Sonotube TL for 21Hz

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I want to do a Sonotube TL with two woofers in a push-pull arrangement where one of the woofers is hooked out of phase and installed backwards in the enclosure. Basically, it'll be sort of like this. http://www.t-linespeakers.org/projects/steve/index.html

I have 8 foot ceilings in my listening area so I suppose I could probably get away with a stuffed 6 footer, but what I'd really like to do is build a TL long enough to take advantage of the 21Hz free air resonance of my 12" drivers.

Woofer specs:

Dual voice coil 8ohm/4ohm
FS 21Hz
QTS .38
QMS 4.2/4.4
QES 0.44/0.42
VAS 13.3 ft³ (376.6L)
SD 0.0532 m²
XMAX 0.460 (11.7mm)
(let me know if I forgot any important ones)

A little basic math tells me...

1128 ÷ 21 Hz = 53.71 feet full wave length
53.71 x 0.25 = 13.428 feet ¼ wave length

13.428 feet = 161.14 inches TL length

Assuming my math is correct, this 13+ foot length presents a problem in my listening area.

I came up with an idea that includes just one 90° bend. The top will only reach as high as about 7'2" leaving some breathing room between it and the ceiling. The rest will be on the floor run along a wall. I have easy access to some 14" x 14" x 14" (1 ft³ internal volume) 3/4" MDF boxes meant for 12" woofers and can probably find some 6' long x 12" diameter Sonotube nearby. I bet I could trim the tubes a little (if necessary) and cut a couple more holes in the boxes and have this thing together pretty quickly.

What do you guys think of this idea? Is there any chance of comb filter effects or any other undesirable operation possible from this design? Should I add something like a 45° reflector to the box in the middle? Thanks.
 

Attachments

  • tl.gif
    tl.gif
    4.1 KB · Views: 1,070
Greets!

A single 12" pipe doesn't have enough Vb to perform well with one of these drivers, much less two. The math is mostly correct, an end correction of (0.613*pipe radius) needs to be subtracted from its length and the SoS will probably be somewhat higher, so worst case is it will be a little too long.

Yes, there will be comb filtering. All things considered, best IMO to build an optimum one fold cab out of 19mm no-void plywood with both the drivers and vent at floor level. Use this little calculator to find optimum length/CSA (don't forget to double Vas): http://www.diyaudio.com/forums/attachment.php?s=&postid=657051&stamp=1117991086

BTW, for my records, what make/model drivers are these?

GM
 
A few more questions for you guys. Is it totally necessary to build a TL exactly to the ¼ wave length of my driver FS? Or can I fudge it a little and make it shorter so it's tuned closer to 30Hz or something? What if I stuff it full of poly-fil?

Or how about two 6' tubes with one 1ft³ box and one woofer for each tube? This will make a stereo bass pair of TLs and each TL will be 7' long (about 1 foot below my ceiling).
 
Hey, thanks for the post. It seems I'm still being moderated since I'm a new member, so that second post I made was actually from a few hours before yours.

Ah, so Sonotube of 12" diameter is too narrow for my driver(s)? Interesting. Yeah, I'll post the full specs.

Radio Shack 40-1350 Realistic Subwoofer (vintage 1989). It was the first dual voice coil woofer I'd ever seen.

19 ounce ceramic magnet
frequency response (-6 dB) 26Hz to 2.7kHz
8 ohm/4 ohm
flux denisty 7.8Kg
Sensitivity 89dB/95dB
FS 21Hz
RE 6.9 ohm/3.5 ohm
QTS .38
QMS 4.2/4.4
QES 0.44/0.42
VAS 13.3 ft³ (376.6L)
SD 0.0532 m²
XMAX 0.460 (11.7mm)
Vd 37.9 in²
Le 2.24 mH/0.56 mH (@ 1 kHz)
No 0.78%/0.79%
Pe 120/60 Watts

I'm not following your math. I barely understood enough about transmission lines to get this far. :) Should I go with a 14" or 16" tube for better Vb? I think in order to keep this from getting too complicated (as this is my first time), what if I went ahead and kept it simple to start with? How about something like the reconstructed El Pipe-O with only one woofer each? http://www.passdiy.com/projects/el-pipe-o-9.htm

I don't think it would be appropriate to go with 6' length because it would require a bunch of stuffing which would lead to poorer performance. If only I had a listening room with higher ceilings. Or lower floors.

Could you explain more about Vb when increasing tube diameter to say 14"? Also could you explain what SoS is? I hadn't seen anything about needing an end correction before (I'm sure I've still got a lot to learn). I couldn't view the xls file. Lastly, could you explain what comb filtering is with regard to audio? I had only heard of it in televisions.

Hey, I just had a brainstorm. How far apart can the driver and the open end be before comb filtering takes place? Better yet, how close together can the driver and open end be before problems occour? Can they be side by side? How about downward firing? I've seen ported home theater woofers where the port and the driver are both down-firing. What about a down-firing TL where both the open end and driver are facing the floor? Will 'floor gain' occour? Is it even desirable? I've got a carpeted floor. If this works, it'll save tons of time and effort (and money) since I could just cut the tubes at 45° angles and liquid nails them back together. It'd just be one fold and vented at floor level, just like you suggested. :) They'd get a couple bolts through both adjacent edges for greater stability and a couple legs to raise it an acceptible height from the floor (whatever that may be). They'd even probably be portable, to some extent.

I could fit two of these in the listening room without too much trouble. If necessary, the driver/open end could even be rotated up so as to aim at the ceiling if that would provide better SQ.

I whipped this up in like two minutes so pardon the sloppyness.
 

Attachments

  • tl02.gif
    tl02.gif
    1.7 KB · Views: 830
Greets!

(your posts rearranged to suit me)

====

>Hey, thanks for the post. It seems I'm still being moderated since I'm a new member, so that second post I made was actually from a few hours before yours.

>Radio Shack 40-1350 Realistic Subwoofer (vintage 1989). It was the first dual voice coil woofer I'd ever seen.

====


You're welcome! A 'golden oldie! I thought those specs looked familiar! I designed/built quite a few different designs using them, though most were a tower design (now AKA ML-TL).

====

>A few more questions for you guys. Is it totally necessary to build a TL exactly to the ¼ wave length of my driver FS? Or can I fudge it a little and make it shorter so it's tuned closer to 30Hz or something? What if I stuff it full of poly-fil?

====

No, and in some cases a good trade-off between size/performance is to tune it to as high as ~(SQRT(2)*Fs), or ~29-30 Hz with this driver. This driver's Fs is low enough to use the higher tuning since room gain will boost it down low and the higher tuning will increase its midbass efficiency, a win-win alignment.

=====

>I don't think it would be appropriate to go with 6' length because it would require a bunch of stuffing which would lead to poorer performance. If only I had a listening room with higher ceilings. Or lower floors.

====

Agreed, at this length an ML-TL is preferred.

====

>Or how about two 6' tubes with one 1ft³ box and one woofer for each tube? This will make a stereo bass pair of TLs and each TL will be 7' long (about 1 foot below my ceiling).

>Ah, so Sonotube of 12" diameter is too narrow for my driver(s)? Interesting. Yeah, I'll post the full specs.

>Should I go with a 14" or 16" tube for better Vb? I think in order to keep this from getting too complicated (as this is my first time), what if I went ahead and kept it simple to start with? How about something like the reconstructed El Pipe-O with only one woofer each? http://www.passdiy.com/projects/el-pipe-o-9.htm

====

You're going to use a high stuffing density to lower the pipe's strong harmonic modes, but contrary to what's been published until recently, the SoS doesn't slow down much with increasing density. Really, the 'classic' TL rule-of-thumb (ROT) to make the TL's cross sectional area (CSA) ~= Sd rolls off/damps most drivers so much that once the pipe is lined, the ~completely damped Fs peak implies a much longer effective pipe length, ergo the false impression of a lower SoS.

For instance, your 12" sonotube design will overdamp the driver to below its Qts. Fine if it's a too high Q driver or you want a ~flat impedance for best power transfer when driven by an impedance matching amp, but the former doesn't apply in this case, and being a wide BW sub driver, I doubt the latter does either, and why I don't consider it a good design for you.

Of course if this is a prime performance goal, then by all means use one tube for both drivers if max acoustic damping is desired or one tube/driver if a moderate amount, but if a ~IB or slight gain response is desired, a much larger CSA will be required. IOW, the pipe's Vb needs to be at least = the driver's Vas, and in many cases 1.5-4x Vas for max performance, so to KISS it (keep it simple stupid) with good performance, design/build it as I already recommended.

====

>I'm not following your math. I barely understood enough about transmission lines to get this far.

>Could you explain more about Vb when increasing tube diameter to say 14"? Also could you explain what SoS is?

=====

CSA for a tube = (dia.^2*pi)/4

Vb = volume of box, or pipe in this case, so assuming dims in inches: (CSA*length)/1728 = ft^3

SoS = speed of sound. It books along at ~1130 ft/sec on average, but varies with the local pressure/temperature. Altitude per se has a negligible impact on it, so not a factor in speaker design.

=====

>I hadn't seen anything about needing an end correction before (I'm sure I've still got a lot to learn). I couldn't view the xls file. Lastly, could you explain what comb filtering is with regard to audio? I had only heard of it in televisions.

====

You haven't been reading the right docs. ;) Do a search on pipe harmonics, it should bring up some
that elaborate on the finer details of pipe action/design.

Why not? Even if you have a Mac, won't Open Office or some emulator allow you to view/use an Excel spreadsheet?

Comb filtering is where the same frequencies from multiple sources, but offset in time (space), add/subtract to create a jagged summed response.

====

>Hey, I just had a brainstorm. How far apart can the driver and the open end be before comb filtering takes place? Better yet, how close together can the driver and open end be before problems occour?

====

There's always going to be comb filtering, but it can be minimized by placing the multiple sources as close together as practical.

====

>Can they be side by side? How about downward firing? I've seen ported home theater woofers where the port and the driver are both down-firing. What about a down-firing TL where both the open end and driver are facing the floor? Will 'floor gain' occour?

====

This driver is way too compliant for bottom firing. The calc'd sag is 5.63 mm, almost its Xmax! For max boundary gain, terminate ~at the floor in a perpendicular plane. Of course the TL's terminus can be floor loaded either way though.

====

>Is it even desirable? I've got a carpeted floor.

====

IMO it is. The way I look at it, there's no such thing as too much acoustic efficiency since it lowers the amp power required/distortion. IOW I'd rather EQ it down than boost it up to make it ~flat in-room. I recommend using spikes to anchor it to the floor rather than just sitting on the carpet.

====

>I could fit two of these in the listening room without too much trouble. If necessary, the driver/open end could even be rotated up so as to aim at the ceiling if that would provide better SQ.

====

While there's some advantages to using 'stereo' subs, there's something to be said for using dual drivers in a bipolar push-pull layout to cancel out their rocking motions/any non-linear excursion distortion WRT build simplicity/SQ, so I prefer the latter since these have enough excursion to make them an issue.

Since ceilings tend to be acoustically 'weaker' than a floor unless only the exterior roof is on the other side, I recommend floor loading.

GM
 
Thanks for taking some time to answer my questions. I appreciate the effort.
You're welcome! A 'golden oldie! I thought those specs looked familiar! I designed/built quite a few different designs using them, though most were a tower design (now AKA ML-TL).
So they can indeed be used in a TL. That's great to know because I wasn't sure if anyone had ever attempted a TL with these oldie-but-goodies.
No, and in some cases a good trade-off between size/performance is to tune it to as high as ~(SQRT(2)*Fs), or ~29-30 Hz with this driver. This driver's Fs is low enough to use the higher tuning since room gain will boost it down low and the higher tuning will increase its midbass efficiency, a win-win alignment.
This is extremely interesting. Hmm, speaking of midbass, I currently have too much midbass from an Obcon enclosure with two Sony tens (vintage 1992) in it (driver specs available upon request) that has a Qtc of around 1 or so with aproximately 1.269 ft³ volume. According to an internet sealed encloser calculator, my drivers want a 1.9 ft³ enclosure. I added a pillow and that helped quite a bit. It has a few dips in frequency response as observed with sine wave sweeps, but it falls flat on its face below 35Hz. The typical bass boost from 70 to about 120 is still there, as is common in most consumer bass products, so I'd like to avoid a repeat if possible on the TL. Incidentally, my bro has a KLH floor sub for home theater and its published frequency response is 40-180Hz. It has a single front firing 10" and a rear firing port. It has very similar performance to the Obcon box. Surprisingly so (it can get louder and has a smoother curve, but falls flat right around 35Hz as well). Heh, that KLH is supposed to be a subwoofer? Dubious. I supose it's ok for non critical listening, as I suspect most consumer bass products are, but it is a bit too slow, muddy, and port noise can be heard etc. This is the sort of thing I want to avoid and why I chose to start learning about transmission lines. I want the effortless, clean bass everyone is always talking about. I prefer SQ over SPL and will do whatever it takes, within my limited budget, to get it.
Agreed, at this length an ML-TL is preferred.
What is the ML in ML-TL? Mass loaded? Does mass refer to the stuffing density? Or just that it has stuffing in it as opposed to an empty one?
You're going to use a high stuffing density to lower the pipe's strong harmonic modes, but contrary to what's been published until recently, the SoS doesn't slow down much with increasing density. Really, the 'classic' TL rule-of-thumb (ROT) to make the TL's cross sectional area (CSA) ~= Sd rolls off/damps most drivers so much that once the pipe is lined, the ~completely damped Fs peak implies a much longer effective pipe length, ergo the false impression of a lower SoS.
Ah, I think I understand. So the driver is damped to the point where it will start to behave as if it were in a larger encloser, even though it isn't? That's sort of what I had imagined happening instead of actually slowing the speed of sound down. That's a relief. Heh, wouldn't slowing down the speed of sound lower octaves and generally make things sound too slow? Kinda like the opposite of trying to speak in a less dense atmosphere like talking after breathing in helium from a balloon?
For instance, your 12" sonotube design will overdamp the driver to below its Qts. Fine if it's a too high Q driver or you want a ~flat impedance for best power transfer when driven by an impedance matching amp, but the former doesn't apply in this case, and being a wide BW sub driver, I doubt the latter does either, and why I don't consider it a good design for you.
I think I see what you're saying. As far as I can tell, my driver's only Q that is too high is the QES at 0.44/0.42. I'm supposed to aim for QES of 0.3 to 0.4, right? In this case, wouldn't a tube of 14" diameter be better than 12"? If QES is electrical and QMS is mechanical, then QTS is the total, right? Anyway, the QTS of 0.38 is on the high side, but probably not enough to turn me away from using tubes instead of wood.
Of course if this is a prime performance goal, then by all means use one tube for both drivers if max acoustic damping is desired or one tube/driver if a moderate amount, but if a ~IB or slight gain response is desired, a much larger CSA will be required. IOW, the pipe's Vb needs to be at least = the driver's Vas, and in many cases 1.5-4x Vas for max performance, so to KISS it (keep it simple stupid) with good performance, design/build it as I already recommended.
Heh, at this point, I'm so confused I don't even know what I want anymore. 12" diameter, 14" diameter, one driver, two drivers...

I think I'd like to keep stereo bass which would require two TLs with one driver each. I have some material that has stereo bass, so this is important to me. Then again, SQ and accurate low frequencies are also important to me. Can I have both?

What is IB? If I was going to tackle woodworking, non-void plywood sounds good. I bet it'd be safer (less dusty) than working with MDF. I'd honestly like to avoid woodworking if I could, and the sonotube idea would allow it. Hence my stubborness to abandon it.

More to come.
 
CSA for a tube = (dia.^2*pi)/4
Eep! Sorry, I don't understand that formula. There's pi, which I can recognise, but I don't understand the ^ or * or /. Are they just easier ways of typing x and ÷?
Vb = volume of box, or pipe in this case, so assuming dims in inches: (CSA*length)/1728 = ft^3
Once I learn how to figure CAS, I know I can do the rest of the calculation. Then I can factor in the end correction and arrive at a good set of parameters (I hope).
SoS = speed of sound. It books along at ~1130 ft/sec on average, but varies with the local pressure/temperature. Altitude per se has a negligible impact on it, so not a factor in speaker design.
Thanks for the clarification. I suck at math and don't use abbreviations or acronyms too often so you'll have to forgive me every now and then.
You haven't been reading the right docs. Do a search on pipe harmonics, it should bring up some that elaborate on the finer details of pipe action/design.

Why not? Even if you have a Mac, won't Open Office or some emulator allow you to view/use an Excel spreadsheet?

Comb filtering is where the same frequencies from multiple sources, but offset in time (space), add/subtract to create a jagged summed response.
I don't have MS office. Maybe I can try that xls file on a computer that does.

That sounds like multi-path in radio wave propigation.
There's always going to be comb filtering, but it can be minimized by placing the multiple sources as close together as practical.
That's good to know.
This driver is way too compliant for bottom firing. The calc'd sag is 5.63 mm, almost its Xmax! For max boundary gain, terminate ~at the floor in a perpendicular plane. Of course the TL's terminus can be floor loaded either way though.
The suspension is definitely rather lightly sprung on these old woofers. I've seen many much stiffer modern drivers. I thought XMAX was measured for one direction? Maybe the way it's measured has changed since the original specs were printed? I've never measured the excursion of them myself. If the published spec of 11.7mm is accurate, it seems similar to modern drivers though.

So what if I just layed the single driver folded tube TL (as pictured above) on its side so both the terminus and driver are perpendicular to the floor? I could still fit two in my listening room, I think.
IMO it is. The way I look at it, there's no such thing as too much acoustic efficiency since it lowers the amp power required/distortion. IOW I'd rather EQ it down than boost it up to make it ~flat in-room. I recommend using spikes to anchor it to the floor rather than just sitting on the carpet.
Ah yes, I've seen spikes in the picture of the bottom-firing HT sub. :)

I'd prefer as flat a response down past the driver's Fs as humanly possible. Something like a drop-off at around 10.5Hz would make me happy. I don't know how much room gain I'll have, so I think I should design for an anechoic chamber and then EQ it for any room gain (if any). I'd feel better doing it that way. However from what I've read, it seems to be a difficult goal to reach without 12 (dancing) Shivas or something, but again I probably haven't been reading the right docs. :)

I'd like it to be musical and would rather have SQ over SPL any day, but does this, by definition, require a shorter TL? If the single driver folded TL is a decent idea, a total length of around 12' folded into two equal sections would fit in my listening room.
While there's some advantages to using 'stereo' subs, there's something to be said for using dual drivers in a bipolar push-pull layout to cancel out their rocking motions/any non-linear excursion distortion WRT build simplicity/SQ, so I prefer the latter since these have enough excursion to make them an issue.
So you're saying that since these drivers have a lot of excursion, it's best to limit it in some way such as through a push-pull arrangement (one hooked out of phase) like this guy did? http://www.teresaudio.com/haven/subs/subs.html

I think I'd prefer stereo subs since these have a wide bandwidth and I was thinking about using it up to about 200Hz or so. Maybe even higher. And now my newbieness is starting to show. :)

I've read through some of the debates for stereo subs vs mono, and think I'd prefer stereo although I understand that mono has its advantages.
Since ceilings tend to be acoustically 'weaker' than a floor unless only the exterior roof is on the other side, I recommend floor loading.
Cool.
 
Here are the specs for the Sony 10" woofer. XS-L100C (vintage 1992)

4 ohm
Sensitivity 90dB/1W/1m
Frequency Response 20 - 2000 Hz

T/S parameters
a 10.6 cm
Sd 353 cm²
Re 3.19 ohm
Fs 28.1 Hz
Qms 2.766
Qes 0.416
Qts 0.362
Vas 104L
Cms 5.829 x 10-4 m/N
Mms 55.03 g
BL 8.632 N/A
No 0.538 %
Pmax 130 Watt
Xmax 6.3 mm
Lvc 0.718 mH

Does this driver look promising for a transmission line?
 
I still want to use the 12" woofers and I think I can with this latest idea. First, can anybody tell me the CSA of a 14" and 16" Sonotube? (I suck at math so be gentle)

One 12" driver's Sd is 82.46 sq inch

Two 12" drivers' Sd is 164.92 sq inch.

The CSA of a 12" diameter tube is 107 sq inch. (as seen on TL web pages)

One driver per tube should work. If I could calculate the CSA of a 14" and 16" tube, I could continue.

I think I understand now that maybe I don't want a TL tuned to 21Hz by length. I could appearantly shorten it to 60 Hz or so and stuff it down to 30Hz or so (and be within the realm of what GM said would work best). But these drivers need a large sealed box due to their low compliance, so I don't know.

The latest idea is basically a compromise between my original really long tube tuned for 21Hz idea and the short tubes seen here. http://www.teresaudio.com/haven/subs/subs.html

Forget all the pictures I've posted so far. If I can get away with a more traditional tubular TL, I'd rather do that.

So according to GM, I want to tune the TL to 29 or 30Hz. According to the link above, it's ok to have a 54.5 inch high TL tuned to 62Hz (empty) so when it's fully stuffed, it'll be around 31Hz.

So taking all of the above into account, it's good to have a TL CSA of either 100% or 125% of driver Sd, and a single 12" driver in a 12" diameter x 54.5" long TL should work ok.

As for the length, 54.5 inches is plenty short enough for my listening area. I could comfortably go up to 72 inches which would be 47Hz and require less stuffing for the same tuning of 30ish Hz. Am I right?

If I wanted to use both drivers in a single enclosure, the combined Sd would be 164.92 sq inch so I've got to come up with the CSA of 14" and 16" tubes to see if this idea is even feasable.

I'd prefer an out of phase push-pull to reduce excursion and run it as a mono sub. If I could afford four modern subs, I'd probably get four Shivas and do two of these TLs for stereo bass.

Sorry to keep posting so much to this thread. It's all in trying to wrap my head around this subject. Any help you guys can offer would be great.
 
Greets!

====

>Thanks for taking some time to answer my questions. I appreciate the effort.

====

You're welcome! If you only knew.

====

>So they can indeed be used in a TL. That's great to know because I wasn't sure if anyone had ever attempted a TL with these oldie-but-goodies.

====

This, and the Eclipse Swan 305, were very popular drivers around here in the 'good 'ol days' since they gave incredible bang/buck, so they've been put in everything from sealed to PA scoop bins.

====
quote:
No, and in some cases a good trade-off between size/performance is to tune it to as high as ~(SQRT(2)*Fs), or ~29-30 Hz with this driver. This driver's Fs is low enough to use the higher tuning since room gain will boost it down low and the higher tuning will increase its midbass efficiency, a win-win alignment.

>This is extremely interesting. Hmm, speaking of midbass, I currently have too much midbass from an Obcon enclosure with two Sony tens (vintage 1992) in it (driver specs available upon request) that has a Qtc of around 1 or so with aproximately 1.269 ft³ volume. According to an internet sealed encloser calculator, my drivers want a 1.9 ft³ enclosure. I added a pillow and that helped quite a bit. It has a few dips in frequency response as observed with sine wave sweeps, but it falls flat on its face below 35Hz. The typical bass boost from 70 to about 120 is still there, as is common in most consumer bass products, so I'd like to avoid a repeat if possible on the TL.

====

The driver's Le, Qts and amount of line stuffing will determine gain, so we're talking apples n' oranges.

====

>Incidentally, my bro has a KLH floor sub for home theater and its published frequency response is 40-180Hz. It has a single front firing 10" and a rear firing port. It has very similar performance to the Obcon box. Surprisingly so (it can get louder and has a smoother curve, but falls flat right around 35Hz as well). Heh, that KLH is supposed to be a subwoofer? Dubious.

====

'Sub' = infrasonic = reproduces the <20 Hz BW. 'LF' (AKA 'low bass') = 20-40 Hz, 'mid bass' = 40-80 Hz, 'upper bass' = 80-160 Hz.

Unfortunately, with the advent of HT and cinema sound marketing types calling the DD LFE system's <120 Hz BW a 'sub' channel, the average consumer considers whatever they hook up to the LFE channel a 'sub' regardless of what its BW is. All they know is that to go really low is ~inversely proportional to price, just like when buying a car, 'speed costs, how fast can you afford to go?"

====

>I supose it's ok for non critical listening, as I suspect most consumer bass products are, but it is a bit too slow, muddy, and port noise can be heard etc. This is the sort of thing I want to avoid and why I chose to start learning about transmission lines. I want the effortless, clean bass everyone is always talking about. I prefer SQ over SPL and will do whatever it takes, within my limited budget, to get it.

====

Well, TLs will please then. FWIW, most folks opt for either large sealed, IB, or EBS vented alignments for high SQ music or HT.

====

>What is the ML in ML-TL? Mass loaded? Does mass refer to the stuffing density? Or just that it has stuffing in it as opposed to an empty one?

====

Correct. No, it refers to mass loading a TL with a vent, AKA vented tower or column design. Properly done, stuffing is minimal since you want all the pipe action you can get.

====

>Ah, I think I understand. So the driver is damped to the point where it will start to behave as if it were in a larger encloser, even though it isn't? That's sort of what I had imagined happening instead of actually slowing the speed of sound down. That's a relief.

====

Correct.

====

>Heh, wouldn't slowing down the speed of sound lower octaves and generally make things sound too slow? Kinda like the opposite of trying to speak in a less dense atmosphere like talking after breathing in helium from a balloon?

====

No, we are amplitude oriented animals so it's the relative amplitude differences we key on, not the 'speed' per se.

====

>I think I see what you're saying. As far as I can tell, my driver's only Q that is too high is the QES at 0.44/0.42.

====

?? Ideally, you want a flat in-room resp0nse with a critically damped (0.5 Qt) audio system, ergo the room gain curve would have to be a mirror image the system's 6 dB/octave roll off slope. Only in your dreams!

Second best is a 0.7 Qt system (12 dB/octave roll off) that matches a perfectly sealed room's ideal 12 dB/octave gain curve. In some rooms you can get 'close enough'.

Since a properly stuffed TL typically has a ~IB response over most of its roll off BW before ultimately increasing at 24 dB/octave, it stands to reason that either a driver in a 0.7 Qtc sealed alignment or a 0.7 Qts driver in a TL are the 'no brainer' choices.

Many folks prefer to use low Qts drivers in TLs though because they sound 'fast', which really just means it doesn't have much bass. Different strokes..........

That said, there's no such thing as too much speaker damping if you think about it, so using a low Qts driver to get the damping and some form of series resistance to raise its effective Qts to get a more tonally balanced response is the 'Hot Ticket'. To get reasonable efficiency down low though normally requires multiple drivers.

So from this it's obvious that the 40-1350 has anything but too high a Qes/Qts for good performance.

All of this assumes an ideal room with the speakers well away from any boundaries though, or pretty much the opposite of what most have for an audio and/or HT room, so 'subs' generally need to be overdamped to compensate for the added gain of a wall/floor or corner position so a 0.32-0.42 Qts driver usually blends the best overall in-room. This puts the 40-1350 ~spot on for most apps, being flexible enough for a wide selection of sealed or vented alignments.

====

>I'm supposed to aim for QES of 0.3 to 0.4, right? In this case, wouldn't a tube of 14" diameter be better than 12"? If QES is electrical and QMS is mechanical, then QTS is the total, right? Anyway, the QTS of 0.38 is on the high side, but probably not enough to turn me away from using tubes instead of wood.

====

See above.

The required tube diameter is a function of net Vb required divided by its length.

Correct.

Qts has absolutely no bearing on whether to use a tube or some other construction/shape.

====

>Heh, at this point, I'm so confused I don't even know what I want anymore. 12" diameter, 14" diameter, one driver, two drivers...

====

I assumed as much, and why I suggested you avail yourself of my experience. ;)

====

>I think I'd like to keep stereo bass which would require two TLs with one driver each. I have some material that has stereo bass, so this is important to me. Then again, SQ and accurate low frequencies are also important to me. Can I have both?

====

Sure, it just means more $$/work for you.

I find this hard to believe since historically it's been a music/HT industry standard to mix all output to mono below ~120-150 Hz depending on whoever is responsible for the 'mix'.

====

>What is IB? If I was going to tackle woodworking, non-void plywood sounds good. I bet it'd be safer (less dusty) than working with MDF. I'd honestly like to avoid woodworking if I could, and the sonotube idea would allow it. Hence my stubborness to abandon it.

>More to come.

====

Infinite baffle, i.e. a baffle acoustically large enough that the driver's rear output will never be heard/felt. Mostly it's used to describe a sealed cab's Vb that's at least 4-10x the driver's Vas.

Yes, plywood is much safer overall to work with.

I hear ya, and have used more than my share of cardboard, concrete and terra cotta tubes, but they are much more hassle than wood once you move away from the 'sub' BW.

'Lucky' us! ;)

GM
 
Let me know if I'm doing this right.

To find the CSA of a 12" tube, let's assume the ID is 11.75" due to the differences in tube diameter, which can vary by +/- .5"

11.75 x 11.75 = 138.0625 x 3.1415 (pi) = 433.72334 ÷ 4 = 108.43083

In other words, CSA of a 12" tube is around 108.4 sq inches which looks pretty close to the 107 I've seen elsewhere.

Assuming I did the math correctly,

12" (11.75) = 108.43083
14" (13.75) = 148.48496
16" (15.75) = 194.82208
Give or take.

Again, single driver Sd is 82.46 sq inch and two drivers is 164.92 sq inch. If I really wanted to do two drivers in a push-pull out of phase alignment, a 16" tube would be best. Thoughts? Criticisms?

One more question. Is 125% of 164.92 Sd close to 194.82 CSA? Thanks.

Edit: Ah, I see you posted before I did.
 
Greets, part deux!

====
quote:
CSA for a tube = (dia.^2*pi)/4

>Eep! Sorry, I don't understand that formula. There's pi, which I can recognise, but I don't understand the ^ or * or /. Are they just easier ways of typing x and ÷?

====

Correct:

'^' = raise to some power
'*' = multiply
'/' = divide

I'm pretty much a computer dunce, so how did you make the divided sign? Regardless, the above are what's used in all the forums I've frequented.

====

>That sounds like multi-path in radio wave propigation.

====

Same principle.

====

>The suspension is definitely rather lightly sprung on these old woofers. I've seen many much stiffer modern drivers. I thought XMAX was measured for one direction?

====

Correct.

====

>So what if I just layed the single driver folded tube TL (as pictured above) on its side so both the terminus and driver are perpendicular to the floor? I could still fit two in my listening room, I think.

====

Can if you want. 'Laydowns' are popular in bedrooms since they can be slid under the bed. They are also occasionally used as faux stages or seating riser platforms in HTs.

====

>I'd prefer as flat a response down past the driver's Fs as humanly possible. Something like a drop-off at around 10.5Hz would make me happy. I don't know how much room gain I'll have, so I think I should design for an anechoic chamber and then EQ it for any room gain (if any). I'd feel better doing it that way. However from what I've read, it seems to be a difficult goal to reach without 12 (dancing) Shivas or something, but again I probably haven't been reading the right docs.

====

With TL alignments this is a 'pipe dream' unless either the driver is high Q and/or the room has significant gain. Anyway, this driver doesn't have enough Xmax/power handling to come close to meeting all your goals, and why TW uses so many drivers.

====

>I'd like it to be musical and would rather have SQ over SPL any day, but does this, by definition, require a shorter TL?

====

Per all that I've posted so far, hopefully it's obvious to you now that length has no affect on SQ per se.

====

>So you're saying that since these drivers have a lot of excursion, it's best to limit it in some way such as through a push-pull arrangement (one hooked out of phase) like this guy did? http://www.teresaudio.com/haven/subs/subs.html

====

No, I'm saying that drivers often don't have the same amount of travel from rest in each direction, so if done in push-pull they will average out somewhat, lowering any non-linear distortion.

GM
 
Greets, part tres!

====

>Here are the specs for the Sony 10" woofer. XS-L100C (vintage 1992)

>Does this driver look promising for a transmission line?

====

After what all I've posted, you tell me......

====

>I still want to use the 12" woofers and I think I can with this latest idea. First, can anybody tell me the CSA of a 14" and 16" Sonotube? (I suck at math so be gentle)

====

It can't be any worse than mine, so give it a try based on what I posted awhile ago.

====


>One 12" driver's Sd is 82.46 sq inch

Two 12" drivers' Sd is 164.92 sq inch.

The CSA of a 12" diameter tube is 107 sq inch. (as seen on TL web pages)

One driver per tube should work. If I could calculate the CSA of a 14" and 16" tube, I could continue.

====

One more time, don't base it on the driver's Sd for best performance! This isn't to say that a pipe CSA = Sd can't work properly, just that in the larger size drivers it requires a low Vas. Indeed, the ideal CSA for some of the newer sub drivers compute to as little as 0.7*Sd! These are not good candidates for TLs either. This isn't the case with your high Vas drivers though.

====

>I think I understand now that maybe I don't want a TL tuned to 21Hz by length. I could appearantly shorten it to 60 Hz or so and stuff it down to 30Hz or so (and be within the realm of what GM said would work best). But these drivers need a large sealed box due to their low compliance, so I don't know.

====

Again, you can't 'stuff ' a 60 Hz line to 30 Hz! What did I say or you read that you interpretted it this way?

====

>The latest idea is basically a compromise between my original really long tube tuned for 21Hz idea and the short tubes seen here. http://www.teresaudio.com/haven/subs/subs.html

>So according to GM, I want to tune the TL to 29 or 30Hz. According to the link above, it's ok to have a 54.5 inch high TL tuned to 62Hz (empty) so when it's fully stuffed, it'll be around 31Hz.

====

No, I said tune its length to 29-30 Hz, big difference! With a 54.5" length the pipe's CSA will be huge for best performance and be too rolled off for decent LF/sub output. The practical limit is 2*Fs, or a 42 Hz pipe length. It will be ~ -3 dB down at 30 Hz compared to the 30 Hz pipe though.

The referenced design uses four drivers, plenty of power, and significant 'shaping' EQ to get the desired results with short pipes.

At this point I recommend you read all the TL/ported info on MJK's site, download the demo MathCad (if you don't have a licensed copy) and his end loaded TL WS to get a better understanding/'feel' for TL design trade-offs.
http://www.quarter-wave.com/

GM
 
Awesome! Thanks for spending lots of time helping me. You've answered more questions than you've raised, and that's a good thing. :)

I was originally going to go with two large sealed enclosures for the 40-1350s, but stumbled onto this transmission line concept about a week ago. I was already aware of the Bose acoustic wave machine and other products such as the wave-guide thing in the rear of a '93 RX-7 and the wave radio, but I didn't know the proper name was transmission line, much less that it could be done as easily as putting a woofer at the end of a tube. My uncle did something like that in the late '80s or early '90s with a 4" driver and a short length of tube in front and a long length in back. He said the resonances of the tube were a little strange at first, but then got used to it. It appearantly sounded very amazing for its size. I think the driver was in the first 1/3 or 1/4 of the total length. It was just straight PVC pipe if I recall correctly. I don't think he stuffed it with anything. For my TL project, it's a good thing that higher frequencies are affected more by stuffing than low. :)

Is there any way to know if a 14" or 16" tube will have enough volume for a Vb of 5.4ft³ if it were compared to a sealed box? The Vas of the speaker being 13.3ft³ and the F3 at 39.08Hz equals a Qtc of .707 (which is what I'd like if possible).

So 5.4ft³ in a TL means a longer 12" tube or a shorter 16" tube. If the above is correct, I'd want around 155L of equivilant volume, but I don't know how to get it.

To get the ÷ I used the character map. The alt code is alt+0247. × is alt+0215 (I'd been using the letter x).

Ok, I'll do more research before asking any more (basic) questions.
 
Greets, part quatro!

====

>In other words, CSA of a 12" tube is around 108.4 sq inches which looks pretty close to the 107 I've seen elsewhere.

>Assuming I did the math correctly,

12" (11.75) = 108.43083
14" (13.75) = 148.48496
16" (15.75) = 194.82208
Give or take.

====

Close enough for gov'mint work!

====

>Again, single driver Sd is 82.46 sq inch and two drivers is 164.92 sq inch. If I really wanted to do two drivers in a push-pull out of phase alignment, a 16" tube would be best. Thoughts? Criticisms?

====

See my previous comments.

====

>One more question. Is 125% of 164.92 Sd close to 194.82 CSA? Thanks.

>Edit: Ah, I see you posted before I did.

====

?? 164.92*1.25 = 206.15, while 194.82/164.92 = 1.1813x = 118.13 %.

Yeah, I'm having a rare fairly long stretch of semi-lucidity, but I'm done for now, I have another project I promised to do.

GM
 
No, I said tune its length to 29-30 Hz, big difference! With a 54.5" length the pipe's CSA will be huge for best performance and be too rolled off for decent LF/sub output. The practical limit is 2*Fs, or a 42 Hz pipe length. It will be ~ -3 dB down at 30 Hz compared to the 30 Hz pipe though.

The referenced design uses four drivers, plenty of power, and significant 'shaping' EQ to get the desired results with short pipes.
Ah, I see. That actually makes sense to me. Thankyou.

And yes, the Sony 10s would make decent TL subs. ;) Moreso than many modern ones. They're already spoken for, but I'll see what I can do. I wonder what two TLs of different tuned lengths would sound like?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.