Lab 12 Based Offset Driver - Mass Loaded - Transmission Line (OD-ML-TL) Design by Bj - Page 8 - diyAudio
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Old 20th December 2012, 11:27 PM   #71
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Default OD_ML_TL Build

I have all the material cut (18 mm Baltic Birch) and am in the process of gluing and assembling.
I have Wool for stuffing, speakers and just got a new laptop with ARTA and REW installed.
I also have an ART dual USB pre and an ECM 8000 mic.
I also installed System Architect 3.30 for the Crown amps.
.
The design that I am building is a little different than the "final" listed earlier in this thread, but it seems to simulate well in HRSP.
I tried to simplify the design as much as possible.
I didn't like the idea of the large external flare, mainly because it is hard to define exactly where the port ends, plus the maximum velocity in the port is only ~ 2.3 M/S so I don't anticipate any port noise.
.
There is a ripple in the response at about 80 Hz that comes and goes with just a few mm's of change in duct or port length, but I am assuming that may go away with some stuffing.
.
I tried to get the driver to mount lower but I could only get it about 5 inches lower, and that greatly complicated the design.
So I am going to live with it just the way it is.
.
I should have some tests of a finished, stuffed cab (or two) with a broken in driver in a week or so.

Dave
Attached Images
File Type: jpg OD_ML_TL Easy Fold.jpg (85.0 KB, 500 views)
File Type: jpg HRSP.jpg (147.7 KB, 482 views)
File Type: jpg SPL.jpg (91.8 KB, 465 views)
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Last edited by Shadydave; 20th December 2012 at 11:31 PM.
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Old 21st December 2012, 12:23 AM   #72
tb46 is offline tb46  United States
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Hi Shadydave,

That should give some interesting information. Looking forward to it.

Regards,
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Old 6th January 2013, 01:10 PM   #73
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Default Partway there

So I finished the first OD_ML_TL box and glued the entire thing except the last side.
I used 18 mm 13 ply Baltic Birch for the entire box.
I used Polyurethane glue and then caulked every joint with Dow Silicone II just to be safe, oh and about 50 Self-Sinking Small Flat Head Square Drive 1-5/8”_#6 screws along with my 6 big wood clamps
These screws McMaster-Carr Stock number 91520A301
I also used threaded inserts for the speaker mount bolts.
These inserts McMaster-Carr Stock number 92105A665. They work well but I had to use a larger than recommended drill (7.4 vs. 7.0 mm)
I screwed the last side on using foam gasket tape to seal it and left out the damping material.
I basically wanted to break in the driver and do a few FR sweeps without damping to see what it really does to the speakers FR.
The first thing I will say is, if you have a couple of designs, each with their own cutlist, don’t get the cutlists mixed up.
I was planning on leaving out the external flare, but…I used the wrong cutlist and am out of Baltic Birch that is long enough to make 4 more baffles. I have allot of 30” X 30” BB but the baffles have to be 33 and something So, I will either leave them with an external flare, which is only 2/3 of the size of the “final” design in this thread, or I will make a glue in piece to fill in the flare.
I am worried that the port is too short, and I do not know how much of the flare actually acts as a tuned port.
So here are a few Pics and some FR sweeps.
I used an ART dual USB pre with a Behringer ECM8000 microphone and REW on an HP ProBook 4530s, 2.3 GHz dual core with 4 GB DDR3, 500 GB drive and Windows 7 pro 64 bit software.
The USB pre does not list windows 7 as a usable O/S and it took me a while to get it working.
Also, the ART dual USB does not allow for calibration like a normal soundcard, or at least I can’t figure that out but the loopback response curve is not all that bad.
It drops off about 1 dB from 30 to 15 Hz and has some ripple maybe 1 dB each way in a sine shape (3 waves) between 14,000 and 22,000 Hz. Not that bad for what I am doing.

.
The FR plot was done with HP-22 Hz-48dB-BW and LP-120Hz-24dB-BW both programmed on a Crown XTi-1002 amplifier.
Also I set the limiters at 20V and then 22V (~93W and 108W) to protect the speakers and give a reference. The SPL numbers are set with a new Radio Shack SPL meter and are within +- 1 dB or probably better.
These measurements are 15 Cm off of floor and 1 meter from baffle surface in the center of the largest room I have.
The room however has concrete floor and walls with a drywall ceiling.
It does have a rug and some furniture like a soft couch and a giant soft chair.
I had wanted to do some measurements outside but the 6" of snow on the ground and the 15 degree temps made that less appealing. Maybe in a few weeks when the sub is finished.
I found when listening to the sub I preferred to use LP = 80 Hz-12 dB-BW and have gone down as low as HP = 20 Hz-48 dB-BW with the limiter set at between 20 and 24 volts. But I have seen some occasionally scary excursions with HP = 20 Hz and limit = 24 V (135 Watts), although only on movies with some big LF content.
I will admit that I really do not even notice that it is there until I either shut off the Crown amp or a really violent low scene comes along in a movie.I can't wait to have 2 of these spread around the room with some EQ on them.
I found it interesting to watch the cone during an RTA sweep with the 22 Hz-48 dB HP filter and starting the sweep at 10 Hz, the speaker cone starts to move with some large amplitude's, much bigger than I ever see even with the movies.
However the large amplitude occurs at 13 to 16 Hz and I can see the motion but hear nothing. Then the amplitude drops way down and i start to hear the speaker.
This makes me wonder if response below 20 Hz really does anything.
.
The pictures show construction at several steps, the gasketing that I used to seal the temp screwed on side panel, the sub hooked up in my den, my measurement setup and a few FR sweeps. I tried to make a comparison of HRSP and the RTA output but the scales are so different that it was hard to do.
I would have liked to do the measurement outside but the 6" of snow and 15 degree weather made that less appealing.
Next I will pull it apart and add damping, then do the measurements all over again.
If the FR curve does not improve quite a bit I am going to make an insert to cover the external flare, increasing the port length. I may also put a 3/4" divider in the port to help with aspect ratio.
So, here it is so far.
The measurements are first HP-22 Hz-48 dB-BW_LP-120 Hz 24 dB-BW. with the limiter set at 18 and 22 Volts.
The second shows the same crossover settings but with a limiter at 20 (93 W) and 22 Volts (108 W) plus the loopback calibration is also in the file,straight line at ~ 105 dB.
Attached Images
File Type: jpg 1_Bonding baffle.JPG (49.4 KB, 409 views)
File Type: jpg 2_Finished box.JPG (34.8 KB, 388 views)
File Type: jpg 3_Path showing caulk and PU glue on angle.JPG (38.7 KB, 131 views)
File Type: jpg 4_Screws and clamps.JPG (43.7 KB, 121 views)
File Type: jpg 5_Gasket on box side.JPG (31.5 KB, 136 views)
File Type: jpg 6_Undamped and gasketed sub.JPG (49.9 KB, 175 views)
File Type: jpg 7_Measurement setup.JPG (50.9 KB, 160 views)
File Type: jpg 8_22-120-limit at 20 and 22 V plus loopback cal.jpg (40.3 KB, 208 views)
File Type: jpg 9_22-120-18 and 22 V limiter.jpg (44.2 KB, 203 views)
File Type: jpg 10_HRSP vs RTA.jpg (41.7 KB, 179 views)
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<---My Transmission Lines from a prior life...Top one Tweeter...Bottom one definitely a Sub
..In space, you can't hear my sub

Last edited by Shadydave; 6th January 2013 at 01:30 PM. Reason: Left something out
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Old 7th January 2013, 11:56 PM   #74
NWCgrad is offline NWCgrad  United States
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Quote:
Originally Posted by Shadydave View Post
So I finished the first OD_ML_TL box and glued the entire thing except the last side...The first thing I will say is, if you have a couple of designs, each with their own cutlist, don’t get the cutlists mixed up.
I was planning on leaving out the external flare, but…I used the wrong cutlist and am out of Baltic Birch that is long enough to make 4 more baffles. I have allot of 30” X 30” BB but the baffles have to be 33 and something So, I will either leave them with an external flare, which is only 2/3 of the size of the “final” design in this thread, or I will make a glue in piece to fill in the flare.
I am worried that the port is too short, and I do not know how much of the flare actually acts as a tuned port.
It is great to see this design being built!!! I plan to build in a few months and will also post the results. Looking at the measured data it seems a fairly good match to the model, will be very interesting to see the effect of the stuffing.

It does seem that the port is a bit short compared to the Bjorno modification (see attachment). Off the top of my head I can't recall if this would significanlty change the tuning of the design.

Great looking sub, i am getting impatient for my build.
Attached Images
File Type: jpg Built versus Original.jpg (15.2 KB, 185 views)
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Old 8th January 2013, 10:06 AM   #75
DrDyna is offline DrDyna  United States
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Quote:
Originally Posted by Shadydave View Post
This makes me wonder if response below 20 Hz really does anything.
Well, these are tuned at around 23-24hz by the look of it, so no, all you'll get below tuning is cone flapping.

This looks really promising though, I'll have to try a TC sounds version this summer once it warms up.

I wonder about tuning it a bit lower for HT use though, would a 16hz tune make the box a lot larger?
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Old 8th January 2013, 01:10 PM   #76
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Originally Posted by DrDyna View Post
Well, these are tuned at around 23-24hz by the look of it, so no, all you'll get below tuning is cone flapping.

This looks really promising though, I'll have to try a TC sounds version this summer once it warms up.

I wonder about tuning it a bit lower for HT use though, would a 16hz tune make the box a lot larger?
Are you basing that on the response curves?
Remember, I am using a 22 Hz-48 dB / Octave High Pass.
.
Beyond that, I have no clue where the tuning is at,
I can say, the T/S parameters changed a bit after break-in of the speaker (if I can believe the DATS system).
I will post in more depth about this as well as the final (stuffed) tests soon.
As soon as the Dura-Tex dries.
.
NWCgrad, they seem to work well according to HRSP.
But, all these designs are kind of a guess, backed up with a simulation.
I am just unsure how long the effective port is with the external flare, and that makes me uncomfortable.

Dave
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<---My Transmission Lines from a prior life...Top one Tweeter...Bottom one definitely a Sub
..In space, you can't hear my sub

Last edited by Shadydave; 8th January 2013 at 01:13 PM. Reason: Added response to NWCgrad
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Old 8th January 2013, 06:18 PM   #77
DrDyna is offline DrDyna  United States
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Quote:
Originally Posted by Shadydave View Post
Are you basing that on the response curves?
Remember, I am using a 22 Hz-48 dB / Octave High Pass.
Negative, I believe when the first sims were first done by bjorno (b, correct me if I'm mistaken) the length of the line and the tuning were very much deliberate based on the driver parameters.

If you were to use a driver with a lower FS, I'm guessing you could tune the cabinet lower (longer?) which would result in less inaudible cone flapping (unloading below the tuning frequency) and lower usable response.
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Old 14th January 2013, 09:30 PM   #78
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Default Finished, for now

I finally finished stuffing the box and doing the final gluing of the side onto the box.
I ran around it with a ¼” round over and put 2 good coats of Duratex on the box.
I put a fresh layer of foam sealant on the speaker and bolted it down using Socket Head cap screws.
Before I put the speaker in, I measured it again using DATS. I was surprised to see that Fs had risen from 22.0 to 22.8 Hz.
So I set it up and did some sweeps, and this time I realized that I could run it at a higher voltage than I was using. I had it limited to 24 V (135 Watts) but I found I could run 29 V (200 Watts) without distressing the speaker.
One thing I did notice is my other woofer cabinets are being excited to the point that I almost can see the cones move.
Anyway, here is a 15Hz to 300Hz sine sweep with a 22 Hz-48 dB/Octave BW_HP and a 180 Hz-24 dB/Octave BW_LP filter and the Voltage limiter set at 29.15 Volts.
.
When I did the first sweeps I saw a big hole at 34 Hz. I’m not sure if this is room acoustics or the speakers response.
I put an 8 dB boost at 34 Hz with a Q of 6 into the Crown amp and the response was almost flat after that.
I should note that I am not using any smoothing on this data. I see if I use 1/6 Octave smoothing my lumpy line will almost get flat, or at least real smooth and the hole at 34 Hz almost goes away. So I guess that is cheating.
.
I may play around with the port some, but with a little EQ it sounds great.
22 Hz-8th order HP...70 Hz-4th order LP with 8 dB boost at 34 Hz (Q=6).

I have a scope across the speaker wires and I love the way you can't tell the sub is even there until there is some really low stuff. Watching the scope really shows me that there isn't much low freq stuff most of the time.

Dave
Attached Images
File Type: jpg tn_Final Box.JPG (78.0 KB, 125 views)
File Type: jpg tn_Finished.JPG (76.3 KB, 67 views)
File Type: jpg tn_Lab 12 Box.JPG (96.5 KB, 58 views)
File Type: jpg tn_Port.JPG (176.2 KB, 74 views)
File Type: jpg tn_Speakon.JPG (86.4 KB, 73 views)
File Type: jpg tn_sweep_stuffed-22hz-150hz-29v.jpg (59.7 KB, 170 views)
File Type: jpg tn_Wool.jpg (358.5 KB, 200 views)
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..In space, you can't hear my sub

Last edited by Shadydave; 14th January 2013 at 09:36 PM. Reason: Bad number in text
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Old 14th January 2013, 10:09 PM   #79
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Quote:
Originally Posted by Shadydave View Post
One thing I did notice is my other woofer cabinets are being excited to the point that I almost can see the cones move.

When I did the first sweeps I saw a big hole at 34 Hz. I’m not sure if this is room acoustics or the speakers response.
Dave,

Looks good, the big hole at 34 Hz easily could be due to the room, but try shorting the other woofers out, they may be acting as tuned bass traps.
Unpowered un-shorted speakers can have surprising influence.
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Old 14th January 2013, 11:47 PM   #80
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Originally Posted by Shadydave View Post
I am just unsure how long the effective port is with the external flare, and that makes me uncomfortable.
Connect the DATS to the driver when it's mounted in the enclosure and do an impedance test. The graphed results can tell you a lot about your built speaker, including the effective Fb.
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