Thank you ThomasW, I will look into the behringer.
Finally figured out "total bypass" on the BFD. This is not what I planned. Unsealed, unstuffed, and unsure if I will finish it. unless I have overlooked something, powerport has not accomplished much. I took the inner pipe out completely and tuning increases 1 or 2 HZ. Now the ports are somewhat loosely connected at the moment. Tuning looks like 28-29 and gadzooks, that is a huge saddle in the meat of the low bass area, 35-40 HZ.
Recap, this is 135 l net volume, with ports predicted to tune to 20-21 HZ. Opinions and conjecture please??
Finally figured out "total bypass" on the BFD. This is not what I planned. Unsealed, unstuffed, and unsure if I will finish it. unless I have overlooked something, powerport has not accomplished much. I took the inner pipe out completely and tuning increases 1 or 2 HZ. Now the ports are somewhat loosely connected at the moment. Tuning looks like 28-29 and gadzooks, that is a huge saddle in the meat of the low bass area, 35-40 HZ.
Recap, this is 135 l net volume, with ports predicted to tune to 20-21 HZ. Opinions and conjecture please??
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It appears that your box is mistuned, and the 'saddle' is a room null. One way to tell for sure is measure the sub outside. 2m groundplane is the standard. If you can't do that, then you need to use a MLS measurement system that allows a gated time window. Those measure the sub's output before it has a chance to interact with the boundries of the room.
BTW your graph indicates that port tuning is to high to augment the natural roll-off of the driver. So in essence your box is functioning like a sealed enclosure.
Here's Tom Nousaine measured plot of the stryke cube. Your plot should be similar if you have everything correct
BTW your graph indicates that port tuning is to high to augment the natural roll-off of the driver. So in essence your box is functioning like a sealed enclosure.
Here's Tom Nousaine measured plot of the stryke cube. Your plot should be similar if you have everything correct
An externally hosted image should be here but it was not working when we last tested it.
...and that TN plot is anechoic?
On second look, my results are a little better than I thought, tuning is at 25 (minimum excursion method) and the room node you speak of does exist at the mic at the saddle center. It helped that you point it out. Room nodes are making my plot look worse than it is. When I went with 135l, I thought it might smooth out this curve, but I am still wishing for more.
"your graph indicates that port tuning is to high to augment the natural roll-off of the driver". Right on! those were my thoughts, and an Fb of 20 would definately flatten it, agree?
What is your opinion on what improvement sealing, stuffing and lining will have on Fb?
On second look, my results are a little better than I thought, tuning is at 25 (minimum excursion method) and the room node you speak of does exist at the mic at the saddle center. It helped that you point it out. Room nodes are making my plot look worse than it is. When I went with 135l, I thought it might smooth out this curve, but I am still wishing for more.
"your graph indicates that port tuning is to high to augment the natural roll-off of the driver". Right on! those were my thoughts, and an Fb of 20 would definately flatten it, agree?
What is your opinion on what improvement sealing, stuffing and lining will have on Fb?
No it's a MLS plot with 1ms of delay. Nousaine has a huge room, 7000sq ft or something like that. He does all his measurements in that room.
Very little can be done now, that will have a major impact on the performance. If you keep this box, add a pad of wool felt gasket material behind the woofer, and try some fiberglass or poly damping to fine tune the sound. Be careful to avoid blocking the ports.
Something else weird about your measurement is that there is a dip starting at 65Hz. That shouldn't be there. The HE-15 has a high Le. That creates a rising output as frequency goes up. (see TN's plot for how this should look)
Now that I've seen the design. A couple of questions. Can you live with a box that's depth is such that the HE-15 can be mounted to fire out the end? So ~18"-20" deep? If so, I recommend doing that with a larger box. Use ports that fire out the end as well.
The original design, as a sofa table, is a minimal depth animal to allow traffic around it, etc. It is "low visibilty" by nature. The inches add up fast. The glass tops for such a design are 16x52 standard. If I do this again (as a sofa table), it will be 1-2" deeper and 2-4" wider. This would get me to 180l and yet another AS-15 assimilation. (thanks for not saying I told you so)
The wife sat on the sofa while I demoed toy story 2 unassisted. She was ready for sex after that, given this unfinished misaligned sub, firing into the sofa, is the best bass I have had .
Also, when you enter the room, it cannot be found, it is invisible. So it has advantages. With nice finish, this concept is a very wife friendly design, and takes up "no" space, meaning it goes in an otherwise unusable footprint of the theater. I like it too. And I wonder what a fastened top (like a 3/4" glass) would do for the tuning.
BTW, thanks for your help.
SOME INITIAL POWERPORT CONCLUSIONS:
1. Based on my prediction calculations, Powerport does shorten the length of the port, but not as much as the equations would calculate. So for this application, powerport equations should not be used too literally. likely, you will need longer ports than calculated, or a larger cabinet (or both in combo).
2. Innaccurate: The margin of error is significant enough to rule out possible construction non-adherence to strict tolerances. In 26 inches I have obtained the tuned performance of a 50 inch length (I was looking for 70 inch performance). If you are a glass half empty type person, you could say I reached 60% of the objective, and that would be the worst interpretation. But I am an engineer, and by those standards, unnacceptable for a first try.
3. Iterative: Using the present design, a predictable model can be established for future iterations, with greater assurance that design criteria can be closely approached. By assigning a reduced acoustic mass to this port configuration, a larger cabinet size can be derived to obtain the design Fb=20-21. And that is probably what I will do. Since the height of the table is a constraint, my ports will stay the same size, and the cabinet will grow to 185L using the other 2 dimensions.
4. Spouse friendly: Given that performance disadvantages of powerport have not been determined here, they may exist. So this cannot be an apples to apples approach to comparing with a flaired conventional port, however, without a doubt, this can and should be used when aesthetic design constraints require a shorter port, where a longer one is prescribed for performance goals. In that light, this project is a success.
5. Labor intensive: This is not for the inexperienced woodworker, nor is it for the person who wants to whip out a fast cabinet. But if you are nuts and confident, you will have a one-of-a kind conversation showpiece, when turned into the sofa with a glass top, will never be confused for a subwoofer. And you can tell your friends you robbed the patent office to make it.
Now having said all that. I know this cabinet will tune lower with several things. Sealing it will lower Fb. So will stuffing it. And if I shorten the pipe lengths a quarter inch, I can probably get another 1-2 HZ lower in the waveguide spacing, though this is a restrictive measure with obvious tradeoffs. Those things should get this alignment (say Fb=22) away from the room problems sufficiently to make it worth putting a finish on it. Or I may give it away. For $160 in material cost, including a nice beveled glass top, this would make a darn nice sub that no money can buy. For under $300, it can surfaced in figured maple. Of course you have to have a decently equipped shop to do it.
1. Based on my prediction calculations, Powerport does shorten the length of the port, but not as much as the equations would calculate. So for this application, powerport equations should not be used too literally. likely, you will need longer ports than calculated, or a larger cabinet (or both in combo).
2. Innaccurate: The margin of error is significant enough to rule out possible construction non-adherence to strict tolerances. In 26 inches I have obtained the tuned performance of a 50 inch length (I was looking for 70 inch performance). If you are a glass half empty type person, you could say I reached 60% of the objective, and that would be the worst interpretation. But I am an engineer, and by those standards, unnacceptable for a first try.
3. Iterative: Using the present design, a predictable model can be established for future iterations, with greater assurance that design criteria can be closely approached. By assigning a reduced acoustic mass to this port configuration, a larger cabinet size can be derived to obtain the design Fb=20-21. And that is probably what I will do. Since the height of the table is a constraint, my ports will stay the same size, and the cabinet will grow to 185L using the other 2 dimensions.
4. Spouse friendly: Given that performance disadvantages of powerport have not been determined here, they may exist. So this cannot be an apples to apples approach to comparing with a flaired conventional port, however, without a doubt, this can and should be used when aesthetic design constraints require a shorter port, where a longer one is prescribed for performance goals. In that light, this project is a success.
5. Labor intensive: This is not for the inexperienced woodworker, nor is it for the person who wants to whip out a fast cabinet. But if you are nuts and confident, you will have a one-of-a kind conversation showpiece, when turned into the sofa with a glass top, will never be confused for a subwoofer. And you can tell your friends you robbed the patent office to make it.
Now having said all that. I know this cabinet will tune lower with several things. Sealing it will lower Fb. So will stuffing it. And if I shorten the pipe lengths a quarter inch, I can probably get another 1-2 HZ lower in the waveguide spacing, though this is a restrictive measure with obvious tradeoffs. Those things should get this alignment (say Fb=22) away from the room problems sufficiently to make it worth putting a finish on it. Or I may give it away. For $160 in material cost, including a nice beveled glass top, this would make a darn nice sub that no money can buy. For under $300, it can surfaced in figured maple. Of course you have to have a decently equipped shop to do it.
Well that seems like a value alright. BTW, is 12 gauge still enough for this kind of power? What do you use for the AS-15?
I'm on my way back to HD for more MDF. 190l net this time with 13 inches of depth. At least I'll have some room there for felt. Where do you find wool gasket felt (inexpensively)? McMaster Carr is pricey.
I'm on my way back to HD for more MDF. 190l net this time with 13 inches of depth. At least I'll have some room there for felt. Where do you find wool gasket felt (inexpensively)? McMaster Carr is pricey.
I use generic 12 gauge wire for subs.
I buy the wool felt material locally. In the yellowpages look under "Gaskets & Gasket Material". Sometimes they have scraps or the end of a roll that they'll sell. It's never cheap, but it's usually cheaper than McMaster-Carr. Note that it comes in differing wool contents. The greater the % of wool, the higher the price. And of course, the more wool, the better it absorbs.
I buy the wool felt material locally. In the yellowpages look under "Gaskets & Gasket Material". Sometimes they have scraps or the end of a roll that they'll sell. It's never cheap, but it's usually cheaper than McMaster-Carr. Note that it comes in differing wool contents. The greater the % of wool, the higher the price. And of course, the more wool, the better it absorbs.
Get 3/8" or 1/2" material. Buy enough to try a second layer for comparison to a single layer.
This is great stuff, use some to create diffraction pads for the front baffle on your mains.
Attach it with hot glue or spray adhesive (coat one contact area for easy removal, coat both surfaces for a more permanent solution
This is great stuff, use some to create diffraction pads for the front baffle on your mains.
Attach it with hot glue or spray adhesive (coat one contact area for easy removal, coat both surfaces for a more permanent solution
I want a little help in confirming my thinking before I set out on a 2nd iteration project. Since the ports Yielded a lower acoustic mass than expected, presumably the cause of misalignment, I want to use this "new" information to better the new design.
Assuming the first box is 135l and is tuned to 25HZ, I plug those numbers into software (using 2 ports 6" dia for the port info) and come up with the equivalent of 2-6" Ports, each 45" long, (the 6" conventional equivalent of these powerports). Let's say I will use these exact same ports in a lower Fb alignment, and I want Fb=20 this time. I change Fb to 20 in the software and then solve for Vb which yields a new Vb of 210l.
Does this make sense? Are there any problems proceeding with this methodology?
Assuming the first box is 135l and is tuned to 25HZ, I plug those numbers into software (using 2 ports 6" dia for the port info) and come up with the equivalent of 2-6" Ports, each 45" long, (the 6" conventional equivalent of these powerports). Let's say I will use these exact same ports in a lower Fb alignment, and I want Fb=20 this time. I change Fb to 20 in the software and then solve for Vb which yields a new Vb of 210l.
Does this make sense? Are there any problems proceeding with this methodology?
Sure you can use the CD.
RS probably won't have a 100watt 20 ohm resistor. All you need is something close. Just create something from the values they have in stock. Be sure to use sand cast power resistors.
I don't know about the digital meter, do a google search maybe someone has corrections for it
RS probably won't have a 100watt 20 ohm resistor. All you need is something close. Just create something from the values they have in stock. Be sure to use sand cast power resistors.
I don't know about the digital meter, do a google search maybe someone has corrections for it
That is too funny. I went radio shack earlier, and I said to myself "If I get this, Thomas is going to say try so and so combination in series/parallel". So I bought 2 of the 100 Ohm, 10 W, and 2 of the 50 Ohm, 10 W so I could have some options.Sorry, I was a chemE. My circuits class was buried somewhere in the freshman year (20 years ago).
How about a parralleled 25 Ohm 20 Watt (2-50's)?
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