The Pensil is not a bass reflex but a variation of an MLTL, for which the physics work different. Transmission line loudspeaker - Wikipedia (basic descirption) and Quarter Wavelength Loudspeaker Design (the math and physics behind it) for more info about this.
For a bass reflex, the size will be more or less 16-20L, a TL type of alignment will be much bigger, but it has other advantages. I prefer TL's above bass reflex, at least when the size is not an issue.
It is a 83 litre ML-TL.
It won’t work in a BR that large. Too small to be a decent horn, so you want a compact ML-TL.
I have a 49 litre one one the books. A smaller custom one might be possible.
dave
I think I covered most of these points when they were originally asked about a week ago, but I'll go through them again, just to reinforce what I said at the time & others have also noted:
'Optimal' is a floating point that varies with requirements. The above is what I would call a reasonable volume & tuning alignment for a conventional vented box using this driver, assuming a voltage source amplifier and about 1/2ohm series R for typical wire, connection resistance.
You say 'the 20L'. Which?
Pass, without knowing what box you are referring to.
That's a quarter-wave design; tuning is not purely a function of the internal volume but the geometry of the enclosure.
Two points there. First, it's a floorstander, and has to be a floorstander because it's a quarter-wave variation and the geometry of the enclosure is a functional part of the alignment. You can't just take the internal volume & change the box dimensions. Secondly, define 'better'.
Only when you define your goals.
You asked that a week ago, and I'll give you the answer I did then: only if you add about 5 1/2ohms of series resistance with a voltage source amplifier, or alternative have an amplifier with roughly equivalent output impedance. It will have a very poor alignment otherwise.
No, this is well-proven physics.
'Optimal' is a floating point that varies with requirements. The above is what I would call a reasonable volume & tuning alignment for a conventional vented box using this driver, assuming a voltage source amplifier and about 1/2ohm series R for typical wire, connection resistance.
You say 'the 20L'. Which?
Pass, without knowing what box you are referring to.
That's a quarter-wave design; tuning is not purely a function of the internal volume but the geometry of the enclosure.
Two points there. First, it's a floorstander, and has to be a floorstander because it's a quarter-wave variation and the geometry of the enclosure is a functional part of the alignment. You can't just take the internal volume & change the box dimensions. Secondly, define 'better'.
Only when you define your goals.
You asked that a week ago, and I'll give you the answer I did then: only if you add about 5 1/2ohms of series resistance with a voltage source amplifier, or alternative have an amplifier with roughly equivalent output impedance. It will have a very poor alignment otherwise.
No, this is well-proven physics.
That can certainly be done for pipes with a relatively small CSA relative to the length, which are fairly easy to fold up. With the kind of length & CSA of the Pensil 12P, it would be difficult / almost impossible to maintain the longitudinal eigenmode if you tried folding it as the internal divider wouldn't be long enough, and a literal impossibility with the Super Pensil 12P.
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Having folded many of Scott’s ML-TL. As the size of the fold becomes more nebulous (when a box is squarish, or depth greater than width. To make a folded Pensil one woold forst have to change the aspect ratio of the cross-section so that the box is wide and shallow. Then the bottom of the line can be folded back and up to create the fold.
You will no long have a pensil, but it should have somewhat similar performance in the bass.
dave
"Yes!!! That is exactly what I am looking for. A 35-45L speaker enclosure that is about 25-30cm X 30-35cm X 50-60cm"
We are only talking 3 litre savings. The box as drawn is 270x1078x254
Dave
Yes I understand that it is only a 3 litre difference but the dimension I stated would give me placement options. If I move the speakers to another room, which I intent on doing, all I would need to do is adjust the stands to bring them at ear height. At a height of 1078mm that would make it harder to adjust. And they might even be higher than my present listening position. Can I get you to make a custom box using the my dimensions?
We are only talking 3 litre savings. The box as drawn is 270x1078x254
Dave
Yes I understand that it is only a 3 litre difference but the dimension I stated would give me placement options. If I move the speakers to another room, which I intent on doing, all I would need to do is adjust the stands to bring them at ear height. At a height of 1078mm that would make it harder to adjust. And they might even be higher than my present listening position. Can I get you to make a custom box using the my dimensions?
I would need some help in deciding which one of these 2 enclosures give the best measurement for the Alpair 12p.Can someone please run these numbers through some measurement software and let me know which one to build? Obviously, I am open to minor dimension alterations.
I tried playing with WinISD but for some reason I could not save the driver's T/S parameters.
Box 1) internal measurements= 24cm X 39cm X 27cm
Box 2) internal measurements= 24cm X 39cm X 32cm
I very much appreciate your help.
I tried playing with WinISD but for some reason I could not save the driver's T/S parameters.
Box 1) internal measurements= 24cm X 39cm X 27cm
Box 2) internal measurements= 24cm X 39cm X 32cm
I very much appreciate your help.
How do you define 'best', and what tuning frequency[ies]?
I'm currently on my laptop so can't look closely at this precise moment in history, but assuming a voltage source amp both look significantly over-sized for the 12P assuming a regular vented box, so will either have a large peak at tuning if tuned relatively high (unless heavily damped), or some form of quasi EBS alignment if tuned relatively low, so may lack LF output unless either boundary-loaded, or used with a high output impedance amplifier / equivalent series resistance.
I'm currently on my laptop so can't look closely at this precise moment in history, but assuming a voltage source amp both look significantly over-sized for the 12P assuming a regular vented box, so will either have a large peak at tuning if tuned relatively high (unless heavily damped), or some form of quasi EBS alignment if tuned relatively low, so may lack LF output unless either boundary-loaded, or used with a high output impedance amplifier / equivalent series resistance.
...and as far as vented is concerned, as predicted (and several of us have pointed out previously) those sorts of volumes are somewhat over-sized for the 12P short of a relatively high output impedance amplifier, with underdamped (peaking) alignments at tuning under anechoic conditions (attached, assuming 1ohm output impedance). With a rear vent and near-boundary positioning, you are likely to experience more significant gain peaking at tuning, and potentially a 'one note' / 'on-off' effect due to that and the relatively narrow vent tuning, unless the boxes are heavily damped. Power handling may also suffer somewhat, and you may encounter some self-resonant effects (standing waves) in the duct due to the length / CSA ratio, although the rear position should mean this latter is unlikely to be a significant problem.
Generally speaking, I've seen worse, but they're not what I'd call particularly good alignments.
Generally speaking, I've seen worse, but they're not what I'd call particularly good alignments.
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Now armed with the tuning frequency.
You can see the bump Scott talks about.
My first rule of vented boxes is that the 1[su[]st[/sup] derivative of th eFR curve shoud not cross zero more than once.
You can see your 2 (poor) alignments along with one in 17 litres that is decent (not the one i use in the Mar-Kens, i have to account for another facet of my designs.
dave
You can see the bump Scott talks about.
My first rule of vented boxes is that the 1[su[]st[/sup] derivative of th eFR curve shoud not cross zero more than once.
You can see your 2 (poor) alignments along with one in 17 litres that is decent (not the one i use in the Mar-Kens, i have to account for another facet of my designs.
dave
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With modern tube amps, experience has taught me to take a caveat emptor stance WRT published specs same as with driver/speaker specs, so if lacking sufficient fancy test gear, use your speakers, ears and voltmeter connected to the speaker terminals to figure your 'useful' highest distortion max volts/power to select new components/speakers, then power = volts^2/speaker nominal ohms rating will be good enough regardless of what Frank or fancy test equipment 'says'.
Absolutely.
As a 'for interest' aside, one thing I have noted: the current fad for high Qm / low RMS / (insert preferred definition here) does not appear to have done production consistency many favours in quite a few cases I could mention. Over the last couple of years, many of the units I've measured targeting low mechanical damping have exhibited greater deviation from spec. & between samples than others which haven't prioritised this quite so heavily. YMMV as ever of course.
As a 'for interest' aside, one thing I have noted: the current fad for high Qm / low RMS / (insert preferred definition here) does not appear to have done production consistency many favours in quite a few cases I could mention. Over the last couple of years, many of the units I've measured targeting low mechanical damping have exhibited greater deviation from spec. & between samples than others which haven't prioritised this quite so heavily. YMMV as ever of course.