midrange enclosure sizing

[jimbones]

lol, ok let me clarify as I may not have been clear. I have existing boxes that I am using for the mids. the tweeter is mounted on a bracket above it. Forget the woofer, I am using something else temporarily just to have something to listen too and it isnt half bad either. the other reason I was trying to stay low on the HP to the mid was I wanted to stay as low as possible on the vocal range. I can certainly go higher 350hz.

[Wolf]

More circuitry is not really something I've ever had to use for BSC unless shaping the response more. It's not normally required.. This can also cut component cost and maybe help with low impedance issues. Don't forget a large coil can induce a bump at Fs of the woofer, and a higher xover can alleviate this issue.

I was under the impression you hadnt built them yet.

Just don't pack in the stuffing as the life can be reduced to where they sound dead.

Wolf

[jimbones]

Wolf I say 250-285hz because that is where the baffle step occurs. I usually try to design around that since I dont have build extra circuitry. so it could be closer to 285hz. Yes I do plan the larger enclosure and I do use lots of damping material. I am using a 0.25cu ft now and it sounds really good.

[rpb]

I agree! I like a very roomy mid chamber, and prefer to add lots of dense fiberglass to absorb as much of the back wave as possible.

[Wolf]

The larger the chamber you can give the mid-range the better. It will sound like it is unhindered and more open. Damping is key but usually a larger size enclosure will not involve peaking as it rolls off.

I really think you can xover higher to the woofer, like 300-400Hz, and keep the mid-range from more IMD and strain. You'll find it easier to blend the weight in the midbass too.

Wolf

[donradick]

Thanks dude. A very polite response to my post. I think we agree on the science.

[jimbones]

In my case I am crossing over at 250 hz. The Fs is 35hz. I am looking at a 0.2 cu ft cabinet. I dont need the cabinet to boost the low end as I am not going that low. As I see it I should be good unless I am missing something. When the drivers are mounted in the final baffle I will get frd measurements to do the final xo design.

[andy19191]

And in many mid designs for a 3 way, you will crossover the mid an octave or more above Fs.
But I think that you inaccurately described what a box does.

Although I thought about including it I didn't describe the function of a midrange enclosure. I was responding to the OP stating "I have to run a sim in a tool just as I would a woofer" and pointing out that if this mattered it would be a less than optimum design and giving the reason why. Of course a quick sim to check it doesn't matter may be wise but that wasn't how I read the OP's post.

To address what may be a source of confusion, a sealed cabinet extends the low frequency response by using a resonance involving the effective mass of the cone and the stiffness of the trapped air plus that of the suspension. A ported box uses this resonance and a second one due to the mass of the incompressible slug of air moving in and out of the port and the stiffness of the trapped air. These resonances increase the frequency response at low frequencies but at the cost of how well the radiated sound follows the input signal. With a midrange in a 3 way one usually has the opportunity to push such resonances well below the passband and increase the fidelity of the sound. I was not referring to resonances of the air within the cabinet volume.

Thanks for the response though which brings out a potential source of confusion involving terminology, T/S parameters and physics.

[billfitzmaurice]

Yes, modeling using T/S parameters is only accurate within the region of pure pistonic response, which is perhaps two octaves above and below Fs. It's not going to show, for instance, break up mode. But I wouldn't go so far as to say that you'd want to cross to a mid an octave or more above Fs. Most of the reason for using a midrange driver is dispersion, and more often than not you want to cross over to it as low as its displacement limited output will allow to take advantage of the wider dispersion it will give compared to the woofer.

[donradick]

Dude, I am not arguing with you, but first of all, aren't the T/S parameters only defined at Fs (or Fb) and only applicable say an octave above and below that value? So if you you run a particular mid-woofer through a wide range of box volumes, the response will not vary say, 2 octaves above Fs.
And in many mid designs for a 3 way, you will crossover the mid an octave or more above Fs.
But I think that you inaccurately described what a box does.
1 -- it absorbs the back wave, otherwise you get destructive interference with the front wave
2 - it adds a springiness support for the woofer
3 - if ported, the port has output that increases low bass (around Fs)
Other than a Transmission line, you do not want any box resonances

[andy19191]

thanks . That answers my question in that I have to run a sim in a tool just as I would a woofer. Thanks Much.

If sound quality is important then generally no you would not want to be in a position where this matters. A midrange enclosure should be large enough so that the crossover controls the response and not the volume (or port in extreme examples). The reason is that a sealed or ported box is using resonance/s to boost the response and so there is a price to pay in terms of degraded transient response. This can be avoided by simply making the volume large enough.

[billfitzmaurice]

As you can see bigger in this case isn't better, as sensitivity within your intended pass band is lower. All a larger mid box does is to rob volume from the woofer chamber.

[billfitzmaurice]

Considering how small the panels are for a mid enclosure I doubt that the difference between 1/2" and 3/4" would be audible, if even measurable.

[fpitas]

And I'll add, whatever the response from the box size, you'll end up re-shaping it in the crossover, so it's pretty non-critical.

[donradick]

Off topic, but germane to mids in three ways.
I've made a couple of three ways using 1/2" BB ply for the mid enclosure.
Someone did a test recently and found that 3/4" BB worked much better for isolating the mid.