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building stereo speakers

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Todd Frye
Navigator

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USA
222 Posts

Initially Posted - 01/09/2003 : 11:18:03

Santa brought me a West Marine CD/AM/FM stereo. I would rather not cut holes in the boat for flush mount speakers... which has now snowballed into making "book shelf" cabinet speakers for below decks. After reading a few books, a two or three driver (speakers) per enclosure system, over a single general purpose speaker per channel, would offer the best sound. I got some blank stares from the people at Circuit City when I said I wanted to make speaker cabinets for my 12 volt stereo. Evidently, the car stereo speakers are not close in quality to the 110 V home stereo speakers. Can any audio experts out there point me in the right direction? Thank you, Todd Frye

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 01/09/2003 : 13:34:14

<b>"Evidently, the car stereo speakers are not close in quality to the 110 V home stereo speakers. Can any audio experts out there point me in the right direction?" - Todd</b>

Todd,

I agree with you about cutting holes in the boat, it is very hard for me to do also.

In both home and auto/boat speakers, you get what you pay for. My brother-in-law manages a high end car audio store and some of the systems they put together for cars are amazing. In his powerboat, he has a rockin' stereo system complete with high end AM/FM/CD, multiple power amplifiers, separate monster bass speakers in their own enclosures, tweeter's,...etc. the whole nine yards. This system is boomin, but it comes at a price. He uses 2 12Vdc batteries, JUST to run the stereo, a third runs everything else. Now, I'm not an audio expert, but I have learned a thing or two from hanging around my brother-in-law.

For superior sound, one must start with the speakers. You can have an awesome stereo, but when coupled to lousy speakers, it can sound horrid. Conversely, a cheap stereo hooked to excellent speakers will sound infinitely better than the first system. Your idea of engineering and building your own enclosures to separate the signals(high's, low's, midrange's) to get the best quality sound might involve a little more investigation. To separate the stereo's signals you will probably need high and low pass filters to send the appropriate frequencies to the tweeters, mid's, and bass. These filter's only allow those frequencies a speaker uses to pass to them. The higher freq's(tweet's) are line of site, so you will want to mount these pointing towards your ear or reflecting off a surface close to the speaker to reach the ear. The mid's are less directional and can just be pointed in the general direction of the ear. Bass speakers can be put anywhere since the low frequencies they produce are omnidirectional. Additionally, you only need one bass speaker since the human ear can't really discern between left and right(stereo) at this frequency range(that is why home theater systems generally only have one powered subwoofer). Since you are only using one subwoofer, you will need a crossover to combine the left and right channels of the bass signal coming off of your radio. Of course you will have to make sure that you match the impedance generally 4-8 ohms of the various speakers. When selecting tweeter's(hard or soft) keep in mind that just because they are small some require lot's of power.

When building the enclosures it is important that they be ported so they resonate at the frequency range of the speaker that is inside them because speakers move in and out to produce sound waves, with bass speakers moving the most. If you didn't have ports or they weren't at the right size, then a vacuum would be created behind the speaker cone that would limit the movement of the cone. For example, a subwoofer moves an incredible amount of air(put your hand next to a real thumper). If this air couldn't freely move in and out, the sound would be muffled and distorted.

Another important aspect is output power of the radio and speakers. The more power the radio/amplifier puts out the better the sound, depending on whether the speaker's can handle it. Most radio's are 4 channel(left, right, front, back) and have a power rating in watts. A 100W(4 X 25) stereo puts out 25watts on four channels. When selecting a radio by it's output power keep in mind that this is usually peak power(volume all the way up and crappy, ouch!) and not RMS(root mean square) which is less. Also, if you are driving a 200W 6 x 9 speaker with only a 25W output channel, you will not get the performance out of that speaker. In this case you will need an amplifier to boost the 25W signal to the optimum operating range of the speaker. When selecting power, keep in mind that the cabin is a very small space and it won't have the acoustics of Orchestra Hall.

You can engineer your own stereo/speaker system and build your own tuned resonant enclosures, but another option would be to let the sound engineers do all this work for you and go to either BoatUS or West Marine and pull a set of boxed speakers from the shelf.
<img src="http://www.boatus-store.com/icatalog/images_c/067_02.gif" border=0><img src="http://www.boatus-store.com/icatalog/images_c/067_03.jpg" border=0>

Don Lucier, 'North Star'
C25 SR/FK
Cradled on the hard, 200ft from Lake Erie

Edited by - dlucier on 01/09/2003 13:36:12

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lewalskim
1st Mate

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USA
70 Posts

Response Posted - 01/09/2003 : 13:37:35

Todd,
Speaker elements are not rated in voltage but rather resistance. Normal home speakers usually have 8 ohms of resistance and audio speakers are usually 4 ohms. What this means is that with the audio source (your new West Marine radio/CD player [output wattage probably rated for 4 ohms]) the 8 ohm speakers will present more resistance to the electrical signals thus not being as "loud" as speakers rated at 4 ohms. You can use either though, just make sure all speakers connected are the same resistance.

I would suggest that you consider some of the small two way (tweeter and mid-range) metal or plastic enclosure speakers from someplace like Radio Shack. They are not too expensive and can be mounted on brackets wherever you want in your cabin. I saw West Marine brand speakers of this type about a month ago on sale at my local WM outlet center. I think that building your own enclosures would be a lot of extra work and maybe more expensive since you'd need to get individual drivers, crossover components, and build the cabinets. I don't want to discourage you but it just doesn't pay to build them yourself anymore. Almost the same as PC's nowadays.

For use on your boat, I doubt that you would get much benefit from 3 or 4 way speakers. The sound quality from extra drivers (woofers and super tweeters) just won't come through in that environment.

Mark Lewalski
"Little Wind"
C250WB #206
Safety Harbor, Fl (aka Tampa Bay)

No sooner did I post this and I find that Don beat me by a couple minutes!

Edited by - lewalskim on 01/09/2003 13:41:16

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Arlyn Stewart
Master Marine Consultant

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USA
2984 Posts

Response Posted - 01/09/2003 : 13:44:31

I agree about cutting holes... my alternative were these marine environment speakers. Mounted within the cabin, they are heard fine under sail but will distort if turned up loud enough to be heard while motoring.

<img src="http://www.cox-internet.com/arlynstewart/speakers_002.JPG" border=0>

Arlyn C-250 W/B #224
R&R N/E Texas and Great Lakes

[url="http://www.cox-internet.com/arlynstewart/"]Arlyn's C250 Mods n Cruisin Stories[/url]

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jheard
1st Mate

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USA
49 Posts

Response Posted - 01/31/2003 : 18:12:40

Cutting holes in the cockpit for flush mount speakers are the way to go for the cockpit. I put mine on either side of the companionway. If I had to do over again, I would put them back by the tiller on the "backrest" of the cockpit seat (the coaming?). It is high enough to hear, but no one ever sits there because of the tiller, so they would not get blocked.

For down below, I plan to use box speakers, similar to the speakers pictured in the post above.

For the stereo, I used a marine FM/CD stereo from West, but I think any regular car stereo would be fine down below.

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