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Old 14th September 2006, 03:07 AM   #21
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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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Old 14th September 2006, 04:04 AM   #22
ScottG is offline ScottG  United States
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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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Old 14th September 2006, 01:21 PM   #23
alexcd is offline alexcd  United States
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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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Old 14th September 2006, 01:42 PM   #24
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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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Old 14th September 2006, 11:11 PM   #25
ScottG is offline ScottG  United States
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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-Part...0_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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Old 14th September 2006, 11:20 PM   #26
ScottG is offline ScottG  United States
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Quote:
Originally posted by ScottG


(in parallel to achieve the required voltage).
correction: that should be *series* not parallel.
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Old 15th September 2006, 12:19 AM   #27
ScottG is offline ScottG  United States
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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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Old 15th September 2006, 02:31 AM   #28
ScottG is offline ScottG  United States
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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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Old 15th September 2006, 12:51 PM   #29
alexcd is offline alexcd  United States
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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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Old 15th September 2006, 07:39 PM   #30
ScottG is offline ScottG  United States
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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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