How to determine the best midrange enclosure?

[retroman]

Hi all,

I've not seen much in the way of rules for determining the size of midrange enclosures where a woofer is present. Since many midranges are open back I understand they need to be separated within their own chamber (along with tweeters) but how does one choose the optimal size? Should they be treated like a small woofer? Should dampening material be used? Browsing at some enclosure plans I am confused as most don't explain how the volume of these separate midrange/tweeter chambers were calculated. I figure their size must have some kind of effect on sound. Your advice and opinions are apreciated!

Retroman

[Dr.EM]

Basically you can treat them like a small woofer, full TS parameters should be available and when used in a box simulator (ie. WinISD) will give you an appropriate sized enclosure. Sealed is normally always used with mids, not ported, though closed and open ended TL's can work very well as well as open baffles. Usually a Q of 0.7 is used for sealed, this is what the sim will normally calculate initially. A higher Q will lead to peaking (smaller box = higher Q).

Damping material should certainly be used, acoustic foam may also be implemented. Sometimes people like to curve the walls or add irregular patterns to the inside of the enclosure with an aim to break up standing waves.

[Henkjan]

the shape of the mid enclosure (internal shape I mean) is also important, if you can avoid the sqare box please do so. iirc there was a thread on this subject ....

[Shefffield]

Cheers,

as far as I know midranges are not to be treated like small woofers. Different to woofers midranges are never used near their resonance frequency, but usually at least one octave above that - preferrably even higher.

So the Q in the vicinity of fb is of no interest and can be ignored. What should not be ignored is the frequency of fb in the planned enclosure. Make sure it keeps a safe distance from the frequency band where the mid driver is used.

Additionally, a small, asymmetrical (as Henkjan stated already) enclosure is to be preferred to minimize unwanted effects standing waves. Be aware though that asymmetrical walls will not affect standing waves, the only cure here is to move them out of the used frequency band by minimizing the cave behind the cone.

Be careful with damping material if you use a high efficiency midrange with a very thin, lightweight cone. These are said to be very sensible for mass coupling.

I hope this helps,
Axel

P.S.: I myself am a friend of no enclosure behind the mid driver.

[planet10]

It is not often that i'm designing a midrange enclosure, but a mid-tweeter enclosure could be considered the same thing.

I treat it just like a bass driver in some senses, but am not often aiming for as low an extension as possible. A smooth controlled roll-off and control of impedance are my goals, http://www.diyaudio.com/forums/showt...52#post1827952

For this reason i often like to execute a midTL (damping procedure is changed over one aimed at bass)

The LF cutoff of a midrange enclosure can be used as part of the crossover, For instance a sealed box with a Q=0,7 mated with an electrical 2nd order butterworth will give you a 4th order Linkwitz-Riley XO. It is a challenge to execute a passive XO around the sealed box resonance peak.

dave

[Andersonix]

I thought the mid range driver's enclosure shape was more about preventing reflections back through the cone than preventing standing waves?