YEA. The rear wave has to go somewhere.
If you had an ~infinitely stiff sealed box (say you took 100 ton granite cube, and drilled a 5 litre hole into it to use as your enclosure), I think that essentially all of the 100-500Hz energy going into that enclosure would be reflected straight back out through the cone.
There is an amusing discussion buried somewhere in the "Beyond the Ariel" thread. If I remember correctly, Geddes was initially modelling his bass boxes as if the cones were solid (to internal sound / reflection). He was badgered about this until he tried modeling them as relatively transparent - and his models became more accurate.
1) Try to ignore it. This is usually my solution 🙂
2) Use a really big box, relative to the driver, so that the leaky part (the cone) is small relative to the stiff part (the box)*. IB mounting - setting your woofers into the walls of your listening room, with no reflective surface behind them - would maximise this.
3) As you say, "some kind of internal diffuser pattern" - taking your inspiration from the snail-shaped Nautilus would maximise this.**
*I have often wondered whether this is largely responsible for the sound quality attributed to some vintage drivers - they often have high VAS and require large boxes.
For example, "The P Audio P180/2242 is a high output low frequency transducer designed with a vintage voicing" seems to mean "The P Audio P180/2242 has specs that demand a REALLY big box"
**I made a FAST where the wideband driver was mounted in a heavily stuffed, open-ended tube that was set into in the bass enclosure (that is, the midrange 'box' was a tube ran right through the woofer box). I think this is a good compromise if you don't want to get as fancy as the Nautilus.
If you had an ~infinitely stiff sealed box (say you took 100 ton granite cube, and drilled a 5 litre hole into it to use as your enclosure), I think that essentially all of the 100-500Hz energy going into that enclosure would be reflected straight back out through the cone.
There is an amusing discussion buried somewhere in the "Beyond the Ariel" thread. If I remember correctly, Geddes was initially modelling his bass boxes as if the cones were solid (to internal sound / reflection). He was badgered about this until he tried modeling them as relatively transparent - and his models became more accurate.
Why? I would have thought it would be the ratio of cone area: box volume that mattered for this. I'd rather use a 24" cone mounted in a 24" cube than a 6" cone mounted in a 6" cube.
1) Try to ignore it. This is usually my solution 🙂
2) Use a really big box, relative to the driver, so that the leaky part (the cone) is small relative to the stiff part (the box)*. IB mounting - setting your woofers into the walls of your listening room, with no reflective surface behind them - would maximise this.
3) As you say, "some kind of internal diffuser pattern" - taking your inspiration from the snail-shaped Nautilus would maximise this.**
*I have often wondered whether this is largely responsible for the sound quality attributed to some vintage drivers - they often have high VAS and require large boxes.
For example, "The P Audio P180/2242 is a high output low frequency transducer designed with a vintage voicing" seems to mean "The P Audio P180/2242 has specs that demand a REALLY big box"
**I made a FAST where the wideband driver was mounted in a heavily stuffed, open-ended tube that was set into in the bass enclosure (that is, the midrange 'box' was a tube ran right through the woofer box). I think this is a good compromise if you don't want to get as fancy as the Nautilus.
Yes probably, but not zero. And then i'll have issues with the lower frequencies. Unless i have drivers that have a very high Qts which is not frequent in the drivers i'm looking for at the moment!
i'll look through the Audio Cyclopedia tonight but if i recall it's congruent to a "blocked impedance"
would prevent driver motion which should allow a better glimpse of what the cone will pass.
would prevent driver motion which should allow a better glimpse of what the cone will pass.
I assume the bigger cone/bigger box will lead to lower frequency resonance and also higher RT. Both seems to be important here: if the resonant frequency is higher than the intended driver use, it helps. Also if the RT is low, it helps.
High RT are usually found in large spaces with very hard surfaces (mountains, rocks, concrete bunker, etc..) they reflect the acoustic energy with less loss between each reflections, thus keeping the bouncing longer.
I may be off track but wasn't this problem one of the reasons that Wharfedale (originally) and then KEF started using in polystyrene in their cones in the '60's? I.e. recognizing the issue of reflected sound waves and then trying to make the cone less acoustically transparent. I recall that they (Raymond Cooke was head of research at Wharfedale prior to starting KEF) started by applying a thin sheet to an existing paper cone and then ended up with the KEF B139. It is described in Gilbert Briggs books (Cabinet Handbook from the '60's, my 5th edition "Loudspeakers" from 1958 is still too early). The results show that the poly' was most effective from above 700c/s. But people with the literature on hand can confirm (or otherwise) my memory. An edition of HFN/RR from the '70's also had an article that addressed issues from frame reflections or at least recognized it as a factor.
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I like the 100 tons granite example. 🙂
So, yeah, in that extreme case, that i can perfectly imagine, the acoustic energy bounces back to the cone. Agreed, it's unavoidable. So the whole enclosure thing is out of the equation.
NOW, is the bouncing back into the cone a good or a bad thing ?
One way or the other, the energy needs to be transformed somehow, or transfered somehow. So, as far as i understand, it should make 2 things:
1. Bounces back into the cone, then the cone absorbs it (which could alter the driver's movement/dynamics)
2. Bounces back into the cone, then it goes through it (which leads to sounds coming from the bounce rather that from the transducer's first sound emission)
Can't see how any of those two things can be positive, in an Hifi way of seeing it.
Good question. The leakage consist of three parts:
#1 - transmission through the cone material per se.
#2 - any output from the cone flexing under load.
#3 - additional output because the amp not being able to clamp the cone at rest position (but that's a motor thing, not a cone problem).
If we are after #1 and can't reduce #2 for obvious reasons then let's at least try to keep the motor part out of the equation.
Locking the cone will alter the flexing pattern a bit because the mechanical properties change (normally, the VC is only clamped so much as defined by #3)
i think it would then make sense to use another 8FE200 internally to test it. I'd say i'll end with some kind of isobaric enclosure, am i right ?
I'll quit now, it's after midnight here and I had my share of treasured 18yrs. Caol Ila ;-) On a weekday, sigh....
how about a 8FE200 that is EQd flat as the inner source (inside the passive enclosure that would act as ''the room''), then i measure outside the whole thing what comes through the passive 8FE200 ?
One reference enclosure with a tiny hole to fit the mic, then one enclosure for the test with both passive and active 8fe200's, with the same EQ correction as the reference enclosure applied on it ?
One reference enclosure with a tiny hole to fit the mic, then one enclosure for the test with both passive and active 8fe200's, with the same EQ correction as the reference enclosure applied on it ?
Oh, now we're talking. Perfect for freezing Berlin, is it ?
I'll follow you on that with a 16yo Lagavullin instead of a beer.
That topic is officially single-malt-worthy.
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