cabin gain/xfer function vs enclosure design

in planning my next sub install i started thinking that the dimensions (cubic feet, tuning frequency and port area) which sub manufacturers list as optimal for their particular drivers. i would imagine that it is safe to assume that their recommendations take into account some degree of cabin gain in order to make the driver sound optimal where it is most likely going to be placed: in a car.

with that in mind, and the fact our boats have little to no cabin gain, are there any thoughts or theories on enclosure design that would be more effective/efficient in an open air marine environment? should we tune to higher frequencies? do will still need huge volumes and ports? thoughts?

A very good subject and acoustics is certainly a favorite of mine.
Yes, an enclosed vehicle cabin will provide a second order per octace gain increase once you get below a certain frequency that corresponds to the longest interior dimension. Also, past a certain sound pressure level the air mass in a sealed cabin will become more rigid and the woofer will really couple better. Longer Xmax can be a big asset in a vehicle. And, even though you have to be concerned with subwoofer orientation, position, standing waves and cancellations, for the most part the vehicle interior is a very forgiving environment and will mask design and execution flaws to a great degree.
The open field environment of a towboat is very different. You just don't have any leverage in the bottom octave so trying to equalize the lowest region will be such an inefficient and losing cause that it will sap the dynamic range out of your system with little benefit in the bass extension. So no amplifier bass boost is typically in order unless its paragraphic or parametric and then you still have to go easy on it. You've got to crossover and tune a boat different from a car and if you don't you're going to have a lot more distortion at higher listening levels. Lots of Xmax is a little less important factor and high mass subwoofers can be counterproductive in a boat versus a vehicle. In a boat you want surface area and efficiency and that includes any enclosure type that will produce more output with equal power. The idea is to get the most output while driving the woofer and enclosure within conservative limits. Whether ported or sealed, the best sounding sub will usually be the one in which its limitations are not exposed.
A subwoofer circuit, whether acoustic suspension, bass-reflex or bandpass, is going to be a fairly self-contained and consistent equation in a boat or car. You just want to avoid any type of orientation or loading that would serve to restrict or choke the output or change the woofer/enclosure's 'Q'. A bass-reflex alignment still needs to be optimized for the particular woofer whether a little higher or lower. You're still going to have well-damped linear circuits versus peaky higher output circuits whether in the car or boat and that's going to be up to the designer and boat owner. Some people are going to want a 'donk' street beat type of bass in their boat while others would prefer something more musical and strict in its reproduction. In any case, I would want a woofer that has a reasonably low natural resonance tuned at a lower frequency until the alignment compromised midbass or power handling. Higher tuning frequencies are generally for more S.P.L. and lower sound quality whether in a car or boat. I really wouldn't differentiate much between the two environments in this particular respect.
Since you don't benefit from the cabin effect in a boat... location, orientation and venting the radiation will always have a huge impact. Each boat is going to be a little different so you have to recognize the opportunities and liabilities and do a good job of taking what the particular boat gives you. And, there isn't a singular prescription that applies to every boat.
Its a start.

David
Earmark Marine

so your assertion is that you wouldnt stray from the manufacturer's recommendations based on the completely different environment? i was under the impression that once you drop below a certain frequency, you will not hear it in a boat becuase it doesn't provide an environment in which the waves will build and be audible.

for the sake of argument lets use 49Hz, which has a cycle every 22.96 feet. Assuming you had a 23' boat, you would be lucky to get that wave to audibly build due to its frequency, and that only complicates as you drop in frequency and the wavelength extends. i have a 15" powered sub in my home audio system that sounds great and tame from 15 feet away. at 30 feet it is a completely different animial and will rearrange every shelf due to lower frequencies building.

so with that in mind, it seems like you would begin your low end approach for a boat sub at a little higher freq than a car, and that you might intentionally stray from the manufacturers recommendations to optimize your low end from a volume, tuning freq, and port area standpoint.

worm,
You are totally misinterpreting how lower frequencies propagate. You can develop 20 Hz in a five foot box. The difference in output between 15 and 30 feet has little to do with the listening distance as a portion of the wavelength and probably more to do with room boundaries.

David
Earmark Marine

my point in referencing the home theater system is that it is a more "open" atmosphere that would be closer in nature to the atmosphere of our boats than to the enclosed cabin of a car. and to that end, even though my house sub is corner loaded, the sound waves have only that corner to refract/reflect from before said waves reach the next wall 30 feet away (ceiling not included). given that, i agree with you that it is more of a function of boundaries.

i think i have a fair grasp on sound propagation, resonant frequencies and how boundaries can create canceling/standing waves that affect sound. with that in mind, and with all of your great info, i am not sure that you have addressed how the enclosure recommendations designed for a closed environment w/ cabin gain translate or fail to translate into the open air environment of boat. a sub and its enclosure's performance is relative to its environment, correct? how much should the car audio recommendations be regarded given the the completely different and unintended environment?

not calling you out, btw....just trying to pursue a different question, i think....

worm,
Let me share this example.
Let's say you are standing 30 feet away from a woofer that is nearly against the wall at one end in a 45 foot long room and you are listening to a bass waveform that is 30 feet long. Change the listening location or change the room length by a quarter wavelength and the bass may drop out completely.
What you are hearing is the sum or subtraction of the direct and reflected bass energy. Every waveform has a compession cycle and rarefaction cycle that are opposite and will either be in phase or out of phase in whole or in partial rotation based on the location between three points which are the transducer, the listener and the boundaries. Change any of the three and the perception will change particularly at lower, longer frequencies. Move to the opposite extreme of the room or house and you may have eliminated all cancellations and placed the reflected energy in-phase with the direct energy resulting in a 3 dB gain.
A car cabin is a different scenerio as is an open field environment of a boat. The acoustic laws are all the same but the manifestation is quite different in each application.

David
Earmark Marine

worm,
Okay, so to answer your question there are no modeling programs that will compensate for the difference in the car and boat. Modeling programs are available and in progress for home theater but these are only relating to sub locations in singular and multiples and their positioning in the room.
The tuning of a woofer and enclosure is a very self-contained and uninfluenced by the environment until you place it or load it incorrectly.
I wish it was different and I'd love to see the data if something becomes available.

David
Earmark Marine

okay. your last post was more of what i was getting at, but it never hurts to rehash the laws of physics. after a little more searching i found this thread:

http://www.wakeworld.com/forum/showthread.php?t=741182

around post 12 is an assertion that you shouldnt follow a particular manufacturers recommendations because of the change in environment. i remember reading some other (mis)info on the interweb about reproduceable low frequencies in a boat and how inefficient it was to pursue them, and thus recommended higher tuning...

Worm,
I totally agree that its not worth pursuing the very lowest registers in a boat because its a losing battle. But I have to qualify that. To do it artificially with equalization is terribly inefficient because that power will disappear into the black hole and you will overstress your woofer and exhaust your amplifier prematurely. You can easily cure 100 percent of a peak with an EQ but you can only cure a small portion of a dip or roll-off without the cure being far worse than the problem. So I wouldn't want to trade lower extension at low volumes for higher distortion and less dynamics at higher volumes.
As long as the woofer and enclosure combination can reproduce low frequencies efficiently then I want to take full advantage of their natural deep bass capabilities. I definitely want whatever I can come by easily. Believe me, you can hear the extra depth from a super low resonance 13-inch sub in a boat, even a moderate one like a JL Audio 13W1.
But to try and get a little extra emphasis like you can with a parametric bass EQ on the JL 1000/1 like you would in a car is just plain wasteful in the context of a boat. One environment rewards you with a 1 for 1 ratio of electrical boost to acoustic gain. The other takes perhaps 10 times the electrical wattage to net the same amplitude. In an environment where the energy rapidly dissapates in every dimension without reinforcing planes we can't afford to abuse the power.
Along those lines, many car audio systems will use a very low crossover point. However, when you limit the bandwidth in an open environment you limit the output. So in a boat you have to run the crossover a little higher so that you have the perception of alot of bass without running your components so hard.
Yes, there are vast differences. I wouldn't buy into what the car S.P.L. forums are doing because they have a single-minded pursuit. And they say it sounds good until you get to hear it for yourself.
You can tune an enclosure higher with a giant hump that will correspond to the most efficient frequency in a car. Gangsta Bass for sure if that is what you want. But you don't have to abandon deep bass in a boat.

David
Earmark Marine

A lot of information here. Thanks!

great discussion. i have done several installs in my various boats, and the last one had the least impressive low end, even with the most guidance i had yet received. I put the cabinet design and selection in the hands of http://pwkdesigns.com/, and he returned a tapped horn configuration using a DD2512, given my space constraints and my amp choice: Zapco c2k 9.0

the sub never blended well, and the output was marginal at best, especially considering my lowly kicker L5 in an undersized ported enclosure played way cleaner and louder.

at any rate, i am going back more traditional in enclosure design...going standard bass reflex again, now just tossing up 2 x JL Audio 13w6v2s, 2 x dd3512s, or 1 x dd9515....decisions, decisions, hahaha!

anyone have any idea how the 13w6's will handle 1200 watts? I know that JL specs them at 500 for continuous w/ 1000 being max, and many on here are feeding the w7 series more than recommended, but would like some real world feedback...that may be the decision factor that pushes me towards the DD3515s....

The horn enclosures are very very touchy.
DD is only 15 minutes from my house and so i've seen them play with all kinds of enclosures and horns when built to spec and the right environment are stupid loud.
Personally I would run the 3515's with carbon cone but I am a little partial to the fact that they are all hand assembled right here in okc.
The guys will build anything you want to the exact specs you want.
Kind of nice to keep the money in the states instead of spending it on a product mass built in a third world country.

Originally Posted by tdc_worm

anyone have any idea how the 13w6's will handle 1200 watts? I know that JL specs them at 500 for continuous w/ 1000 being max, and many on here are feeding the w7 series more than recommended, but would like some real world feedback...that may be the decision factor that pushes me towards the DD3515s....

I have a 13W6v2 running on an Alpine PDX1000.1. The birth sheet on the amp says it puts out 1150 watts RMS (give or take...my memory isn't perfect). I run the sub as hard as I can and have never had a problem. The sub is in a sealed box 95% the size of the volume suggested by JL.

Worm,

A buddy of mine runs a 13W6 off a 1000/1 and it sounds great. He hasn't had any issues yet. I thought it was overkill but he got a killer deal on the amp when a local store shut down. Are you asking about 1200 Watts per sub or 1200 between the two?

Sean----thats good to know info. if i understand things correctly running it slightly undersized and sealed will allow you to run a little more power vs oversized and ported

Mike---is your buddy running ported or sealed? I am using a Zapco c2k 9.0. It makessomewhere around 1200 watts off of each channel. Mine happens to be the 4 ohm version so it will be 2400ish bridged at 4ohms or 1200 x 2 at 2 ohms. I plan on running two...

I could consider 2 x 13w7s, but they would have to be sealed, and at w/ their D1.5 ohm voice coils, I feel like they would be underpowered with this amp. At 3ohms, they would likely be seeing less than 1k watts while being sealed...

Certainly you can tune an acoustic suspension woofer/enclosure for deeper bass extension at the cost of some midbass transients and power handling. Or, you can go to the other extreme with a smaller enclosure with more power handling and even a pronounced hump in the bass output. For my taste, I prefer a well-damped and linear woofer/enclosure with a Q in the medium range.
Don't forget to figure acoustic output into the power handling equation. If you get 3 dB more output from a bass-reflex enclosure and it essentially has the same power handling then I call that a 100 percent increase when looking at the ratio of power to output. There is no reason why a bass-reflex enclosure can't handle just as much power as acoustic suspension. At and around the tuning frequency a bass-reflex will exhibit less woofer excursion. If tuned properly in respect to the woofer's resonance, if using a steep subsonic filter for protection below its bandwidth and if staying away from destructive bass boost EQs, its very safe to go the bass-reflex route. For me the overriding aspect is that I never want to expose the lowpass amplifier and subwoofer's limitations so a bass-reflex system provides me with the most conservative operation of those components to get an equal output. I can't say that bass-reflex applies to every boat and application but in general we sure can use the extra acoustical leverage in an open boat.

David
Earmark Marine

Worm -
I think you need to look at a couple other variables besides just the enclosure characteristics. Is This for the C.C. 230 or 220 . Sorry to hear your luck with peter as I think he is very good at what he does ,but the marine industry is slightly different than the norm for his business.I think most of your concern lies with getting the bass free from the dual layer construction of your boat which tends to trap the acoustics into the hull.I believe your efficiency problem lies more with the cumulative results of the box and location. Tough to tell in the picture,but the port is the opening at the observers feet that extends back to the enclosure. Things need to be tuned slightly different in this application,but the end result is impressive

These Treo's are powered by a Arc Audio SE 4000

Here is a picture of a 220 with a ton of output and a design that overcomes this boat(not others)
included a picture of the grill for the walkway that still needs to be installed
sorry for the cell picture

Some things worth pointing out about the above Chucktronics installation. They have gone to considerable lengths to vent the radiation out of the locker and its adjoining gunnel cavities. This is evidenced by the collective surface area of the three vents that are visible. Without this large venting area there is far less impetus for the bass radiation to flow from the locker and the output tends to suffer, not to mention the tonal construction. That's a well designed install that shows real understanding of open boat acoustic challenges.

David
Earmark Marine

Chuck---
The 220 was actually sold yesterday....sad to see her go, there are a ton of things I prefer about that boat to the 230, which I still have.

While I do agree that the dual layer construction was/is an obstacle to overcome in these boats, you wont convince me that the PWK cabinet was optimal. This will be iteration #5 for subs in the is boat.
---Iteration #1 was the factory Polk
---Iteration #2 was a Kicker 12" L5 sealed (factory specs), oriented through the walkway opening
---Iteration #3 was a Kicker 12" L5 ported (tuned 38 Hz, just under factory air space), oriented with both the sub and port facing up
---Iteration #4 was DD2515 in PWK tapped horn enclosure

Out of all of these Iterations, the DD2515 was walked all over by the Kicker L5, both ported and sealed (from a pure spl perspective, and sound quality was just as good). That is regardless of orientation, and whether or not the observer's seat was open or closed. My walk way door, which is roughly the size of the one shown above, has been removed in favor of a vent that does improve output immensely.


David---
While I only have a little over half of the surface area of venting that the above install shows (not to mention the extended port that exits in the middle vent), I did recognize and experienced the benefit to use the walk through opening as a vent to allow more radiation in to the cockpit...same thing with opening the observer's seat when idle. The whole point in this exercise has been explore how the recommendations of the car sub manufacturers behave in an open air environment for which they were not intended, as you recognized above.

Couple of things that I have learned in the 6 boats and several iterations of each:
1. Efficiency (as David always preaches) is paramount (say that w/ 5700 watts and 8 dedicated stereo AGMs hahaha).
2. Bigger is not always better (as evidenced by my PWK cabinet)
3. Venting is essential.

I plan going back to ported and orienting the sub up on my next install up in my 230. The jury is still out on my subs...