Check my First Box & Measure in anechoic chamber

[endrek]

Hi, i just finished my first design, a 18'' Fane Colossus 18XB in a 221L bass reflex box i designed.
Now i had the oportunity to check the response of my speaker in an anechoic chamber, and see the frequency response.
I'm trying different configurations of damping material inside and measuring the frequency response, so i can see and measure wich configuration will be best.
Now i upload the graphics, and when i get home i'll upload some pictures about the mounting and the box.

1.-

Blue line is with full damping material // green line no damping material


2.-

Blue line is with full damping material // green line with half damping material


I haven't got time to try more configurations, but hope i wil try to convince them to let me have some more fun.


Do you think is it good enough? Do you think i made a crappy design and should throw it to the bin? Any advices??


One question i have is, someone told me something about....(can't remember wel..) that if you want to measure frequency response of a subbass speaker, you have to be at "far field", not at 1m, like i've been doing. Can anyone explain me this please?

Here are the freq response with the hole span:
1.- No damping material


2.- Half loaded damping material (BACK AND UP)


3.- Fully loaded with damping material



Thx for your help in advance.
Don't be cruel, its my very first toy i make


pd: measures done with good microphone (omnidir & flat resp) and Pulse Labshop

[revboden]

Is this for a PA system?

[weltersys]

Originally Posted by endrek

Hi, i just finished my first design, a 18'' Fane Colossus 18XB in a 221L bass reflex box i designed.
Now i had the oportunity to check the response of my speaker in an anechoic chamber, and see the frequency response.
I'm trying different configurations of damping material inside and measuring the frequency response, so i can see and measure wich configuration will be best.
Now i upload the graphics, and when i get home i'll upload some pictures about the mounting and the box.

1.-

Blue line is with full damping material // green line no damping material


2.-

Blue line is with full damping material // green line with half damping material


I haven't got time to try more configurations, but hope i wil try to convince them to let me have some more fun.


Do you think is it good enough? Do you think i made a crappy design and should throw it to the bin? Any advices??


One question i have is, someone told me something about....(can't remember wel..) that if you want to measure frequency response of a subbass speaker, you have to be at "far field", not at 1m, like i've been doing. Can anyone explain me this please?

Here are the freq response with the hole span:
1.- No damping material


2.- Half loaded damping material (BACK AND UP)


3.- Fully loaded with damping material



Thx for your help in advance.
Don't be cruel, its my very first toy i make


pd: measures done with good microphone (omnidir & flat resp) and Pulse Labshop

If your response curves are correct, your "sub" is 20 dB down at 50 Hz from 250 Hz.
Frankly, I don't think you could have screwed it up that badly, I suspect the measurements are way off.

An anechoic chamber good down to below 150 Hz would have to be huge, and have many truckloads of fiberglass.

As far as damping, it seems to only have a slight negative effect in the range where a sub would be used.

Measuring a sub at more than one meter is more representative of the "real world", as large subs measured close appear to be more like 1/4 space than half space. Measuring at 100 watts at 10 meters rather than one watt at one meter is better when using subs that are "bigger than a bread basket".

Art

[endrek]

well... the anechoic chamber is from a university, it's quite big...maybe....10meters x 7meters.
The measures i don't think it's badly done, because i've checked again and again. And they also helped me.
I think the problem is, that maybe i have to do the measure 100W@10meters as you say?
Can it be possible that my design is not good enough and thats why i have so big difference between 50Hz and 250 Hz?

My design is :
638(W)x685(H)x519(D)
then i calculated a port length of 240 but tunning the system....to achieve a Fb of 36 i finally ended up trimming to 130, and achieving a Fb of 39-40. Do you think it is too high?
My answer to tunning up so high, is that hardtek music never has many really big subfreq below 38...And i was thinking that anyways with the Xover i would make the range for this something aroung 38-200Hz. Am I thinking wrong?

Well thanks a lot for you help, as always
Really appreciate it

pd: yes it is part of a PA i'm designing. (i'm a newbie that instead of copying a design, tryed to make one, and have some fun)

[endrek]

here you go a slideshow of all the building process, and some pictures about the measures.
ImageShack(TM) slideshow

[Arty]

I mase a suspicion, but i might be wrong.
anyways, would you be so kind to do an impedance mesurement for Your sub?
range should be from 20 hz to 400 hz.
I em dying to see the result.


Allso, does the used microphone has a calibration graph available?

[weltersys]

Originally Posted by endrek

well... the anechoic chamber is from a university, it's quite big...maybe....10meters x 7meters.
The measures i don't think it's badly done, because i've checked again and again. And they also helped me.
I think the problem is, that maybe i have to do the measure 100W@10meters as you say?
Can it be possible that my design is not good enough and thats why i have so big difference between 50Hz and 250 Hz?

My design is :
638(W)x685(H)x519(D)
then i calculated a port length of 240 but tunning the system....to achieve a Fb of 36 i finally ended up trimming to 130, and achieving a Fb of 39-40. Do you think it is too high?
My answer to tunning up so high, is that hardtek music never has many really big subfreq below 38...And i was thinking that anyways with the Xover i would make the range for this something aroung 38-200Hz. Am I thinking wrong?

Well thanks a lot for you help, as always
Really appreciate it

pd: yes it is part of a PA i'm designing. (i'm a newbie that instead of copying a design, tryed to make one, and have some fun)

7 meters is not acoustically large for low frequencies, that is the wavelength of 50 Hz.

That is like testing a speaker with a 375 Hz bottom end in a one meter "room".

Your cabinet looks reasonable in size, bracing and porting.
I have 4 inch speakers in sealed cabinets that do better than 20 dB down at 50 Hz from 250 Hz.
Either their test results are wrong, or your speaker is broken.

Get a dB meter, set it down a couple meters (or 10 if you have wide open spaces) from the cabinet and run sine waves through at various frequencies and see and hear for yourself.

While you are at it, confirm the Fb is what you planned, the cone movement will be at minimum at Fb, and will increase rapidly below.

[endrek]

Originally Posted by Arty

I mase a suspicion, but i might be wrong.
anyways, would you be so kind to do an impedance mesurement for Your sub?
range should be from 20 hz to 400 hz.
I em dying to see the result.
Allso, does the used microphone has a calibration graph available?

1.- They have a Cesva verification "tester" that emits 94db@1KHz , then i put the microphone inside, and measure with the software/hardware, if it is different from 94dB, due to the Pulse Labshop sensivity, i adjust de sensivity so it gives me 94dB. But as far as i know, this is only needed for the "sensivity response" right? So i have 2.82 V at the amplifier (1W) and the chain of measure is adjusted to 94 db @1kHz.

2.-I haven't got the curve done, because i haven't had time, but i did it without taking all values. Just moving the freq generator frequency knob and checking the minimum voltage between the 2 maximums.I'll try to get some time, and convince them i can go again, and take values one by one and make an excel graph, so you can see.
But for the impedance curve(graph), they told me to wait for the Audio precision so we can measure/draw it exactly.

Thanks again for all your help.

[endrek]

Originally Posted by weltersys

Either their test results are wrong, or your speaker is broken.

Get a dB meter, set it down a couple meters (or 10 if you have wide open spaces) from the cabinet and run sine waves through at various frequencies and see and hear for yourself.

While you are at it, confirm the Fb is what you planned, the cone movement will be at minimum at Fb, and will increase rapidly below.

hmmm
you mean that my driver is broken??? The box is air tight, and with silicon.

Can it be a problem of wrong design?

And i think, that now (like i did...) i can confirm, that with the stable wave generator with a sine wave output and a AC voltimeter (Fluke 187, so not cheap one.....like the one i tryed first...(my tester jeje)) And i measured a minimum around 38-39-40.

[revboden]

THIELE SMALL PARAMETERS
FS Hz 33 Hz
RE Ohms 6.5 Ω
Qms 5.77
Qes 0.358
Qts 0.337
Vas Ltr 236
Vd 0.803
CMS (mm/N) 0.13
BL T/m 25.9
Mms grms 173
Xmax mm 7.5
Sd cm2 1131

These are from Fane.
I'd check the driver