19 Hz TL

[ingvar ahlberg]

Hi Dave, looking for advice!
Seeing that i was about to mess up Andrea´s thread i start this as i can´t stop fiddling with the idea of a TL for the RCF L12P48.
4 meters of pipe will make a large cabinet but could be kept within 250l. I´ve looked around but cant find any reference to TL´s for this driver.
In the late 70´s i got hold of a few KLH 10" units ( i think same as in the Baron ). Reading an article in HiFi news and a 60´s book by Klinger i designed a 30Hz TL ( very much a copy of IMF´s Monitor and the HiFi news Radford design )
This came out faboulus with good extension and stupid definition, could play pretty loud with a PL400 too. When the KLH supply ran dry and yet a friend wanted a pair i bought two Peerless 10" that on paper looked ideal, also in real life looked very similar to the KLH units, a bit smaller magnet. This ended up in disaster, no bass whatsoever! Sounded like a kitchen radio and as i did´nt know where to look for problem my TL career took a break then. Ready to take it up again, but would realy appreciate all advice and input, I dont mind failure in cabinetbuilding can allways put the wrecks in the fireplace but would like to know more this time.

[joensd]

Well, I´m not Dave but if you can´t find a TL-design with that driver (which is rare anyway) you´ll need the T/S-parameters of it and play a bit with the mathcad-worksheets of Martin King.
You can download this great tool here.

There´s also quite a bit theory to get you started.
What really helped me alot was also Bob brines site.

Besides you´ll find a lot of threads here where GM (forum member) gave insight on how to tackle TL-design and the like. Can´t find that thread for now but will get back.

Jens

[joensd]

for example :
New ML TQWT project
How to use Martin J. King's software to design a TL loudspeaker?
Perfect TL with MJK mathcad graph?

[ingvar ahlberg]

Thanks a lot Jens!
The printer is spitting out papers so i´ve got literature for the entire night.

[planet10]

Shooting for 19 Hz means you need to rely heavily on box geometry to kill harmonics since damping material gets less effective as you go down in frequency

dave

[GM]

True, but with a driver like this, any theoretical sonic advantage of a TL is wasted on a low tuned alignment since any 'nasties' of a mass loaded one has decayed away by the time it gets high enough in frequency for us to perceive. Also, to keep amplitude distortion low, a fairly low XO point is required.

Assuming these specs, the step response of this 16Hz ML-TL is a 'beautiful thing' :

Fs = 19 Hz
Vas = 270 L
Re = 5 ohms
Qes = 0.44
Qms = 4.4
Qms = 0.4
Le = 3 mH (estimated)
BL = 11.3985
Sd = 506.709 cm^2 (estimated)


L (in) 84.154
S0/SL mult. 2.4367
S0/SL (in^2) 191.376
X0/Zdriver (in) 29.673
vent (in) 81.15
rp = 3"
Lp = 17"
density = 0.2lbs/ft^3

Vas or Vb(ft^3) 9.32
Fs or Fb (Hz) 16


Due to its length, the footprint is small, so either standing up or laying down up against a wall could be made semi-unobstrusive if color and/or pattern matched to either the wall or floor. Even folded in half it's not all that big (by my standards ).

GM

[ingvar ahlberg]

Allright!!
Thanks GM (its not You making all the Corvette´s is it)
This looks like something, 215cm long pipe folded makes ideal height for putting the AMT on top. X-over will be 80-100Hz active starting with the old Accuphase P300 as amp until i´m finished with the bridged Zen v5.
What i dont understand is the lenght, 215 cm would be fs of roughly 40 Hz, but there´s a few figures in Yor post i´m not familiar with, could You direct me to a place of info?
The guys at the local lumberyard are eagerly awaiting my next purchase and my Wife looking at sketch of this cabinet deemed it nice and small.

[ingvar ahlberg]

Hi again GM, found a lot of Your earlier posts, also read Yor post in my thread over a coupple of times, as English is not native to me it sometimes take a while to understand abbreviations.
Thanks again, this will be fun!

[GM]

>Thanks GM (its not You making all the Corvette´s is it)
====
You're welcome! No, owned/hotrodded a few in what some say was a misspent youth though.
====
>What i dont understand is the lenght, 215 cm would be fs of roughly 40 Hz, but there´s a few figures in Yor post i´m not familiar with, could You direct me to a place of info?
====
This is a mass loaded TL, so doesn't need to be anywere near a 1/4WL long. MJK's http://www.quarter-wave.com/ should enlighten you.
====
>.......as English is not native to me it sometimes take a while to understand abbreviations.
====
Sorry about that, so many of you with 'foreign' names communicate so well in English that I have to look at the flag to make sure you're not a 'local'. Anyway, so many folks now are using MJK's Mathcad PORTED and/or MLTQWT worksheets that I just post what to input in the various fields so that all you have to do is plug them in, then scroll down to get it to calculate the various graphs. Note that it calculates Qts, so no need to input it.

Actually, I need to update my design calculator to list 'Zport' in lieu of 'vent'.

GM

[ingvar ahlberg]

Thanks again GM and Dave!
Tried Mathcad and did a Check in JBL Speakershop. So i nailed a crude chipboard proto together and tested.
This makes a real crazy bass unit! I get definition on par with a voice of the theatre but at 20 Hz! All the low frequency resolution that this RCF driver is unique in is still there but tendency to "overshoot or sluggishness" is all gone.
As i´m a bit oldfasioned on drawings, first paper, pen, ruler and the old TI and then the cad drawing i´ll need this weekend before posting anything.
Will supply all drawings and photos as this will be adaptable to other drivers.

No, owned/hotrodded a few in what some say was a misspent youth though.

Youth is ment to be unwisely spent, otherwise, we would have been made accountants right after high school.