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Minimus 7 Loudspeakers - Measurements

slightly off the current topic, but: how much is TOO much acoustic batting/damping material/wadding/fiberfill/whatever you call it in these? perhaps the better question might be: what is the 'correct' or recommended amount?

THANKS
 
1" thick on the walls but not close to the woofer driver. You could put a bit more behind the tweeter an extra inch or two.

Damping lessens mid bass cavity resonances in the box, makes the box appear slightly larger at the fundamental resonance (Fc), and lowers the Q (Qtc) at Fc.

These small boxes need the Q at Fc to be a bit high to get the most output there and this is the reason to not overstuff.
 
parts order

Just took delivery of a silver pair of Minimus 7's. Pretty rare in the UK from what I can find. They sound pretty good but do need some balancing between the tweeter & woofer.

So I'm gonna order me some parts but that raises the question - Should I buy several of the resistors & capacitors as they are +/- 2% & 5%? or would the possible maximum differences make no audible difference?

Thanks in advance from the UK
 
Trip to the thrift store today netted a nice pair of black mini 7's for $5.

Can't help but order parts to upgrade 'em, my 7w's sound so good . . .
 
Would increasing the cabinet volume improve the speaker at all? Or would I have to go back to square one regarding the crossover?
 
I think if you keep the baffle width and driver spacing the same, the box volume could be optimized for the woofer, and the crossover won't need tweaking. Your next step is to model the woofer in WinIsd or similar if you have not done so. It might even be in this thread.

I seem to remember someone made a custom cab for these.
Looking forward to seeing what you come up with!
 
I was thinking having the woofer in its own cabinet, and the baffle extending up above the cabinet to hold the tweeter. I could keep spacing the same, and width the same, then just deepen the cabinet.
I tried an online calculator for a rough estimate, and got interesting results for a ported box, slightly bigger at 2.27 liters with a 1" by 4.32" port.
f3=75hz and fb=71hz
 
Sir.Byrd said:
Would increasing the cabinet volume improve the speaker at all? Or would I have to go back to square one regarding the crossover?
Click to expand...

The crossover frequency is far enough away that you would not have to change it.

This is a standard sealed box system and therefore the woofer (if the front baffle were mounted flush to a wall) has a 2nd order high-pass transfer function in the bass. The response is completely defined, for small signal drive where distortion is low, by Fc, Qtc, and driver efficiency.

Fc is determined by cone mass and the combination of the suspension stiffness and the air spring. A bigger box lowers Fc by providing a more compliant air spring and Qtc goes down because of the change in reactance at resonance.

The lower Fc provides more bass extension but the lower Qtc reduces the output, slightly, around Fc. The problem with a very small system such as this, is that the woofer does not have much Xmax, and more importantly volume displacement, which means that the woofer will easily overload with heavy bass lines at high output. A higher Fc reduces Xmax below Fc since the rolloff is faster and less Xmax is required at higher frequencies for a given SPL. The higher Fc with higher Qtc will have more output and more displacement at Fc but it is the lower frequencies that will tend to overload the driver faster.

Fc in the unmodified system is somewhere over 100 Hz and if the source material had no content below Fc then in this particular case the higher Fc system would have more displacement. But most music has lots of content below 100 Hz and the increased extension with a bigger box and lower Fc would then lead to increased displacement.

Bass boost also increases displacement and if you find that you can get enough level with some bass boost then you might want to try a bigger box. Keep in mind that as you increase the box size Fc will asymptotically move closer to the driver free air resonance (Fs) and it takes an infinitely large box to reach Fs. There is a point of diminishing return in increasing the box size.
 
Sir.Byrd said:
I was thinking having the woofer in its own cabinet, and the baffle extending up above the cabinet to hold the tweeter. I could keep spacing the same, and width the same, then just deepen the cabinet.
I tried an online calculator for a rough estimate, and got interesting results for a ported box, slightly bigger at 2.27 liters with a 1" by 4.32" port.
f3=75hz and fb=71hz
Click to expand...

Moving to a vented system greatly increases the power handling around Fb, but below Fc you basically have only the suspension stiffness to limit the excursion, the port acts as a leak. I generally prefer vented systems but especially when they are large and low tuned say 20- 35 Hz.

I'd say try it, it is the only way to learn, but perhaps build a quick and dirty cabinet to try out different ideas. Also, don't be afraid to throw out the book and tune lower. You might try a cabinet twice as large as you plan tuned to 45 Hz. Low tuned vented systems tend to have an early roll off shape closer to closed box systems but with much more power handling around Fb because the port does the work and the cone displacement theoretically goes to a minimum. A double woofer MTM or MMT version in a 10 liter cabinet might be very interesting.

You might have more satisfying results experimenting with a system with an 8" or larger driver since it will generally have much more volume displacement.
 
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I will think about all of this and come back to the idea in a few weeks when I have some money to spend on parts.
 
So the $5 pair of mini7's turned out to have blown tweeters. And exploded tweeter caps. First time for me but my AV contractor friend says that he sees that all the time, but mostly in DJ systems.

It didn't take me long to figure out that buying replacement tweeters for two minimus 7's costs approximately what a pair of used working minimus 7's costs on ebay.

And then i found these:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280719098460

Anyone want to place any bets on how well they match the ones i took out? fwiw the pair I bought is 40-2030C, made in japan.
 
Pete,
Do you think WinIsd gives a reliable estimation of how much power the woofer will handle at given tuning/alignment?

Thanks for the info.

Pete B said:
Moving to a vented system greatly increases the power handling around Fb, but below Fc you basically have only the suspension stiffness to limit the excursion, the port acts as a leak. I generally prefer vented systems but especially when they are large and low tuned say 20- 35 Hz.

I'd say try it, it is the only way to learn, but perhaps build a quick and dirty cabinet to try out different ideas. Also, don't be afraid to throw out the book and tune lower. You might try a cabinet twice as large as you plan tuned to 45 Hz. Low tuned vented systems tend to have an early roll off shape closer to closed box systems but with much more power handling around Fb because the port does the work and the cone displacement theoretically goes to a minimum. A double woofer MTM or MMT version in a 10 liter cabinet might be very interesting.

You might have more satisfying results experimenting with a system with an 8" or larger driver since it will generally have much more volume displacement.
Click to expand...
 
I don't know but maybe you can make a deal with Sir.Byrd and send him the woofers so he can build a 2.5 way.......:D

Then grab another stock pair.

Just trying to cause trouble.


ericj said:
So the $5 pair of mini7's turned out to have blown tweeters. And exploded tweeter caps. First time for me but my AV contractor friend says that he sees that all the time, but mostly in DJ systems.

It didn't take me long to figure out that buying replacement tweeters for two minimus 7's costs approximately what a pair of used working minimus 7's costs on ebay.

And then i found these:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280719098460

Anyone want to place any bets on how well they match the ones i took out? fwiw the pair I bought is 40-2030C, made in japan.
Click to expand...
 
skywave-rider said:
I don't know but maybe you can make a deal with Sir.Byrd and send him the woofers so he can build a 2.5 way.......:D

Then grab another stock pair.

Just trying to cause trouble.
Click to expand...

I would probably just build a matching subwoofer if anything.
I have two spare woofers already though, I need to glue the magnet back on to one of them.
 
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