# DIY AP Vent



## jbholsters (Jun 17, 2009)

So, I was going to use ScanSpeak vents in my a pillars, but after looking into the wheel well, they were a little to big in diameter. I just happen to have a box of wall vents laying around and figured I'd see what I could do with them.

First 2 pics are obviously of the front and back of the vents. You can buy these at any hardware store.

















Next pic is of a piece I peeled off an Rmax insulation board, a screen I hacked out of another wall vent, and a piece of ABS plastic.









Next the insulation is placed into the vent.









Now the screen from the sacrificed vent is inserted with the lip facing up and out the back.









Next the plastic strip is inserted over the rear screen and up under the rear lip of the vent. Since the ABS is springy, it stays in place.









Last shot just shows the insulation through the vents.









If the impedance needs to be adjusted, you can pop out the ABS, ad/remove insulation and trim the height of the ABS ring accordingly.

The vents should help somewhat with keeping debris out of the insulation, but fabricating a hood would also help. The vent can be siliconed into the hole, and further sealed with a piece of butyl deadening mat.


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## Mic10is (Aug 20, 2007)

whered u get the vent? i cant find those things at Home Depot or Lowes. I been looking for those types of vents to do my external venting for awhile


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## jbholsters (Jun 17, 2009)

Those are about 20 years old. But I was at ACE the other day and saw them with the door supplies (locks, screen, etc...) You can also get them from Mcmaster Carr. LINK Scroll down to the "Mini Wall Louvers". They also make them out of plastic. 


EDIT: it wont' let me link to the right page for some reason, you can follow the link and go to the next page, or just type in page 643


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## Mic10is (Aug 20, 2007)

jbholsters said:


> Those are about 20 years old. But I was at ACE the other day and saw them with the door supplies (locks, screen, etc...) You can also get them from Mcmaster Carr. LINK Scroll down to the "Mini Wall Louvers". They also make them out of plastic.
> 
> 
> EDIT: it wont' let me link to the right page for some reason, you can follow the link and go to the next page, or just type in page 643


where in PA are you?


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## jbholsters (Jun 17, 2009)

Hollidaysburg, which is right outside of Altoona.


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## Aaron'z 2.5RS/WRX (Oct 24, 2007)

Sweet a tunable DIY Variovent...


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## Mic10is (Aug 20, 2007)

whats the outside diameter of that vent? I still cant find those things anywhere. found some PVC ones with tiny louvers, but nothing like that


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## ErinH (Feb 14, 2007)

Aaron'z 2.5RS/WRX said:


> Sweet a tunable DIY Variovent...


thing is, those variovents are about $10/pair. Not knocking the DIY, just in this case I don't really know if a trip to HD or Lowe's would be anymore beneficial than just ordering a set of variovents. You might save a couple bucks, at most.

I can see the use of one of these if you need a vent of a different size, though.

Just my $.02.


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## jbholsters (Jun 17, 2009)

Mic10is, those ones are 3". Did you check ACE? I was in there yesterday, and they had 1,2,3, and 4" ones. IM me your address and I'll send you a couple.

AAron'z, you can take the scanspeak ones apart and add more fiberglass as well.


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## jbholsters (Jun 17, 2009)

bikinpunk said:


> thing is, those variovents are about $10/pair. Not knocking the DIY, just in this case I don't really know if a trip to HD or Lowe's would be anymore beneficial than just ordering a set of variovents. You might save a couple bucks, at most.
> 
> I can see the use of one of these if you need a vent of a different size, though.
> 
> Just my $.02.


One advantage is that the newer ones (unlike what is pictured) have double vents, inside and out, which will help with keeping water and snow out. I'd still make a hood to cover them though.


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## Mic10is (Aug 20, 2007)

took some drivin around. ACE didnt have any but he said check with a local lumber supply place and they did have them. pretty neat lil suckers. not sure they are deep enough tho but gonna give it a shot today


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## jbholsters (Jun 17, 2009)

So I finally got around to installing my AP vents. I couldn't use the ScanSpeak vents as they were a little too big for where I wanted to put these. My kicks vent into the A pillars of my car. The front of that area is right behind the fender well, so that's where they went.

In the first picture you can see the vent installed after I cut the holes. I used a 3" hole saw with plenty of cutting fluid (although the metal was quite thin in this area). After the vent was installed and the entire area cleaned down with denatured alcohol, I covered it with Dynamat Extreme. After that was applied, I went ahead and glued down some CCF in preparation for MLV.









In this pic you can see that I added an additional piece of CCF and that it is cut away to the side that is open to free air.









Next the MLV was cut and installed. All of the edges were sealed with aluminum ducting tape. The MLV was also taped to the inside of the outer fender.









The factory neoprene piece was then put back









The last image shows the factory panel reinstalled.









Before all the sound deadening was applied I tuned the vent and flattened the impedance of the driver (Hybrid L6-7.1" mid). All I can say is wow! These have massive mid bass impact now.


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## jbholsters (Jun 17, 2009)

For those that are interested in learning how to tune AP enclosures here are instructions from the old Image Dynamics Aperiodic Membranes that were discontinued some time ago.

The following information has been designed to help you get the most out of your Image Dynamics RM resistive membrane kit. 


GENERAL INFORMATION 

1. It is recommended that the enclosure be fabricated from medium density fiberboard (MDF) or better quality of wood, with a thickness of 3/4‚Äù. The enclosure should be both screwed and glued. Do not use staples or a nail gun. Pre-drill all screw holes to prevent splitting the MDF. 

2. For best performance, the trunk should be completely sealed from the passenger compartment of the vehicle. You can do this by using fiberglass, expanding foam, or stuffing the gaps around the enclosure. Also, the rear deck should be sealed as much as possible. The better the trunk is sealed the better the low bass performance. 

3. The enclosure only needs to be big enough to fit the speaker, with the magnet about 1/2‚Äù away from the membrane. The membrane will usually be positioned on the back side of the speaker enclosure. This is because this is the only part of the enclosure large enough to fit the resistive membrane. 

4. The rear of the membrane does not have to be vented into a trunk. It can be used in a hatch back or truck, with the rear of the membrane vented to the outside of the vehicle. One very important thing to remember is that the membrane must be isolated from the elements when attempting this fashion of installation. If the membrane becomes slightly wet, it will highly degrade the sound quality of the subwoofer system. 

5. It is important that the membrane material be held in place firmly for best performance. If the membrane material is allowed to move around, you will not get the best results due to non-linear resistance. This does not mean that the membrane material has to be compressed tightly. 

6. It is recommended to use a divider when two subwoofers are used. A divider adds support to the enclosure and the membrane mounted on the rear of the enclosure. 



MEMBRANE ASSEMBLY INSTRUCTIONS 

1. Step one will be to assemble the enclosure with the exception of the rear wall of the enclosure, which is where the resistive membrane will be located. The back of the enclosure where the membrane is will not be attached until after the membrane is assembled. 

2. The second step in assembling the resistive membrane is to cut the holes for the membrane in the MDF. Be sure to cut the holes for the membrane square and to the exact dimensions shown on the step one drawing. 

3. Step three will be to attach one piece of the perforated metal over each of the holes in the MDF. Carefully, align the pieces of perforated metal with the cutouts in the MDF. Screw the metal down to the MDF with enough screws to hold it in place firmly. 

4. Run a bead of silicone along the inner edge where the perforated metal and MDF meet inside the cutout. Place the membrane material inside the cutout, pressing it into the silicone bead firmly. Initially, use only one thickness of membrane material. 

5. Attach one piece of perforated material over the resistive membrane material. Center the metal over the cutout and membrane material area, and secure it to the MDF using a sufficient number of screws to hold it in place firmly. 

6. Assemble this rear panel piece to the rest of the enclosure. You are now ready to install the enclosure into your vehicle. 

7. If the proper amount of membrane material is not as thick as the wood, you will need to modify the method of installation. One method would be to reduce the thickness of the surrounding wood by using a router. Another method would be cut the perforated metal down to the size of the opening in the wood and make a wood trim ring to hold the membrane together firmly. 


RESISTIVE MEMBRANE TUNING INSTRUCTIONS 

1. Tuning the resistive membrane is not a difficult task. It requires some time and some common test equipment. When tuning a resistive membrane enclosure, our goal is to achieve the flattest impedance curve possible. By adjusting the amount of resistive membrane material, you can achieve an almost flat impedance curve. 

2. Equipment necessary for tuning resistive membrane enclosures: 

- Autosound 2000 test disc 101 
- Resistors, 25 watt, 10 ohm and 50 ohm 
- Volt / Ohm meter 

3. Set up test equipment as indicated below: 

A. Connect 50 ohm resistor in series on the positive lead of the speaker wire going to the enclosure. 

B. Connect test leads from volt / ohm meter across positive and negative speaker leads on the speaker side of the resistor. Set the meter to read AC volts. 

4. Using track 40 on the Autosound 2000 test disc, calibrate the test equipment as follows: 

A. Disconnect speaker lead going to the enclosure after 50 ohm resistor and connect 10 ohm resistor across the positive and negative speaker leads. Leave volt / ohm meter connected as before on the 10 ohm resistor side of the 50 ohm resistor. 

B. Turn system on and play track 40. Adjust volume control of the system until you read 1 volt on the volt / ohm meter. DO NOT ADJUST VOLUME CONTROL AGAIN AFTER THIS POINT ! 

C. Remove 10 ohm resistor and reconnect speaker leads to speaker. 

D. Make sure all seats, trim panels, etc. are in place while making measurements. 

5. You can now begin to make impedance measurements. With the system set as it is now, 1 volt is equal to 10 ohms of impedance. For example, if on track 30 you have a voltage reading of .65 volts AC, it equals an impedance of 6.5 ohms, 2 volts equals 20 ohms, etc. Begin at 20 Hz and take readings at 5 Hz intervals up to 90 Hz, and either write them down on a sheet of paper or plot them on a graph. This will give you a good look at what is happening. 

6. Deciding whether to add or remove membrane material is determined by what frequency the impedance peak occurs at. If the impedance peak occurs at or near the resonant frequency of the speaker, there is too little material in the resistive membrane. If there is an impedance peak somewhere in the higher frequencies near where Fc of the enclosure would be if the enclosure was sealed, then there is too much material in the resistive membrane. Add or remove material until you have the flattest impedance curve possible. If you have 

Continued from page three... 

a fairly flat impedance curve, but overall it is considerably higher in impedance, it indicates that there is too much material in the membrane. 

7. You will never achieve an absolutely flat impedance curve. Usually, the result you will achieve will be a broad rise in impedance over an octave or an octave and a half. At approximately 20 Hz the impedance will be near the RE of the speaker, and it will remain close to thatfigure until the broad rise begins. At the higher end of the broad rise in impedance, the impedance will get lower, and settle back to the nominal impedance of the speaker. 

8. Sometimes it is necessary to listen to the enclosure and alter the amount of membrane material. If after tuning the enclosure for the flattest impedance it lacks low bass, this would make it necessary to remove more membrane material. Most of the time the system will sound best with the flattest impedance curve. 


THANK YOU FOR PURCHASING THE IMAGE DYNAMICS RM RESISTIVE MEMBRANE KIT. iF ANY OF THE INSTRUCTIONS ARE UNCLEAR, OR YOU CANNOT ACHIEVE RESULTS YOU ARE SATISFIED WITH, OR YOU SIMPLY HAVE QUESTIONS, PLEASE FEEL FREE TO CONTACT US. 


22125 South Vermont Avenue 
Torrance, California 90502 
(310) 787-2399 FAX (310) 787-7699 



CUTOUT SIZES FOR MEMBRANES 

Signifies actual resistive membrane area... 

KIT # DIMENSION A DIMENSION B 

RM-10 8.0‚Äù 8.0‚Äù 

RM-12 10.0‚Äù 10.0‚Äù 

RM-15 12.5‚Äù 12.5‚Äù 

RM-18 14.5‚Äù 14.5‚Äù


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## npdang (Jul 29, 2005)

Curious why you would use an AP membrane in a car door, which is generally large enough to be considered "free air?"

Have to admit it does look cool though.


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## MaXaZoR (Apr 1, 2007)

Looking at it, I think it's his kicks and not the car door.


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## jbholsters (Jun 17, 2009)

jbholsters said:


> My kicks vent into the A pillars of my car. The front of that area is right behind the fender well, so that's where they went.



It vents into the kick panel, which in turn vents into the pods.


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## t3sn4f2 (Jan 3, 2007)

I always wonder how much outside noise come in through those type of vent setups and get horn loaded by the driver cone........


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## jbholsters (Jun 17, 2009)

t3sn4f2 said:


> I always wonder how much outside noise come in through those type of vent setups and get horn loaded by the driver cone........


That's why I installed the MLV and channeled the air movement around the side of the pillar. I have not noticed any increase in road noise after the mod. Another benefit of doing it the way I did, is that as long as the tape sealing everything stays put, it will keep moisture out of the AP vent as well.


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## HawaiianBassHead (Sep 18, 2007)

wow, and here I am trying to tune an aperiodic enclosure for an SLS 8" by ear thinking I can somehow get it to sound good lmao... with no eq'ing just getting it more of the punchy upper note impact that I think is missing. eh, sounds like I need to get me a woofer tester from PE and add/remove membrane to get it flat 1st then go from there with eq... well... gonna finish what I started playing with and see where it leaves me for now lol. 

I planned on doing ap for a while and never actually read up on it this much. figured on adding/removing membrane to tune but never realized why I was doing it. to get the imp curve flat so it see's similar power throughout bandwidth sounds like what I'm trying to do...


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## jbholsters (Jun 17, 2009)

Yes, you need to get the impedance curve flat. The PE woofer tester will work. You can also download some programs for free that will work via your PC. Some of the companies that sold AP kits back in the 90's included a network that went in line that corrected most of the equalization. But it is easily done with most head units and DSP's that are available today.


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## Hernan (Jul 9, 2006)

Could we have any benefit on using an AP enclosure at a door?
I think that the QTC will go up, and some energy should be absorbed by the membrane.
Using a low q midbass this does not look as a bad idea.

What I'm trying to get is a higher qtc and lessen the energy of the backwave going into the door.

Comments? Thanks!


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## narvarr (Jan 20, 2009)

Hernan said:


> Could we have any benefit on using an AP enclosure at a door?
> I think that the QTC will go up, and some energy should be absorbed by the membrane.
> Using a low q midbass this does not look as a bad idea.
> 
> ...


I'm in the same boat as you. I am looking to do the same thing with my doors as well with a pair of DLS RW6 subs for mid bass.


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