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Old 30th December 2003, 10:22 PM   #1
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Default AV12 Design Aggravation

Ok, I've lost all trust in WinISD. I am getting really strange, strange stuff when I'm trying to design my AV12 subwoofer. I already have the three 3" precision ports and the 500-watt plate amplifier, and I'm waiting on the woofer.

I need some help here. I don't have the money for a good speaker design software piece, and I am in need of some help designing the enclosure for my AV12. I want response down to 22 Hz at least, and I need reasonable group delay. I don't want a boom box if it can be done in such a way that it won't boom. A linkwitz transform circuit is out of the question, but passive radiators are not. I would still prefer to use the Precision Ports, but I could live with a pair of 15" passive radiators.

I hope I'm not asking too much. I have the amp and the ports over here in my room, and I am going on Thursday to get the material for the box.
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Old 31st December 2003, 12:06 AM   #2
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Unless you build a large box, 3 3" ports will wind up too long.

These drivers really need a PR to reach a low tune as they're designed to work in smallish enclosures and have quite a bit of Sd that overwhelm reasonably sized ports.

How about a Linkwitz Transform and a small sealed enclosure?

Pete
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Old 31st December 2003, 02:31 AM   #3
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Ok, I guess I will need to save all my flared ports for some other project and bite the bullet and buy the PRs. At least John has them on sale for the time being, which means that I can get them for less than I would normally have to pay, which would be something around $150 if they weren't on sale.

The costs for this thing are really adding up.

$40 for MDF
$300 for 500W amplifier
$90 for two PRs
$0 for the woofer (because I won it in a contest to design a new logo for Stryke as it changes to Acoustic Elegance here in January).

That all totals out to about $430.

I will also have to buy a couple more cast frame driver mounting kits for the PRs...

Click the image to open in full size.

Here's the dish: Stryke Audio is changing its name, and it is going to focus on developing a line of complete, finished speakers. Their current DIY offerings will be marketed under the name AE Speakers, so I guess I now have an AE Speakers AV12.
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Old 31st December 2003, 03:05 AM   #4
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Err, is there a different thread where you explain what kind of box you are building with this?

I feel like I am coming into the middle of something here.
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Old 31st December 2003, 04:02 AM   #5
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I have decided to have an enclosure whose internal dimensions are 14"x18"x19", and it will use a pair of 15" PRs to handle the load. It will sort of be like the existing Acoustic Elegance Thunder 12" Subwoofer.
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Old 31st December 2003, 04:42 AM   #6
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Perhaps you don't need the Drone Cones, (that's the real name for Passive Radiators, by the way-the one their inventor, H.F. Olson, gave them).

According to Isaac, (F4ier), a vent flared on both sides has equivalent wind noise to a vent with twice it's area. Note-that is twice it's cross sectional area, not twice it's diameter. In fact, multiply the diameter by two and the cross sectional area goes up four times!

Anyhow, a 3" port with flares at both ends should be equivalent noise-wise to a 4" port without flares. Let us look at a 2.8 Ft³ box-yours-with two 3" diameter ports.

The port length goes down to 25.37 inches. Yet it has the noise of two 4" diameter ports, which would have to be 46" long!

I will admit that 25 inches is not that short, but I feel it will be doable. And the volume of the vents together is only 7% of the box's total internal volume.

Get yourself a fourth Precision Port, and a couple of elbows for 3" pipe, and you might be able to save $90.
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Old 31st December 2003, 04:05 PM   #7
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Well, the thing is that I'm trying to keep this thing small. It's already going to be insanely heavy and I need it to not also be huge and insanely heavy. I need at least three ports because SVS uses three 3" flared ports on their PB1+ which uses a woofer that is very similar to the AE Speakers AV12 in performance. Going with the Passive Radiators would allow me to use a box that is not a three-feet-tall, two-feet-wide silo, and still reap the benefits of low port noise. If you can simulate a box for me using the three 3" ports that isn't insanely big, and will give me good output to something like 18 Hz, then I will go ahead and use the ports. But I am going for a compact package, and the Passive Radiators will allow me to achieve that. And I won't have to spend a lot of time designing enclosure bracing. Those PRs are looking mighty tasty since they will let me keep the enclosire size down.
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Old 31st December 2003, 05:58 PM   #8
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BAM:

Personally, I think you can get away with two 3" ports. However, if you are committed to using three 3" ports, then the ports themselves will have to be longer, and there will be even more space taken up.

If you want to use 3" ports to tune this to 22 Hz-that was your original tartet, 22 Hz-then they will have to each be 40" long. their internal volume-all three ports added together-will be ½Ft³.

So, your internal volume, now 2.8 Ft³, should increase to 3.2³. Of course, there is always the matter of actually obtaining PVC elbows and fitting these these ports in the box. I mean, theoretically it can be done, but it will be a labyrinth, (not an Acoustic Labyrinth, an early term for the Transmission Line, lol) in there.

Up to you. It could be fun, or it can just be too much of a drag and you can order the PR's.

PS: Lately I have heard good things about downfiring ports. Klipsch has said that when a speaker is placed against a wall, the velocity slows down. I wonder if elevating this cabinet a couple of inches and having downfiring ports actually slows down the port velocity-since the air is coupling to the floor-and will allow you to use smaller, (or fewer and therefore shorter), ports. The only reason ports cannot be small is the air velocity, after all. Just speculation on my part.

Might be worth starting a thread over.
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Old 31st December 2003, 07:38 PM   #9
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I'm going to go ahead and do the PRs, then, because I want small. This thing is going in a dorm room for the next 4 years, and then probably into an apartment for 2 or 3 more years.

All my friends spent their money on their cars. I spend my money on my sound system.
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Old 25th January 2004, 10:09 PM   #10
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Update: I discovered that my original ported design was actually 8 cubic feet, and the port dimensions I was getting actually made sense. However, the AV12 only needs 4 cubic feet to go EBS so my previous design idea hits the scrap pile. I am building the Stryke recommended 3-cubic foot box with the double 15" 1400g Passive Radiators. For those of you using an AV12, only 4 cubic feet are necessary. You might have to step back to double 4" ports. I don't know. I'm just going ahead with the recommended box.
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