Thanks Scott.
Didn't Martin J King make some spreadsheet for this? I followed an MLTL discussion (mostly Bob Brines FE167 based design) on this forum some years (or decades) back. I can't remember why I did not explore building one earlier. I understand an MLTL is in effect a ported box where the cross-section and height of the box and port and driver location have been so that the quarter-wave resonance of the box was a bit higher in frequency than the resonance frequency of the port. From what I remember the ratio of the height to either the depth or the width (can't remember which, maybe both) in an ML-TL must exceed 3:1 hence my proposed box with a height of about 45" and a depth of about 15" should work. And from what I remember the advantage the ML-TL has over a ported box is that the bass response is more extended as the resonance of the port is lower than the (quarter-wave) resonance of the box. Is my understanding of ML-TL in the ballpark?
Edit: Are MJK's spreadsheets available in the public domain? They aren't here: http://www.quarter-wave.com/ or here http://t-linespeakers.org/design/MJK-for-dummies/index.html
Thanks, Dave. Before Covid came and disrupted our lives, we had plans to visit Vancouver/Vittoria in the summer of 2020. Now we are still waiting for consulates to reopen for tourist visas (other visas are being issued). That said...
Done the MAOP 7 it is. The question now remains if I should consider 2 x 8" vs 4 x 6". Among the 8" the SB23CACS45 looks good with its highish Qts of 0.37. Similarly among the 6", the choice would be between the Prestige L16RNX or SB17CAC35. The former looks like it works better in smaller boxes (at least for ported alignments). Erin's review of the SB17CAC35 wasn't very complimentary when it came to its bass capabilities mostly related to its very limited excursion. https://www.erinsaudiocorner.com/driveunits/sbacoustics_sb17cac35-4/
What T/S parameters do I need to consider if I want to use the woofer in an MT-TL? Fs? Qts? Vas?
What is Zd? I know Z signifies impedance. How does one compute Zd? Since it is a "woofer placement" I assume it is some distance of the woofer from the floor or top of the cabinet. If I were to consider a Blade clone would Zd be the average of the "placement distances" of all 4 woofers?
Granted having the woofer close to the full range leads to better integration. Assuming the crossover is at 300Hz, it would mean that the helper woofers are not more than 0.25m from the full range right? Here again the Blade style WAW has an advantage in that IF there is an issue with floor bounce it would be averaged out since the 2 woofer pairs are at different distances from the floor.
The Blade concept with 4 x 6" woofers looks more and more enticing. In this case (4 woofers), for the quarter-wave load, would the height of the woofer from the floor for an ML-TL would be an average of the height of the lower pair of woofers and the upper pair?
Your Facets design uses the Peerless 830870 which is only 4". Why did you choose such a small "woofer"? Why not its bigger cousin - the 830990? How does one determine what size of woofers to use?
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Do come by when you make it.
Term choosen by Martin. It is the driver distance from the closed end of the box
Assuming the crossover is at 300Hz, it would mean that the helper woofers are not more than 0.25m from the full range right?
13560/300/4=about 11 inches=0.287m
Yes, the average.
It will hit 35 Hz (F10) anechoic in Scott’s ML-TL, and it comfortably fir into an ML-TL with the same cross-section as the µFonkenSET. We were working within a specific compromise. When freed from that we went to the large Silver Flute W14. It goes s low, moves more air.
dave
Thanks again, Dave. I don't know if you remember but we did have some conversations on this forum maybe 15 years ago. You live in a beautiful neck of the woods. If and when we make it there, it would be my 3rd and my wife's 2nd visit to Vittoria/Vancouver/BC.
A little digging and I found this thread. Scott's post #4 explains it well.
https://www.diyaudio.com/community/threads/sb-acoustics-sb23nrxs45-8-mltl.285332/
When determining box size and choice of driver, I assume the box size would double if we double up on the woofers. For example, in the above link, Scott worked on a box for the SB23NRXS45 and the box was 48in x 9.5in x 13.5in which is pretty big (about 100l). If we were to build an MLTL with 2 x SB23NRXS45 we would need a box that is 200l.
Using WINISD for the same woofer (SB23NRXS45) I get a box volume of 75L (QB3) so would this be the box size for this woofer?
https://www.diyaudio.com/community/threads/accidental-mltl-technique.231951/
Working backwards, if my box is (46"x 6"x 14" internal) 2 cu. ft. (56 litres) and I have 4 woofers sharing it, I would have to choose a woofer that works in 0.5 cu. ft. The SEAS L16RNX seems to fit that bill. What do you think?
https://www.madisoundspeakerstore.c...l16rnx-6-aluminum-cone-woofer-h1488-08-8-ohm/
It looks like the woofer has to be as close to the top of the speaker as possible while the port is close to the bottom.
I do. IIRC you wer looking forward to fresh salmon?
Double the cross-section, same height, same Zd, 2 vents (or equivalent)
dave
Fresh salmon is always welcome. We eat everything - any meat will do. So far we've tried bison, caribou, alligator, pigeon, etc. We are equal opportunity meat lovers.
I took the SEAS L16RNX H1488-08 into WINISD. It gave me a QB3 volume of 11 litres with a 9" (24cm) long x 2" (5cm) dia. port. Tuning freq of 42Hz. I am fine with 42Hz as this is the open low E on the bass guitar. There is very little information below this except maybe on some classical pieces. The B string on 5 string basses can go as low as 30Hz but I do have a corner loaded 15" TC sounds subwoofer on the rare occasions I need to cover this last octave (20-40Hz).
4 drivers would require a box of 44 litres or about 1.6 cu. ft and a single 4" (10cm) dia. x 9" (24cm) long port would suffice. WINISD also computes "Ist port resonance" which is around 700Hz. Halving this to around 350Hz leads to a very long (20" or 50cm) port.
I also took the SEAS L16RNX3 H1869-08 into WINISD. For 4 woofers I got a box of 35 litres (1.25 cu. ft) tuned to 38Hz with a single 10" long x 3" dia. port.
Assuming that 2 woofers would be above the full range and 2 below, a good approximate for Zd would be anything between 8" to 9" (diameter of woofer + radius of full range). Zv would be around 43-44".
Something like this
https://www.diyaudio.com/community/attachments/1650220363767-png.1045607/
Dave,
With reference to post #1993 by you, I have attached the image you shared of a 4 x woofer design.
The 4 woofers share the same cabinet volume? Or the top 2 push-push woofer are in their own space, and the 2x woofers below the wide-band are in the ML-TL part?
With reference to post #1993 by you, I have attached the image you shared of a 4 x woofer design.
The 4 woofers share the same cabinet volume? Or the top 2 push-push woofer are in their own space, and the 2x woofers below the wide-band are in the ML-TL part?
Attachments
I'm not Dave but since post #1993 was penned by me I'll try and answer this.
I am sorry but the sketch which was just a crude cut-paste of Dave's Tysen V2 design does intend to have all 4 woofers sharing one common box volume. I know the sketch does not look like it but it's just a side view. In reality, the MAOP7 would be isolated in a conical enclosure that exits out the rear of the speaker. Something like this:
I assume that this cone would have a volume of about 1.7-2.0 litres (12cm dia x 37cm length).
Assuming the box is shaped like the image below, it would have an internal volume of about 50 litres (12cm x 37cm x 115cm). This would leave about 48 litres for the 4 woofers + bracing. From post #2010 we get that we need about 43 litres for the 4 woofers so we get about 5 litres for bracing.
The current driver options are:
https://www.madisoundspeakerstore.c...l16rnx-6-aluminum-cone-woofer-h1488-08-8-ohm/
https://www.madisoundspeakerstore.com/Mark Audio MAOP-7 122mm Magnetic Arc Oxidized Full Range Matched Pair
The cabinet will be 44-46" tall (internal); the full range would be between 8-9" (diameter of woofer + radius of full range) from the top of the cabinet and the rear-facing port would be about 2-3" from the bottom of the cabinet. Dave or Scott will be able to provide more exact details.
Coming from the world of multi-way drivers (where even older full-range drivers like the JX92 had a helper tweeter like the G2si) I have some apprehension about the HF response of the MAOP 7. If I find it lacking I might consider adding a helper tweeter above 5K or 10k either rear or front-firing. Two options that are locally available are the Wavecor TW013WA01 and the Fountek Neo X 2.0.
http://www.wavecor.com/TW013WA01_specifications.pdf
https://diyaudiocart.com/image/data//vendors/gowrishankar/fountek/Neo X 2.0/fountek-neo-x-20-specifications.pdf
Hope this helps.
Navin
P.S
Dave is better equipped to answer if all of the above makes any sense and if the proposed ML-TL will work.
I haven't seen Scott on this thread lately, I hope he is well.
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As drawn it looks like they are in different size boxes.
If you are going to flip/mirror a pair of drivers on the bottom, the top ones will be the same as the bottom ones. Like in Twin Frugel-Horns.
But it is possible to reorient the taper of the midTL to ensure the enclosure space for the woofers are common. As we did in our A12pw MTM.
dave
Absolutely. Just one question does the MidTL box have to be rectangular? I was thinking it would be easier to make a cone from fibreglass or hard cardboard or even find a planter with the required dimensions. A fibreglass cone with a wall thickness of 5mm would be stiffer and occupy less space in the box than a rectangular cone made of 12mm wood.As drawn it looks like they are in different size boxes.
If you are going to flip/mirror a pair of drivers on the bottom, the top ones will be the same as the bottom ones. Like in Twin Frugel-Horns.
But it is possible to reorient the taper of the midTL to ensure the enclosure space for the woofers are common. As we did in our A12pw MTM.
dave
If we need 43 litres for the woofers, 6 litres for the MidTL and another 6 litres for the bracing it totals 55 litres or 2 cu. ft. Would a requirement of 6 litres be a fair assumption for the volume of the bracing?
Since the internal height and depth are more or less fixed at 44" and 14" respectively. To achieve a box volume of 2 cu. ft. the internal width would have to be 5.6". If bracing takes more than the estimated 6 litres, I could increase the width accordingly.
Do you think that a complement of 4 x SEAS L16RNX (Aluminium cone) woofers would make a good match for the A7?
Is the design I am thinking of (box volume, box dimensions, port diameter and location, etc.) pass your sanity check? If you discount my 50mm Jordan Watt module / Volt woofer experiment from the 80s, this is my first real full range build.
P.S
If I do not reply for the next few days, it's because I am scheduled for surgery on Monday morning (India Time) and will be out of commission till at least Wednesday afternoon, maybe even Thursday or Friday (depending on my recovery).
If i was going into production i would be doing a more exotic midTL for these. Likely 3D printed, but a steeper taper can be acheived and the midTL made to take up less of the cross-section area.
SEAS tends to build good stuff but i am not familiar with that woofer, so can only comment based on what is published. The really really bad ringing at 4k is scary, but the hump starting about 500 Hz is likely more of an issue. I look for flat response out to at least 1kHz, and much smoother response.
If i had a set of these, first thing i would do is a coat of modPodge.
dave
SEAS tends to build good stuff but i am not familiar with that woofer, so can only comment based on what is published. The really really bad ringing at 4k is scary, but the hump starting about 500 Hz is likely more of an issue. I look for flat response out to at least 1kHz, and much smoother response.
If i had a set of these, first thing i would do is a coat of modPodge.
dave
Not an issue. The shift at ~500Hz is baffle-step. Seas don't measure on a large baffle, they use smaller test boxes the dimensions of which they used to provide on their website but recently removed (sigh). I've got them saved somewhere. Note that it remains a pure piston up to the single concentrated bell mode at ~5KHz -there is no sign of any resonant or TL modes in the FR or impedance curve until that point -a damn good bit of cone and suspension design.
Since you'd be crossing low, it shouldn't be a major issue unless it's low order (probably not a good idea), but you can hit it with a bottomless speaker-level parallel notch filter. By doing so you break circuit and kill the resonant-amplified HD that will otherwise occur at multiples of that 5KHz frequency lower down the frequency range.
Since you'd be crossing low, it shouldn't be a major issue unless it's low order (probably not a good idea), but you can hit it with a bottomless speaker-level parallel notch filter. By doing so you break circuit and kill the resonant-amplified HD that will otherwise occur at multiples of that 5KHz frequency lower down the frequency range.
I am a DIYer. I'll likely never make more than 1 pair.
The woofer will be crossover over at 300Hz or so. The 4k peak though scary would be several dB down if I used a 12db/oct slope.
What is ModPodge? Where does one get it?
I believe SEAS uses a 28-litre box. No idea of the baffle dimensions used. The dotted line is supposed to be the IB response.
http://www.seas.no/images/stories/prestige/pdfdatasheet/h1488-08_l16rnx_datasheet.pdf
Assuming I'd be crossing over at 300Hz/12db the response would be 40-50db down at 4k-5k.
It will help kill the ringing at the top and smooth things out a bit. In India you will likely need to find an equivalent. A PVC compound that dries flexible, and probably best desctibes by the brand i first used, Puzzlecoat.
https://www.t-linespeakers.org/design/tweeks.html
Dave
7 litres for 5.5in drivers, baffle dimensions 295mm x 210mm (HxW), driver centred 101mm down from external top. Just dug it out. 28 litres was for 10in units (not that the Vb matters in this case). The dotted line is the mathematical T/S derived IB curve.
Your peak is about 13dB above the nominal. Depending on the baseline HD levels you may get away with it, but be prepared to address it if it isn't.