My DIY subwoofer isn't sounding the best and I'm not sure what the problem is exactly (how to identify it via tests/measurements). The problem is in the higher bass region, above 50Hz, and is affected by where I set my DSP LPF. The problem is it has a sort of thump sound to it that doesn't sound right, and it only occurs on "sudden" bass notes like drum beats, but not on "sustained" bass notes. The thump sound stands out and makes it easy for me to localise the sub's sound even when using 90Hz 8th order LPF, which seems a bizarre thing to be occurring.
To pre-empt some possible responses: I designed the sub in WinISD as a vented box with an extended bass shelf tuned to ~24Hz. It's a 120W driver with only a 90W amp, and WinISD calcs the max excursion at 6mm (with 90W) vs manufacturer spec'd Xmax of 9mm - so I don't think it's a problem there. Additionally, max excursion is at 37Hz, and at 60Hz it's down to 3mm, and 1mm at 80Hz - so excursion is even less of a potential problem in the upper bass region. Port velocity is max 10m/s at 24Hz, but only 1m/s at 60Hz. Also port gain is like -16dB at 60Hz, so I don't think it's a problem there either. Putting my ear near the port also confirms no problem from it (and the port is on a different face to the driver). So the problem definitely seems to be coming from the driver.
Edit 3: Forgot to mention, I don't think there is anything wrong with the driver physically/mechanically. It moves fine when I press it by hand. I'm going to drag it out soon and look over it for issues like loose screws and tinsel slap.
A possible source of the problem could be group delay introduced by the LPF? In the WinISD screenshot below, I can see 2nd order ButterWorth @ 90Hz is a rather smooth curve, 4o puts a little hump in it, and 8o is quite a big hump. Could this be the problem I am hearing? Because when I change these settings in DSP on the fly (and I'm listening to the sub only - no speakers), yes the problem becomes a little better, but it doesn't become perfect, and I wonder if it only seems a bit better because the sub is now playing more sounds around 200Hz? Because when I stick it on 8o@60Hz the problem is reduced even further without hearing anything in that 200Hz area, and yet the group delay is apparently even worse. So what gives?
Edit 2: FYI the song sample I am testing against is from 3:20 to 3:40 on this song. Using 2o@85 I can hear heaps of the jingles and stuff from the song. With 4o I can only just hear some non-bass notes, and with 8o I can only hear bass but the thump issue is more pronounced.
I have used UMIK-1 and REW to EQ this sub in the past. Looking back at some measurements I've done, the following seems to be the last one I did with EQ applied and LP 8oBW@85Hz. I'll do some more soon to see what the current state of things are, but nothing distortion wise stands out to me on that plot. But maybe the peak at 140Hz is a problem? Perhaps I need a PEQ just to knock that down? If that is the problem I am hearing, perhaps reducing the LPF to ~60Hz has been enough to move away from that peak, and alternatively reducing the order increases the sound around that peak so that it blends in? So maybe that peak is the problem?
Edit 1: Tried -10dB + 8-12Q at ~150Hz but it didn't seem to make a difference.
Anyway, any advice on what/how to test would be appreciated. One thing I wonder about is doing measurements in REW with sweeps, those seem more like the sustained bass notes I mentioned at the start which aren't a problem, and not so much like the sudden and impactful bass notes like kick drums that are the problem. Is there any way to better simulate quick notes in REW?
And further to this, whilst excursion doesn't seem to be a problem in WinISD, could "dynamic" bass be causing a problem (eg a sustained bass note being played with a drum hit over the top)? I think probably not because this is happening at rather moderate volume levels (the music I'm playing from PC is at like -20dBFS after DSP and considering the volume setting), so I should be miles away from xmax. But perhaps there is some other property of the driver that is related to dynamics?
To pre-empt some possible responses: I designed the sub in WinISD as a vented box with an extended bass shelf tuned to ~24Hz. It's a 120W driver with only a 90W amp, and WinISD calcs the max excursion at 6mm (with 90W) vs manufacturer spec'd Xmax of 9mm - so I don't think it's a problem there. Additionally, max excursion is at 37Hz, and at 60Hz it's down to 3mm, and 1mm at 80Hz - so excursion is even less of a potential problem in the upper bass region. Port velocity is max 10m/s at 24Hz, but only 1m/s at 60Hz. Also port gain is like -16dB at 60Hz, so I don't think it's a problem there either. Putting my ear near the port also confirms no problem from it (and the port is on a different face to the driver). So the problem definitely seems to be coming from the driver.
Edit 3: Forgot to mention, I don't think there is anything wrong with the driver physically/mechanically. It moves fine when I press it by hand. I'm going to drag it out soon and look over it for issues like loose screws and tinsel slap.
A possible source of the problem could be group delay introduced by the LPF? In the WinISD screenshot below, I can see 2nd order ButterWorth @ 90Hz is a rather smooth curve, 4o puts a little hump in it, and 8o is quite a big hump. Could this be the problem I am hearing? Because when I change these settings in DSP on the fly (and I'm listening to the sub only - no speakers), yes the problem becomes a little better, but it doesn't become perfect, and I wonder if it only seems a bit better because the sub is now playing more sounds around 200Hz? Because when I stick it on 8o@60Hz the problem is reduced even further without hearing anything in that 200Hz area, and yet the group delay is apparently even worse. So what gives?
Edit 2: FYI the song sample I am testing against is from 3:20 to 3:40 on this song. Using 2o@85 I can hear heaps of the jingles and stuff from the song. With 4o I can only just hear some non-bass notes, and with 8o I can only hear bass but the thump issue is more pronounced.
I have used UMIK-1 and REW to EQ this sub in the past. Looking back at some measurements I've done, the following seems to be the last one I did with EQ applied and LP 8oBW@85Hz. I'll do some more soon to see what the current state of things are, but nothing distortion wise stands out to me on that plot. But maybe the peak at 140Hz is a problem? Perhaps I need a PEQ just to knock that down? If that is the problem I am hearing, perhaps reducing the LPF to ~60Hz has been enough to move away from that peak, and alternatively reducing the order increases the sound around that peak so that it blends in? So maybe that peak is the problem?
Edit 1: Tried -10dB + 8-12Q at ~150Hz but it didn't seem to make a difference.
Anyway, any advice on what/how to test would be appreciated. One thing I wonder about is doing measurements in REW with sweeps, those seem more like the sustained bass notes I mentioned at the start which aren't a problem, and not so much like the sudden and impactful bass notes like kick drums that are the problem. Is there any way to better simulate quick notes in REW?
And further to this, whilst excursion doesn't seem to be a problem in WinISD, could "dynamic" bass be causing a problem (eg a sustained bass note being played with a drum hit over the top)? I think probably not because this is happening at rather moderate volume levels (the music I'm playing from PC is at like -20dBFS after DSP and considering the volume setting), so I should be miles away from xmax. But perhaps there is some other property of the driver that is related to dynamics?
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