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Re: 4Pi - alternate compression driver mounting? [message #95147 is a reply to message #95144] Fri, 28 January 2022 17:38 Go to previous messageGo to next message
areohbe is currently offline  areohbe
Messages: 20
Registered: May 2021
Chancellor
Excellent explanation, as always, Wayne.

Here is my initial test the other evening. I was mostly just trying to verify my UMIK + REW setup was working.

There's still no dampening in the box. I did throw a blanket in the bottom but that didn't seem to change much. Not sure there's much to really glean from this for now.

/forum/index.php?t=getfile&id=2995&private=0
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Re: 4Pi - alternate compression driver mounting? [message #95148 is a reply to message #95147] Sat, 29 January 2022 10:41 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18271
Registered: January 2001
Illuminati (33rd Degree)

As expected, the trend looks right but there's a lot of "grass" from all the nearby reflections. All those deep notches are from interference with some object's reflection that's 180° out-of-phase.

The things we really need to know - and so we need an environment that's reflection-free enough to see - is we need to know what's going on between 100Hz and 400Hz and we need to find the vertical nulls which are around 1.2kHz.
Re: 4Pi - alternate compression driver mounting? [message #95149 is a reply to message #95148] Sat, 29 January 2022 20:33 Go to previous messageGo to next message
areohbe is currently offline  areohbe
Messages: 20
Registered: May 2021
Chancellor
New setup. Think we're getting somewhere...

/forum/index.php?t=getfile&id=2996&private=0

/forum/index.php?t=getfile&id=2997&private=0
Re: 4Pi - alternate compression driver mounting? [message #95154 is a reply to message #94478] Mon, 31 January 2022 01:43 Go to previous messageGo to next message
areohbe is currently offline  areohbe
Messages: 20
Registered: May 2021
Chancellor
Doh! Just realized the roll offs in the highs is because I didn't zero out the high and low gain. Laughing
Re: 4Pi - alternate compression driver mounting? [message #95155 is a reply to message #95154] Mon, 31 January 2022 09:21 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18271
Registered: January 2001
Illuminati (33rd Degree)

Yes, you're working with much cleaner measurements now.

Get some stuffing in the cabinet and see if you can do anything with that peak around 120Hz. That is the difficult region I often talk about.

You'll notice the stock cabinet gently rises from 100Hz to 150Hz and then gradually drops to around 200Hz. This is the result of the positions of the midwoofer driver, port and insulation. It prevents the really big peaks and dips.

The peak in your cabinet is not unusual. I've seen a lot of cabinets like that. It doesn't sound terrible, but you do notice a throaty sound in male voices and other things. It just sounds "boxy."

So try lining the walls with insulation and also try placing a sheet that spans the cross-section of the cabinet between the port and the woofer. Might even use two of those. That cross-section "divider" sheet has proven to be the most effective, in my experience.
Re: 4Pi - alternate compression driver mounting? [message #95157 is a reply to message #95155] Mon, 31 January 2022 14:08 Go to previous messageGo to next message
areohbe is currently offline  areohbe
Messages: 20
Registered: May 2021
Chancellor
Thanks, Wayne! That was my suspicion. Good to know I wasn't too far off.

Think this gives me enough confidence to move on beyond MDF and start procuring some birch and working on the final cabinet design.
Re: 4Pi - alternate compression driver mounting? [message #95159 is a reply to message #95157] Mon, 31 January 2022 15:00 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18271
Registered: January 2001
Illuminati (33rd Degree)

I would strongly suggest adding insulation first. Especially the cross-section sheet. Try it straight. Try it diagonal. Make sure you can mitigate that peak at 120Hz.

I say this because you might find that your efforts to damp the peak are illusive, and you might end up moving the port. This is best learned while you're still in the "cut and try" mode.
Re: 4Pi - alternate compression driver mounting? [message #95160 is a reply to message #94478] Mon, 31 January 2022 16:05 Go to previous messageGo to next message
areohbe is currently offline  areohbe
Messages: 20
Registered: May 2021
Chancellor
Do you have to be so reasonable, Wayne?! Laughing

Heading out to pick up some R-13...
Re: 4Pi - alternate compression driver mounting? [message #95192 is a reply to message #94478] Fri, 04 February 2022 20:15 Go to previous messageGo to next message
areohbe is currently offline  areohbe
Messages: 20
Registered: May 2021
Chancellor
Hmm green is the new measurement. Bout the same? Maybe worse? Crying or Very Sad
/forum/index.php?t=getfile&id=3010&private=0
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Re: 4Pi - alternate compression driver mounting? [message #95196 is a reply to message #95192] Sat, 05 February 2022 10:43 Go to previous messageGo to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18271
Registered: January 2001
Illuminati (33rd Degree)

The response in the 100-200Hz region is about the same, so I think you want to look at things you can do about stuffing. Hopefully you can find a solution with damping material. Not sure what's going on above 1kHz, but it looks like there are a lot of reflections. Could be also way off-axis in the vertical, but that wouldn't explain the dip around 2.5kHz.
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