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View Full Version : Sub facing in, or out??



morgan040
03-23-2011, 02:22 PM
I've been moving my sub around in the footwell with different boxes and sizes and ported and sealed, just trying to see different setups and see what sounds better.

I found that it didn't really matter what box I used it always sounded better when the sub faced into the foot well. So my question is why do all the manufactures keep making boxes that face out towards the driver??

Is it because it looks "cooler" or is it supposed to sound better that way.

I was hopeing some exile people could give me some advice on why they designed there sub box that way,

And yes I agree it looks way nicer to see a sub there than just a carpeted wall, the wall actually is kinda tacky.

http://img.photobucket.com/albums/v383/morgan040/IMG00005-20100409-1426.jpg

EarmarkMarine
03-23-2011, 03:17 PM
morgan,
The Exile subs used are at minimum 12-inch in a large bass-reflex enclosure so that almost necessitates that the woofer is exposed. If side-firing the required gap between the woofer and hull would eat up valuable displacement thats needed for the enclosure. Add to that the floor hump and particularly short height under the dash on a Moomba. Plus, bass-reflex enclosures are externally 50 to 75 percent larger than sealed.
The reason for why a side-firing sub has more output than a direct radiation version can be two fold depending on how its executed. First, you are getting the reinforced loading effect of the interior boundaries of the underdash cavity in the same way a home speaker would benefit from being up against the wall (add 3 dB), or down against the floor (add 3 dB), or in the corner and on the floor (add 9 dB). The effect is not quite as pronounced in a boat because you don't have the protracted planes as with expansive floors, walls and ceilings. But you do get a major boost. Also, this tends to put the stored and released energy from the underdash cavity in phase with the woofer's radiation when the woofer is oriented into the cavity rather than out at the edge of the cavity. Your perception can be somewhat biased too because loading into the cavity tends to function as a bit of a midbass filter so the bottom end will sound a little fundamental heavy by comparison.
Actually, direct radiating can have the advantage of better midbass transients and attack so there is a bit of trade-off either way.

David
Earmark Marine

c.rix
03-23-2011, 03:26 PM
Honestly the factory has no idea what they are doing with their sub set ups. They just cut a hole and drop a sub in not sealed or anything It would probably be ok if It were a "free air" sub but stock isn't. I personally don't like the sub facing toward me on my setup both of my 12's face to the sides of the boat. I played around with it a bit and decided I like the sound like that that best with the sub not facing me I felt like i could hear the sub moving? maybe just my imagination?

With the exile set ups I would imagine it never hurts to have your product visible :)

NCSUmoomba
03-23-2011, 11:32 PM
David makes some good points, and with competent people designing the boxes and subs specifically to be used a certain way, the results will be great. However, most people know very little about system setup and design and are lazy too. The will put the sub in as easy as they can, and they want to see it so they can show it off. I think it is pretty stupid. I knew from my car stereo work that loading the sub helps quite a bit. I built my sealed box with the sub firing towards the bow and downward. It is a SVC 10" 400WRMS unit that originally had a 70Wx2 amp bridged pushing it (280Wx1) and it was pretty loud. My friend that does car stereo work said that it was the best sounding 10 he had ever heard. I know other folks who have the sub in the kick panel area where you can see it, and they like to show it off. I tell them that it is pretty, but I can barely hear it. I would rather hear the bass than look at a speaker.

Brianinpdx
03-24-2011, 11:44 AM
Morgan -

You answered your own question. The Exile enclosure is an engineered system that takes into count a lot of the elements discussed in this thread. I dont mean to sound harsh when I say the box in that photo just plain takes up to much space and renders the helm area useless. There is no right or wrong answer here when it comes to execution.

Here's the important stuff... What we did, and why we did it. maybe some of this will play out in your own journey.

Materials - to many enclosures are built out of sponge like mdf that doesnt last a season. We used composite materials cut on a precision CNC mill.

Size - We designed the enclosure to maximize the tunning for the Exile woofers. And opted for a bass reflex design because of the open air requirement of boats.

Woofer size - we opted to go with a 12" / 15" woofer (supra designs), because we stopped making 10's 3 years ago. I feel a 12 is a substantial upgrade, where is most 10's on the market are not. working with a 10" woofer would indeed make for an easier install. No doubt there.

Firing alignment - we felt most people want to see the woofer. It's a personal choice type of thing. It really came down to the human factor. If people are going to spend big bucks on a sub upgrade they want some show off factor. from a purely technical application, we felt a top to bottom suspension was best, even over a side firing because it couples to the helm for +6db extra woof. and the enclosure would also be physically holding the woofer best weight wise.

Fit and finish - we opted to use a wrapped fascia cover to match the boat interior.

Overall design requirement - Mandley was our test bed from the LSV and it came down to not extending more than 5"s from th base of the hump. so he can retain the use of one of the drink holders and maintain foot space. this means the box goes up, over the kick plate.

Everything is a compromise when it comes to a good woofer plan. To say that one way or the other is better, is just plain nonsense. The bottom line is theory must meet application. To all those that want a great off the self do it yourself solution the exile box is just that. for all of those that want to build their own, hopefully some of the "why we did it" will help you out...

I think its great that you went to the effort to try so many things. My suggestion for you would be to review the box size compared to your woofer and try to shrink that enclosure down so you have some foot space. Also pay very close attention to the woofer power handling and available amplifier power you have.

Feel free to pm me if you need some help.

-Brian
Exile Audio

philwsailz
03-24-2011, 05:43 PM
from a purely technical application, we felt a top to bottom suspension was best, even over a side firing because it couples to the helm for +6db extra woof. and the enclosure would also be physically holding the woofer best weight wise.



HUH?

Brian, you lost me this time. Does this have something to do with, uh, hmmm... ????


Nope, you just lost me. :D



Can you explain what you are trying to say here? Right now to this audio engineer, it makes no sense.

Phil
Kicker

philwsailz
03-24-2011, 06:16 PM
Morgan-

David nailed it. When you change the loading of the enclosure by placing it next to a boundary, you get the gain over a band of frequencies as David suggests. You do lose transients as was suggested due to filtering.


If you are familiar with what a transformer does, you can draw a good analogy in your brain. A transformer can take an analog electrical waveform and through magnetics increase the amplitide at the sake of current. Ever heard of an impedance matching transformer?

We can do this acoustically too; a horn is an example of an acoustical transformer taking low amplitude high pressure sound and changing it into high amplitude low-pressure sound, (or vice versa, depending on which end of the horn you are listening to... :) ). This is done by using the horn as an acoustic transformer. The driver by itself is not very loud. when you put the horn on you "hook it up" to the air. You match the impedance of the driver to the listening envorinment with the horn.

When you boundary load your woofer enclosure, you are changing the acoustical load the woofer and enclosure sees; you are changing the way the woofer "hooks up" to the air in the listening environment. When you do it right, you get gain, as David points out. You are basically taking advantage of a change in the impedance match between the woofer and the air. You are not creating a horn, but you are changing the coupling of the woofer to the listening envorinment. Remember though, you are creating a crude acoustic transformer. You can have a trade off just like you trade amplitude for current in an electrical transformer. The loss of transients due to filtering as David points out is one of the trade offs.

Now having said that, I might have written something just as hard to understand as Brian's comment I tease him about. :D

Hope that insight helps shed a little different light on why you hear what you do.

Phil
Kicker

EarmarkMarine
03-24-2011, 07:12 PM
Phil,
I completely understand and totally agree with everything you said. Mostly I enjoyed the contrasting langauge that hopefully helps put things into perspective for those that take an interest. While its a very crude analogy, I sometimes explain a woofer trying to couple with a highly compliant open-air environment to a 1000 hp pro stocker thats trying to get traction with super skinny tires. Its a mismatch unlike the rigid air mass of an enclosed automobile cabin for example. Anything that you can do to better couple a woofer to the air is going to pay dividends. You need all the leverage you can get in a boat. Many people unknowingly do the opposite and inject mistakes that can be very counterproductive. So while a bit technical, I still think this discussion is an important one.
Btw, for everyone, don't think for a second that you can't get a 10-inch sub that will absolutely rock your boat. I've seen a single 10" have water outside the hull dancing and sending droplets well into the air. All 10s are not made equal.

David
Earmark Marine

Brianinpdx
03-25-2011, 11:20 AM
Phil - I was traveling all day yesterday sorry for the delayed response.

I should probably dig up the RTA snapshots for you but I’ll try to explain. When our design group met and went over conceptual idea’s for enclosure design on the LSV, 4 working methods for execution where discussed.

1 – side fire - vented
2 - front fire – vented
3 – top fire – vented
** we also looked at sealed as well.

Here’s some of the pro’s and cons we came across

Side fire modeled well but when built and placed into the helm, tended to offer the most rattle as it transferred energy into the haul. Version one was tuned at 42hz. My acoustical engineer Bill Hasbrook wanted to wanted to look at lowering the tuning to 36hz and modifying the port. We opted to do this in a top firing proto.

The top fire proto was built and tuned downward and it was a night and day improvement over the side fire, but frankly it was to dramatic because the woofer and port load directly into the helm itself. The RTA viewed multiple narrow peeks above +5dB and above the tuning frequency. During a frequency sweep of the sealed design, it was also found that the LSV helm was producing several 1+2db deviations at 28hz and also 41hz. Interestingly, the Outback helm we swept with the same enclosure spiked at 33hz and had no other deviations to speak of. We found this odd as it seemed to be very similar construction. Some of these peeks where changed by the fasica height as it acted to enclose the helm cavity itself. It wasn’t a pretty situation. It was clear that visuals where getting in the way of excecution.

Also parallel to this development was a front firing design. The group felt that from a marketing perspective, that owners are going to want to see their investment. This was reinforced by two high end retailers we seek input from.

The final design ended up becoming a front firing 2.3cu enclosure tuned @36hz that produced a fairly linear response. The venting was left top firing and proved to be the best happy harmony. Yes, looked at theoretical phase issues. Yes, we also looked at internal bracing / construction issues. Yes, I know about fitment issues. There where a lot of angles in this enclosure design. The results are fantastic and probably one of more expensive solutions on the market.

*** David’s comments about a 10” are agreeable. Not all 10’s are created the same. The same is true for 12’s and 15’s and 18’s too. It should be qualified when discussing these things that we are speaking about expensive woofers here. I know of no entry level 10” woofer, or 15” woofer for that matter that will rattle water. Most of the stock situations regardless of size are entry level factory solutions. This whole discussion is traveling beyond the land of stock.

Here’s a link to the 15 we do for the Supra helm and also Malibu helm. It breaks down the box design very clearly.

Box is here (http://www.youtube.com/watch?v=B1kFGCqnQMo)

-Brian
Exile Audio

EarmarkMarine
03-25-2011, 01:00 PM
There are some inconsistencies whether in the realm of real world or theory.
Its unusual to tune a bass-refex enclosure 10 Hz below the woofer resonance.
Looking at the displacement and port dimensions I question whether its actually tuned that low in reality. Placing a bass-reflex port within the under-helm cavity and independent from the woofer which is direct-radiating will undoubtedly change the tuning of the circuit and the delicate phase relationship between the port and woofer. The helm cavity will add an unpredictable capacitance to the port circuit and thus a phase rotation that has nothing to do with wavelength other than the impact will be non-linear just like any bass-reflex circuit in itself. With every different woofer/enclosure alignment the relationship to the helm cavity will change. There is no available mathematical modeling for this. It may very well sound fantastic but its a crap shoot at best. To imply that it was modeled in advance and with any level of predictability is well...Again, I'm not questioning that the outcome sounded great, just some of the technical speak and other assertions...many of which far more knowledgable would find disagreeable too.
There is no way you could do a side-firing bass-reflex 12-inch. As stated before it would consume too much displacement to have adequate space to vent out the side. This added space would have to come at the cost of the enclosure's internal displacement. If you place the woofer and/or port too close to the hull then you will potentially change woofer's 'Q', choke the output due to a reduction in the pathway surface area or change the tuning relationship. And, you would certainly lose more leg/foot room. This option would have and should have been dead in the water from the beginning.
Despite the asthetic considerations a side-firing 10 will get a boost in gain that a front/direct firing 12 will not. That boost can offset much of the 50 percent increase in surface area going from a 10 to a 12 and the added gain that increase in surface area will net.

David
Earmark Marine

NCSUmoomba
03-25-2011, 02:51 PM
Brian, I am just curious, did you guys try a down firing? Also for any of you guys, is there any way (I should say easy way) to get an idea of how far away from the object the sub is boundary loading into should be mounted from? Is it based on box volume? Speaker diameter? Woofer excusrion? Would the space for a port be similar?

I am considering moving my sub enclosure from underneath my helm so I can make room for a larger ballast sac under the bow seat. My two thoughts are making a custom seat base with the sub inside of it, or a bow filler cushion thing with the sub inside it. Either way downfiring will fit better, but I don't know how it will respond acoustically.

I love these discussions. It is great to have Brian, David, and Phil on this forum. You guys are awesome.

EarmarkMarine
03-25-2011, 04:49 PM
BrianNCSU,
You will see home downfiring subs and ports that benefit from walls and corners. But give them a try on the patio and you might be surprised how much they labor. You will also see downfiring subs in automotive like the JL Audio Stealthbox for example. Before that Stealthbox design is finalized they have done exhaustive testing and listening in the actual vehicle for which it was designed. So if some aspect of the speaker and enclosure parameters change then this is compensated for in the design. Also, the vehicle is a very forgiving environment because it is an enclosed cabin with a second order per octave rise in the low frequencies. A woofer will couple very well in that rigid air mass. Now an open air environment of a boat is very different and unforgiving of any error or design that serves to choke the output. And, anytime you reduce the radiating surface area of a woofer you are initially doing the very opposite of what you need. Of course you are taking advantage of the sole as a reinforcing plane in a downfiring scenerio but if the sub is too close to that plane then you will change certain parameters and initially lose important gain. So our rule is this. Take half the diameter of the woofer. For example, if its a 12 then space it off by 6 inches and so on. Sometimes you are utilizing a downfiring scheme because you have a larger woofer in a very limited vertical space. In this case you may knowingly make that compromise...and we have many times when the situation dictates. Certainly never mix downfiring within an enclosed seating console or locker that must be venting to allow the bass radiation to freely flow from within that cavity. In this case you are choking the output twice. Again, we have done this when there was no better option. But we recognize the cost.
In general and when possible, we repeatedly do a sidefiring bass-reflex enclosure off the hull. We don't force a larger woofer and enclosure into that small space where there isn't ample room for the fluid-like bass radiation to flow. And we need adequate room for the woofer and vent to properly couple together without misalignment from the original design. A bass-reflex enclosure is a very self-dependent and contained circuit that is largely immune to the influence of the environment as long as you give it a little common and unobstructed space. All else in the way of boundaries, orientation and room dimensions are infuencing your perception but not the actual tuning. We have found this extra space around the woofer/port/enclosure is essential to good bass tonal construction. And I doubt there are many who have done as many marine subs and had the real world applicational experience over the last 12 or so years as us. There aren't many who understand acoustics as well. Having said that, there are those particualr boats that are the exception and you have to take the best option available. Its part of taking the best that a boat can give and choosing the leper with the most fingers.

David
Earmark Marine

WaterBullDawg1980
06-03-2011, 08:35 AM
David, Phil and Brian;

Just reading through this thread again while I sip my morning coffee here in the office and I wanted to thank all of you for the support you provide on our forum. It's not everyday that an entire community can be educated by the experts with such open and honest dialogue.

This in particular is a fantastic read.

Well done!

https://velocity.t-nation.com/forum_images/e/5/e5168_ORIG-clapping_gif2.gif