Some basic FR measurements - Page 2 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

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 23rd January 2013, 09:35 AM   #11
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
I use holmimpulse HOLM Acoustics for gated measurements and REW REW - Room EQ Wizard Home Page for doing pink noise (with RTA) in room measurements (also great for measuring impedance curves)

I like your thinking with using audacity, but I think that using REW with pink noise and some averaging in the RTA you will probably get a better in room representation.

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 23rd January 2013, 01:39 PM   #12
Alex M is offline Alex M  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: Hampshire, UK
Thanks for the helpful suggestions.

I still can't see any obvious source for reflection at that distance. I wondered whether it might be a front-back reflection inside the mid-treble cabinet, since the boxes are about 35cm front to back, and the ultra-lightweight HDA midrange cone is notorious for passing the reflected backwave. However the tweeter is closed at the back, and the crossover is at about 3.2 kHz, so you wouldn't expect any substantial internal echoes at higher frequencies than that. I will try measuring with the speakers further away from the walls, just to see.

Yes, I see that "size" in Audacity defaults to 512 - a quick test reveals that increasing this extends the bass response accordingly, but I haven't repeated my measurements with this setting.

I am definitely feeding my amp white noise: it is track 65 of the Hi-Fi News Test CD, marked "white noise". Pink noise sounds like a waterfall, instead of the "hiss" I hear with this track.

It had indeed occurred to me to measure the drivers individually with and without the crossover, to test whether they (the mid in particular) are working consistently with the published specs.

I will also measure with a different (solid state) amplifier to eliminate my 300B amp as a possible cause of the HF rolloff.

Finally I will investigate other software packages. Holm appears not to be available for a Mac, but I will try REW.

Alex

Last edited by Alex M; 23rd January 2013 at 01:41 PM.
  Reply With Quote
Old 23rd January 2013, 05:20 PM   #13
diyAudio Member
 
speaker dave's Avatar
 
Join Date: Nov 2009
Location: The Mountain, Framingham
There are definitely strong reflections going on, as evidenced by the periodic ripple. The lower curve is worse and the 6dB peak to trough indicates that the reflection strength is about 1/3rd the direct sound strength. It could also be a reflection at the microphone end. What is your mic support/stand like?

White noise is correct for this type of analyzer.

David S.
  Reply With Quote
Old 23rd January 2013, 10:35 PM   #14
Alex M is offline Alex M  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: Hampshire, UK
I've now installed REW on my MacBook, and started to have a look through the comprehensive manual and FAQ. There are instructions for using an SPL meter to calibrate a microphone, which reminded me that I have an old RS analogue SPL meter (modded as per Eric Walin's instructions), which I dusted off after ten years in storage and put new batteries in. I had forgotten that it also has a fixing for a camera tripod, which I had never used, but might well be handy.

I'll experiment and report back!

Alex
  Reply With Quote
Old 25th January 2013, 09:14 AM   #15
Alex M is offline Alex M  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: Hampshire, UK
I think I have solved the reflection issue. I re-did the measurements on one of the speakers using the RS analogue SPL meter instead of my homebrew microphone, and used a higher data length for the FFT in Audacity, and got the result below, which looks much more encouraging: I don't see the ~800Hz repeat at all.

The mic I was using before consisted of the Panasonic capsule in the end of a 30cm plastic tube, which was wrapped in tape to suppress vibrations: my feeling is that the reflections occurred along the interior length of the tube (possibly through the cable), and would have been relatively undamped at high frequencies.

The overall response is much smoother through the midband too. I will experiment with REW over the next few days to try to improve the measurements.

Alex
Attached Images
File Type: gif LH channel new SPL meter.gif (35.6 KB, 35 views)
  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
Some FR measurements of the new FE166En Bob Brines Full Range 19 3rd May 2012 09:42 AM
Basic tests and measurements for OPTs percy Tubes / Valves 12 1st September 2007 08:59 PM
Very basic questions regarding LSPCad and measurements fjhuerta Multi-Way 2 28th January 2006 03:41 PM
Some FR Measurements of 4" Pioneers Sherman Multi-Way 19 21st October 2004 05:58 AM
Digital FR Measurements Rarkov Digital Source 1 14th November 2003 11:59 PM


New To Site? Need Help?

All times are GMT. The time now is 12:26 AM.


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