What did i do wrong?

viktor giljevic

New member
Jan 13, 2020
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Hello!
I"m building a 3way top speaker with 12" B&C 12ndl88 taking the bass duties from 80-300hz.Using winisd and recommended volumen of 40 liters and tuning f=65hz by B&C i made my reflex test box but it seems not working well.Open field mesurment,box on the ground.mic 15cm off the ground 5meters from the box.
Suggestions?
Thanks!
 

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Stef Smits

Freshman
Apr 4, 2017
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Just going from the pictures (not always the smartest thing ;)) I think the dip in your response comes from the cavity above (coherence doesn't look bad enough at the given frequency).
To verify it you can simply block it off and test again.

PS: obviously use the same measurement conditions as the first time.
If this does not solve the problem, you should check your measurement setup.
 

Chris Hindle

Freshman
Apr 18, 2011
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Montreal
Umm, if the enclosure is missing "stuff" that takes up space in the woofer cavity, your measures are meaningless.
You need to get the internal volume to where the enclosure will be operating to measure what's really happening.
Chris.
 

Stef Smits

Freshman
Apr 4, 2017
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Going from the pictures, the enclosure for the 12" is separated from the rest, so that would not be the case.
It is however that the cavity for the mid/high has his own resonance frequency which gives an invalid measurement.
 

Uwe Riemer

Freshman
Mar 3, 2011
105
2
18
Germany
Hello!
I"m building a 3way top speaker with 12" B&C 12ndl88 taking the bass duties from 80-300hz.Using winisd and recommended volumen of 40 liters and tuning f=65hz by B&C i made my reflex test box but it seems not working well.Open field mesurment,box on the ground.mic 15cm off the ground 5meters from the box.
Suggestions?
Thanks!
First you need to learn how to do a meaningfull measurement, those strong dips in coherence in the DUT`s passband are concerning.
Put the box in the air, something like 2m should be sufficient and take a measurement in the nearfield, let´s say 30cm away, halfway between the cone and the port.
Get rid of the crossovers first and don´t forget to hit the peak finder button. The correct reference delay is important, if the measurement process uses Windowing. You found the correct reference delay, when the phase trace stays flat near zero in the middle of the passband.

The empty cavity for Mid/High is not helping like the others said already. It might help to fill this cavity with damping material.
 
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viktor giljevic

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Jan 13, 2020
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Hello!
Thank you for your input!Going to finish the box on weekend and try to mesure like Uwe said.
@Uwe Was denkst du was mache ich falsch mit Smaart?Drücke "find" vor jeder messung.
 

Uwe Riemer

Freshman
Mar 3, 2011
105
2
18
Germany
Hello!
Thank you for your input!Going to finish the box on weekend and try to mesure like Uwe said.
@Uwe Was denkst du was mache ich falsch mit Smaart?Drücke "find" vor jeder messung.
Let´s keep it in English.
I don´t know Smaart, I´m using Systune.
A strong reflection can fool the peak finder, putting the microfone 15cm above ground could cause this.
 

viktor giljevic

New member
Jan 13, 2020
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Hello!
The test box is done so i did some mesurment Uwe sugested in his post above.The purlpe trace is the first mesurment with mic ca.30cm from the box between port and cone(pic1).The yellow trace is 2m from the box at the same height,but the neighbours house is 12m opposite the box, witch i think did the strong dip.The last pic is without crossover mesured like the purple trace.
 

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Uwe Riemer

Freshman
Mar 3, 2011
105
2
18
Germany
Hello!
The test box is done so i did some mesurment Uwe sugested in his post above.The purlpe trace is the first mesurment with mic ca.30cm from the box between port and cone(pic1).The yellow trace is 2m from the box at the same height,but the neighbours house is 12m opposite the box, witch i think did the strong dip.The last pic is without crossover mesured like the purple trace.
The last picture contains the most information for me, but what about you, Viktor,
anything unusual you can spot ?
 

viktor giljevic

New member
Jan 13, 2020
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Hello!
@Peter the box will be used between 80-300hz should i dampening it anyway?
@Uwe above 400hz the trace dont look good but i dont want go that high,i"m not so experianced in reading traces i got smaart for a year now.
Thank you !
 

Peter Morris

Senior
May 8, 2011
1,009
98
48
Australia
Hello!
@Peter the box will be used between 80-300hz should i dampening it anyway?
@Uwe above 400hz the trace dont look good but i dont want go that high,i"m not so experianced in reading traces i got smaart for a year now.
Thank you !
Yes you should - there is still a need to control things that are out of band, they may be 12dB down at 300Hz (for example) but their effects can often be heard and they can impact on the clarity of your system.