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aperiodic concept for midrange in doors

Printed From: the12volt.com
Forum Name: Fiberglass, Fabrication, and Interiors
Forum Discription: Fiberglass Kick Panels, Subwoofer Enclosures, Plexiglas, Fabrics, Materials, Finishes, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=125621
Printed Date: March 28, 2024 at 4:38 PM


Topic: aperiodic concept for midrange in doors

Posted By: teenkertoy
Subject: aperiodic concept for midrange in doors
Date Posted: January 12, 2011 at 12:56 AM

For reference, this is the best page I found regarding aperiodic enclosures: AP Enclosures-The Aperiodic Cookbook (https://www.teamaudionutz.com/tutorial/1/AP_Enclosures-The_Aperiodic_Cookbook). After many hours tinkering in the garage, this design finally came to me moments from falling asleep. I will be installing 6" midrange drivers in these enclosures in my doors, with the "vent" going into the door cavity similar to the standard infinite baffle setup. So here is what I will be building over the next week or so.

The design starts with a 12" x 12" square of ABS plastic. Mount the speaker onto the panel. Take a piece of PVC pipe with an inside diameter just large enough that it can slide over the backside of the woofer. Cut it down and add an endcap to minimize the total air volume inside it. Great, now you have a very small sealed enclosure that you can mount using the large ABS sheet (which can be trimmed to any shape).

posted_image

Now take another pipe slightly larger than the first pipe, and slide them together. Choose a size so that there is a decent gap between the tubes. Grab some fiberglass insulation and fill this gap. Now you have a medium inner tube with an endcap, a bunch of insulation wrapped around it, and a larger outer tube sandwiching it all together.

posted_image

Now disassemble everything. Using whatever tools you can, create lots of slots longwise in both tubes. I'm aiming for a width of 1/4" to 3/8" and as long as possible. Most resources I have found recommend the surface area of the vent should be about 1/2 the surface area of your woofer. So for my 6" woofer (28 sq in.), I should have about 14 sq inches worth of vents.

posted_image

Notice how if you only drill slots on half or three quarters of the circumference of each tube, you can twist them to vary the amount of air allowed to "leak". Should be a super easy way to tune the aperiodic vent. For more coarse adjustments, of course we can change the amount of fiberglass we stuff in there.

One thing not noted on the drawings is to be sure the ends of the pipes are sealed. The ONLY path from the rear of the woofer to the outside of the enclosure needs to be through the inner slots, through the fiberglass, and then finally through the outer slots. I plan to find some rubber gaskets for this in the plumbing department at the hardware store.

--

Comments and critique welcome!

-J

-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.



Replies:

Posted By: teenkertoy
Date Posted: January 13, 2011 at 3:48 AM
Quick update:

Could not find both 5" dia and 6" dia ABS pipe, so changing the plans a bit. Using only 6" dia pipe now, and drilling holes into the side instead of creating slots (much easier this way). Fiberglass will be on the inside of the 6" pipe, sealed against the holes by thin rings of 6" pipe that have a slit cut in them, so they act like a C-clip pressing the fiberglass against the inside wall of the 6" pipe.

posted_image

To glue the ABS together, I'm using a sweet technique I found elsewhere. Keep all the fine dust-like shavings created when cutting/sawing/sanding the abs pipe into shape. Then, mix it with a little bit of acetone to create a thick sludge. I find the bottom of a coke can works great for this. Apply the sludge (generously) to both faces you want to "weld" together, and clamp overnight. Working time once you mix the shavings and acetone is at least a few minutes, or until the acetone evaporates. I'm surprised how well this worked, it's like welding with a q-tip !

posted_image

I'll post some more over the next few days.

posted_image

-J

-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.




Posted By: teenkertoy
Date Posted: January 17, 2011 at 2:21 AM
Initial results, not installed in the doors, hanging free in the garage. The rear wave is not sealed from front wave with the AP enclosure, but then again suspending the woofer without any enclosure is the same way.

Hanging woofer without any enclosure shows an impedance peak of 15 ohms, and a valley of about 4.5 ohms.

Hanging woofer in aperiodic enclosure shows an impedance peak of 8 ohms, and the same valley of 4.5 ohms.

Reduced peak by half, which is expected. Should be interesting after installing in the doors.

-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.




Posted By: z03mz03m
Date Posted: January 17, 2011 at 11:31 AM
Wow you've done a little more research than I have so far! I need to finish reading that site and see if I want to try making something like this or just buy those pre-made ones from Scan Speak for $7.

-------------
Dodge Magnum in progress:
Pioneer DEH-80PRS - PPI Amps - Dayton Subwoofer(s) - Exodus Anarchy's - Vifa Tweeters - Kinetik Battery




Posted By: teenkertoy
Date Posted: January 17, 2011 at 4:52 PM
If you can build a simple enclosure and make the ones from Scan Speak work, go for it. I doubt all the effort I'm putting into this project is really needed, but I don't have much room in the doors to work with (and I really enjoy the process).

-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.




Posted By: z03mz03m
Date Posted: January 17, 2011 at 10:47 PM
"(and I really enjoy the process)"

I kind of thought that might be the case. You seem to be a bit like myself, always doing things the hard way even though you know there is an easier way just because you like experimenting. lol

I'm building a .5cuft ported box tuned to 40 Hz that I'll try the anarchy's in my car to see what they can do like that. Then I'll probably end up buying the scan speak's and building an enclosure using them too. Then I'll know which one I think sounds better. posted_image

-------------
Dodge Magnum in progress:
Pioneer DEH-80PRS - PPI Amps - Dayton Subwoofer(s) - Exodus Anarchy's - Vifa Tweeters - Kinetik Battery




Posted By: teenkertoy
Date Posted: January 18, 2011 at 2:10 AM
More progress. Instead of fiberglass insulation as a leaky membrane, I'm using some fibrous carpet padding. This is the older-style stuff with many strands of fabric, not the newer plastic-foam-style stuff.

posted_image

The padding is held in place by a strip of sheet metal along the top edge because the woofer basket needs the clearance. The bottom is held in place by a C-shape section of the 6" pipe that has been trimmed down to size.

posted_image

Installed in the door, makes for a very tight fit. Cannot comment on performance yet, need to get some sleep first. And yes, that is Grace Water Shield roofing material on the door, don't laugh (okay maybe a little). It's 1/10'th the cost of dynamat or other "professional" products, the adhesive is a thousand times better, it weighs the same, and does not smell like asphalt. I'm using it to seal the door as air-tight as possible, not prevent sound from coming through the door.

For that, I have a sheet of Acoustiblok ready to lay over the top. If you're not familiar with it, take a look. They claim one 3mm (1/8") layer of Acoustiblok in a standard stud wall will result in more sound reduction than 12-inches of poured concrete (they have independent lab tests to prove everything they claim, and after hearing their product in action, I believe it).

posted_image

-J

-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.




Posted By: z03mz03m
Date Posted: January 18, 2011 at 10:16 AM
Holy jackhammers! That Acoustiblok is what I need for my loud ass exhaust! How much did you pay for how much? and did you just order it from their site? I'm really excited about that!posted_image

Your enclosures are looking awesome too. I hope all that work was worth it!

-------------
Dodge Magnum in progress:
Pioneer DEH-80PRS - PPI Amps - Dayton Subwoofer(s) - Exodus Anarchy's - Vifa Tweeters - Kinetik Battery




Posted By: z03mz03m
Date Posted: January 18, 2011 at 3:56 PM
Do you know if a lot of water gets into your doors? you might want to make a semicircle that protects the fabric from getting wet. My doors get a lot of water in them and I would hate for you to get those vents soaked.

-------------
Dodge Magnum in progress:
Pioneer DEH-80PRS - PPI Amps - Dayton Subwoofer(s) - Exodus Anarchy's - Vifa Tweeters - Kinetik Battery




Posted By: teenkertoy
Date Posted: January 19, 2011 at 1:46 AM
z03mz03m wrote:

Holy jackhammers! That Acoustiblok is what I need for my loud ass exhaust! How much did you pay for how much? and did you just order it from their site? I'm really excited about that!posted_image


I ordered two 4' x 5' sheets at $65 each, which comes out to $3.25 / sq ft. Shipping was about $25 from Florida to California, which is reasonable considering how much it weighs. You can request a demo, they sent me two 1' x 1' panels with some literature for free. If that's all you need, maybe that's the way to do it.

Regarding moisture, yeah the doors get some. I'll have check on it after the next rain and see what happens, but I'm hopeful.

-J

-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.




Posted By: krazylegs
Date Posted: February 11, 2011 at 12:36 AM
that acoustiblok stuff is only good with a air baffle its no better than any other sound deadening material for cars in fact its possibly less effective due to no adhesive to seal it and its rigidity it is better than nothing i guess but as for your enclosure very impressed ive never dealt with ap systems before i have an suv where space is abundant though i have acquired a small car that i now have fantastic ideas for

-------------
chevy korsica build progress
00%]--------exterior
00%]--------interior
00%]--------engine
15%-]-------sound system
00%]--------computer
just your average redneck kustomizer




Posted By: teenkertoy
Date Posted: February 11, 2011 at 1:03 AM
krazylegs wrote:

that acoustiblok stuff is only good with a air baffle


Please explain more, I don't know what you're talking about yet.


krazylegs wrote:

as for your enclosure very impressed ive never dealt with ap systems before i have an suv where space is abundant though i have acquired a small car that i now have fantastic ideas for


Thanks, glad you could gain something from reading.

-J

-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.




Posted By: krazylegs
Date Posted: February 13, 2011 at 5:16 PM
you need an air space between two layers of material to allow for the sound to dissipate the transfer of sound waves between mediums is where energy is lost sound waves travel easiest through solids next liquids and last gas or air dynamat is sponge like it has small microscopic air bubbles sandwiched between hard rubber so its constantly changing between mediums in a small distance killing the sound

-------------
chevy korsica build progress
00%]--------exterior
00%]--------interior
00%]--------engine
15%-]-------sound system
00%]--------computer
just your average redneck kustomizer




Posted By: teenkertoy
Date Posted: February 13, 2011 at 9:07 PM
I don't claim to be an authority on the subject, but I think I have a good grasp of what's happening. This is as much in reply to you as it is for me to learn. I see three things.

Damping a surface (applying dynamat to sheet metal) reduces that surface's tendency resonate. This is accomplished by adding mass to flat sections of sheet metal where it is least stiff and most likely to resonate. Mechanical vibrations of the car (including the vibrations caused by speakers mounted in the doors) are less likely to be turned into acoustical energy, reducing one source of unwanted noise. One analogy would be a heatsink; the heatsink dissipates thermal energy (small-scale vibrations) as heat, instead of allowing the thermal energy to build up and be released as radiation and light (like the sun).

Sound barriers like mass loaded vinyl, lead sheeting, acoustiblok and others, reduce sound from passing from one pocket of air to another by reflecting it. They are used to keep road noise, traffic, engine, exhaust, and other noises outside of the cabin from crossing into the cabin. In addition, they are used in doors and trunks to keep the rear wave of a speaker from entering the cabin or interfering with the front wave of the speaker. Essentially the material becomes part of the infinite baffle in some installations. One analogy would be a mirror for light waves; the mirror does not absorb or drastically alter the light, it just prevents it from passing through by reflecting it.

Absorbent material is the type I think you are describing. Sound waves in the air are converted into mechanical energy by the material and are dissipated as small amounts of heat. Unlike a sound barrier, absorbents reduce the acoustic energy of a system instead of simply deflecting it. This is why anechoic chambers must use absorbent materials, otherwise acoustic energy would stay in the room defeating the entire purpose. For car audio, absorbent material is easy to use for higher frequencies (dashboard covers), but for lower frequencies it becomes unpractical, and thus barriers are preferred.

The separate air chambers I think you refer to would be similar to what is found in double-pane windows, or to the extreme found in recording studios.

-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.




Posted By: krazylegs
Date Posted: March 28, 2011 at 5:43 PM
i agree this discussion should be explored to give people the truth about noise control and the application of it

as for the discussion dynamat is a damping material true reducing resonance on the panels but are working in conjunction with its absorbency you need both on almost all applications as for

as for sound barriers the metal door panels covered in dynamat would do a much better job because the practical application of akoustiblok mounting it and all in such a small space but even sound barriers cant be totally rigid or they would just relay the sound through it the best application would be all three noise reducing mediums but in wich order is another discussion too

-------------
chevy korsica build progress
00%]--------exterior
00%]--------interior
00%]--------engine
15%-]-------sound system
00%]--------computer
just your average redneck kustomizer




Posted By: teenkertoy
Date Posted: March 28, 2011 at 5:58 PM
I don't want to kill the discussion by complaining about your grammar, but I can only guess what you're trying to say. It would make much more sense if you use things like periods, commas and the like.

Dynamat and other damping materials have (nearly) no absorbent properties, I'm not sure what you mean about that. The metal doors covered in a damping material is perhaps a decent sound barrier, sure. However mild damping of the door panels (25%-50% area) with a mass loaded, sealed, mechanically isolated, floating sound barrier like MLV is better from experience. I agree though it can be very tight to fit all of this material behind a door panel, especially some that have limited to no extra space back there.

I think we're both trying to say the same thing here, that all three materials used intelligently is the best method.

-J

-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.




Posted By: teenkertoy
Date Posted: March 28, 2011 at 6:01 PM
For anyone else still curious about the enclosures, they certainly did what they claimed. The impedance peak is minimized, though the bass is severely reduced. I believe with some very fine tuning of the membrane material I could get it "just right", though I've decided to leave the woofers in the doors like stock, infinite baffle style.

-------------
Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.




Posted By: krazylegs
Date Posted: April 03, 2011 at 11:44 PM
i think we are trying to say the same thing i was under the impression you were only going to use the mlv as dampening

-------------
chevy korsica build progress
00%]--------exterior
00%]--------interior
00%]--------engine
15%-]-------sound system
00%]--------computer
just your average redneck kustomizer





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