Calculations of bass-reflex enclosures - generally !!! - diyAudio
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Old 7th October 2005, 02:41 PM   #1
Notax is offline Notax  Montenegro
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Exclamation Calculations of bass-reflex enclosures - generally !!!

I opened this tread to talk about calculations of Bass-Reflex enclosures.

Is there a differencies between results we got with simulations, and the best results for some bass unit in real? If there is differencies, why is that? And how we can correct calculations to got the best in real, without much eksperiments with different enclosure volumes, and tube lenghts for the best Fb.
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Old 7th October 2005, 06:19 PM   #2
Notax is offline Notax  Montenegro
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Default Example

For example. Vifa XG18WH00-08. Data sheet.


Nominal impedance [ohm] 8
Voice coil resistance [ohm] 5.7
Sensitivity [dB] 86
Free air resonance [Hz] 34
Voice coil height [mm] 14
Air gap height [mm] 4
Voice coil inductance [mH] 0.53
Eff. diaphragm Area [cm2] 129
Moving mass [g] 11.8
Force factor [Bl] 5.6
VAS [l] 45
Qms 1.77
Qes 0.46
Qts 0.36

Optimized for 8-14 ltr
reflex enclosures


With simulations we got enclosure Vb=30 L. Vifa recommands BR 8-14 L. I am sure this smaller is better.( and higher Fb then simulated) I try it in many aplications, and it is like that. Higher Qts bigger deviation from calculation. What now? What with simulations ?
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Old 7th October 2005, 09:35 PM   #3
RJ is offline RJ  United States
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Quote:
From this vent-tuning study is can be seen that calculating the vent dimensions is tricky business. From practical experience I have learned to multiply the vent length by 0.6-0,7 to get the targeted Fb. Quite some deviation from all the nice math.
So, no clear recommendation but get help from someone with measuring equipment if you want it right.
Here's the Web site;
http://home1.stofanet.dk/troels.grav...ENT-TUNING.htm
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Old 8th October 2005, 12:26 AM   #4
Notax is offline Notax  Montenegro
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Quote:
Originally posted by RJ


Here's the Web site;
http://home1.stofanet.dk/troels.grav...ENT-TUNING.htm
Very nice link. Thank you.

My question was does it can be made corections of standard calculations with T/S parameters to got same (Vb, Fb, Dp, Lp) as its best at the end of eksperiments (and meausurements).
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Old 9th October 2005, 04:18 AM   #5
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Hi Notax,

I plugged those values into speaker workshop and tried different alignments and I see what you mean, however I would say it is more likely that they have made an error on the datasheet than that there are errors in the calculations/simulations

If the sims are out by a fatcor of 100% there would be a lot of very dissapointed DIY'ers out there

I simulated and built a tuned enclosure for a Vifa M26WR-09-08 with a 70L enclosure (recommended between 50L - 100L by Vifa) and it worked out very close to the simulated one.

sure you will get some small differences in tuning freq due to not 100% knowing the exact box volume, but these should be minor.

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Old 9th October 2005, 04:32 AM   #6
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Data sheet parameters show average parameters for drivers, not the parameters of the one driver you have.

Parameters change once any power is applied and once the cone moves from rest.

Losses in the box and port effect the tuning.

How the port is shaped and how it is mounted (what's at the ends) effects the tuning.

If you are going to be really picky about your tuning, you need to be more careful with your measurements of driver parameters and your modeling of what you are building. A simple model will probably not be exactly right because it doesn't account for everything that exists in reality.
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Old 9th October 2005, 06:12 AM   #7
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All very true, but with that particular datasheet it says optimised for a 8-14L box which when moddeled seems to give very sub-optimal performance based on the TS params provided...... non-flat and very poor low end extention.... I think iether the params are incorrect or the 8-14L is incorrect either way I think they made a mistake or are trying to appeal to people who want a small box rather than an optimal one

Vifa actually has a reputation for having very good driver to driver consistency which match the published specs very well.... others are not so crash hot... but yeah the best way is to measure them yourself!

Tony.

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Old 9th October 2005, 07:06 AM   #8
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Also it's important that the drivers are burnt in, parameters can differ significantly from a brand new one. For example, 10 hours with pink noise or a deep sinewave with visible cone excursion could help.
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Old 9th October 2005, 10:10 AM   #9
Vikash is offline Vikash  United Kingdom
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Default Congrats Tony

Quote:
Originally posted by wintermute
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Old 9th October 2005, 10:12 AM   #10
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Thanks Vikash hopefully at least some of them have been usefull

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