GM
Thank you for making the effort to answer each question. It has helped me understand what I am doing
I think I have crunched all the numbers for now to stay within the desired visual footprint. There must be whole areas where I might not be understanding something and missing a chance to reduce this footprint further while keeping to the tuning target
I should end up with an MDF structure that is made up of all the sides and partitions except for the top. This will give good access to the tunnels
Access to the tunnels will allow inserting various tapered TPU or XPS inserts as well as fibrous materials for further tuning
3D printed top will mean tunnel length can be increased using printed or CNC'ed plate layers
Table saw can decrease height 😀
Baffle will have a printed over face with the driver inset
Would I be right in thinking that this should leave many avenues of tuning to get this good? I have a calibrated mic, pro sound card. Our little rugby oval has a little concrete stage if that would help with measurements. I also have access to the school hall
Would this be a good game plan to give the Pioneers a fair chance? And if they don't sing after further tuning, then I am hoping that this implementation would allow me to test other drivers to try to find my targets of desktop monitors that can faithfully allow close listening to all bass guitar notes?
Thank you for making the effort to answer each question. It has helped me understand what I am doing
I think I have crunched all the numbers for now to stay within the desired visual footprint. There must be whole areas where I might not be understanding something and missing a chance to reduce this footprint further while keeping to the tuning target
I should end up with an MDF structure that is made up of all the sides and partitions except for the top. This will give good access to the tunnels
Access to the tunnels will allow inserting various tapered TPU or XPS inserts as well as fibrous materials for further tuning
3D printed top will mean tunnel length can be increased using printed or CNC'ed plate layers
Table saw can decrease height 😀
Baffle will have a printed over face with the driver inset
Would I be right in thinking that this should leave many avenues of tuning to get this good? I have a calibrated mic, pro sound card. Our little rugby oval has a little concrete stage if that would help with measurements. I also have access to the school hall
Would this be a good game plan to give the Pioneers a fair chance? And if they don't sing after further tuning, then I am hoping that this implementation would allow me to test other drivers to try to find my targets of desktop monitors that can faithfully allow close listening to all bass guitar notes?
Given you have little idea of where you are starting, being able to tune whatever you build is GOOD. As suggestted earier, unless you like too much bottom, you will likely end up stuffing whatever line you have till at least close to aperiodic. The actual shape wil beles simportant than al the damping. Make sure you tease it well.
And remember 19mm MDF is not as “good” as 15mm quality plywood, you will need to overbuild it in an attempt to overcome MDF’s disadvantages.
dave
Hello Dave
It's now tomorrow here, good morning. I am not using 19 mm, it 9 mm. Just for a quick and cheap test box. I don't enjoy making dust and mess as I am a chronic rhinitis sufferer and after many years of working with epoxies, I have also developed a sensitivity
That is why I have been trying to get a box sorted, so I may use more advanced construction methods and avoid wood dust and chemical vapours and such. I wish this cab was already confident enough to not do MDF test builds but rather dive straight in
I have my tentative numbers for cutting for now. I am going to run these into FreeCAD this morning to get a visual impression of this CAB. My numbers for internal dimensions are W 14.4 x H 59 x D 32.94. This is pretty much max in a good visual footprint on the desk
If there were more chances to reduces this size further while keeping the low 30s extension, then I would rather work more on that now too
Thanks and regards
Randy
It's now tomorrow here, good morning. I am not using 19 mm, it 9 mm. Just for a quick and cheap test box. I don't enjoy making dust and mess as I am a chronic rhinitis sufferer and after many years of working with epoxies, I have also developed a sensitivity
That is why I have been trying to get a box sorted, so I may use more advanced construction methods and avoid wood dust and chemical vapours and such. I wish this cab was already confident enough to not do MDF test builds but rather dive straight in
I have my tentative numbers for cutting for now. I am going to run these into FreeCAD this morning to get a visual impression of this CAB. My numbers for internal dimensions are W 14.4 x H 59 x D 32.94. This is pretty much max in a good visual footprint on the desk
If there were more chances to reduces this size further while keeping the low 30s extension, then I would rather work more on that now too
Thanks and regards
Randy
Lol I know, and I don't really much want to use MDF or wood at all. That's why I am still sitting here and not at Bunnings. If I was more confident in the box than I would make nano carbon fibre and resin or wood flour and resin cabs that would not have any flat surfaces and be very damped but would a lot of expensive materials to waste on a box that would get thrown away
You're welcome!
I really don't know how to answer this (till I kept rewriting this into a mini tutorial
); I mean we're always trading efficiency for BW and net Vb sets max LF gain BW between Fs - Fhm* and the more misaligned the driver specs/box design, the more EQ required, be it via acoustic (damping) or digital frequency shaping, so within these parameters there's dozens? hundreds? of combinations depending on how narrow the differences with the understanding that down low the room dominates and that hearing acuity is rolling off so fast below ~120 Hz that it's tough to notice much difference until distortion is quite high or until you can find the 'sweet spots' in the room modes for both speakers and listening position (LP).IOW the typical LF box design only controls a very narrow BW octave** wise, so actual distinctly audible 'variations on a theme' will be quite few IME and once you've measured the in room location of all four (speakers, desk, you) it wouldn't surprise me that you'll need to start again from scratch if significant digital EQ isn't used.
LF historically was (still is for at least one manufacturer TTBOMK) normally measured either way up in the outdoor air or ground plane, so if the concrete pad is big enough to support a full size ~34 Hz/whatever tuning, then it's a good plan.
If in a school hall/gym, it's my understanding that it's best to 'fly' them at its summed 3D odd harmonic, so only as a last resort unless it's documented, which in theory it should be part of its design specs.
* Upper mass corner frequency [Fhm] where it rolls off from its acceleration to mass controlled BW where T/S theory peters out, so any bandwidth response plot beyond these points are strictly due to (inputted) inductance (mH) and/or mass roll off, with on-line freeware generally just flatlining it:
Fhm = 2*Fs/Qts'
Flc = Fs*Qts'/2 [normally never used]
Qts' = 2*Fs/Fhm
Qts' = Qts + any added series resistance [Rs]: http://www.mh-audio.nl/Calculators/newqts.html
** Octaves
Fh = Fl*2^n
Fl = Fh/2^n
n = ln(Fh/Fl)/ln(2)
where:
Fh = upper frequency
Fl = lower frequency, or the XO point in this case
n = octave spread
ln(2) = 0.6931
Thank you very much for going into that, much appreciated
I think a saving grace would be that the modular approach will leave an option to seal the box as various volumes
If this doesn't work, then the only thing that will fit on the desk and that I know can do the job is a pair of my 7" drivers in a 20L 34hz reflex crossing to a 100w array of small full range drivers in a desktop cab. It makes for a wider box then I want to live with
I think a saving grace would be that the modular approach will leave an option to seal the box as various volumes
If this doesn't work, then the only thing that will fit on the desk and that I know can do the job is a pair of my 7" drivers in a 20L 34hz reflex crossing to a 100w array of small full range drivers in a desktop cab. It makes for a wider box then I want to live with
9mm MDF is going to be a super powerful tone generator around 150hz and tell you little unless you invested in extraordinary bracing and padding (try automotive 3-layer). Much better/easier to start with just about any speaker/cab and insert cardboard dividers to learn their incremental effects on deep(er) bass. After you reached low-enough you can replace with braced thin plywood or build from scratch, adjusting baffle-width/line-CSA/volume to get the desktop SPL you actually want. Don't you have a pair you can listen to in situ at the desk that you might experiment with?
This is how she models. I had an error in my notes with partition wall thickness. After correcting, the external height is 63.7 cm, depth is 26 cm and width is 17 cm
This is how she looks without her top on. I am now working on another model. That one will allow better driver height adjustment and will be external width 17, depth around 34 cm and height under 50 cm
Any thoughts on saving this project file as "Flatwounds"?
This is how she looks without her top on. I am now working on another model. That one will allow better driver height adjustment and will be external width 17, depth around 34 cm and height under 50 cm
Any thoughts on saving this project file as "Flatwounds"?
Last edited:
That board between driver and port should be maximally anti-vibration reinforced. If all or part of the front baffle is flippable you'll have more options.
New drawing. Better visual impact W 17 x H 39 x D 34 cm. Bent the pipe in 6 segments in a table and used the numbers for the openings. Mouth and vent stay the same as previous
This is all the narrows, missing the sides. The driver sits one third pipe length. The baffle is in two layers, with the thicker top layer being detachable. The outer sides will be detachable too
Any votes on "flatwounds"
This is all the narrows, missing the sides. The driver sits one third pipe length. The baffle is in two layers, with the thicker top layer being detachable. The outer sides will be detachable too
Any votes on "flatwounds"
Partitions removed. The fillets are not for air flow. It is for fillet reinforcement of a junction. Does a job in boat building, couldn't do any harm here. This whole ring will be fibre and resin. Mdf partiions wil slot in and glued in and also glued to the left panel for the left speaker and right panel for the right speaker. The other side panels will be detachable
I have changed my mind about making the face detachable. Instead, the inside face with the cut-out will be detachable. Makes sense as that where alternative drivers will fit
I have changed my mind about making the face detachable. Instead, the inside face with the cut-out will be detachable. Makes sense as that where alternative drivers will fit
Greets!
Not a design criterion per se unless you choose to make it so, just simple physics of the situation.
No, not for the same driver since T/S theory gain (acceleration) BW, i.e. all the BW that basic box design software works with, so with a 40 Hz Fs, 400 Hz upper mass corner (Fhm = 2*Fs/Qts'), then Qts = (40/400)/2 = 0.2 and 40-800 = 0.1 Qts'
Of course all else equal, the 0.1 Qts'' will be the most efficient and the earliest one to roll off down to Fs, ergo we're trading (lower) LF gain BW for a narrower, higher efficiency BW and vice versa.
From this it becomes obvious that if we want max practical gain BW from a driver, then it will be a very narrow one such as a typical 20-80 Hz subwoofer = 0.5 Qts' for flattest response.
(Qts'): (Qts) + any added series resistance (Rs): http://www.mh-audio.nl/Calculators/newqts.html
Not a design criterion per se unless you choose to make it so, just simple physics of the situation.
No, not for the same driver since T/S theory gain (acceleration) BW, i.e. all the BW that basic box design software works with, so with a 40 Hz Fs, 400 Hz upper mass corner (Fhm = 2*Fs/Qts'), then Qts = (40/400)/2 = 0.2 and 40-800 = 0.1 Qts'
Of course all else equal, the 0.1 Qts'' will be the most efficient and the earliest one to roll off down to Fs, ergo we're trading (lower) LF gain BW for a narrower, higher efficiency BW and vice versa.
From this it becomes obvious that if we want max practical gain BW from a driver, then it will be a very narrow one such as a typical 20-80 Hz subwoofer = 0.5 Qts' for flattest response.
(Qts'): (Qts) + any added series resistance (Rs): http://www.mh-audio.nl/Calculators/newqts.html