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ANNIHILATION Sub coming SOON! - Page 2

post #31 of 140
Thread Starter 
Quote:
Originally Posted by eXa View Post

Longer with the same diameter only lowers the tuning. To get the velocity down you need to have more area in you port(s)
8in port out of the question cause be to hard to find. What if i add 2 more 6 in ports?
post #32 of 140
"Would three 4" models be good enough versus a single 6"? As LTD02 mentioned, I'm talking about 'per woofer'. The only issue is the front baffle size. Those 4" ports are about 7.25" in diameter, which means the baffle would need to be at least 27" tall and 23.5" wide. The box would only need to be about 28" deep to yield 7.5cuft. So the ports would still need an elbow.

Ideally the flat pack was designed to use plastic ports because a slot port would add a lot of extra weight with at least 2 big slabs of MDF. These would already need to be shipped in 2 packages because of the weight."

smaller ports don't flow as well as a larger port, but 3 4" ports have more area, so it probably works out "good enough" either way and with the 4" they have a larger radius which better, c.p. forget the elbow if possible. add about 3" of internal space and go with whatever tuning that produces.

the old 4645 cab from jbl is about where you'd end up within those constraints. rounding over the edges, recessed baffle panel and flush mount grill might be kind of nice. no where near as raw as the annihilator. :-)



I don't know...doesn't feel quite right yet on something like that but I like that you are thinking about a ported flat pack. might help some folks out!
post #33 of 140
I don't think the baffle would be big enough to handle two 8" ports as they are just way too big. If you have never seen a piece of 8" PVC then you have no idea, but I can assure you that two 8" ports would be impossible.
post #34 of 140
"What if i add 2 more 6 in ports?"

then all four would have to be about twice as long.

i suppose it is a fair question...but at some point you have to ask yourself if perhaps that had already been considered. :-)
post #35 of 140
Thread Starter 
Quote:
Originally Posted by Martycool007 View Post

I don't think the baffle would be big enough to handle two 8" ports as they are just way too big. If you have never seen a piece of 8" PVC then you have no idea, but I can assure you that two 8" ports would be impossible.
So 4 6in ports at 27in in length would work and bring down the velocity?
post #36 of 140
Thread Starter 
I dont have the time yet to sit and play with win. I have to be up at 4am tomorrow frown.gif but this weekend i will simulate it and build it in sketchup
post #37 of 140
"So 4 6in ports at 27in in length would work and bring down the velocity?"

that will lower port velocity, but the tuning frequency will increase dramatically up to something like 25hz. that's not what you want.
post #38 of 140
Quote:
Originally Posted by eXa View Post

3.14*(3*3)=28.26
(3.14*(2*2))*3=37.68

Thoose 3 4" would have 33% more area than a single 6"

Yes sir, I understand that neat stuff and know they will be better. But I'm wondering if that extra will be enough for this ported box.
post #39 of 140
sorry erich, that was the close cousin of the 4645c, the s1s-ex used in the synthesis line. more or less the same thing. just a rough idea of how an 18" could look with a triple flared port.

also, email sent.

dimensions of 34" tall x 21" wide (golden ratio proportions, so it will look pretty :-) ) x 28" deep, with 3/4" stock and 1.5 cubic feet for bracing, driver, and ports, nets out to 9 cubic feet on the button.

three 3.5" flared ports x 24" long would tune that cabinet to 18hz, which would be just about perfect. the trick we used here was to make the cab just a little bigger, so the ports could be a little shorter, so no bends would be required, and we still get a good medium-low tuning. might even be a hair lower with the straight ports firing directly into the rear wall and/or with a little stuffing in the sub, but i'd target 17-18hz with the SI/Dayton dynamic driver duo.

btw, three 4" ports x 24" long would tune the cab to 20.4hz or so, which is a little high, but maybe with rear wall interaction and stuffing it can be brought down into the 17/18hz ballpark.

marketing guy comedy...this one has a bigger dustcap than the 2242..."cover up those voice coil leads! yes sir!"


Edited by LTD02 - 10/10/13 at 12:07am
post #40 of 140
Quote:
Originally Posted by Erich H View Post

So one 6" port will do okay with one of those woofers? If so, that would make a flat pack design much easier.

Now I dont have that woofer, but based on how it performs in modeling it seems is that it can be done in a box that is not too big (6-7 cft.) and is tuned somewhere between 18 and 20Hz. The 6" tube will be short enough that it should be possible to fit it in it the box and ports speed seem to max at approx 25m/s. Of course its only a model and I am not at all convinced the 18HO perform the same way in a real box. At least recent posts on here suggest that it measures somewhat different than my models predict. Now I am in no way an experienced designer so I might well be wrong but i think it might be possible. The following models include 2. order HPF, 4.order LPF and a little boost around tuning. They are at max rated excursion and all hovers right at 25ms port speed.
Based on what i have seen here recently, and other places, I think it is difficult to predict the exact port length, but both winisd and UNIBOX seem to overestimate the length. Based on that, I assume the the real port length will be shorter than predicted and that the port resonance will be higher in frequency than what is shown. It also makes the port easier to fit in the box. For the 3 models below my best guess is that they all come in between 22" and 27" inches depending on box size and tuning. That is with a port end correction of 1.0 instead of the usual 0.7.










Edited by splotten - 10/10/13 at 1:55am
post #41 of 140
I don't see any problems with those models...they seem fine at first glance...

"Now I dont have that woofer, but based on how it performs in modeling it seems is that it can be done in a box that is not too big (6-7 cft.) and is tuned somewhere between 18 and 20Hz. The 6" tube will be short enough that it should be possible to fit it in it the box"

that's the whole trick...with a 6" port and 18hz tuning in a 6 cubic foot enclosure, the port would need to be ~34" long. with 4" or so of minimum backspacing and 0.75" for the rear wall, that gives a cab depth of 39".
post #42 of 140
since shipping is a big part of this, isn't there a light weight mdf?

edit: trupan ultralight mdf appears to only be about ~15% lighter.
Edited by LTD02 - 10/10/13 at 2:10am
post #43 of 140
Quote:
Originally Posted by LTD02 View Post

I don't see any problems with those models...they seem fine at first glance...

"Now I dont have that woofer, but based on how it performs in modeling it seems is that it can be done in a box that is not too big (6-7 cft.) and is tuned somewhere between 18 and 20Hz. The 6" tube will be short enough that it should be possible to fit it in it the box"

that's the whole trick...with a 6" port and 18hz tuning in a 6 cubic foot enclosure, the port would need to be ~34" long. with 4" or so of minimum backspacing and 0.75" for the rear wall, that gives a cab depth of 39".

Please re-read my post . I have edited it while you answered.
post #44 of 140
the overshoot is for slot ports, particularly those along a boundary like the floor, not round ports exiting in the middle of the panel like this.
post #45 of 140
Quote:
Originally Posted by LTD02 View Post

the overshoot is for slot ports, particularly those along a boundary like the floor, not round ports exiting in the middle of the panel like this.

I dont believe that is always the case. There was a good read at Troels Gravesens site, that I think you also linked a number of times. I seem to suggest that even a round vent well off the floor has a tendency to tune lower than predicted. - Or must be much shorter to achieve the desired tuning than calculated.

Test with undampened box.



"The table shows the tuning frequencies from the chosen vent lengths compared to the calculated lengths with the k value set at 0.732.
As can be seen, the difference between actual and calculated vent length has diminished."
(Compared to the dampened box below)


Test with dampened box.



"The table shows the tuning frequencies from the chosen vent lengths
compared to the calculated lengths with the k value set at 0.732.
As can be seen, there's a major discrepancy between measured
and calculated values and the vent has to be much shorter than predicted."


http://www.troelsgravesen.dk/vent_tuning.htm
Edited by splotten - 10/10/13 at 3:34am
post #46 of 140
i wonder if the common element that is being overlooked is the flaring. slot ports are where this problem seems to have been first identified and they tend not to be rounded over at all. moreover air flow in a narrow slot is worse than for a round port of equal cross sectional area. most of the common port tubes have some sort of significant flare on them relative to their diameter and problems haven't been being reported so much with them.

collo has done quite a bit of testing and shows that chuffing is significantly greater on non-flared ports all other things equal. that turbulence at termination may be exacerbating the impedance difference between the air in the port tube and the air surrounding the enclosure.

that's the best theory that I can come up with that seems to fit all the data presented so far. thus it would seem there are a couple of choices. go with a short port, with no flare, benefit from the lower tuning caused by the air getting all jammed up around the exit, capture the lower tuning frequency, and hope that compression and chuffing aren't too bad...or build a longer port, with a large flare, have no chuffing, but not benefit from the air jam up and have to build a larger cab.

something about that strikes me as right as there is never a free lunch, well, almost never. :-)
post #47 of 140
another strategy could be to stuff the enclosure (add damping), but in ricci's test while that drops the tuning frequency all other things equal, it also drops sensitivity quite a bit too.

http://www.data-bass.com/data?page=content&id=79

so, i'm not sure that is a solution either, just another potential tradeoff.
post #48 of 140
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

another strategy could be to stuff the enclosure (add damping), but in ricci's test while that drops the tuning frequency all other things equal, it also drops sensitivity quite a bit too.

http://www.data-bass.com/data?page=content&id=79

so, i'm not sure that is a solution either, just another potential tradeoff.
Morning folks
Alot i seen has been discussed and bit over my head. All this is worrying me about the annihilation sub.
post #49 of 140
"All this is worrying me about the annihilation sub."

wait till you see what happens when you put your tuned-to-perfection subwoofer in your room and take your first measurement...then you will have much more to worry about than whether the cab comes in tuned to 16hz or 18hz. :-)~
post #50 of 140
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

"All this is worrying me about the annihilation sub."

wait till you see what happens when you put your tuned-to-perfection subwoofer in your room and take your first measurement...then you will have much more to worry about than whether the cab comes in tuned to 16hz or 18hz. :-)~
Haha so thats the worst 16 or 18hz awesome. Maybe i should be more worried about my room and foundation.
post #51 of 140
Quote:
Originally Posted by frankie2075 View Post

Morning folks
Alot i seen has been discussed and bit over my head. All this is worrying me about the annihilation sub.

It's no big deal, there just needs to be a couple details ironed out before the design is ready for primetime. That is part of the design process.
It will be an easy build once things are finalized.
post #52 of 140
Thread Starter 
Quote:
Originally Posted by jpmst3 View Post

It's no big deal, there just needs to be a couple details ironed out before the design is ready for primetime. That is part of the design process.
It will be an easy build once things are finalized.
Yea i got a month left still before i start the build so i guess its enough time to sort it all out.
post #53 of 140
Absolutely, just minor tweaks to the number, length and diameter of the ports. No big deal at all there.
post #54 of 140
Thread Starter 
ANNIHILATIONSUBWOOFER.png

How does it look?
Bracing?
Edited by frankie2075 - 10/12/13 at 7:22am
post #55 of 140
Thread Starter 
Hope its as simple as it looks when building it on the computer.
post #56 of 140
that sure is coming right along...nice job.

more bracing on that rear panel. might also go a little heavier with the bracing that is in there.
post #57 of 140
Thread Starter 
okay will rework the bracing and add some more! thanks
post #58 of 140
Thread Starter 
okay i reworked the bracing to beef it up and also added some.
added flare port love how its looking!
ANNIHILATION_SUBWOOFER_CORNER_VIEW.jpg
Edited by frankie2075 - 10/12/13 at 7:21am
post #59 of 140
Thread Starter 
got a little carried away put subs in model

ANNIHILATIONSUBWOOFERfully.png
post #60 of 140
Thread Starter 
Someone know how i can figure out with the bracing and subs and ports the internal cuft?
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