Brahma or Shiva Iso? (1 Viewer)

[AjayM]

Hmmm, what about an Isobaric shiva design with a set of PR's? Say the Adire alignment, which is normally 85 liters...halve it down to 42.5 liters. Is it possible? Maybe have to add to much mass to the PR?

Andrew

 

[Brian J Dupuis]

Nah, I didn't use any, really. I think I used PE Box, from Parts Express, to arrive at the dimensions. Just a sturdy cube with some 2x2 cross-braces and too much Gorilla Glue.
As you may have noticed, the driver is on sale now for $100, making it a steal. There are some good buys on PE sub amps, also.

I hadn't noticed the price, thanks for the heads up... I believe I'll place an order in the morning. Are any of the PE amps recommended? I think I saw you mention that you went with the Adire amp because it was sealed... are none of the PE amps sealed? I'd like to have the amp mounted on the sub if possible and don't want to wind up with an inappropriately featured amplifier if I can help it.

 

[Jack Gilvey]

Hmmm, what about an Isobaric shiva design with a set of PR's? Say the Adire alignment, which is normally 85 liters...halve it down to 42.5 liters. Is it possible? Maybe have to add to much mass to the PR?

I'm having trouble modeling that properly, but it could come down to how much mass the PR can handle, as you point out. It should work better than with a vent, though, as vent lengths can really get out of hand with an isobaric.
In much the same way as decreasing box size requires a longer port for a given tuning, more mass is required for a PR as Vb decreases.

 

[ThomasW]

Here's a graphic to illustrate the need for EQ with high excursion drivers. This is Tom Nousaine's measurement of the Stryke HE-15. The 1203, 1503, 1803 will all have a somewhat similar plot.
Link Removed
Look at the bottom of the plot where it says "Log-Frequency-Hz". Find the 100.0, then count to the left 3 lines and look at the curve. This is a peak at 70Hz. See how steep the line is climbing from from 30Hz. This is a result of the voice coil inductance.
Parametric EQ is needed to flatten that peak. It's the same situation with the 03 series drivers.

 

[Brian J Dupuis]

Look at the bottom of the plot where it says "Log-Frequency-Hz". Find the 100.0, then count to the left 3 lines and look at the curve. This is a peak at 70Hz. See how steep the line is climbing from from 30Hz. This is a result of the voice coil inductance.

Fantastic explanation, Thomas, thank you. I suppose people are willing to add the extra power and equilization necessary because these high excursion drivers provide significantly more output than comparably sized lower excursion drivers, yes? That does make sense now.
I think I'll stick with my current plan of the Dayton DVC and the PE 250W sub amp. Keep it simple for my first project. Besides, DIY projects aren't static results, they're lifelong journeys, right? I'm sure I'll be in here next time looking for an IB design to go in my crawl space .
Thanks again guys! I'll provide progress reports when I get moving on the construction.

 

[Robert_J]

Though I see no way to order it with the boost defeated, they have a PDF file describing the technique.

According to PE Paul and others at the PE Tech Talk Board, the new amps come with the boost defeated. I have two at home right now but haven't checked.

-Robert

 

[Jack Gilvey]

Fantastic explanation, Thomas, thank you. I suppose people are willing to add the extra power and equilization necessary because these high excursion drivers provide significantly more output than comparably sized lower excursion drivers, yes?

Thomas' explanations are always thus.
I see two things happening with these high-excursion drivers. First, the huge motors tend to have those huge inductance peaks, the effects of which can be seen in Thomas' graph. Second, the massive, stiff suspensions necessary to keep everything aligned during the huge excursions of which these drivers are capable can raise the Fs of the drivers to the point where they might need some eq boost down low, depending on the desired extension.

 

[Brian J Dupuis]

I see two things happening with these high-excursion drivers. First, the huge motors tend to have those huge inductance peaks, the effects of which can be seen in Thomas' graph. Second, the massive, stiff suspensions necessary to keep everything aligned during the huge excursions of which these drivers are capable can raise the Fs of the drivers to the point where they might need some eq boost down low, depending on the desired extension.

But once properly powered and eq-ed, they pound pure hell I guess. Maybe I'll get some spare time later and try one of these beasts out too, depending on how this one goes. I'm sure I could talk my neighbor into buying my "old" Dayton sub.