Exponential Ports!!!!

[venki]

Hi all,

i dont know if this topic has already been discussed in this forum . i was thinking .... if the port of a bandpass (or any ported) box be such that the length is decided by the helmontz resonator eqn, and the area expoentially increases from throat to mouth (just like horns)(something like the "wicked one" in Decaware ), will the efficiency increase? Will this really work ? I read somewhere that the area in the helmontz equation is the minimum area of the port. Any thoughts on this?

Venki

Ps:Sorry for my grammar

[sreten]

Hi Venki,

simple answer is no it won't work.
The "horn" is far too short to work at bass frequencies.

/sreten.

[Rademakers]

It's a fairly common concept. Of course it doesn't need to be exponential, other hornflares are possoble as well.

The Band Pass Horn ussually is a hybride of a 4th order BP and a hornshaped port. In concept any order BP is possible. But most BPH are 4th order, basically just horns that are to short to fully function as an horn. For example the HD15 from speakerplans:

http://www.speakerplans.com/index.php?id=hd15horn

An other concept is the hybride of a basreflex and a horn:

http://www.iven.nl/fotoarchief/fotoa...ap%20sm18b.jpg

I read somewhere that the area in the helmontz equation is the minimum area of the port. Any thoughts on this?

A basreflex is based on a mass-spring principle, where the Helmholzresonator is the mass and the air inside the box works as an spring. So the area is just a part of the equation to form the mass and therefore in this case you can not aspect the smallest area to be the actual area of the port since the difference is quite large.

Eiter by looking at the basreflex or BP aspects you can predict the response, because they can act as both do. For instance lowering f3 by stacking multiples. The concept does however focus on 50 -60 Hz and up most of times to be effective.

Wkr Johan

[venki]

sreten and Rademakers Thanx for the Quick replys..

Hey Rademakers, you mean this should work ..neways are there any advantages of using the configuration over the conventional bass reflex boxes ? Are there any rules (eqns for eg) for designing such boxes?

Thanks in Advance,
Venki.

[Relax]

So, Rade, could you describe a little more in depth how the Wicked one by decware should/does work?

Wherever I ahev asked this question I have usually gottent the whole "the horn isn't long enough to produce bass" yet I have builat several and all blow my mind.

[Rademakers]

Depends on the design parameters. The horn length needs to be close to 1/4 wavelength of the frequency it's going to support. The low cut off can be pushed down by using a larger rear chamber and/or front chamber at the cost of powerhandling. By putting it in 1/4 th or 1/8 th space the f3 is lowered.

Benefit would be the high efficiency compared to basreflex. Downside is that it doesn't go really low, 4th order BPH make excellent kickbins.

There are some 4th order BPH mainly used in PA that can go pretty low, they're also pretty big as well. The low end extension in those cases mostly depends on the principle of the 4th order BP which has increased efficiency in trade of bandwidth.

"The Wicked One" would behave in a similar way. The length of the horn is long enough to support hornloading down to an estimated 70 Hz (upper bass frequencies). The horn mouth however is way to small to support full hornloaded efficiency down to 70 Hz (each driver takes half).
Anything under that frequency is mostly going on the 4th order BP principle.

@Relax: "It's not a horn". So what, you're still impressed

The sound of a 4th order BP can be very impressive. Same goes for TL, basreflex, 6th order BP, etc etc..
It doesn't have to be hornloaded to be impressive.

@Venki:

4th order BPH's can be simulated with Hornresp (see diy Wiki), same goes for the basreflex-horn-hybrid (that last one should be seen as an short back loaded horn (aka rear loaded).

Wkr Johan

[venki]

Thanks for the info
Rademakers,

Hey by the way will i be able to simulate the 4th order BP box with exponential ports using the Hornresp program???

I read somewhere (in some website) that we can make a horn shorter for the same frequency by:-

finding the mouth area of the horn and dividing it by 5(rule of thumb i think) and reducing the length of the horn to flare till this area.

If this works (i have not tried),this should work more or less like the flared reflex box. am I correct. Any thoughts on this?

The above method would compromise for the efficiency.

Venki.

[Coolin]

Originally posted by venki
Thanks for the info
Rademakers,

Hey by the way will i be able to simulate the 4th order BP box with exponential ports using the Hornresp program???

I read somewhere (in some website) that we can make a horn shorter for the same frequency by:-

finding the mouth area of the horn and dividing it by 5(rule of thumb i think) and reducing the length of the horn to flare till this area.

If this works (i have not tried),this should work more or less like the flared reflex box. am I correct. Any thoughts on this?

The above method would compromise for the efficiency.

Venki.

Nope, hornresp wont simulate this.

"finding the mouth area of the horn and dividing it by 5(rule of thumb i think) and reducing the length of the horn to flare till this area."
This sound more like (if you can) get the mouth placed in a corner you can do this because the walls will extend the rest of the horn.
You would still have the effeciency though.

[venki]

Hi Coolin,

I dont think the 1/5 rule is restricted to coner horns...but not sure...
let me try and find the link...

Thanx,
Venki.

[Rademakers]

Hey by the way will i be able to simulate the 4th order BP box with exponential ports using the Hornresp program???

Yes, you can, but:

Look at it as a (4th order) BPH rather then a 4th order BP with exponential ports. So it's now designed like a horn, meaning you're not going to choose chamber volumes and tune it to a specific frequency.

The design characteristics would be a large rearchamber, a large frontchamber and a short horn (instead of port). The horn doesn't need to be exponential tho. Other horn flares like conical, hyperbolic, catenoidal and about anything in between is possible. Exponential is a good start.

Wkr Johan