VIFA tweeter response - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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 15th June 2017, 11:02 AM   #1
Piersma is offline Piersma  Netherlands
diyAudio Member
 
Piersma's Avatar
 
Join Date: Jan 2003
Location: Netherlands
Default VIFA tweeter response

hi all,

I have done some frequency response measurements on my modified Vifa Vivace speaker setup. Now i am trying to interpret the VIFA tweeter XT25SC30-04 measurement results, but I am unable to come to justified conclusions.
I have done a "in house" (freq.response)measurement and a outside measurent. The results quite differ. The tweeter is flush mounted on a 12" or 30 cm bafle.
The lowest red graph is the "in house" measurement, blue and green are the outside. Measurements where taken on 1 meter and on .25 meter distance.
Could somebody please comment on the results?
Attached Images
File Type: png Tweeter reponse.png (44.7 KB, 338 views)
Attached Files
File Type: pdf xt25sc-30-04.pdf (717.1 KB, 14 views)
  Reply With Quote
Old 15th June 2017, 07:02 PM   #2
diyAudio Member
 
Join Date: Aug 2007
Location: Sofia
Send a message via Skype™ to Mario Pankov
Is your in house measurement gated? It looks as its not. Outside one also appears to have been taken slightly offaxis, you need to make sure your mic is properly centered. The bump at what appears to be 1.4Khz looks like a diffraction product.

What exactly bothers you and can you provide more information on how you measured them, what measurement rig you use and is it calibrated?
  Reply With Quote
Old 15th June 2017, 07:04 PM   #3
ICG is online now ICG  Germany
diyAudio Member
 
Join Date: Jul 2007
Location: Sound Cloud 9
The rise in the lower frequency range is normal and caused by the baffle step. On the upper end it looks like you've not been exactly on axis with the mic because it got a similar drop off in the datasheet at 30. I do not suspect you to be that much off of the angle but the short measuring distance isn't very forgiving on errors there at a driver which beams that much.

For the impulse response: It reflects the different measurement distance. But it looks like it was heavily smoothed, so there's not that much information you can read out of it. And there's another important error in it: It shows the response on the measurement BEFORE the impulse (that would be the 0ms mark). That can, per definition, not be the actual impulse response since the response can't happen before the impulse.

How does your setup look like? Do you have a DSP somewhere in the signal chain?

edit: too slow..
__________________
After all is said and done, usually more is said than done.
  Reply With Quote
Old 16th June 2017, 09:55 AM   #4
Piersma is offline Piersma  Netherlands
diyAudio Member
 
Piersma's Avatar
 
Join Date: Jan 2003
Location: Netherlands
First of all, i use Holmimpulse. The testrig is E-MU 0202 soundcard and a calibrated Samson MM01 microphone. The testrig is fully functional and calibrated. After a good thought i realized that the inhouse measurements were taken with a logarithmic sine sweep and the outside measurements were taken with a square noise (improved MLS). The woofer and mid in and outside measurement were consistent, there were only minor differences.
Because I took the inhouse measurements more than six month ago, there might be an small issue with a on axis error.

@Maria Pankov
The outside measurements were gated and the microphone was (fairly) good centered. I would agree, the 1.5kHz bump looks indeed a diffraction product. The flange is absolutely not perfectly countersunk.
What bothers me is the quick and steep roll-off at fairly low frequencies, I would expect the tweeter to extend to a far greeter range.
Which of the measurements would you consider the most valid?
@ICG
The baflestep frequency is expected to be in the 400Hz range, and definitely not in the 1kHz range.
The preset recording delay of 1500ms causes the impulse to show-up before zero.
There is no DSP in the signal chain.
1/N (N=3) frequency smoothing was applied to the graphs.

Thanks for your comments!
Attached Images
File Type: png Tweeter resp.png (12.0 KB, 286 views)
  Reply With Quote
Old 16th June 2017, 10:00 AM   #5
Lojzek is offline Lojzek  Croatia
diyAudio Member
 
Lojzek's Avatar
 
Join Date: Feb 2012
Location: Croatia
See the measurement options and check if the high pass function is on. Try recording a raw measurement.
__________________
Mankind is created for eternity.
  Reply With Quote
Old 16th June 2017, 10:40 AM   #6
Piersma is offline Piersma  Netherlands
diyAudio Member
 
Piersma's Avatar
 
Join Date: Jan 2003
Location: Netherlands
The highpass function is indeed on and set to 1kHz. You propose to setup the measurement without the highpass function?
But I guess you mean without smoothing .

Last edited by Piersma; 16th June 2017 at 11:09 AM.
  Reply With Quote
Old 16th June 2017, 11:19 AM   #7
ICG is online now ICG  Germany
diyAudio Member
 
Join Date: Jul 2007
Location: Sound Cloud 9
Quote:
Originally Posted by Piersma View Post
@Maria Pankov
The outside measurements were gated and the microphone was (fairly) good centered. I would agree, the 1.5kHz bump looks indeed a diffraction product. The flange is absolutely not perfectly countersunk.
What bothers me is the quick and steep roll-off at fairly low frequencies, I would expect the tweeter to extend to a far greeter range.
Which of the measurements would you consider the most valid?
@ICG
The baflestep frequency is expected to be in the 400Hz range, and definitely not in the 1kHz range.
The preset recording delay of 1500ms causes the impulse to show-up before zero.
There is no DSP in the signal chain.
1/N (N=3) frequency smoothing was applied to the graphs.
I misinterpreted your post, I was thinking about measurement with and without baffle. The driver without baffle would lead to an increase level in the mentioned range.

Generally you can only compare exactly measurements which are made under the same circumstances and settings. Even the air pressure and temperature can change a lot (any sun shining on the mic?), if not any other thing changed, especally in the range the mic got the greatest tolerances. Did you put a foam cap on the mic outside? (Guess no) You still haven't told how you measured it. Height from the ground? Distance to the next reflective surfaces? Any surroundings, table, tripod, clamps etc? What else changed?

The E-MU 0202 actually IS a dsp, on the digital side EVERYTHING runs through it. So even slightly changes on the settings can actually change a lot.
__________________
After all is said and done, usually more is said than done.
  Reply With Quote
Old 16th June 2017, 11:30 AM   #8
ICG is online now ICG  Germany
diyAudio Member
 
Join Date: Jul 2007
Location: Sound Cloud 9
Quote:
Originally Posted by Piersma View Post
The highpass function is indeed on and set to 1kHz. You propose to setup the measurement without the highpass function?
But I guess you mean without smoothing .
The reason to measure is to get informations of the driver and to compare it. If you constantly change the measuring circumstances, you can't compare the measurements. Why don't you etablish a standard measuring method? A hp of 1 kHz is too high.

What measuring amp for the driver do you use? (Don't use any class d amp)
__________________
After all is said and done, usually more is said than done.
  Reply With Quote
Old 16th June 2017, 12:28 PM   #9
diyAudio Member
 
Michael Chua's Avatar
 
Join Date: Jul 2006
Location: Calais, ME
Default XT25TG30 in box Response

For comparison, this is the raw response of my XT25TG30, taken with Omnimic.

Note the dip at about 2.7kHz when the tweeter is in a speaker box. All dome tweeters exhibit this behavior unless the baffle is IEC size.

More details are at Robin Tower.

Regards
Mike
Attached Images
File Type: jpg XT25_RAW_05-meter_crop.jpg (33.1 KB, 253 views)
__________________
ampslab
  Reply With Quote
Old 16th June 2017, 02:52 PM   #10
Lojzek is offline Lojzek  Croatia
diyAudio Member
 
Lojzek's Avatar
 
Join Date: Feb 2012
Location: Croatia
Quote:
Originally Posted by Piersma View Post
The highpass function is indeed on and set to 1kHz. You propose to setup the measurement without the highpass function?
Set it low enough so it doesn't alter natural response of the driver.
__________________
Mankind is created for eternity.
  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
Tweeter frequency response flatisgood Multi-Way 10 10th April 2017 02:59 PM
Proac response 1sc clone with Vifa? alvinlim Multi-Way 0 17th February 2006 12:33 AM
Puzzled by tweeter response joeling39 Multi-Way 12 19th January 2005 02:27 PM
Vifa, extra lines in response curve graph? Layberinthius Multi-Way 3 31st March 2004 10:48 AM
Vifa P21 response - just checking Mos Fetish Multi-Way 5 24th July 2003 04:21 PM


New To Site? Need Help?

All times are GMT. The time now is 11:47 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki