Open Baffle question.

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

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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.
 
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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........
 

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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" :eek:

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 :
An externally hosted image should be here but it was not working when we last tested it.


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Thanks Jerome,

I actually built mine with 18" :D

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?
 
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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


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.
 
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.
 
Actually the low crossover frequency like 85 odd hertz is probably correct. It is a 6dB per octave filter and plotted on paper will show a roll off to the right of 85 Hz.
If you look leftwards going from say 300 Hz to 85 Hz it looks like a bass boost. The catch here is that you loose sensitivity .
The difference between this and an active circuit is that the 2.83 V sensitivity with the active circuit will give the same SPL at 300Hz as the stock speaker. But the amp must be capable of providing the headroom required for the dB of bass lift. In a passive circuit the 300Hz sensitivity will be much less than the stock speaker sensitivity. But then it avoids additional electronics and a power amp.
 
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i couldn't too highly recommend the inexpensive active cross-over Behringer CX3400 (I think). Amps are cheap, lots at the local second-hand store. By my thinking, a 1980 amp* is a perfect match to the world's greatest 2010 speaker.

For low bass, lots of reasons to mix it and create one great sub. Lots of reasons to put it in a corner.

For my taste in sound, I'd sure NOT want to end up with any box resonances (or room resonances) to dove-tail with bass peaks on recordings. That way you have a (small) chance of having great big bass without one-note boooom.

You might be surprised at how few recordings have much stuff at 40 Hz (and not even those occassional brief but important moments). Loud drums at 80 Hz sound quite low, organ pipes too.

*I was tempted to say "1960" but didn't want to be controversial.
 
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Thanks Guys,

Currently the bass sounds great on stuff like acoustic double bass etc..
but say if I play some reggae, it sounds like I am just hearing harmonics.

Just ran a slow test sweep, and I can hear signal down to 30hz (Again don't know whether is this just harmonics)
Interestingly though, the tone went almost silent - Huge dip from 150Hz - 160hz Anyone know what might be causing that?

I have just bought a test mic so when it arrives I'll hopefully be able to post some graphs - more reliable than me trying to describe.
 
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Many truly discouraging large, sometimes narrow, peaks and dips due to room resonances below 200 Hz.

Mic testing will drive you nuts.

But I've recently started using a new system that does work nicely. A fellow named Markus posted a link on this forum to a download of white noise 400 Hz and south. You just kind of wave the mic around where your head is (no need for precision) and watch results cumulate for 30 seconds on a freeware computer oscilloscope spectrum analyzer. That's it.

I think white noise will give a rising power with lowering freq (as compared to pink which is flat). But that really doesn't matter, even if you notice it, since there is no such thing as flat except to mics.

And then you can use the spectrum analyzer to see what is on your reggae recordings. There's no fooling a spectrum analyzer, even a free one. Clear as day.
 
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aurality, you might want to try wiring your mids and woofers in reverse phase.
lukasz suggests doing that if there is a dip in the crossover region.
you should be able to get enough bass out of 18" ers.
instead of spending extra £ on going active you might also try separating the woofers from the main speaker, put them on larger baffles and move them closer to the corners of the room.
mids behave much better when on separate baffles as added benefit.
 
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