ML TQWT (what the h..k is that)

[Flodstroem]

Hello again

Now I have started with my TL (Transmission Line) speaker projekt.
I have choosen a value at a couple of parameters for this type of speaker that I would like to try to reach in the calculations (eg. F3, freq. 20-90 Hz and cone excursion).

First calculations on this type of speaker (the TL) ended up with a to large speaker system for our living room (14-15 cub. feet)

Then I tried the ML TQWT type of speaker. What the heck is that ?
A very simple explanation: it´s kinda combination of a TL and a bass reflex speaker. (design Martin J. King). ML TQWT= Mass Loaded Tapered Qarter Wavelength Tube. In this case it will be a one folded "Tube" (9-10 cub.feet)

The frequency response of that type of speaker seems to suit my porpose with respect to frequency response, and deep bass.

A problem for a novice like me in calculation speaker is that I am not realy sure how to evaluate the plots that came out from this calculations. Trial and error will be very expensive if I had to re-build the cabinets because they will be rather large speakers even though I choose to build a ML TQWT.

If refering to the attached plots I find it rather interesting if looking at the 20 Hz region. F3 is landing on 22-23 Hz and the respons is decent flat up to 90 Hz where the "high bass" will take over. Cone excursion looks fine and also the time delay response.

But I´m a litle bit worried about the sound pressure level generaly. Is this a bad or a decent plot level (when calculation a ported box (type bass reflex) the SPL is higher upp (ca 95-98 dB) but f3 will be far from 22-23 Hz (also cone excursion at 20 Hz will be worse)

The calculations at this stage is in the beginning and I´m sure it could be done more to this work.

Sorry the attached file is not as clear as it should be, but there is often a problem for me when I choose to work with new programs for free ("Math CAD"), in Virtual PC at a Mac and converting files to .pdf and then try to cut files to under 180 kbits. I lot of steps that could go wrong.

I would like to hear a comment to this plots (20-90Hz) from the friends at the Forum, I would appreciate that.

Thank´s in advance

[Earl K]

Hi Flodstroem

- I don't know anything about transmission lines / so I'm pretty neutral on the subject.

- What are the "supposed" benefits of a transmission line ?

- After looking at all the included graphs, I realize that I prefer the "look" of the "Red- Trace" more so than the "Blue-Trace". ( They aren't labelled , I guess for a reason )

- I didn't see any advantage offered by the blue trace ( except maybe the "terminus" plot which I don't know how to interpret. ( Though it "looks" like floor/room loading to me ).

[Robh3606]

Hello

Neat project!! I really don't have any experience with Transmission Lines but I have some questions.

"If refering to the attached plots I find it rather interesting if looking at the 20 Hz region. F3 is landing on 22-23 Hz and the respons is decent flat up to 90 Hz where the "high bass" will take over. Cone excursion looks fine and also the time delay response."

You are using them over a limited range and will cross them over to another driver. What driver?? I was concerned with the step like response but if you only use them from 90hz down the level can be raised back up. With room gain you may not need too.

"But I´m a litle bit worried about the sound pressure level generaly. Is this a bad or a decent plot level (when calculation a ported box (type bass reflex) the SPL is higher upp (ca 95-98 dB) but f3 will be far from 22-23 Hz (also cone excursion at 20 Hz will be worse) "

You are trading efficiency for extension. Why are you worried??? Power handling or max SPL?? Both?? What power levels are the Excursion curves at?? 1 watt, 10 watts or PE 100 watts?? 2215'S don't have as much X max as the newer drivers. I would take a look at excursion curves at the power levels you will be driving them at.


Rob

[Flodstroem]

Hi

Thanks Earl K and Rob for your comments

Rob:

You are using them over a limited range and will cross them over to another driver. What driver?? I was concerned with the step like response but if you only use them from 90hz down the level can be raised back up. With room gain you may not need too.

I had a chanse to buy a pair 2012H and I did. I will use them for the frequency range 90 to 800 Hz(or 1200) depending if using a 2441 or a 2421 as mid (2380A or 2344) on top will be a 2405.

Rob

You are trading efficiency for extension. Why are you worried??? Power handling or max SPL?? Both?? What power levels are the Excursion curves at?? 1 watt, 10 watts or PE 100 watts?? 2215'S don't have as much X max as the newer drivers. I would take a look at excursion curves at the power levels you will be driving them at.

The excursion plot is referanced to an input level of 1W/8 ohm. Must there be a big x-max if cone excursion is small at an reasonable power level? This typ of speaker have a much smaller cone excursion than a ported bass reflex would have in the frequency range 20 to 25 Hz.

A short explanation to the plots:
plot I and II: I=Phase and II=Far field Transmission line ("TL") system and infinite baffle SPL responce. Red trace: TL, Blue trace Infinite baffle (eg. the systems sound/frequency response in the listeners room compared to a infinite baffle speaker).

plot III and IV: Woofer and Terminus (port) III= phase and IV=far field SPL level response. Red trace: Woofer, Blue: Terminus (port)

plot V and VI: TL and Infinite baffle impedance, V=phase VI= impedance ohms
Red trace: TL, Blue trace:Infinite baffle

plot VII: Woofer displacement (at 1W/2.8284V 8 ohm). Red trace: woofer Blue trace: infinite baffle

plot IIX: Sound pressure in time domain (eg. a response to an impulse and damping efficiency/resonances/ringing)

My arguments to shoose to build TL as my main speakers:
I have had bass reflex since 1970 and have heard the TL and how they could compete and win compared to the bass reflex regards to bass dynamics/ definition and to distortion.

But no benefit without as much drawbacks: the TL speakers will be bigger than an optimal bass reflex(ported box) would be

I mean this is the main benefits (compared to a bass reflex) to start to build these speakers:

Better Group Delay
Faster response to music transients
Better bass response to deep bass in the 20-25 Hz region, more efficient (at a lower distortion).
A flater slope respons under the cut off frequency (22-23 Hz). not as steep as with a reflex enclosure.

Another benefit to the enclosure model for me is that I could easily convert the speaker to fit my 2245H (change the baffle and make a bigger port) to get even a better sub bass response (an f3 at 19-20 Hz maybe), but this is also possible for other designs.
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To those who don´t know what kinda speaker the Transmission Line are I could only say this:

It is a kinda backwards tapered Horn design, but differs to a general horn design though this speaker have the driver mounted in the wider "mouth" end which is closed. The small end is open and is kinda port or mouth. It s total lengths is calculated to be a quarter wavelength of cut off frequency.
The benefits to a horn is not unknown: high efficiency and lower distortion compared to other speaker design (if we dont count physical dimensions).

ML TQWT, Mass Loaded Tapered Quarter Wavelengt Tube
If you take a TL speaker, and then close also the small end (the tapered TL is now closed in both ends). then move the driver mounting place to somewhere
in the midle of the speaker, calculate the dimension to a port (for a tapered quarter wavelengts tube) in the wider end, then you have an ML TQWT speaker. This model of speaker is very similar to a ported reflex enclosure but have the benefits to why I have shoose to build it

regards