TQWT W4-656S A few questions.

I am considering building TQWT for a pair of Tang Band W4-656S 4" full range drivers .

They will be mains for a 'Musical Home Theater'--if one could imagine. My GF says I can build tall speakers, as long as they are neat looking. She really likes the look of Martin J. King's ML TQWT's and Andrew Brandon's Zigmahornet (a TL). I however am entertaining the thought of a MTM TQWT with two 656's and a TANG BAND 25-302S

I am asking for help from all the accomplished TL and MTM builders in this forum. I have been reading this forum for about a month and hunting around on the net for TL info. Dave's (a.k.a 'Planet10') T-Line Speakers website is awesome!!

How does one go about altering some of these designs to 'fit' the 656's?

I have read the post about killowatt's project and I am conserned with lobbing. Should I ditch the MTM idea and go for a 2.5 ? or just a 2-way with a sub? There are so many questions...

I am asking for a few answers and maybe some direction... I am very open to any changes...exept the 656's --I already bought them.

Hi Swirv

Where to start...

Firstly, well done for choosing TLs, you won't regret it:)

I am not familar with the drivers, so I can't help on specifics so I would suggest downloading some of the design programs from Dave's website and having a play with the numbers, if you have any problems with the terminology, etc. then we will be pleased to help.

Don't worry two much about lobing, it only is a real problem with the amount of drivers that Kilo wanted to use , or if you have them spaced widely apart.
If you tuck them closely into the tweeter and choose your crosssover frequencies with care then you will have no problems.

Good luck
crossover freq

the issue is that I want to cross the 656's real high...like 6-7khz I do not want any crossover points in the 'musical' freq band. the w4-656 has a freq responce of 65-15k with a spike at 8k
I want to take full advantage of this drivers extended range but want to ad 'air' above 15k all without hitting that nasty spike the 656 has at 8k. Would having two drivers upto 6.5k seperated by a tweeter have lobbing problems. I guess my question here is: at what freq does it really become a problem?

It may not really be an issue.. I really havent made a solid call on the MTM.

Ive been breaking in the 4's using a 3 ft. getto test box (aka cardboard) and they are getting deeper by the day. I can hear the potential of these 'lil 4" drivers. They already go way lower than my modified LX5's I havent measured anything ...point is: the reason I was going to do MTM was to get more cone space for more low-end. I now think I can get away with just one and a tweeter at 6.5k

Like I said before... Im new at this level of design and will take any and all input. And thanks in advance for the help.

Chris, so is that avatar done with Lightwave, the lens flare looks familiar :)

Lobing only becomes a problem with the drivers more than a quarter wavelength apart at the lowest frequency they reproduce, but it sounds like you are already happy with just one driver per side!

As I said earlier, I don't know the drivers you are using, but by the sound of your experience in running in these drivers, I would go for using one per side with the tweeter in an open baffle dipole, with a QWTL with a decent 8" driver crossing over at about 200 Hz for the bottom end, but then I am strange:xeye:
I had asked in another thread about open balfle design. I read that a Qts around .5 was desired for a good open baffle setup. The 3" version of this driver is an exelent candidate for an open baffle. however these 4' drivers have an Xmax of 3mm. and a Qts of .35.
I played around with the test enclose by opening the box. The speakers lost any resemblence of bass, closed they pumped out some decient lows. I know I cant expect a lot of bass from these things.. but I do want to take advantae of their willingness to go down to around 80-100Hz. The sub in the setup will be a subwoofer in the sence of HT. 80Hz down as low as I can get :D without ******* off my neighbors. I would however like to be able to use these without the sub for some musical program. As an engineer I do not like to use a mono sub on music. I have had issues with phase problems in really good stereo mixes when anything is summed. I would only use the sub for HT and maybe to augment the mains when played loudly.

If someone can lend me more knowledge towards an open baffle design that will work with this driver I will throw it into the pot.

... still dont have my mind made up on what type of enclosure for these lil bugers....
Hello Swirv,

If you want to design a TL or TQWT for your drivers then I would recommend using my MathCad worksheets. You can find older versions at Dave's site (www.t-linespeakers.org) or newer versions at my site (www.quarter-wave.com). Both sites contain links to the free MathCad Explorer Version 8 program for running the calculations.

After you decide which type of speaker enclosure you want to design, you need the T/S parameters of the drivers. Measured values are the best but if all you have is the manufacturer's specification values that will have to do. Running the worksheets is not too difficult but you may need to mess around for a day or so before closing in on an optimized design.

Bottom line is that you need to engineer the enclosure using the MathCad worksheets. This is the most accurate method that I know of available to the DIYer (and it is free, such a deal). Also on my site, you can find a short article on how to model two drivers in a single enclosure in the "General Speaker Related Articles" section. If you are planning to use an MTM alignment you will still need to design a baffle step correction circuit. If you plan on mounting one driver on the front of the enclosure and the second on the back wired in phase then you can neglect this circuit, the driver placement will eliminate the baffle step loss at low frequencies.

Have fun,

Martin J. King
swirv said:
however these 4' drivers have an Xmax of 3mm. and a Qts of .35

With a Q like that a TL like quarter-wave design is probably more appropriate than a voigt.

As to an MTM with 4" drivers, i have been noodling over a bipolar MTM (ie 4x4) with the Foster FE103A. I figured out that 5k was as high as i could take the 4s given how close i could get the drivers -- and this is with the baskets of the 4s actually touching, but rotated and a small footprint tweeter tucked into the v made by the drivers.

a starting point?

I found a spreadsheet that would give me an example TQWT and I pluged in some numbers from the TB W4-656S data sheet. I took this data an made a CAD drawing of the figures given. I havent pluged this into Martin J King's software yet (still trying to figure it all out... :xeye: )
This is what I came up with :

Re: a starting point?

swirv said:
I found a spreadsheet

That is a classic TQWT and they are very hit (15%) & miss (the rest). Martin can correct me if i'm wrong, but i think that you can get away with Qt, Fs, and Vas to do a basic model. An Sd is needed for the geometry in the model.

the big problem is that the numbers tag band gives out don't necessarily have any relationship to the actual parameters.

The only parameter Im missing is the voice coil inductance. How important is this to your calculation?

If it is nessasary I will build a testing circiut and find the value. The other parameters are there...I just had to figure out all the different abreviations for the parameters-- some are just labled slightly different...
As far as TQWT's go, I heard a pair several weeks ago pushed by a tube amp - they were using the fostex driver - I was surprised at how good they sounded -

In the spirit of "pointing you in the right direction" - since they're being used for stereo and HT -

I suggest that you select what you believe to be the best choice in already worked out designs where someone else has done the development - If there is nothing readily available in such a design for the Tang band, then use them in the rears.

Bet you'll be happier in the long run. While part of the fun of DIY is doing your own thing - personally, I think there would be a lot of hassle and grief trying to get up to speed from scratch on a speaker design.


Ken L