The Journey Begins - Passive to Active

[Dan Twomey]

I have everything prepped so in the next few days I can complete my conversion of my line arrays from passive to active. I'm starting my MiniDSP 2x4HD with the same settings as the original passive crossover.
Both fourth order LR crossing at 2.5khz. The first questions I'm pondering is how to correctly measure them. On a point source it's easy. Just center the mic 1 meter from and directly centered on the driver and away you go.
My best guess for now is center my mic in the middle of each line one meter away and see what I get? I can also measure from listening position and start tuning from there?
Thoughts anyone?

Regards,
Dan

 

[Dan Twomey]

Google is my friend. I found the following post on measuring line arrays.
Measuring line arrays.

Your measuring distance should be equal to or greater than the length of your line. If you have one line of drivers longer than the other (for instance 5 ft. of tweeters and 6 ft. of woofers) use the distance that's the greater of the two. Also measure the left and right horizontal angles so you can see the lobe and adjust your crossover topology as desired. Vertical location of the mic can also affect the response quite a bit.

Regards,
Dan

 

[jtalden]

I have no experience with line arrays, but am willing to help you analyze your data for delay timing.
My expectation is that the LP will be significantly easier to work with than the 1 m mic position for setting the XO delay timing. You also may have cleaner measurement using the right speaker for the delay timing analysis as there is likely to be less sidewall interference of the room.

Also:
I don't think there is any particular advantage in using an LR4 XO. There may even be some advantage to using a lower order XO. You may want to try both and see if one sounds better. A lower order XO provides more overlap and may help smooth out the horizontal off axis response a little bit in the XO range. The only way to determine that is to take some off axis measurements of both setups after the delay timing has been determined. With the side-to-side driver arrangement this could even make the situation worse so this is not a strong recommendation - just a thought.

 

[Dan Twomey]

I've decided to take my speaker designer's (Rick Craig) advice and take my first initial measurements (coming soon) at one line length away and centered.
Since, how to measure line arrays is the subject of some debate. I think I'll accept Rick's point of view as my own standard. At least that way I'll have some sort of
consistent point of reference.

Also, I really like the fact that the MiniDSP is so flexible. I can change XO's, levels, and a variety of other values with a couple mouse clicks.


Regards,
Dan

 

[Dan Twomey]

Here we go. What can I learn from a very basic and unscientific measurement of a single (the right on in this picture) line array?

 

[Dan Twomey]

The following measurements were take a line length away (5ft.) and centered height-wise (3ft.)

Here is the bass line alone.

 

[Dan Twomey]

Here is the tweeter line alone.

 

[Dan Twomey]

And a full range measurement.

 

[Dan Twomey]

While not flawless. A musical listening session was very pleasant. MDAT file attached here

 

[Dan Twomey]

Something else that caught my interest is that Fountek recommends a 2nd Order XO at 2000Hz for these ribbon tweeters.

Regards,
Dan

 

[sm52]

Here is the tweeter line alone.

some special tweeters. They play up to 20 Hz, only 30 dB quieter than at HF. Measurements turned out incorrectly?

 

[jtalden]

While not flawless. A musical listening session was very pleasant. MDAT file attached here

We can learn a lot from this data, however it is not usable in determining the best delay timing for the LP position. In order to do that we need the mic position to be on the line of sight from the LP to speaker. In the picture, the mic is perpendicular to the front of speaker. This data would be okay for delay timing if you intend to toe-in the speakers to point directly at the LP, but I assume they are currently at the intended orientation, pointed ahead, toward the back wall. With side-to-side drivers the delay timing error may be significant at the LP. There is no problem measuring at the line length or further back at the LP - your choice. We also need to use the REW acoustic timing feature for all measurements.

Here is what we learned from this data.
XO range = 800-6k Hz for about 30 dB rolloff.

The best and worst XO delay timing for this XO setting is shown below. The current timing is also shown. It falls between the 2 nearer the worst. I smoothed the traces to 1/3 just to make the differences easier to see.

Note that in the SPL chart above that the best XO delay timing still results in a sag in SPL through the XO range. We can probably mitigate this sag with changes to the XO filters. You could try either But-4 filters, or try overlapping the LR-4 filters by changing the woofers frequency to 2.3 or 2.4 kHz and the tweeters to 1.8 kHz. This can also just be addressed with EQ after the setup so trying the alternate XO filter settings is just an alternate approach. I just depends on how much you want to tinker with the XO settings and what your approach to overall PEQ is going to be.

Next Steps
Remeasure as before, but with these changes:

• Place mic in the line of sight from the LP to right speaker. [The distance should be at least the current distance. It can be greater though. Keep the mic placement at least 3 ft from any wall.]
• Activate REW acoustic timing [Let me know if this is new for you.]
• It is okay if you want to chose different XO filter settings, but I am only able to help analyze 2 or 3 more setups for timing delay settings.
• It's best to clarify other any questions you have before making new measurements.

 

[jtalden]

Something else that caught my interest is that Fountek recommends a 2nd Order XO at 2000Hz for these ribbon tweeters.

Regards,
Dan

This very conservative for this application. Each of your TW's will be working a very small levels of both power and displacement so there will be no issue with any resonable XO filter changes you want to make.

 

[Dan Twomey]

It's best to clarify other any questions you have before making new measurements.

Hmmmmm.....this is the toughest question of all. What should my goals be and how will that be reflected
in the measurements?

My overall goal is to optimize these speakers for their current position and room. From what I've learned so far the
final result will correct some (perhaps not all) XO and phase issues and will resemble some sort of 'house curve'.
You can see my sub in the pic and it's not part of the equation right now. I'm going to 'optimize' my arrays first and then
try and integrate the sub later.

Regards,
Dan

 

[Dan Twomey]

Next Step

I'm going to measure both speakers from the LP with the acoustic timing reference activated.
Prior to these measurements I'm going to change the XO settings to woofers frequency to 2.3kHz and the tweeters to 1.8 kHz.

Acceptable?

Regards,
Dan

 

[jtalden]

Hmmmmm.....this is the toughest question of all. What should my goals be and how will that be reflected
in the measurements?

My overall goal is to optimize these speakers for their current position and room. From what I've learned so far the
final result will correct some (perhaps not all) XO and phase issues and will resemble some sort of 'house curve'.
You can see my sub in the pic and it's not part of the equation right now. I'm going to 'optimize' my arrays first and then
try and integrate the sub later.

Regards,
Dan

Yes,
The final result should be close phase tracking between the woofers and tweeters at the LP position. That results is maximum SPL response across the XO range prior to PEQ.

The SW to woofer XO can then be setup similarly to how the woofer to tweeter is being done.

PEQ can then be used to smooth the response to follow your chosen house curve.

 

[jtalden]

Next Step

I'm going to measure both speakers from the LP with the acoustic timing reference activated.
Prior to these measurements I'm going to change the XO settings to woofers frequency to 2.3kHz and the tweeters to 1.8 kHz.

Acceptable?

Regards,
Dan

Yes.
The LP mic location is the best option in my opinion.

The new mic position at the LP may influence XO SPL response. I was not thinking of that when I mentioned the XO filter changes so maybe it is better to just use the same LR-4 at 2 kHz and see if that XO range SPL sag is still present. Either way is fine. If what you try does not work out well we can adjust the XO again as needed.

[The XO changes I mentioned were to highlight some of the options possible to us to address a sag in the XO SPL.]

 

[Dan Twomey]

OK, let's see if I got this right. Both XO's LR4 at 2.5kHz with acoustic timing signal active.
All measurements at LP.

 

[jtalden]

OK, let's see if I got this right. Both XO's LR4 at 2.5kHz with acoustic timing signal active.
All measurements at LP.

This file doesn't contain the individual woofer and TW measurements so it cannot be used top correct the XO delay timing. Maybe you were looking for other information, but there is not much to learn from these measurements.

The acoustic timing was properly applied these measurement so that change worked well. You selected the right channel as the reference channel for all measurement and that is good.

To run an XO delay timing analysis the we need at least the same measurement as in your original file of Post-9. A more complete set of measurements would include...

6 Measurements

1. R Woofers (alone) [See note below. Acoustic timing reference turned off for this measurement only.]
2. R TWs (alone)
3. L Woofers (alone)
4. L TWs (alone)
5. L Woofers+TWs (both together)
6. R Woofers+TWs (both together)

Note: It is not easy to measure the R Woofers alone when the right speaker is the reference channel so disable the acoustic reference for this measurement only. I will be able to determine the timing manually for the right woofers if all 6 measurements are provided.

 

[Dan Twomey]

Excellent. Hopefully, I will have time to do this today.

Also, I believe the following link will help me understand what you’re trying to achieve here?
Time Alignment

Regards,
Dan

 

[Dan Twomey]

Here we go. I find time alignment very interesting. I noticed that a well-known and very successful (Troels Gravesen) speaker designer always physically aligns his
drivers. An option not available in my current line array design.

Regards,
Dan

 

[jtalden]

It is not necessary to physically time align the speakers if you are using a DSP XO as we are here. The DSP provides the capability to delay the timing of one of the drivers as needed such that the arrival time at the LP is identical for woofers and tweeters. We can find and confirm the correct delay setting by using the REW alignment tool. That at is what I did here.

Manipulation of the measurements:

1. Determined the actual timing of the right woofers measurement and shifted its timing accordingly.
2. Offset one channels timing to match the other, i.e., adjusted out the minor miscentering of the mic.
3. Offset all measurements equally to position the impulses relative to 0 ms.
4. Vector averaged the L,R TWs
5. Vector averaged the L,R Ws
6. Used the REW alignment tool to determine the delay needed to achieve close phase tracking through the XO range.

Results:
Close phase tracking was found when the woofers polarity was inverted and the delay left unchanged. Inverting the polarity of the woofers in the miniDSP is the only change needed for ideal time alignment at the LP.
The resulting SPL support in the XO range was very good and the phase tracking was very close throughout the XO range (charts attached).

 

[Dan Twomey]

Many thanks for all the work you put in helping me sort this out.

Regards,
Dan

 

[Dan Twomey]

Is it helpful to look at the time differences in the impulses of the tweeters and woofers? This is left woofers and tweeters.

Regards,
Dan

 

[jtalden]

Yes, but...
Below is the correct chart showing impulses of the left W's and TW's as was posted in Third.mdat. The chart you posted does not have the legend selected, but it looks like it is the right W's and TW's. Remember that we didn't use the REW acoustic timing feature on the right woofers so the impulse is shown in the wrong position as measured. The first action I listed in Post-22 was to determine and adjust the actual impulse timing position of the right woofers. That moved the relative position similar to the same positions as shown in the left woofers and tweeter below. The methodology I used to determine the actual timing of the right woofers is very accurate so there is no question as to whether it was done correctly.

I will also attach my final mdat file. It reflects all the preliminary adjustments to the measurements as listed in Post-22 and the final alignment tool analysis results.