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cab13367
01-03-2010, 12:48 PM
Okay, time for another one of my dumb questions. My Kicker ZX700.5 has a bass boost control knob on the amp and a remote bass level control knob for the sub channel (channel 5). The manual says that the bass boost control knob gives increased output (o-18db) at 40 Hz. So increasing this knob increases the volume of sound just at 40Hz? Or 40 Hz and below? So why would I want to turn up just this part of the frequency/frequency range?

I also have a remote bass level control knob. Is this a separate volume control knob for channel 5 and is different than either the bass boost control knob and the input level (gain) knob on the amp?

Finally, how do I set the gain on channel 5 - should I have both the bass boost control knob and the remote bass level control knob at zero when I set the gain? If not, where should I have them set when I set the gain?

Thanks,

Al

mmandley
01-03-2010, 01:07 PM
The separate boost knob, the one with the phone line looking cord is really just a Volume control. It has no effect on the bass frequency.

Its used so that if you have your Gains cranked up for the high volume bass hit, then at low volume you will have way to much bass, or say if you get a heavy bass song playing and its just too much bass, you can turn only the sub down.

When you visited thats the knob i have on my dash and can turn down the sub but still keep the rest of the amp cranked up.

As for the dials on the sub, you will have 3 seperate sets.

Channel 1,2 channel 3,4 and lastly channel 5.

Channel 5 is at the top by its self and has the boost dial, frequency dial and Gain dial.

Set the frequency as you normally would, you want it set so when the bass if kicking out you cant tell its under the dash. You want your bass set so its very non directional to your ears.

Setting the boost is more like that extra umph to the amp, i keep mine right around 3/4 its the same as a bass dial on your stereo boosting your overal bass frequencies by + what ever.

The gain is just that, a gain and thats the one you have to tune so when your at 80% max volume you arnt over driving your sub. I had mine set to like 75% i think. My system still needs to be dialed in now with that new sub i got.

Hope it helps and makes sense for you AL

On another note im going to work on that stereo Tech tune with Brian at Exile for Feb i think. Portland Boat show is coming up in a couple weeks, then the Seattle show so i figure he will be busy. < Plus gives me more time to get all my new gear installed proper. >

philwsailz
01-04-2010, 10:21 AM
Good morning, and Happy New Yrear!

mmandley is right, and his description is good. The remote knob you can mount at the helm provides control over the volume level of the subwoofer and nothing more. His example of how it can be used is spot on too!

The bass boost control at the amp adjusts the amount of boost, (centered at 40 Hz) that the amp adds to the subwoofer. this is like a graphic equalizer, only it has just one slider, right at 40 Hz. When you turn it up, you add a "hump" to the sub-amp's frequency response, right at 40 Hz.

Be careful with the bass boost knob; the 40 Hz boosting one at the amp. When properly used, the bass boost knob is only there to correct for shortcomings of the total stereo system's low-end response. A well designed system will sound best with bass boost barely turned on, or even off.

Here is a classic example:
Say a guy, (we'll call him Newby Norm) has a woofer mounted free-air in the footwell wall area of the driver's helm seat, (yeah, I know, driver's seat and helm are redundant! :D). The wall provides a barrier between the storage area in the bow rider section and the feet of the driver. The wall the woofer is mounted to is thick, solid, and rigid; that would be a good panel to mount a woofer to. BUT... this wall does not totally seal off the forward storage area... The wall does not go all the way up to the underside of the dash, but stops short. In this situation, the sound pressure coming off the back of the woofer can, (and will) go over the top of the footwell wall mix with the sound coming off the face of the woofer. The sounds have same or similar amplitude, but are largely out-of-phase and therefore cancel each other out. The result is little or no bass.

In this instance, Newby Norm wants more bass, so he turns up the bass boost. Problem is, he is turning up the 40 Hz frequency for both sides of the woofer, and even though the amp is working harder, and the woofer is moving A LOT more, there is no more bass output; the sounds from both sides of the woofer are still mixing and cancelling out. At the same time, the woofer is moving at or near its mechanical limit and is prone to failure due to excessive excursion, and the amp is working way harder than it should have to, moving the woofer so far in and out... the amp will get pretty darned warm in this situation, and if it is at or beyond its ragged edge, could fail for its own reasons...

The thing Newby Norm needs to do first is examine his stereo system for problems. Had he identified the problem with the big air gap at the top of the footwell wall he could have fixed it first. Sealing off that wall would provide a huge increase in low frequency performance... The bass would have been louder and better without touching the bass boost knob...

This is but one very simple example and there are many other examples that Brian, David, myself and/or others could go into. The point I am trying to make is this: turning up the bass boost to make up for poor low-frequency performance should be done AFTER you consider all the possible acoustical and mechanical reasons for the lack of bass. Is your free-air installation correct? Is the free-air mounting wall completely sealed between both sides? Is your woofer enclosure the proper size? Is it leaking? If you are using a ported box is it tuned too high? Too low? Did ytou accidentally wire your dual voice coil woofer so that the coils are out-of-phase?

Sorry for going off on a tangent of sorts, but this seemed a good time to go into a little discussion on the bass boost knob. Use your bass boost with care, and if you have it turned way up, consider looking into the reasons why you have it turned up so much. Your system will last longer and run cooler with as little bass boost as possible.

good luck!

Phil
Kicker

EarmarkMarine
01-04-2010, 01:36 PM
cab,

If you're looking for more sub output, I'm not sure that the Bass Boost, as a form of equalization, is the best answer.

Unlike an enclosed vehicle cabin, an open boat environment makes it very difficult to produce 40 Hz at any real amplitude. Your sub is already rolling off at a significant rate at this low frequency which is to say that its certainly functioning with far less efficiency as compared to a higher octave. So at 40 Hz, 3 dB of amplifier output will produce much less than 3 dB of acoustic output. So we're pushing the train uphill.

As compared to one octave higher there's not a high percentage of music fundamentals at 40 Hz. However, pressing your amplifier over a narrow bandwidth, particularly at the bottom octave is extremely taxing. Its easy to premature exhaust your amplifier this way with very little output gain.

If you're looking for more output while maintaining good tonal construction and without exposing signs of strain, then you might try abandoning the bass EQ feature in favor of other tuning techniques.

Try raising the crossover frequency to slightly above 100 Hz which has an immediate and positive impact on output. The idea is to increase gain over several octaves versus a narrow spike and to increase gain over a bandwidth which more efficient to produce in a boat.

Less gain at 40 Hz usually translates to more than that in offsetting positive gain in the one to two higher octaves, once correctly tuned.

In vehicles we have the benefit of 'cabin gain' and in vehicles we try and avoid the vehicle's natural extra midbass response and we try and keep the woofer separated from lower male vocals. But different priorities apply in a boat.

So after a little experimentation with a broader bandwidth and gain, return to your woofer/enclosure relationship and make sure that doesn't require some additional attention.

While I'm being a little more direct than Phil and Phil is using a different example, I believe we're on the same page relating to concerns over a bass boost in a boat and especially when the woofer/enclosure relationship may be less than optimum.

David
Earmark Marine

cab13367
01-04-2010, 07:22 PM
Phil, David,

Thanks for taking the time to reply - your comments are very helpful. I already have the crossover set at around 120 Hz - should I try lowering it to 100?. I think the problem is with my enclosure as the footbox is not completely sealed - it is open to the ski locker on the port side and is open to the under floor cable chase on the aft end. Plus there's a hole on top where all the cables running thru the foot box exit. This footbox is very difficult to seal and I don't want to go thru the trouble of cutting out the footbox and building a custom enclosure. Is there a sub that would work better for this application than the 10" Polk/Momo MM2104 that I am currently using? Do u think I need more power than the 210w that the zx700.5 is putting out?

What about the subwoofer level control on the head unit? It goes from -15 to +15. I currently have this set to 0. Can I turn this up to get more volume? Is this just another volume control like the remote bass knob?

Thx.

Al

philwsailz
01-05-2010, 11:10 AM
I think you may have largely identified your primary issues in your description above... You have a lot of "leaks" as you well know. You may be limited in the amount of bass you can get in your current configuration. I think you may have a woofer that is less than ideal for the application as well...

I think the head unit bass control, (+and -15) will put you in the same place as I described above... You make the woofer move more, you make the amp work harder, and all you do is increase the sound pressure on both sides of the woofer. Without isolating the two sides of the woofer, the opposite pressures will mix and cancel.

Think of it mathematically: If the woofer is moving a tiny amount, you might make +1 pressure units on the front of the woofer and at the same time make -1 units of pressure on the back. When you allow the front wave to mix with the back wave you in effect add them together, and you get the following equation: 1+(-1)=0. Now turn the bass boost in the head unit all the way up. The woofer moves more, a lot more, so much in fact that is is producing +10 units of pressure on the front of the woofer! But is is also making -10 units of pressure on the back side. With an imperfect free-air baffle, or with lots of "leaks" tha allow mixing between the front and back of the woofer, the mathematical result is the same, 10+(-10) still equals zero. Does that make it clearer?

There is no way to equalize an out-of-phase condition

There are a few tricks you can try. While they are not purist and not totally correct, not correct the way David or I would do it if it were our boats, ( I suspect we both would be building enclosures) they can help nonetheless...

* Get some closed cell foam, stiff stuff like really firm upholstery foam and try stuffing it into the holes and leaks you identified. While this is a poor fix, it is an easy fix and it is cheap. It will not eliminate the problem of the leaks/holes but it can reduce it.

* Try swapping the positive and negative wires on the back of the woofer. At the 120 Hz crossover frequency you are currently set at, you may be acoustically out-of-phase with your full-range coax speakers. You might find that one way or the other gives you more bass, or the psycho-acoustic illusion of more bass.

* If the back of the subwoofer shares space with a full-range coax, consider using some sort of cup, bowl, bucket, or other rigid "enclosure" behind the coaxial speaker. This will prevent to coax speaker's mid from being modulated by the pressure waves coming from the back of the subwoofer. this can clean up the sound, and can reduce the chance of out-of-phase energy being mixed.

I am not super-familiar with that Polk sub but quick research tells me it is a sub designed for small sealed enclosures. Typically, this type of sub has a fairly low resonance, a low "Q" and a pretty large Vas... I know, blah blah blah... Engineering talk...
What this tells me, ( I still have not found the Thiele-Small paramters to say for sure) is that you will be happier with that woofer if you put it in an enclosure, and if I am guessing, probably a sealed with a volume of between .65 and .85 cubic feet... that is pretty small as sub enclousures go, so you can likely do it without taking up a lot of space.

Beyond that, if you don't want to mess with a box, you might want to look into a true free-air sub; one that is designed for the task... Polk has them, so does Kicker, Wetsounds, and others. David will be real good at describing the relative strengths and differences of the multiple brand's offerings; I am slightly biased, so I prefer to keep my comments with regard to brand preference out of the discussion... :D

Finally, and I know it sounds "hokey" but even if you end up building a box, think about the points I made above, particularly regarding the sub's phase. Depending on the woofer's location, even though it is elecrtrically in-phase, it might not be acoustically. Flipping the wires for polarity is an easy thing to try, and it will be interesting to hear the difference!

Good Luck!

Phil
Kicker

cab13367
01-05-2010, 11:49 AM
Phil,

Thanks for the additional ideas. I've posted a pic below so you can see what the foot box looks like. It's a box as opposed to just a vertical panel. I understand what you are saying about the front wave mixing with the back wave, but the only place that the back wave is leaking out is thru the hole on the top right of the box as you can see in the pic. The rest of it is leaking into the ski locker and into the underfloor chase which I don't think leaks out above the floor. As an FYI, I had a two channel amp that I was running bridged (400wx1) before the Kicker and I had plenty of bass but it was boomy. When I removed the amp, I noticed that I had the bass boost on (+18 db - it was either on or off and I had it on) so maybe that's why it sounded boomy. Mike Mandley from this forum had the same issue and he stuffed his footbox with a loosely folded painter's drop cloth and he said that made the bass tighter so I tried the same thing. The bass does sound tighter now than before but it doesn't have as much volume. Maybe the drop cloth is suffocating the sub.

Part of the reason I am opposed to building an enclosure is that I don't want to suck up the footwell space (and I like the clean look of where it's currently installed) so one option is to go with the Kicker SKM10 marine sub box and woofer. It's got a shallow, but wide box that I think will fit down there without giving up a lot of room and it doesn't involve a lot of cutting. Do you think that will give me the bass I am looking for?

The other easy fix seems to be to buy the right free air sub for the current footbox situation. I think David said JL Audio made the best free air subs by a wide margin so I am hoping he will make a recommendation as to which JL sub I should get.

The third option would be to go thru the effort of completely sealing the footbox properly using a combination of seaboard panels and self expanding foam out of a can to seal the under floor chase and the hole on top.

There is no coaxial speaker on the other side of the footbox.

I will also try swapping the terminals on the sub (actually, I think my head unit has a sub phase switch so I can switch it there).

Thanks,

Al

http://i250.photobucket.com/albums/gg276/cab13367/IMG_1000.jpg

EarmarkMarine
01-05-2010, 12:36 PM
cab,

A bass boost is the last method to use in your particular situation where you've got an acoustic suspension woofer loaded into a free-air application that isn't even isolated front to rear. In fact, a bass boost will add to the problem rather than providing a solution. For now leave your crossover as is. And, take Phil's suggestion on experimenting with the phase.

I see two different paths you could follow to improve your lows given what you have.

If you're absolutely going to stay with your existing mounting configuration, instead of an enclosure, then you've got to convert to a real free-air sub. Sony, Kenwood, Clarion, Alpine, JL Audio and a few others make true free-air subs. JL Audio might make the best free-air sub but 200 watts is a little light for that model. The Alpine would do better with 200 watts. But your MOMO will not sound much better regardless of the steps you take as it is currently being used. Again, Phil is accurate in his assesment of the MOMO's parameters.

As applied to free-air, the distant opening on the port side is a non-issue since the pathlength is so long. However, you would want to seal up the hole atop the hump which is very close to the sub. Total front to rear isolation is critical but only in close proximity (within several feet). Another issue is that the fiberglass hump is constructed with a very thin wall of fiberglass so this mounting surface could be reinforced to create a far more rigid baffle. This would provide a dramatic improvement over what you have now.

Perhaps the best option is to position a side-firing small sealed enclosure over the top of the hump and extending toward the bow. This requires zero modification to the hump other than a carpeted cover panel over the existing opening. You could use your existing MOMO sub for the short term provided it hasn't become too fatigued from running it undamped. Eventually you could replace it with a 2-ohm woofer. This is an easy fit, especially in an '06.

Currently your sub is in the bilge and all of your coaxials are in the coaming, so they do not share space and do not require further isolation. So you're good in that respect.

David
Earmark Marine

philwsailz
01-05-2010, 12:41 PM
The SKM10 is a good choice, since it is a water-proof, ready made sealed subwoofer system. It is not noticeable from the outside, but the front of the box is attached to the back of the box under and around the woofer with a bracing scheme that is molded-in during manufacturing. The result is a very rigid enclosure which is not typical of a typical "plastic" enclosure. If you have a place to put it, it could work well for you.


I kind of like your option of attempting to seal the enclosure... It would be worth trying to figure out what volume you would end up with as a result though, just right there in that box. It might be too large, and it might be too small too, but if it were in the ballpark, it would not be too hardto do, and I kind of like how it looks now. I would pull the drop cloth out though... :) some sort of damping material will do a better job; pink fiberglass, or even some dacron polyester fiberfill... Your drop cloth is probablyt only reducing the net volume of the enclosure and not providing any damping.


Keep us informed of your decisions, and I look forward to David's comments; he will have some ideas for you too...

Phil
Kicker

jmvotto
01-05-2010, 01:12 PM
Al, I am following along closley and this is great info from you experts out there. Phil, David and Brian.

We have a very similar system ( (jl m6600, polk db651 and the polk momo sub)so i am axious how it turns out. I went to my local audio place that does high end auto, boat and home. they carry JL and Alpine.


i asked them about a free air sub for the boat and they steered me to the BA G3( tazz has this in an enclosure) They recomended this over both the Jl and the Alpine.

Al, we can split the Buy one get one free for slight over 100.00 below.


http://www.crutchfield.com/p_065G3104/Boston-Acoustics-G310-4.html?search=boston+acoustics+sub&ssi=0&tp=111&tab=features_and_specs

http://mobile.bostonacoustics.com/car/car_product.aspx?category_id=17&family_id=137&product_id=404

cab13367
01-05-2010, 01:41 PM
cab,

A bass boost is the last method to use in your particular situation where you've got an acoustic suspension woofer loaded into a free-air application that isn't even isolated front to rear. In fact, a bass boost will add to the problem rather than providing a solution. For now leave your crossover as is. And, take Phil's suggestion on experimenting with the phase.

I see two different paths you could follow to improve your lows given what you have.

If you're absolutely going to stay with your existing mounting configuration, instead of an enclosure, then you've got to convert to a real free-air sub. Sony, Kenwood, Clarion, Alpine, JL Audio and a few others make true free-air subs. JL Audio might make the best free-air sub but 200 watts is a little light for that model. The Alpine would do better with 200 watts. But your MOMO will not sound much better regardless of the steps you take as it is currently being used. Again, Phil is accurate in his assesment of the MOMO's parameters.

As applied to free-air, the distant opening on the port side is a non-issue since the pathlength is so long. However, you would want to seal up the hole atop the hump which is very close to the sub. Total front to rear isolation is critical but only in close proximity (within several feet). Another issue is that the fiberglass hump is constructed with a very thin wall of fiberglass so this mounting surface could be reinforced to create a far more rigid baffle. This would provide a dramatic improvement over what you have now.

Perhaps the best option is to position a side-firing small sealed enclosure over the top of the hump and extending toward the bow. This requires zero modification to the hump other than a carpeted cover panel over the existing opening. You could use your existing MOMO sub for the short term provided it hasn't become too fatigued from running it undamped. Eventually you could replace it with a 2-ohm woofer. This is an easy fit, especially in an '06.

Currently your sub is in the bilge and all of your coaxials are in the coaming, so they do not share space and do not require further isolation. So you're good in that respect.

David
Earmark Marine

David,

Thanks for the response. If I go free air, is the JL Audio 10W3v3-2 the one I want? Since it's a 2 ohm sub, the Kicker will deliver 420w instead of 210w so will that be enough to adequately drive this sub? If I go the free air route, do I still have to seal the top hole and the hole below the footbox that leads to the under floor pipe/cable chase?

Also, the footbox is actually stouter than you think - it's at least 1/2'" thick, maybe even 3/4" - it's not just thin fiberglass. I'll measure it the next time I remove the sub.

Do you have a recommendation as far as some good songs to use for tuning/testing a stereo system? Something with a wide range of sounds and some good bass segments?

Thanks,

Al

cab13367
01-05-2010, 01:44 PM
The SKM10 is a good choice, since it is a water-proof, ready made sealed subwoofer system. It is not noticeable from the outside, but the front of the box is attached to the back of the box under and around the woofer with a bracing scheme that is molded-in during manufacturing. The result is a very rigid enclosure which is not typical of a typical "plastic" enclosure. If you have a place to put it, it could work well for you.


I kind of like your option of attempting to seal the enclosure... It would be worth trying to figure out what volume you would end up with as a result though, just right there in that box. It might be too large, and it might be too small too, but if it were in the ballpark, it would not be too hardto do, and I kind of like how it looks now. I would pull the drop cloth out though... :) some sort of damping material will do a better job; pink fiberglass, or even some dacron polyester fiberfill... Your drop cloth is probablyt only reducing the net volume of the enclosure and not providing any damping.


Keep us informed of your decisions, and I look forward to David's comments; he will have some ideas for you too...

Phil
Kicker

Phil,

I'll remove the drop cloth and see how it sounds. I think you're right, ultimately, sealing the footbox is probably my best bet. Then I can use the equipment I have and will have the clean look I like. I do plan to install a heater in the boat though and the water lines will have to run through the underfloor pipe chase, thru the footbox, and out the hole on top so I need to do that first before I seal it with the expanding foam.

Phil, David,

Thanks a bunch for your input. It's so generous of you to share your knowledge with me and others on this forum. You guys are the best.

Al

cab13367
01-05-2010, 01:48 PM
Al, I am following along closley and this is great info from you experts out there. Phil, David and Brian.

We have a very similar system ( (jl m6600, polk db651 and the polk momo sub)so i am axious how it turns out. I went to my local audio place that does high end auto, boat and home. they carry JL and Alpine.


i asked them about a free air sub for the boat and they steered me to the BA G3( tazz has this in an enclosure) They recomended this over both the Jl and the Alpine.

Al, we can split the Buy one get one free for slight over 100.00 below.


http://www.crutchfield.com/p_065G3104/Boston-Acoustics-G310-4.html?search=boston+acoustics+sub&ssi=0&tp=111&tab=features_and_specs

http://mobile.bostonacoustics.com/car/car_product.aspx?category_id=17&family_id=137&product_id=404

Joe,

I thought you were happy with the bass out of your system? I thought maybe your footbox is better sealed than mine.

If I buy another sub, it will be a 2 ohm sub to get more output out of the amp. Also, I've looked at that Boston sub but the fact that it has a foam surround (instead of more durable rubber) is a show stopper for me. Don't know why they spec'd such a nice sub with a foam surround.

Thanks anyway,

Al

jmvotto
01-05-2010, 02:14 PM
Al,

I am happy but this thread certainly has me thinking??

then the Jl is probably the sub for you.


David,

What is the song on the youtube video on the 2009 super air nautique? i love that video.

When i get enough cash i be upgrading to the HLCD, hopefully you''l be able to ship to western NY.

EarmarkMarine
01-05-2010, 04:25 PM
cab,

Acoustic suspension for a sealed box woofer is a fixed relationship. So you can't approximate it with a quasi-sealed or aperiodic enclosure and have predictable results. Go with free-air (infinite baffle) or acoustic suspension (small sealed). One or the other. But no combination or mixing your schemes.

The JL Audio 10w3v4-2 is not a free-air sub and should not be used in your floor. Its just for enclosures whether sealed or bass-reflex. The appropriate JL sub is the M10IB5-SG-TB and its only avaiable in 4-ohms.

If you are 'free-air' it means an infinite and unobstructed volume of air (the entire bilge for example). A free-air 10-inch sub usually requires a 3 cu. ft. enclosure or larger so that the woofer's 'Q' is unchanged which is the basic qualifier for free air. You cannot have too large of an enclosure. However, it should be sealed or isolated front to rear by a 1/8 wavelength 'to' and 1/8 wavelength 'from' the nearest large opening, for a total round-the-world path equal to a 1/4 wavelength of the lowest frequency you're expecting to reproduce, which would be approaching the woofer's free-air resonsance. And the resonance is higher on a free-air driver. From this you can deduce that a.) the hole in the top of the starboard hump must be sealed and b.) the hole in the port hump or other distant openings do not matter.

In contrast, if you go sealed then it should be at or close to the optimum displacement (averages .65 internal net on most 10-inch drivers) and that means absolutely air tight in the strictest interpretation.

David
Earmark Marine

philwsailz
01-05-2010, 04:30 PM
cab,

Acoustic suspension for a sealed box woofer is a fixed relationship. So you can't approximate it with a quasi-sealed or aperiodic enclosure and have predictable results. Go with free-air (infinite baffle) or acoustic suspension (small sealed). One or the other. But no combination or mixing your schemes.

The JL Audio 10w3v4-2 is not a free-air sub and should not be used in your floor. Its just for enclosures whether sealed or bass-reflex. The appropriate JL sub is the M10IB5-SG-TB and its only avaiable in 4-ohms.

If you are 'free-air' it means an infinite and unobstructed volume of air (the entire bilge for example). A free-air 10-inch sub usually requires a 3 cu. ft. enclosure or larger so that the woofer's 'Q' is unchanged which is the basic qualifier for free air. You cannot have too large of an enclosure. However, it should be sealed or isolated front to rear by a 1/8 wavelength 'to' and 1/8 wavelength 'from' the nearest large opening, for a total round-the-world path equal to a 1/4 wavelength of the lowest frequency you're expecting to reproduce, which would be approaching the woofer's free-air resonsance. And the resonance is higher on a free-air driver. From this you can deduce that a.) the hole in the top of the starboard hump must be sealed and b.) the hole in the port hump or other distant openings do not matter.

In contrast, if you go sealed then it should be at or close to the optimum displacement (averages .65 internal net on most 10-inch drivers) and that means absolutely air tight in the strictest interpretation.

David
Earmark Marine

^^^X2^^^

Well put David!!!

Phil
Kicker

EarmarkMarine
01-05-2010, 05:44 PM
jmvotto,

We're happy to ship anywhere in the states.

As for the music in the video, I had to ask someone. I'm more of the technical and application spokesman.

I believe the artist is 'Akon', the album is 'freedom' and the song is 'keep you much longer'.

David
Earmark Marine

brain_rinse
01-05-2010, 06:27 PM
I really don't think you'll be happy with a free air sub. In my opinion free air subs are throwing good money after bad. If you're going to upgrade, I'd recommend either 1.) a small sealed enclosure and put it on the other side (or on top of) of the drivers footwell (simplest option) or 2.) cutting out some of the front of the footwell and inserting a sealed enclosure with a larger front panel that covers the face of the existing footwell. (harder to do, and even harder to describe, ill see if i can put together a quick diagram.) Again, this is just my opinion as I've yet to hear a free air sub that would make me happy.

cab13367
01-06-2010, 02:58 PM
So it appears that even if I decide to go "free air" I still have to seal up two of the three holes in the footbox - the one on top and the one under/in front of the woofer than leads to the pipe/cable chase under the floor of the boat. And I have to invest in a free air subwoofer.

So I got to thinking about pre-fabbed sealed enclosures and ran across an ad in the local craigslist for the sealed enclosure below, brand new, for $20. Apparently, he bought a stock of them at a closeout somewhere. I checked the dimensions and it will fit just fine under the dash - I can just screw it directly to the face of the footbox. It's not too deep so it won't take up a lot of the room down there. I know that it's not water proof but this is more of an experiment, to see how my sub would sound in a sealed enclosure and I'm only spending $20. The dimensions are stated as 20.25"W x 13.88"H x 5.88"D but I don't know if that is interior or exterior. If interior, then the interior volume is 0.96CF which is 50% more than the recommended volume of 0.66CF for my sub. I supposed I can just screw in a few lenghts of 2x4 inside the box to get to the desired volume. BTW, does the recommended volume of 0.66CF include the volume displaced by the sub or not?

So Phil and David, do you think this enclosure would work okay with my sub? Is the shallow rectangular shape a concern vs a square box shape? Should I reduce it's volume a bit or just try it as is? My sub has a top mount depth of 5-1/2" so it should fit depth wise.

If it turns out that the sub sounds worlds better in a sealed enclosure, then I may have to build a custom one after all.

Thanks,

Al


http://images.craigslist.org/3n83pb3l05O85Rf5S3a13557666b7a41e1c5b.jpg

brain_rinse
01-06-2010, 03:32 PM
Top mount depth for your sub is 5 3/4", and I'd bet the stated box dimensions are external measurements. So if it fits it will be very very close. Ideally you'd have an inch or more behind the magnet, so I'd keep looking. Also the recommended sealed box volume of .66 does not include the sub displacement. Good luck, I think you'll be amazed by the sealed box improvement over factory.

philwsailz
01-06-2010, 03:36 PM
I would assume that those are external dinemsions.

We can assume it is likely built from 5/8ths material, or 3/4 material. At the dimensions provided, and assuming a perfect rectangular enclosure, that gives us a gross interior volume of somewhere between .59 and .61 cubic feet.

Then, as you notice the baffle and the two sides, (vinyl covered) are inset, and it sort of appears that there is an angle to the enclosure; i.e. the top is shallower than the bottom. The scalloping in the inside back of the enclosure further points to the probability that this is an engled box. Both these points tell me that the enclosure might be as small as .5 cubic feet, maybe smaller. In my opinion, that is really too small for what you are looking to do.

Another thing to point out. The scalloping on the inside back of the enclosure is there to provide extra mounting depth. If your subwoofer is deeper than the enclosure is, it will not fit.

One more thing. 10-inch woofers are the worst of the group, (amongst 8's, 10's, 12's, and 15's) at having a very wide range of cutout dialeters. A 10" woofer can have a cutout diameter as small as 8-3/4 up to 9-1/8th as I recall from my history as a design engineer designing enclosures for other major brands. The enclosure you are looking at is probably a compromise in terms of its hole cutout. Make absolutely sure you center the woofer perfectly in the hole, or you will find some screws do not bite and/or you end up with leaks.

You are only talking 20 bucks, so it is a cheap experiment, but $20.00 would go a long way towards buying material to build something that is exactly right for your woofer.

If you can, take the time to find out if your woofer will fit prior to handing over the money.

Phil
Kicker

EarmarkMarine
01-06-2010, 06:08 PM
cab,

An automotive box probably won't last through the first season in a boat. The seams quickly fail although the vinyl and carpet coverings tend to conceal the failure for an additional season or two. There's no point in going with a sealed enclosure thats not sealed.

Even if the woofer would fit depth wise, you need an additional inch of clearance for the vented pole piece to breath. Otherwise, you're introducing noise.

My advice is to get past the fact that the box is so cheap and do it once the correct way and be finished with it.

David
Earmark Marine

tazz3069
01-10-2010, 04:11 PM
Cab
I used this sub enclosure for my 10" Boston Acustic G3 Sub. I bought it at www.audioformz.com. It fits just on the other side of the foot rest on the driver side. I used a little poly cotton to fill the cavity. The bass is amazing. I also have the Kicker MX700.5 amp and could not be happier with the sound. I did set my freq. to 100 hz. Check uout my pictures of the install.

Tazz

http://moomba.com/msgboard/picture.php?albumid=11&pictureid=2016

cab13367
01-11-2010, 12:47 AM
Cab
I used this sub enclosure for my 10" Boston Acustic G3 Sub. I bought it at www.audioformz.com. It fits just on the other side of the foot rest on the driver side. I used a little poly cotton to fill the cavity. The bass is amazing. I also have the Kicker MX700.5 amp and could not be happier with the sound. I did set my freq. to 100 hz. Check uout my pictures of the install.

Tazz

http://moomba.com/msgboard/picture.php?albumid=11&pictureid=2016

tazz,

Those are some spendy enclosures. I'd rather build a custom one. Do you have the dual or single voice coil G3 (are you running it at 2 ohm or 4)?

Thanks,

Al

Razzman
01-11-2010, 10:31 AM
Al, a sub does not need lots of space behind it, it's the volume that's what counts. Also all subs have a range to work within, example a lot will recommend .75cf but work just fine in the range of .60-1.0cf. Displacement is never given as all are different so i'm guessing around .80 or less displaced with the MoMo which is just fine. The .66cf is Polks optimum, but in a boat you'll never notice it. Well let's put it this way, 500% better than free air! :p

If you don't want to make a custom box then you can use this one with precations taken to protect it. Need more back space? Look at the box, it has a lip running around it that looks to around 3/4". I would "glue & screw" a 3/4" face to it of plywood or mdf. That gives you more back space behind the magnet. Coat the box with two layers of resin for waterproofing and add small rubber feet to the bottom for support.

The shape of the box is fine, in fact the more obtuse angles the better as i understand it. A perfect square box supposedly reflects the sound waves back on themselves cancelling some out.

Make a facia board out of hardboard or plexi running across the whole area like Newty did, carpet it and use velcro to hold it to the box face hiding all but the sub. It will also give you a surface to extend your heater outlet to.

My two cents :p

Razzman
01-11-2010, 10:37 AM
Btw and no offense to our pros! My brother in law has an automotive box in his boat which we resin coated real good inside and out. He almost sank the boat back in July with water 1' deep in the boat. The box survived believe it or not and is still in use!

cab13367
01-11-2010, 02:50 PM
All,

Thanks for all your posts. I decided not to get the box pictured but instead, bought a similarly shaped box (rectangular but deeper at the bottom than at the top) but is deeper and not as wide. I bought it from the same guy for cheap - it's used but in great shape and well made. It's currently got a 4" port on the side but I am removing that and making it a sealed enclosure. I will also seal it really well inside with silicone sealant at all the seams. There is at least 1" of air space between the the magnet and the back of the box and the opening is perfectly sized so that all 8 mounting screws bite solidly into the mdf (for a good, tight seal).

The gross volume of the box is 0.87CF. Polk says to deduct 0.10CF for the volume displaced by the sub so I'm at 0.77CF vs the 0.66CF recommended for this sub. It's easy enough for me to glue and screw a couple of measured pieces of 2x4's inside the box to get right at 0.66CF - should I do this or is 0.77CF just fine?

I am going to mount this box upside down and screw it to the face of the footbox to minimize the room it takes up. If this ends up sounding good, I will at some point build a custom box, one that is properly coated against the elements but I will probably go with a 2 ohm 12" sub.

I'll let you know how it sounds once I get it done and will post up some pics.

Thanks,

Al

philwsailz
01-11-2010, 04:39 PM
.77 cu ft should be okay for you. That is within 20% of recommended volume. It will play a tiny bit lower, although you probably will not hear it, and the total Q will be slightly lower than in the .66 box, but again, you will not be able to notice it.

When you go to build the custom box, consider a void-free 3/4" 13-ply plywood instead of any material manufactured from dust and resin, i.e. do not use MDF or particle board.

The acoustic benefits that are real for MDF are more for the higher frequency midrange and "tweeter" frequencies found in full-range home cabinets. This is due to two things. MDF is a very damped material, i.e. it doesn't "ring" like other wood materials. Additionally, its damping and resonance are uniform from board to board, and therefore the use of MDF in home cabinets results in repeatable predictable results when compared with hard woods or other solid materials, which can have varying densities and resonances.

The wavelengths associated with subwoofer enclosures are too long to develop any standing waves or resonances that can be attributed to the material alone, so a high-quality plywood is fine acoustically. It has the added benefit of being dimensionally stable with varying humidity levels.

No matter how well you coat an MDF enclosure, (Sorry Razz) it will eventally be compromised somehow. The "crack in the armor" will allow water to get in, and the MDF material will swell. From here it is a downhill battle as the swelling will cause more cracking of whatever protective coating you put on, and more cracking will cause more moisture intrusion.... It is a vicious cycle once it has begun. I restore wooden boats occasionally as a hobby and can attest to the good behavior plywood can have under water. You will never catch me using MDF in a boat for anything.

Finally, car audio companies use MDF for their subwoofers because it is cheap, it is easily milled, and it is a material that "folks around speakers" have been familiar with for a very long time. To me those are not good reasons to use it in a boat.

Keep us posted!

Phil
Kicker