Time Align Drivers in 3-way speaker system

[michael goldstein]

I have read a good deal on the web, including miniDSP and still do not see a concrete way of time aligning 3 drivers (T/M/W) in a loudspeaker. I've spent hours trying. This is not the same as time aligning surround sound loudspeakers. What time aligning I have done is by distance measurements between the drivers. It is not sensitive enough when the drivers are very close to each other. My system is triamped via miniDSP 8x10 HD. I am not really computer competent and have been using REW rather primitively for years. Help would be appreciated. Thanks, mike (michiganmike711)

 

[jtalden]

The REW alignment tool helps make this process easier.
Basic steps for one method to do this:

• Mic placed on listening axis 1-2 m in front of the right speaker
• Both XOs active in the DSP
• Set Acoustic Timing active in REW. Use the left channel speaker as the reference
• Sweep set to full range for the system design [20-20k Hz for example].
• Measure right channel:
  1. T
  2. M
  3. W
• Confirm that T impulse is located reasonably near 0 ms. [If not, place the cursor on the peak of the T impulse and then use the overlay impulse chart control 'Set t=0 at cursor'. That will move all 3 impulses the same amount and will still retain the relative timing of all 3. The T is now the reference for delay adjustments to M and W and will not be adjusted.]
• Set an FDW of 4 or 5 cycles for all measurements.
• Open the alignment tool and select the T (top) and the M (bottom) and then adjust only the M as needed for polarity, level, and delay to obtain closest phase tracking throughout the XO range.
• Remove the FDW and then save the 'aligned copy' of the adjusted M and also save the 'Aligned sum'.
• Reset an FDW of 4 or 5 cycles for all measurements.
• In the alignment tool select the 'aligned sum' (top) and W (bottom) and then adjust only the W as needed for polarity, level, and delay to obtain closest phase tracking throughout the XO range.
• Remove the FDW and save the 'aligned copy' of the adjusted W and also save the 'Aligned sum'.
• Optionally we can use REW 'Trace arithmetic' A + B to combine these 3 drivers into the calculated overall response [(T + Aligned copy of M) + aligned copy of W]

Apply the adjustments made to the M and W in the DSP and repeat the 3 measurements and also measure the combined channel response (T+M+W). The measurement will exactly track the predicted response.

The close mic position and the FDW should allow for no major room influences in the XO range, but if the M/W XO range still has strong nulls the test conditions may need to be adjusted.

For more detail and discussion of alignment tool in general see this thread.

 

[michael goldstein]

JT, I need help with several of the above recommended steps. I will refer to each corky dot line as though it was numbered. My ignorance will become abundantly clear.
* Line 3: To establish the left channel as the reference, do I play only the left channel full sweep with the mic placed in front of the right channel?
* Line 5: I am interpreting the directive that a] only the right channel is playing and b] that each driver of the right speaker is measured separately. Since the acoustic time signal is high frequency based, I found that for a woofer, I had to have both the tweeter and woofer outputing with the mid silenced. I silenced the tweeter right after the acoustic timing signal arrived, leaving only the woofer's output to be recorded.
* Line 7: FDW is Frequency Dependent Window? How does one set it? I found the term FDW in the Impulse Help section.
* Line 8: What is the Alignment Tool and where do I open it?
Thanks in advance. mike

 

[jtalden]

JT, I need help with several of the above recommended steps. I will refer to each corky dot line as though it was numbered. My ignorance will become abundantly clear.
* Line 3: To establish the left channel as the reference, do I play only the left channel full sweep with the mic placed in front of the right channel?

No, We are measuring the drivers in the right channel. So:
In the measurement panel 'timing' box select 'Use acoustic timing reference'
In the measurement panel 'Output' box select 'R'
In the measurement panel 'Ref output' box select 'L'
When 'Start' is selected the L channel is sent a short high frequency sweep as a timing reference just before the measurement sweep is sent to the R speaker.

* Line 5: I am interpreting the directive that a] only the right channel is playing and b] that each driver of the right speaker is measured separately. Since the acoustic time signal is high frequency based, I found that for a woofer, I had to have both the tweeter and woofer outputing with the mid silenced. I silenced the tweeter right after the acoustic timing signal arrived, leaving only the woofer's output to be recorded.

No, see previous answer.

* Line 7: FDW is Frequency Dependent Window? How does one set it? I found the term FDW in the Impulse Help section.

Use the 'Help' search box and enter 'Impulse response windows'. Read that entire section in help. It shows the button to push as well as the various settings.

* Line 8: What is the Alignment Tool and where do I open it?

Attached is a screen shot with the alignment tool and IR windows IR windows controls open. Play with the controls circled to see their effect.

This can be a challenge to learn, but well worth it if you intend to use it regularly. If this is a one time setup, I recommend you just post the 3 measurements in an mdat and request the needed delay changes.

 

[danhamiltonnn]

Hi JT, i might need your help to take a look on my file, correct me if the reading i took was not sufficient. As you explained @ #2, do the following steps as your recommendation. Just that i'm stuck once i got the reading, you were saying get R output by using L as ref,and vice versa for L output. How do i align time alignment between LT,LM, LL and LS while R as ref, then RT, RM, RL and RS while L as ref, perhaps some illustration may help me to understand the concept for time align. I attached a file below for your reference. My issue here is I dont have any reference sample .mdat for adjustment, the before (mine) and after. Do you mind demo us by using my attached file.

Two attachments:
1. DSP before tune (Data taken prior tuning by the shop) you might perform better result from REW
2. DSP after tuned (Data taken after tuned with time alignment), I want to compare whether is it well tuned ?

Thanks

 

[jtalden]

Since the 2 main 3-way speakers are the same design containing T, M and W, the correct XO timings are the same for both speakers. Only one speaker needs to be measured. I suggested measuring the R speaker using the L as the acoustic reference. The option is to reverse that and measure the L using the R as reference. You did both and also included 1 or 2 SWs. The SW timing should be done after the mains are time aligned. This is because the main speaker timing is best done at 1-2 m mic distance and the SWs must be time aligned based on measurements with the mic at the LP. The main speaker measurements here are pretty noisy suggesting they were possibly taken with the mic at the LP.

I suggest the original plan is best followed for Step 1, i.e., time aligning the T, M, W in one of the main speakers. Step 2 and possibly Step 3 is then needed to time align the SW(s) to the main speakers.

Step 1 (reworded):
Setup

• Place the R main speaker in its intended position for your listening setup (If that is known and available). [The L main speaker can be anyplace in the room.]
• Place the mic about 1.5 m distant from R speaker and on the line of sight from the LP. [Sitting at your LP you would see the R speaker T or M driver directly behind the mic.]
• Both XOs active in the DSP
• Set Acoustic Timing active in REW.
• Set the R channel as the measurement channel and the L channel as the reference.
• Set sweep to full range for the system design (20-20k Hz for example).

Measure R channel

1. T
2. M
3. W

Notes:

1. These 3 measurements are all that is needed. Just provide the 3 measurements in the mdat. They can be taken either before or after your own timing adjustments. Either way any changes I suggest will be delay changes from the timing delay settings you used for the 3 measurements. There is no need for me to analyze both before and after your adjustments or both speakers as the suggested delay timings will be the same.
2. If 3 of the measurements you posted above already meet these criteria then identify them and I will use them for the analysis.

 

[danhamiltonnn]

JT, Thanks for the suggestion. In this case, some of the part cannot be done due to the distance is too short between speaker and LP. This is a measurement for Car audio. So not possible to keep mic at LP 1 - 2 m distance away from speaker.
You were saying measure only one side is sufficient, however, each driver is not located the same distance as LP.

1. As starter, how do i do time alignment from each speaker to LP for left channel between tweeter (LT), midbass (LM) and woofer(LL) since they are at different distance, then the same goes for right channel between RT, RM and RL to LP. Below insert showing the speaker all at different distance. As per my understanding, once they are aligned, the sound from each speaker shall travel the same time to LP, correct me if i'm wrong since i'm new to this. ( Suggested step 1, using left as ref to measure right, then right as ref to measure left, with this step, i have no idea how to use the data align it to LP)

2. The measurement obtained from REW, there is a delay showing 0.9481 ms, and it varies for other speaker as well. What is this delay mean? Is this delay from the program itself, or the delay between driver and LP ? What do i do with that delay? ( sorry for the weird question)

3. The measurement that i posted before are good for analysis. But my .mdat contained 6 measurements, is 3 measurements sufficient for analysis based on the insert(no.1) as i attached above?

Thanks again for your feedback

 

[jtalden]

Sorry, my method of timing analysis is not helpful for auto applications. The direct sound is normally not dominate because of so many early reflections. You will be much better served to find help from someone with auto setup experience.

 

[danhamiltonnn]

Thaks for the response

 

[Vladimir_1953]

I have read a good deal on the web, including miniDSP and still do not see a concrete way of time aligning 3 drivers (T/M/W) in a loudspeaker. I've spent hours trying. This is not the same as time aligning surround sound loudspeakers. What time aligning I have done is by distance measurements between the drivers. It is not sensitive enough when the drivers are very close to each other. My system is triamped via miniDSP 8x10 HD. I am not really computer competent and have been using REW rather primitively for years. Help would be appreciated. Thanks, mike (michiganmike711)

Because of the many reflections in the car interior, the best result is given not by momentum, but by phase in real time. I use the Smaart v.7 Transfer Function program for this

 

[danhamiltonnn]

Because of the many reflections in the car interior, the best result is given not by momentum, but by phase in real time. I use the Smaart v.7 Transfer Function program for this

Do you mind showing me your method and setup by using smaart v7, I'm not sure smaart allow usb mic for measurement, anyway I have both usb and xlr mic with i/o interface.

 

[Vladimir_1953]

Do you mind showing me your method and setup by using smaart v7, I'm not sure smaart allow usb mic for measurement, anyway I have both usb and xlr mic with i/o interface.

I think this conference will not correctly discuss third-party software ...
Therefore, I propose to switch to personal correspondence.
Or go here:
https://www.avnirvana.com/threads/tuning-with-the-minidsp-c-dsp-8x12-dl-and-rew.5370/#post-53471