Open Baffle question.

[Aurality]

I built a pair of lampizator p17 like the photos below:




I am adding a pair of subs to the setup and was wondering if it would be
possible/sensible or what problems I would expect to hear If I placed
the subs on top of the open back box - behind the baffle effectively
almost blocking the back of the mid and tweeter drivers?

I understand this would interfere with the back wave of those drivers?
or maybe just the mid since I am using a ribbon tweeter with sealed
back as appose to conventional driver...

Is it a recipe for disaster? I am only tempted because the subs I have in
mind are a perfect fit...


Secondly.. assuming the first placement is an absolute no no...
if I placed the same subs approx 2" away from the backs of the drivers
so there was still gap all the way round, would that be a bad move too?

Excuse my vocabulary.. But I hope you get the sentiment of my question
In a nutshell I just wondered if it would completely ruin the sound.

[Richard Ellis]

Like this??

No you shouldn't, the pressure wave from the sub will hit the cone of the Mid setting it in motion..........
Note the example you have given, the Sub is near to the floor to better "couple" to the floor...and the distance from the subwoofer to the Mid cone is a measured precise distance. The output of the Sub will be diminished if it is "lifted" from the floor.....the backwave of the Mid "should" be unobstructed.

__________________________________________________ ____Rick........

[Aurality]

Thanks Richard,

That's what I needed to know. Lots to learn!

[Aurality]

Oh I diden't see the pic.
Yes, positioned like that but I forgot to mention that the sub has a downward firing driver (BK Monolith)

[jerome69]

It is a bad idea because you create a cavity resonance in the midrange. You will ruin the sound.
Why do you need a sub ? You already have a 15"

Read this : Greencones
I think this loudspeaker needs a serious redesign of the crossover ...
If you want more bass, you should increase the woofer inductance to 15mH.
You can use this crossover :


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[Aurality]

Thanks Jerome,

I actually built mine with 18"

But since I listen to a lot of reggae I am missing a lot of the real low stuff..
it's there, down to 40hz but a lot quieter in that lower range so I probably need some EQ to help it along..

What frequency will it cross over with a 15mh inductor?


*edit* I think I worked it out... approx 85Hz?

[jerome69]

Originally Posted by Aurality

But since I listen to a lot of reggae I am missing a lot of the real low stuff..
it's there, down to 40hz but a lot quieter in that lower range so I probably need some EQ to help it along..

Yes

Originally Posted by Aurality

What frequency will it cross over with a 15mh inductor?
*edit* I think I worked it out... approx 85Hz?

No, 300Hz The 15mH helps to go lower.

[ashok]

Might be better to use an active drive for the sub and use an electronic crossover ( passive + active) to get you the bass lift and HF rolloff respectively. It should be better than just an inductor with an iron core .

I've done this and it sounds quite good. Didn't try the (passive) inductor only as I cannot get such high values easily.

[Aurality]

Thanks Ashok, I'll look into that if I have no luck with the passive!


Thanks Jerome, How come when I type that inductor value into this
calculator Crossover Design Chart and Inductance vs. Frequency Calculator(Low-pass)
I get a value of 84.89Hz for that inductance value (15mh)?

Sorry, Like I say lot's to learn here.

[picowallspeaker]

That chart is for 1st order (only L)
For 2nd order (L+C) , 15mH plus 68uF gives about 300Hz corner frequency