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Old 22nd June 2011, 06:39 PM   #1
alfiax is offline alfiax  United States
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Join Date: Oct 2005
Default Approaching a simple and cheap NS4-194-8a build

Having grabbed a pair of these from Madisound during the recent Aurasound clearance, I figured I should probably make some use of them, perhaps as a small, single-driver desktop speaker. However, I've never done a scratch design before and would appreciate any input on the following ideas. Simplicity and relative compactness would be a goal, so I'd rule out horn-type designs from the start. Ideally, deducting the cost of the plywood (already on hand), I'd like to spend about as much as I did on the drivers (about $8).

1. Looking at the Qts, these guys come close to being optimally damped as they are-- does this mean they are good candidates for OBs? If so, I'm somewhat confused about the process of panel dimensioning- what size should they optimally be? I understand that I can do some experimenting with corrugated cardboard, but don't have anything like a measurement mic to help me out.

2. If I want to push Q up a bit a sealed arrangement seems like it would work well.

3. Qts is probably too high for any kind of BR approach, right?

Any input you could offer would be appreciated.
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Old 22nd June 2011, 08:13 PM   #2
sreten is offline sreten  United Kingdom
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Location: Brighton UK
Hi,

Unless your open baffles are very large bass loss will be dreadful, not workable.

Sealed boxes will work, there is not much point going over say 150% of Vas.
So around 6 litres sealed will work.
Vented will also work in the above box volume, tuned to 50Hz, this will give
far more lower bass volume capability and efficiency down to 40Hz, but it
will overload easier with very low bass signal frequencies.
a 1" diameter port needs to be 3" long for ~ 50Hz in a 6L box.
I'd use a larger diameter port lined with open cell foam to a 1" opening, 4" long.

rgds, sreten.
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Old 23rd June 2011, 07:23 AM   #3
Tom V is offline Tom V  United States
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This might give you some ideas:
"Tiny Towers", stupid simple build for TB W4-930SF

The online calculator I used was:
http://www.mh-audio.nl/ReflexBoxCalculator.asp
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Old 23rd June 2011, 12:26 PM   #4
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Join Date: Jun 2010
Location: NRW and Munich, Germany
Hi,

I´ve done a quick´n´dirty simulation of the driver with the manucaturer´s specifications.
AJHorn tells me not to go under 8 liters - and use a special design of bass reflex which starts at 50cm^2 and ends at 15cm^2 on the outside - a short transmissionline, if you want.
Port Length is 20cm.
Result is a not-too-tiny speaker of about 38x28x13cm - but bass results should be rather impressive.

I´ve added the result of my simulation. You have to substract about 2-3dB for real-world sound pressure and forget about the curve beyond 1kHz.

Regards Thomas

Click the image to open in full size.
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Old 24th June 2011, 04:18 AM   #5
alfiax is offline alfiax  United States
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Wow, thanks for all the input and suggestions. I pretty quickly caught on about the OB results-- but some of the model results from Tom V and Thomas' setup suggest performance could be a lot better than I expected. I'm thinking of taking a look at ajhorn or some similar sim programs to play around with different options-- are any recommended (and cheap?)
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Old 24th June 2011, 06:02 AM   #6
Tom V is offline Tom V  United States
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Like I say I have used the mh-audio calculator and have had good results, but the recommendations it gives for this drive seem screwy, way huge (24l ?). So maybe a grain of salt is in order......
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Old 24th June 2011, 01:07 PM   #7
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK
Hi,

FWIW there is no such thing as a free lunch. It is tempting with a high Fs
low Vas driver to simply stick it a far bigger cabinet than Vas, say 10L.

For sealed this is fairly pointless, 5 to 7 L is far more sensible. For vented
you do not want that peaking bass roll-off typical of oversized boxes,
its a recipe for a one note boom box bass, which does not sound good.

More modest extension with at most a bass "shelf" is a far better idea.

For vented I'd say maximum 7L, if a sub is involved 3/4L sealed.

rgds, sreten.

KISS - excessive alignments are far more sensitive to exact details,
they interact more with large signal driver variations, basically they
are more difficult to get right, and often simply the wrong choice.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 24th June 2011 at 01:13 PM.
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