DiyMobileAudio.com Car Stereo Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
45 Posts
Discussion Starter #1 (Edited)
Edit...
1. when mentioning I lost 10db moving the ported box in trunk. I had it 6” from the rear facing the rear first, wanted trunk space back so pushed it towards the front of the car to give me about 2’ of trunk space. That made me lose 10db.

I would of course build a panel to the face of the box to make it look nice and flush

2. If taking my ported box facing into the cabin. Why is it so important to seal the trunk. Even tiny holes. I have yet to find real proof that it matters. People say to stop waves canceling but lest be honest here, there is not going to be much bass waves coming thru some tiny holes that are probably behind interior trim. And what tiny amount might come thru the said holes is going to be so small it’s highly unlikely it could have impact on the front waves where the subs and port face.
I would love to hear and see real proof and not just because it’s what people have read in forums. If it was an infinite baffle setup then of course it makes sense. But I think as time passes people have mixed things up and assumed it mattered for front facing ported boxes.
When talking small holes what is y’all’s definition of small 1” or less or?

I’ve been thinking it would be nice to have my trunk space back. If i was to make a wall or seal off the trunk with subs and port facing into the cabin would I lose much spl vs being in a ported box rear facing as close to the rear of car as possible? I took some measurements with the box facing to the rear about 2’ from the rear (so I could have some trunk space) and lost about 10db So I moved it back It would be a lot if work to seal the trunk only to lose spl. Would I need more power to maintain the spl? I’m guessing the bass would be more defined and SQ oriented with a sealed trunk? Or am I wrong. I currently have a B2 audio 2500.1 pushing 2 skar evl 12s ported.
 

·
Premium Member
Joined
·
676 Posts
I’ve been thinking it would be nice to have my trunk space back. If i was to make a wall or seal off the trunk with subs and port facing into the cabin would I lose much spl...
First make sure your not confusing the SPL for trunk resonance which can make the rear facing bass to seem to sound louder.

Next it will depend on the vehicle in most cases for forward firing setups and what kind of rear seat setup/backing the vehicle has. I’ve seen it advised on other threads that it is important that the wall match the angle of the rear seats as to not create a triangle dead space behind the rear seats.

Also note that sealing off the trunk involves more than just the wall. You’ll have to seal off the rear deck too! Sedans have a lot of small nooks and crannies designed to let airflow for cabin pressure relief when closing doors/trunk.

Lastly you may have to play with the sub phase a little bit to get it sounding spot on.

It’s definitely easier to have them face rearward.
 

·
Registered
Joined
·
45 Posts
Discussion Starter #3
So a lot of work and possibility of losing output? One thing I’ve read but no one really says (They’ve just read it and repeating it). Why do all the small holes reall matter. Maybe I’m confusing spl with the dB of a system. Maybe they the same. But how can some small holes leading into the trunk make any difference? The trunk isn’t the subwoofer box is it? I
would just like to turn my box around then add a face/wall to seal it off. And I would have it the exact same angle as my rear seat and the box port would be right where the ski hole is. If I anyone knows if it’s a definite loss of bass might not be worth it.
Is there other downfalls, like hearing the driver distortion?
 

·
Premium Member
Joined
·
676 Posts
I have a forward firing setup with sealed subs. Took a while to get it sounding right. The more I sealed off the cabin from the trunk the better it got. My personal experience. When I say seal, I mean butyl rope gooped up into the tiny crevices at corners of rear deck, butyl rope along the front of the wall where it seals to the cabin, MDF closing off larger wholes of the rear deck, layer of CLD on the back of the sub wall where it seal to the trunk, layers of CLD sealing rear deck, layers of Gorilla waterproof patch and seal over the CLD, and then MLV lining the entire trunk (including the lid).

dB, SPL , sub bass... its pressure from sound waves. Holes equal pressure leaks.

The main gist is to separate the front wave from the back wave in the rest of the trunk. Look into IB setups that use the trunk as the enclosure and you’ll get more of an idea. But the more the back-wave interacts with the front wave, you have higher chances/incidence of possible cancelations occurring.

The idea of the box rear facing close to the back of the trunk puts the forward facing wave in closer phase relationship with the back wave emanating from the enclosure. So that both waves arrive at the listener in closer phase with each other rather than canceling each other.

I feel no one really says because no one can guarantee you wont lose dB’s for all the hard work. It’s kind of a try it out and see.

Others with more experience can chime in. But my 2 cents is anything attempting to get more trunk space usually compromises something. That maybe lower SPL or same SPL but heck of a lot more labor and time.
 

·
Registered
Joined
·
45 Posts
Discussion Starter #5
I’ve researched IB a lot when building my home theater. I understand that concept. I just don’t understand how small holes can make a difference when I’m using a box and not doing IB.. Are you talking like Fractions of a dB? Or something you immediately could hear? And the sealing is to completely seal the front of the subs from the back?
 

·
Registered
Joined
·
223 Posts
You don’t have to worry about small holes. Moving the box forward and sealing it off will now shorten the length of the cabin. You will notice the peak frequency is different. You may lose low frequencies and gain higher. Test it out and see with something temporary.
 

·
Premium Member
Joined
·
676 Posts
I’ve researched IB a lot when building my home theater. I understand that concept. I just don’t understand how small holes can make a difference when I’m using a box and not doing IB.. Are you talking like Fractions of a dB? Or something you immediately could hear? And the sealing is to completely seal the front of the subs from the back?
The subs are in a sealed enclosure. The enclosure is then sealed to the cabin off from the trunk.

Maybe back wave is the wrong word? I’m referring the the incident wave emanating from which ever way the cone is facing and any possible reflected waves that can interact with the incident wave. If forward firing you want to keep those reflected waves away from the forward firing incident wave to the best of your ability. This usually entails a baffle to separate. That baffle should include the wall and the rear deck to fully separate. Holes in a baffle can compromise the baffle’s efficacy. All the small holes can end up adding up to a larger single hole.

Unfortunately I didn’t take measurements. But definitely not fractions of a dB.

Not trying to be an authority, I’m just one experience amidst a site of many. See what others chime in:thumbsup:
 

·
Registered
Joined
·
45 Posts
Discussion Starter #8
Edited first post
 

·
Registered
Joined
·
533 Posts
But the more the back-wave interacts with the front wave, you have higher chances/incidence of possible cancelations occurring.
This. Even if u have a box rather than an IB set up, some of the sound waves from the sub are going to go into the trunk and reflect back. Becuz these reflected waves have traveled a longer distance, they will be out of phase w/ the waves that went forward. This will cause destructive interference, and that in turn will reduce the cleanliness and dBs of the bass.

How much is debatable and probably depends a lot on the car. But the more u seal off the trunk from the passenger cabin, the more u reduce this effect. See this website for more info about box position and reflected waves: https://www.installer.com/tech/index.php?page=aiming

Moving the box forward and sealing it off will now shorten the length of the cabin. You will notice the peak frequency is different. You may lose low frequencies and gain higher.
This will also have an effect on your bass. How much depends primarily on the depth of the trunk compared to the passenger cabin. The deeper the trunk and the shorter the cabin, the more noticeable the effect will become.

I’ve seen it advised on other threads that it is important that the wall match the angle of the rear seats as to not create a triangle dead space behind the rear seats.
Another good point... I speak from experience that u do not want to leave that dead space in there! It forms a resonance chamber that typically resonates at 150-300Hz. So it will really boost the midbass coming from the subs, which sounds horrible.
 
1 - 9 of 9 Posts
Top