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Old 7th January 2004, 02:01 PM   #1
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Default EBS: Powerport application

Well, after using an HE-15 in a sealed design for awhile, I am stepping out. I have come up with a design to build a sofa table (the kind you put in back of the sofa) sub with massive capability. In looking at the ported designs of this driver, as succesful as they are, seem to underutilize this driver at normal port frequencies. Specifically, it has been challenging to broaden port area enough to really minimize port compression for this 6 liter driver. 2-6" ports would be great, but the port lengths (60" or more for 18 HZ extension) would support 100HZ + pipe res problems, etc, etc. They would be impractibly large, adding 2.3 cf just for the ports, assuming you could fit them in.

Look at the link below for the patent description of Powerport.


So in a roughly 200l cabinet, Fb=18, approx inside dimensions 12w x44l x 26tall, I am proposing 2 powerports running vertically on each side of the sidefiring driver, exiting at the top of the cabinet. Using Unibox, 2-6" ports would need to be 60" long each, an acoustic mass of 105kg/m^4 for each one. Using the powerport software obtained some time ago from ThomasW, using a 3" foam filled pvc connector, concentrically located, to connect the 8" diameter wave guides, each port will be approx 28" long. For each port, one wave guide to be mounted to the bottom of the cabinet, the other mounted at the exit on top of the cabinet. The resulting output should (theoretically) benefit from port area 50% greater than a single 6" or 2-4" (33% reduction in port velocities). At 1000 W the port output (and noise reduction) would be greatly enhanced, though at 100W, no real benefit.



Having the driver mounted on a large face (firing into the sofa potentially) will present bracing and resonance damping challenges, and the driver will only have 2" to breathe at the back (10" mounting depth in a 12" dimension). Since the ports exit on top of the cabinet, there can be no port noise, none. Any port noise would be noticeable in the sofa location I think. There is always the option of turning the cabinet upside down and this may well be a smart design change. I was just planning the ports into the cabinet aesthetics, with some nice carved feet on the bottom, Heavy Glass top, I am trying not to make this look like a sub, a secondary consideration. A sub man and wife can both admire.

As far as construction, I will turn the wave guides on the new lathe. Woodworking knowledge/tools is no problem. The 6" PVC will sit in the cabinet mounted on a brace with a flair routed on the reverse input side, required for the powerport.

This is a sketch of my idea, and I am making a drawing now and would like to get started. Tell me what you think. This will not be a simple project, and will be a result of several months of learning and research. If there is some interest I will post photos as work progresses.

I am unable to locate the powerport software on-line, maybe ThomasW can help, or if you want it just e-mail me, it is an excel file.

Here is a link to the patent office with some interesting reading from Polk:


MichaelPolk Patent
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Old 7th January 2004, 05:28 PM   #2
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Attaching the excel file, a picture is worth a lot of spelling errors.
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Old 8th January 2004, 01:51 PM   #3
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Old 8th January 2004, 04:30 PM   #4
jaybird is offline jaybird  United States
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Default Not to discourage you

You might want to reconsider building a subwoofer that you can't move around the room. I just built an ebs endtable and it kicks some but in the low end, but is disappointing in the mid bass. It is great for movies, but is too easy to locate when you listen to music. My next subwoofer will be sealed/front firing.
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Old 8th January 2004, 10:43 PM   #5
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Yes, there is some compromise when you are trying to build a location specific sub, not a great way to set out.

But maybe with predominantly direct radiating positioning, close to the listening position (sofa table), these issues will work out. I know many people who make a coffee table with some success. Is this usually a bad idea?

This will be parametrically EQ'd with the BFD anyway, so maybe there is hope.

C'mon critics, I know you are out there. Look at the program and patent and tell me whether there is plausibility in this idea.

Michael
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Old 9th January 2004, 11:37 AM   #6
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Old 9th January 2004, 12:36 PM   #7
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I looked at the PowerPort concept and decided it was too much work (or more likely I was too lazy....) Note I can upload a copy of the program files if people are interested.

My original ported HE-15 design using a single flared 6" port has survived the test of time. To this day it contiunes to amaze visitors with it's effortless and detailed output.

Now obviously it's not in the same league as a dipole or IB sub. But I will say I've never heard a conventional 'box' sub regardless of cost or design that sounded any better.

I've driven this sub to literally house shaking SPL's (note that the Fs of the house itself appears to be ~16Hz), and never have there been any indications of port compression or chuffing.

If the 6" AeroPort flares are still available, I recommend trying them. They allow a single 6" flared port to flow as much air as a straight 8" port. They also keep the port a 'reasonable' length.
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Old 9th January 2004, 01:20 PM   #8
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Hello ThomasW

I remember you saying somewhere, that you wonder about that driver's performance in say a larger box than your 180l AS15. Besides the weight consequence, that would also create a larger saddle in the response, not a bad idea maybe, Comments?

I saw your clio resting of your project, but I don't know much about these curves (how to interpret them) and what they represent. Is there an output curve somewhere that shows the spectrum at reference outputs? I saw one TC sounds project from a few years back, tuned to 23 HZ, that showed obvious port losses with 2-4" ports, and he even recommended doubling his port area (if it were feasible).

.Click the image to open in full size.

Smaller ports of the same area is disadvantageous, comparing this with a single 6", but not much.

So it looks like some work to only modestly improve the low end. Since you have seen powerport, and know what it is trying to do with it's waveguide theory, would a 50% increase in port area be beneficial when it comes to 16HZ, 10HZ?

BTW, I found a 1.5 inch roundover bit and I'm planning on making flairs as required for the project
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Old 9th January 2004, 02:22 PM   #9
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Ambitious project, I like it.

I think ThomasW sent me this same info when I was in the early stages of building my Maelstrom Sonosub and I wanted to do the Power Port thing, but I was going to make mine moveable (up and down) in a vertical port, but I couldn’t get a port at the bottom of the enclosure where it needs to be for the Power Port design to work properly. As ThomasW stated I also found the Power Port to be too difficult, if you read the white paper you will discover that the stem diameter and length as well as the proximity of the valve head to the opening is all interrelated and critical for proper operation. I decided that turning several different valves with different stem diameters was too much trouble for the little gain you get, so I just used the valve idea as a Port Plug and a decorative finial to dress out the top of an ugly Sonotube. CAT makes some custom subs just like what you are describing except without the Power Port, but if your sub will be out in the middle of a room with no wall boundaries close by (like a coffee table sub) then you will be wasting a lot of SPL and you wont be able to tweak it much.

You could just run the ports horizontal so they will fit in the enclosure, also have you modeled the drivers you whish to use in a appropriate size box, if you can keep the velocity down below 18m/s you will have no port noise in even the most extreme conditions. BTW you mentioned a sketch of your design, did you post this, I couldn’t find one.

I got lucky and only had to make one prototype to figure out the best glue up method since Oak is an open-grained PIA to turn.

Here is my finished (turned) valve.
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Old 9th January 2004, 02:56 PM   #10
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KingDaddy

Yes that is similar to what I had in mind. I would not make it one piece, although that is beautiful. I think I would turn the wave guides and connect them. Using the software (see link above), what appears to change tuning the most is changing the connector diameter, thereby changing the annulus area (and tuning) significantly. Seems tuning could be accomplished with a method unconventional. Rather than change port length or "valve" (wave guide) height, fix those parameters and change inside tube diameter. As it is better to start with a long (conventional port) port and tune shorter, it is better to start with a conservatively thin (as opposed to conservatively long) connector (powerport) and wrap it to extend the diameter (ideas on materials please?).

That is my take on the spreadsheet.

My sketch is the written sketch on the first post. If you run the spreadsheet, I preloaded my numbers into it, it requires a 3" dia connector, So PVC would be my choice as 3" dowel rod is pricey, $40 for 3 feet. Fill the PVC with expansion foam to negate any acoustical influence, cut to length.

I'd love to see your whole project, do you have a photo?
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