Probably already debated, but still i have to ask:
In a sealed enclosure, even if it's ''waterproof sealed'' it doesnt change the fact that any sound or noise that is inside the enclosure will pass through the cone and bigger the cone, bigger is the potential reflections & flutter echos are, also bigger cone means bigger enclosures and worst of those effects.
On the other hand, if you damp the inside of the enclosure like hell, you might reduce the acoustic energy (overall transducer efficiency) and at uncontrolled frequency... and also the internal volume, which all leads to other problems.
So what is the solution(s) ?
An enclosure with some kind of internal diffuser pattern that would break the reflections and reduce flutter echoes, or just massive damping, or a mix of both ?
(i'm talking about the 100-500hz frequencies, basically, lower or higher are less of i problem i believe.)
In a sealed enclosure, even if it's ''waterproof sealed'' it doesnt change the fact that any sound or noise that is inside the enclosure will pass through the cone and bigger the cone, bigger is the potential reflections & flutter echos are, also bigger cone means bigger enclosures and worst of those effects.
On the other hand, if you damp the inside of the enclosure like hell, you might reduce the acoustic energy (overall transducer efficiency) and at uncontrolled frequency... and also the internal volume, which all leads to other problems.
So what is the solution(s) ?
An enclosure with some kind of internal diffuser pattern that would break the reflections and reduce flutter echoes, or just massive damping, or a mix of both ?
(i'm talking about the 100-500hz frequencies, basically, lower or higher are less of i problem i believe.)
Basically, i think the famous ''boomy'' feeling of the bass often comes from the 3rd and 4th octave and that's because of poor impulse response (bass reflex) + the flutter echoes that can be heard through the cone (and port if any).
I might be wrong, though. 😎
I might be wrong, though. 😎
Since it's difficult to test all that when said transducer is active, i think the best way to test it would be to put a speaker...within a speaker. 
You run a pink noise or a sweep, then see what comes through the cone of the bigger inactive driver. Educated-guess here: everything higher than 1khz or so will be blocked, and assuming the smaller active driver is a flat source, it will be louder and annoying mostly between 100hz and 300hz, based on the enclosure size and damping/internal treatment.
I'm thinking out loud, it's monday. 😀
You run a pink noise or a sweep, then see what comes through the cone of the bigger inactive driver. Educated-guess here: everything higher than 1khz or so will be blocked, and assuming the smaller active driver is a flat source, it will be louder and annoying mostly between 100hz and 300hz, based on the enclosure size and damping/internal treatment.
I'm thinking out loud, it's monday. 😀
Thanks for this topic! I usually pad the whole space behind every driver i give an enclosure, at least until the enclosure starts to run out into a quarter-wave, transmission-line or acoustic labyrinth. I have a simple quarter-wave (driver mounted at line end) stuffed densely in the first third, loosely in the second and not at all in the last third. This works like a charm, providing a modest boost and relief at line fundamental and no ringing above, because of that damping. What i see in HobbyHiFi, all this bass-reflex and underdamped quarter-waves using Helmholtzchambers still ringing, and the lo mechanical damping craze is heaven.
with an "inactive" driver how would prevent it from behaving like a passive radiator(?) which would muck up the results of what would be coming through the cone? (it's gotta be monday if i'm pondering this...)
partly done that with the Radian + Raal 🙂
then for the 100-500hz, if i'm taking the OB route, i'll have other kinds of problems. And, anyway, resonances from the room/furnitures
Can't.
The inactive driver would start to ''badly'' resonate... at his Fs.
But it's no big deal for most drivers in that case since we're testing higher frequencies.
If a stiff cone is connected to a significant mass, such as a heavy voice coil, then sounds will tend to reflect off of it, rather than pass through it. The amplifier will also tend to damp the movements of the cone due to reflections (when the amp is on, which presumably is all we care about). This is why you can build up pressure inside of a speaker cabinet. If reflections passed right through the cone, then all boxes would behave like open baffles, and we would never see the resonance frequency of a speaker change due to the volume of air in the box behaving like a spring.
I want to say more... but I'm out of time.
I want to say more... but I'm out of time.
started to have those reflexions in my mind after hearing your 21'', Tom. And after your comments about the enclosure not being prepped for 100hz+... Then i thought to myself ''What is the biggest ''LEAK'' if not the enclosure... The cone!''
The typical small enclosure/small cone probably results in less flutter echoes and at higher frequencies, thus making it less annoying. And, as what people calls it, ''faster, punchier''.
But what if you take a bigger cone, in a small/medium sized sealed enclosure, then treat the internal panels to reduce reflections without overdamping it ? Basically, treat the inside of the enclosure pretty much like you would for a room.
I'm not sure how it would be measured and applied, but i guess a Reverberation time of less than 300-500 ms would be a good start.
Maybe i'm just overthinking it and ''overdamping'' the hell out of it is the way to go. But i doubt it, last time i precisely tested that it wasnt convincing.
If you're damping something, the (acoustic) energy is transformed (into heat) and lost. Therefore, you further reduce the efficiency of the overall system. Which, in the absolute, is the wrong way, IMO.
If you're damping something, the (acoustic) energy is transformed (into heat) and lost. Therefore, you further reduce the efficiency of the overall system. Which, in the absolute, is the wrong way, IMO.
i'd do that. 😛
but will it give a reliable result ? I mean, shouldnt we test it exactly as the driver behave in the reality (moving) ?
If i understand correctly, the ''ultimate best'' enclosure would be a huge IB ? No cancellation in the lower frequencies but no acoustic energy that bounces back into the cone internally... (thinking out loud again, will need a beer soon.)
what would be the effect ?
another idea would be to 9vdc it. You push it outward, stays in that position (50% of xmax?) then you do the test with the internal active speaker. But what will it tell us better than letting it free ? (just wondering)
all tests that are pretty easy to make. With few beers.
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