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Old 10th October 2007, 03:01 PM   #1
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Hi,

I'm a total newbie to both electronics and woodworking, so for a first project I'm trying to come up with something modular that I can embellish as my skills (and budget) improve. I thought I'd start with a powered speaker consisting of a LM3875 monoblock kit from Audiosector and a single full-range driver in a simple enclosure (to be used as a portable iPod amp). If all went well, I would probably construct another one of these in the future for stereo. Then, I might like to put together a preamp (I'm thinking of the Kookaburra from Twisted Pear), with an extra output for a subwoofer. Finally, I'd construct a powered subwoofer to round out the sound.

Questions:
1. What would be the best type of enclosure to use? I was thinking about sealed or ported, but I'm concerned about whether I'll be able to get much bass out of this. I want the system to be listenable prior to the addition of a subwoofer.

2. Can anyone recommend a good driver to use? Would the distance between the preamp and the powered speakers (at least several feet) be problematic?

3. Are there any further considerations that I should be aware of?

Thanks very much in advance
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Old 10th October 2007, 03:36 PM   #2
gni is offline gni  United States
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Quote:
Questions:
1. What would be the best type of enclosure to use? I was thinking about sealed or ported, but I'm concerned about whether I'll be able to get much bass out of this. I want the system to be listenable prior to the addition of a subwoofer.
The best type of enclosure is what sounds best to you; I like
acoustic suspension first, open baffles have their place, ported are
tricky, horns are next to impossible. . . A good acoustic suspension
sounds good; they offer reasonable low frequency extension without
too much distortion. They do take more power but within reason they
work well in smaller rooms and are listenable before the addition of
a subwoofer.

The single driver might need a baffle step compensation circuit
which might be incorperated into the amplifier. . .

Quote:
2. Can anyone recommend a good driver to use? Would the distance between the preamp and the powered speakers (at least several feet) be problematic?
See some of the great projects on the DIY auidio website. Parts
Express has projects also; driver recommendations are also made.
The driver needs to have the correct specs for sealed or ported or
even single driver; what have you listened to and what do you
like and dislike -- that will determine what your system will be
made from.

Distance from the preamp and the powered speakers should be
kept a short distances. . .up to about 12 feet unbalanaced and
hundreds of feet balanaced. Depending on the preamp and the
amplifier, you might be able to get away with more distance; it
all depends on how much interference you can accept. I've run
over 40 feet of unbalanced with acceptable interference and small
loss of overall sound quality.

Quote:
3. Are there any further considerations that I should be aware of?
A system of this type will be listenable and very affordable; the
ease of assembly is also a factor. K.I.S.S. factor: Keep It Simple. .
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Old 10th October 2007, 04:53 PM   #3
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Quote:
Originally posted by gni

The driver needs to have the correct specs for sealed or ported or
even single driver; what have you listened to and what do you
like and dislike -- that will determine what your system will be
made from.
I haven't actually listened to much different equipment at all, but I do have some idea of what I'm aiming for: flat frequency response with good detail, enough bass, and some sense of air/space. Basically, just as close as possible to accurate reproduction of the music as it was recorded.
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Old 11th October 2007, 03:22 AM   #4
gni is offline gni  United States
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Don't we all.. . .to some extent. Maybe you should try to listen to
some different speakers to see the direction you want to go in.

There are some speakers on the market that have what is considered
"flat" response but sound harsh to the ears; each different type of
speaker system will interact with you differently. Ever been in a room
with someone with hearing loss. . .they crank up the treble and just
plain crank it up. To them, it now sounds flat or pleasing to their ears.

Most people don't use 'studio monitors' in their home because they are
designed to be 'flat' to some standard. I like my acoustic suspension
designs! It might be a little like politics: if you were brought up
being a conservative then you are likely to continue being a
conservative since that is what is familiar.

Maybe you should start out with a good kit loudspeaker and amp
and see how you like it. . . change the cabinet when ready. . .add
power later. . . but it is going to take some serious listening tests.

Full-range drivers might sound harsh to most people; a properly
constructed version will give hours of listening without the urge to
turn the darn thing off. Breakin time is really necessary for the full
range single driver.

Most people on the DIY forum have some preference. . .some founded
and other just set in their ways.
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Old 11th October 2007, 12:34 PM   #5
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Thanks for all of your feedback so far. It's been very helpful. I posted a thread asking about the FR125S in the full range driver forum. Do you know whether one of these could be driven effectively from an LM3875? I've read some really positive things about this driver, but some people seemed to think that it wasn't a good match for a chip amp.
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Old 11th October 2007, 12:50 PM   #6
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
Hi,
my listening is restricted to a few British speakers/drivers and a very few Continental.
The FR125 is reputed to be quite nice as a full ranger.
Combining the amp and box makes it more difficult if it does not work well. I would keep them separate, at least until you have convinced yourself they make good partners.

A twisted pair of interconnects without screening can go a lot further than 12feet (4m) if the pre-amp is designed correctly. Yes, source impedance (Rs) overrules all!
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regards Andrew T.
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