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Old 18th May 2009, 05:01 PM   #1
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Default How to determine the best midrange enclosure?

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
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Old 18th May 2009, 05:36 PM   #2
Dr_EM is offline Dr_EM  United Kingdom
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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.
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Old 19th May 2009, 08:36 AM   #3
Henkjan is offline Henkjan  Netherlands
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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 ....
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Old 19th May 2009, 03:11 PM   #4
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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.
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Old 19th May 2009, 06:57 PM   #5
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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
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Old 19th May 2009, 07:01 PM   #6
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I thought the mid range driver's enclosure shape was more about preventing reflections back through the cone than preventing standing waves?
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Old 10th January 2017, 05:08 PM   #7
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Quote:
Originally Posted by Andersonix View Post
I thought the mid range driver's enclosure shape was more about preventing reflections back through the cone than preventing standing waves?
While a main purpose of the enclosure on a midrange is to isolate the back wave from the listener as much as possible, I think if a standing wave frequency is within the passband of the midrange it could be excited to a significantly higher SPL at that particular frequency than the reflected backwaves at various other frequencies - think of a tube resonator on a marimba for example? Though, if you were to put a midrange on an enclosure with no damping materials I think the level of the reflected sound coming back out through the cone will be both significant and negative.

There are dramatic differences, both measurable and audible, to different damping materials to be used inside the mid's enclosure - I have not found a sorce to replenish my favored material which is a natural fiber padding that was used making furniture called "Tufflex". An enclosure lined with Tufflex is remarkably dead - significantly more effective than any other insulation materials I've tried, particularly better than polyfill pillow stuffing!
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Old 10th January 2017, 05:19 PM   #8
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Are we talking midwoofer or mid or even mid-hi ?

crossing points 80hz, 350hz or 800hz are all very different.
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Old 10th January 2017, 06:25 PM   #9
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Several times I have used terracotta flower pots. They have a number of advantages for a mid enclosure. Most are circular and tapered so the standing wave issues are minimized. They are quite rigid. (May benefit from damping with body seal etc...haven't tried that yet.) They come in a variety of sizes. Easily available. They even have a hole "pre-drilled" for wires!

There ARE issues in fixing them to the baffle. If the casting is not completely flat on the top rim take them outside and find a concrete path. Then simply place them upside down and rotate them on the concrete/cement until they are "sanded" to a uniform and flush surface (easier than it sounds). Then you need to glue them to the baffle with a lot of silastic etc. I won't add a lot of data here. A wooden annulus increase the various bonding ares and strength etc. or use wires and those screws with hooks or "eyes" at the top then tie them to the baffle etc. Most people will have their own ideas about what's best for them and their skill set. That's the only messy and time consuming bit. I guess you could just glue the smaller ones but I like a belt and braces approach for the heavier ones.
Cheers Jonathan
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Last edited by Jonathan Bright; 10th January 2017 at 06:30 PM.
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Old 10th January 2017, 09:22 PM   #10
twinter is offline twinter  United States
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Jim Moriyasu published a two issue article in Speaker Builder, Issues 7&8 in 2000, titled, "A Study of Midrange Enclosures". He performed frequency response and subjective testing on numerous midrange enclosure configurations. Some of his recommendations were 1) size enclosure volumes for lower Qts', from 0.5 to 0.7 2) avoid spherical, egg shaped, or cubic enclosures due to internal wave resonances 3) rectangular enclosures with sound damping material performed well.

Also, chamfer the baffle opening rear edge, through which the rear of the midrange mounts, to prevent cavity resonances.
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