Is there a hidden IAS stacking penalty?

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Ascendic wrote:

With frenzy charges x 4 which give 9% IAS and 5% IAS each (from the skill gem and base frenzy) which equals a total of 71% IAS.

If each charge gives a 5% and a 9% increase, that's a 14% increase per charge, which is a 56% total increase for four charges. I don't see where your 71% comes from.

Also, the bonus you're getting from the charges it additive with your other increases from passives/mods/buffs/etc. Those are still applying when you have no charges, so the time listed when no charges are up is not the base time, it already has some increase.

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Ascendic wrote:

You're right it was supposed to say 56% I am not sure where the 71 came from. Still it doesnt seem a 56% difference when it only goes from 0.43 to 0.41?

Which is because of the second part of my post - the attack time listed on the skill when you don't have charges up already has other increases applied to it. If, for example, your passives, etc give you a 50% increase to attack speed already, then you're going from 50% total increase to 106% total increase - and the effect of that difference is not the same as going from 0% increase to 56% increase.

Can you link your weapon(s), relevant gems, and any gear with attack speed mods, and your passive build here, and I'll see if I can explain the calculation.
Also if you could post a screenshot (F8) of your character panel offense tab for the frenzy skill with and without charges that would help as well.

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Ascendic wrote:

0.31 from 0.43 seems like a better bonus.

That seems more reasonable with the numbers you suggested - are you sure you weren't previously looking at the character panel for the default attack rather than frenzy? It gets much less benefit from the charges, so the slower attack time would make sense, and the panel defaults to showing the default attack when opened.

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TheRabbit303 wrote:

Ivory Bow: 1.35 attacks per second
+11% Attack Speed (bow mod)
+9% Attack Speed (gloves mod)
+11% Attack Speed (passives)

Without Frenzy charges, your attacks per second would be:
1.35 * (1 + 0.11 + 0.09 + 0.11) = 1.7685
which would be an attack speed of 0.565451 seconds!

Incorrect.
Note: I'm rounding values as I go here, which will introduce some slight error, but this should be good enough.

The 11% attack speed on the bow is a local mod affecting the base attack speed of the bow. It's 1.35 * 1.11 = 1.5 attacks per second base from the bow.
This base value is affected by all the other increases:
1.5 * (1 + 0.09 + 0.11) = 1.8 attacks per second, each attack taking 0.556 seconds.

With the frenzy skill and four charges, that's
1.5 * (1 + 0.09 + 0.11 + 0.35 + 0.36 + 0.20) =
1.5 * 2.11 = 3.8 attacks per second, or 3.165 seconds per attack, which is pretty close to what you're seeing.

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TheRabbit303 wrote:

Uhm, shouldn't it say MORE attack speed in that case?

Are all local mods multiplicative and not just added to the multiplier?

Haven't seen anything about that in the mechanics thread...

No, it's additive. But it's affecting the base value of the item, not the attack speed of the skill, and is additive with other modifiers to that (which would have to come from more mods). It's saying "The base attack speed for using this bow is 11% faster than a normal bow of this type" - whereas you attack speed increases from passives and skill are saying "your attacks are X% faster" and are affecting the base speed which you get from the bow.
I'm pretty sure that now all local mods which are % increases affect the base values of the item.

Look at the bow, and you'll notice it reports it's attacks per second as being 1.5, because it factors in local increases - that bow's attack speed is increased such that it does 1.5 attacks per second, where an ordinary ivory bow only does 1.25. If the local mod was just additive to the regular attack speed increases, that number would be incorrect, and we wouldn't be able to display the value on the item like that.

That's correct. Not all the local modifiers always worked that way a while back (damage always has), but they were changed to do so partially for consistency, but mostly because if both those swords say "16-28 damage" then they should both do 16-28 damage, rather than those being meaningless numbers which aren't even used in the actual calculation. And it doesn't make sense for two swords which say they do the same damage to give different results because they interact with your stats differently.
The same logic applies to local mods affecting defenses on armour, or to things like attack speed and critical strike chance on weapons.

It an item shows a modified value for some stat because of it's mod, that displayed value is what you get from the item. then your own stats apply to that. Unless something about your stats changes, two items giving you the same value will end in the same result, regardless of how the item's value was improved from the base.

Note that this only applies to local mods - the ones which only affect the item they're on. These are things like increased armour/evasion/ES on armour pieces, and increased attack speed/crit chance/damage on weapons. Those are also the ones which cause that property of the item to be displayed in blue as an updated value.
So you don't really need to understand local vs nonlocal mods, you just need to know that the value the item tells you when you look at it, including the modifier if it's blue because it's modified by the item's mods, is the value you get when you equip the item