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Measure reflex tuning?
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LjudLahger View Drop Down
Young Croc
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    Posted: 16 April 2014 at 9:32pm
Can I do this in any simple way? My idea was to put my berry ecm8000 mic, in or close to the port and play white noice. The deq would then show a spike at tuning or what?
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dlyxover View Drop Down
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Points: 1502 		Post Options Post Options   Thanks (0) Thanks(0)   Quote dlyxover Quote  Post ReplyReply Direct Link To This Post Posted: 16 April 2014 at 10:19pm
That should do it but
I place the mic in the centre of the port level with the baffle
If you can use pink noise would prob be better

or try running test tones at the tuning frequency, when you hit the frequency the cab is tuned the cone should be still as the port is doing all the work.



Edited by dlyxover - 16 April 2014 at 11:40pm
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Teunos View Drop Down
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Yes that will be more than adequate for measuring (static) resonant frequency. Just be careful that you don't get a too high SPL in the port, i don't know what damage it can do at high volume.
Here is a screenshot of smaart with a tuning measurement i once did of an 8'' for a small midtop. (notice the rather high tuning, this was before adjusting the port lengthWink).


Edited by Teunos - 16 April 2014 at 10:30pm
Best regards,
Teun.
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LjudLahger View Drop Down
Young Croc
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Points: 838 		Post Options Post Options   Thanks (0) Thanks(0)   Quote LjudLahger Quote  Post ReplyReply Direct Link To This Post Posted: 16 April 2014 at 10:38pm
Thanks for your response!

I really dont know the color of the noice, its what the deq got ;-)

And cool that it could work, ill have a go in the weekend.

Spl would not be a problem, new 2 x 6,5' + 1'   :-)

The thing is that im going to do slotreflex and use the sides and I have somewere before heard that it could lower fb. So I have to investigate. It will be a high tuning of ca 105hz.
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bitSmasher View Drop Down
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Measure cabinent impedance
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ceharden View Drop Down
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As above, measuring the impedance vs frequency is the most accurate way to determine the tuning.

All you need is a signal generator (one on the PC would be fine), amplifier, a resistor of around 10Ohms, a reasonable multimeter and a spreadsheet.

There are instructions around on the web and there are also applications (I think Room EQ from Home Theatre Shack does it) which automate it for you.
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csg View Drop Down
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the biggest problem sticking a measurement mic in a port and looking at the output will be wind noise on the mic...you will need an excellent windshield.
“The fact is this is about identifying what we do best and finding more ways of doing less of it better”
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LjudLahger View Drop Down
Young Croc
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Awsome tips

I will the use protection on the mic.
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Elliot Thompson View Drop Down
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Measuring the impedance (shown in the photograph below) will give you the true tuning of the box.




If you are using a microphone you will only get the frequency response. You will not get accurate results aiming the microphone at the port with, the assumption the microphone will only pick up sound solely from the port if, the main objective is seeking the port tuning.



Best Regards,
Elliot Thompson
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Teunos View Drop Down
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Regarding the above, here is a screenshot i made of smaart with the same 8'' but now with the impedance measurement overlaid. The impedance measurement is made by doing a TF across a reference resistor, pretty much the same as elliot's setup for LIMP i assume. Doing this in smaart gives me instant viewable results for design verification, and when doing the final tuning i also do it in Limp. However, i find measuring the tuning frequency with the mic in the port gives quite a good idea of where the tuning frequency isWink
Best regards,
Teun.
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Elliot Thompson View Drop Down
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Points: 5175 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 17 April 2014 at 1:57pm
One of the benefits about measuring the impedance curve is determining how well the VAS of the driver correlates to the enclosure it is residing in. Another benefit is telling you how much “work” the driver needs to do based on the impedance peaks at the given frequency. Simulators cannot give you this type of accuracy. A Simulator assumes the TS Parameters of the driver does not change (from its free-air response) once it is placed in an enclosure.



Best Regards,
Elliot Thompson
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dlyxover View Drop Down
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I've just tried measuring the impedance using smaart but every driver and cab I tried said 90Hz. 
Im doing something wrong!

Can some hold my hand through the procedure? (via PM as to not hijack this tread)

cheers

  
In the Truth there is no news, and in the News there is no truth
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