Once the adjustment is made, repeat the measurement to confirm that change was successful. Update: DIY point source kit This point source horn combines a unique mix of features that make it very appealing. It is a lot of work to get to the point where you know what ... Jump to the next Waveguide Shootout > In one day we compared a bunch of compression drivers and waveguides. They are also a little more difficult to integra... Update: I'm now offering crossover upgrades. It has the extremely... Update: After hearing some Econowaves and various driver and waveguide/horn combinations, I have found that not all drivers and waveguides ... An acoustic diffuser is generally more difficult to design and build, hence more expensive. Should we RTA both side, all 4s? the subwoofer is 25 to 30ms late here. The simple answer is yes, but in reality it's a phase alignment issue. In short, if phase is misaligned, the subwoofer won't correctly integrate with the mains. Once configured correctly, the information under that tab should look similar to the image below: Now, on the "Data Analysis" tab, select the "Detect Time Zero" option The information under this tab should now look similar to the image below: Step #4: Set your initial time-alignment settings For the best results, you should adjust the time alignment settings on your head-unit to closely mirror the physical distances of each speaker from the measuring point. The image below shows the equipment that I currently use for my measurements: -. For the best results, do not have any other programs open at the same time as HolmImpulse. You should hear noise through the selected speaker for a few seconds, and then shortly after that the frequency and impulse response of the speaker will be displayed, similar to the image below: Step #6: - Set time zero lock At this point, select the "Data Analysis" tab again, and then the select the "Time zero locked (time alignment)" option, then click on the "Use" button. Nice write up on “Time Alignment”, could you perhaps do an article on your recommendation on how to use a RTA correctly on a vehicle that do not use a center channel? Simply repeat step #7 for the other speakers in your car for which your head-unit or external processor offers time alignment options. The mains are set to 2.8meters distance, with the subwoofer set to 3.8meters distange on the Tag processor, which I have assumed offsets any processing delay of the SMS-1. The simple answer is yes, but in reality it's a phase alignment issue. This time however choose one of the other "Measure" options on the "Measurements" tab. Note that you can zoom in on the impulse response by selecting the section you want to zoom (with the mouse or touchpad). Time alignment usually relates to imaging, but phase alignment tends to refer to frequency response. Fortunately it's quite simple to time align a subwoofer, but is it necessary? I suggest zooming in until the scale is plus/minus 20 cm or so. Rythmik has a 3-page article on phase alignment: http://www.rythmikaudio.com/phase1.html Step #2: - Connect everything up This step is pretty straightforward - connect the PC's audio output to your head unit (most have sort of "aux in" interface that can be used for this moment). Adjust your head-unit's Balance and Fader controls to make all of the sound come out of the first speaker that you want to align, then perform another measurement as outlined above. It is useful in deter... Selenium D220Ti, B&C DE250, BMS, Faital pro ... Diffuser panels: why you need them and how to make your own, Point source horn - building my prototype, How to measure your crossover with Holm Impulse, Active crossover listening tests - conclusion. I think the spectrogram plot is showing the subs are slightly ahead in time alignment. To time-align the speaker in this example, the time alignment options offered by the head-unit or external processor will need to be adjusted to subtract 4cm from the speakers' position relative to the microphone, the intent here being to ensure that the rise for both of the initial positive peaks intersects (or is as close to intersecting as possible. play around with the delay until you got the average near 0. this actualy means that not the subwoofer needs to be delayed, but the mains* Subwoofer’s already have a native delay due to the amp processing the incoming signal, so unless you are able to delay your mains (most surround receivers can do this), there is nothing you can do to time-align your subs to the mains, just phase align. Make sure that it is properly secured as your measurements will be off if the microphone moves. Also, select the "Keep in/out stream active" option and click the "Start" button to start the stream. In short, if phase is misaligned, the subwoofer won't correctly integrate with the mains. Finally, set the head unit volume low enough so the output from the microphone isn't clipped (you can check this using the "Monitor" feature of HolmImpulse and checking the recording level during the initial measurement). The impulse response graph should look something like what it does in the image below: Step #7: Measurement and adjustment Now, it's time to do some time-aligning! If you switch back to the "Measurements" tab now, you'll notice that the impulse response is now starting at or very close to the zero point on the scale. On my current head-unit, a Premier 980BT, the time-alignment adjustment screen looks like the following image: Step #5: - Perform initial measurement Now, perform your first measurement. Time alignment usually relates to imaging, but phase alignment tends to refer to frequency response. This is my first attempt at building a point source horn. Also, place the microphone as close as you can get to your usual listening position. It generated much more interest than we... Update (March 2013): I posted previously that this amp had failed. You should end up with something like looks like the image below: The example impulse response graph above shows that the just-measured speaker (in blue) is about 4cm forward of the reference speaker. Subwoofer Position: Time alignment vs frequency response Common wisdom says that a subwoofer has to be positioned the same distance from the listener as the satellites to avoid timing issues (unless you have some sort of delay compensation and most budget set ups don't.) For this measurement, I suggest selecting the speaker that is furthest from microphone and using your head unit's Balance and Fader settings (and, if necessary, the subwoofer output level) to ensure that sound is coming only from that speaker. Most audio enthusiasts are smart enough to let someone else do the design work. To time-align the speaker in this example, the time alignment options offered by the head-unit or external processor will need to be adjusted to subtract 4cm from the speakers' position relative to the microphone, the intent here being to ensure that the rise for both of the initial positive peaks intersects (or is as close to intersecting as possible.). Efficiency Bandwidth Product (EBP) is a number which shows the trade-off between efficiency and bandwidth of a driver. We first started measuring... Update (June 2017): This post initially announced our intention to create a point source horn kit. previous construction photos > Fitting the parts together. http://www.holmacoustics.com/holmimpulse.php. in the pefect world it should be all 0. ignore the big spikes. Attached is a … ). For the example above, a correct adjustment would look like the image below: And that's basically it! Step #3: - Configure HolmImpulse for measurement Open HolmImpulse and, under the "Device and Signal" tab, select the "Square Noise (Improved MLS)" option. Fortunately it's quite simple to time align a subwoofer, but is it necessary? Step #1: - Get your tools together The first step is of course to get your hands on the correct equipment, which should consist of a laptop or netbook PC to run HolmImpulse (Windows XP or Windows 7), a microphone (which does not have to be too accurate, as you are not doing frequency response measurements with it), a means of connecting the PC's audio output to your car audio system and of course a copy of HolmImpulse itself, which is available from this site: - http://www.holmacoustics.com/holmimpulse.php.

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