Off on another Idea - I never stop: Tweeters

[SwissXC90]

I can hear my High Performance tweeters but want a bit more from them.

Looking at my tweeters they use a 3.3uF bipolar electrolytic capacitor as the crossover on the High Performance system.

Interestingly, the Premium speakers use a 3.3uF WIMA 63V MKS4 capacitor, which are around 4x the price of the electrolytics, and a much better quality capacitor.

Here's an original Volvo Premium tweeter from the XC90 D-Pillar, you can see the WIMA 3.3uF cap mounted on the tweeter. That tweeter sells for USD 165 new:



And here is a standard High Performance tweeter, with the 3.3uF electrolytic capacitor. They sell for around USD 85 new:


Pictures have been shamelessly stolen from the internet. I'd give credit to the author if I knew him. But I don't.

Some DynAudio tweeters have 2 x resistors in series with the caps as well to dampen down the response a bit. Depends on what year / what speaker system is fitted.

So I just bought myself 4 x WIMA caps for 1 CHF each (0.75 GBP each), and it's dead easy to disconnect the electrolytic and fit the WIMA capacitor.
The WIMA caps are readily available everywhere. 63V is enough.

I am doubtful if it will make much of a difference but I thought I'd try it anyway.

Of course, I could swap all 4 tweeters for DynAudio tweeters.... but before I start down that path I want to do the cap test.

Speaker crossovers are all about matching speaker impedance and frequency response with capacitors for the right roll-off curves, coupled with matching the tweeters to the mids and woofers etc for the proper overall sound.

Just replacing an electrolytic with a WIMA cap is a real shot in the dark with no guarantee of any audible difference whatsoever.

But for 4 CHF (3 GBP) for 4 caps, I'll give it a go.

I can do the front door tweeters and the D-pillar tweeters incredibly easily, with very little dismantling.

I can temporarily disconnect the electrolytic cap, solder in the WIMA cap on one side of the car, and do a left vs right channel comparison to see if I can hear a difference.

I won't bother with the two-way coaxial rear door speakers, the mounting of the cap is more difficult as the electrolytic is on the mounting arm for the tweeter, so they can stay as they are. And I don't sit in the back...

BTW, the XC90 with High-Performance sound is a 10-speaker system:
2 x Front door tweeters
2 x Front door midrange/woofers
2 x Rear door woofers
2 x Rear door tweeters (mounted co-axially on the woofer)
2 x D-pillar tweeters (for the 3rd row passengers)
10 in total

The caps were mail order at my local electronic store, so I have to wait a week for them to arrive. I'll report back on progress at the end of March 2018.

[SwissXC90]

WIMA think they are good:

WIMA: The Capacitor for High End Audio Applications
https://www.wima.de/wp-content/uploa...WIMA-Audio.pdf

I am hoping for this to be true:

The capacitors in the signal path certainly have the most direct influence on the audio signal. Consequently real improvements in the sound can be achieved just by exchanging inferior quality capacitors

[SwissXC90]

My order is ready for pickup, I hope to trial fit the WIMA caps this weekend....

I did some research and based on the graphs of Equivalent Series Resistance ESR the WIMA MKS4 metallized polyester film caps should allow more signal to the tweeters.

But will I hear a difference....???

I'm hoping on data similar to this graph:


The standard wet type electrolytic cap is the green line.
The polymer cap is the red line.
In the above diagram the ESR is around 7 ohms for electrolytic at 5 kHz.
The equivalent polymer cap is around 0.5 to 1 ohms.
Of course, the capacitor value and brand all have an impact but the above is a good approximation.

Indeed reading the specsheet of the WIMA MKS4 shows an ESR of around 0.5 ohms at 5kHz.

Given that the tweeter is 8 ohms, that will result in a total impedance change at 5kHz from roughly 15 ohms (8 ohms speaker plus say 7 ohm ESR) to 8 ohms, resulting in twice the voltage, and twice the voltage is a 5.5dB gain.

Human ears can easily detect a 3dB gain, so I should hear 5 to 6dB.

So the math says I should hear a difference... let's see (hear)...

[oragex]

I swapped the base ones with the premium red capacitor ones in my S60. Got the premium ones for about £2 at the breakers, all S60 with HU-803 or HU-850 have them.

They are worth, won't blow your mind, but certainly did improve the sound.

I think the XC70 has some even beefier tweeters in the rear pillars.

[SwissXC90]

So I removed the 4 tweeters and fitted new caps to them today.

The 4 Volvo tweeters are 6 ohm tweeters, with 3.3uF electrolytic caps as basic crossovers.

I first did a comparison front channel left vs right sound test on music I know well, some Dire Straits.

I decided to add the 3.3uF WIMA cap in parallel with the existing electrolytic, thus giving 6.6uF of capacitance (capacitors in parallel add), to boost some of the lower high frequencies as well.

Did I notice a difference?
I believe I did.
The higher frequencies on cymbals are a bid louder, which helps the sound.

So I soldered the WIMA caps in place, using good old radio tech construction skills: the solder join makes the physical mounting connection as well as the electrical connection

Had to re-position the first cap slightly as it blocked the connector from mating properly.

All in all about 1hr work including going upstairs to solder and downstairs to try them out. And totally reversable if I decide to remove them.

Let me see if I can upload a pic....

[SwissXC90]

Interestingly I found a website that allows you to calculate the crossover network and tell you the capacitor size for a given frequency

The Volvo uses a first order 6dB/octave crossover for the tweeter.

Plugging the values into here:
https://www.v-cap.com/speaker-crosso...rderCalculator

We see that with tweeter impedance of 6 ohms and a 3.3uF capacitor (original) the crossover frequency is about 8 kHz.
By changing the crossover capacitor to 6.6uF as I did, the crossover frequency moves down to 4 kHz. (double the C, half the F).

[SwissXC90]

Finally uploaded the pics.

The WIMA MKS4 3.3uF 63VDC capacitors bought from Conrad Electronics (an electronics parts shop in Germany and Switzerland). They cost I think about 1 EUR each, or a bit less:


Fitted to the front tweeters:


Fitted to the D-pillar tweeters: