Frequency response charts show what the real-terms output of the speaker is when playing a frequency at a constant volume. If you modulated a constant sine wave output moving up the range, you won’t get the same output ‘volume’ consistently. For example, in ear monitors might have multiple drivers built in, and there won’t be equal crossover between them, causing a dip in those crossover frequencies.
With these single-driver speakers, I’d guess the chart would be mostly solid across the response range, but drop-off at the top and bottom ends would be quick and that bass drops off before the sub-bass ranges. There may even be some dip and then a blip in the response due to materials resonance.
Sunday I’m free, I’ll try to squeeze in some testing. My original plan was to plot freq response curves. Multiple speakers, same chassis and hilt, a room EQ mic and software, with pink noise in a mild dampening surround setup.
The speakers I have are VECO, KR, Smuggler’s, TCS WOW, and a variety of AliExpress ones, which are likely the same as some of the aforementioned. We’ll see.
Ultimately, all we need to know is at what frequency these speakers turn into resistors rather than speakers. If possible, it’s probably best to measure at a realistic distance, say 2 feet or so. If we measure too close, the back-wave cancellation effect might not be taken into account.
See all those overtones? Not only are those overtones audible, but they create distortions as well. I tried a bunch of different filter settings, and they all have these overtones. I’m not sure if these are normal for butterworth filters, or if my filter implementation is buggy in some way. Either way, it’s difficult to recommend using filters based on this.
I should also mention that these spectrograms are more sensetive than my ears. The 10w speaker might look like it can play 70Hz sounds, but it’s not until around 100Hz that my ears can hear it.
Initial tests of the filtering code seems to suggest that it’s working quite well.
However, it seems to cause some amplifications at some frequencies, which is not expected, and if that amplification leads to clipping, then that might explain the overtones we’re seeing.
I can’t seem to tell any difference by ear, but the speaker definitely vibrates less at lower frequencies.
I think for this speaker, the recommended cut-off frequency should be somewhere in the 120-150 Hz range. An 8th-order filters seems to work well, but we might want to do more testing to figure out what is actually best.
You need to work and test with the WOWsound TCS 28mm 3W (4W peak) bass speakers, or the Smugglers Outpost ones, but not the “TCSS standard 2W VECO bass speakers”, because they have the worst sound quality.