| ScottG, check out this B&C 12TBX100 design - Click HERE for Original Thread |
| alexcd |
| I copied your tips from the Perceive 2.0 thread but modifying them as did Ant. I would like to use the sand but we're talking at least 500lbs worth. So here's my basic cabinet design so far. |
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| ScottG |
| quote: | Originally posted by alexcd
..but we're talking at least 500lbs worth. |
Hmm.. GOOD! :D
Its OK to alter the construction.. BUT it won't be nearly the same.
You would be better served by reducing the spacing for sand to 1 inch spacing on all sides but the top, and 2 inches on the top. It would still be extremely heavy of course.. but that helps out quite a bit.
I tried to cover the need for weight in my "voodoo of vibration in loudspeakers thread" - but it doesn't seem to get through. Hmm, try reading this review on a loudspeaker - the drivers though expensive aren't terribly special (except the ribbon in its linear region), what really *makes* this loudspeaker special is the rigidity of the driver coupling and the massive amount of weight:
http://www.positive-feedback.com/Is...dkdesignsf7.htm
Other issues:
Note that unless you corner load the sub (and have a fairly low crossover point - say 40 Hz or less), you may experience the same problems that Shin did with max spl. On the other hand 102 db isn't exactly quiet - but this is a subjective thing and really depends on what you want. The other *possible* solution is to increase the size of the vent to about a 5 inch diameter.. but that increases length considerably.
Another thing..
With the driver closer to the ground you'll get a bit more low freq. room "lock", BUT the freq. balance may be tilted up a bit more higher in freq., requireing even more care with loudspeaker summation.
Finally..
You have about the optimum volume to spl for 20 Hz at 2.25 internal cubic feet - so if you have calculated volume correctly then it should be good.
In any event - do what you want, I'm only here to make suggestions. The bottom-line is this is your subwoofer (or at least the one you are putting the sweat equity into), so only do what you feel you are capable of. ;) |
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| alexcd |
| I feel a little slow but how does your suggestion about the sand apply to the driver baffle? It would obviously leak into the inner enclosure unless there was some sort of barrier. You mentioned concrete which is something I was trying to get away from doing but how is that implemented as well? I really need a visual here. |
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| ScottG |
| quote: | Originally posted by alexcd
I feel a little slow but how does your suggestion about the sand apply to the driver baffle? It would obviously leak into the inner enclosure unless there was some sort of barrier. You mentioned concrete which is something I was trying to get away from doing but how is that implemented as well? I really need a visual here. |
I'll try working on that latter today in ms paint. It'll look like cr@p though.
So give me some time and hopefully you'll be able to litterally see what I was trying to describe. |
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| alexcd |
What can I do to reach 20Hz without distortion and louder than 102dB?
4 or 5" port?
larger or smaller enclosure?
I am up for any shape as long as it's not too massive. I can maybe deal with a longer port if I were to be allowed a slot style. It can face the wall, floor, room, be corner loaded, whatever you think would work best. This is going in my friend's basement so there's a lot of hard walls to bounce sound off of (and probably a lot of dampening that we need to do.) |
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| ScottG |
This is a side cut-away *without* the concret side baffle.. I'll get to that in a little bit.
Note that the only intended "scale" here is to show the difference between the 2 inch Top fill of sand vs. the 1 inch sides and bottom..
Key:
brown = mdf 3/4 inch
grey = bolts & spikes with support "plates"
black = vent tubeS with connection "plates", and screws (at the "but" joints of the mdf)
white = ultra fine sand
light blue = pure silicone caulk
blue = air |
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| ScottG |
| quote: | Originally posted by alexcd
What can I do to reach 20Hz without distortion and louder than 102dB?
4 or 5" port?
larger or smaller enclosure?
I am up for any shape as long as it's not too massive. I can maybe deal with a longer port if I were to be allowed a slot style. It can face the wall, floor, room, be corner loaded, whatever you think would work best. This is going in my friend's basement so there's a lot of hard walls to bounce sound off of (and probably a lot of dampening that we need to do.) |
Well there is no such thing as without distortion..
The BEST thing is to room-corner load the sub. That will give you considerable gain without increasing excursion.
..a 4 inch or 5 inch port will require either a taller enclosure OR require some bending of the vent/pipe. Bends (particualarly sharp 90 degree bends) screw-up airflow - and it isn't something I'd generally suggest. What makes this worse is that MOST available pipe bends ARE 90 degrees.
You could actually both corner load AND have a taller enclosure made to look something like this pedestal (..and you could even build in the up-lighting like it has to use as a pedestal):
http://www.hammacher.com/publish/72000.asp
Now it *may* be the phase angle vs. impeadance or even Shin's room that is causing the "ceiling" in spl's that he is experiencing. Don't know.
If it is ultimatly power related then you could always purchase this for a bit more power and bridge it (..the lowest cost per watt):
http://www.behringer.com/EP2500/index.cfm?lang=ENG
(check elsewhere for lower prices)
If its the room then it may not be something you will experience.
Additionally remember I originally spec'ed 2 of these subs connected in parrallel - which adds almost another 6 db AND when placed correctly in the room even's out the spl through-out the room. |
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| m0tion |
| Interesting that you would recommend putting great effort into perfectly the enclosure and using what has been described as an extremely well constructed driver and then recommend pairing it with the "lowest cost per watt" amplifier :cool:. Do you believe the quality of amplification really matters that little with a subwoofer? |
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| ScottG |
| quote: | Originally posted by m0tion
Interesting that you would recommend putting great effort into perfectly the enclosure and using what has been described as an extremely well constructed driver and then recommend pairing it with the "lowest cost per watt" amplifier :cool:. Do you believe the quality of amplification really matters that little with a subwoofer? |
Ask yourself this:
"does lowest cost per watt = poor quality?"
What concernes me the most on an amplifier for sub freq.s is the power supply. The greater the available current, the better I like it. The greater the "instantaneous" current, the FAR better I like it.
If it were up to me the amp would have a choke loaded input power supply & and massive "reactance type" choke-out. I can guarantee you that the behringer has neither.. BUT it likely has a large bank of capacitance (and thereby current "resevoir") just to meet the large power requirements of this AB amp.
Additionally you have to factor price into the overall budget. While it may be massive construction using a relativly expensive driver - whats the cost of this? Prob. less than 450 US. What would you suggest as appropriate here, an amp costing 1000 US or more? In this instance then its a matter of practicallity - trying to achieve the "best" for the least for the given application.
Note that I'm not opposed to the idea of a 1000+ US DIY amp, its just that it doesn't seem practicle. |
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| alexcd |
| You definitely dont know how some people do things if you justify buying an expensive amp because you bought an expensive driver. Us common folk run out of project money and have to settle. I've heard about that amp and will recommend it to my friend. He wants to build a UCD700 but those are more expensive and I'll bust it over his head if he asks me to build one more thing for him. |
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| alexcd |
| The concrete is definitely the most confusing part of the design. Thanks for the diagram of the sand but can you show the driver bafle? |
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| ScottG |
| quote: | Originally posted by alexcd
..and I'll bust it over his head if he asks me to build one more thing for him. |
:D
Ok, here is a side view with the concrete (actually just cement) baffle.
The Key is the same except:
Light Grey = cement baffle. &,
The little bit of orange'ish color is actual still just mdf - this time however it is 1 inch instead of 3/4 inch mdf.
(..and note that 1 inch mdf isn't really a full 1 inch - this means that the air space that is to be filled with ultra fine sand should be almost exactly the same "thickness" as the actual dimension of the 1 inch mdf.)
I'll provide a view of that orange 1 inch mdf from another perspective in the next post. |
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| ScottG |
Here is the "spacer" (orang'ish brown) portion of 1 inch thick mdf:
(..note that the ultra fine white sand is absent in the picture here.. its just the 1 inch mdf spacer on top of the 3/4 inch mdf "exterior" box panel. That same 3/4 inch mdf baffle would be on top of the cement baffle.) |
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| alexcd |
| Does the 1" MDF need to be square or will a circle work just as well? |
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| ScottG |
| quote: | Originally posted by alexcd
Does the 1" MDF need to be square or will a circle work just as well? |
A circle is fine as well - but its likely to be more work cutting the interior circle and then the exterior circle additionally.
Are things starting to look more identifiable? |
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| alexcd |
eh... the router would already be out.
I figure all this will add 250lbs per cab. |
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| ScottG |
| quote: | Originally posted by alexcd
eh... the router would already be out.
I figure all this will add 250lbs per cab. |
What do mean by the router being "out"? You'll need one for the circular cuts. You could get by with them using a saber saw, but I wouldn't recomend it! ;) (i.e. beg, borrow, or steal one with a straight bit capable of more than 1 inch in depth.)
It might add that much weight, BUT you'll have a friend helping you with the sub inversion and placement after you have finished filling it from the bottom. (..obviously you'll only fill it *very* close to where you'll be placing it.) |
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| alexcd |
I meant that I'll have my router out to cut that center circle anyways.
I'll ask him about the weight.
Which side do you suggest I fill it from? I can cut a hole in the base and plug later if that's the best option. |
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| ScottG |
| quote: | Originally posted by alexcd
Which side do you suggest I fill it from? I can cut a hole in the base and plug later if that's the best option. |
AH!
Time to go back and read the instructions *carefully*. You don't need to cut a hole in anywhere for the filling. The bottom exterior box panel is attached last AFTER filling with sand.
Remember, while the construction is very easy (except for the cement baffle - which is not what I'd call difficult), the key is planning your build! ;) |
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| ScottG |
Urgg.. I just did some analysis of the port size needed for the additional power.
Now I'm *NOT* sure that air velocity and *actual* power work out correctly in WinIsd.
When I modeled Shins it was based on 64 watts which should provide plenty of gain considering a supposed 1 watt/ 1 meter in room nearing 87 db at 20 Hz. (..in other words at 64 watts there is a power factor increase of X6 = +18 db theoretically).
If I up the power to 256 watts AND the vent diameter to 5 inches then the program calls for 61 inches of vent length to comply with its max velocity spec.. This would make for a very high (almost 6 foot) box that is quite "thin". (..or it would require some pipe bends, or perhaps an exterior pipe.)
Again though, I'm not really sure what's happening with the power requirement vs. acoustic output. If indeed because of the impeadance vs. phase the sub is basically "p!ssing" away power - does this mean that the power vs. velocity "holds up" for the max velocity vent diameter requirement? That I can't tell you.
But hey, since RonE is more technically astute than I am - why not ping him for the answer? |
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| m0tion |
Scott:
What exactly would you consider a "large" bank of capacitors? I wasn't implying that you have to spend a lot on an amplifier to get a quality amplifier, I definitely don't buy into the "costs more must be better" audiophile hype. I do, however, recognize varying degrees of quality in amplifier design and found it interesting the very great lengths you go through to perfect the cabinet design and the exacting specifications you have for the drivers you choose. None of this has to do with price, but it just seems like you're saying all this and then "oh, any old amplifier will do, just make sure it has a lot of power". Maybe this is accurate for a subwoofer amplifier, I was honestly curious, is power output the primary most important specification to look for in a subwoofer amplifier? |
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| ScottG |
| quote: | Originally posted by m0tion
Scott:
What exactly would you consider a "large" bank of capacitors? I wasn't implying that you have to spend a lot on an amplifier to get a quality amplifier, I definitely don't buy into the "costs more must be better" audiophile hype. I do, however, recognize varying degrees of quality in amplifier design and found it interesting the very great lengths you go through to perfect the cabinet design and the exacting specifications you have for the drivers you choose. None of this has to do with price, but it just seems like you're saying all this and then "oh, any old amplifier will do, just make sure it has a lot of power". Maybe this is accurate for a subwoofer amplifier, I was honestly curious, is power output the primary most important specification to look for in a subwoofer amplifier? |
It may have "seemed" like that, but that wasn't what was intended. ;)
In general power output is not the most important spec. - not by a long shot if the design is fairly efficient at low freq.s (..and doesn't p!ss away power).
The problem here was specific to this design - i.e. that Shin wasn't getting anymore than 102 db at 20 Hz with it despite having 500 watts of UCD700 to work with. The behringer should provide more than double that power when bridged - so thats why I mentioned it, i.e. that it is a cost effective solution IF more power is required to go beyond the 102 db figure. (..again though, assuming that more power will actually provide more output.) Additionally, Thylanter has mentioned that this amp (or actually the amp from which it was derived) is a very good amp. Also to come anywhere close to its power rating it must have more than a little bit of current on "tap". So with this amp we have both a LOT of power and by neccesity quite a lot of current in reserve - combine that with its cost and it is nearly an ideal solution (..provided the fans aren't noisy or don't start at lower power levels).
As to my thoughts generally -
1. You want a *low* output impeadance here for a greater dampening factor.
2. You want lots of current in the power supply - in particular to:
A. support the full power requirement for the amp at *any* time, &
B. effectivly "flood" the output to reject driver induced "return" back emf.
Now its rare (commercially) in anything but a class A amp that "A" above will be fullfilled (..which is why you'll see things like "average" listed for the amplifers power output). "B" is complementary to "A". In fact "B" (along with dampening factor) is where you'll notice audible differences and this is a reason to have a "big" amplifier.
Of course if its a fairly low voltage amp (like most solid state amps are) - you could always achieve this "flood" effect with SLA batteries (in parallel to achieve the required voltage). Generally the larger the current capacity of the batter(ies), the greater the overall clarity and "slam" (for a sub). Combine both 1 and 2 and you'll typically find the listener's subjective response as something like - "wow another half octave of extension with MUCH greater clarity!". |
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| alexcd |
| quote: | Originally posted by ScottG
Urgg.. I just did some analysis of the port size needed for the additional power.
Now I'm *NOT* sure that air velocity and *actual* power work out correctly in WinIsd.
When I modeled Shins it was based on 64 watts which should provide plenty of gain considering a supposed 1 watt/ 1 meter in room nearing 87 db at 20 Hz. (..in other words at 64 watts there is a power factor increase of X6 = +18 db theoretically).
If I up the power to 256 watts AND the vent diameter to 5 inches then the program calls for 61 inches of vent length to comply with its max velocity spec.. This would make for a very high (almost 6 foot) box that is quite "thin". (..or it would require some pipe bends, or perhaps an exterior pipe.)
Again though, I'm not really sure what's happening with the power requirement vs. acoustic output. If indeed because of the impeadance vs. phase the sub is basically "p!ssing" away power - does this mean that the power vs. velocity "holds up" for the max velocity vent diameter requirement? That I can't tell you.
But hey, since RonE is more technically astute than I am - why not ping him for the answer? |
So with anything greater than 200W I should be using a 5" port. That's a little rediculous unless I can shape it a bit. Would it be bad to only use the 3" port and one of those EP2500's in parallel to two drivers in seperate cabs? |
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| alexcd |
| I've actually seen one of these (EP2500) apart and can tell you there is a decent amount of reserve. With a pure sinusoidal output the rails should not droop more than 10% or sustain about 81% of the RMS power specified by even the shadiest technician. The toroid seems to be no more than a 750VA-1000VA so that is going to limit power the most. I would still expect good things for $490 (retail.) |
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| ScottG |
| quote: | Originally posted by alexcd
So with anything greater than 200W I should be using a 5" port. That's a little rediculous unless I can shape it a bit. Would it be bad to only use the 3" port and one of those EP2500's in parallel to two drivers in seperate cabs? |
This all depends on how power "translates" with respect to port velocity.
If a doubling in power ='s virtually a +3 db increase in spl then 64 watts should be plenty. 64 watts = 18 db of gain that adds to your 83-84 db of spl (1 watt 1 meter) at 20 Hz - and this does NOT include any room gain or additional boundry gain (beyond the floor loading for the port which is already factored in).
In effect then you should have 102 db of spl without any serious turbulance from the port with only a single boundry (the floor) at 64 watts.
Now if the combination of phase angle and impeadance are effectivly "sapping" power - then what is actually 64 watts in a resistive load may require something more like 3 times that amount of power to achieve the same 102 db (i.e. perhaps 256 watts "+" are required to achieve 102 db).
The question is then does the turbulance increase proportionatly to the power increase? I wouldn't think so (because I think of port velocity as proportional to port spl), but I could be wrong. IF it isn't then you don't need anything more than the 3 inch diameter port AND more power (i.e. the higher power amp). IF it is, then you need a larger diameter port. See the difference?
I agree that the 5 inch diameter is not practicle unless it has a bend, HOWEVER - aren't there "U" bends for plumbing?
That would be something I would be comfortable recomending that would not cause a great deal of air flow resistance because it isn't an "abrupt" bend.
Here is one:
http://spapartsnet.com/Plumbing-Par...00_517_0_1.html
I could easily see *3* 1.5 inch ports (..assuming the internal diameter is 1.5 inches). That would equal 4.5 inches and would amount to a total length of 49 inches for each 1.5 inch port. The "U" bend then would provide the ability to almost halve that length in the cabinet (i.e. about 30 inches). (i.e. envision 3 ports in one cabinet each going up about 30 inches and down the remaining 19 inch distance - factoring in the length of the U bend section as well. The U bend could be almost touching the top of the cabinet interior.)
If you wanted an even greater diameter port you would be looking at perhaps *2* "U" bends for each port.
This would of course decrease cabinet volume some AND you would only be able to use the "pipe within a pipe and silcone caulk between" construction up to the first "U" bend near the top of the cabinet - neither concerns me however based on your requirements.
Finally,
When I suggested 2 drivers - that was intended to convey 2 seperate sub BOXES (i.e. 2 boxes each with their own driver AND with identical porting). IF connected in parallel that will net you an additional +6 db provided the amp can double power into a 4 ohm load over an 8 ohm load. In other words each with their 3 inch port based on a max spl of 102 db would net you 108 db. BUT part of that increase is predicated on power - so IF power was the problem you might not see a 1:1 relationship for half of that increase (i.e. 3 db of the 6 db increase). |
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| ScottG |
| quote: | Originally posted by ScottG
(in parallel to achieve the required voltage). |
correction: that should be *series* not parallel. |
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| ScottG |
I just did some analysis for *3* 2 inch diameter ports (total port diameter = 6 inches). The resulting required length would be 88.6 inches for each 2 inch pipe.
Using 2 U bends you could practically bend the length into 1/3rds without substantial turbulance. In other words about 30 inches up from the sub's bottom and then a bend going down about 27 inches and finally a bend going back up about 20 inches (..and the 2 bends adding to the total length to achieve about 88.6 inches).
The interior volume should nominally be 2.25 cubic feet. From there you would need to calculate the ports displacement and add that amount to the 2.25 cubic feet. As a pure guesstimate - if another cubic foot suffices for the displacement compensation then the total would be 3.25 cubic feet.
The shape of a pedestal for corner placement would be moderatly tall and somewhat "thin". For the "thin" factor I'd suggest an internal width and depth slightly larger than the cone - or about 12.5 inches each. IF we calculate 12.5 inches for width and depth then to obtain our "height" for the *estimated* volume of 3.25 cubic feet would = about 36 inches.
Of course from there you would add on the exterior proportions so you might be looking at something about 17 inches for the width and depth and about 44 inches in total height including the base.
Thats about perfect for a pedestal.
The 6 inch diameter port would allow for more than 400 watts of input without excessive turbulance - regardless of the power vs. acoustic velocity question.
Loading it in a corner would net you at *least* another 6 db of output at 20 Hz.
It should be reasonably unobtrusive esthetically in any setting AND might be easier to manuever because of the shape.
From a basic design (altering volume and size where neccesary), thats a pretty good starting point IMO. |
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| ScottG |
My calculations are *way* off on vent length.. (I was calculating based on one vent of 6 inches in diameter)
3 * 2 inch vents = only 30 inches each..
..no bends are neccesary. SWEET! |
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| alexcd |
| It makes sense that it's only 8" longer than a single 3" port because 3 x 2" ports is only 1/3 more area than a single 3" port. I dont think that will help much since it's actually 25% smaller than a 4" port. What do you think? 5" seems right to me but it's insanely long. I can build a slot port with as tapered corners as possible. |
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| ScottG |
| quote: | Originally posted by alexcd
It makes sense that it's only 8" longer than a single 3" port because 3 x 2" ports is only 1/3 more area than a single 3" port. I dont think that will help much since it's actually 25% smaller than a 4" port. What do you think? 5" seems right to me but it's insanely long. I can build a slot port with as tapered corners as possible. |
3 * 2 inch ports - the air velocity is the same as a 6 inch port for the same power rating (..presumably the the greater surface area of the pipe walls are slowing things down a bit). It surpasses a 5 inch considerably. (Hmm, this is not unlike the "free lunch" for using multiple small capacitors instead of one large one.) |
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| alexcd |
I thought the air would be proportionate to the cross-sectional area of the port.
3 x A(2") = 3 x pi*1^2 = 3pi in^2
1 x A(6") = pi*3^2 = 9pi in^2
Maybe I'm not getting something but I am pretty sure that's how it works. |
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| ScottG |
| quote: | Originally posted by alexcd
I thought the air would be proportionate to the cross-sectional area of the port.
3 x A(2") = 3 x pi*1^2 = 3pi in^2
1 x A(6") = pi*3^2 = 9pi in^2
Maybe I'm not getting something but I am pretty sure that's how it works. |
What can I say?
Download WinIsd, input the paramaters for the B&C driver and alter the power in the parameter section to see the differences for yourself.
http://www.linearteam.dk/default.aspx?pageid=winisd
Specifically input for 512 watts (Pe) in the parameters section of the driver sheet.
Then model that driver with :
Box of 63 liters and a vent tunning of 19 Hz.
First use 1 port with a 6 inch diameter and you'll return a value of:
vent length = 88.62 inches & mach = .14
Then use 3 ports with a 2 inch diameter and you'll return a value of:
vent length = 29.54 inches & mach = .14
..even though the crossectional area isn't the same - the airspeed supposedly is the same (..and airspeed under .2-.15 mach is often spec'ed at the point where you shouldn't incure audible turbulance).
If you use 1 port with a 4.5 inch diameter you'll return a value of:
vent length = 49.02 inches & mach = .25 |
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| alexcd |
| Stupid software always trying to prove me wrong... Ok, point taken. Sounds like 3 2" ports should be enough anyways. I'm not going to argue you there. Maybe I can start this project as soon as I finish the current 3. I've got my hands full with a friend with deep pockets. It's fun to play with someone else's money. haha |
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| ScottG |
| quote: | Originally posted by alexcd
Stupid software always trying to prove me wrong... |
:D
..and I did try it out with other software as well! :) |
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| alexcd |
| What software did you use and did you keep the port lengths the same for basis of comparison? |
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| ScottG |
| quote: | Originally posted by alexcd
What software did you use and did you keep the port lengths the same for basis of comparison? |
the same (and the results were not identical, but close)..
....
http://www.pvconsultants.com/audio/eq/boxcircuit.htm
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http://www.ajdesigner.com/phpvent/s...on_length_l.php
....
I also looked at excursion as well at 1 watt 1 meter (multiplier * inches)..
..a 3 * 2 config. was about a 3rd less excursion than the 1 * 3,
..a 5 * 2 was almost the same as a 1 * 4.5
(the reason I spec'ed the 2 inch was for access to the U bend pipe which I have only been able to find as large as 2 inches in diameter. Again though, I'm not sure that it is actually 2 inches in diameter - somthing you'll need to check.)
Also a note on construction..
Because this IS a basement setting, you could always use sonotube in a tube within a tube and sand fill between INSTEAD of the box construction that I recomended. That would likely make the construction considerably easier (..no need for bolting the exterior tube to the interior tube). Alternativly you could use a tube within a box, (and sand fill between) for a more traditional box esthetic. Here however the driver/port would either be facing the floor or the ceiling. |
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| alexcd |
| Option C, I hope... can we just make the enclosure larger and use a shorter port? I can go up to 3-3.5ft^3 easy if you think it would be worth it. |
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| ScottG |
| quote: | Originally posted by alexcd
Option C, I hope... can we just make the enclosure larger and use a shorter port? I can go up to 3-3.5ft^3 easy if you think it would be worth it. |
That will give the low freq. response a "knee". It will be audible, BUT with a slightly higher high pass "rumble filter" placed at port tunning freq. or 1 Hz below that, then the response will become a bit flatter again in-room.
However at 3.5 cubic feet it will require one 5.7 inch diameter pipe at a length of almost 50 inches for 512 watts of power. Contrast this with "only" 256 watts of power in the same volume and the pipe drops to 5 inches in diameter and 37.5 inches in length.
I'd almost guarantee you that this configuration *will* be able to support the full bandwidth at considerably higher spl's. Here excursion will be MUCH less for the port and double for the driver for a given power level (..so you will need the "rumble filter"). Phase will be considerably flatter up to about 45 Hz. Note though that part of the reason why the driver excursion doubles is due to the fact that is is contributing more to overall spl - AND more at 1 watt (..so it isn't apples to apples). Of course this also means that non-linear distortion will increase - even at 1 watt.
(..i.e. there is always give and take.) :dead: :smash:
Here I think its more a matter of what you want the sub for..
If its more for HT than music then - Yes, I'd probably up the volume and do this. If its more for music - then NO, I'd stick with something a bit closer to the original plan.
For a "middle of the road" approach:
5 * 2 inch ports drops the port excursion enough, (.while still keeping driver excursion low - with a rumble filter), that I'd stick to that.. That *SHOULD* provide low distortion AND pretty high spl's with NO vent noise. Again though, just a suggestion. |
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| alexcd |
| How about 750W per driver since that seems like what the EP2500 can put out cleanly?... and it would be for music mostly. |
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| ScottG |
| quote: | Originally posted by alexcd
How about 750W per driver since that seems like what the EP2500 can put out cleanly?... and it would be for music mostly. |
URRGGGGG! :D
Give me tomorrow for that one.. ;) |
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| alexcd |
| I hope I'm not testing your patience. I really appreciate the help though. |
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| ScottG |
| quote: | Originally posted by alexcd
I hope I'm not testing your patience. I really appreciate the help though. |
No I'm good. In fact this is what I expected - plan, plan, plan - THEN "pull the trigger" and build.
I did it at 1000 (which is closer to the next +3 db multiple of 1024).
I increased volume slightly to still maintain low *driver* excursion to at least the tunning resonance. This allowed for a bit lower *port* air excursion and considerably reduced port length.
I came up with this:
80 Liters (2.825 cubic feet) nominal internal volume.
6 * 2 inch ports = 47.37 inches in length. (..obviously use the "U" bends for bending it here if a lower enclosure height is preferred.)
That lowers port excursion near to what the 5 inch is (in the 3.5 cubic foot enclosure) while keeping driver excursion much lower. No port noise with this design.
Again a rumble filter (LR 4th order at 18 Hz) - should be included.
Will it be able to utilize the full 1000 watts? Probably not, but I think its likely to come fairly close while still maintaining lower overall distortion.
If that sounds acceptable to you then the next thing is to find out what the interior diameter of those 2 inch U bends are really. (i.e. email a supplier or see if its available at a dealer near you.) On the other hand if you are OK with a 5 foot high box then you don't even need to consider this.
Also remember that with virtually all music (other than some organ music and some club music) will *NOT* have large spl's near (or lower than) 20 Hz. Here it will likely be side-band decay and hall reflection decay - and 102 db is *MORE* than enough for it. It isn't enough though for some HT effects material, however. |
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| alexcd |
| Instead of facing all the ports down, can i fire them against a wall or other solid surface? |
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| ScottG |
| quote: | Originally posted by alexcd
Instead of facing all the ports down, can i fire them against a wall or other solid surface? |
You could do that BUT..
1. you'll want it VERY close to the ground for boundry coupling.
2. IF there is a bend then it should be closer to the *center* of the pipe, and this may pose a problem IF the sub isn't very deep (..or wide depending). |
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| alexcd |
| Basically this is going to look like Shin's enclosure unless I use the U-joint. |
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| ScottG |
| quote: | Originally posted by alexcd
Basically this is going to look like Shin's enclosure unless I use the U-joint. |
Sounds about right, though larger volume and a bit higher. Though not with the v-shape esthetic cut. This would require a downward (or upward) port with no bends. But there are reasons for the downward port and the air loading near the floor that have nothing to do with esthetics or wrapping a port in a box. |
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| alexcd |
Does it matter that the 2" (?) cement baffle + 1.5" MDF and 1" of sand is only slightly less than the mounting depth of the sub (5.3")? Usually I like to give the driver area to breath but in this case that would be difficult to angle out into the inner box.
Seperately, should I brace the rear of the subwoofer (magnet)with any kind of bracketry? |
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| ScottG |
| quote: | Originally posted by alexcd
Does it matter that the 2" (?) cement baffle + 1.5" MDF and 1" of sand is only slightly less than the mounting depth of the sub (5.3")? Usually I like to give the driver area to breath but in this case that would be difficult to angle out into the inner box.
Seperately, should I brace the rear of the subwoofer (magnet)with any kind of bracketry? |
Doesn't matter. 2 inches should be good (..generally the thicker the better, but 2 inches should be good enough). If you wanted to change the cement baffle out for a steel plate (from perhaps a local steel fabricator), then you should prob. consider something approaching 1/2 inch (and of course get them to make the cuts and perhaps weld the bolts or make recessed cuts/drilled for the bolt heads).
The angle cut isn't neccesary here - the passband is so low in operation that any resonance should be much higher and effect it little if any.
Do NOT brace the sub magnet. Here the frame is VERY robust and we specifically want the vibration exiting the frame into the cement baffle and ONLY the cement baffle. |
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| alexcd |
I couldnt get him to go for the multiple 2" ports or 5' enclosure. We settled on a single 4" x 32.25" port (2.8cuft.) The air flow shouldnt be much of a problem.
OK, time to go build some passive crossovers for some other speakers. |
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| ScottG |
| quote: | Originally posted by alexcd
I couldnt get him to go for the multiple 2" ports or 5' enclosure. We settled on a single 4" x 32.25" port (2.8cuft.) The air flow shouldnt be much of a problem.
OK, time to go build some passive crossovers for some other speakers. |
Thats not too bad - it keeps driver excursion low which will keep distortion low. On the other hand it will also limit spl because of port excursion. Still, if he can get 105 db in-room for music at 20 Hz with low distortion then I don't think he is doing too badly. :D (..and if he corner loads the thing it will offer that much more spl's OR lower non-linear distortion.)
Note that with this configuration driver excursion below resonance is still pretty low. In this instance then (like Shin's), I wouldn't automatically spec. a "rumble filter", rather I'd try it (with and without) with your friends most demanding music and see if it seems to make a difference. |
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| alexcd |
| Will a slot port work as well if I aimed it down? I am thinking of coming straight up the back of the box and along the top. So, one 90* bend but I would use PVC pipe to smooth the corners. Is that okay? I can reduce the height of the enclosure significantly this way which is what my buddy wants. |
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| alexcd |
| Oh yeah, I forgot to mention that he also shot down the sand idea, sorry. I'll try it myself some day but this is just going to be a well braced enclosure. |
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| ScottG |
| quote: | Originally posted by alexcd
Will a slot port work as well if I aimed it down? I am thinking of coming straight up the back of the box and along the top. So, one 90* bend but I would use PVC pipe to smooth the corners. Is that okay? I can reduce the height of the enclosure significantly this way which is what my buddy wants. |
I've seen (somewhere) that something closer to a slot was actually better.
IMO its all down to how low friction the sidewalls of the port are and that IF there is any bend, that the bend is "gradual" rather than "abrupt". A "pure" 90 degree bend is horrible. A 90 degree bend that happens over a gradual arc should be OK. Remember, the port represents a "slug" of air mass that is in effect a driver diaphram without a motor (the mechanical compliance is essentially the structure of the pipe and any internal resistance it has). Effectivly that "slug" needs to be able to freely "pump" back and forth.
Bummer about the "sand".. sounds like another compromised design. :( |
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