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Old 27th January 2007, 12:42 AM   #21
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Old 27th January 2007, 12:43 AM   #22
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Old 27th January 2007, 12:44 AM   #23
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Old 27th January 2007, 01:00 AM   #24
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Greets!

Looks good to me! I'm curious though why your specs match the manufacturer's except Vas and Le, which is much lower/not listed: http://www.mach5audio.com/index-2.html

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Old 27th January 2007, 02:32 AM   #25
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Hi GM,
Le is not used at all in the simulations and I ran a check to see if the published MJ-18 parameters are consistent, they weren’t. Read the submitted document.

b

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Old 27th January 2007, 03:35 AM   #26
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Greets!

Understood, I just wondered where you got the 2.6 mH value, like calc'd it from the simmed impedance plot or just picked a value. WRT to mathematically resolving T/S specs, as you know, changing Vas alone isn't going to work in this case, so when doing box, and especially pipe, alignments using published specs, working with whatever makes it biggest usually works best overall.

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Old 27th January 2007, 07:05 AM   #27
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GM,

Your observations are correct; the plain truth lies somewhere else between all these interacting numbers.

I iterated Vas, Mms, Cms, BL and the Sensitivity both for the 4 and 8” versions and came up with two probable candidates that I thought were too optimistic in the first place, the Sensitivity and the BL-factor.

Then I hesitated because the Sensitivity is normally only valid for mid frequencies or only important above the normally chosen crossover frequency’s, not of much use for a sub TL.

When the Sensitivity that is dependent of Vas, (I thought fs and Qes was ok) I chose the former to be too high and by lowering, Vas was also affected, I also suspected BL was somewhat high, then Mmd must be slightly lower…..

So my rash conclusion became; if the Sensitivity is to high then the only parameter left is Vas that in this case probably also is somewhat high…. I will stop here and agree once more with you; all parameters are interlocked with each other and I just took a convenient step to just lower the Vas value.

See the difference when comparing the 2 different Vas values based on the last larger TL; MJ-18-TL_st-200-300+10in.GIF and setting Le=0 (mH).

Conclusion; I was very lucky this time . Using a lower Vas value for this sub made not much harm but for other cases it could be disastrous i.e. if a more sensitive type of speaker is simulated using less damping and is more critical when tuning dimensions, volumes and so on.

b

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Old 30th January 2007, 05:32 AM   #28
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Greets!

Lucky indeed! Sometimes Fate smiles on us. Speaking of M5A, eventually there will be a 12 Hz TL write-up on their 'testbed' site: http://testbed.mach5audio.com/?cat=5

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