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jrad12381

HELP building ported enclosure

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jrad12381

I built a sealed enclosure that came out to right around 2.5 ft after bracing, and subwoofer displacement. I am using an SSA XCON 15" sub running off a Rockford Fosgate T1500bdcp amp. This is mounted under the drivers helm in my MXZ, and the double baffle on the box is carpeted, and mounts to the fiberglass bulkhead under the helm. Like this:

http://www.themalibucrew.com/forums/index.php?/topic/36132-2012-22-mxz-system-install/

The sub sounds great at low volumes, it is deep, and clean. At higer volumes my dash starts flexing a lot, and the sound quality gets worse. I am not sure if it is the subwoofer sounding bad, or the dash causing resonate vibrations that make the sub appear to sound bad. Also I still think I would like more output from the sub.

I am thinking about building a ported box for the sub. If I cut some of the fiberglass bulkhead I can build a box with 4.5-4.7 cubic feet. I am not sure to go with aero port design or a slot port design. I may not have the volume for a slot port design, and I am not sure if the box shape will allow a slot port design. In order to get the most volume I will have to go with a pentagon shape. Kinda like the design below (looking at front of box)

/----]

[___]

If I do a design like above the dimensions will be 26W on the bottom, 20"tall, 21" wide on the top, and 22" depth.

My question is can I do a slot port on the right side of this box? Does the width of the slot port affect sound quality, output? I know the wider it is the longer it will have to be to accomadate the same tuning frequency.

I also know aero ports take up much less internal box volume to get the same tuning frequency.

What do you guys think. Obviously I have a lot on my mind. GRRRR

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my malibu

First I would check to see if the amp is clipping high volume. Also make sure the box is completely sealed .

Be happy to help design a port box

Ports can be made in many configurations

More power means bigger port to stop port noise

Port displacement is all that matters .

Edited by my malibu

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jrad12381

First I would check to see if the amp is clipping high volume. Also make sure the box is completely sealed .

Be happy to help design a port box

Ports can be made in many configurations

More power means bigger port to stop port noise

Port displacement is all that matters .

I would be interested in a box design. I have all the specs for the sub in front of me, and have been sitting here going over different ideas. I have calculations for 2- 4" aero port designs, 1- 6" aero port, a slot port with kerf cut (makes box volume on the smaller side).

I am pretty sure the box is sealed well. I pulled out the speaker in the walk through, and was able to feel along the seams of the box, and felt no air. The box is braced, glued, screwed, caulked, and bed liner sprayed, on the inside, and out. The sub is rated at 1750 RMS, and many people push them much past this level. My amp is running at 2 ohm, the birth sheet says 1700 RMS at a 2 ohm load. I have the gains set 1/4, my deck, and 3/4 volume, and the exile ZLD to control volume. My voltage is in the low 14's when running. So Im not sure if clipping is the problem.

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Earmark Marine

jrad,

Here are a few generalizations.

Versus a sealed enclosure, a bass-reflex enclosure can potentially add another 1/3rd octave of deep bass extension before reaching its half power point. It can also give you an additional plus 3 dB of output in the lower octave even in the most conservative sound quality alignment. So it can be very impactful.

Also, you can run with different size bass-reflex enclosures with different port displacements and lengths to obtain a similar tuning frequency to a limited degree before you see substantial compromises in other performance areas.

A larger enclosure with a larger port volume will generally have more output.

A smaller port volume can be over-driven resulting in noise. A longer excursion woofer can also over-drive the port so the tuning frequency isn't the only consideration.

A slotted port that shares the outside construction walls will not steal as much displacement so the wall thickness of the port isn't as big of a concern.

You can also give up a bit of deep bass extension and linearity in exchange for greater output over a narrower bandwidth with an SPL alignment.

In any case I highly recommend a good computer modeling program based on the Thiele Small parameters of your particular woofer. Results can be very predictable if you go by the numbers. One prescription does not fit all 15" woofers.

But, back to your existing set-up. I might pause before changing out what you have. Maybe there are existing reasons why your equipment is not up to par. It could be the enclosure. You would want to know the exact system Qtc of your woofer/enclosure. Is the enclosure completely airtight? As you gently push the woofer in it should return to neutral very slowly. If it doesn't you don't have a good seal and that means losses. Using a subsonic filter? Equalization or bass boost can be a factor. They might give you an effect you like at low volumes but keep you from reaching the maximum volume potential. The wrong crossover frequency can really kill output too, especially at higher volumes.

Apply manual pressure to parts of the dash to find which parts are sympathetic resonators. Have someone apply that same pressure to the same place to damp the dash noise and take another listen. You are going to have to resolve that issue in any case.

David

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Deephaven

Great driver, will really come alive ported.

Curious as to what you would describe as reduced SQ. As David alluded to the first step is determine the fault...even though again that driver really prefers to be ported.

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jrad12381

David thanks for the reply!

I have the xover set at 80 hz, and the sub sonic filter is preset at 28 Hz on my amp. I have had it turned on and off with very little difference. In my current setup the enclosure is mounted to the fiberglass bulkhead so puts a good amount of force on the entire dash setup at higher output levels. I have a few ideas on how make it so the subwoofer enclosure does not mount to the bulkhead, either way requires me probably building a new box. I do feel that I could use some more bass output to keep up with the rest of my system, which makes me think that a ported enclosure is in my favor.

When I use a port size calculator for 2- 4" aeroports at 16" length the total volume used is .22 cubic feet. To get the same frequency respone in a slot ported box using the manufactuers recomendations Im looking at .75 cubic feet. Does that sound right? Thats why I was considering using aero ports.

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jrad12381

jaredsiphone101.jpg

Here is the box design I have came up with to get the maximum box volume possible if I go ported. Let me know if you think this odd shape will work for a ported box. I figure the port will go on the right side of the front panel.

Edited by jrad12381

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Earmark Marine

I looked up the specs on that sub. A very low Qts. As mentioned above by Deephaven...a great woofer for a bass-reflex application. Btw, they provide some nice enclosure illustrations too.

A terribly chopped up enclosure shape with multiple extensions isn't good as a rule but the example shown with moderate exterior angles should be just fine. It won't change a thing. You are mostly concerned with the interior termination of the port so it is sufficiently distanced from the rear wall. A port sharing the outside wall will extend the effective port length by an inch or so. Terminating into a rear corner will extend the effective port length even more. These are easy scenarios to avoid or account for.

An Aeroport has a fixed surface area which will dictate the port displacement. The slot port is arriving at the same resistance but without any dimensional restrictions. So the difference isn't surprising. A larger surface area is going to mean a longer length to tune the same resulting in a greater port volume. It's a ratio thing. In order for the displacement to increase substantially both the surface area and length must increase in order to resonate at the same frequency.

If you like to run with heavy bass emphasis it will force you to lower the crossover frequency in order to arrive at the same half power intersection with the coaxials. Try this just for grins. Move the xover up 10 to 15 Hz which will force you to gain down the sub. Then see how it behaves differently at really high output levels. Also, the moment your sub over-drives the coaxials' midbass contribution any and all bass tonal construction goes out the window. The integration is crucial for plausibly musical bass. And, if you have an EQ with a bass crossover frequency control, set it at its highest point so that you do not have redundant filters. A brick wall crossover is not to your advantage in an open field environment. And, check the phasing relationship between the sub and satellites.

David

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nyryan2001

Jrad- that T1500 is a great amp, that BDCP with likley be delivering a true 1500 watts even with the boat off at 12.3-12.5V. Thats a lot of power and a lot of sub excersion in a sealed enclosure, could be why you are not getting the response you want.

I had never heard of that sub, so had to go look it up.... that is a quality sub, and very very capable of delivering some heavy hitting bass, here is a video of it on a very very high quality Sundown 1500watts, likely more in the 1700 range:

With the 26W on the bottom, 20"tall, 21" wide on the top, and 22" depth dims you spec'd, and allowing an approx .2cf volume for sub displacement, you are at about 4.6cf mins any vents, or blocking and bracing using 3/4" wood. If you do a slot port vent you"ll be around 3.6-3.8cf, which is still exceptional and will sound great.... that will be a HUGE box for a VLX... I dont know if I have ever seen or heard of a box that big in a VLX. I barely was able to cram a 4cf slot ported box in my 247.

I was on the verge of using aero ports myself, but had mine done as a slot vent so it was a close 2nd option for me. Using their oonline calculators it seems like you can get very very close to exact specs if you go slow and take your time.

I reccomend you go 3/4" wood, in my experience, the more dense the box, the better the sound... and going with birch/vs MDF, you can get some of that density back going 3/4" vs 1/2 or 5/8".

I am very interested in your build, pls keep us updated and post pics!

Edited by nyryan2001

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jrad12381

Thanks I will be going with 3/4 baltic birch that is 13 ply, or 1" MDF. Both will be double baffeled and braced. I can get both from a lumber year about 15 miles from me. The MDF is half the cost.

P.S. I guess I need to update my boat make on my profile. This is going in an MXZ.

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nyryan2001

ok, with it being a MXZ, than I do have some additional thoughts:

your height might be too much... you are showing a 19" height...at 20" you are pressing against the stuff under the dash if I am correct... depending on what you choose to cover or coat the box, you loose that height, and then you have you steering cable running under there, gotta make room for that somehow so you dont pinch it....

You also have to be able to access your 2 fuse boxes under dash... have enought room to be able to see in there to figure out what is what, but also get a hand on each fuse if you need to. 1" is not enough for that... but its even less than 1" when you add all these things up.

Then say you elevate the box on plastic spacers 1/2" so you can some airflow because it def will get wet under there... then also the front edge of the box, because it is so long, front edge will likely be on top of some part of the carpet so you loose another 3/8" or so there.

just watch your height taking this stuff in to account, gotta be able to get to the fuses.

Edited by nyryan2001

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Deephaven

David pretty much nailed the response on your questions, but I thought a little background on the sub might be helpful for others.

Many of you have probably heard of RE audio. Their brainchild and head designerm, Scott, left a while back and start Fi Audio. Fi's forum is on SSA's forum pages. The owners of SSA designed a sub with Scott to not address the mainstream in car audio but instead have something with better fidelity while maintaining the potential for a ton of output. As you know most car audio companies who make subs with big power handling gear their drivers to be one note wonders. This woofer is not that way at all.

That being said, the parameters are such that it loves a ported box.

As for some details that David shared that are clear to me, but maybe not others: The slot port and aero port for the same cross sectional area will be the same length. The material thickness then is the only differentiator in how much box space they take. That being said, the advantage of an aero port is you can get away with less port area than with a conventional port and still not have port chuffing noises. Of course you can also "aero" your slot port by using substantial roundovers on them.

The disadvantage of a boat over a car is that the chuffing noise is more easily heard in open air. This is of course because you have no cabin gain like you do in a car and since it'll be right at your feet and aiming at you instead of hiding in a trunk it takes more of a difference between the output of the sub and the output of the chuffing noise to "mask" the sound that it is making. So how does this pertain to port area? You should try to keep your port velocities below 15m/s unless of course your full throttle listening occurs when you are not in the drivers seat and a little noise to reduce your box size is acceptable.

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jrad12381

OK I have a few questions:

How do you calculate port velocity?

When I use a port calculator do I use total box volume (example 24Wx20Hx20D= 5.55 cubic feet) Say I want this box tuned to 33 Hz , and my port will be 3"Wx18.5" H and to get a frquency of 33HZ the port would have to be 18.6" long. So total port area is .60 ft cubed. So I would take the .60 and the .20, as well as the cubic foot usahe of any braces and minus that from the 5.55. So in this scenario 5.55-.60 =4.95 -.20=4.75^3

Does that sound rignt?

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Bobby Light

Based on the numbers you gave and assuming a material thickness of 3/4" you'll be well under 4 cu ft after all displacements. Your port length will be more around 26".

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jrad12381

Oh yeah I forgot to say that was internal volume. Those arent my tru dimensions, I just wanted to make sure I am calculating things the right way.

Soooo any idea on how to calculate port velocity?

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Bobby Light

If you model it in winISD it will give you the port velocity, also give you a ton of other good info of how your box "should" sound.

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jrad12381

Also does anyone have experience with aeroports? I like the fact that I can use them to tune the box by easily changing there length.

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Bobby Light

I used a 4" aero on my last ported 12", sounded really good. I wouldn't hesitate to use one as it makes changing your tuning easy if you want to. You're probably gonna want to use a 6" rather than two 4" for that 15" though. Keep in mind the flange end is about 1.5 the diameter of the circumference of the port diameter. Makes for tricky placement.

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Deephaven

I've got a few in my basement. If round is in the plans, Aero's are what I'd use. And indeed the easiest way to "calculate" port velocity is to use WinISD.

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jrad12381

Initially I was thinking about building a box with a kerf cut and I may still, but the aeros are nice to figure out what fequency I would like to listen too. I can get a 6" aero (9" flange in the box but it would be tight. I think I am better off with 2- 4".

I tried to download winISD on my computer from linear team but it wont open.

I played with the sub today, and trued to remove the box to check for leaks. This definitely is not going to happen unless, I break the front facade off. I may have a leak because if I push the sub in, it returns somewhat fast. The sub is impressive, and at hi volumes it flexes the crap out of my dash. I really hope by going with a ported box that does not mount to the fiberglass bulkhead will eliminate the abuse the dash is taking.

Edited by jrad12381

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Bobby Light

Pushing the sub in and it returning fast isn't really an indicator of a leak. If you can push it in very far with little resistance that would be a better indicator. Or if you can push it in with steady pressure and it's slow to return to zero that's really an indicator of a leak. If you try to push it in and it's hard to do, then returns quickly to zero from where you had it pushed in that would be an indicator of a properly sealed box. Bottom line is if it's had to push in, doesn't stay, and you don't hear any air pushing out of the box it's probably sealed ok.

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Bobby Light

Forgot to add if you have really nasty vibrations in the dash area it can make the sub sound blown. Kinda sounds like what you have going on currently.

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Deephaven

Initially I was thinking about building a box with a kerf cut and I may still, but the aeros are nice to figure out what fequency I would like to listen too. I can get a 6" aero (9" flange in the box but it would be tight. I think I am better off with 2- 4".

I tried to download winISD on my computer from linear team but it wont open.

I played with the sub today, and trued to remove the box to check for leaks. This definitely is not going to happen unless, I break the front facade off. I may have a leak because if I push the sub in, it returns somewhat fast. The sub is impressive, and at hi volumes it flexes the crap out of my dash. I really hope by going with a ported box that does not mount to the fiberglass bulkhead will eliminate the abuse the dash is taking.

That sub will return fast no matter what you do. Plenty of motor force.

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Earmark Marine

Is there motor force if you have no current traveling through the voice coil?

David

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nyryan2001

I really hope by going with a ported box that does not mount to the fiberglass bulkhead will eliminate the abuse the dash is taking.

if you are really after trying to keep vibration to a minimum in your dash, consider trading a little more CF space to make the box even more dense.... The more dense your box, more bass will come out the port and thru the sub directionally vs vibrate in all directions out from the box into your dash. so we are talking about using 3/4" birch... consider putting additional panels of MDF inside the box on the larger panels you can do it on. even using 1/2" or 3/8" MDF will make quite a difference, making your box acousticly twice as dense.

Some of the pro guys in car audo even use dynamat inside their boxes to get extremely tight punchy bass. You are going to have a big challenge there, that is a high end big pounded sub, a solid 1500 watts, and that box is going to be huge, amplfying it all, within inches of the dash.

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