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Old 4th March 2004, 12:44 PM   #11
MarkMcK is offline MarkMcK  United States
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Default W4-654S in a small box: A design exercise.

The small box pictured above, measuring 15 by 17 by 25 centimeters with an internal volume of .15 cubic feet, is not the optimal enclosure. If, however, you have a need for a loudspeaker in a very small box, this is a possible solution with fairly good fidelity. Compared to a larger enclosure, the required pre-filter is more complex and more expensive. This small loudspeaker is most lacking in bass extension. Fs is about 160 Hz. Yet, because of rear loading, without the pre-filter, the output is still rising even below Fs. With the pre-filter, F3 is below 100 Hz. There is no ripple or other anomalies in the response. You cannot, however, beat physics. Distortion levels below Fs are high.

The attached graph shows the near field response (microphone placed 12 cm away from driver, data truncated at 25 ms.

With the small box pre-filter, I can listen to these loudspeakers. I can even seriously listen to them. I notice the lack of bass extension, the higher distortion, and coloration of some mid bass sounds. I also notice better than average clarity and detail in the midrange and treble, and a defined soundstage dependent upon the musical selection.

Mark
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Old 1st July 2004, 02:20 AM   #12
MarkMcK is offline MarkMcK  United States
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Hi all,


Here is another modification for a different Tang Band four-inch driver. This time it is a PPM cone and a lovely little neodymium motor assembly.

I have posted details of the W4-1052SA modifications to my Web site.

You can only get there by following the links I post to this forum. I will duplicate this message on the "Has anybody heard these" thread.

The modification is simple, inexpensive, and can be undone. This will not void warranties or anything else. The sensivity of the driver after modification is unchanged. In its stock state the rise in upper mid to treble response is greater than specified sensitity. Also, so little mass is added to the cone that T/S specs change no more than the difference between Tang Band's T/S published spec and actual measured specs. In other words, it is unimportant should you want to listen to the sound of the box air mass in resonance and port the enclosure.

After modification, the driver sounds accurate. The improvement is easily heard and brings the performance and accuracy to a level that is equal to any four inch on the market.

Here is the link:

http://madspeaker.com/Projects/TBW4-1052SA.htm
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Old 1st July 2004, 06:13 AM   #13
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Mark,
Where in Ohio are you?
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Old 1st July 2004, 07:33 PM   #14
MarkMcK is offline MarkMcK  United States
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I am in central Ohio. Capital city and all that.

Mark
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Old 16th August 2004, 09:36 PM   #15
MarkMcK is offline MarkMcK  United States
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Default TB881S glue ring mofication

My Tang Band modifications posted to this thread are out of order. The W3-881 modification is the first modification I talked about on this forum. You can find performance results in the system picture thread with additional explanations of why the W3-881 benefits from modification. In addition, to really mix up the order of this thread I will be adding posts of one update and one modification that are already part of different threads on this forum.

This posting, however, details how to make one series of modifications to the W3-881. This modification series is different from the modifications pictured in the system pictures thread or the upcoming brick and mortar publication. This modification uses a glue ring addition to the cone and a plug replacement for the dust cap.

While this modification is different from the brick and mortar modification, it is still valuable in that it corrects a number of problems in the stock unit and does bring performance to hi-fi levels. This modification is also easier to complete with less risk of a mistake ruining a driver. Indeed, the only difficult task is removing the dust cap, and that task is fairly easy to accomplish.

The dust cap shape consists of one piece with two shapes. One shape is the central dome; the second is the flat ring or rim used to glue the dust cap to the cone. The preferred method for removing the dust cap is to use an Exacto knife to cut away the dome portion of the dust cap, leaving just the rim ring. Then, with the blade edge facing away from the cone, slide the tip between the dust cap rim and the cone. Lift upward to cut the remaining ring of the dust cap rim. Using needle nose pliers, pull on one of the cut ends and peel the remaining rim away from the cone.

Next apply a thin bead of GemTac glue to the cone as shown in the picture. The glue ring is made from a bead of glue .75 to 1 mm in diameter and three mm in from the inside diameter of the surround.

Last, center and secure a plug to the pole piece to replace the dust cap. A photo is included with a US nickel for comparison of size.

Good designing and good building,

Mark
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Old 17th August 2004, 01:11 PM   #16
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Genious thread. I have some similar drivers in hand - those found in the Logitech Z680 5.1 surround speakers.

Br.

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Old 17th August 2004, 03:41 PM   #17
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Mark,

Do you think there would be further benefit in fabricating a solid copper ring (shorted turn) which could fit in a step machined into the base of the new turned aluminum phase plug, or making the phase plug from solid copper?
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Old 17th August 2004, 05:14 PM   #18
Bill F. is offline Bill F.  United States
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Mark,

Bravo! Great work! And thanks for making it so accessible to DIY laymen.

Would you care to describe for us how you go about hunting down the resonant culprits in these various drivers, how you read response/decay graphs of stock units and devise a plan of attack? Or is it largely random cut and try?

I'd be very interested in the processes and reasoning you use to arrive at improvements.
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Old 17th August 2004, 05:38 PM   #19
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Default Re: TB881S glue ring mofication

Quote:
Originally posted by MarkMcK
the upcoming brick and mortar publication
Tell us more... i'm almost ready to order it, and with only a vague idea of what it will be about or how much it will cost -- just based on the high quality of the posts made to date.

dave
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Old 17th August 2004, 07:33 PM   #20
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Whereabouts in Ohio are you, Mark? Always looking for a local Ohioan to talk speakers with and to help each other out. I'm located near Columbus, in Hilliard.
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