Attached is a … 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 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.) previous construction photos > Fitting the parts together. Update: DIY point source kit This point source horn combines a unique mix of features that make it very appealing. 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). 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. 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. Most audio enthusiasts are smart enough to let someone else do the design work. Fortunately it's quite simple to time align a subwoofer, but is it necessary? This basically sets the measurement you just performed as the reference measurement. Once the adjustment is made, repeat the measurement to confirm that change was successful. This time however choose one of the other "Measure" options on the "Measurements" tab. 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. 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. 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.). In short, if phase is misaligned, the subwoofer won't correctly integrate with the mains. I think the spectrogram plot is showing the subs are slightly ahead in time alignment. We first started measuring... Update (June 2017): This post initially announced our intention to create a point source horn kit. 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? The simple answer is yes, but in reality it's a phase alignment issue. For the best results, do not have any other programs open at the same time as HolmImpulse. ). Time alignment usually relates to imaging, but phase alignment tends to refer to frequency response. Efficiency Bandwidth Product (EBP) is a number which shows the trade-off between efficiency and bandwidth of a driver. http://www.holmacoustics.com/holmimpulse.php. 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 suggest zooming in until the scale is plus/minus 20 cm or so. Should we RTA both side, all 4s? For the example above, a correct adjustment would look like the image below: And that's basically it! On my system's current head-unit, that adjustment looks like the following image (the listening position is the right front seat): Make the first measurement by selecting the "Measurements" tab and clicking on one of the three "Measure" options. 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. Also, place the microphone as close as you can get to your usual listening position. 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. 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. 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. 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. This is my first attempt at building a point source horn. Rythmik has a 3-page article on phase alignment: http://www.rythmikaudio.com/phase1.html The simple answer is yes, but in reality it's a phase alignment issue. Note that you can zoom in on the impulse response by selecting the section you want to zoom (with the mouse or touchpad). Also, select the "Keep in/out stream active" option and click the "Start" button to start the stream. Make sure that it is properly secured as your measurements will be off if the microphone moves. Example I would like to see is what steps should be taking first like time alignment, crossover point etc.…. This can be done very quickly with a tape measure and significantly reduces the time spent fiddling with HolmImpulse to get it right. Time alignment usually relates to imaging, but phase alignment tends to refer to frequency response. 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’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. Simply repeat step #7 for the other speakers in your car for which your head-unit or external processor offers time alignment options. 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.