Kef Q100 Speaker Drive Unit Testing

As with the Kef HTS3001SE I tested, I ordered a set of the Kef Q100 Bookshelf speakers in order to remove and review the raw Q100 driver itself. I really wanted to see how this coaxial design performed. Zaph had already tested this one but I wanted to do Klippel LSI testing on it to see how the suspension performed. He actually mentioned this in his writeup and I thought it would be cool to provide the results. Of course, since I had it on the test baffle I did some other standard measurements as well. The one I was interested in, but didn’t perform on the HTS3001SE driver was tweeter frequency response performance with movement of the woofer. I don’t necessarily have an easy way to test this so I did something a bit different: I used a 9v battery to statically ‘fix’ the woofer either in the coil out or coil in position and measured the response. I then compared this to the woofer at rest performance of the tweeter and did a direct comparison. This is discussed further below.

Let’s get on to the testing, but first … the obligatory pictures …

This driver is quite the little beast. A very large motor and pretty substantial surround make this one of the largest 5.25″ drivers I’ve personally seen. Although I didn’t weigh it, it is fairly heavy due to the woofer’s ferrite magnet as opposed to neodymium. This results in large and heavy. I can’t exactly measure the voice coil but comparing it to the tweeter assembly, it appears to be a few mm larger in radius so I’d estimate VC diameter at roughly 55mm. It is best to rear mount this driver given the very tall surround at approximately 12mm, but for the purpose of my test I front mounted it.

If you look at the ‘Tangerine’ waveguide/lens/whatever you want to call it, you’ll notice there’s actually a phase plug on the tweeter. The HTS3001SE does not have this.

For those who want to read about the Tangerine waveguide, click this link (PDF format). There’s also discussion on the radial ribbing of the other Uni-Q cones, which this driver doesn’t employ.

Raw Driver Physical Measurements

First off, given this isn’t sold as an individual driver, I have taken my own measurements. These are rough measurements taken with my not-so-recently calibrated calipers, but should be good within +/-1mm.

Dimension	mm
Outer Diameter	143
Mounting Diameter	120
Mounting Depth	83
Effective Piston Diameter1	109
Effective Piston Diameter2	60
Flange Thickness	0.34
Mounting Tab Thickness	0.65
1) Half surround to half surround; including space consumed by coincident tweeter.
2) Half surround to half surround; NOT including space consumed by coincident tweeter.

Test Results

To make things a bit easier to manage, I’ve broken down the test results in to two sections:

1. Woofer Testing
2. Tweeter Testing

Part I: Woofer Testing

Woofer Thiele-Small Parameters and Impedance

Note: When determining the full suite of T/S parameters, the effective diameter of the driver is needed to calculate Vas, Bl, etc. Most of the time this can simply be measured by measuring the diameter of the driver from half-surround to half-surround since the motor must control the entire cone area. However, in this case, the entire cone does not move. Therefore, the effective diameter (and resulting Sd) is not the entire diameter of the driver. The effective diameter here is determined by subtracting the static tweeter assembly from the overall effective diameter of the woofer. See physical measurements section above for all values.

Electrical Parameters
Re	3.09	Ohm	electrical voice coil resistance at DC
Le	0.256	mH	frequency independent part of voice coil inductance
L2	0.427	mH	para-inductance of voice coil
R2	3.39	Ohm	electrical resistance due to eddy current losses
Cmes	318	µF	electrical capacitance representing moving mass
Lces	18.82	mH	electrical inductance representing driver compliance
Res	29.82	Ohm	resistance due to mechanical losses
fs	65	Hz	driver resonance frequency

Mechanical Parameters
(using add. mass)
Mms	12.834	g	mechanical mass of driver diaphragm assembly including air load and voice coil
Mmd (Sd)	12.108	g	mechanical mass of voice coil and diaphragm without air load
Rms	1.352	kg/s	mechanical resistance of total-driver losses
Cms	0.467	mm/N	mechanical compliance of driver suspension
Kms	2.14	N/mm	mechanical stiffness of driver suspension
Bl	6.35	N/A	force factor (Bl product)

Loss factors
Qtp	0.365		total Q-factor considering all losses
Qms	3.878		mechanical Q-factor of driver in free air considering Rms only
Qes	0.402		electrical Q-factor of driver in free air considering Re only
Qts	0.364		total Q-factor considering Re and Rms only

Other Parameters
Vas	3.6615	l	equivalent air volume of suspension
n0	0.241	%	reference efficiency (2 pi-radiation using Re)
Lm	86.02	dB	characteristic sound pressure level (SPL at 1m for 1W @ Re)
Lnom	87.14	dB	nominal sensitivity (SPL at 1m for 1W @ Zn)
Sd	74.46	cm²	diaphragm area

Woofer Large Signal Analysis with Klippel’s LSI Module
Displacement Limits			thresholds can be changed in Processing property page
X Bl @ Bl min=82%	>4.2	mm	Displacement limit due to force factor variation
X C @ C min=75%	1.9	mm	Displacement limit due to compliance variation
X L @ Z max=10 %	2.8	mm	Displacement limit due to inductance variation
X d @ d2=10%	17.1	mm	Displacement limit due to IM distortion (Doppler)

Woofer Frequency Response

Measured at 2.83v/1m. Stitched with a nearfield measurement at approximately 500hz.

Woofer Harmonic Distortion

Part II: Tweeter Testing

Small Signal Parameters

Electrical Parameters
Re	2.84	Ohm	electrical voice coil resistance at DC
Le	0.018	mH	frequency independent part of voice coil inductance
L2	0.011	mH	para-inductance of voice coil
R2	0.5	Ohm	electrical resistance due to eddy current losses
Cmes	110	µF	electrical capacitance representing moving mass
Lces	0.28	mH	electrical inductance representing driver compliance
Res	1.09	Ohm	resistance due to mechanical losses
fs	902.6	Hz	driver resonance frequency
Loss factors
Qtp	0.491		total Q-factor considering all losses
Qms	0.678		mechanical Q-factor of driver in free air considering Rms only
Qes	1.769		electrical Q-factor of driver in free air considering Re only
Qts	0.49		total Q-factor considering Re and Rms only

Tweeter Frequency Response

Tweeter Harmonic Distortion

Tweeter Response vs Woofer Position

I thought it would be interesting to see how the position of the woofer cone impacts the frequency response of the tweeter. This matters when you’re listening to music and isn’t captured by a standard sine sweep. To measure this performance I simply connected a 9v battery to the woofer’s terminals in positive polarity, then negative polarity which resulted in an approximate +/-3mm shift in cone direction. I ran a sine sweep over the tweeter while the woofer was a) at rest, b) fixed out, and c) fixed in. The pictures below illustrate these different configurations.

Woofer at rest:

Woofer fixed out:

Woofer fixed in:

The following results are of the three positions discussed above overlaid on one another. The lines are labeled per the woofer position. Note: The SPL level is not absolute here. I performed the test at the same volume level throughout but it is not intended to reference any set test paraemter such as 2.83v/1m or 1w/1m.

End

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