Ported NF UXL-18 Build - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 47 Old 08-06-2016, 02:06 PM - Thread Starter
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Ported NF Build

I currently run a dual infinity 1260 nearfield which does a good job, details are in Nearfield build: which drivers to use and how many? and there is assorted data in the VS thread too. The salient points from that experience are that running a NF sub for the TR impact is a tricky balancing act, run it too high and/or too loud as the upper reaches of the sub bass range become a bit bloated but then you need to run it loud to induce the TR you need.

The TR threads (nods to @coolrda @dominguez1 @MKtheater @derrickdj1 ) have also clearly demonstrated the efficacy of a ported sub over a sealed sub when it comes to TR, all the evidence says that a ported sub has more TR per SPL (if you get what I mean) aka a port produces relatively higher particle velocity.

All in all this means I think my perfect TR/NF sub is something with a port and that has strong output in the 10-50Hz range. My pair of infinity are definitely being pushed pretty hard to deliver that <20Hz content so I have thought that something beefier is required if I wanted to push it further.

An opportunity came up to pick up another UXL-18 (my main subs are a pair of UXL-18) 2nd hand so I snapped it up as I figured it would fit the bill nicely. So here we are, I have no fixed plans for this other than I have an UXL-18 and a space behind the sofa to put it in. This places a hard constraint on the size with absolute maximum dimensions of

18" deep (hard limit)
5' wide (soft limit, could be 1' wider if really necessary but prefer to avoid that)
2' high (hard limit)

Ideas so far;

- standard ported, tuned into the low teens and then rolled off using EQ above my target pass band
- big sealed and EQ'ed really really hard to pound out 10-30Hz and then rolled off as above
- 6th order band pass focused on that low end to provide a natural roll off and to use ports for all the output (NB: no idea if this is implementable, sounds nice on paper)

I'll use this thread to document/discuss ideas/designs and then eventually it will roll into the build side of things. I imagine this will take me months as I have a bunch of other speakers to finish first
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post #2 of 47 Old 08-06-2016, 03:26 PM
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Depending on the seating, couch vs chairs, something like the Bum Buster I built might work. It uses a UM 18. A UXL would be even stronger and maybe easier to tweak for the right FR.
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post #3 of 47 Old 08-06-2016, 03:31 PM
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Have you measured your frequency response at the nearfield position? The reason why I ask is I was using 4 x martycubes (20hz tune)with HT18's 3" directly behind my seats. The one issue I have is the subs are practically in the middle of the room which 'causes a 20db deep null from 19hz-24hz. Without running a vibsensor sweep, I'm not sure how this suckout would correlate to actual TR. I started using PA-460, mbm drivers and increased the tune to 28hz for nearfield and feel it is a drastic improvement both in TR and SQ over the HT18's... and even HST18's when I briefly tried it with 4 UXL18's up front in Marty's.
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post #4 of 47 Old 08-06-2016, 04:33 PM
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I posted some data on the ULF thread today. The FR of the vented sub has a drop off in the below 20 Hz area. The back of the sub is around 3 ft from the corner of the room and the front is 4 1/2 feet roughly. I did this same experiment with the Mini Marty with basically the same results. I was testing the Mini Marty sealed by blocking the ports vs vented(ports open). TR was great in the vented model. Your Home Theater ULF Score

Further discussion can be done in the ULF thread to keep this build thread on track.
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post #5 of 47 Old 08-07-2016, 06:24 AM - Thread Starter
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Quote:
Originally Posted by lz7j View Post
Have you measured your frequency response at the nearfield position? The reason why I ask is I was using 4 x martycubes (20hz tune)with HT18's 3" directly behind my seats. The one issue I have is the subs are practically in the middle of the room which 'causes a 20db deep null from 19hz-24hz. Without running a vibsensor sweep, I'm not sure how this suckout would correlate to actual TR. I started using PA-460, mbm drivers and increased the tune to 28hz for nearfield and feel it is a drastic improvement both in TR and SQ over the HT18's... and even HST18's when I briefly tried it with 4 UXL18's up front in Marty's.
there's some measurements in this post (and the few posts before that)

there's a null in the mid 20s too however the question is whether the TR is induced by the initial wave or is also affected by the room itself. My data is inconclusive on this as I have a sharp null and there is evidence of a depression in the TR albeit nowhere near as deep or sharp. Is this a function of the response of my sofa or the contribution of the room? or quite possibly a bit of both.

It will be interesting to see if this is affected by using a larger ported sub especially if I use multiple ports as there will then be multiple output points delivering energy to the seats.
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post #6 of 47 Old 08-09-2016, 06:44 PM
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post #7 of 47 Old 08-10-2016, 03:35 PM - Thread Starter
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Quote:
Originally Posted by dominguez1 View Post
I would go the ported route with the option to seal? You could experiment with both?
I'm thinking it would be good if I could design the cab so that I can change tuning after the build is complete. For example to be able to go from 12-16-20Hz (or whatever) like the old SVS subs used to but without the chuffing issues they had. I will have to model it but I suspect that entails being able to vary the length of the slot port. Whether this is buildable is another question
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post #8 of 47 Old 08-20-2016, 03:29 PM - Thread Starter
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I may have to change the title of this thread ....

I'm struggling with the intended design here. The design goal is more TR in the low to mid teens, less output higher up. The initial thought was bigger driver (hence the UXL-18) and ported however I don't think this fits. I need maybe 50% more space to make that work as it seems like a 13-14ft3 box with a monster port is required and I only really have maybe 8ft3 + port. So alternatives..... bear in mind I have 2 positions + 3 uxl-18 and 2 infinity 1260 to play with along with a sp-6000 and an inuke 3000.

1) just go with a big sealed box and EQ it hard to wring every last drop of excursion out of it in the 10-20Hz range, ditch the infinity
2) port the UXL-18 to whatever tune fits, ditch the infinity
3) keep the infinity as is, add another UXL-18 up front?
4) switch the infinity into a big low tuned ported box (maybe 12Hz tune in 8ft3?), work out how to add the UXL-18 up front
5) switch 1 UXL-18 up front into a *big* ported box, drive 2 really hard NF
6) investigate alternative, probably more complex, box designs

options 4-6 sound interesting to me, more work required!
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post #9 of 47 Old 08-21-2016, 03:28 PM - Thread Starter
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posted some info attemping to model a sealed sub vs a ported sub in particle velocity terms. From a PVL point of view, option 4 is an obvious choice over option 1. The added phase rotation of the low tune port might complicate implementation of option 4) though.
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post #10 of 47 Old 08-21-2016, 10:06 PM
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I struggled with ported vs sealed thinking about using some Infinity drivers for the sealed subs. I didn't have room to do both so, I went ported with the UM 18. The sectional couch is larger than a regular couch and would just one ported box work?

I am happy with the TR of the ported Backbum Buster sub centered behind the sectional couch. I had a small sealed UM 18 sub as an extra and coverted it to an end table with a piece of glass on top. I also have two Mini Marty's in the back of the room.

Model something like the a Cyclops to fit the space. It is around 8 cu ft and can be fashion as a sofa table behind the seating. The Backbum Buster is around 12 cu ft and styled as a sofa table. In the pic, the Backbum Buster has the two boats and flower pot on it.
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post #11 of 47 Old 08-24-2016, 04:31 PM - Thread Starter
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the boats are a nice touch

Quote:
Originally Posted by derrickdj1 View Post
So what have you decided to build? Are you still going to use the ULX drivers?
I thought I'd reply here instead. The short answer is, yes but I'm not sure how. I've come up with a sketchup model for that BP6 sub I mentioned in the other thread which looks a bit like a WW2 pill box



the left port is from the rear chamber, so handles the low end, and the right port is from the front chamber, and so handles the mid bass (sort of, 40-70Hz). My thinking was to have both sources of PVL arriving from as close to the same location as possible.

To peel back the layers.... red line is the rear chamber port path, blue is the front chamber



and the driver itself, a good old infinity 1260w



I'm tempted build this purely because it looks quite amusing more realistically I'll build it to scratch an itch to see whether this idea actually works and works well for efficient delivery of TR

Plan B is just a simple, shallow, sealed box and EQ it hard. If I don't use this NF then I will then build 2 more similar boxes, put my existing 2 UXL into them and simply stack the 3 of them in the front alcove.

For those not reading the ULF thread, this is a 6th order bandpass sub which is designed to go nearfield and hence deliver maximum particle velocity in the sub bandwidth. My thinking is that this will allow me to reduce the audible output and hence avoid any thickening of the bass delivered by the main subs/speakers.

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Note that I'm not concerned by the phase rotation found in a 6th order bandpass because I will design an FIR filter that corrects this so it merges with the main sub correctly.
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post #12 of 47 Old 08-24-2016, 06:20 PM
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That should work well for behing the couch/seating. I've got a buddy using the Infinity 12 drivers. It is down right incredible for NF placement. This should be a nice build. I'm looking forward to see the progress.
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post #13 of 47 Old 08-24-2016, 06:53 PM
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^ VERY CURIOUS ABOUT THAT BUILD IN POST #11

subbed. . .

looks like a fun build, and the testing could be something I haven't seen around here . .
tell me more

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post #14 of 47 Old 08-24-2016, 08:17 PM
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@3ll3d00d

This is the first sub in existance that I know of that is being build to specifically focus on maximizing Particle Velocity, and the resulting Tactile Response increase! Just awesome...really.

What would be the tune of the ULF chamber?

If I may suggest, perhaps building it so that the midbass vent is centered right at chest height. @SBuger did this here with his 1200D and as a result has never experience midbass with that much 'knock the air out of you' punch.

I would aim the ULF vent right at your seat to maximize the 'wobble' effect of ULF.

Really looking forward to this build!!
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post #15 of 47 Old 08-24-2016, 10:27 PM
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This should be an exciting build! I think this could turn out to be something VERY cool to get the absolute most out of ULF and midbass TR from a nearfield sub! Subscribed!

I'm interested as well as to what you think the ULF tune will be.
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post #16 of 47 Old 08-25-2016, 09:24 AM - Thread Starter
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Quote:
Originally Posted by dominguez1 View Post
What would be the tune of the ULF chamber?
the rear chamber is tuned to ~17Hz, the front chamber to ~45Hz

I probably need to revise this though as I need to account for;

- possible large coil effect which would affect the low end response, the params measured by @rhodesj in this post suggest there is a bit of this effect going on though the data I measured in DATS suggests a v small variance from the specs
- effect of the port entry/exit and folds on the tuning, the front chamber port is particularly sensitive to length by the looks of it
- enclosure size... if this one works then I'll want to build another one to expand coverage across the whole available space in the sofa... need to factor this into port placement too
- wood usage.... obviously want to maximise use of a sheet or two of mdf

here is my measured data btw



Quote:
Originally Posted by dominguez1 View Post
If I may suggest, perhaps building it so that the midbass vent is centered right at chest height. @SBuger did this here with his 1200D and as a result has never experience midbass with that much 'knock the air out of you' punch.

I would aim the ULF vent right at your seat to maximize the 'wobble' effect of ULF.
the current port height is about 40cm as I was thinking of aiming it at the base of the seat, I will play with the port layout though to see if I can raise the front chamber port up a bit.
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post #17 of 47 Old 08-25-2016, 09:41 AM - Thread Starter
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one other note... if I pull the output down to more reasonable levels (say 90dB peak) then the velocity is in the region of ~2m/s throughout the passband, still at least an order of magnitude more than an equivalent sealed sub
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post #18 of 47 Old 08-25-2016, 10:24 AM
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Quote:
Originally Posted by 3ll3d00d View Post
the rear chamber is tuned to ~17Hz, the front chamber to ~45Hz
Is there any way you can make tuning just a bit lower than 17hz for the ULF? That is still awesome but when I had my JTR cap 2400 (port tune 17.5hz) directly behind me (driver and port about an inch away from the back of my chair) I missed a lot of the ULF strong wobble sensations in movies like TIH where I think a lot of it is centered around 14-15hz. I know 17.5hz is very close but I could tell a HUGE difference in that wobble effect compared to when I had the Rythmik FV15HP (tuned to 12hz - very low tune for ported) and also with one of my sealed 18's (with an LS of coarse to bring up the low end). BUT a less steep HPF may help and allow you to get a bit more out of those lower frequencies as opposed to a more steep drop off like what the Cap2400 had. There is also the whole RG thing (I don't get much at all, if any in my room from my NF subs) if you get it in your room, but I'm talking about actual output at certain frequencies with a nearfeild sub for maximum TR. It seems to me that there a bunch of movie material out there that has a lot of ~15hz frequencies in them. So a 15hz tune or a hair lower even might be the sweet spot if possible. I don't know for sure if that would mean making the ports a little bit longer or a little bigger box, or both. It might not be feasible with the space you have to work with etc. If not, I'm sure it'll still kick some major butt! Just my 2 cents from my experience with super close nearfields.
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post #19 of 47 Old 08-25-2016, 03:36 PM - Thread Starter
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Quote:
Originally Posted by SBuger View Post
Is there any way you can make tuning just a bit lower than 17hz for the ULF? That is still awesome but when I had my JTR cap 2400 (port tune 17.5hz) directly behind me (driver and port about an inch away from the back of my chair) I missed a lot of the ULF strong wobble sensations in movies like TIH where I think a lot of it is centered around 14-15hz. I know 17.5hz is very close but I could tell a HUGE difference in that wobble effect compared to when I had the Rythmik FV15HP (tuned to 12hz - very low tune for ported) and also with one of my sealed 18's (with an LS of coarse to bring up the low end). BUT a less steep HPF may help and allow you to get a bit more out of those lower frequencies as opposed to a more steep drop off like what the Cap2400 had. There is also the whole RG thing (I don't get much at all, if any in my room from my NF subs) if you get it in your room, but I'm talking about actual output at certain frequencies with a nearfeild sub for maximum TR. It seems to me that there a bunch of movie material out there that has a lot of ~15hz frequencies in them. So a 15hz tune or a hair lower even might be the sweet spot if possible. I don't know for sure if that would mean making the ports a little bit longer or a little bigger box, or both. It might not be feasible with the space you have to work with etc. If not, I'm sure it'll still kick some major butt! Just my 2 cents from my experience with super close nearfields.
the question here is how much of the effect is delivered by TR vs PR? I don't know the answer to this and I don't think there is a generic answer as it depends on something we can't currently measure directly (PR), or at least we don't have a practical way to measure it right now.

FWIW I'm running a pair of UXL-18 powered by a speakerpower SP1-6000 at the front and I do get some of that PR sensation when the ULF gets going. The sealed pair of 1260 also measure as providing TR down to 15Hz or so already just by cranking up the LT on them. The downside is that they distort when it gets going down low. So if we're looking for TR then the ported build, as is, should still provide it as the port is providing significant PVL down <=10Hz even with a HPF in place.

This makes me think that careful use of EQ should allow me to dial in a flat TR down to ~10Hz even with the current tune. This will be guided by high resolution accelerometer measurements (I have one of these http://eu.mouser.com/ProductDetail/M...ujutHjMA%3D%3D and a preamp for it).

Having said that, it would be nice to drop the tune lower (this was the original plan in fact, to target 12Hz or so). I need to remeasure the area available to check exactly what I can fit in there. It will make for a more complicated build but I might be able to make better use of space by laying out the port as a slot that snakes around the interior and just place hte exit ports as appropriate on the front.
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post #20 of 47 Old 08-25-2016, 08:01 PM
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post #21 of 47 Old 08-25-2016, 10:45 PM
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Yes, it does need a name!
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post #22 of 47 Old 08-26-2016, 07:24 AM
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Quote:
Originally Posted by 3ll3d00d View Post
- possible large coil effect which would affect the low end response, the params measured by @rhodesj in this post suggest there is a bit of this effect going on though the data I measured in DATS suggests a v small variance from the specs
Keep in mind that large coil effects aren't reflected in TS parameters. That's exactly why they're a problem, as the effect doesn't show up in TS measurement and normal modeling.

The frequency response measurements I took were close mic'd inside my house, and at a very low drive level. If you want to validate the performance of the 1260w you could build a sealed test box and haul it outside for proper ground plane measurements at varying drive levels, and compare to a model based on the TS you measure. Then you'll know for certain if the large coil issue impacts the 1260w.

Alternatively, you could just apply the generic large coil fix to the TS parameters, run your model, and see if the response you get is a problem.

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post #23 of 47 Old 08-28-2016, 02:36 PM - Thread Starter
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Quote:
Originally Posted by dominguez1 View Post
This sub needs a name.

I hereby proclaim thee as:



The Particle Velociraptor



Yes?
haha I thought of a v similar name definitely needs a name though, I have not had inspiration yet so we'll run with that until further notice!
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post #24 of 47 Old 08-28-2016, 02:38 PM - Thread Starter
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Quote:
Originally Posted by rhodesj View Post
Keep in mind that large coil effects aren't reflected in TS parameters. That's exactly why they're a problem, as the effect doesn't show up in TS measurement and normal modeling.

The frequency response measurements I took were close mic'd inside my house, and at a very low drive level. If you want to validate the performance of the 1260w you could build a sealed test box and haul it outside for proper ground plane measurements at varying drive levels, and compare to a model based on the TS you measure. Then you'll know for certain if the large coil issue impacts the 1260w.

Alternatively, you could just apply the generic large coil fix to the TS parameters, run your model, and see if the response you get is a problem.
ah yes good point, I will have to drag my current NF sub out for some measurements then. The reason I mentioned this is because applying the adjustment in hornresp completely trashes the modelled response so I do need to deal with this before the build commences.
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post #25 of 47 Old 08-28-2016, 03:30 PM - Thread Starter
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I measured the space available again

If I'm designing to accommodate 2 boxes in there then absolute max dimensions are 25" tall x 19" deep x 42" wide.

top of seat is at about 16"
middle of the chest is probably around 25-27" in typical seating stance
mlp is left middle of the space (if you look down on it) so would be at the right end of one box
secondary listening position is more towards the right side

I think this suggests the following for port positioning/design

- the front chamber should be "firing" towards the middle so the front (mid bass) port can be placed in pretty close proximity to the 2 main seating positions
- the front port should be at the top of the box
- 2 ULF ports should employed to maximise ULF headroom (before audible issues occur)
- the 2 ULF ports should be split left and right, height not so important
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post #26 of 47 Old 08-28-2016, 03:32 PM - Thread Starter
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the discussion over in the MBM thread suggests I should try to push the front chamber port tune a bit higher up than the current tune, not sure how feasible this so will play with the model
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post #27 of 47 Old 08-28-2016, 05:51 PM - Thread Starter
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at 2V, this dual reflex design produces >1m/s from 12Hz to 90Hz

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100L rear chamber with 140cm long 170cm2 port (intent is to have 2 85cm2 ports)
16L front chamber with 35cm 80cm2 port

the resulting PVL

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note how the rear port doesn't really seem to add *that* much to the front port

this made me think about a 4th order bandpass design, i.e. remove the rear port

70L rear chamber
18L front chamber with a 50cm long 90cm2 port

the resulting PVL

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and compared to the BP6, red lines show the advantage of the BP6

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this suggests that a BP4 might be a good choice where space is more limited (e.g. you want to run multiples) and/or where you want to give more weight to mid bass PVL without completely giving up on the low end (as you would do with a mid bass tuned bass reflex)
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post #28 of 47 Old 08-29-2016, 04:25 PM - Thread Starter
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Next iteration of the design coming up.... introducing .... The Ventilator

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external volume is ~245L
140L rear chamber with 4 40cm2 (10*4) ports that are 124cm long each for a tune of approx 16Hz
20L front chamber with 2 37.5cm2 (12.5*3) ports that are 40cm long each for a tune of ~46Hz (based on z)

front (mid bass) ports are at the top for chest impact
rear (ULF) ports are in the middle to place them at approximately seat height

multiple ports employed to distribute the output across the baffle to attempt to distribute output (i.e. achieve the distribution you get from an array of sealed NF subs)
this also gives the option to block one ULF port and push the tune down to ~14Hz (NB: this will reduce maximum output due to potential port noise issues)

5V delivers ~95dB (+/- 3dB across the passband) which yields the following PVL

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note that, without a HPF, this produces >2m/s from <10Hz (can't tell exactly but probably 7-8Hz, hornresp only goes to 10Hz) to ~90Hz. Obviously this is dangerous as I could destroy the driver. Fortunately I have an accurate accelerometer so I should be able to measure excursion at a given drive level and then set a limiter instead of using a HPF.

some interior detail; red arrows for the front chamber vent paths and blue for the rear chamber, slot ports all round and the front chamber is quite shallow and slotted into the full height of the box placed in the middle of the baffle

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I've attempted to minimise the amount of extra wood required for the vents but this is clearly still going to be a bit of a mission to build with the no of pieces to cut.... lets hope it is worth it!

hornresp model for reference

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Last edited by 3ll3d00d; 08-29-2016 at 04:29 PM.
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post #29 of 47 Old 08-29-2016, 05:09 PM - Thread Starter
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Next step is going to be trying to verify whether they large voice coil effect if an issue here. I have a test box spare that should do the job, just need to pull a driver out and fit it.
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post #30 of 47 Old 08-30-2016, 09:46 AM
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This design appears to be for just the one driver, were you intending to build two of these given you have two drivers? How difficult would it be to include a second driver in a vertical arrangement? (I'm guessing the port areas would need to change?) Apologies if these seem obvious questions!
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