Cheap and simple Open Baffle (a la MJK) - diyAudio
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Old 18th March 2012, 12:15 AM   #1
sreten is offline sreten  United Kingdom
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Default Cheap and simple Open Baffle (a la MJK)

Hi,

This was prompted by the rather excellent performance of the
Vifa TC9FD18-08 :Zaph|Audio see the Dec 4th 2011 entry.

Vifa TC9FD18-08, 3.5" Full Range: Madisound Speaker Store

Now have a look at MJK's : http://www.quarter-wave.com/OBs/OB_Design.pdf

My suggestion for the woofer to go with the above is two of these :

GRS 12PF-8 12" Paper Cone Foam Surround Woofer 292-412

Criminally cheap for 4. Will be 93dB sensitivity for a pair albeit 4 ohms.

Use MJK's baffle and FR positioning, stack the woofers below.
Remember to chamfer properly the rear of the FR's opening.

For the bass c/o in MJK's article you need to halve the inductor value
and double the capacitor value, which works out cheaper, all good ....

Other than modest efficiency what is there to complain about ?
(Though the circa 85dB on axis may sound a bit more in room
due to the extra rear radiation, for farfield listening postions.)

I haven't built them, but they seem a compelling proposition.

rgds, sreten.

P.S. don't think for one minute these are high power handling
speakers because the two bass units give a rating of 240W.
They will be suited to normal modest hifi amplification.
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When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 18th March 2012 at 12:41 AM.
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Old 19th March 2012, 12:17 AM   #2
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Smashing!!! How original and unique. You are a internet star!!!
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Old 19th March 2012, 12:52 AM   #3
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Default Similar to these

Here's a similar design.


The best affordable DIY open baffle loudspeaker I've listened to so far.
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Old 19th March 2012, 03:06 PM   #4
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by fastbike1 View Post
Hi,

Yes it is similar but also different it some respects. The main difference
is the nominal difference in the bass driver and FR drivers sensitivity.

In the ultra this is 2dB and in the above its 8dB, its all very much
as described by MJK. In his article the difference is 6dB but I recall
reading somewhere for the active version the bass was lifted by a
further 2dB for best balance so 8dB should be fine.

I can't comment on now the Ultra 2dB (+ the drivers 3.5dB peak)
works compared to MJK's design, but I guess baffle size needs
to be a lot larger so you get less baffle loss in the bass.

The above is much closer to MJKs arrangement, you've got a total
difference of 12dB at 35Hz (driver has a 4dB peak) to play with.

I would be tempted to fold the baffle a little to reduce width,
but inherent in the above arrangement is the baffle loss that
is needed for balance allows a relatively small baffle.

It is very much a version of MJK's design, a very cheap version.

rgds, sreten.
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Old 19th March 2012, 03:08 PM   #5
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by motosapien View Post
Smashing!!! How original and unique. You are a internet star!!!
Hi, the real star is of course MJK, (and Zaph), great article, rgds, sreten.
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Old 19th March 2012, 03:36 PM   #6
sreten is offline sreten  United Kingdom
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Default Prices

Hi,

The Vifa FR's are $12 each
Vifa TC9FD18-08, 3.5" Full Range: Madisound Speaker Store

The GRS bass units $12 each (for 4)
GRS 12PF-8 12" Paper Cone Foam Surround Woofer 292-412

The inductors are $11 each
4.0mH 18 AWG I Core Inductor 266-562
4.5mH 18 AWG I Core Inductor 266-564

The FR film capacitors $7 each
Dayton Audio DMPC-25 25uF 250V Polypropylene Capacitor 027-438
The bass unit capacitors $7 pair
125uF 100V Non-Polarized Capacitor 027-362
Dayton Audio DMPC-10 10uF 250V Polypropylene Capacitor 027-428

That makes a grand total of ~ $125 per pair (+postage).

rgds, sreten.

Air cored inductors with reasonably low DCR don't make any real sense
here, it would be cheaper to go active with T-amps than buying those.
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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; 19th March 2012 at 03:55 PM.
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Old 20th March 2012, 02:22 PM   #7
boone is offline boone  United States
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Parts Express has the Vifa so everything could be combined and shipping would be free!
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Old 20th March 2012, 02:31 PM   #8
Tea-Bag is offline Tea-Bag  United States
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Have you considered the highs might stink? The graph's dont look too impressive.
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Old 20th March 2012, 06:40 PM   #9
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The Vifas have been pretty successful in this role in several designs. I think they sound pretty good. The graphs actually look pretty good for an extended range driver.

Quote:
Originally Posted by Tea-Bag View Post
Have you considered the highs might stink? The graph's dont look too impressive.
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Old 20th March 2012, 07:03 PM   #10
Tea-Bag is offline Tea-Bag  United States
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I was thinking more along the lines of adding a tweeter if needed.
I played with MJK's smaller baffle a couple years ago. The best full range IMO was the FF85K. Now out of production, but Madisound does offer the newer version.
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