Sealing the trunk off? Need Help
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=42916
Printed Date: May 01, 2024 at 11:31 PM
Topic: Sealing the trunk off? Need Help
Posted By: ophidia31
Subject: Sealing the trunk off? Need Help
Date Posted: November 13, 2004 at 9:14 PM
I have a little dilema. I built my subwoofer to fire into the cabin of my car. It doent seem as loud as it should be. So I asked the one guy I know who has sort of the same setup. He says that what rear waves that get generated from the sub reflect off of the trunk and cause the destructive interference with the front wave. So in order to cancel that he said i needed the seal the trunk off from the cabin of the vehicle or to port the trunk so it all has somewhere to go. I did notice that when i open my trunk that it does get louder and more defined in the vehicle, even when the windows are open. So does anybody have any hints or tips on helping get rid of my problem? here is a link to my pictures of it so you know a little about what im talking about : https://www.cardomain.com/memberpage/430050/2
Replies:
Posted By: customsuburb
Date Posted: November 13, 2004 at 9:23 PM
It sounds like cancellation big time to me. Try putting that sub in a proper sealed box and see if it sounds better. Or, if you wanted to keep your fiberglass front you made you could just build a box behind it and you'd be done.
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Posted By: ophidia31
Date Posted: November 13, 2004 at 9:44 PM
the fiberglass front is just that. a front. i have the sub in a sealed enclosure attached to the rear of it and the sub pokes through. its in the proper size enclosure and that was a little bit of my first problem and thought that could have solved it. it helped a little but wasnt enough obviously. you said build a box behind it. do you mean to have an enclosure go around the sub enclosure? i was thinking something like that and packing it with a deadening material. or do you think i can just cover the sub enclosure in the deadening material instead. ive always had my stereos with the subs in the trunk. im new to having them this way. since my seats fold down in this car id figured i try soemthing new.
Posted By: Rushman
Date Posted: November 13, 2004 at 9:57 PM
Im pretty sure he means to completely seal the sub in its own enclosure. Maybe even somehow attaching it to the existing fiberglass work , nice job on the entire system by the way. I dont know if it will make any difference at all but I was going to suggest reversing the polarity just for a few moments to see if that made any difference. I dont think it should in an IB set up but its all I could think of rather than adding the extra enclosure. Keep us posted.
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99 F-one fitty
Pioneer Premier H/U
Alpine EQ
Kicker 1200 amp
4 Kicker comp 10s
6 kicker SS65.2 components
Posted By: ophidia31
Date Posted: November 13, 2004 at 10:14 PM
the sub is in an enclosure already and the enclosure is attached to the front fiberglass piece. so its not an IB setup. alot of people think that lol i can remove the enclosure from the fiberglass piece if i ever needed to. i tried reversing the polarity, both by physically switching the wires or by using the reverse phase option on my hu. but to no avail there wasnt a difference in the sound.
Posted By: stevdart
Date Posted: November 13, 2004 at 10:51 PM
No, switching the phase won't work in this case. The rear waves are travelling far enough back to the rear of the car, then reflecting toward the cabin to cause a noticeable 180 degree phase cancellation wave. The two waves (front and rear) are cancelling each other out. When you opened the trunk and found it to be louder, that proved it. The open trunk allowed the rear waves to escape the vehicle, so only the front waves arrived and were unimpeded. https://www.installer.com/tech/aiming.html identifies this problem. ------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: Poormanq45
Date Posted: November 13, 2004 at 10:56 PM
"I did notice that when i open my trunk that it does get louder and more defined in the vehicle, even when the windows are open."
The reason that it got louder is because you created what resembles an Infinite Baffle. Meaning the Air movement created by the front of the cone does not meet the Air Movement created by the rear of the cone. A few subs perform best in Infinite Baffles, or really large boxes.
I don't think that your problem is Phase cancellation. Trunks are usually irregular shapes (Not squares). This causes the sounds waves to Not "bounce" directly back at the Cone. For the sound waves to cancel each other out, they would have to be approximately 180 Degrees phase of each other. With the irregularities of a trunk, this does not usually occur.
Annyway... I would suggest that you better insulate the Cabin from the trunk space. This should prevent any, if there is any, cancelation from occuring
I think the problem is that you have an improperly sized "enclosure". To fix this, you could measure the entire volume of the trunk space
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Posted By: ophidia31
Date Posted: November 14, 2004 at 7:18 AM
stevdart wrote:
No, switching the phase won't work in this case. The rear waves are travelling far enough back to the rear of the car, then reflecting toward the cabin to cause a noticeable 180 degree phase cancellation wave. The two waves (front and rear) are cancelling each other out. When you opened the trunk and found it to be louder, that proved it. The open trunk allowed the rear waves to escape the vehicle, so only the front waves arrived and were unimpeded. https://www.installer.com/tech/aiming.html identifies this problem.
thanks for the link. so, this is what i got from it. since there is better response with the sub in the back of the trunk becuase the rear waves dont travel as far and dont end up being 180* out of phase. so, that being said if i built a wall behind the enclosure, sealing it off 95% from the rest of the trunk, it would more than likely react the same way that it would if the enclosure was farther back in the trunk? is that correct? my amp rack is going to be a wall right behind the enclosure to help with trunk space, so if what i asked was true i should be able to use this as part of the wall to seperate the enclosure from the rest of the trunk. since the back wave wont travel as far and hit off of something (wall/amp rack) before it gets to the rear of the trunk.
Posted By: stevdart
Date Posted: November 14, 2004 at 10:47 AM
I think you're on the right track, as that is what I was thinking as well.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: ophidia31
Date Posted: November 14, 2004 at 12:00 PM
stevdart wrote:
I think you're on the right track, as that is what I was thinking as well.
Ok cool. at least we're getting somewhere. lol and poormanq45, im going to dynamat the entire rear deck area and seal off any holes that i may see and and use some minumum expanding foam for the smaller ones that are hard to reach. that way was the one thing i was told to do first. since im finding these different ways ill do em both. anyone else have tips?
Posted By: uthinkuknoaudio
Date Posted: November 14, 2004 at 12:50 PM
"ditto" what stevdart said
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"I don't play games. I play Nakamichi and that for real yo" - Probably some japanese kid said this in the early 80's trying to sell stereo out of his trunk lol.
Posted By: ophidia31
Date Posted: November 15, 2004 at 4:02 PM
anybody else got ideas?
Posted By: Most Wanted
Date Posted: November 15, 2004 at 4:36 PM
what you need to do is Seal off the Front of the woofer box to the cabin. youll need some Great Stuff Sealent and divise a plan, Also use the rubber gloves TRUST me, Anytime working with great stuff, It does get messy, Its a red can at the hardware store. get the Box as close forward as you can and build it into the car as much as you can, what you want is the Woffers to fire directly into the cabin and seal them off from the trunk. What kind of car is this in??
Posted By: ophidia31
Date Posted: November 15, 2004 at 6:52 PM
That great stuff is well, great. used it on my old car to fill in some big areas. it is indeed quite messy and sticks to everything lol i have an 01 buick regal gs. dont have any rear speakers and i already sealed off those openings. there is one left that i need to seal where the 3rd brake light is. other than that it should be all the little holes and things. sealing the front from the back was the first thing i was going to try and see how that works out for me. does it need to be entirely sealed? if i miss a couple small holes will it make a difference? all of the major ones are going to be sealed up. just curious if i miss a couple little ones if that make a difference?
Posted By: Rushman
Date Posted: November 15, 2004 at 6:55 PM
I dont think tiny pin holes or bolt holes will make an audable difference to your ear.
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99 F-one fitty
Pioneer Premier H/U
Alpine EQ
Kicker 1200 amp
4 Kicker comp 10s
6 kicker SS65.2 components
Posted By: Most Wanted
Date Posted: November 15, 2004 at 10:58 PM
little holes will be fine, You said you were covering the rear in dynamat so that will cover the little holes. The sides, top and bottom are the biggest concerns, you need a good tight seal, that will cure all your issues. even with a box i still seal them into the cabin area when firing forward.
Posted By: ophidia31
Date Posted: November 17, 2004 at 4:40 PM
Thanks for the help guys. took the car apart and dynamated up everything that i saw could have been a problem. was a noticeable difference and stopped about 90% of the cancellation and is noticeably louder. had to turn my gains down on the amp and the subwoofer control on the deck. it still gets a little louder when the trunk is open but ill have to deal with it. its not a drastic change like before.
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