A question of resistance measurements on Philips MR SQ8 drivers - diyAudio
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Old 12th August 2010, 04:59 AM   #1
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Default A question of resistance measurements on Philips MR SQ8 drivers

Hi...have a set of the Philips SQ8 Mid Range drivers that are stamped 8 ohm but only measure 6.5 ohms. Any explanations for this deviation from stamped spec or would this be common?

My concern is that using these particular MRs in conjunction with 8 ohm Philips LF and HF drivers which measure an actual 7.9 ohms would create a relatively unbalanced 3-way system in which the Mid frequencies would be overly pronounced given their lower actual resistance.

Any insight would be much appreciated.
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Old 12th August 2010, 12:01 PM   #2
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Read through this
Resistance vs. Impedance
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Old 12th August 2010, 08:52 PM   #3
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Default More light please?

Thanks for the tutorial, but the question of why a group of six identical raw midrange drivers all marked as 8 ohm impedance will show differing measurements remains. Four show initial readings of 7.5 to 7.9 ohms while two others read only 6.5 ohms at their initial measurement.

What would such a variation be indicative of? Poor manufacturing quality control? Voice coil problems? Or is this within acceptable parameters of deviation?

And finally, is such a variation important in considering a speaker system build as it relates to raw driver matching?

I swapped out a 8 ohm HF unit in one speaker for an identical but 4ohm rated HF driver and the 4 ohm driver was appreciably louder.

This goes to my original concern relating to Philips SQ8's whose initial measurement shows a 6.5 ohm measurement (in the raw) decoupled from any crossover.

Pardon my apparent thick-headedness ,but I thought that as an initial starting point in speaker builds, driver matching was of some significance.

Any illumination would be most appreciated.

Last edited by VinylHampton; 12th August 2010 at 09:02 PM.
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Old 12th August 2010, 09:27 PM   #4
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There shouldn't be that much difference in the reading. Are the serial numbers consecutive or close?

When you say initial measurement, are you finding the reading settles down a lot?
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Old 12th August 2010, 09:48 PM   #5
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Please detail your resistance measurement equipment and technique.

Unless you understand all the possible sources of error, and what 4-terminal measurements are for, I would not expect repeatable and predictable measuremets better than +/- 0.5R wit your typical 3.5digit digital meter.
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Old 12th August 2010, 09:52 PM   #6
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The serial numbers are consecutive and the readings of the measurements on the raw drivers go from 6.5 to 7.1 ohms.
I just measured a whack of raw Sansui tweeters marked 4 ohms and they all measured between 3.6-3.9 ohms.

It's the 1.5 ohm deviation from marked impedance on the SQ8s that has me wondering ,ergo my questions related to matching driver impedances on a speaker build project.

Last edited by VinylHampton; 12th August 2010 at 10:08 PM.
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Old 12th August 2010, 10:07 PM   #7
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Probably not up to any electronic lab standards yet if my simple measurement process of using a Digital Multimeter with two clip probes yields repeatable and consistent measurement results on an assortment of raw drivers, uncoupled from any Xover and are consistent (+ or - 10 percent of listed impedance) and furthermore are duplicated by measurements using an analog multi-meter, can I not safely assume that the readings on this particular pair of SQ8s give rise to some concerns regarding speaker matching.

The Philips LF and HF drivers I intend to mate the SQ8s to all fall within 10 percent of their marked impedance ratings, whereas the SQ8s do not.

My question remains. Is this, or should it be, of any concern.
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Old 13th August 2010, 12:02 AM   #8
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Quote:
Originally Posted by VinylHampton View Post
Probably not up to any electronic lab standards yet if my simple measurement process of using a Digital Multimeter with two clip probes yields repeatable and consistent measurement results on an assortment of raw drivers, uncoupled from any Xover and are consistent (+ or - 10 percent of listed impedance) and furthermore are duplicated by measurements using an analog multi-meter, can I not safely assume that the readings on this particular pair of SQ8s give rise to some concerns regarding speaker matching.

The Philips LF and HF drivers I intend to mate the SQ8s to all fall within 10 percent of their marked impedance ratings, whereas the SQ8s do not.

My question remains. Is this, or should it be, of any concern.
No.
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Old 13th August 2010, 03:18 AM   #9
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Short, succinct and clear enough even for me...thanks Cliff and everyone else...although I still hope to discover the what, whys and hows of what I believe to be either aberrant production practises, the questionable accuracy of manufacturers impedance ratings or my own inadequate rudimentary measurement techniques.
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Old 13th August 2010, 02:56 PM   #10
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Well I would be concerned about a difference of that magnitude and look into doing a set of T/S tests to see what's what.

I would not like to use those drivers. For a modern production system that error is way out of normal.
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