midrange enclosure

[fpitas]

I've seen guys use a sturdy large-diameter pipe to the back of the cabinet, and try different amounts of stuffing, and closing or not closing the back of the pipe. That way you can experiment.

[Dave Bullet]

One thing to bear in mind with oversized sealed enclosures is the high pass effect / rolloff at lower frequencies - essentially your F3 shifts up. That's what I found and had to compensate in the crossover since the rolloff began around 300Hz with a box Qtc below 0.5. I was trying to create as much distance as possible to the back wall to allow varying densities of stuffing to absorb backwave. I probably should have also targetted a transient perfect Qtc 0.5 enclosure size.

Another good thing to do is have a removable back on your test box. That way you can effectively run it open back - placed where you normally would and see if there is any acoustic cancellation to take into account in your XO plus how it sounds to you.

[analogkid442]

One thing to bear in mind with oversized sealed enclosures is the high pass effect / rolloff at lower frequencies - essentially your F3 shifts up. That's what I found and had to compensate in the crossover since the rolloff began around 300Hz with a box Qtc below 0.5. I was trying to create as much distance as possible to the back wall to allow varying densities of stuffing to absorb backwave. I probably should have also targetted a transient perfect Qtc 0.5 enclosure size.

Another good thing to do is have a removable back on your test box. That way you can effectively run it open back - placed where you normally would and see if there is any acoustic cancellation to take into account in your XO plus how it sounds to you.

Thank you for making me think about a .5 Q. I will try this out. This will be tri-amped so I will be using an electronic crossover.

[analogkid442]

I've seen guys use a sturdy large-diameter pipe to the back of the cabinet, and try different amounts of stuffing, and closing or not closing the back of the pipe. That way you can experiment.

Yes, this is what I was thinking. Thank you.

[curt_c]

James Moriyasu did a nice study on midrange enclosure and a writeup in audioXpress magazine. Basically he concluded, the bigger the better. Yes, you do need to add stuffing, how much though is usually empirical.

I concur. Consider what the midrange enclosure has to accomplish: A closed enclosure has to attenuate the majority of the backwave energy from the speaker. In addition the enclosure has to minimize any standing wave propagation in the driver’s bandwidth. These are both tall orders that even the most expensive commercial designs still wrestle with, - or just ignore. Since most midrange designs frequency bandwidth put the drivers in the mass controlled region, a typical sealed box modeler is generally not appropriate, as box Q doesn’t come into play, and often results in a very small enclosure.

C

[AEIOU]

I concur. Consider what the midrange enclosure has to accomplish: A closed enclosure has to attenuate the majority of the backwave energy from the speaker. In addition the enclosure has to minimize any standing wave propagation in the driver’s bandwidth. These are both tall orders that even the most expensive commercial designs still wrestle with, - or just ignore. Since most midrange designs frequency bandwidth put the drivers in the mass controlled region, a typical sealed box modeler is generally not appropriate, as box Q doesn’t come into play, and often results in a very small enclosure.

C

If you are interested in reading his articles, I have copies in PDF format and I can email them to you, just send me a Private Message here at the Forum Message Center.

[Wolf]

Those papers are why Jeff's 'Davids' had such a large mid chamber. Basically you allow the midrange to operate 'unhindered' by giving it a sizable volume. It can really change the tonality of the midrange just by using a differently sized enclosure. A while back, dlneubec and I used the same mids in our very different builds, and the sound of the midrange (while xovered differently) was night and day. Not that either sounded bad once the xover was in place, but the sound was markedly different.

Later,
Wolf

[ernperkins]

I remember a dlneubec and Paul Kittinger designed speaker where the mid enclosure was a mini-transmission line with varying densities of stuffing, all to reduce the back wave as much as possible. That was an interesting approach. IIRC Dan designed the mid enclosure.

[PWR RYD]

I remember a dlneubec and Paul Kittinger designed speaker where the mid enclosure was a mini-transmission line with varying densities of stuffing, all to reduce the back wave as much as possible. That was an interesting approach. IIRC Dan designed the mid enclosure.

Hi Ed. If we're thinking about the same design, I seem to remember Paul designed that mid TL and either he or Dan stated one of the goals was to extend the bottom end of the bandwidth.

[PWR RYD]

Hi Ed. I remember that design. I seem to remember Paul or Dan saying they used the TL to extend the bottom end of the midrange's pass band.

[malboro2]

In my first line array, I used separate pvc pipe with a closed back and 4lb/cu ft stuffing. The isolation from the rest of the system was nice.

In any essentially closed speaker enclosure, you want as little sound that goes out the back of the speaker returning from the back of the speaker enclosure to go back through the front of the enclosure. This back wash sound may not be directly perceived by the human ear if its within 30 milli-seconds of the front sound. However, while disregarded by the brain as not being the direct sound, there is NO reason to believe that it is not perceived at all.

Closed pipes resonate at only odd harmonics. When distorted, even a little bit of odd harmonics is noticeable and disagreeable as listening to chalk screech on a board or a cat screeching. But when not distorted, lower numbered odd harmonics control the timbre, and upper numbered odd harmonics control the edge or impact of the music.

A properly designed and lengthy closed tube with 4lb cu inch of fiberglas insulation will absorb nearly 98% of the back sound, so that only 2% of the sound will return to go through the speakers to muddy the direct sounds. This two percent will add additional timbre and clarity rather than soft fatness.

However, you may not be able to hear any of this, depending on your age.

[craigk]

A properly designed and lengthy closed tube with 4lb cu inch of fiberglas insulation will absorb nearly 98% of the back sound, so that only 2% of the sound will return to go through the speakers to muddy the direct sounds. This two percent will add additional timbre and clarity rather than soft fatness.

.

please explain how this works, the 2 % thing. so 1 % and 3 % are bad ?

[Dave Bullet]

Thank you for making me think about a .5 Q. I will try this out. This will be tri-amped so I will be using an electronic crossover.

Are you applying your active crossover in the digital or analogue domain? Can you please tell me the component chain you're looking to use?

Reason being - I'm really intrigued by Charlie Laub's work on LADSPA plug-ins for digital crossovers. Was trying some combinations for a 12", 6.5" and 1" 3 way and it was a lot of fun.

All I need now is a >= 6.1 HDMI or USB based DAC. So interested in whether you are going the hardware or software route for your crossover.

[malboro2]

please explain how this works, the 2 % thing. so 1 % and 3 % are bad ?

It was a generalized rounded number. It might be as little as .5 % or as great as 4 %.. I didn’t actually measure it; I took the number from some other data at the time I was doing the research which was back in 2009, when I had a different name here.

[malboro2]

I've seen guys use a sturdy large-diameter pipe to the back of the cabinet, and try different amounts of stuffing, and closing or not closing the back of the pipe. That way you can experiment.

There is actually some research that suggests 4 lb/cu ft to be the best amount.