my latest project.. FR measurments

mAJORD · 4th December 2005, 07:31 AM

Hey peeps, Just did some FR measurments using speakerworkshop on my little bookshelves/satillites..

which consist of: peerless 830881 4" nomex phase plug driver mated with a Vifa d26nc-55-06 in a 3.2L vented enclosure, tuned for about 78hz. the tweeter is offset.

the front baffle is 130mm wide by 260 high

Xover is at 3500Hz 12db/oct linkz , I have a 6db amp side series attentuation on the tweeter.

Ive used the method as per claudio negro's guide , with the exeption of induvidual driver measurements.. i.e I did a Gated, on axis with accoustic center. Considering the drivers are so close I figured it will surfice for the moment..

I had some problems with the nearfield measurement due to the phase plug, it prevented me from getting close enough to the driver, so i compensated by moving away from the port aswell.. I think this has had an effect on low freq cutoff as it is around 80hz using a sweep..

anyway I was wondering if anyone has any ideas on the big dipper at 1 and 8k.. it appears on both my far field (non gated) and gate measurments. I tried some slightly different room positions and re marking my points for gating. but it only lessend it slightly.

I also did a simple sine sweep measuremnt with audiotester and had a big dip at 9k again.. noticable around the very bumpy non gated graph.. the 1k dip was impossible to tell as a result.

so does anyone have any ideas, or hints on where I should concentrate on? , could tweeter placement have such a huge impact?

the tweeter certainly would have nothing to do with the 1k dip anyway so Im a bit lost. im quite happy with the rest of the results myself, it looks like I may need a db or so extra attenuation on the tweeter but from a FR pt of view i think the xover points looking ok

any comments, good or bad appreciated!

B4 · 4th December 2005, 11:08 PM

Can you change the length of the port or stuff it and run another sweep to see if it changes position.

claudio · 7th December 2005, 12:25 AM

Hi,
are the drivers flush mounted?

Regards,
Claudio

B4 · 7th December 2005, 12:59 AM

I think we would all agree that we would need much more information then was given by mAJORD.

mAJORD · 7th December 2005, 12:28 PM

sorry ppl ,

no they are not flush mounted at this time, they will be when im decided on a baffle.

do you think that would make such a difference?

here is a pic of my dodgy test box tog ive an idea of positioning of things.

one thing that has concerned me was my need to do a 90deg port bend, something I did not want to do , but really had no choice to keep it a reasonable distance from the reard.. despite making the cabinet very deep

http://www.users.on.net/~majord/peerlessmini.JPG

claudio · 7th December 2005, 03:26 PM

8000 hz corresponds to 2.16 cm: measure from the tweeter center this distance to see if it corresponds to something.

900 Hz =19 cm: does this value remember you something (inside cabinet dimension, for example)?

Regards,
Claudio

mAJORD · 8th December 2005, 09:46 AM

thanks carlos

19cm

almost the depth of the cabinet (from cone to rear internal wall.. around 17cm

also, almost the length of the port .

2.1cm only relates to the edge of the tweeter faceplate. the
flushmounting shoudl cure this .

4th December 2005, 07:31 AM	#1
mAJORD diyAudio Member Join Date: Apr 2004 Location: Brisbane Australia	my latest project.. FR measurments Hey peeps, Just did some FR measurments using speakerworkshop on my little bookshelves/satillites.. which consist of: peerless 830881 4" nomex phase plug driver mated with a Vifa d26nc-55-06 in a 3.2L vented enclosure, tuned for about 78hz. the tweeter is offset. the front baffle is 130mm wide by 260 high Xover is at 3500Hz 12db/oct linkz , I have a 6db amp side series attentuation on the tweeter. Ive used the method as per claudio negro's guide , with the exeption of induvidual driver measurements.. i.e I did a Gated, on axis with accoustic center. Considering the drivers are so close I figured it will surfice for the moment.. I had some problems with the nearfield measurement due to the phase plug, it prevented me from getting close enough to the driver, so i compensated by moving away from the port aswell.. I think this has had an effect on low freq cutoff as it is around 80hz using a sweep.. anyway I was wondering if anyone has any ideas on the big dipper at 1 and 8k.. it appears on both my far field (non gated) and gate measurments. I tried some slightly different room positions and re marking my points for gating. but it only lessend it slightly. I also did a simple sine sweep measuremnt with audiotester and had a big dip at 9k again.. noticable around the very bumpy non gated graph.. the 1k dip was impossible to tell as a result. so does anyone have any ideas, or hints on where I should concentrate on? , could tweeter placement have such a huge impact? the tweeter certainly would have nothing to do with the 1k dip anyway so Im a bit lost. im quite happy with the rest of the results myself, it looks like I may need a db or so extra attenuation on the tweeter but from a FR pt of view i think the xover points looking ok any comments, good or bad appreciated!

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4th December 2005, 11:08 PM	#2
B4 diyAudio Member Join Date: Nov 2005	Can you change the length of the port or stuff it and run another sweep to see if it changes position.

7th December 2005, 12:25 AM	#3
claudio diyAudio Member Join Date: Feb 2002 Location: Italy	Hi, are the drivers flush mounted? Regards, Claudio

7th December 2005, 12:59 AM	#4
B4 diyAudio Member Join Date: Nov 2005	I think we would all agree that we would need much more information then was given by mAJORD.

7th December 2005, 12:28 PM	#5
mAJORD diyAudio Member Join Date: Apr 2004 Location: Brisbane Australia	sorry ppl , no they are not flush mounted at this time, they will be when im decided on a baffle. do you think that would make such a difference? here is a pic of my dodgy test box tog ive an idea of positioning of things. one thing that has concerned me was my need to do a 90deg port bend, something I did not want to do , but really had no choice to keep it a reasonable distance from the reard.. despite making the cabinet very deep http://www.users.on.net/~majord/peerlessmini.JPG

7th December 2005, 03:26 PM	#6
claudio diyAudio Member Join Date: Feb 2002 Location: Italy	8000 hz corresponds to 2.16 cm: measure from the tweeter center this distance to see if it corresponds to something. 900 Hz =19 cm: does this value remember you something (inside cabinet dimension, for example)? Regards, Claudio

8th December 2005, 09:46 AM	#7
mAJORD diyAudio Member Join Date: Apr 2004 Location: Brisbane Australia	thanks carlos 19cm almost the depth of the cabinet (from cone to rear internal wall.. around 17cm also, almost the length of the port . 2.1cm only relates to the edge of the tweeter faceplate. the flushmounting shoudl cure this .

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