Hi Joe,
Since there haven't been many people interested I'll respond to that one
here then we should probably move this offline if you decide to continue.
The next step would be coming up with the best compromise of cabinet
size, output SPL, (loudness) bass response and driver size/cost for your
requirements. That can be a bit daunting or not based on your overall
experience, but I can help fill in the blanks if you fill in others.
Once you arrive at the right "blend" of parameters for your design
you'll dimension it, get out the saws and screwdrivers and build it.
Building small speakers in itself is simple, designing them to
specification takes a little work.
If the design process asks too many questions, we can also convert this
into a "small, medium, large" kind of project, which would be much more
straightforward, but reduce the opportunity to learn about the process
itself. If so, you can safely ignore everything below this paragraph and
just pick one of the three.
------------------- DESIGNING THE SPEAKER --------------------
Cabinet size:
Along with driver selection, cabinet size (and porting, which comes
later) *generally* determines how low the freq response can go. If
you're not sure just come up with a rough set of dimensions that would
work well for your shack and we can take a look.
Output SPL: (loudness measured @ 1 meter)
Very modest 85-90db
Average to loud 90-100db
Rock the room over 100db
Bass response:
This parameter has the most impact on cabinet size, driver selection and
overall cost. In general, a -3db response anywhere below 100hz will
cause the overall cabinet size and driver size/cost to climb rapidly.
That isn't necessarily a bad thing, but if you want flat response down
to 40hz at 100db SPL your design will end up several times larger than
placing that -3db point at 100hz. 150hz hits the "high value" spot on
the curve, but higher than that generally doesn't gain much.
Driver size/cost:
Excluding highly specialized units, drivers run from 3" to 8" and cost
roughly $12 to $185 each. As I mentioned before, I happen to like Tang
Band drivers for high-value, relatively small full-range speaker
designs. Limiting the range to $25 - $55 US will yield any number of
truly excellent designs. You can use any brand or driver you want, of
course, but I can only help model those that have published Thiele-Small
parameter data ("TS parameters") available.
...
References/sources:
Selected Tang Band drivers: (this URL may be too long to work, sorry)
http://www.parts-express.com/wizards/searchResults.cfm?searchFilter=&srchExt=MFG&perPage=27&sortBy=3&layout=GRID&page=1&srchPrice=&srchCat=576&srchMfg=276&srchPromo=&srchAttr=
General drivers, mounting hardware, stuffing, port tubes etc
http://www.parts-express.com
http://www.madisound.com
Free design software:
WinISD http://www.linearteam.dk/
FRD Consortium http://www.pvconsultants.com/audio/frdgroup.htm
Many others! - Google "speaker design software"
Disclaimer:
Yes, I do DSP and audio design for a living, but my interest here is
simply raising awareness of the benefits of quality audio in amateur
radio equipment and operation. I will not benefit from this financially,
but in turn I ask that any designs or models I generate assisting
hobbyists not end up in commercial products.
73,
Jim, N7CXI
Joe Camilli wrote:
I would be interested in a project of this type. What would be the next
steps?
Joe N7QPP
On Tue, Feb 2, 2010 at 3:02 PM, Jim Barber <audio...@charter.net
<mailto:audio...@charter.net>> wrote:
Seems like a perfect, low-impact DIY opportunity to me.
Tang Band (for example) makes a number of excellent full-range
drivers that work well in small, ported cabinets. For those in the
US, a trip to Home Depot for a quarter sheet of MDF, (Medium
Density Fiberboard, listed by them as a "hobby panel") perhaps some
rubber feet and a few inches of Schedule 40 PVC for a port tube
could yield a better quality speaker than you can easily buy on the
open market, regardless of price.
If there's (A) a way of reaching consensus on desired size,
appearance and driver characteristics and (B) a few people actually
get interested enough to build one, I'd certainly donate a working
acoustic design. (and/or provide links to freeware design software
for those that want to learn for themselves)
There's still a suitable power amp to deal with, but there are any
number of suitable (kit or assembled) amp modules available as well.
73,
Jim, N7CXI
[snip, for sanity's sake]
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