Strange TQWT behavior with the small TangBand W3-871S - diyAudio
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Old 8th April 2005, 05:55 PM   #1
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Default Strange TQWT behavior with the small TangBand W3-871S

Hello everybody !

Very impressed by a french TQWT kit seen in a loudspeakers shop, based on Fostex FX-120, I decided to study and build my own TQWT enclosure for home-cinema speakers. I choosed the TangBand W3-871S for its perfectly flat frequency response and its good 0,6 qts regarding to its small size. I spent very much time on the Internet, studying the behavior of quarter wavelengthes, and looking for well-working plans, to have an overview and extrapolate a "building theory". I knew it would be a harsh job, but I have been quite disapointed by the result, almost the same as in a sealed enclosure. . (look at the picture, taken with a calibration mic and True RTA 3)

The box has been built with the driver placed at 1/3 of the length, the length is 1/4 of the Fr (110Hz) and the port has the same surface as the driver Sd. The box is two times deeper than the loudspeakers diameter, as I can see it on every TQWT enclosures I saw.

I then saw the "needles" enclosure for VISATON FRS8 and was surprised to see it was tuned at 50Hz, which goes completely against the tehory !

So, if anyone could explain me this, I'd be glad because I don't understand why would'nt it work with me, and why an ultra-low-tuned enclosure works
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Old 8th April 2005, 06:35 PM   #2
joensd is offline joensd  Germany
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which goes completely against the tehory !
Talking about "against the theory": have a look here:
http://www.visaton-bausaetze.de/hifi...i/lancetta.htm

Also have a look here :
TQWT for the TB W3-871S
I built the QWT posted in post4. A picture and measurements can be found in post44.
Looks similar to your graph. I also expected a little bit more below 100Hz but I can tell you the difference between the QWT and a BR I tried is not small. Although the QWT doesn´t go much deeper it does so with more "clarity" in the bass.
Any hints to what enclosure you used?

greets
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Old 8th April 2005, 07:41 PM   #3
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Here is the picture of the plan. The quality is bad due to the obligation of small size. As I don't reinstalled Photoshop, I couldn't compress it more.

It's a classical folded TQWT with frontal port. Notice the ratio of the dimensions of this port are the ones of the gold number


I saw your speaker, but you seem to have put a much smaller port that looks like a bass reflex The frequency response is like mine, and I tried to put a reflex port, because using CAAD4.1, I could expect a 65Hz f3 but that's totally wrong ! The reflex port just "kills" the subtles details of the sound. I hate reflex loading anyway for hifi purposes.
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Old 8th April 2005, 08:52 PM   #4
zobsky is online now zobsky  India
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i think there is another plan "cyburgs needle" (Cyburgs-Needle for Tangband W3-871S) which deals with a lower tuned enclosure for the 871 . please post your opinions if you build it.

regards
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Old 8th April 2005, 11:46 PM   #5
Lionel is offline Lionel  France
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Sorry to be so brutal... But the real question is what the **** are you waiting from a small cheap speaker ?
If you are waiting surprise perhaps it could be ok, but if you are waiting HiFiifi...
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Old 9th April 2005, 01:11 AM   #6
MJK is offline MJK  United States
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The box has been built with the driver placed at 1/3 of the length, the length is 1/4 of the Fr (110Hz) and the port has the same surface as the driver Sd. The box is two times deeper than the loudspeakers diameter, as I can see it on every TQWT enclosures I saw.

Quote:
It's a classical folded TQWT with frontal port. Notice the ratio of the dimensions of this port are the ones of the gold number
Unfortunately, it would appear that you used the classic rules of thumb and probably got the classic results. The classic TQWT does not perform very well. If you want better performance, you should try some of the newer methods for designing this type of enclosure.

Also, if you use a cheap driver then right from the start you are probably limiting the potential of the final results. You get what you pay for in life. Try one of the Fostex drivers as a minimum.
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Old 9th April 2005, 01:38 AM   #7
joensd is offline joensd  Germany
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Sorry to be so brutal...
Rather
Quote:
But the real question is what the **** are you waiting from a small cheap speaker ?
Maybe something special or whatever (great imaging, almost perfect treble response without being harsh........)?
Quote:
If you are waiting surprise perhaps it could be ok, but if you are waiting HiFiifi...
I personally was surprised and IMO I got plenty of Hifi.
If you´re talking about bass..., no you can´t expect wonders.
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Also, if you use a cheap driver then right from the start you are probably limiting the potential of the final results. You get what you pay for in life. Try one of the Fostex drivers as a minimum.
Unfortunately you (almost always) get what you pay for but for a 3" you get quite a bit with the Tangband.
I´ve only the Fostex FE-167E to compare with and I can tell you that it has weaknesses the Tangband hasn´t and is just as well a compromise. And to not sound negative in any way both are great speakers for the money.
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Old 9th April 2005, 08:20 AM   #8
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Then what do you call "new methods" ?

The TQWT with the FX-120 (that I'm also building from a plan) uses exactly the same techniques but goes down to 40Hz, which is pretty low for a 70cm high speaker !

I thought of tuning it down to half the Fr (55hz) but then there may be a dip between 150 and 50 Hz !

I also thought associating a transmission line on a bass reflex port, or putting a TL at the end of the existing TQWT.

What do yout hink about it ?
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Old 9th April 2005, 11:51 AM   #9
MJK is offline MJK  United States
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Then what do you call "new methods" ?
Accurate computer modeling and measuring of the raw drivers and the completed system. Analytical predictions before you build so that good design trade-offs can be made.

One question, how did you determine the length of your TQWT so that the quarter wave tuning was at 110 Hz? If you used the classic equation

L = 1/4 x (c / f)

then your initial length was wrong, your line is way too short. This equation only works for straight TL's. Also, by adding a restriction at the open end you have mass loaded the TQWT and lowered the quarter wave frequency. Did you account for this in your design?


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I thought of tuning it down to half the Fr (55hz) but then there may be a dip between 150 and 50 Hz !
Quote:
I also thought associating a transmission line on a bass reflex port, or putting a TL at the end of the existing TQWT.
You have "thought" about several ideas, now you need to engineer the idea so it becomes a design concept. Reading the web and scaling other unheard designs is not the approach I would take. Looking at other designs for ideas to explore is fine.
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Old 9th April 2005, 01:28 PM   #10
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I didn't take into consideration the fact that there was a restriction at the port but when drawing the plans, I took into consideration it was a folded tqwt, and calculated the length from the middle of each part, in the middle, which makes an average length so I suppose it is almost the same (I hope)

I tried yesterday evening to increase the length by putting thick paper sheets to form a tunnel after the port, but the result was acoustically worse, not for the bass response but for the sound quality.


I just realize that I didn't even post a photo of the prototype. It is made of 10mm MDF, I suppose it rigid enough

Here it is : http://youyoung21147.site.voila.fr/DSCF1719.JPG


I'm still searching the net to find exotic or well-working enclosures, and I'll also try your MathCad worksheets, but then I need MathCad . I hope I won't have to spend too much timme cutting wood, because I don't have much time as a student
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