Hi, i'm trying to design a loudspeaker able to go down to 30 hz at -3db, with accptable dimensioni.
I think to a 3 or 4 ways tower around 100 - 120cm, using transmission line. I'm not so expert of this kind of design so i'm looking a similar project or someone who can do it in the past so can help me.
I think to a 3 or 4 ways tower around 100 - 120cm, using transmission line. I'm not so expert of this kind of design so i'm looking a similar project or someone who can do it in the past so can help me.
Last edited by a moderator:
The first step is to obtain or measure the T & S parameters of the bass speaker that you wish to use. This will assist in choosing the enclosure that will give the required performance. Personally I dislike transmission line loading as the rear energy that is released is delayed excessively and quarter wave harmonics intrude.
https://www.diyaudio.com/community/...-and-rs28f-in-a-waveguide.354778/post-6583883
See if that gives you any ideas. It's -6dB at 29Hz from a 2 way, but room gain will/should get that in your ballpark.
See if that gives you any ideas. It's -6dB at 29Hz from a 2 way, but room gain will/should get that in your ballpark.
Active or passive?
What brands of drivers are available to you, and what is your budget(besides the box)?
What brands of drivers are available to you, and what is your budget(besides the box)?
If the TL is properly designed and executed as designed, 1/4-wave harmonics will not be an issue whatsoever and neither will the output from the line's terminus. Some woofers will not do well in a TL, of course, which is true for some woofers in other enclosures.
Paul
I'm open to choose the driver accordingly but as first i have looked into the CIARE HW321. It' a 12 inchiesta woofer. Attached the parameters
Could you give me an example of woofer with good T&S parameters for trasmission line design ?
Another question is: do you know a software that can help to simulate a transmission line design response ?
hi alessandro,
i suggest hornresp for simulating the TL. you will find a sticky thread in the subwoofer forum here on diyaudio.
attached a very rough first hornresp simulation for a mass loaded quater wave TL.
edit: i did the simulation for 2 V input - so the SPL will be slightly higher for 2,82 V (1W@8Ohm)!
regarding folding of transmission lines (and further hornresp information) you will find very good information on www.diysubwoofers.org/sheets/
i suggest hornresp for simulating the TL. you will find a sticky thread in the subwoofer forum here on diyaudio.
attached a very rough first hornresp simulation for a mass loaded quater wave TL.
edit: i did the simulation for 2 V input - so the SPL will be slightly higher for 2,82 V (1W@8Ohm)!
regarding folding of transmission lines (and further hornresp information) you will find very good information on www.diysubwoofers.org/sheets/
Attachments
Last edited:
Transmission lines are nothing but a hack, be it a good one, before we understood using Helmholtz to manage the resonance point. A properly designed ported enclosure will surpass it in capability easily. There really is no valid engineering reason to build one today. If they had any advantage, they were not that sensitive to driver variation. They require more volume than better performing ported enclosures.
You have to start with drivers capable of going that low. 30 Hz is a subwoofer range. 12 inch, very low Fs.
WHY on earth do you want a F3 of 30 Hz? Not in a room! You are forgetting room gain. My subs measure flat IN ROOM to 20 Hz, but my F3 is 50 Hz ( critical Q sealed alignment) They happen to be 2 cu. ft. each. Low Q needs big boxes. Personally, I much prefer Critical Q for the SUB. What alignment of the mid-bass depends on the driver and where my crossover is. If a floor standing 3-way, it is hard to beat the traditional monkey-coffin as you can raise the woofer crossover to where any mid can work sealed and it is easy as pie.
Do NOT think about eq-ing to push smaller higher Fs drivers low. Distortion skyrockets.
Jumping off the cliff with no experience to do a full range multi-driver system is pretty brave. Might I suggest looking at some of the kits or established and documented designs?
as you can see in my simulation (could also be called a bass reflex box) you cannot define if a vented box is "only helmholtz resonator" or "only transmission line". as the thread starter plans to build a tower, it is very likely that it behaves somwhere between "pure bass reflex" and "pure (mass loaded) transmission line". by simulating you can optimize the design without bothering what it is called...
edit: advantage of the "transmission line" simulation in hornresp is that you can adjust the driver position to minimize resonance peaks and dips.
Last edited:
When i said to have no experience i mean only on transmission line design. I built many loudspeakers but only bass-reflex and vented closed.
The transmission line choice comes to me because trying to design a box with 30hz at -3db, the volume results too big. it seems that with transmission line design it's possible to reduce it having good performances.
Yea, F3 @ 30 is a BIG box. Damn physics. Look at the selection of drivers. Some are designed where only a PR works ( a 20 foot 4 inch port is hard to fit) and can get very low. I still question your goal as way too bloomy in a room.
Do note, the vast majority of drivers made today are designed for vented alignments. The Qes/Qms choices favor ported. High EBP.
MDF is cheap so have a go at it.
STV, How do you differ "bass reflex" from ""vented, which was nothing but the term used before Thiel and Small gave us the math. Now we can call them QB3, C4 etc. Closed ( B2) is only a special case of a vented with the vent closed. All of these alignments are defined by the same math. You can think of a TL as a highly resistive port that uses a lot more total volume. Just to get us on the same syntax. All follow the principal of Helmholtz and the behavior is actually the same math as electrical filters, which was Theil's discovery, where Small gave us the fudge factors for real life.
A couple of other maybe minor advantages of TL. They are quite tunable after the build using stuffing and the bracing is built into the design.
In either ported, TL , or the MLTL suggested above it might be worth considering a slight bass shelf tuning which might integrate with room gain better than taking the f3 all the way out to 30Hz. It would also make the unloading point lower.
In either ported, TL , or the MLTL suggested above it might be worth considering a slight bass shelf tuning which might integrate with room gain better than taking the f3 all the way out to 30Hz. It would also make the unloading point lower.