here is a simple question ( i think )
On a given unit 8" W 200 S - 8 Ohm of Visaton manu specs say for example
15 l/closed - - 72 Hz/0,75
20 l/bass reflex BR 19.24 (length 14 cm) 45 Hz -
30 l/bass reflex BR 19.24 (length 11 cm) 39 Hz -
50 l/bass reflex BR 15.34(length 13 cm) 33 Hz -
In case one needs to work with these data but the enclosure must have 2 woofers what is the procedure after that ?
One may design a 50 L enclosure and proper bass reflex and stack one at the top of each other ?....
The other might be to have a common enclosure but then how many litters and what bass reflex and where this is going to be located ....
will it be one bass reflex or 2 ?
will it be one bass reflex next to each other
or will it be one bass reflex next to every unit ?
On a given unit 8" W 200 S - 8 Ohm of Visaton manu specs say for example
15 l/closed - - 72 Hz/0,75
20 l/bass reflex BR 19.24 (length 14 cm) 45 Hz -
30 l/bass reflex BR 19.24 (length 11 cm) 39 Hz -
50 l/bass reflex BR 15.34(length 13 cm) 33 Hz -
In case one needs to work with these data but the enclosure must have 2 woofers what is the procedure after that ?
One may design a 50 L enclosure and proper bass reflex and stack one at the top of each other ?....
The other might be to have a common enclosure but then how many litters and what bass reflex and where this is going to be located ....
will it be one bass reflex or 2 ?
will it be one bass reflex next to each other
or will it be one bass reflex next to every unit ?
Some people believe that when you use two bass drivers in the same cabinet, you should isolate the volume for each driver. In essence, you make two cabinets within the box.
You will need to make up your own mind on this, because not everyone believes it is important. In my opinion, if the bass alignment is a vented box, then each driver should have its own volume and its own vent. If it is sealed, the two drivers can share the box volume. I do not have a scientific basis for this opinion, it is just my engineering judgment.
You will need to make up your own mind on this, because not everyone believes it is important. In my opinion, if the bass alignment is a vented box, then each driver should have its own volume and its own vent. If it is sealed, the two drivers can share the box volume. I do not have a scientific basis for this opinion, it is just my engineering judgment.
"if the bass alignment is a vented box, then each driver should have its own volume and its own vent" - not necessary, a single vent is OK
It's OK to use 100litres and a double area port.
Jim, it could sometimes make a difference but a modal analysis will clear up this issue.
Jim, it could sometimes make a difference but a modal analysis will clear up this issue.
I should clarify what I meant.
Multiple LF drivers in a single box volume with a single vent will work, and the rules for doing so are well defined (no controversy there).
However, many people believe that the quality of the bass is a bit better when the two drivers are isolated from each other. I have noticed it with vented boxes (on two occasions), but I could not tell any difference with a sealed box design. With the vented box, it was a small improvement when we went to a divided enclosure to isolate the two woofers. A small improvement, but to me, a worthwhile improvement.
Multiple LF drivers in a single box volume with a single vent will work, and the rules for doing so are well defined (no controversy there).
However, many people believe that the quality of the bass is a bit better when the two drivers are isolated from each other. I have noticed it with vented boxes (on two occasions), but I could not tell any difference with a sealed box design. With the vented box, it was a small improvement when we went to a divided enclosure to isolate the two woofers. A small improvement, but to me, a worthwhile improvement.
On a different slant the divided enclosure may naturally have a bit more bracing (the dividing wall) and any standing waves will be higher in frequency.
Rob.
Rob.
But this is the thing, standing waves will not be higher in frequency when two identical enclosures are built together into a double enclosure.
So the dividing wall becomes acoustically invisible?
Does that count for push push drivers mounted on opposite sides of the enclosure as well ?
Every days a school day 😀
Rob.
Why wouldn't the modal behavior change when you change internal dimensions? Standing wave patterns are defined by internal shape and size and the speed of sound in the enclosed medium.
Imho the frequency of the lowest standing waves more often than not will shift upwards. That (e.g. in a sub) could be beneficial.
Yes, it does. But not very much. The acoustic impedance of the port is relatively high at frequencies other than those that will induce standing waves in the port itself. Partly because the surface area of it also is relatively small compared to other boundaries. With long (or even bent) ports in small enclosures though, effects may superimpose. When you measure port noise, the predominant ‘leak’ almost always is the port resonance itself, not so much the standing waves in the enclosure.
Virtually yes, but not physically.
Well spotted, yes except the location of the virtual wall changes.
In this case, the reflection from an internal divider happens to be the same as the wave that is travelling from the other woofer when there is no divider.
..and are affected by the position of the driver or drivers.
I've seen this topic come up when comparing reflex and transmission lines. A coming together of the two effects is exploited in the MLTL.
It could work either way though, and one thing the driver and port have in common is that they are both physically fixed external variers of the internal pressure.
How about taking advantage of having two woofers and tune them differently to smooth the response?
SJ, I think I misread your last question. You weren't talking about anything modal, were you. Options/variables to what are you referring?
JBL / Greg Timbers did that with their 'Imaginary Equivalent Tuning'. Might allow (if you can tune to a specific room) you to smooth the response a bit, at the price of a more complex load. I should add that GT, while noting it worked fine for the two speakers he used it in, noted the term was a matter of pure marketing necessity outside his control, & with hindsight wasn't convinced it brought any advantages over what might have been done with identical LF driver volumes & tunings. I have the feeling he may also have been using it to get around some marketing decisions that obliged bass alignments on previous speakers that he didn't care for.
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