My Bipole needle, and your thoughts.

[O_ROD]

I've always wanted a set of bipole speakers for music listening and have 4 TangBand W3-665SC (very similar to W3-871's) lying around, along with a fresh sheet of 5/8 MDF.

My plan is to build the Cyburg needle, doubling it's width, and adding another driver to the rear. The hope is to maintain the Needles sound characteristics while opening up the soundfield and adding bass output.

This will be my first full range project so I was wondering if I could get some expert or experienced opinions on this idea before I cut the MDF. Perhaps someone can plug the idea into a simulator to see it's projected response?

I'd appreciate your thoughts and help on this idea. I'm curious to see how much output below 60Hz I can obtain in room. I'll be sure to show the response as I haven't seen another project like this as of yet.

Thanks...
Bryan

[Jim Griffin]

Bryan,

Instead of the Needles as a starting point for a bipole speaker I would suggest that you use the TABAQ as your model. The original design for the TABAQ is discussed in this forum with various postings and is summarized at:

http://coolcat.dk/bjoern/TABAQ_TL_for_TB.pdf

Bjorn did a comparison of simulations for the TABAQ and the Needles designs at:

http://www.diyaudio.com/forums/attac...amp=1145466691

No doubt as to which one I would choose as a starting point as the TABAQ should be much easier to build and adapt to a bipolar configuration.

Jim

[O_ROD]

Thanks Jim, that's an extremely easy design. I love it.

I read the link between the differences of a Bass Reflex and a QW but I still find it hard to believe the TABAQ is not a BR. The line length is small, how is it that the box is tuned so low?

I suppose doubling the line length of the tabaq would also yield the proper size for a bipole. But I could always build 4 of these with a single sheet of MDF and use 2 on each channel. I'd basically like some more bass output in my 19x12' room.

[O_ROD]

Seeing as I'd have to change the unit from cm to inches. Is it ok if I just round off the measurements and get them as close possible? I'm having a hard time converting this design to using 5/8" MDF.

[Jim Griffin]

On conversion of the dimensions for the TABAQ from cm to inches what I would suggest is that you focus on the internal (inside the box) values. Get those right and you can add the thickness of your material around those internal dimensions. But you can use some reasoning to get practical values. As an example the 12.8 cm x 10 cm internal cross-sectional area of the tube converts to 5.03" x 3.94" which is 19.82 sq. in. Clearly, if you round up to 20 sq. in then a 5" x 4" tube would do the trick. Another one is that the driver is located at 52 cm (20.47") above the port tube partition so a close enough value would be 20.50". We are not talking rocket science 4 decimal values in this design so use common sense where appropriate.

What I would do for a bipole is to think of two TABAQ boxes back to back (port tubes exiting from both front and rear of the box) and then maintain the same internal volume for each of the two boxes while deleting the back panels. I would thus maintain the same box width as for a single box but double the internal depth of the bipole box to account for the increased internal volume. As an example the 12.8 cm (5.03") internal front to back dimension for one box becomes 25.6 cm or 10.06" for the two. I would use 10.0" front to back internal dimension as my build to dimension for the bipole box.

You can also use a false bottom to space the drivers closer to ear level as I did in my CSS FR125S/WR125S biploar design at:

http://homepage.mac.com/tlinespeaker...LDesignPak.pdf

Jim

[Bjohannesen]

Hi O ROD, just some comments about the tuning of the cabinet and BR.

By using the small opening in the bottom, you mass load the pipe, which lowers the tuning frequency. If the line was straight with an opening with the same cross section area of the pipe, the cabinet had to be taller for the same tuning frequency.

If you play around with Martin J King´s software, you get a feeling of how a TL (quarter waves) react to changes in the design. This is the funny part of it

If the TL is undamped, you will see a double hump in the impedance (like a BR) and addtional minor peaks in the higher frequencies. When the pipe is damped, the TL is approaching a singe hump speaker in the impedance curve. Now it does not look like a BR at all.

Take a look at Brines

Hi from Bjorn

[O_ROD]

Thanks Bjorn, I have a somewhat small understanding of a quarter wave, but the impedance curves and responses show the difference. If the line opening was any bigger, then that would basically unload the box and essentially make it a BR? The response of the QW is much smoother with a nice roll off.

Bjorn, what would you expect the differences to be between your TABAQ and the bipole idea I'm working on? If there's not much effect I may just build the regular TABAQ's since there an easy build and judging from others, very effective. Heck I could even build 4 of em.

I really like Jim's idea of building the bipoles using "back to back" TABAQ's. Still small in stature and easy to build.

[planet10]

Originally posted by Jim Griffin
What I would do for a bipole is to think of two TABAQ boxes back to back (port tubes exiting from both front and rear of the box) and then maintain the same internal volume for each of the two boxes while deleting the back panels. I would thus maintain the same box width as for a single box but double the internal depth of the bipole box to account for the increased internal volume.

More recent thinking has that a bipole should be wider than it is deep, The easiest way is to double the internal width.

Another way to look at it is to take 2 TABAQ (missing opposite side panels) and place them side-by-side. The port then remains on the front.

Put a driver on the front & one on the back. I suggest a holey brace to couple the rear of the 2 drivers together.

dave

[O_ROD]

Seems like a more simple idea, thanks planet10. just curious how bracing the 2 drivers together would make a difference? I understand the logic behind the idea, and it makes sense, but in real life, is there an audible difference?

Just a quick question, is it really worth turning this idea into a bipole? Basically, if you had 4 of these drivers, would you make a bipole, or would you build the original TABAQ? or maybe something else? I just want to get the most out of these small drivers for music listening, whatever that may be. Experimenting isn't much of an option due to budget restraints.

I'd love to hear some opinions, you guys have alot of experience and quite the knack for wood work!

[hm]

Hi,

an alternative for a bipol solution might be

http://www.hm-moreart.de/89.htm

important is the distance of the drivers,
take less the distance of your ears.

My simulations show 2 driver 1 e.g. horn
doubles the problems, you might get to much at 80 Hz
covers the lows.

Therefore I take a cross setting of the membran
movement and horn mouth distance.

free plan