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Taking Measurements for a 3-way

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  • dcibel
    replied
    a4eaudio Ha! How the times change, I’m a full VituixCAD convert now! 2018 seems like such a distant past.

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  • a4eaudio
    replied
    Originally posted by dcibel View Post
    That sounds promising, I'll have to give it a close look, I had downloaded it some time ago but never got around to diving in.
    dcibel - I was Google searching for something about Vituixcad and came across this post. I thought you might find it amusing, now that you are a leading resource and proponent for Vituixcad.

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  • jcandy
    replied
    Just a few cautionary notes. Its very difficult (for a hobbyist) to reconstruct the anechoic SPL from a large woofer. One reason is that the diffraction engines that are available in popular software and used in the anechoic reconstruction (combining near-field and far-field data) are rather approximate, and limited to relatively high frequencies. The low-frequency error inherent to these algorithms can propagate in different ways into the final modeled anechoic response depending on other details of the workflow.

    If box models are used in the low-frequency reconstruction, then certain errors can appear here as well (in particular for cone+port summation in vented systems) since viscoelastic effects not retained in the standard TS models will significantly influence the low-frequency range. This type of error fundamentally affects design of vented boxes and is generally under-appreciated in the community, so its not really specific to anechoic SPL reconstruction.

    Regarding the reconstruction of off-axis SPL (and power response) from on-axis data using modeling tools, this calculation too contains errors that may mislead the designer. Cone geometry (and tweeter faceplate or waveguide geometry) affect the off-axis response, as do complicated diffraction effects not retained by the simple diffraction engines (diffraction again). Thus, I feel that these types of modeling tools are extremely useful to gain a physical understanding of the radiation pattern of rigid pistons mounted on an infinite baffle, but they're less useful for high-precision modeling of actual designs.

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  • 3ll3d00d
    replied
    The author of vituixcad has documented an approach - https://kimmosaunisto.net/Software/V...eparations.pdf - which I think covers what you're trying to do

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  • dkalsi
    replied
    Originally posted by civit View Post

    If you use the included diffraction tool it will automatically simulate off axis responses for a given.driver on a simulated baffle, create a bunch of polar frd files and load them into the project. Super fast way of simulating designs using the directivity sonogram. It really is head and shoulders above other cover simulation tools.

    The merger tool allows you to combine near and far measurements and works really well, and the split tracer tool is the best I've seen for getting fr data from an image. It's just an incredible piece of software for the hobbyist.

    Sorry to bump this thread, but I'm hoping to get a littler more insight on how measurements should be performed. I've used Xsim/WinPCD for crossover modeling before, but I'd like to learn a little more about VituixCAD.

    My Measurement Equipment Includes: Focusrite Scarlette Solo, Behringer EMC8000 Mic, Dayton Audio DATs,
    My Software:L ARTA - Demo Version - and Vituix CAD


    Additional Facts:
    1) I do not have the option to take outside measurements
    2) Nearest boundaries for inside measurement are 4 feet (i.e., basically a room with 8 feet ceiling)
    3) I do not have a turn table setup to take off-axis measurements (will build one in the near future.
    4) Measurement gear is hooked-up using "Semi-Dual" diagram as provided in ARTA

    Based on the above, what is the best way to use VituixCAD? My thinking below:


    1) Take farfield measurements of the Tweeter, Woofer, and Tweeter + Woofer (paralleled) - all on axis with the tweeter (i.e. the design axis)
    2) Use gating to remove reflections from the measurements in Step 1, and save all files with minimum phase
    3) Using WinPCD - Acoustic Off-Set Tab, determine the Z-offset of the drivers
    4) Now lets say all measurements in Step 1 were taken at 30" from baffle on axis with the tweeter ---> Now take another measurement of the woofer on the woofer axis at the same 30" baffle distance (if the speaker includes a stepped baffle to better align the woofer with the tweeter, make sure you are measuring distance from the stepped portion of the baffle). Again save woofer's response using minimum phase
    5) Take near field measurements of the port and woofer.
    6) Using VituixCAD's "Merger Tool", merge the nearfield Port Response and nearfield Woofer Response (adjusting for diffraction effect), with the Woofer's farfield response. Save file with "Minimum Phase".
    7) Use DATs, measure tweeter and woofers (in-box) impedance
    Because I did not take any off-axis measurements of the tweeter, using VituixCAD Diffraction Simulator, create the baffle, indicate the tweeter's radiating diameter, indicate the mic's listening position, load the tweeter's half space response, and check off - "Full Space", "Directivity", "Vertical Plane", "Negative Angles", and "Feed Speaker" ------> click okay

    9) Because I also didn't take off-axis measurements of the woofer, perform the same steps above in Step 8.
    10) Upload the tweeter and woofers impedance response as measured by DATs
    11) Specify each driver's location relative to the design axis. For example, if the design axis is the tweeter axis, indicate 0, 0, 0 for X, Y, Z coordinates for the tweeter. If the woofer was 167mm below the tweeter, and 3mm in front of the speaker (because I used a stepped baffle on my current build), then indicate, 0 for X, -167mm for Y, and -3 for Z.

    12) Begin crossover desing.

    Based on the above steps, I have the following questions:

    1) Do I check the checkbox next to ARTA's "Dual Channel Measurements Mode" when all my connection are in "Semi Dual" mode
    2) Is the only time the response of the Woofer that measured on the Tweeter Axis utilized is when one is calculating Z-offset?
    3) For VituixCAD, should all drivers measurements be on axis with each individual driver (while still maintaining same measurement distance from baffle)
    4) Does VituixCAD calculates the design axis based on how one enters the location of the drivers on the baffle? For example, if I entered 0,0,0 for XYZ coordinators for the tweeter, will Vituix will simulate response based on that point in space?
    5) Because no actual off axis measurements were performed, and instead the Diffraction tool was utilized to simulate off axis response relative to design (i.e. mic location) axis, is there any concern with indicating the design axis in two different locations (i.e., one of the main screen where each drivers' XYZ coordinates were indicated, and also within the Diffraction tool where the driver and mic locations need to be indicated).
    6) In Step 8 above, when loading the woofer's "half-space" response, am I to use the woofer's response obtained on the tweeter axis or the woofer's response obtained on the woofer axis?
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    Last edited by dkalsi; 03-26-2018, 11:44 AM.

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  • civit
    replied
    Originally posted by dcibel View Post

    That sounds promising, I'll have to give it a close look, I had downloaded it some time ago but never got around to diving in.
    If you use the included diffraction tool it will automatically simulate off axis responses for a given.driver on a simulated baffle, create a bunch of polar frd files and load them into the project. Super fast way of simulating designs using the directivity sonogram. It really is head and shoulders above other cover simulation tools.

    The merger tool allows you to combine near and far measurements and works really well, and the split tracer tool is the best I've seen for getting fr data from an image. It's just an incredible piece of software for the hobbyist.

    Leave a comment:


  • dcibel
    replied
    Originally posted by civit View Post

    This is why I'm doing my designs in VituixCAD with ARTA; it's really easy to make polar plots and manage long lists of FRD files. It can even do optimizations which take into account both power response and axial response. The power response in that case is not simulated based on driver diameter (although it can do that too using its diffraction simulation tools, which create polar responses) but based on your measurements. Amazing for free software.
    That sounds promising, I'll have to give it a close look, I had downloaded it some time ago but never got around to diving in.

    Leave a comment:


  • civit
    replied
    Originally posted by dcibel View Post

    Even at that the power response is still just an approximation of reality since it's not evaluating the diffraction at each angle, and some drivers breakup doesn't follow the piston math so much.
    This is why I'm doing my designs in VituixCAD with ARTA; it's really easy to make polar plots and manage long lists of FRD files. It can even do optimizations which take into account both power response and axial response. The power response in that case is not simulated based on driver diameter (although it can do that too using its diffraction simulation tools, which create polar responses) but based on your measurements. Amazing for free software.

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  • dcibel
    replied
    Originally posted by dkalsi View Post

    Civit - great point. That is definitely something I am concerned with. So.....the only way for any software to predict this power response accurately is by using files where the frequency response was developed on axis with each respective driver....correct?
    Even at that the power response is still just an approximation of reality since it's not evaluating the diffraction at each angle, and some drivers breakup doesn't follow the piston math so much. But you are correct, using on-axis measurements for each driver can provide a better approximation of the power response. Soundeasy isn't the most straight forward thing to use, but I haven't found anything as accurate as it for off-axis performance because you can design using measurements that are on-axis with each driver.

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  • civit
    replied
    Originally posted by dkalsi View Post

    As decible suggested - its worth the exercise for verifying the technique employed with real-world measurements, which it looks like you have done successfully.

    Endless learning in this hobby ..... :-)
    I take a lot of measurements precisely because I don't know what I'm doing. Using a measurement package with good support is really helpful; OmniMic is probably best in that regard since it seems to be popular here, but I'm in ARTA. I think I'll do some another set of single-point measurements of my current project tonight, and process them the way dcibel has suggested.

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  • dkalsi
    replied
    Originally posted by civit View Post

    I think you have a good handle on the tradeoffs. Measuring your mid and woofer on the design axis will probably not effect their FR in the range you intend to use them, but I would still follow the protocol I described (measure each on axis at same distance, merging with nearfield, minimum phase) simply because it allows more accurate simulation of off axis behavior and perhaps more importantly, a more accurate depiction of the power response.....
    Civit - great point. That is definitely something I am concerned with. So.....the only way for any software to predict this power response accurately is by using files where the frequency response was developed on axis with each respective driver....correct?

    I know I'm missing something here!?!?!?

    I'm thinking that, when trying to determine the power response of a speaker, it is the power response relative to some point in space. For me, the starting point is the tweeter axis (ie., the "Design Axis"). I would need the software to generate power response relative to that starting point. If, say in WinPCD, I input all files that were obtained on axis with the tweeter, and I specify in WinPCD that this response that I am utilizing for the mid or woofer was obtained with the mid placed 6" below the tweeter and the woofer placed 14" below the tweeter, and all z-offsets have been calculation relative to the Design Axis, then after specifying the radiating diameter of the mid and woofer, I'm thinking the software will be better able to predict the power response (because its starting from actual measured response on the Design Axis vs predicted response on the Design Axis).


    As decible suggested - its worth the exercise for verifying the technique employed with real-world measurements, which it looks like you have done successfully.

    Endless learning in this hobby ..... :-)

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  • dcibel
    replied
    Originally posted by dkalsi View Post
    Just to be clear, any extraction of minimum phase should occur ONLY after merging from far-field and near-field correct?
    Minimum phase is a direct result of the frequency response, so it is the last step of the process, always.

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  • dkalsi
    replied
    Just to be clear, any extraction of minimum phase should occur ONLY after merging from far-field and near-field correct??? From what I understanding, minimum phase calculations are impacted by the "tails" of the FR.

    I had saved the following from DLR's post:

    "Remember that offset is relative, that is, it's a value required so that the two minimum-phase files sum to the measured sum. If you change either file, the relative offset needs to be updated to account for the change.

    The absolute value of the offset isn't really important. All it amounts to is the difference between the two measurements that "aligns" the time delays between the measurements to correspond to the difference required for the generated phase of each driver file. There is no "correct" offset, only the offset needed for the measurement phase as generated for the SPL of the files."

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  • dcibel
    replied
    Originally posted by civit View Post

    I didn't know this. It seems like measuring from as far as is practical would be beneficial in this case. TIL.
    Yes, that's correct with the exception that the further you move away, the more reflections are introduced to the measurement, so you want to be as far away as possible while providing as large a gate as possible and still provide a reflection free measurement. It's a catch 22, so indoors you end up being as close to the speaker as possible while still qualifying for "far field" status.

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  • dcibel
    replied
    Originally posted by dkalsi View Post


    Civit,

    Sincere thanks for responding and sharing your experience. From what you describe, it makes sense why PCD, winPCD, and VituixCAD require driver placement information and radiating diameter information.

    I can't remember the exact tread, but I had saved the following post by Jeff B:

    "Well, I wouldn't have placed the mic between the two drivers on the two-way. Personally, I feel any axis other than the tweeter axis is less than ideal. So, for a three-way, and I have done many, I would recommend that the mic be on the tweeter axis here too. The bottom line is that the design axis should be the axis you plan to listen on. Most people listen on the tweeter axis due to the tweeter’s roll-off as you move off-axis is much more significant than the woofer’s is. I wouldn’t recommend that someone design with the mic between the two drivers and then listen on the tweeter axis. Their response on this axis will be a little different than what they saw in their design work."

    Again, there is a high likelyhood that I might be misinterperting Jeff's post. I assume Jeff was taking all measurements the design axis (i.e., tweeter level).

    With typical close proximity between the tweeter and the mid, I would assume the mid treble would not terribly rolled off. I couldn't imagine the mid being more than 10 degrees off axis??!? In regards to the Woofer, even if we are 60 degrees off axis, it really shouldn't matter around 200hz - 300hz correct?

    I guess I also need to interpret how the modeling software is analyzing the files. By taking all measurements on axis, does it calculate that the what the response should be on the design axis (based on placement info and radiating diameter info).
    Well tweeters will have narrowing directivity in the top octaves, so keeping the tweeter as the design axis ensures that the high frequency response will only drop as you move off axis. If your design axis is not the tweeter axis, the high frequency response can be a bit less predictable. Your question about off-axis response I think are best answered by using your mic and taking some measurements so you can observe the real-world data for yourself.

    Like I said, the offset values in PCD only affect the phase so that the simulation adds in the correct "time of flight" to the minimum phase that you've provided, the off-axis simulation when you move the mic around is an approximation at best.

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