ML-TQWT for a 15" JBL, any suggestions?

[Flodstroem]

Hello.

I have an idea for to build an ML-TQWT (Mass Loaded Tapered Quarter Wave Tube, by M.J.King) for a JBL 15" woofer.

In my project I have been using M.J.Ks´ calculation sheets. But I lack the full version of the MathCad, I have only been using the free ware v.8 (explorer) but with great success. Unfortunately, I cant save my own calculated files in formates other than the "print-command" pdf file format. Those files are however to large to post in here so I had to print (in pdf) one page at a time (with help from Adobe Acrobat) and then I could convert each single side to a JPG file so I came under the magical 102.4kB maximum allowable attachment size (Phuuuuu...!!!! ).

Ok. Thats it, the speaker was first kalkulated using a 90" long tube, but was later shortened to only 80" in total length. Due to I have only built two models of the ML-TQWTs´for JBLs´(for an 8" and also for a midrange 10"), so I dont have any experience in woofers. Now, my question are: is this a design that could be sounding ok, or should I go back and use the longer tube?

The plots in here : 90" first" (only SPL page posted first)

Any comments would be appreciated.

Regards

[Flodstroem]

and 80"

[bjorno]

Any comments would be appreciated

Its impossible to give any comments whether you have boxed in an interval where within a recommendation can be made as we don’t now what driver you are using.

b

[GM]

Greets!

Which one, or neither, is theoretically better will depend on the room and your desired performance goals for it, so we'll need to know more to critique them. BTW, which driver is it?

Assuming you have WORD, you can save each of them as a 'rtf', so all of the WS will display as a WORD doc.

GM

[Flodstroem]

Sorry, I had troubles with posting the plots so I forgot to mention the driver its an old one, JBL 2215H, but its a fantastic low frequency driver.

Was first planning to build a TL but changed my mind when discovering the minimum size for to get good enough SPL in the lowest frequencies. Then I looked at other possibilities and finally I fell for the ML-TQWT as it seems to that low Qts JBL drivers could be used for that configuration. But Im not sure.

I want to build this type of speaker mainly because in most of the TL concept it lacks the common "box"sound and I like the wider and opened sound they produce. The first I built was a small one for an 8" JBL (type LE8 but is a 2115A). Next ML-TQWT building project was a sort of a test speaker, a midrange (JBL 2012H) for to use integrated in the bigger bass cabinet. You could imaging it finished, the speaker will looks like an MTM speaker: bass at the bottom, midrange at top and higts and UHF in between

GM, I dont have Word on my Power-Mac computer and because of that I had to work on Virtual PC and in Windows-98. This is more complicated then I want to admit but it works so far. Thanks anyway for your inputs.

Regards

[GM]

Greets!

Well, with what little info I have, either will work, though the lower tuning can exceed Xmax in the ~25-45 Hz BW if there's not enough boundary gain, but FWIW I prefer lower tunings around/at Fs.

IIRC, you can use Open Office instead of MS WORD to save your sims.

GM

[Flodstroem]

Thanks GM. Im aware of the Xmax and thats one reason for tuning higher but also is the size of cabinet. If looking at room gain, what could be expected of gain magnitude under f3 (yes you must know room size/volume etc, but I was thinking more general).

I also have done calculations with JBL 2245H, an 18" woofer and even if driving it as high as 500Watts ( ) it didnt exceed the Xmax. Maybe this driver is a better alternative for this speaker project though I have both drivers in stock.

The plots for the 2245H is similar to the 80" 2215H plots but the length was 4" longer and f3 landed on 26 Hz ca.

input data for 2215H fs=20, Re= 5.7, Bl=17.846, Vad=723.9 lit. Sd=880 cm2, Qed=0.218, Qmd=5.5
Box: (which gave me the plots):
S0=1" x 21"
SL=17 x 21"
z driver=52"
z port=64"
r port=2.76"
l port=5"
stuffing=0.35

Consider this, if building a bass reflex instead of this ML-TQWT, what should be expected regarding benefits/drawbacks if using the same dimensions (hight would be ca 40-41")? More standing waves? Higher group delay? is variables that first came to my mind.

Comparing a ML-TQWT to a bass reflex: is there a drawback for the bass reflex regarding the "box-sound" coloring the music?

I have plenty of questions because of my small experience to building speakers so you just have to accept all my future questions and this is really fun.

Also I plan to buy some hardwares and softwares for to be able to do measurements on my speaker building project and for that I know what to buy. Only thing is that I really must learn how to use it.
Regards

[bjorno]

its an old one, JBL 2215H, but its a fantastic low frequency driver.

Yes it is!

b

1(2)

[bjorno]

2(2)

[Flodstroem]

Hi bjorno, Thanks for the plots, however could you do some comments about your plots?

The Bl product you has been using is not correct (JBL value I presume and it is wrong) M.J. King found out it was the value I have since then been using (17,846).

What is your thoughts about this speaker compared to a bass reflex? Should be interesting to know that.

Regards