Vented Enclosures

[evil0ne]

I'm curious. What's it like to have a subwoofer thumping right in front of you? I get to drive the boat and while I'm willing to play along with the "need" to have tunes while riding, I don't want to be beaten to death by a speaker. I swore off of that idea after being stage left in front of the speaker stand at a Robin Trower concert ("Bridge of Sighs") in San Bernadino. There are still some Stratocaster notes that in my right ear just make my head ring.

The sub really isn't for the rider it's for the passengers in the boat. The sub being right in front of you isn't nearly as annoying as WetSounds blasting your ears in the back of the boat. The low frequency versus high frequency makes it much less annoying IMO.

[philwsailz]

I'm curious. What's it like to have a subwoofer thumping right in front of you? I get to drive the boat and while I'm willing to play along with the "need" to have tunes while riding, I don't want to be beaten to death by a speaker. I swore off of that idea after being stage left in front of the speaker stand at a Robin Trower concert ("Bridge of Sighs") in San Bernadino. There are still some Stratocaster notes that in my right ear just make my head ring.

There is a difference when you are in a boat; certainly when compared with a car. In a car it is realy easy to get so much bass going that you are literally presurizing the interior. That can put a lot of pressure on your eardrums.

In a boat, it is different, as you are not in a confined space. The low frequencies can seem as loud, but they are not as annoying, since you are in open air...

There are things that can be WAY more annoying than a subwoofer in a boat:

a stereo that is just flat WAY too loud
a stereo that is badly out of tune, i.e. set up wrong
a stereo that has either really bad or messed up speakers
a stereo that is turned so far up that everything is clipping
A stereo that has its EQ messed up maxed out. Treble is the worst; it can turn sound into a knife.

When a sub is set up right, it will just thump along, kind of give you a little massage, and help fill out the rest of the stereo.

[philwsailz]

The sub really isn't for the rider it's for the passengers in the boat. The sub being right in front of you isn't nearly as annoying as WetSounds blasting your ears in the back of the boat. The low frequency versus high frequency makes it much less annoying IMO.

slow to reply, I am.... (in my best yoda speak)

Evil is 100% correct. I agree completely!

[tige']

I am in the process of installing my first sub and learning as I go.

I am installing it at the drivers feet in the "kick board". There is an area that has three sides enclosed - the floor of the boat and then a closet bottom and side.

I made a front and the other side. The total volume is only about (guessing here, didn't actually measure anything because it is an odd shape) 2 cu ft (or less).

Listening to the stereo it sounded OK - but I just pulled the RCA inputs to the tower and in-boat amps speakers so I could just listen to the sub itself and WOW - it doesn't sound good at all!!

The sub is a Marine Alpine 10" Type R free air sub. I wasn't too concerned with making an air tight box becasue it was a free air sub, I figured some enclosure would be better than nothing.

But as Phil states it weezes, vibrates, hisses and rattles.

So here is my question - Am I better off to just add a port so the air has somewhere else to go, hopefully minimizes the unwanted noise or to redo everything and make it an airtight box?

To redo everything I would basically have to create a box that slides into the space I have rather than trying to make my box out of what was there (which I am sure now looking back was a mistake).

But I am also concerned that the box will still rattle the closet floor and the wall that the closet door is on making the hardware rattle anyway...

[chpthril]

I am in the process of installing my first sub and learning as I go.

I am installing it at the drivers feet in the "kick board". There is an area that has three sides enclosed - the floor of the boat and then a closet bottom and side.

I made a front and the other side. The total volume is only about (guessing here, didn't actually measure anything because it is an odd shape) 2 cu ft (or less).

Listening to the stereo it sounded OK - but I just pulled the RCA inputs to the tower and in-boat amps speakers so I could just listen to the sub itself and WOW - it doesn't sound good at all!!

The sub is a Marine Alpine 10" Type R free air sub. I wasn't too concerned with making an air tight box because it was a free air sub, I figured some enclosure would be better than nothing.

But as Phil states it weezes, vibrates, hisses and rattles.

So here is my question - Am I better off to just add a port so the air has somewhere else to go, hopefully minimizes the unwanted noise or to redo everything and make it an airtight box?

To redo everything I would basically have to create a box that slides into the space I have rather than trying to make my box out of what was there (which I am sure now looking back was a mistake).

But I am also concerned that the box will still rattle the closet floor and the wall that the closet door is on making the hardware rattle anyway...

These ??? may have been asked/answered in another thread so sorry if so. What boat do you have? Pics of your sub set up may be a bib help.

What amp do you have driving the sub, and how is it set up and wired ( I believe the Alpine is a 4ohm SVC) i.e, gain, x-over's, what RCA outputs from the H/U where used, etc.

An infinite baffle sub can sound great when driven properly and the amp is set right as long as you have a solid baffle-board to separate the front and rear of the sub. More info will help give us an idea of what needs tweaking.

[philwsailz]

But as Phil states it weezes, vibrates, hisses and rattles.

So here is my question - Am I better off to just add a port so the air has somewhere else to go, hopefully minimizes the unwanted noise or to redo everything and make it an airtight box?

To redo everything I would basically have to create a box that slides into the space I have rather than trying to make my box out of what was there (which I am sure now looking back was a mistake).

But I am also concerned that the box will still rattle the closet floor and the wall that the closet door is on making the hardware rattle anyway...

Okay, real quick, a little edumacation...

A ported box is louder due to several things, one of which is that there is air moving in and out of the box at the port, and that air is making sound. The air moves in and out just like the woofer and this rapid in and out movement is what makes sound pressure. The weird thing to grasp is that when the woofer is moving out, SO IS THE AIR IN THE PORT. The air moves IN PHASE with the woofer over the tuning range of the enclosure.
Picture a spring with a weight on the end. you are holding the other end of the spring and shaking it. When you find that right speed to shake the spring, you will find a frequency where when you move your hand down, the weight is coming up and when you move your hand up the weight goes down. This perfect situation shows that spring and weight system at resonance.
Air is compressible, and the tuning of the box allows the air inside to act like that spring. the woofer is the motive force for the spring, (your had was the motive force in the above analogy) and the air in the port is the weight. When we tune a ported box, we use math and measurement to dial in that specific resonant tuning.As a result we set up a system where when the woofer is moving out and making a positive pressure wave, so is the air in the port. Conversely, when the woofer is moving inwards, so is the air in the port. From this you can begin to realize that a ported box can and will have higher internal pressures inside when compared to a similar sealed box!!!!

We do not install ports to "let the air out"

Okay, that was a not so quick edumacation.






To your question...

No, adding a port to make the noise go away will not work. The probability is that you will make MORE noise, and as a result make even LESS bass...

It is possible sometimes to do what you describe and use other parts of the boat to help define the enclosure but it rarely works. You do not know how stiff that other part is, how resistent to flexing it is, etc. Even if you get it sealed, the thing will flex and give too much most of the time; it will not sound good. Yes, you are going to be way better served to build a complete box that totally contains the air and the woofer. Make sure your construction is air-tight, caulk the backsides of the joints, etc. You need to be air-tight in your construction for sealed OR ported boxses, for the reasoning I shared above.

Adding bass to a boat will always show you that you have rattles of hardware, hinges, latches etc. You will need to tighten those things, pad them, or whatever to prevent them fro rattling, or to prevent the noise. That is the nature of the beast...

Write back and let us know more. As Mike said, pictures are good.

Sorry for the long note, but I find this stuff fascinating. I hope you do too!

[rushin]

Are there any good pre-made enclosures out there? I have the tools and ability to make one, but I just feal like being lazy.

[philwsailz]

Go look at this one.

http://www.kicker.com/skm10


I thnk JL has started offering a marine sub enclosure this year, but in general, there are very few true marine subwoofer enclosures out there that you can buy pre-made.

The Kicker SKM10 is sealed, so you want to get some power to it, but when it is dialed in it hammers. Plus the thing is totally waterproof. You can throw it in the lake and not worry about damaging it or sinking it...

[tige']

Phil,

The analogy of the spring helps. I am a Mechanical Engineer so that makes sense to me, it's all the electronic stuff that leaves me scratching my head.

Resonance and harmonic frequencies are the same concepts when referring to sound as to mechanical objects but a little different to grasp (at least for me!).

Anyway, a little more info about my project as you and Mike requested.

I have an Alpine 10" marine sub with a Cadence SQA-1 amp. I have tried reversing the speaker wires but didn't notice much difference with the wiring out of phase. And, guess I probably wouldn't until I get the sub enclosure working better??

The HU is a Clarion M475. I am using the sub RCA outputs with the NF volume maxed out at 6 (and have tried other settings). I have also played with the amp settings, but didn't notice much difference especially in the crossover frequency.

I included pics of the sub location before and after the installation. In the before picture you can see the box section of the closet (behind the fuse box). To the far left you can see the closet door. The sub location is triangular shaped due to the slanted floor.

As far as looks go, I am happy with how it turned out. I was able to cut the carpet from the bottom of the closet box and pull it down to cover the front of the speaker enclosure.

But the bottom panel of the closet knocks, the closet door rattles (but not too bad) and other noises can be heard throughout the area. I know that my enclosure is not even close to be air tight - back to "Oh, it is a free-air sub. It will be fine." syndrome.

The biggest thing that I noticed (and this is hard to explain) is that the sound from the sub is not a woof woof type sound. But more of a clap, a quick distinctive clipping noise. Like hitting a coffee can with a drum stick (but that is exaggerated). And when it really gets ask to drive some low end it will distort. I am new to subs but familiar with how home speakers should sound, I worked in the home audio/video dept at Sears for about 7 years in my younger years - long before subs were popular. And the way this is now, it doesn't deliver the sound I would expect from a regular 10" home speaker woofer.

When I have the other speakers playing it doesn't sound bad. But when you turn off the in-boats and towers so you can just hear the sub there is definitely a lot of room for improvement.

[chpthril]

Tige',

I'm gonna say that maybe your box is too small, here is a site that has a calculator for odd shaped boxes such as yours www.the12volt.com :http://www.the12volt.com/caraudio/boxcalcs.asp#rec

The sub and amp look like a good match, sub is rated at 300rms/900pk and is a 4ohm SVC, the amp puts out 500W's rms @ 4ohm. Couldn't find the manual for SQA-1, so I can only take a stab at the settings. Gain - there is a great gain setting tutorial floating around here, should pop up with a search. Bass Boost - set to zero. Cross-over Switch (Hi-Low-Off/All pass) - set to Low if it has this switch, but being a mono amp, it may not and will be low-pass only. Cross-over Hz's - set at 80Hz.

A leaking box is not the same a vented box, this leaking may be contributing to the poor sound. For that sub a box it not needed, but can make a sub sound better. All that is needed with that sub is a wall to mount it too that will separate the front of the sub from the back. I'm kinda feeling that you may be redoing what you got to some degree

[tige']

Mike, you are correct about the box. I forgot to mention that the manual specs out a net 4.85 cu ft sealed box - even though it is a free air sub?? I guess that is just the recommend size if you do enclose it. It also seems really big....My box is roughly 2 cu ft.

I would have to get creative to get a box that big in there, plus (and more important) I don't want to give up that much storage space for it.

The sub amp has input gain, crossover settings and a Bass EQ control knob. As well as a, low pass or flat switch. There is also a remote subwoofer control knob (that only works in low pass mode).

I have it in low pass all the time but have played around with all the other settings. It just depends on what I am listening to where it sounds the best. But I am pretty close to what you are recommending.

I did originally try it with just the front panel (having it completely open on the side you can't see in the pictures) and it didn't really sound any different. BUT, I never did try it with just the sub.....

[philwsailz]

Hmmm... the description of the sound, like a stick hitting a coffee can..... THAT description, and what I hear in my head makes me think that while the box can be done a lot better, there might be another problem.

The box and the carpet look SUPER by the way...

Hmmm...

A first recommendation I might have would be to find a known good sub enclusre, (borrow one?) and connect it to your amp. I think you owe it to yourself to make sure your electronics are functioning properly...

If that works out fine, then I would remove YOUR woofer from the enclosure and make sure it is mvoing in and out smoothly and freely. Some of your description of the sound kind of reminds me of a stuck or rubbing voice coil. Hook it up to the amp at low volume and listen closely; get your ear real close so that you are only hearing the sound from the front of the woofer. Make sure it sounds nice and smooth without rubbing or creaking or other noises.

If we can get all that going, radio, amp and sub without the box, then we can work on dialing in a proper box for ya.

Make sense? Lets make sure the electrcal components are working properly; my gut says otherwise for some reason...

[tige']

Phil,

You read my mind. My plan was to do exactly that - borrow a sub and see how it sounds. Then I have some scrap plywood laying around, I might throw together a temporary bigger, air tight box and see how my sub sounds in that.

I know plywood isn't the greatest..but I am curious to see what this might sound like in a bigger air tight box.

If that works out, I will try to find some of the 13 ply you recommend and make an air tight box the size I need.

I just hope I can get the carpet back off where I just glued it

[tige']

Phil,

I moved the questions I had for you about my particular install to another thread (if anyone is interested in what my situation was you can do a search on the thread title "sub woes").

But, where I am at now is that I decided to built a ported box just to compare before I finalize the install of my sealed box. Who knows, I may be installing a ported box

One of things that I am trying to figure out, which would be a great addition to this thread, is the location of the port.

I am interested in learning about both the location of the port in the enclosure itself (is the front better than the side? Above or below the speaker? If the side is it better, is it better in front or behind the magnet) and how the port is affected by it's surroundings.

Could you share your expertise on this?

Thanks

[philwsailz]

Oh wow...

Location is not as critical as some would have you believe. I remember chuckling about a competitor's on-line comparison of their product vs. the product I had designed for the company I worked for. They rationalized that since the port opening was not on the woofer baffle wall, but on an adjacent wall, (90 degrees away) that the sound from the port was 90 degress out of phase; absolutely preposterous...


SO... Without making heads spin:

INSIDE THE ENCLOSURE:
port location does not matter; just try not to end the inside terminus of the port right next to and aiming at the backside of the woofer cone. This to prevent any mechanical noises from travelling down the port to your ear.
One must keep the interior port end at least a diameter away from an opposed wall. Put another way, if you have a 4" diameter round port, placing the end of it 1" away from a wall or panel causes a restriction which affects air flow, and messes with tuning. If you have a 4" port, keep the end of the port at least 4" away from a wall.

OUTSIDE TERMINATION
It does not matter from an acoustical standpoint, with the exception of a few very esoteric rationale which really do not count for our purposes. There is no mathematically-defined perfect port exit, but it does sometimes make a difference on listening. For a boat, it is easiest and usually loudest for the port to be on the same face as the woofer, or on an adjacent wall, but not exiting out the back. There is no bad location however.

Way more important is the desire to make the port have as much area as possible. I think I have already pointed to that above, but quickly:
* small diameter ports an have shorter tube length for your desired tuning frequency, but as a result have very high air velocities which can cause turbulence and make "chuffing" and other undesirable noise.
* large diamemter ports have long tube lengths for the same desired tuning frequency, but have very low air velocities for the same volume. This lets the port make more music and less noise.
As a result the enclosure with teh larger diameter, longer-length port will play louder and have less distortion that the small-port box.