Marine subwoofers (JL M10) ported versus sealed

[MidnightSensi]

So, I've been looking at either porting or sealing a pair of JL Audio M10W5s for work (so, this is semi-commercial, but, I'm doing it for my own interest to see if I should even bring up the option at work). Right now I seal a pair of 10" JL Audio marine subwoofers, but I've been considering porting them.

I've been playing with WinISD per reading on this forum, and it seems like if I port them I can basically double my output around 30Hz and get a 50% gain or so at 50Hz. That's a pretty big deal!

Here is the comparison, using all JL Audio's recommendations for sizes and everything....

Here is my design (they would go under the backseat, I only drew the driver and port on the one side, the big box is the middle is something else):

Some questions:

1. I'd need a drain hole if I ported, in case water got in through the port.... would a 1/16" drain hole be a problem?

2. Am I reading the WinISD graphs correctly, is it that big of a difference if I port? Are there any downsides I'm missing other than the box has to be bigger?

It's a 13" long port, with a 3" inner diameter. I was considering using the Dayton porting kits and painting the outer port with AWL-Grip to make it look nice.

Any help would be great, It's been fun playing with this today!

 

[MidnightSensi]

Oh, the drivers are JL AudioM10W5's:

http://marine.jlaudio.com/pdfs/11386.pdf (PDF with all the specs)

I just realized that the port length would actually be 10.44-in because I'd use a 2.75 Dayton Audio port kit... which says its 3" but someone on Parts Express reviews said it was actually 2.75 inside diameter.

I wonder how I account for the bend?

Also, I don't see how to tell if I'll have port noise (I just downloaded WinISD pro)

 

[Torgus]

porting a woofer in a marine application has fail written all over it imo. i could be wrong but me thinking about it it just seemes like a bad idea...i mean with all the moisture in the air and the fact the port is sucking and pushing air in just screams bad idea imo. not to mention you would have to treat the wood on the inside, mold will grow in there, and i doubt the back of the woofer will like being in a high moisture enviroment.

then again i could be wrong.

 

[MidnightSensi]

It's a marine driver, but, yeah, I see what you mean... salt air back and forth might not be the best regardless..

Anyway to soup up a sealed box? Just add lots of volume?

 

[highfigh]

Oh, the drivers are JL AudioM10W5's:

http://marine.jlaudio.com/pdfs/11386.pdf (PDF with all the specs)

I just realized that the port length would actually be 10.44-in because I'd use a 2.75 Dayton Audio port kit... which says its 3" but someone on Parts Express reviews said it was actually 2.75 inside diameter.

I wonder how I account for the bend?

Also, I don't see how to tell if I'll have port noise (I just downloaded WinISD pro)

When you look at the box that comes up at first in WinISD, it has Driver, Box, Vent Plot, Project tabs. Click on the Vent tab and in that, you should see Vent No., Diameter and Length. Next to Length, it has a Vent Mach box.

 

[highfigh]

porting a woofer in a marine application has fail written all over it imo. i could be wrong but me thinking about it it just seemes like a bad idea...i mean with all the moisture in the air and the fact the port is sucking and pushing air in just screams bad idea imo. not to mention you would have to treat the wood on the inside, mold will grow in there, and i doubt the back of the woofer will like being in a high moisture enviroment.

then again i could be wrong.

There are lots of marine systems with ported boxes. The easy way around the problems is to coat the box with polyester resin, inside and out. That way, there's no exposed wood. Another way is to use synthetic materials, like Star Board, with whatever bracing is needed. Star Board is the material they use for cockpit table tops, panels and doors in a lot of boats. Being a marine woofer, some of which are made specifically for infinite baffle applications, the back side is as impervious to the moisture as the front.

 

[highfigh]

Honestly, in the boat, I doubt that you'll "hear" 30Hz. If you go about 35' away, no problem. I would use a slightly smaller sealed box and with the increased Qts, it'll be punchier than the larger box. You need that extra punch outside because there are less boundaries for the sound to reflect off of. If you can face the woofer down or at a side wall (gunwales work for this, too), use the larger box and the reflection will add to the total output. If it was an enclosed space, the transfer function would be increased but you can still get really good sound in an open cockpit boat.

What kind of boat is it?

 

[MidnightSensi]

Yeah, I'm not really worried about my box rotting because I was planning on building it using honeycomb or a foam core (good stiffness and acoustic properties, plus light) and then glass around obviously. However, JL has told me that even though its Marine it still needs to cleaned and such.

Honestly, in the boat, I doubt that you'll "hear" 30Hz. If you go about 35' away, no problem. I would use a slightly smaller sealed box and with the increased Qts, it'll be punchier than the larger box. You need that extra punch outside because there are less boundaries for the sound to reflect off of. If you can face the woofer down or at a side wall (gunwales work for this, too), use the larger box and the reflection will add to the total output. If it was an enclosed space, the transfer function would be increased but you can still get really good sound in an open cockpit boat.

What kind of boat is it?

ts an open cockpit performance boat, so, maybe the furthest you would get from the sub is 6ft. Right now we put in the JL IB5 and just run it free air...sounds like **** imo.

For the MW5, JL Audio recommends a 0.875 cubic foot box for most applications, it seems like in WinISD about the only thing I can do is increase the low end performance by making the box bigger... but if you say in an open environment it wouldn't make the difference, I'd rather use a smaller box and get more punch. It's also less of a pain to build and easier to pitch.


I could fire them into that seat area, because that CAD drawing is just the frame, that's completely closed off (but not sealed, the seat just sits on top and then you lift the seat to get to the storage)... but I could put two boxes on either side and fire them into middle of the seat or even into the bulkhead that in behind that seat. Then would I just add a vent so that the bass can escape into the cabin? So two subs in sealed boxes, and then a fairly large vent for the bass to get out?

Thanks a ton for the help, its fun messing with this stuff

 

[sparky77]

Is this actually going to be in a salt water envrionment or just fresh water? Either way I think you could minimize some of the moisture and salt issues by using the old mud boggers technique for air intakes, and cover the ports with nylon stockings. Try it for yourself, put a stocking over a cup and splash some water over the opening, and see how much actually makes it through.

 

[highfigh]

Yeah, I'm not really worried about my box rotting because I was planning on building it using honeycomb or a foam core (good stiffness and acoustic properties, plus light) and then glass around obviously. However, JL has told me that even though its Marine it still needs to cleaned and such.

ts an open cockpit performance boat, so, maybe the furthest you would get from the sub is 6ft. Right now we put in the JL IB5 and just run it free air...sounds like **** imo.

For the MW5, JL Audio recommends a 0.875 cubic foot box for most applications, it seems like in WinISD about the only thing I can do is increase the low end performance by making the box bigger... but if you say in an open environment it wouldn't make the difference, I'd rather use a smaller box and get more punch. It's also less of a pain to build and easier to pitch.

I could fire them into that seat area, because that CAD drawing is just the frame, that's completely closed off (but not sealed, the seat just sits on top and then you lift the seat to get to the storage)...

Thanks a ton for the help, its fun messing with this stuff

A boat can sound good but when the engine is running, all of the bass extension will go unnoticed. For that matter, most of the best aspects of great sound go away when you're outside, other than not having standing waves. I worked on boats, both doing audio and servicing them and great sound is just not a practical goal, in the sense of being able to listen for, and hear the fine details.

Free air subs only sound good when the front of the driver is completely isolated from the rear and then, only if what it's mounted in is large enough. A panel that's barely larger than the cone will never do the bass any justice because it needs the plane of the front to create reflections. It's less efficient but you could build a bandpass box. Done right, it will add depth and punch, protect the woofer(s) and doesn't have to be really huge. Even less efficient but cleaner sounding is an iso-bandpass and that uses a smaller box.

"but I could put two boxes on either side and fire them into middle of the seat or even into the bulkhead that in behind that seat. Then would I just add a vent so that the bass can escape into the cabin? So two subs in sealed boxes, and then a fairly large vent for the bass to get out?"

You just described a bandpass box. If you ever listen to a car system with a sub and open the window by different amounts to hear the differences in the depth and quality of the bass, what you're doing is listening to the secondary enclosure's tuning, from inside that enclosure. The sub is the primary enclosure (especially if it's sealed), the passenger compartment is the secondary enclosure and the window opening is the vent.

Who did you talk with at JL- Ward?

 

[TLS Guy]

Oh, the drivers are JL AudioM10W5's:

http://marine.jlaudio.com/pdfs/11386.pdf (PDF with all the specs)

I just realized that the port length would actually be 10.44-in because I'd use a 2.75 Dayton Audio port kit... which says its 3" but someone on Parts Express reviews said it was actually 2.75 inside diameter.

I wonder how I account for the bend?

Also, I don't see how to tell if I'll have port noise (I just downloaded WinISD pro)

I have not run the driver, but I would bet the port is too small. Your program should be able to calculate vent air velocity. 27 m/sec would be max for a non critical application. for critical application try and keep it below 18 M/sec.

 

[MidnightSensi]

A boat can sound good but when the engine is running, all of the bass extension will go unnoticed. For that matter, most of the best aspects of great sound go away when you're outside, other than not having standing waves. I worked on boats, both doing audio and servicing them and great sound is just not a practical goal, in the sense of being able to listen for, and hear the fine details.

Free air subs only sound good when the front of the driver is completely isolated from the rear and then, only if what it's mounted in is large enough. A panel that's barely larger than the cone will never do the bass any justice because it needs the plane of the front to create reflections. It's less efficient but you could build a bandpass box. Done right, it will add depth and punch, protect the woofer(s) and doesn't have to be really huge. Even less efficient but cleaner sounding is an iso-bandpass and that uses a smaller box.

"but I could put two boxes on either side and fire them into middle of the seat or even into the bulkhead that in behind that seat. Then would I just add a vent so that the bass can escape into the cabin? So two subs in sealed boxes, and then a fairly large vent for the bass to get out?"

You just described a bandpass box. If you ever listen to a car system with a sub and open the window by different amounts to hear the differences in the depth and quality of the bass, what you're doing is listening to the secondary enclosure's tuning, from inside that enclosure. The sub is the primary enclosure (especially if it's sealed), the passenger compartment is the secondary enclosure and the window opening is the vent.

Who did you talk with at JL- Ward?

Interesting. I'm not really super concerned about sound quality because I know what we define as good just isn't possible in that environment, I just want it to be an improvement, also by building a box I can use the box to hold up the seat...so it would kind of provide double duty.

I'm going to investigate the bandpass box. I really like that idea, it seems like the sealed woofers would be better based on what you said about the low bass and that the bandpass would give it a little extra umph. Also that would be better for packaging and I could even maybe do something cool with the top (plexiglass?)

I have an Infinity Kappa Perfect system in my truck, so, I know what you mean about the venting with the windows. I'll play with WinISD in bandpass..

At JL I can't remember who I talked too... I called tech support and spoke with someone there. Do you have someone you recommend?



Thanks!

 

[MidnightSensi]

Who did you talk with at JL- Ward?

I just called them again and they said they didn't have any recommendation for a bandpass enclosure with these subs... I think the tech people I'm talking to are just reading cue-cards, because, they just give canned answers.

I'm playing in WinISD right now trying to make a bandpass box for a pair of them, but, the enclosure size seems big and I want the box to be simple to make...

I'm trying to tune it higher, like 45Hz, based on your recommendation that we can't hear the lower bass in a boat...

 

[annunaki]

Tech support (regular "joe" techs anyway), especially at JL, will never give a response to something that may cause a higher rate of failure with their products. (Bandpass loaded woofers tend to have higher rates of failure due to the user being unable to hear the distortion clearly)

Most tech support depts. have become useless for the most part. There are a few that are still good though.

Bandpass is difficult to get right, let's put that out there to start. Wide bandwidth is difficult to achieve without the enclosure(s) getting quite large. The wider the bandwidth (typically) the larger the enclosure. Bandpass requires high degrees of accuracy for volume. .05ft^3 (in error) can change the tuning a fair amount and result in what sounds like a "one note wonder".

 

[TLS Guy]

Tech support (regular "joe" techs anyway), especially at JL, will never give a response to something that may cause a higher rate of failure with their products. (Bandpass loaded woofers tend to have higher rates of failure due to the user being unable to hear the distortion clearly)

Most tech support depts. have become useless for the most part. There are a few that are still good though.

Bandpass is difficult to get right, let's put that out there to start. Wide bandwidth is difficult to achieve without the enclosure(s) getting quite large. The wider the bandwidth (typically) the larger the enclosure. Bandpass requires high degrees of accuracy for volume. .05ft^3 (in error) can change the tuning a fair amount and result in what sounds like a "one note wonder".

I agree completely that bandpass is problematic. I did a lot of work on those in the early and mid eighties. I have built three finished designs.

The first was the best. A second order band pass design using two 6" SEAS woofers, two sealed enclosures and one common vented one.

I built them for my father who was enamored with Lowther units at the time. They did the job, and they were small enough for him to take two back on the plane to England. They spanned two octaves just about.

The others were isobarik second order band pass.

The problem is that with larger drivers you end up with a large cabinet, unless you make them isobarik, and then efficiency is low.

In my view only second order band pass designs have acceptable distortion and time delay.

There are a couple of advantages to band pass second order. The roll off is second order, so you get more deep bass then with standard QB 4 alignments. You have good control of the total Qt of the system, so you can make the bass very tight.

You have second order roll off on the top end, usually around 90 Hz, which means that you can make a nice acoustic crossover with sealed second order bass/mids. However you still need an electronic crossover above the high end cut off, to stop HF radiation from the port.

My view is that for a boat you will go through a big hassle for little gain for a system on a boat if you go down the band pass route.

Some of you may remember that KEF had a huge bandpass enclosure,with mid and tweeter on top that you could rotate. Although that speaker had prodigious bass output, Qt always sounded too high to me, with poor bass articulation, despite the vari Q control in the tape loop.

This was the last bandpass I built.

It has a couple of 9" morel units in isobarik configuration. Tweeters are Scanspeak D 29s, with the dual magnet sealed extended range W75s, tow per enclosure in individual sealed compartment. Acoustic crossover is at 90 Hz.

They are very good if you don't push them too hard. It is easy to bottom the drivers. They are powered by venerable Quad 303s at the moment one per speaker. They provide 45 watts per channel, so that is 90 watts per speaker. With that power I feel there is not much chance of damaging the drivers They are in our Eagan quad four town home currently. They produce enough deep bass that I worry about complaints from the neighbors. But in the current application they are fine.

These I built just to fool around.

They use a couple of 12" Madisound woofers in isobarik configuration. There is good output from 27 Hz to 90 Hz. I set Qt at 0.5 and the bass is very tight. They are power hogs though, and you have to push them. I use them in the first level of this home. It is a big space with a lot of bass leakage, and the two KEF B 139s needed a little subtle reinforcement stating at 80 Hz. For this they are doing the job fine, but high spl subs they are not.

However with them organ CDs down there sound very impressive and they do blend well with the main speakers.

So if you really are keen to do a band pass I can try and help.

 

[MidnightSensi]

Yeah, it seems like the box would be really big and lots of precision would be needed to make it. That's okay for a special sub, but, this is still a boat and outside.. I'd just like some extra output than what I get now.

I was thinking something like this:

It was mentioned earlier that firing into a stiff wall would make the output more... would something like the above work? A sealed box fired into a big vent that goes out into the cabin... Then on top I'd put an access panel in case someone needed to replace the subwoofer...

This afternoon I've been looking at designs like this:

Basically based on what you guys said earlier, if I fire into something I can get some more output... so would a sealed box like that work? Something like that would be neat because I could backlight the top or something.

 

[MidnightSensi]

The space I have to work with, if I did a dual sub system (one sub on either side of the seat)...it would be a 23" deep space, by 12" wide, by 12.5" high .... with the 12" by 12.5" face being fired into the cabin.

So, that pretty much kills a lot of options. If I use 3/4" starboard its 1.44 cubic foot interior space... so I basically need to go sealed and do something like that image I posted above or something like the bagend low profile sub I showed above.

 

[TLS Guy]

Yeah, it seems like the box would be really big and lots of precision would be needed to make it. That's okay for a special sub, but, this is still a boat and outside.. I'd just like some extra output than what I get now.

I was thinking something like this:

It was mentioned earlier that firing into a stiff wall would make the output more... would something like the above work? A sealed box fired into a big vent that goes out into the cabin... Then on top I'd put an access panel in case someone needed to replace the subwoofer...

This afternoon I've been looking at designs like this:

Basically based on what you guys said earlier, if I fire into something I can get some more output... so would a sealed box like that work? Something like that would be neat because I could backlight the top or something.

I think I would just use a sealed box and add Eq. Don't forget you can Eq a sealed unit. Of course that will limit overall power. However I doubt you want to blast it excessively on a boat. At least in harbor you would not be popular. Under way I doubt quality will be a priority due to engine noise, unless this is sailing boat.

 

[MidnightSensi]

Nah, it'll get blasted for sure. Sandbars, etc.

I'm going to design a sealed box with an angled front, so the woofer will fire into a stiff piece of starboard and hopefully create some gain. I will post the design.

(btw, I have two Infinity Kappa Perfects sitting right here that came in today...so.. I might start on a build per the plans at the top pretty soon. I'll probably do it with an extended front lip for a grill cloth though, but thats another thread )

 

[TLS Guy]

Nah, it'll get blasted for sure. Sandbars, etc.

I'm going to design a sealed box with an angled front, so the woofer will fire into a stiff piece of starboard and hopefully create some gain. I will post the design.

(btw, I have two Infinity Kappa Perfects sitting right here that came in today...so.. I might start on a build per the plans at the top pretty soon. I'll probably do it with an extended front lip for a grill cloth though, but thats another thread )

No sand bars on Benedict lake thank goodness. I think we would drive you off Benedict!