Speaker measurement difficulty - What's up? - Page 3 - 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 20th March 2017, 02:23 AM   #21
diyAudio Member
 
Jack Hidley's Avatar
 
Join Date: May 2007
Location: Danville, CA
Send a message via Skype™ to Jack Hidley
Legendre,

Creep is really complicated.

The primary suspension element in the driver, the spider, has the majority of the total of friction in it. This is because it is composed of many interwoven fibers. These fibers have friction between them. It takes a certain minimum force to overcome the friction and displace the suspension to a new position. Once at that new position, the cone assembly may stop at this new position because the new orientation of the fibers may reach an equilibrium of forces. The spider portion of the suspension has a lot of hysteresis. In fact it has multiple hysteresis loops, not just one. This makes its stiffness very uncertain.

For a blocked impedance measurement, you need to keep the vibrating portion of the driver from moving. The only really good way to do this is to have the coil separate from the cone assembly and lock it in place. If you lock the coil in place at different distances from the motor, you can look at some types of drive nonlinearities, such as inductance variance.

To get good impedance measurements, you need to minimize any environmental vibration and sound. Remember, the driver works just as well turning sound into current as it does current into sound. For best results it is normally always better to mount the driver so its cone is perpendicular with the ground.

The measurement settling issue alone, severely limits how consistent the impedance measurements can be. To get around this, some measurement systems take a wide band measurement, then do a curve fit on the impedance data to a driver model of what the impedance curve should look like. Other systems use a sine wave technique with programmable settling parameters.
__________________
Jack Hidley
ACS
  Reply With Quote
Old 20th March 2017, 02:34 AM   #22
diyAudio Member
 
Join Date: Jan 2008
Location: Toronto and Delray Beach, FL
Hardly sounds like the old KLH company that made classy gear in the "New England sound" period. Lots of classy old HiFi names have been sold to definitely unclassy new factories in emerging nations.

Yes, blocked impedance is the impedance when blocked from moving.

Jack Hidley is right, proper impedance measurements can't be done just sitting on the bench on the magnet. But slight stiction or failure to return to static position wouldn't affect impedance differentially or as you seem to have described it.

If the suspension was really non-linear or had some kind of lazy, break-in, dead cockroach, or other weird behaviour unsuitable for a speaker, you could get some kind of impedance change from trial to trial. But unlikely to be consistent and repeatable.

Strange.

Can you simply tell us if the speaker (or raw driver sitting on your bench) makes clean sound or not.

B.
__________________
HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio

Last edited by bentoronto; 20th March 2017 at 02:41 AM.
  Reply With Quote
Old 20th March 2017, 02:41 AM   #23
diyAudio Member
 
legendre's Avatar
 
Join Date: Jan 2017
Location: USA
@bentoronto

Both of the KLH speaks play just fine, last time they were in a system - they are one of several pair of small utility speakers that I keep around. I use them when I'm in the early shake-down phases of an amp rebuild / test job, and so forth. They have a reasonable power limit, are very small, and cheap enough that a destructive accident won't break the bank. The sonic qualities are such that I can quickly tell if something is way off.. and that's their job.

I've never put music through the bare driver, though the various test signals (sine, tri, square) all sound out as you would expect.. without any weird defects / buzzes etc.
  Reply With Quote
Old 20th March 2017, 02:48 AM   #24
diyAudio Member
 
legendre's Avatar
 
Join Date: Jan 2017
Location: USA
Quote:
Originally Posted by Jack Hidley View Post
Legendre,

Creep is really complicated.
Image that, a complex material property!

But yes, I totally get what you're on about.. and my sense is that the 'creep' factor plays into the driver break-in phenomenon. If we can't count on the home position of the voice coil within the gap, neither can we count on a given impedance or response at any frequency. Sure, there will be common trends, but absolute values must shift a bit.

If that's true, then it would seem that a well-broken-in driver would have fewer issues with creep, due to material break-in. Is that the case, or am I off?
  Reply With Quote
Old 20th March 2017, 03:03 AM   #25
diyAudio Member
 
legendre's Avatar
 
Join Date: Jan 2017
Location: USA
KLH LS #1 - after 48hr rest

Instruments: Fluke 8050A DMM (cal'd), Wavetek 111 funct. generator (sine) monitored on Racal-Dana 9904 frequency counter. The impedometer circuit uses a 1K 1% 1/2W metal film current limiting resistor and an 8R 1% 1/2W metal film resistor hand selected for precision 7R997 value.

(Note: Due to possible 'creep' factor, 15 sec settling time is allowed from the moment the LS is switched into the meter circuit until the DVM measurement is taken. This figure was chosen somewhat arbitrarily, based on the RoC of the reading after the DUT is switched into the circuit.)

Freq - Impedance (R)

20 - 12.13
25 - 12.17
31.5 - 12.18
40 - 12.25
50 - 12.30
63 - 12.51
71 - 12.70
80 - 13.0
90 - 13.4
100 - 14.2
113 - 16.16
126 - 20.63
143 - 26.23
159 - 20.32
180 - 15.45
200 - 13.76
250 - 12.97
315 - 12.38
400 - 12.30
500 - 12.36
630 - 12.48
800 - 12.60
1000 - 12.74

And this is an 8R speaker!? Wow.. seems more like 16R to me, but then again, we'll see what happens when I shake it up a bit.

Last edited by legendre; 20th March 2017 at 03:21 AM.
  Reply With Quote
Old 20th March 2017, 03:04 AM   #26
Tweet is offline Tweet  Australia
diyAudio Member
 
Join Date: Jan 2015
If you have an oscillator and an amplifier handy set it to 40c/s and drive your speakers at a low level (just below Xmax of your bass driver) for about 20 minutes.
It should then be ready to be measured after about a 30 minute cool down period. That should stabilize measurements for you. Cheap loudspeaker drivers can vary as much as 20% from their advertised specs, that's the reality of manufacturing that DIY'ers face.

C.M
  Reply With Quote
Old 20th March 2017, 03:12 AM   #27
Tweet is offline Tweet  Australia
diyAudio Member
 
Join Date: Jan 2015
From that measurement you are seemingly measuring the crossover network as well as the driver. It's 'in box' resonance appears to be around 143c/s which would appear to be typical of a small box driver of 4".

C.M
  Reply With Quote
Old 20th March 2017, 05:01 AM   #28
diyAudio Member
 
legendre's Avatar
 
Join Date: Jan 2017
Location: USA
This one is quite a bit different from the first series. And again, this is the self-same speaker, post-disturbance..

KLH LS #1 - Series #2 - Gently pushed, pulled, banged, bounced, shouted at in a disaproving tone and generally disturbed & perturbed - after 48hr rest.

Instruments: Fluke 8050A DMM (cal'd), Wavetek 111 funct. generator, Racal-Dana 9904 frequency counter. (Note: Due to possible 'creep' factor, 15 sec settling time is allowed from the moment the LS is switched into the meter circuit until the DVM measurement is taken. This figure was chosen somewhat arbitrarily, based on the RoC of the reading after the DUT is switched into the circuit.)

20 - 7.55
25 - 7.69
31.5 - 7.63
40 - 7.70
50 - 7.85
63 - 8.08
71 - 8.31
80 - 8.66
90 - 9.20
100 - 10.15
113 - 12.38
126 - 16.68
143 - 21.85
159 - 15.81
180 - 11.21
200 - 9.53
250 - 8.55
315 - 7.93
400 - 7.86
500 - 7.87
630 - 8.06
800 - 8.19
1000 - 8.35

As you can see, the variations are large.. to the point that they render the measurements almost pointless. We can see the same trends in Z, but the absolute values are shifted significantly.

Last edited by legendre; 20th March 2017 at 05:28 AM.
  Reply With Quote
Old 20th March 2017, 05:05 AM   #29
diyAudio Member
 
legendre's Avatar
 
Join Date: Jan 2017
Location: USA
Quote:
Originally Posted by Tweet View Post
From that measurement you are seemingly measuring the crossover network as well as the driver. It's 'in box' resonance appears to be around 143c/s which would appear to be typical of a small box driver of 4".

C.M
Correct. As I said previously, this KLH 9900 is a small 2-way HT satellite / bookshelf speaker. I suspect the 'crossover' is just an NP electrolytic cap in series with the tweeter leads. Isn't that typical for a basic 2-way? The woofer is like 3" or so, with a 3/4"-1" dome tweeter. Nothing at all special or fancy, just one of several pair of utility speakers I keep around for testing work.

Last edited by legendre; 20th March 2017 at 05:24 AM.
  Reply With Quote
Old 20th March 2017, 06:47 AM   #30
Tweet is offline Tweet  Australia
diyAudio Member
 
Join Date: Jan 2015
Here in a free loudspeaker impedance testing program which I occasionally use, I find it quite useful for quick impedance checks. Making up a simple jig easily makes testing that easy, not like that with SpeakerWorkshop.

It would require a full duplex soundcard though, I use a SoundBlaster Audigy Rx soundcard which is readily available. As I say the program is free but donations are appreciated.

https://www.acustika.org/

C.M

Last edited by Tweet; 20th March 2017 at 06:52 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
speaker measurement geometry astrojet Multi-Way 4 3rd April 2016 06:29 PM
speaker measurement questions Josephjcole Full Range 35 3rd June 2005 03:19 AM
Speaker measurement help in Atlanta david yost Multi-Way 2 27th April 2005 10:01 PM
speaker measurement software ucla88 Multi-Way 22 23rd February 2005 04:54 PM
speaker's load measurement GAK Multi-Way 1 8th February 2004 11:30 PM


New To Site? Need Help?

All times are GMT. The time now is 02:15 AM.


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