Upgrading Z906 speakers

My old Z5500 speakers were starting to play up and I’ve loved them and had them for around 15 years now.

I published this page to keep my research as there was lots of bad info out there and I’m sure others are looking at similar issues to me.

The common issue with the Z5500 is the capacitors inside the amp have connections that fail due to the vibration of the bass. I could fix this quite easily but didn’t have the time and felt it was time to upgrade anyway.

After 15 years of daily use they have held up really well, I doubt a newer system will last anywhere near as long, with modern Caps usually failing after just 3 years.

Anyhow, the control pod was starting to power off and shut down, it works fine apart from this issue which points to the power cap inside the amp needing to be replaced or resoldered into place.

The only comparable speakers I found were the Logitech Z906, these have been out for a few years now and have similar power outputs to the Z5500.

Bear in mind you can spend 1000’s on a home cinema setup and I’m a firm believer that if you can get 80% of the quality for 20% of the cost you go with it and save some money, plus larger systems take up more space, generate more heat and use more power!

It’s like buying a very fast sports car and then only driving to the supermarket in town and back again!

I did replace all of the satellite speakers on my Z5500 with higher quality Kef 1002 egg speakers so was curious to see if these could be used on the Z906.

So will the Keff egg 8 ohm speakers work on the Z906 which has “4 ohm” speakers?

I decided to measure the resistance across the Z906 speakers without a connection and found them to be around 6ohms, when I measured the Kef Speakers it was 7ohms.

In reality you can add 8ohm speakers to a 4ohm system and it just means instead of getting 100% of the rated power this is reduced by around a third which just means you have to turn the dial up a little to compensate but were not running anywhere near the max power.

NB: (You can’t go the other way by fitting 4ohm speakers on an 8ohm system, as this will draw too much current and burn out the amp in a fairly short time.)

The Kef eggs are plenty loud enough even with the reduced power and actually make a better match for the Z906 than they did on the Z5500.

Kef egg 1002 specs

crossover frequency 3kHz (internal for tweeter cone)
frequency range 120Hz-22kHz
amplifier requirement 10-100 watts (we’re only using about 30watts)
sensitivity 86dB
maximum output 104dB SPL @ 1m
impedance 8 ohms

The official overall specs of the z906 speakers from Logitech are..

Total watts (RMS): 500 watts-
Subwoofer: 165 watts (6 ohms, at 52 Hz, at 10% THD)-
Satellites: 335 watts RMS (5 x 67 watts per channel 4 ohms at 3.85kHz, at 10% THD)
Maximum SPL: >110 dBC
response: 35 Hz – 20 KHz (this includes the woofer remember!)
Input Impedance: 8,000 ohms, min
Signal to Noise ratio, A-weighted: >95dB

This is very general and does’t give the info you need but when you check out the drivers specs that are used you get

NOMINAL IMPEDANCE 8 W
DCR IMPEDANCE 6 W
SENSITIVITY 1W/1m 88 dB
FREQUENCY RESPONSE 120 – 20KHz
FREE AIR RESONANCE 120 Hz
VOICE COIL DIAMETER 20 mm
AIR GAP HEIGHT 4 mm
RATED POWER INPUT 15 W
MAXIMUM POWER INPUT 30 W

So it seems that the Z906 is probably an 6ohm rated system and the 4ohm power ratings are quoted to make it seem more powerful. Bear in mind that the Z906 speakers are only rated to a power input of 30w and logitech are claiming 67w RMS output due to the lower ohm rating used in the calculation and setting this at 3.85kHz!

Without getting too nerdy, ohms range considerably in use and the quoted figures give a baseline to work from and compare.

Interestingly the small egg speakers range is 120hz to 22khz, which is well matched to the Z906 crossover and gives another 2khz, which does improve the top end considerably.

The kef speakers have a tweeter mounted in the centre of the speaker which gives them a higher range, and they are very well built.

How does this compare with the old setup on the Z5500?

The Z906 are very good, and they don’t have the aggressive bass of the Z5500, which if I’m honest would be rather intrusive in movies and dominated music. When you set the bass output correctly it is a very well balanced setup and works really well.

The Z5500 was probably 70% more powerful than we needed, the volume was rarely above 40%, the current setup is set to around 50% volume for a similar output to the z5500 in our small living room and works well. It doesn’t crank up as high but is better suited to a home listening environment. (There is also a hidden way to crank up the Z5500 even higher that the dial would normally allow)

The bonus is the smaller footprint the woofer takes up and the additional optical input.

There are better quality hifi speakers out there but these have lower frequency ranges and would require a lower crossover, typically down to around 80hz and this can’t be set in the Z906 without getting out your soldering iron!

Also a bigger speaker will be wasted when it’s only fed around 30W of power, so don’t get large speakers unless you are prepared to also get a higher power amplifier and powered sub woofer and throw out the z906.

Posted in Gadgets, Movies.

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