4/28/2023 0 Comments Fuzzmeasure impulse responseThis in turn brings its own issues with noise – wind, traffic, or birds and insects. To do better, I would have to take the speaker outside and raise it as far off the ground as possible, and away from any walls, trees, and so on. In my case, the best I can do indoors is 1.2 meters, as my ceilings are 2.4 meters high – in other words, I will raise the speaker off the floor so the driver being measured is halfway between the floor and the ceiling. To reduce this frequency, we need to move the driver being measured further away from any reflecting surfaces. The difference is 3.6 ms, and this is is the maximum T we can use for our gate, so the lowest frequency we can measure is 1/0.0036 or 275 Hz. If the driver and microphone are a meter off the ground, the length of path B will be 2.24 meters, so the first reflection will be seen after 2.24/340 = 6.6 ms. With the microphone a meter from the speaker driver, the sound will take 1/340 = 0.0029411 seconds to travel this distance, or about 3 ms (milliseconds). If the gate length is T seconds, then the lowest frequency we can measure is 1/ T Hz – in practice, I figure on perhaps twice that.Īt sea-level, the speed of sound is 340 meters/second. Once the time-domain signal is gated, it can be converted back into the frequency domain, with the result being the frequency response of the speaker, without any room effects! The limitation of this method is that it works only down to a certain frequency, determined by the length of the gate. A more feasible approach for most of us is to simply remove the reflections from the measurement data, by cutting off the signal just before the first reflection and thus leaving just the speaker’s impulse response – this is called a gated measurement. The brute-force approach is to use an anechoic chamber – a room without reflections. So, to determine the response of the speaker without the room, we need to do away with the reflections B, C, and so on. For practical purposes, we’ll just assume that there is a single impulse from each driver.) (There is an additional complication in our case: since we are measuring an open-baffle speaker, there is also an impulse arriving at the microphone from the driver’s rear radiation. Real example of impulse response of speaker and room And so on reflections upon reflections will then result.įigure 2. A signal generated by the loudspeaker will be first received by the microphone along the direct path A. Shortly afterwards, the microphone will receive another signal – the reflection from the floor – along path B. Then the microphone will see a reflection off the ceiling, via path C. In Figure 1 below, I’ve drawn a loudspeaker and a measurement microphone from the side. ![]() For loudspeaker design, though, we want to exclude the room effects by using a gated measurement. Up until now, we’ve used in-room measurements – that is, measurements that include the response of the room as well as the loudspeaker. I will assume that by now you’re comfortable with this fairly complex active system and the miniDSP user interface. I urged caution several times in order to ensure that the miniDSP settings and the wiring and connections were all done properly. ![]() Previously, I used a fairly rough-and-ready approach to get the speakers set up and basically working. In this project, each channel uses one miniDSP as a four-way crossover, with three output channels driving amplification for the main open-baffle panel and the fourth output channel feeding a subwoofer. These diminutive units have won me over as a practical and affordable solution for all kinds of applications in an audio system. In the first part, I explained how to use a pair of miniDSP 2×4 crossover-equalizer units to build the first prototype. This is the second part of a tutorial on using the miniDSP for implementing an open-baffle loudspeaker.
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