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Old 31st January 2006, 02:36 AM   #1
cirvin is offline cirvin  United States
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Default Beginner bookshelf speakers

Hello all!

I have some questions reguarding general speaker cabinet design and a possible project of mine.

I want to build a nice little stereo system for a friend, and I'm having some trouble figuring out what I'm going to do about speakers. I've been searching on google for the past couple days, but it seems to me that basic information on speaker cabinet design is hard to come by. Lots of sites documenting speakers people have built, but not really any explination on why the design is the way it is.

First of all, I realize that cabinet volume needs to be matched to the driver, but does the cabinet need to be rectangular? Can it be any other shape as long as the internal volume is kept constant?

Do drivers need to be recessed in the front panel? I've seen many sites that recomend it, but why?

How much benefit is gained by having rounded edges on the front panel? Why?


Returning to the stereo project, after I searched around a bit I found this design.

http://users.d-web.com/dbrown/db41/db41.htm

It seems to meet my requirements of being simple, small, decent (sound wise), and low cost. I am a little worried about the LF reproduction, some of the music my friend listens to has a decent amount of bass in it.

Does anybody have any tips or suggestions for a first timer?

Thanks for hearing me out.
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Old 31st January 2006, 03:52 AM   #2
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I think the best advice a lot of people on this forum would give to a newbie such as yourself is to buy a ready-made kit or to build someone else's design such as the one in your link.

A great place to find kits and projects is www.partsexpress.com , and while you're there you might consider ordering a copy of The Loudspeaker Design Cookbook. A great site for "bookshelf" and other small loudspeaker designs is www.zaphaudio.com.

Your budget will be a large determining factor in what you end up building, so providing that will help others here steer you in the right direction. If you plan on building your own cabinets then the types of tools you have, or can get, is also part of the overall equation.

As for the design you referred to, I would consider going with a larger woofer if your friend likes bass, as well as porting the enclosure (how big is the listening room?) - either that or consider adding a small sub to the set-up.

Hope this helps.
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Old 31st January 2006, 07:47 AM   #3
Wodgy is offline Wodgy  United States
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The best website for actually understanding why a designer makes the choices he does is John Krutke's www.zaphaudio.com . He generally has a decent discussion of various interesting factors that impact a design. If you read through all the projects on his site and look at the graphs, you'll learn quite a bit about speaker building. Obviously he doesn't cover every aspect of each speaker design, but that would take pages and pages of text and graphs. His descriptions usually strike a balance between informative and accessible.
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Old 1st February 2006, 08:21 PM   #4
cirvin is offline cirvin  United States
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Thanks for the info, got some better search terms out of those links too.


Zaph had an intresting article explaining the recession of drivers and rounded edges, so that question is answered, though I'm still fuzzy on the enclosure shape. I read about a certain ratio somewhere, but I see oddlly shaped drivers. Hmm, more reading for me I suppose.

As for the bookshelf speakers, I figure I can cheat and pull up the bass a bit with and EQ and reccomend that the speakers be shoved up against a wall.


I'm going to start looking around at matirial prices and all that fun stuff later this week.


Thanks for the help!


EDIT:
The listening environment will be a bedroom, about average size for a teenager. Budget? Flexible, though I'd like to keep costs down as much as I can without too much of a sacrifice. I do have access to a wood shop with a table saw, planer, joiner and hand tools.
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Old 1st February 2006, 09:31 PM   #5
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I'm no expert, but as far as enclosure design, I know a few things to avoid, that are generally considered 'rules of thumb'.

Avoid equal length edges. Cubes would be bad, perfectly square tops are not so good, but having every side a rectangle is good. Less possibility for standing waves and resonance that way.

Along the same lines, avoid edges that are direct multiples of each other. For instance, avoid an 8 X 16 baffle. Again, resonance issues.

If you can, avoid parallel surfaces. This is tricky, from a cabinet making perspective, so a lot of people don't do it, but look at many of the really advanced DIY projects, and how they avoid parallel walls whenever possible.

If you can do those things, then the shape doesn't matter as much, the volume is more important. It will have an effect, but it won't be drastic, unless you go with a really extreme shape, like very long and thin.

You can use other shapes. A sphere might not be so good, but an egg might be interesting. I saw some nice fullranges with a parabolic cross section.

Anyway, for your first speaker, don't get yourself into anything too complex. I'd start with someone elses basic design, speakerbuilder.net has some nice 'budget' designs (like this one: http://speakerbuilder.net/web_files/...ts/DBP/dbp.htm ), and by the time you are done, you'll have learned a lot, and gotten some practice, and if you mess up, it won't be too bad. Then for your next project, go nuts.

peace,
sam
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Old 2nd February 2006, 06:47 AM   #6
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One thing to add about flush mounting speakers is that there are some drivers that are designed be surface mounted. The GR Reasearch M130 is one but there are others.

A design you might want to have a look at is the MBOW speaker by dennis murphy. There is a MBOW version with a seas tweeter that would be a reasonable cost. The MBOW 1 with the hiquphon tweeter would be pricey. The GR Reasearch M130 is a very good driver, quite inexpensive, and does not require flush mounting. The designer is one of the best in DIY audio.

www.murphyblaster.com
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Old 2nd February 2006, 07:13 AM   #7
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For a bedroom you want it fairly small, and a small bookshelf speaker is going to get about as loud as he is likely to get away with.

I'd say choose drivers that someone else has used in a design where the crossover is documented.

A good starting point is a small 2 way vented speaker with a 6.5" midbass and a 1" tweeter. Drivers like Vifa P17, Peerless HDS, Seas are likely good choices.

Box design is pretty simple. Make it solid and include internal lining (eg open cell foam), stuffing if it is sealed. Include bracing to make it stiffer. A simple rectangular box is a good start. Rounding the edges is not necessary. Recessing drivers looks a lot better but I wouldn't say that is critical either.

Download WinISD to simulate. You are dealing with NET box volume. A box is tuned by its volume, and the diameter and length of the vent. Start with ~ 40 Hz tuning for a typical 6.5" midbass driver. Tuning higher will often give a bit of bass boost typical of many bookshelf speakers - initially more impressive. A more typical audiophile approach is to design for a flat response, or tune even lower which may in your room sound better if there is some room gain at work.
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Old 3rd February 2006, 12:28 AM   #8
cirvin is offline cirvin  United States
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Thanks for all the information!

I think I will go with phidauex's suggestion and build that unit. Small, cheap and seemingly decent sounding.

Next step, find MDF.


Thanks everyone!
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Old 3rd February 2006, 12:53 AM   #9
dvdwmth is offline dvdwmth  Canada
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the dayton classic drivers are a great deal and that designer is well respected, but you'll get much better quality from the mbow (mb27). The seas tweeter is competitive with some of the best regardless of price and the gr research m130 was recently tested and was up there with some very excellent drivers.

If I had to choose a small two way project to build for myself, the mbow would definately be on my short list with only a few others.
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