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Old 27th February 2007, 07:18 PM   #1
Bogwan is offline Bogwan  United States
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Default Question regarding midrange enclosure size?

Iím thinking about using a Seas MCA15RCY (H1252) midrange in my latest project, and I have a basic question for which I canít find the answer. In a sealed cabinet with a Qtc of 0.7, the corresponding Vb for this driver is only 1.5 liter. If this midrange is mounted in a much larger box, for example a 10 liter dedicated MT enclosure, would it have any deleterious effects on performance? Common sense tells me that placing the rear wall of the midrange enclosure as far away as practical, or perhaps deleting it altogether, is desirable to minimize reflections back to the cone, but the calculations seem at odds with this assumption. The midrange will be crossover over around 350 Hz, LR2. Thanks in advance.
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Old 27th February 2007, 07:21 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

With what bass unit and baffle size ?

The answer does vary depending on circumstances.

/sreten.
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Old 27th February 2007, 08:09 PM   #3
Bogwan is offline Bogwan  United States
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Quote:
Originally posted by sreten
Hi,

With what bass unit and baffle size ?

The answer does vary depending on circumstances.

/sreten.

The bass unit will consist of a Seas CA26RFX (H1305) driver in a 70-liter ported cabinet tuned to 34 Hz. The baffle width of the bass cabinet will be 13 inches, but I was thinking about putting the MCA15 in a seperate MT cabinet (that will sit on top of the woofer cabinet) having a width of 8 inches with rounded edges. Unless of course, you'd like to talk me out of this plan.
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Old 27th February 2007, 08:41 PM   #4
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Hi,

Don't count on my answer here because I would also like to confirm my understanding and am hoping the experts can point out my errors if any.

The enclosure serves as a high pass filter, so we select the right size for the woofer to come up with the right response, such as Q, F3, etc.

Since you are building a 3-way, you would need the right size for the woofer. As for the mid range, you would have an electrical filter in your XO network to control the response unless you want your mid range enclosure to serve as a high pass filter.

I prefer to make the midrange enclosure to be very large so I don't need to worry about the high pass effect of the enclosure. I would use the XO network rather than the enclosure size to control the response. This is because in a small enclosure the "air spring" is very stiff, and I suspect it is very non-linear, while the response from the XO network can be a lot more linear. In a large enclosure, I can stuff substantially more amount of accoustic damping materials to kill the effects of the standing waves.

So I don't normally think we need to worry about the size of the midrange enclosure. I would just make it as large as practically possible. Of course, long parallel walls within a large enclosure lower the resonance frequencies, and at low frequencies the damping materials are un-effective. The way to deal with it is to partition the internal space. Matrix damping is one of the ways to deal with the problem.

Regards,
Bill
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Old 28th February 2007, 01:25 AM   #5
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Considering most mids don't reproduce low frequencies i would think the compliance of a large enlocure wouldn't have any effect? Also tuning for a particualr Q may not be needed for a mid for the same reasons. So I guess I'm the oposite of HiFiNut, put them in a small enclosure and stuff it. I'm pretty new to this so I could totally wrong though
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Old 28th February 2007, 09:44 AM   #6
sreten is offline sreten  United Kingdom
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Hi,

For that bass unit you will need to attenuate the MC15RCY due to baffle step effects.

If this is an L-pad work out the parallel value of the two resistors.
This is your source impedance.

Plug into "New Qts with Series Inductor " here : http://www.mhsoft.nl/spk_calc.asp

You no longer need 1.5 L for Q=0.7, you need more.


/sreten.
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Old 28th February 2007, 10:48 AM   #7
mrtech is offline mrtech  Israel
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hi
run it in bass box pro or other design software
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Old 28th February 2007, 02:19 PM   #8
Bogwan is offline Bogwan  United States
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Quote:
Originally posted by sreten
Hi,

For that bass unit you will need to attenuate the MC15RCY due to baffle step effects.

If this is an L-pad work out the parallel value of the two resistors.
This is your source impedance.

Plug into "New Qts with Series Inductor " here : http://www.mhsoft.nl/spk_calc.asp

You no longer need 1.5 L for Q=0.7, you need more.


/sreten.
Sreten, thanks very much for your advice. However, I don't quite follow your reasoning. Are you suggesting that I use an L-pad to attenuate the MCA15 or an RL contour network? The larger issue I'm considering is whether attenuating the MCA15 is a good thing at all. Perhaps I should use two woofers in parallel to avoid or reduce the level of BSC needed. I would like to keep the cabinet volume around 70 - 75 liters. Any woofer suggestions?
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Old 1st March 2007, 06:52 AM   #9
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Bogwan


Sreten, thanks very much for your advice. However, I don't quite follow your reasoning. Are you suggesting that I use an L-pad to attenuate the MCA15 or an RL contour network? The larger issue I'm considering is whether attenuating the MCA15 is a good thing at all. Perhaps I should use two woofers in parallel to avoid or reduce the level of BSC needed. I would like to keep the cabinet volume around 70 - 75 liters. Any woofer suggestions?

Hi,

Depends how you intend to crossover bass to mid and how you
intend to implement baffle step compensation. If you crossover
lowish then you'll have to put BS correction on the MCA15RCY.
Then your original bass unit unit would likely be fine.
But you would then have near subs+sats, not really a 3-way.

3-ways are very tricky things to design.

/sreten.
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