Check my First Box & Measure in anechoic chamber - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 11th May 2011, 09:05 PM   #1
endrek is offline endrek  Spain
diyAudio Member
 
Join Date: Sep 2010
Question Check my First Box & Measure in anechoic chamber

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.-
Click the image to open in full size.
Blue line is with full damping material // green line no damping material


2.-
Click the image to open in full size.
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
Click the image to open in full size.

2.- Half loaded damping material (BACK AND UP)
Click the image to open in full size.

3.- Fully loaded with damping material
Click the image to open in full size.


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
  Reply With Quote
Old 12th May 2011, 02:11 AM   #2
diyAudio Member
 
revboden's Avatar
 
Join Date: Feb 2011
Is this for a PA system?
  Reply With Quote
Old 12th May 2011, 07:47 AM   #3
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by endrek View Post
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.-
Click the image to open in full size.
Blue line is with full damping material // green line no damping material


2.-
Click the image to open in full size.
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
Click the image to open in full size.

2.- Half loaded damping material (BACK AND UP)
Click the image to open in full size.

3.- Fully loaded with damping material
Click the image to open in full size.


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
  Reply With Quote
Old 12th May 2011, 10:44 AM   #4
endrek is offline endrek  Spain
diyAudio Member
 
Join Date: Sep 2010
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)
  Reply With Quote
Old 12th May 2011, 11:09 AM   #5
endrek is offline endrek  Spain
diyAudio Member
 
Join Date: Sep 2010
here you go a slideshow of all the building process, and some pictures about the measures.
ImageShack(TM) slideshow
  Reply With Quote
Old 12th May 2011, 09:09 PM   #6
diyAudio Member
 
Join Date: Feb 2011
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?
  Reply With Quote
Old 12th May 2011, 09:10 PM   #7
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by endrek View Post
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.

Last edited by weltersys; 12th May 2011 at 09:13 PM.
  Reply With Quote
Old 12th May 2011, 10:24 PM   #8
endrek is offline endrek  Spain
diyAudio Member
 
Join Date: Sep 2010
Quote:
Originally Posted by Arty View Post
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.
  Reply With Quote
Old 12th May 2011, 10:31 PM   #9
endrek is offline endrek  Spain
diyAudio Member
 
Join Date: Sep 2010
Quote:
Originally Posted by weltersys View Post
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.
  Reply With Quote
Old 13th May 2011, 04:34 AM   #10
diyAudio Member
 
revboden's Avatar
 
Join Date: Feb 2011
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

Last edited by revboden; 13th May 2011 at 04:39 AM.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Dual Chamber Speaker Box suministros Multi-Way 17 20th May 2010 12:23 AM
Separated or Same Chamber Box? suprastar17 Subwoofers 2 19th April 2005 03:32 PM
DIY anechoic chamber! Snickers-is Multi-Way 33 13th March 2005 08:30 PM
Help on Dual Chamber Reflex box & car audio response Q's please (LONG) beady Car Audio 7 6th August 2004 12:57 PM
Help on Dual Chamber Reflex box & car audio response Q's please (LONG) beady Multi-Way 0 3rd August 2004 11:09 PM


New To Site? Need Help?

All times are GMT. The time now is 11:31 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2