Need help with small passive sub for motorcoach theater system

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I am a journalist working on a magazine article where I install a 5.1 home theater system in a diesel motorcoach. Since space is limited and wiring nearly impossible to pull, I am forced to live with the existing wires and space. The coach came originally with a cheap home theater in a box deal and it had a small passive Panasonic sub in a storage cabinet.

I have already upgraded all the other speakers, Blueray DVD, TV 40" LED LCD and a Samsung reveiver. Now I have a Samsung 5.1 AV receiver because it was one of the only ones I could find with a sub speaker level output. I am NOT able to run any type of preamp RCA wire to the sub location so I am forced to only use a passive sub and of course it has to fit. The current sub is about 8" wide and 13" tall and 15" wide. It has to go through a cabinet door so I need to stay really close to these dimensions.

So can someone help me design a DIY passive sub using an 8"' driver of the size above that will operate on 100 watts which is all the receiver puts out. The receiver has adjustable crossover and the front and surround speakers are Polk M10s is that matters. They claim -3db at 65hz if that matters and a 89db sensitivity. I will build and finish the box myself because it is hidden in a cabinet anyway so looks are not too critical.

Thanks in advance for your help

Don
 
Ok Woof, I ordered the parts today. Of course the Tang Band was out of stock and is on back order so I have to wait a week or so for it to arrive. Then I can start building the box. I thought about ordering the plate amp and feeding it with the receiver subwoofer speaker outputs but for now I am going to run it passive. If it seems starved for power Ill try the plate amp. With the low efficiency of the sub it may need it.

Thanks
 
This is an excellent small footprint design.
Cerberus

The woofer in that design is great, and the tiny enclosure is nice too, but personally I like it loud and I hate port chuffing (noise caused by excessive air velocity). In that respect, the Cerberus is a terrible design, the port is way too small. In my experience, the absolute minimum port diameter for that woofer is 3 inches with a healthy flare on both ends but a port that size won't fit in a Cerberus sized box.

There are a lot of good designs using that woofer, but for my personal needs, the Cerberus is the worst I've seen and I wouldn't recommend it.
 
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The woofer in that design is great, and the tiny enclosure is nice too, but personally I like it loud and I hate port chuffing (noise caused by excessive air velocity). In that respect, the Cerberus is a terrible design, the port is way too small. In my experience, the absolute minimum port diameter for that woofer is 3 inches with a healthy flare on both ends but a port that size won't fit in a Cerberus sized box.

There are a lot of good designs using that woofer, but for my personal needs, the Cerberus is the worst I've seen and I wouldn't recommend it.

Down firing plus inside of another cabinet, I doubt chuffing will be audible. In the OP's case, size was of concern & I don't think he will be disappointed. If chuffing is audible inside of another cabinet, you can always increase the diameter & run the port external. I do agree there are many designs for this sub. My favorite is 2 cu ft with a 3" port - 24" long.
 

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I am a journalist working on a magazine article where I install a 5.1 home theater system in a diesel motorcoach. Since space is limited and wiring nearly impossible to pull, I am forced to live with the existing wires and space. The coach came originally with a cheap home theater in a box deal and it had a small passive Panasonic sub in a storage cabinet.

I have already upgraded all the other speakers, Blueray DVD, TV 40" LED LCD and a Samsung reveiver. Now I have a Samsung 5.1 AV receiver because it was one of the only ones I could find with a sub speaker level output. I am NOT able to run any type of preamp RCA wire to the sub location so I am forced to only use a passive sub and of course it has to fit. The current sub is about 8" wide and 13" tall and 15" wide. It has to go through a cabinet door so I need to stay really close to these dimensions.

So can someone help me design a DIY passive sub using an 8"' driver of the size above that will operate on 100 watts which is all the receiver puts out. The receiver has adjustable crossover and the front and surround speakers are Polk M10s is that matters. They claim -3db at 65hz if that matters and a 89db sensitivity. I will build and finish the box myself because it is hidden in a cabinet anyway so looks are not too critical.

Thanks in advance for your help

Don

Ok Woof, I ordered the parts today. Of course the Tang Band was out of stock and is on back order so I have to wait a week or so for it to arrive. Then I can start building the box. I thought about ordering the plate amp and feeding it with the receiver subwoofer speaker outputs but for now I am going to run it passive. If it seems starved for power Ill try the plate amp. With the low efficiency of the sub it may need it.

Thanks

You can always use an amp with speaker level inputs or add a speaker level to line level converter or use an amp with balanced connections. You can probably get away with just sending pre level down the speaker wire without noise too. All of these options are possible. Don't negate the amp or you will not really improve the performance from the original setup.

An RV or bus is a large mass and plenty of power is needed for desirable operation, especially when the system is used while the bus is in motion to overcome road noise.

Also, the sub does not necessarily need to be in the same spot as the original. You could mount it in another location in the bus too. It may even sound better further away from the listening area and you can use a more substantial sub with more power.
 
I do plan on slightly changing the dimensions of the box while still yielding the same basic 1331 cubic inches or even more so I may be able to get away with a larger port. I have to fit the sub in the existing cabinet so the dimensions have to fit the door to get it in the cabinet.

I do not have the option of moving the sub as I could not get wires to it easily or at all. The whole coach is prewired and I dont have access to the AV cabinet to pull new wires without a lot of work. Not to mention the existing wires are TINY. I wish I could at least upgrade the wire diameter but no go.

If I can squeeze 1500-1600 cubic inches would it be worth the effort? some people warned that two cubic feet is better so I assume a little bigger is better than just 1 cubic feet.

I will try it with the receiver only as it has to be better than the molded plastic cabinet panasonic sub that came with it. If its not enough I will add the plate amp. I dont use it ever while going down the road so its only a home theater system when parked.

Thanks again for the ideas
 
Why do you feel the plate amp will be required? The AV receiver already has a built in sub amplifier that utilizes the adjustable crossover and it is rated with more power than the plate amp mentiones in the cerberus design, almost double in fact.

Plus if I use the receiver amp it has a built in EQ program and mic that sets levels etc
 
Why do you feel the plate amp will be required? The AV receiver already has a built in sub amplifier that utilizes the adjustable crossover and it is rated with more power than the plate amp mentiones in the cerberus design, almost double in fact.

Plus if I use the receiver amp it has a built in EQ program and mic that sets levels etc

Well you didn't mention that part. :D If the integrated system has more power than the suggested plate amp then the setup may work just fine.

Do you have another speaker system, even a multi way that you could connect one cabinet to get an idea of how things will sound before you even build the new cabinet? The crossover will roll off any HF so it will act as a sub anyway for test purposes.

For the application you are trying to achieve, a cubic foot of air space will be enough.
 
Actually I have a cheap sub already there now so I have listened to it along with the Polk M10 speakers that I just added into the various cabinets. The Polks were a HUGE upgrade to the tiny panasonic speakers that were in the coach to begin with. They were part of a home theater in a box system so I know the speakers were pathetic. Single cone about 3" diameter with a box about 4" square.

I feel sure any quality driver in a bigger box will be fine for this application compared to where I started. The parts are on the way now but I may upgrade the port to a 2 or 3" and try to make the cabinet a bit bigger based on the comments here also. I have some room to make it longer and wider just not deeper. That will give me room for the port also.
 
I'm curious, what model is the Samsung?

I'm also wondering if anyone has designed a tapped horn that small...I don't see one at http://www.billfitzmaurice.com but I thought there was a tiny one at some point. I had a coworker getting amazing bass out of 5" drivers with horns laid along the floor of different vehicles, so a horn or tapped horn with a small driver might work well for this application.

Also consider stuffing the box to increase the apparent volume-though if ported, not around the port airflow. And if the port is venting into another cavity, it may not act as you expect.
 
Ah, the Samsung is 6x100. So the sub is comparatively underpowered-roughly the sub should have as much power as the rest of the system. But since that's the receiver that works for you, just gotta deal with it.

Makes me think even more of a tapped horn.

Can you post a picture of the cabinet? Might trigger more ideas from some folks. Something I did in a car was have my friend's shop fiberglass in one of the panels. I wonder if that's possible in your application.
 
Too late now Head Unit. The cabinet is already being built by a buddy of mine as I type. I modified the design above and made the cabinet a bit larger and went with a larger port or 3" with a flare. So I hope it all works out ok. The cabinet will be a simple 3/4" MDF then covered with black ash covering from parts express. It will be hidden in a cabinet anyway so mostly it will not matter about looks.

It should be rocking in less than a week. Ill report back once its finished.
 
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