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Old 15th June 2008, 09:28 PM   #1
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Question Newb looking for some expert advice for his first project (5.1 speakers)

Hi All

I am looking to get stuck into my first speaker project (it's been on the todo list for so long!)
the project is this.

I have the remains of two sets of creative surround sound speakers (all the speakers are made by cambridge soundworks) ... while these are nothing particularly special i thought they would be a good way for me to get into designing enclosures etc.

so i have 2x 6in subs, 10x 2 1/2in speakers (1 of these has a dented cone... any suggestions on how to pop it back out?) and 1x 3in speaker which was the centre speaker for one set ( see attached image ) . i have no idea on Thiele-Small parameters as emailing csw was less than helpful... so i will have to do this myself once i have the kit.

my thoughts were to create a 5.1 surround sound set using these speakers... but being new to this subject the wealth of different enclosure designs is a little overwhelming.

in terms of requirements:

i'm mainly looking for audio quality... the room they will most likely end up in is pretty small so volume is not important.

build material will probably be mdf for cost reasons.

there is no requirement for enclosure size it can be as big as it needs to be, floor-standing or bookshelf.. whatever would sound best.

i don't currently have an amp to drive them... that will be another days DIY project.

so my question to the experts is... with all the above in mind what kind of enclosure design would be the way to go for all this (so a design for a subwoofer, a centre speaker, front speakers, and rear speakers)? i'm not afraid of hard work and i am pretty technically minded...and in truth if it all goes wrong i'm not too worried... half the fun is in the journey... if someone says do a 6th order bandpass with isobaric speaker setup for the sub, or get out the soldering iron and make some crossovers then count me in!

thanks in advance for any and all suggestions

Tim
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Old 19th July 2008, 03:15 AM   #2
hy fy is offline hy fy  United Kingdom
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Default recycle!!!

Hi, isnt it frustrating when no one replies to a perfectly valid question...

Without T/S figures its very hard to build suitable enclosures without some trial and error. The small "full range" speakers have most likely very low sensitivity and poor bass and power handling. The 6" "bass" was most likely aligned previously in an isobaric configuration , internally face to face(clamshell). This makes for a small box and some removal of error effects within the drivers but requires more power. The original box is probably about the same size as needed for one driver in its normal alignment.(Isobaric loading halves normal required volume for a given driver) This method with bandpass is often employed in compact systems to produce greater perceivable low end.

It all depends on the type of sound you are after. If it were my project, I would build two cabinets with a simple reflex(ported) low end on the 6" with a simple OB(open baffle) panel for the smaller speakers. You could use a front loaded horn to increase output and sensitivity also.
A reflex box will generally be about twice as large as a sealed unit but has the advantage of low distortion, increasing the bass output increasing power handling and reducing cone movement. (above Fs/resonant frequency))I would try building a box similar dimensions to the original but with only one driver at the front and one port(nothing inside the box) If the port is too big it will sound boomy and the very low notes will move the speaker more than desirable, if it is too small, there will be less weight and output you may also hear air turbulance as the port is active on the low end. A large diameter port must be made longer to tune it down. Small diameter ports tend to be very noisy.
You could of course build a much more complicated cabinet such as a transmission line or rear horn(very large for bass) but it would probably cost more than the value of the drivers.

There is much info here and elsewhere on small line arrays, open baffles and horn loading


Simplest of all is OB (open baffle) this is basically a panel on which the speakers are mounted, it acts as a basic divide between the waves from the front and back of the speakers. OB gives less output and power handling but sounds very erm....open and natural as there is no cabinet to "colour" the emergence of the waves.

You really are not going to get much decent output from all speakers in a 5.1 setup even if you have a high-end amp, but as a stereo pair, the results will be worthy im sure. You should find a simple passive crossover circuit,1st or 2nd order will suffice. If you use bandpass for the low end you may get away with only a simple capacitor for the highs.


Experiment with horn designs from simple materials(cardboard, fibreboard etc will do) and see how it sounds,the path length leading to and the area of the horn exit will determine its low frequency cutoff so the bigger the horn the lower it goes. As you have a number of speakers it will be easier to find the right impedance to balance the system without extra components. Eg if your 2.5" speakers are 8 ohms each, you can have an overall impedance of 2,8 or 32 ohms per channel( 4 per box)



Hope this helps. Good luck!!!
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Old 19th July 2008, 03:47 AM   #3
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Location: Utah
Tim,

It's not worth your time and effort to use those parts in those old speakers. Buy some good value raw drivers and start from there. Or build a kit that is already designed. My advise is to built the biggest and most efficient front and center channel speakers that you can afford and have room for and use the old speakers for surrounds. Then build a good subwoofer.
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Old 19th July 2008, 05:42 AM   #4
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The project is created to make others understand the topic .speakers play an important role into it.
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