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Bass reflex not so good
Bass reflex not so good
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Old 27th June 2020, 07:50 PM   #1
francesco81rs is offline francesco81rs  Italy
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Default Bass reflex not so good

Hi everyone.
I would like to ask for help with the sound of a bass reflex.
There is something that does not convince me and many other people, there seems to be something "dirty" in the system response.
I believe there is some resonance, and I would like to ask you for help in identifying and I hope to solve the problem.
The bass is inserted in a 3-way system, is used up to about 500Hz and has 2 woofers.
The speakers used are 416-8B GPA and the cabinet, as you can see from the picture, I think I am right in saying that it is very hard.
The front is 40mm (beech) and the rest 30mm (birch)
the interior was filled with polyester fiber, obviously without saturating the internal volume.
Also you can see from the impedance curve, currently the system is tuned to 35hz.
We made a 25hz attempt, the overall response improved, but the "confusion" in the sound is there.
Thanks a lot for any help you can give me.
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Old 27th June 2020, 07:58 PM   #2
planet10 is offline planet10  Canada
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Bass reflex not so good
Big box with very little bracing. Even with walls that thick it is likely to move. Amechanics stethescope will quickly tell you how much.

What does a sim of the alignment look like?

dave
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Old 27th June 2020, 08:38 PM   #3
ScottG is offline ScottG  United States
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I doubt that the "dirty"/"confused" sound has anything to do with the venting. (..subjective responses like this usually are from problems higher in frequency.)

It looks like the the port has to much fiber near it - with that extended impedance "shelf" below 20 Hz.

I'd also make sure that the coupling between driver and baffle was physically secure and air-tight (..though the driver's resonance doesn't look bad, but it does look substantially suppressed in magnitude, again - typically the result of to much "fill"/fiber).
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Old 27th June 2020, 09:04 PM   #4
planet10 is offline planet10  Canada
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Bass reflex not so good
As Scott mentions, one usually does not use volume fil in a reflex box, just wall lining.

dave
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Old 27th June 2020, 09:49 PM   #5
ILikeFoodz is offline ILikeFoodz  United States
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Others can correct me if I'm wrong, but I believe running the bass driver all the way up to 500 Hz might be causing some intermodulation distortion into the midrange, which could cause the sound you're talking about. Is the confusion sound much better if you play the speakers at a low volume? Lower volumes will have lower IMD.
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Old 27th June 2020, 09:53 PM   #6
giralfino is offline giralfino  Italy
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OK, I'm the only one that sees a problem in the impedance graph? Too many irregularities? It is just a bad measure/methodology or it is a valid impedance? If the latter the speaker is full of vibrations or other problems. Can I see an impedance graph of a standalone driver?

Ralf
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Old 27th June 2020, 10:19 PM   #7
planet10 is offline planet10  Canada
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Bass reflex not so good
Bumps are either driver resonances or box resonances. What doe the speaker impedance of a bare drive rlook like given the same measurement kit?

dave
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Old 28th June 2020, 07:12 AM   #8
GM is offline GM  United States
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Hmm, based on published specs and assuming only minimal series resistance for wiring, the cab is ~0.7 Qtc sealed sized in Hornresp, so vented is under-damped to the point where it's a good size for a single driver tuned to Fs and for best overall response, use the pioneer's [2*Vas/1.44] = Vb tuned to Fs.

For now, stuff the vents to get a ~46 Hz single impedance peak.

GM
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Old 28th June 2020, 07:16 AM   #9
TBTL is offline TBTL  Germany
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Are you listening indoor?
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Old 28th June 2020, 09:31 AM   #10
Scottmoose is offline Scottmoose  United Kingdom
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What GM says. I'd also point out you're running a 50ohm Y axis on a logarithmic scale, which may visually emphasise resonances at lower impedance levels. Shift the visual over to 50ohm with a linear scaling & see what you think then.
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