simulating variovent with MJK sheets?

[Henkjan]

I am designing a pair of speakers (using the FR125) for my 11 year old daughter. since her wish is that they should not be too large (yes, this sh*t starts already at a young age), I thought of making a aperiodically damped (aka variovent, aka controlled leakage, etc) CB. (I first proposed the miniOnkens, but even these were considered too large)

a thought came in my head to use MJK's mathcad sheets for this, using the BR sheet and then "applying" damping material in the port to simulate the variovent.

anyone has ever done this? @MJK: do you expect this to give good results? and related: in your sheets you give 1 lb/ft³ as max damping material density, why's that?

 

[gurley123]

I'm not sure about simulating aperiodic vents. I've yet to use the mathcad sheets. However, according to the last few posts by Planet 10, many are now perfering the 4.5 liter aperiodic cabs for the FR125. These are a bit smaller than the MiniOnkens.

Maybe she'll like those?

 

[Henkjan]

that should give a starting point as well as a fall-back position... thanks.

I'll start the design on the speakers in a week or so (want to finish a pair of table-top TLs first) so if anyine can add some thoughts on this, please do so... and if I'm the 1st to try this, I'll report back here about the results

 

[Henkjan]

Maybe she'll like those?

the design is more or less agreed apon, it will not be the average sqare box....

 

[gurley123]

I'm glad it worked out for you.

11 yrs old and already getting a good set of speakers. That's too cool. My little sister is 17 and I don't think she's heard a decent stereo yet (we never lived in the same house, or else she would have.)

I'm toying with the idea of making her a cool little mini system with some cheap fullrangers and a tripath amp. Looks like it could be fun.

 

[Henkjan]

well, I have to admit it was the special design I have in mind and the FR125's good looks that made here give in (I had been trying to build a pair of decent speakers for her for a long time already, but she's not realy into music yet), but I'm sure she'll appreciate the result when they are ready

 

[maxro]

a thought came in my head to use MJK's mathcad sheets for this, using the BR sheet and then "applying" damping material in the port to simulate the variovent.

anyone has ever done this? @MJK: do you expect this to give good results? and related: in your sheets you give 1 lb/ft³ as max damping material density, why's that?

The 'ported box" work sheet allows densities over 1lb/ft3 in the port section. IIRC, Planet10 had mentioned some reservations about using this method for aperiodic simulation, but I think it to be the best solution thus far. I guess the question is: what is the stuffing density of a Variovent?

 

[Scottmoose]

Depends on what's required. You can sim aperiodic well enough using Martin's sheets.

 

[Henkjan]

OK, let's fire up the quattro uh mathcad

 

[Scottmoose]

You've been watching Ashes to Ashes haven't you?

 

[gmilitano]

I've pulled together some information on Aperiodic Speaker Enclosures that should serve as a good starting point.

The variovent datasheet does not list a density of the vent.

Typically the goal is to flatten the impedance curve and the best way to do this is trial and error with impedance plots. With a smaller driver, I suspect you will want some low freq help.

 

[Henkjan]

thanks for the link, nice bedtime reading

 

[GM]

Richard Small's take on it:

GM

 

[GM]

G.A. Briggs altogether different take:

GM

 

[bjorno]

FYI, For you who need the referenced figure 7-4 in GM: s aru.gif picture.

b

1(1)

 

[Henkjan]

again: thanx!

 

[Henkjan]

so, with the encloser determined by the design and the size of the driver at ~4 liter, and a small BR tube I had lying around as starting points I mod-d the BR sheet to have stuffing in the port and increased the amount of stuffing until the response was flat

 

[Henkjan]

this is with 5 lb/ft³ stuff dens in the port, which means I'll have to cram ~20 grams of BAF into a 1" 9cm long port

the small ripple just above 700Hz is from a port resonance there, but since I will place the port at the rear I do not worry too much


the effect of the stuffing is best seen in the impedance plots, here the one of the damped port enclosure

 

[Henkjan]

and this is in a 4liter cb

 

[gmilitano]

Did you sim an impedance plot for a sealed box?