I am building a ported enclosure for the 1503. I have seen/studied the AS15 project and consider it a good idea. The size of the box seems unnecessarily large, though I understand it was a no compromise venture, and well done.
Modeling it, it looks as though I could shrink the enclosure from 200l to 140l if I can snake a longer port (40 inches or so for a similar 5.75" id pvc, tuned to 19 HZ). I probably would use a 180 or elbow to make a longer port. The output looks to be very close to the 8 cf AS15 project. I am also considering making wood flares using a large roundover or table bit.
Are there any drawbacks to a port this long? Or any reason I should not attempt this (assuming it is physically possible).
Modeling it, it looks as though I could shrink the enclosure from 200l to 140l if I can snake a longer port (40 inches or so for a similar 5.75" id pvc, tuned to 19 HZ). I probably would use a 180 or elbow to make a longer port. The output looks to be very close to the 8 cf AS15 project. I am also considering making wood flares using a large roundover or table bit.
Are there any drawbacks to a port this long? Or any reason I should not attempt this (assuming it is physically possible).
Re: long port
Rodd Yamashita
Exactly, Small warns of this in his paper on vented system.hitsware said:
Rodd Yamashita
Do you mean pipe resonance? If so, modeling software can keep you away from that, yes?
Example: For a sub that will be crossed under at 80, what is the minimum pipe resonance one should accept? 150? 250?
Michael
Example: For a sub that will be crossed under at 80, what is the minimum pipe resonance one should accept? 150? 250?
Michael
Michael,
A 40” pipe is going to resonate at about 82Hz. This is the second harmonic of 41Hz and the third harmonic of about 27Hz. Point being that the driver will produce these harmonics distortion products that will resonate in the port at these frequencies (higher harmonics as well to a lesser degree). These amplified frequencies will add to the overall output of the speaker and muddle the bass.
BTW, where can I find out about the “AS15 project”?
Rodd Yamashita
A 40” pipe is going to resonate at about 82Hz. This is the second harmonic of 41Hz and the third harmonic of about 27Hz. Point being that the driver will produce these harmonics distortion products that will resonate in the port at these frequencies (higher harmonics as well to a lesser degree). These amplified frequencies will add to the overall output of the speaker and muddle the bass.
BTW, where can I find out about the “AS15 project”?
Rodd Yamashita
As the longer port intrudes into the volume of the box does it then decrease the internal volume of the box itself and if so, how much?
That is to say you could have a very small enclosure that is nothing more than a box cavity filled with a serpentine port.
Heck, why not scrap the box all together and just mount the driver at the end of a tube.
That is to say you could have a very small enclosure that is nothing more than a box cavity filled with a serpentine port.
Heck, why not scrap the box all together and just mount the driver at the end of a tube.
http://home.att.net/~tom1/page7.html
also
http://www.diyvideo.com/forums/showthread.php?s=&threadid=999&highlight=as15
Thomas and Jon calculated 25" for this large 8cf (about 200L effective airspace) enclosure.
also
http://www.diyvideo.com/forums/showthread.php?s=&threadid=999&highlight=as15
Thomas and Jon calculated 25" for this large 8cf (about 200L effective airspace) enclosure.
Michael,
The warning about port length given by Small suggests ports that are more than 2X the diameter will be susceptible to noise generation. So 25” give you a pipe resonance of 132Hz, which is the 2nd harmonic of 66Hz and the 3rd harmonic of 44Hz.
I’ve looked at this driver with BassBox Pro a dozen different ways and can see no good way to get response down to the 20’s (<30Hz) without a 6 to 12 db dip in the response curve. This dip, at its worst (with 8cu.ft. box and fb of 18.5Hz) starts to drop from 200Hz and drops at about 4db/oct to –13db at 30Hz and a 6db bump at the fb of 18.5Hz before dropping out of sight. Not sure how to fix this without either raising f3 into the 40+Hz range or using an equalizer.
Not sure what to tell you. Maybe I’m missing something. I’ll look at it again when I get home.
Rodd Yamashita
The warning about port length given by Small suggests ports that are more than 2X the diameter will be susceptible to noise generation. So 25” give you a pipe resonance of 132Hz, which is the 2nd harmonic of 66Hz and the 3rd harmonic of 44Hz.
I’ve looked at this driver with BassBox Pro a dozen different ways and can see no good way to get response down to the 20’s (<30Hz) without a 6 to 12 db dip in the response curve. This dip, at its worst (with 8cu.ft. box and fb of 18.5Hz) starts to drop from 200Hz and drops at about 4db/oct to –13db at 30Hz and a 6db bump at the fb of 18.5Hz before dropping out of sight. Not sure how to fix this without either raising f3 into the 40+Hz range or using an equalizer.
Not sure what to tell you. Maybe I’m missing something. I’ll look at it again when I get home.
Rodd Yamashita
I can't imagine what you are looking at. Try the HE-15 t/s params. In a ported box, I get 112+ db at 20 HZ, nearly flat. Needs some eq preferably parametric (especially in a sealed app)
Michael
Michael
Room Gain.roddyama said:
In the links you provided, Thomas points out that the room response must be included in the overall response. Not having the exact room response used by Thomas, I used an approximation of 3db/oct raising response (going down in frequency) starting at 400Hz. This brought the curve to with in +-3db at 120db (with 250W input).
There were a couple other items emphasized in this link:
The overall port length for this design is 25.5” and it must be a flared port (not covered by Small in his early paper).
The box size cannot be made smaller then about 6.5-7cu.ft.
And this quote “Making any changes in the design will result in a sub that doesn't perform up to the full potential of the HE15/BP1503”.
Rodd Yamashita
PS: for a 140l box try a 4"dia. flared port 17" long.
I don't think so. Every thing says 4" is tooooo small. noise compression, etc. You mean dual 4" ports???
6" flared is the absolute minimum from reliable sources. Or 8" unflared.
Also, you must still have something wrong, room gain doesn't help that much and all modeling has been done outside of room gain. 4-7 db at 20HZ is all we'll get.
Sorry but maybe something is still amiss in your calcs.
Can you at least duplicate the 8cf model that Thomas W realized?
Michael
6" flared is the absolute minimum from reliable sources. Or 8" unflared.
Also, you must still have something wrong, room gain doesn't help that much and all modeling has been done outside of room gain. 4-7 db at 20HZ is all we'll get.
Sorry but maybe something is still amiss in your calcs.
Can you at least duplicate the 8cf model that Thomas W realized?
Michael
What do you want me to say Michael. You want a box size of 140i = 4.9cu.ft. even though Thomas warns of box sizes smaller than 6.5cu.ft. I’d much rather have a 4” flared port 17” long than a 6” flared port 40” long. The box is too small for a 6” port tuned to 18.5Hz. You can settle for a higher f3 and shorten the port length, but you will have created an entirely new design, which is fine if that’s what you want. But if you’re going to base the design on AS-15 sub than you have to abide by everything Thomas is telling you, not just the parts that you like.
Sorry, but the Coyotes are beating the Redwings and I’m a little testy about it.
Rodd Yamashita
Sorry, but the Coyotes are beating the Redwings and I’m a little testy about it.
Rodd Yamashita
Being from Phoenix, I can't help with that.
My thoughts (and why I started this thread) were to examine a smaller enclosure than that used in the AS-15, using longer ports (bends, 180's etc). It may be a poor idea. I've yet to be disuaded. But thanks for your interest.
Micjhael
My thoughts (and why I started this thread) were to examine a smaller enclosure than that used in the AS-15, using longer ports (bends, 180's etc). It may be a poor idea. I've yet to be disuaded. But thanks for your interest.
Micjhael
I noticed that before I posted, just ribbin'ya😉masterp2 said:
It's not a bad idea at all, but neither is 4" ports. I have 4"dia ports (one per) in my TAD1601 sub boxes. They work fine. 17" seems a bit long, but the flairs may somewhat counter that issue. I'm pretty certian that a 40" port is a bad idea, no matter what the diameter (less than 20" or so😀 ).masterp2 said:
If you already have the drivers and your heart is set on the box size, than go for it. Just leave yourself an opening so you can backtrack (at least to replace the port) if you don't like the results. Don't be worried about the special 6" flairs. Here's exactly what you need from Madisound.😀
Rodd Yamashita
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Doktor_Ssyko said:
Yes. As Thomas W., the man who did the AS-15 project, said on this forum: "Imagine the port is a solid block of wood".
Doktor_Ssyko said:
You have just described a Transmission Line enclosure.
I don't want to offend. I am just being inventive, I can't help it.
Studying the AS-15, and it's success, it appears that:
1. Box size was constrained by available port technology for the DIY'er. A smaller box, while it may model better for response, was not possible because it would require porting that would not fit, or would be too long for resonance requirements.
2. A minimum of 6" flared porting is required for airspeed requirements.
Well, what if porting technology was available that changed/shortened the port length?
Is anyone familiar with Polks Powerport software? It appears that it converts the conventional cylinder of air, into an annulus of air. The calculations dramatically shorten the port length, but require innovative fabrication abilities to make the parts.
Thoughts?
Studying the AS-15, and it's success, it appears that:
1. Box size was constrained by available port technology for the DIY'er. A smaller box, while it may model better for response, was not possible because it would require porting that would not fit, or would be too long for resonance requirements.
2. A minimum of 6" flared porting is required for airspeed requirements.
Well, what if porting technology was available that changed/shortened the port length?
Is anyone familiar with Polks Powerport software? It appears that it converts the conventional cylinder of air, into an annulus of air. The calculations dramatically shorten the port length, but require innovative fabrication abilities to make the parts.
Thoughts?
masterp2
I have found seen the marketing stuff on the website for powerport, where did you get the software?
If you want a small box to go that low, I think you might be better looking at a sealed box with a Linkwitz transform circuit, it would be much easier in construction, and in my experience, small boxes with big ports are never very satisfactory.
I have found seen the marketing stuff on the website for powerport, where did you get the software?
If you want a small box to go that low, I think you might be better looking at a sealed box with a Linkwitz transform circuit, it would be much easier in construction, and in my experience, small boxes with big ports are never very satisfactory.
Michael,
Now you can take it one step further then Pinkmouse suggests. Leave a space in the closed box for a port. You can use the 4” X 17” flaired port tuned to 18.5Hz or the PowerPort tuned to what ever.
I also ran the model tuning for 25Hz and your 6” port. The result is a cutoff of 22Hz with a 6” X 18” flaired port. Not a bad compromise for a 40% reduction in box size.
Rodd Yamashita
Now you can take it one step further then Pinkmouse suggests. Leave a space in the closed box for a port. You can use the 4” X 17” flaired port tuned to 18.5Hz or the PowerPort tuned to what ever.
I also ran the model tuning for 25Hz and your 6” port. The result is a cutoff of 22Hz with a 6” X 18” flaired port. Not a bad compromise for a 40% reduction in box size.
Rodd Yamashita
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