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2x8" PPSL midtops made from junk
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bob4 View Drop Down
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Joined: 29 February 2004
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Points: 1843 		Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 9:03pm
ok, here is a close-up measurement of the plenum:
Gen0me, I think your simulation was right on the money considering the rather approximative data I supplied you with! The bass bump is at 100 Hz, rather than the 80 Hz predicted by hornresp. The mid honk is also a bit higher than the 350 Hz in your simulation, and instead of a single peak there are two narrow peaks at 400 and 500 Hz.

Not bad!!  




Edited by bob4 - 20 June 2017 at 9:04pm
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gen0me View Drop Down
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What is this deep between mountains on 450hz? Is it room or enclosure?

Edited by gen0me - 20 June 2017 at 9:16pm
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bob4 View Drop Down
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I took out the hf horn to disconnect the second crossover, and noticed that the gasket of the second woofer was sticking out over the edge and preventing the hf horn from properly sealing. Shaved off the offending bit with a knife, and as a result bass response improved considerably, while farting air noises decreased by the same margin

Disconnecting the second crossovers hf output improved woofer/hf balance tremendously.

Now the box sounds pretty ok for what it is. Very percussive and coherent. The mid honk and the big dip around 1 kHz dont bother the listening experience too much. But i will do some further tweaking with eq once my inuke is here, and maybe even modify the passive crossover.

I only had a hifi amp for testing, but it does go loud. Can't crank it up too much at home anyway. Also no chance doing "far field" measurements obviously, but the closeup measurements of the plenum provide enough data to mull on for the time being.
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bob4 View Drop Down
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Originally posted by gen0me gen0me wrote:

What is this deep between mountains on 450hz? Is it room or enclosure?

Not sure to be honest. I think it is the box, since it shows up consistently in all the sweeps I did at different positions and distances.
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gen0me View Drop Down
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Lrc~35cm gives that deep.
Standing wave on side of hf horn rear chamber seems to be responsible.

Edited by gen0me - 20 June 2017 at 9:45pm
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bob4 View Drop Down
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Points: 1843 		Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 10:01pm
Yes, I think I will have to add some wadding to both chambers under and above the plenum, let's see what that will do. I also stuffed a slice of foam around the back of the plenum, and now I vividly imagine I can hear an improvement LOL
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gen0me View Drop Down
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Some damping material should also move the bottom(100hz) mountain lower(Vrc). Im not sure how it will affect the 450hz standing wave. Could move it lower and make bigger differences there.
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bob4 View Drop Down
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Points: 1843 		Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 21 June 2017 at 9:41am

So, I did some quick sweeps with and without a piece of "acoustic" foam (pulled from the same DAS audio Factor 8 cabs) lining the back and sides of the plenum. I did ten sweeps in two sets (first with foam, then without). First one with the mic in the middle of the plenum, and then four with the mic at each corner of the plenum. 

Here are four traces, two pairs of measurements for the upper and lower right corner of the plenum (viewed from the front).

PURPLE: upper right corner with foam
RED: upper right corner without foam
KHAKI: lower right corner with foam
GREEN:lower right corner without foam  

Looking forward to taking the cab to a bigger room or outdoors to do some measurements with the mic further away to see how this rollercoaster evens out over distance





Edited by bob4 - 21 June 2017 at 9:44am
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mini-mad View Drop Down
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That canyon at 450 looks a bitch! Really hope that's a standing wave for that room....

Looks like you're having serious fun with that box! Nice and punchy around 90-100.

Keep up the good work my friend iv been looking forward to this on a daily basis it's lovely to see some one making dust and actually having fun in this forum.
If it sounds like a gorilla is trying to escape, turn it down.
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bob4 View Drop Down
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Points: 1843 		Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 21 June 2017 at 2:33pm
Thank you very much for the encouraging words mini-mad! I've been building a couple of cabs from other peoples plans over the years, and done a lot of system aligning and listening, big PA/soundsystems, hifi at home etc.

But listening to aa box that you have designed yourself from scratch gives a very different pleasure that is hard to describe.
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bob4 View Drop Down
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Continuing assembly of number two...
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......sanding down 1 mm of wood by hand is a grind.....
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