Hi all,
I've just read through this thread (yes, all of it), and I'm still a little bit confused about something, which is nothing new for me.
I think I'm seeing that Jim's design here is basically modifications to the Pensil series to tune it for the Alpair 10.3 driver, right?
However, when I look at the plans (from Frugal-phile) for the Pensil 10.2, it appears to be quite a different design. Mainly, it's slot ported rather than a tube port. For you experts, that may be a minor thing, but for a beginner like me, this is a very different design, since it requires different tooling and materials.
Am I missing something key here? Is there a plan somewhere for this 10.3 version that I haven't found? I saw Dave's answer several pages back, and it looked like he basically said to just use the Pensil and make the dimensional adjustments that Jim called out in the OP, but I'm not sure I could swing that, seeing as how I'm building these for someone else, and can't afford to screw them up by missing a step somewhere.
I guess I'm asking or a little bit of handholding to get me started in the right direction... sorry!
I've just read through this thread (yes, all of it), and I'm still a little bit confused about something, which is nothing new for me.
I think I'm seeing that Jim's design here is basically modifications to the Pensil series to tune it for the Alpair 10.3 driver, right?
However, when I look at the plans (from Frugal-phile) for the Pensil 10.2, it appears to be quite a different design. Mainly, it's slot ported rather than a tube port. For you experts, that may be a minor thing, but for a beginner like me, this is a very different design, since it requires different tooling and materials.
Am I missing something key here? Is there a plan somewhere for this 10.3 version that I haven't found? I saw Dave's answer several pages back, and it looked like he basically said to just use the Pensil and make the dimensional adjustments that Jim called out in the OP, but I'm not sure I could swing that, seeing as how I'm building these for someone else, and can't afford to screw them up by missing a step somewhere.
I guess I'm asking or a little bit of handholding to get me started in the right direction... sorry!
No, this is Jim's own MLTL design, and is not a modification of a pensil. The pensil I designed for the 10.3 is (with all the dark inevitability of Greek Tragedy) the Pensil 10.3. If you type 'Pensil 10.3' into your choice of search engine, you should locate the plans. They are different designs, withdifferent alignments & objectives so ultimately a case of 'name your poison'.
Thanks Scott, I see it now. I assumed that the full Pensil series set included the latest versions. That's what I get for assuming.
So what's the sonic difference between the Pensil 10.3 and Jim's MLTL design?
I see that his uses a tubular port vs your slot port, and the primary dims are different, but overall fairly similar in total materials and build effort.
For a large room (24'x36' with 10' ceilings) with hard surface (brick/plaster) walls, which would be better, do you think? I have the option of placing them either in the corners or closer to center, on either side of a TV stand.
So what's the sonic difference between the Pensil 10.3 and Jim's MLTL design?
I see that his uses a tubular port vs your slot port, and the primary dims are different, but overall fairly similar in total materials and build effort.
For a large room (24'x36' with 10' ceilings) with hard surface (brick/plaster) walls, which would be better, do you think? I have the option of placing them either in the corners or closer to center, on either side of a TV stand.
Elmojo, my designs for the Alpair 10.3 and its origin are described in my initial posting which started this thread. I used the same process for each Alpair driver--the original Alpair 10 or 10.1 version which has a metal cone, the second or 10P has a paper cone while the last one is the 10.3 which has a metal cone.
My objective for all MLTLs was to realize a flat on axis response across the frequency band. The goal was to have the 3 dB down point to be in the mid 30 Hzs region for all three examples. The driver is located one third of a wavelength (given the length of the line) down from the top of the enclosure in each case. My simulations indicate that the frequency responses of all of these enclosures would measure nearly identical given that similar construction techniques are used for all constructions. Whether any sonic differences would be realized between these three MLTL would be a function of the characteristics of the various cones and any minor variations of the enclosures.
You can use either a round port tube or construct a rectangular port tube as long as the internal area of the two are the same and the length of the tube is the same. Now a rectangular tube for a 'slot' tube may block air flow within the MLTL if it is completely across the enclosure so realizable care must be used to prevent blockage.
For a room as large as yours I would recommend that you focus more on choosing an area within where you will do the most listening. Work out the best speaker placements in that area. I doubt that you can realize quality sound all over your entire space.
Now if you want great sound through out the room you would need a set of speakers designed for wide directivity in the horizontal plane but more limited directivity in the vertical plane. My Modified CBT24 project does have excellent coverage in my room which is roughly the same floor space as yours but with an 18 feet high apex ceiling. These speakers control reflections from the floor and ceiling better than a single point source speaker would achieve.
My objective for all MLTLs was to realize a flat on axis response across the frequency band. The goal was to have the 3 dB down point to be in the mid 30 Hzs region for all three examples. The driver is located one third of a wavelength (given the length of the line) down from the top of the enclosure in each case. My simulations indicate that the frequency responses of all of these enclosures would measure nearly identical given that similar construction techniques are used for all constructions. Whether any sonic differences would be realized between these three MLTL would be a function of the characteristics of the various cones and any minor variations of the enclosures.
You can use either a round port tube or construct a rectangular port tube as long as the internal area of the two are the same and the length of the tube is the same. Now a rectangular tube for a 'slot' tube may block air flow within the MLTL if it is completely across the enclosure so realizable care must be used to prevent blockage.
For a room as large as yours I would recommend that you focus more on choosing an area within where you will do the most listening. Work out the best speaker placements in that area. I doubt that you can realize quality sound all over your entire space.
Now if you want great sound through out the room you would need a set of speakers designed for wide directivity in the horizontal plane but more limited directivity in the vertical plane. My Modified CBT24 project does have excellent coverage in my room which is roughly the same floor space as yours but with an 18 feet high apex ceiling. These speakers control reflections from the floor and ceiling better than a single point source speaker would achieve.
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Thanks for the comments Jim. I wish I was smart enough to understand all of that, but I think I got the gist.
One thing that still puzzles me is that the pencil design doesn't seem to have a port "tube" at all. The plans just show a simple slot at the very bottom of the enclosure, almost as if the front baffle was just cut too short. I built a TABAQ a while ago, and it had what I think of as a rectangular port, since there was a partial floor in the main cavity that formed a rectangular channel. This is where it seems to me that the Pensil series and your MLTL designs differ. What am I missing?
One thing that still puzzles me is that the pencil design doesn't seem to have a port "tube" at all. The plans just show a simple slot at the very bottom of the enclosure, almost as if the front baffle was just cut too short. I built a TABAQ a while ago, and it had what I think of as a rectangular port, since there was a partial floor in the main cavity that formed a rectangular channel. This is where it seems to me that the Pensil series and your MLTL designs differ. What am I missing?
Elmojo, I think your observation about the Pensil design is correct. The slot is just the baffle cut shorter than the end of the structure. It is a neat approach as it eliminates a slot port 'tunnel cover' which would extend inside the cabinet.
My port tube is more conventional and is just above the bottom of the cabinet and not against the bottom boundary as in the Pensil.
My MLTLs (and all that I have seen) are not an exact single answer solution. The designer has the option to vary his design dimensions to achieve his objectives. You get to vary the dimensions until your are satisfied.
My port tube is more conventional and is just above the bottom of the cabinet and not against the bottom boundary as in the Pensil.
My MLTLs (and all that I have seen) are not an exact single answer solution. The designer has the option to vary his design dimensions to achieve his objectives. You get to vary the dimensions until your are satisfied.
So if I was thinking of just building a set of floorstanders, likely with the Alpair 11MS drivers, without a separate powered sub at this point, would you think I'd get better sound (low end especially) from the Pensil or MLTL cabinet? Or is that the wrong question entirely and not one that can be answered with the information at hand?
Actually the pensils are MLTLs, they just happen to be a specific alignment thereof of my own devising. MLTLs in general are like any other cabinet type however: for good results, they have to be designed for a given drive unit. There are certain exceptions to that, but in general it's a good rule to follow, so the standard advice is 'stick to the driver an enclosure was designed for'.
Assuming the 10.3, in terms of differences you can expect, Jim's MLTL targets more bass extension than the pensil, which is partly derived from 'traditional' alignments, and targets a bit more 'slam' through the power region c. 60Hz - 120Hz with a flat impedance curve. So it depends where your priorities lie, although from the sound of it, Jim's design will likely suit you better.
Assuming the 10.3, in terms of differences you can expect, Jim's MLTL targets more bass extension than the pensil, which is partly derived from 'traditional' alignments, and targets a bit more 'slam' through the power region c. 60Hz - 120Hz with a flat impedance curve. So it depends where your priorities lie, although from the sound of it, Jim's design will likely suit you better.
The pensil, like all bass enclosures, only functions in the low frequency region. The same applies to Jim's MLTL. Above that (notwithstanding minor variations in diffraction effects &c.) the box only provides a solid mounting point for the drivers. If the driver inherently has a 'bump in the middle region' that you dislike, then you will need to EQ it: the box alone can't help unfortunately.
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Dear Mr Jim,
If I want to use 2 drivers per MLTL box, should I double the box volume (by doubling the width, for example) and port area as well?
What would happen if I use a slotted port with the same area of the diaphragm(s), with no port length, as in a voigt pipe?
Thank you very much!
Nilton
Hello Nilton
You can find further details about dual Alpairs MLTL here:
Alpair 10.3 dual help.
Scott Lundgren posted plans regarding dual Alpairs drivers cabinet and port dimensions:
https://www.diyaudio.com/forums/full-range/341853-alpair-10-3-dual-help.html#post5894769
Or in metric, Russian, if you wish:
Широкополосная акустика — рай меломана и сладкая середина (и только?) — малые и большие формы - Акустика - DA Stereo
Dave Dlugos posted wiring options:
http://www.planet10-hifi.com/downloads/Dual-Driver-Wiring.pdf
There´s an interesting video from Pierre Leloup of those cabinets:
Markaudio Alpair dual M10 GEN 3 MLTL test cabinet - YouTube
I´m not sure about square ports, this is not a Pensil or Voight, anyway you may use any 2 1/2" - 75mm PVC or Fenolite comercial tubes :
https://produto.mercadolivre.com.br...&reco_id=2bbcd13b-bef8-47e3-ad53-a2e32a8ec735
and redimension them with this useful calculations:
http://p10hifi.net/FAL/downloads/ChangingPortSize.pdf
Hope this helps and good luck
You can find further details about dual Alpairs MLTL here:
Alpair 10.3 dual help.
Scott Lundgren posted plans regarding dual Alpairs drivers cabinet and port dimensions:
https://www.diyaudio.com/forums/full-range/341853-alpair-10-3-dual-help.html#post5894769
Or in metric, Russian, if you wish
: Широкополосная акустика — рай меломана и сладкая середина (и только?) — малые и большие формы - Акустика - DA Stereo
Dave Dlugos posted wiring options:
http://www.planet10-hifi.com/downloads/Dual-Driver-Wiring.pdf
There´s an interesting video from Pierre Leloup of those cabinets:
Markaudio Alpair dual M10 GEN 3 MLTL test cabinet - YouTube
I´m not sure about square ports, this is not a Pensil or Voight, anyway you may use any 2 1/2" - 75mm PVC or Fenolite comercial tubes :
https://produto.mercadolivre.com.br...&reco_id=2bbcd13b-bef8-47e3-ad53-a2e32a8ec735
and redimension them with this useful calculations:
http://p10hifi.net/FAL/downloads/ChangingPortSize.pdf
Hope this helps and good luck
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Thanks to JC for his excellent series of links on using multiple drivers. Essentially, with my MLTL design you would double the cross-sectional area of my design which needs double the box volume. You can do that by changing the dimensions of the MLTL via varying the depth and/or width as you choose. The port area for a round port tube, as in my prototypes, changes the port diameter by a factor of 1.4 (squared becomes 2) which doubles the port area.
Another consideration for going from 1 to 2 drivers is for the impedance of the combo. Remember that the Mark Audio A10 driver is a nominal 8 ohms impedance. Thus two drivers wired in series would yield a 16 ohms impedance for the pair. Wired in parallel the two drivers becomes a 4 ohms load which may not be compatible with your amplifier. Review the planet 10 page linked by JC on some of the options when you connect the drivers.
Nominally, I am not in favor of two full range drivers in the enclosure running full frequency unless you intend to, say, create a dipolar arrangement (one driver firing forward and the other driver firing (in phase) backward). For the dipole arrangement you have the drivers covering different spatial areas within the listening room above the baffle step compensation region so no interference between the two drivers. Having two drivers firing forward in the same enclosure concerns me for the higher frequency range as it creates interference unless you filter as suggested by planet 10.
I have successfully used a MLTL with a slot port which converts the port area of a round port to the rectangular dimensions.
Finally, my MLTL design is not intended to be for a Voight transmission line speaker arrangement.
Another consideration for going from 1 to 2 drivers is for the impedance of the combo. Remember that the Mark Audio A10 driver is a nominal 8 ohms impedance. Thus two drivers wired in series would yield a 16 ohms impedance for the pair. Wired in parallel the two drivers becomes a 4 ohms load which may not be compatible with your amplifier. Review the planet 10 page linked by JC on some of the options when you connect the drivers.
Nominally, I am not in favor of two full range drivers in the enclosure running full frequency unless you intend to, say, create a dipolar arrangement (one driver firing forward and the other driver firing (in phase) backward). For the dipole arrangement you have the drivers covering different spatial areas within the listening room above the baffle step compensation region so no interference between the two drivers. Having two drivers firing forward in the same enclosure concerns me for the higher frequency range as it creates interference unless you filter as suggested by planet 10.
I have successfully used a MLTL with a slot port which converts the port area of a round port to the rectangular dimensions.
Finally, my MLTL design is not intended to be for a Voight transmission line speaker arrangement.
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