Thanks xrk,
I have some cardboard tubing but it's very thick strong stuff, I was thinking of just using some 90mm pvc as I have plenty from some experiments last year.
To aid adjustments I was thinking of making the port external (initially)so I could try a few different lengths easily.
Here's a question I couldn't find the answer for readily;
If I use an external port does it's volume count towards total enclosure volume? Using my 90mm tubing gives me lengths around 20-25cm, 1-1.5 liters?
I have some cardboard tubing but it's very thick strong stuff, I was thinking of just using some 90mm pvc as I have plenty from some experiments last year.
To aid adjustments I was thinking of making the port external (initially)so I could try a few different lengths easily.
Here's a question I couldn't find the answer for readily;
If I use an external port does it's volume count towards total enclosure volume? Using my 90mm tubing gives me lengths around 20-25cm, 1-1.5 liters?
90mm dia duct is very big. How big is your driver? Duct Sd should be circa 20% to 33% of cone Sd.
In general, if the duct if placed internally reduces the chamber volume - it reduces overall volume. If externally it does not. For the purposes of my simulations in Akabak, the main chamber volume is separate from volume contained in the duct.
In general, if the duct if placed internally reduces the chamber volume - it reduces overall volume. If externally it does not. For the purposes of my simulations in Akabak, the main chamber volume is separate from volume contained in the duct.
Dunno; vent area is a function of driver displacement [Vd = Sd*Xmax] and box tuning [Fb]: https://www.trueaudio.com/st_ventq.htm
GM
GM
Just try to keep velocities in the port below 15m/s or so as a rule of thumb. Some people prefer to stay below 10m/s.
A 3in driver will usually by need more than a 3/4in dia vent.
So I got around to finishing one today 
Very, very rough build, not sure it's 100% sealed yet?
I'm still playing with the port, seems to sound better without the 4 x 4.5 cm tube? Just a 4.5 cm hole in the baffle.
Some light lining behind the front driver, then stuffed for about a foot below it, well away from the rear port at the bottom. Did some listening with various levels of stuffing before sealing the bottom.
It's got some bass, it's nice and open sounding, there's certainly plenty of colouration but that's due to my rushing the build and using whatever materials I could lay my hands on for cheap.
Bottom line, I'll be building the second one.
Very, very rough build, not sure it's 100% sealed yet?
I'm still playing with the port, seems to sound better without the 4 x 4.5 cm tube? Just a 4.5 cm hole in the baffle.
Some light lining behind the front driver, then stuffed for about a foot below it, well away from the rear port at the bottom. Did some listening with various levels of stuffing before sealing the bottom.
It's got some bass, it's nice and open sounding, there's certainly plenty of colouration but that's due to my rushing the build and using whatever materials I could lay my hands on for cheap.
Bottom line, I'll be building the second one.
Attachments
Hi GM
I looked at the link provided, but something does not make sense. Here is the formula as provided:
S(V) >= 0.02032 * f(B) * V(D)
where: S(V) = square inches and V(D) = cubic inches.
Does f(B) = frequency of box tuning? If so, the formula seems counter intuitive to me. If so it means that the lower the tuning frequency, the smaller the port size. For example, for a given driver with a given V(D), the port will be larger when the box is tuned to 40Hz than when tuned to 20Hz. Let me use a driver I have as an example. It has a V(D) of 40.3 cu.in. (80.3sq.in. (SD) X 0.5" (Xmax)). So, for a tuning of 40Hz (f(B)), S(V) >= 0.02032 X 40.3 cu.in. = 0.8189 cu.in. But for a tuning of 20Hz, the S(V) >= 0.41 cu.in. To me that is counter intuitive. And I missing something here?
Thanks,
Deon
Nice work. Seal the leaks as they kill bass. Line area to side of and behind driver with felt or foam to reduce coloration.
So I got around to finishing one today
Very, very rough build, not sure it's 100% sealed yet?
I'm still playing with the port, seems to sound better without the 4 x 4.5 cm tube? Just a 4.5 cm hole in the baffle.
Some light lining behind the front driver, then stuffed for about a foot below it, well away from the rear port at the bottom. Did some listening with various levels of stuffing before sealing the bottom.
It's got some bass, it's nice and open sounding, there's certainly plenty of colouration but that's due to my rushing the build and using whatever materials I could lay my hands on for cheap.
Bottom line, I'll be building the second one.
Greets!
Hmm, 80.3*0.5 = 40.15"^3
Sv = 0.02032*40*40.15 = 32.634"^2 and since area is halved/octave, 20 Hz = 16.317"^2
Yes, F(B) = box tuning [Fb].
Yes, a number of things pertaining to audio seem counterintuitive........what happens as the driver goes down in frequency? Its excursion needs to increase by a factor of four/octave to maintain a flat amplitude response, but of course it can't, so output becomes increasingly power limited, ergo the vent has less box pressure to excite it = smaller Sv required.
Conversely, if you started at 20 Hz and reduced Vd by a factor of four/octave with increasing frequency to maintain a flat amplitude response as opposed to max Vd, then Sv would shrink with increasing Fb.
GM
Well what a difference a day makes.
The speaker sounds much bassier today, the glue was obviously still very wet when I tested them yesterday.
Looking forward to starting the 2nd.
Well I built the second, got a bit tired messing about with port lengths so finally put a 12" sub together
Have had the woofer sitting about for years. Currently the enclosure is actually open on the bottom, just sitting on the carpet, quite a leaky box (poor mans aperiodic) without any stuffing or bracing yet but oh boy is there bass now
I think even with this loading/tuning method I was probably asking a bit much of my tangbands, they only have .5mm excursion I believe? Selecting the "small" size option in my amps menu seems to free up their sound somewhat as it rolls them off below 100hz.
Have had the woofer sitting about for years. Currently the enclosure is actually open on the bottom, just sitting on the carpet, quite a leaky box (poor mans aperiodic) without any stuffing or bracing yet but oh boy is there bass now
I think even with this loading/tuning method I was probably asking a bit much of my tangbands, they only have .5mm excursion I believe? Selecting the "small" size option in my amps menu seems to free up their sound somewhat as it rolls them off below 100hz.
Attachments
I just built a TABAQ style TL out of foamcore with a TC9FD as per xrk971's method. I tuned them to 65 Hz and stuffed them with rockwool. No BSC but have it flat against a wall. It is very bright and bass disappointing. Maybe I have overstuffed or there is a leak somewhere, so will have a tinker with them tomorrow.
Internal dimensions 120 mm x 120 mm * 830 mm (4.75" x 4.75" x 32.75")
Vent 16 mm high x 62 mm deep (20/32" x 2 14/32")
Internal dimensions 120 mm x 120 mm * 830 mm (4.75" x 4.75" x 32.75")
Vent 16 mm high x 62 mm deep (20/32" x 2 14/32")
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There can be quite a bit of mucking around to get the bass right mate. Stuffing is key.
Try them without any just to get an idea.
What I've also discovered about my room is that there is very little bass in certain locations, especially near field, the further I get away the more bass there is.
Try toeing them in so the axis cross before you, should tame the treble a bit.
All else fails, it's subwoofer time
Try them without any just to get an idea.
What I've also discovered about my room is that there is very little bass in certain locations, especially near field, the further I get away the more bass there is.
Try toeing them in so the axis cross before you, should tame the treble a bit.
All else fails, it's subwoofer time
Loose stuffing above driver but not below - and try reducing length of vent. My calculations on Tabaq showed 4in long but testing proved only 1.25in needed. This seems more true with high Qts drivers. It needs BSC though or will sound bright. Tc9 not best driver for Tabaq. If you have P830986 that is wonderful Tabaq driver with 1mH and 8.2ohm BSC. Deep deep bass.
Thanks for all the advice. They were overstuffed. Tried them empty and then added a more modest amount of stuffing. They sound much better now. The reason I chose this design is that I have a spare pair of TC9FD drivers and want to make a pair of bedroom speakers and like the columnar look. They don't need to go loud but I want some bass extension to avoid having to use a sub.
I'm glad that worked out. If you want to hear what a Tabaq with a P830986 can sound like (I believe that is the OEM driver in the commercial Tabaq) check out my sound clips here:
http://www.diyaudio.com/forums/full-range/88787-tabaq-tl-tang-band-125.html#post4691749