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.
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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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).
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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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.
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
For now, stuff the vents to get a ~46 Hz single impedance peak.
GM
Thanks! That's what was 'bugging' me earlier, but too sleep deprived to figure it out plus the peaks are significantly lower than they historically are when dual 8 ohm AlNiCo Altec are wired in parallel.
Then again, Bill has had to replace a lot of worn out Altec/EV tooling, so may be moot.
GM
Then again, Bill has had to replace a lot of worn out Altec/EV tooling, so may be moot.
GM
It appears that Francesco measured only 1 ( of 2 ) woofers present in the box ( with the 2nd woofer flapping in the breeze, so-to-speak, >> acting as a mechanical microphone ).
That's a sure way to get some unreliable/// hard-to-dissect results.
Ah, second woofer acting as another "vent"/passive-radiator. That explains the < 20 Hz irregularity in impedance.
(..the un-connected driver acting as a passive-radiator could result in a "dirty" sound: with too much excursion and it's surround causing audible problems.)
Still, the driver's resonance in-box has a very low magnitude for its Qe - almost always the result of to much "fill". (..the "peak" of the driver's resonance should be closer to 40 ohms at a minimum.)
(..the un-connected driver acting as a passive-radiator could result in a "dirty" sound: with too much excursion and it's surround causing audible problems.)
Still, the driver's resonance in-box has a very low magnitude for its Qe - almost always the result of to much "fill". (..the "peak" of the driver's resonance should be closer to 40 ohms at a minimum.)
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Wrong measure
Oops, sorry!
What a stupid measure I had done.
Tonight I will do it again with the parallel connection of the two woofers, and using the linear scale.
However, the "dirty / confused" sound sensation is there; with the two woofers connected (certainly) in parallel.
As soon as possible I will also give you some photos of how it is done internally, so that you can better see the "filling".
The internal volume that I had calculated was based on the alignment tables and I had chosen the QB3.
They are around 350L and it seems to me to be a volume very similar to the Altec Valencia project, obviously multiplied by two.
Do you think the cabinet can be used with this internal volume?
Oops, sorry!
What a stupid measure I had done.
Tonight I will do it again with the parallel connection of the two woofers, and using the linear scale.
However, the "dirty / confused" sound sensation is there; with the two woofers connected (certainly) in parallel.
As soon as possible I will also give you some photos of how it is done internally, so that you can better see the "filling".
The internal volume that I had calculated was based on the alignment tables and I had chosen the QB3.
They are around 350L and it seems to me to be a volume very similar to the Altec Valencia project, obviously multiplied by two.
Do you think the cabinet can be used with this internal volume?
..is that 700 liters total per loudspeaker?
350 liters per driver is not so great as far as bass reflex is concerned (for this driver), unless you are "tailoring" the freq. response for a specific result (..boosted bass and truncated lower freq. (sub-bass) response relative to the average.) That amount of volume isn't bad for a sealed design though.
While true for probably 97% of 15" woofers available nowadays, there's a small number of manufacturers that build modern versions/variants of the pioneer's ultra wide range drivers; with GPA building new, improved versions to Altec specs, which BTW the 416 started life in '48 as the 803 designed for an 800 Hz XO.
Time marched on and due to many material, manufacturing advances combined with increasing power the 803/416A was born with up to a 1200 Hz XO at high SQ, so 500 Hz is considered a waste of an excellent 15" ultra wide range woofer by many. Indeed, me and some others have run the original 416s, 515s wide open with just a tweeter horn capped off at ~5 kHz where they finally take a nosedive, though with the understanding that they have limited polar response, but more than you might think due to their curvilinear cone, careful doping Vs modern 'flat' cone drivers.
GM
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