keith_correa
Well-Known Member
From what you say it seems like you want the rear waves to reflect back to the woofer. Typo?
Transmission Line Speaker Build by me - My second project
- Thread starter Hari Iyer
- Start date
The enclosure in between the two floorstander is a seperate sub-woofer (4th order Band-pass) which is connected to a separate DNM 5.1 home theater amplifier. The transmission-line floor standing is connected to a Denon AVR-1604 AV Receiver.
Opps, its a typo. Thanks for brining it to my notice. The rare wave will channel down through the guide and not reflect back on the woofer due to the absence of the rear wall.
Thanks once again buddy.
Thanks for your feedback Vinod. I will try and make a sketch of the inside ASAP. The design is simple, i used 2Sd area for the 1st pipe and 1Sd area for the 2nd and 3rd pipe. Also the terminus area is 1Sd at the rear of the enclosure. The total length of the enclosure is 96 inches, which gives a tuning freq of 34Hz. The resonating freq of the woofer is 38Hz. Hence the tuning freq is 5Hz below the resonating frequency. (The Qtc of the woofer is 0.34). I calculated all the odd harmonics of the line first (1st, 3rd, 5th & so on) and damped them with Racron polyster fiber. Then also calculated the odd harmonic of the woofer (1st, 3rd,5th & so on) and damped them too. Most of the odd harmonic will fall in the 1st pipe. Only the 1st harmonic (fundemental resonating freq) will be in the 3rd pipe. Each pipe is approx. 32 inches in length. The tweeter is housed in a altogether seperate enclousre completely isolated from the woofer chamber (there is a 2" thick partiation between woofer and tweeter encloure to prevent viabration getting transmitted to the tweeter).
The cross-over is the most important part of the design. I used a 1st order cross over because of the following reasons,
1. Zero phaseshift at the cross-over point.
2. Good trainsent response due to fewer cross-over elements.
3. Easy to do adjustments after listening as fewer components are involved
4. Faster settling time as fewer components are involved
5. No enery storage or relase by capacitors and inductors as fewer components are involved.
I did use some compensating circuits like Zobel compensator for the woofer, Parallel Notch circuits for the woofer to shape the response of the woofer. Used series and parallel notch filter for the tweeter, used contour circuits for the tweeter, and used finally a baffel step compensator. The total passive components are 15 which include only 2 filter components. The rest are all for response shaping.
If you noticed the enclsoure is time aligned and also take cares of the diffraction effects casued due to the baffle step by using a sloping baffel for the tweeter. I have reduced the foot-print for the tweeter to reduce the baffel step. Also all edges are rounded to prevent hearing fatigue.
shershah
New Member
air in the pipe HAS mass
Typically the terminus area are 15% to 20% of the area of the line and this is sometimes called mass loading of the line. This helps in
increasing the low frequency response but the mid-range suffers a bit due to some standing waves in the higher harmonics of the line.
In my design the area of the terminus is same as the area of the line and is not mass loaded. I do agree that air in the pipe has mass and thanks for brining to my notice.
This is not a typo. Do read A. R. Bailys May1972 article from wireless world.
The inventor of t-line explains this in a very simple way. This is a article where he improves his own design by using triangular waveguide. This is a very easy cabinet design to make. If i can get drivers similar to those mentioned in the design i also wanted to go DIY way. (HELP needed)
I am not posting the article since it might have copyrights. Search it in google and you will get it.
In simple words if there is a flat surface at the back. Some part will get reflected back to the driver itself which will interact with the driver. This interaction can be reduced using triangular waveguide.
Congrats on a very well conceived and executed project. Very interesting tweeter positioning. From the pics I could make out the alignment of acoustic centers but could you elaborate on how distance between the drivers is arrived at?
Currently I am using the same tweeter in my bipole. Even for an uncompensated 1st order, it sounds really good
. I am still experimenting with the aligning of acoustic centers and reduction of diffraction artifacts.
BTW this thread needs to be in the DIY section.
Regards.
Currently I am using the same tweeter in my bipole. Even for an uncompensated 1st order, it sounds really good
. I am still experimenting with the aligning of acoustic centers and reduction of diffraction artifacts. BTW this thread needs to be in the DIY section.
Regards.
If you give a link to the article, I don't think you are infringing on the author's copyrights.
keith_correa
Well-Known Member
Wouldn't a TQWT design also achieve this?
The TQWT also achieves the same but is challenging to calculate the slope by changing the ratio gradually between the close and open ends. TQWT are typically mass-loaded and the terminus end is tapered from closed to open end. This helps in reducing the standing waves in higher harmonics.
Indeed this article had arrived at the wireless world and the deisgn uses ideas from A.R.Baileys original design of 1972. I have modified the design for channelling the wave guide from behind rather than the front baffle. You can try using the 5.25" kevlar cones from Peerless in this design (Resonating freq = 57 Hz) and hence would get a lower octave of around 28Hz with this method. The current speaker sounds excellent with this design and would put many of the professional loudspeakers to shame. As the design in this speaker is completly different than what is shown in this article even from the inside there would not be any copy right infrigments.
I still have not photographed the rare of the speaker. Will post pictures of the back of the speakers when done. Currently am out of station due to office priorities.
Congrats on a very well conceived and executed project. Very interesting tweeter positioning. From the pics I could make out the alignment of acoustic centers but could you elaborate on how distance between the drivers is arrived at?
Currently I am using the same tweeter in my bipole. Even for an uncompensated 1st order, it sounds really good
BTW this thread needs to be in the DIY section.
Regards.
I had measured the distance between the speaker frame and the dust cap of the woofer and off-set the tweeter by that difference. I assumed that the tweeter is reasonably flat vis-a-vis the baffle. I found the difference to be around 1" between the speaker frame and the dust cap. You can use the below method:
1. Keep a steel foot ruler across the speaker frame along the diameter of the woofer.
2. Use one more steel foot rule to measure the difference in mm from the dust cap to the ruler in the point 1. This is the difference in the acoustic center which you will need to align w.r.t the tweeter.
Once you have arrived at this distance you can offset the drivers by either using a sloping baffel (more difficult) or use the method in my design to offset it.
As per my research in the web, the offset will be useful only if you are using a 1st order filter as the 1st order filter has zero phase shift and you will require your acoustic wavefrount to also be with zero phase shift. For higher order filters there is already a phase shift introduced by the cross-over hence the time-alignment will anyway not help.
Also there is a overlap of frequency between the woofer and tweeter due to the gradual roll-off due to the 1st order filter. This would cause cancellation of certian overlap frequncies if they are not aligned in time and the sound stage will lose detail. Hence all 1st order filter design will have to use somekind of time-alignment for allowing coherent sound stage. This will enable both acoustical coherence and zero phase shift due to 1st order filter. Also the drivers need to be wide-bandwidth type to have atleast response of 3 octaves on either side of the cross-over frequency to prevent any resonance effect in the overall speaker system
keith_correa
Well-Known Member
The picture looks like its a vented enclosure and not a TL. Putting an angled obstrucition behind the woofer could deflect the wave but the correct angle to deflect the wave needs to be ascertained. Also the partition needs to be hard like a ceramic tile for 100% deflection of the wave. More over the deflection works well only for mid to higher frequency as low frequency would get diffused. In my design there is no flat back wall as there is a partion in the entire length diagonally across the speaker box, so there is no back wall for the tweeter. Image a triangle having a opposite side and a adjacent side and a hypotonuse. The woofer is now mounted on the adjacent side there by avoiding the flat back wall where the woofer waves cannot deflect back. The length of the line will decide the tuning frequency of the line. The hypotnuse now becomes the back wall for the speaker box. Hope this helps.
keith_correa
Well-Known Member
Yes, it is a vented cab. I was not trying to depict a TL - was just wondering what deflecting the back waves would do for the sound in a vented cab.
See fig. 1 below, is this what your enclosure looks like? Is the volume shaded in grey unused?
See fig. 2 below. In a vented cab., what if we try to deflect "some" of the back waves of the woofer like this "V" shaped corridor running only behind the woofers? Just wondering.
See fig. 1 below, is this what your enclosure looks like? Is the volume shaded in grey unused?
See fig. 2 below. In a vented cab., what if we try to deflect "some" of the back waves of the woofer like this "V" shaped corridor running only behind the woofers? Just wondering.
Attachments
Yes, my speaker box looks some what similar to your figure one. The 1st pipe is 2Sd. The 2nd pipe is split into one more partation bisecting it of 1Sd each. This gives a total of 3 pipes in the TL speaker. The sound wave is guided from the 1st to the 2nd to the 3rd pipe and total length is 96". This gives a tuning freq of 34Hz. The terminus area is also 1Sd. You will require to intelligently damp the enclousre at the odd Harmonics for a balanced sound. Do not damp the fundamental resonance of the enclsoure or the woofer. Concenetrate on damping the 3rd Harmonic, 5th Harmonic and 7th Harmonics. You will need to measure the wave-length corresponding to these harmonics for the damping. You will need to use light damping evenly across the line so that you do not damp any other part of the wave. This will ensure a smooth mid-range and good even and tight bass. The trick lies in the damping of the line, the density of the damping material and the weight of the damping across the cross-section area. Get it well and you have a great sounding speaker and mess up with it and you have standing waves inside the enclousure.
Yes, i have used the grey shaded areas as mine is a TL enclsoure.
shershah
New Member
YOU ARE A GOD OF TL, TUNING FREQUENCY, Sd, INTELLIGENT DAMPING OF ODD HARMONICS, AVOIDANCE OF DAMPING OF FUNDAMENTAL RESONANCE OF ENCLOSURE, AND OF DAMPING THIRD, FIFTH AND SEVENTH AND ALL (AUDIBLE) ODD ORDER HARMONICS BEYOND THAT. YOU ARE GOD OF ALL THE SMALL TRICKS!
YOU ARE THE ONE!
lead us, you golden one! - to that promised (and, not costly) land of audio-nirvana:clapping:
Hey Shershah,
That's too much of a compliment. I am just a novice and just spend some time doing a bit of research in the web. That's all. I have used my research in my works. I had many failed attempt before i could finally arrive at a quite a decent sounding pair of box. If you look for Dr.A.R.Bailey's article this design has appeared way back in 1972 in the magazine Wireless World. The God of TL is obviously Dr.Martin King who has done tons of work in the TL space and he has modeled the TL enclosure using his mathcad.
BTW its difficult to get the TL enclosure right in the 1st attempt. I had to make and break 4 boxes previous to this to get things right. Its patience which pays at the end. For all DIYers the suggestion will be to get the basics right and try to implement it in your ideas and if something does not work as you planned then do not give up. Do more research and at the end you will get that perfect sounding box which you always dreamt off. If you do not have the patience and the will then better settle down for a commercially availble one, because to build a good quality speaker system is not only a science but also an art. Mind you do not expect that DIY will always be cheap because you will need to factor in your failures too while attempting a good quality speaker system. You need to be very passionate about getting the perfect sounding box only then it works and will take lot of your personal time and energy.
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