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#31 Re: Purifi-based monitor - options

Posted: Mon Oct 04, 2021 8:22 pm
by IslandPink
It's a slightly bigger volume and a shorter port - but I like the effect of the wadding around the port interior. I will do a simulation first.

#32 Re: Purifi-based monitor - options

Posted: Wed Oct 06, 2021 7:48 pm
by IslandPink
Unfortunately he explains nothing about his choice of volume and port size/length.
I did a basic Hornresp set-up for it with unlined port, then changed the port diameter ( on the basis he'd put felt in there ) until I got the closest match to the measured impedance curve ( with lined port ). This came out about 20cm^2 area, which suggest the port acts as if it's about 5cm dia ( though more damped ).
If I sim that for SPL it looks like this -
PurTroels_SPL.JPG
PurTroels_SPL.JPG (49.45 KiB) Viewed 278 times
The group delay doesn't look too pretty.
So I'm not sure this convinces me to build it.

#33 Re: Purifi-based monitor - options

Posted: Thu Oct 07, 2021 6:49 pm
by chris661
A peak before rolloff will tend to ring.

Make the port longer to drop the tuning. The result should be a smoother frequency response, and I'd also expect the group delay to improve and/or push issues down in frequency.

Another option would be to go sealed, and EQ the speaker + room result.

Chris

#34 Re: Purifi-based monitor - options

Posted: Thu Oct 07, 2021 7:25 pm
by Ant
Try an aperiodic slot rather than a port? God knows how you would model it though
Ten square inches per cubic foot of cab volume was about the best info i could come up with for sizing

#35 Re: Purifi-based monitor - options

Posted: Fri Oct 08, 2021 9:43 pm
by chris661
IIRC, Hornresp can model it if you morph it into an offset-driver alignment.

Chris