simpler route. I had a computer model of a compression driver and I would simply fit the models impedance curve to the measured one. Since you know that only mechanical parameters are significant you only need to manipulate the mechanical ones (and the Bl). Then fit the impedance to the open throat case and maybe an open back case and you have all the parameters that one needs in a model. This is an iterative process but once you get a fit in all two or three cases you can be sure that the parameters that you have are the correct set.

As anyone who deals with compression drivers knows it is very difficult to determine things like moving mass, compliance, Bl, etc. My techniques works, but there may be others. But they are certainly not "useless".
Ok, but what is the benefit or value add for many others like me being not on your level or having less experience using the impdenace curve driver face down? What is the practical use if one wants to build a new speaker and needs to design a cross-over?

Your suggestion was given around the discussion aligning/center an diaphragm with help of the free air impedance. So, can we use your method face down to the table to align the diaphragm as it was suggested by the guy for which I provided the link in this thread?

What is your prefered method to align an diaphragm?
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Old 16th September 2017, 02:21 AM   #14690
Kindhornman is offline Kindhornman  United States
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Docali,
I would think a series of impulse responses would be more appropriate for time or Phase alignment that anything an impedance curve could tell you in that regard. The true impedance traces would be much more valuable for XO development and while looking for any mechanical resonance problems.
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