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Designing an active 2-way speaker crossover
- Thread starter Rick Sykora
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dc655321
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If that's a response to me, I did not refer to a single channel measurement.
Do you want to use a USB loopback? Doesn't this part of the quote above still remain: "USB microphones with latency variations by default are not recommended for speaker engineering due to timing and phase variations and normalizations."
dc655321
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Not necessarily, but it's what I have at the moment.
I don't know if that statement still applies to or effects the acoustic timing reference method available in REW.
I have been also aware of timing/latency issue associating with USB microphone loopback in time-domain measurements of our audio system, even though I could successfully measure my room acoustics with REW (wavelet analysis) and "single" Behringer ECM8000 mic connected to "the" PC with CEntrance USB Micport Pro as shared here to here.
Nowadays, therefore, I do not use USB mic loopback routing (ECM8000 + Tascam US-1x2HR) in any of the time-domain measurements of my system, but I use it only for Fq response measurements using separate/second PC by the "Cumulative White Noise Averaging" method, as shared here through here.
Nowadays, therefore, I do not use USB mic loopback routing (ECM8000 + Tascam US-1x2HR) in any of the time-domain measurements of my system, but I use it only for Fq response measurements using separate/second PC by the "Cumulative White Noise Averaging" method, as shared here through here.
OP
- Thread Starter
- #26
Yes, and there is no mention of any direct change to REW that alters the need for a non-USB mic. While USB loopback is supported and uses an acoustic timing ref, it does not work for multiple sweeps. Since each driver requires a sweep, seems USB mics still cannot be used by speaker design with REW. @JohnPM please correct me if I am mistaken.
EDIT: In a later conversation with John, found my mistake was due to some wording on the REW website. The multiple sweeps reference on the REW website help was for setting multiple repetitions (of sweeps) for a measurement session. I originally mistook this to mean measuring multiple times using an individual sweep. Bottom line, if you continue in this thread, USB mic measurements are fine as long as you use an acoustic timing reference. See post #35 below for details.
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If we just measure driver for crossover, can we just measure the frequency response and use extract minimum phase? I had read a lot of guides and this is what they all use. Of course at the end when we want to verify the phase response of speaker we can't extract minium phase.
Then you should start reading other guides as soon as possible
As long as the system being measured behaves as a minimum phase system, your statement is true.
For loudspeakers this is usually true as long as the driver performs ideal pistonic movements.
That is, the stiffer the material of the driver, the greater the frequency range in which the driver behaves almost like a minimum-phase system.
Here are a few examples of phase frequency responses of "phase*** versus minimum phase" - ordered from good to bad.
As long as the phase frequency responses are parallel, Minimum Phase can also be used instead of Phase.
*** phase = minimum phase + excess phase
1'' metal tweeter - Phase vs. Minimum Phase
0.75'' silk tweeter - Phase vs. Minimum Phase
4'' Midwoofer - Phase vs. Minimum Phase
8'' woofer - Phase vs. Minimum Phase
As an interim solution if you have " well behaved" drivers and do not push the crossover frequency too much, the method works quite well, but certainly not as a general solution to speaker design.
Update: All measurements shown were performed as dual-channel measurements.
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OP
- Thread Starter
- #29
I will add briefly to @ctrl's shared wisdom. I used a UMIK-1 for my own purposes and made usable measurements with it. The accuracy of the measurements may have been good in some cases and lousy in others.
I decided to ditch it when I did Directiva and wanted measurements with better accuracy. It took me a while so actually did in the middle of the r1 project. When I needed to splice driver responses together, got some decent results. But judging a simple FR plot that looks right and knowing that the underlying data is accurate enough to create a sim model is different. Knowing others (@ctrl at the very least) would scrutinize and knowing I could readily defend was motivation!
I decided to ditch it when I did Directiva and wanted measurements with better accuracy. It took me a while so actually did in the middle of the r1 project. When I needed to splice driver responses together, got some decent results. But judging a simple FR plot that looks right and knowing that the underlying data is accurate enough to create a sim model is different. Knowing others (@ctrl at the very least) would scrutinize and knowing I could readily defend was motivation!
Thanks for your input. Which part is UMIK-1 lacking and what microphone you change to? I will need better mic than umm6 from now on.
OP
- Thread Starter
- #31
Can't say I know for sure, but suspect it has to do with where in the chain that allows phase comp.
New mic is a Dayton emm-6. Not because it has great performance, but was recommended and got a decent deal on it.
Yes, you are mistaken. Multiple sweeps has nothing to do with measuring individual drivers, it is a way of improving S/N for a measurement if using a longer sweep isn't suitable or to try and suppress tonal interference. For polar measurements the acoustic reference would probably work best if generated by a speaker other than the one being measured to avoid potential issues when far off axis.
OP
- Thread Starter
- #33
dc655321
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AFAICT, yes, still problematic. But primarily because of misunderstanding, not technical limitations
I've had this conversation previously with @617 and @Juhazi. Again, would much appreciate @JohnPM's insight or even just references to study, as I don't see the issues some claim.
Then again, I'm wrong often enough to still have doubts
USB mics do not have any means of providing a loopback connection, so can't be used with the normal timing reference mode used for measurement. The acoustic timing ref was added to address that, and works well. The timing reference is a 5 kHz - 20 kHz linear sweep detected by cross-correlation with the source signal to a precision well below the sample interval, typically within a few microseconds. There may be issues in highly reflective environments or if the mic is far off the axis of the speaker providing the timing reference as in both cases there might be reflections at high frequencies stronger than the direct sound. The off-axis problem can be addressed by using a separate speaker to provide the timing reference, assuming the mic and reference speaker stay in the same place while the speaker being measured is rotated on its axis.
A second issue that can affect USB mics is a clock rate difference to the signal source. The mic gets its clock from the USB interface and some are less accurate than others. REW has an option to detect and correct that through the use of a second timing reference signal at the end of the measurement sweep.
A second issue that can affect USB mics is a clock rate difference to the signal source. The mic gets its clock from the USB interface and some are less accurate than others. REW has an option to detect and correct that through the use of a second timing reference signal at the end of the measurement sweep.
OP
- Thread Starter
- #36
AFAICT, yes, still problematic. But primarily because of misunderstanding, not technical limitations
I've had this conversation previously with @617 and @Juhazi. Again, would much appreciate @JohnPM's insight or even just references to study, as I don't see the issues some claim.
Then again, I'm wrong often enough to still have doubts
I‘m happy even though I spent money on the EMM-6. At least I know how I can get good results with my laptop using the UMIK-1 mic. Can measure outside without having to move the indoor setup.
Hello @JohnPM,
Thank you indeed for your kind notes which, I assume, would validate and support my room acoustic measurement (here to here) by REW using CEntrance USB MicPort PRO + Behringer ECM8000.
BTW, with your above perspectives, the USB audio interface Tascam's US-1x2HR, US-2x2HR and US-4x4HR which I referred in my post #19 would be acceptable?
You may find the spec sheet for US-1x2HR (which I currently use with Behringer ECM8000);
https://tascam.jp/int/product/us-1x2hr/spec
Or, do we always need some further precision evaluation of each "USB audio interface" for compatibilities with REW?
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So if i understood correctly, using the UMIK-1 with REW acoustic timing ref, will provide accurate measurement for crossover design in VituixCAD.
Is the above correct? There is so many contradictory information on this subject that its difficult to understand what the actual truth is ...
Is the above correct? There is so many contradictory information on this subject that its difficult to understand what the actual truth is ...
Is this mic custom calibrated?
Given the uncertainty regarding the USB mic (i have a cross spectrum calibrated UMIK-1), i'm considering getting an EMM-6, but they seem out of stock since 2019 on Cross Spectrum.
