Midrange and tweeter enclosures

[murat]

Hi,

Beginner question: I will use the bass in an enclosure but keep the midrange and tweeter seperate. The question is how important is it to kill the radiation of the midrange (~500-5000 Hz) from its back? Since these units usually have sealed backs, can I mount them on a thick piece of cardboard? And the same question for the tweeter.

Thanks a lot. Cheeres,

Murat

[tiroth]

You must deal with the back wave from all drivers, although since most tweeters are sealed back you can potentially ignore them.

How you deal with the back wave (sealed, aperiodic, TL, open baffle) will determine the response and radiation pattern. Midrange and tweeter lend themselves more easily to OB because the size requirements scale inversely with low frequency cutoff.

The simplest design would be to seal the midrange.

I don't know what cardboard has to do with anything; you can build your speakers from aluminum or pasta or whatever you want, but there are obviously some tradeoffs in cost, strength, damping, etc.

[adason]

if you only need to cover 500-5k on midrange it helps to put in on open baffle, baffle does not need to be that big
there are many threads and sites about this
sound is less constrained
that is my experience

[adason]

can I mount them on a thick piece of cardboard?

sure you can
and they will sound like it too!

[murat]

[QUOTE]the size requirements scale inversely with low frequency cutoff.

Yes, that is why I was thinking of cardboard for midrange and tweeter only. Not for the bass. The midrange will need much smaller mechanical damping compared to bass. As the the sealed back of midrange also takes care of back radiation greatly, then, what is wrong with a thick cardboard? If I am not wrong as a baffle it will deal with the diffraction at the boudaries of the speker so it is necessary otherwise I would even skip it. Can one see what is wrong with this picture??

[454Casull]

Originally posted by adason


sure you can
and they will sound like it too!

As long as it doesn't rattle, it won't sound that bad. It's a valid method for quick & dirty OB testing.

murat - what you're describing is an open baffle speaker, which is quite different from a sealed-box speaker. For one, you don't have to deal with internal damping or bracing, which makes it much simpler to design and build. Two, the backwave of the driver won't come through the cone and possibly color the sound in some way. Three, the baffle vibrations will have a much smaller impact on the sound than the vibrations of the walls of a box. Four, the size of the baffle determines the point at which dipole cancellation (6dB/octave, IIRC) occurs, and a larger baffle will lower the rolloff point. Five, the positioning of a dipole speaker isn't the same as doing it for a monopole (non-dipole) speaker.

[RobWells]

I only know of one sealed back mid range speaker. Nearly all of them are open backed.

Rob

[454Casull]

Originally posted by RobWells
I only know of one sealed back mid range speaker. Nearly all of them are open backed.

Rob

? Are you talking about the driver?

[RobWells]

Originally posted by 454Casull

? Are you talking about the driver?

Yes - Isn't he ?

""As the the sealed back of midrange also takes care of back radiation greatly, then, what is wrong with a thick cardboard? If I am not wrong as a baffle it will deal with the diffraction at the boudaries of the speker so it is necessary otherwise I would even skip it""


Rob

[adason]

there is some terminology misunderstanding
you guys have to distinguish if you are discusing the driver or the enclosure

some midranges come with closed back, so called cup, which is designed to limit low frequency response of the midrange driver and make 3 way box construction much easier
in this case it does not matter if placed on open baffle enclosure or into small closed box, frequency response would be the same
offcourse the shape of baffle/enclosure would influence fr response in part....