Modify old speakers to fit into a boat sound system

[Sailboy]

Helllo, I'm a brand new member, and know very little about speaker electronics. I am a boat carpenter/woodworker/shipwright by trade. My interest in vintage audio is quite recent. I've been getting a big kick finding amazing audio gear for next to nothing.

My problem is space. I live on my 40 foot trawler and my "livingroom" or salon if you will is 8 ft by 8 ft. I don't want dinky little suroundsound speakers. I want to use Polk Audio Monitors 4.5's as background speakers. Being that they're ported can I discard the boxes and build the components into a cavity in the boat? Will they perform correctly?

Sure would appreciate any input.

 

[Sailboy]

If i build a new box with a different shape but the same cubic space, how is the sound affected? Is there some formula for this - or some reading i can do to understand this?

 

[Foxx510]

The crossover components(electrical circuit in the speaker box that separates the sound for the tweeter and woofer) are designed around the dimensions of the speaker cabinet, so if you say flush mount them in a cavity or change the size or shape of the front panel(known as the baffle) they won't sound right.

What you can most likely do successfully is keep the baffle the same dimensions, and keep the same internal volume, but that might not be of any use to you by the sounds of it.

 

[weltersys]

Being that they're ported can I discard the boxes and build the components into a cavity in the boat? Will they perform correctly?

Yes, they will. Foxx510's comments are correct, crossovers are designed around the baffle size and may compensate for the "baffle step" transition, but the Polk Audio Monitors 4.5 are designed as "bookshelf" speakers, implying they are often placed on a wall, similar to what you may be doing. Keep the cabinet volume and port sise and shape the same, and you will be good to go. Design the "toe in" to cross the center of the listening area.

At any rate, any difference in response can be corrected with a graphic equalizer, which are available either separately, or built in to amplifiers.

The speakers I made for my sailboat, in that cabin, were among the best I have ever heard, using Seas co-ax and helper woofers. Rocked the boat with a 10 watt 12volt amp. I also used a third speaker (without the extra woofer) hooked up from left + to right + as a "Phantom Stereo" speaker located by the entrance, so no matter where you were seated in the cabin you could hear stereo. The wiring of + to + for the phantom speaker insures only the difference information between left and right are played, so it does not have to support bass, since most bass is mixed mono.

Art

 

[whgeiger]

Moisture is the Enemy

If i build a new box with a different shape but the same cubic space, how is the sound affected? Is there some formula for this - or some reading i can do to understand this?

The more irregular the shape of the cavity the better (the more diverse the set of standing wave frequencies and the weaker the relative intensity of each). There are formula for these but their exploration in this setting is not mission critical. If this is an ocean going vessel, I would be more concerned about driver mortality due to the moist/corrosive atmospherics. Stay away from reflex enclosures that circulate air in and out of the back chamber. Sealing paper cone drivers should also be explored. Do not use organic damping materials inside the enclosure.

Regards,

WHG

 

[chrisb]

The more irregular the shape of the cavity the better (the more diverse the set of standing wave frequencies and the weaker the relative intensity of each). There are formula for these but their exploration in this setting is not mission critical. If this is an ocean going vessel, I would be more concerned about driver mortality due to the moist/corrosive atmospherics. Stay away from reflex enclosures that circulate air in and out of the back chamber. Sealing paper cone drivers should also be explored. Do not use organic damping materials inside the enclosure.

Regards,

WHG

BINGO

 

[Sailboy]

Awsome input. Thanks. The more irregular the shape of the enclosure? Could you expand on that a little. I don't quite follow.

The Polk speakers sound a little boxy as they are. Too much internal echo. Which way on what parameter do I go to correct that? Does anyone know?

 

[whgeiger]

Notes

Awsome input. Thanks. The more irregular the shape of the enclosure? Could you expand on that a little. I don't quite follow.

The Polk speakers sound a little boxy as they are. Too much internal echo. Which way on what parameter do I go to correct that? Does anyone know?

When signal wavelength becomes comparable to an internal enclosure dimension, a standing wave appears. The larger the volume of air bounded by this dimension the greater will be the wave's negative effect on system frequency response. For small enclosures, a lining of acoustic fiberglass board should be sufficient to mitigate enclosure resonances.

Most likely the suspension compliance of the 6-1/2 cone drivers used has changed, which has caused the system to become "detuned" (the driver resonant frequency is no longer suppressed by enclosure acoustics). This would account for their "boxy sound". To understand the process see

Bass reflex - Wikipedia, the free encyclopedia

Recommend you buy new loudspeaker drivers to go with the enclosures you plan on building. There are lots of good kits/designs out there from which to choose.

Regards,

WHG

 

[Sailboy]

I planned on putting speakers into the ceiling - headliner with a mahogany soffit type structure around the perimeter. The height is restricted to 4 inches, but in terms of volume I can move laterally.