Crossover Point

[Crocodile]

Further to my Mission M34i thread, I've been playing. They're currently bi-wired from the A/B terminals of my Rotel RA-1062.

What this has allowed me to do is listen to the HF & LF independently. I've found that the problem of harshness that I'm experiencing seems to be down to the tweeter's inability to reproduce distorted guitar, without doing an impression of a duck with laryngitis! Playing further with some test tones, I'm very surprised to hear the tweeter doing it's best to reproduce tones as low as 500Hz. I'm not at all surprised to find a 1" speaker struggling with tones this low.

My (very limited) understanding of the crossover is that it should prevent anything below the crossover frequency (2.4KHz in this case) from reaching the tweeter. I would expect to hear near silence from the tweeter until approaching the crossover point - or have I misunderstood completely?

 

[Anonymous]

Crocodile:
Further to my Mission M34i thread, I've been playing. They're currently bi-wired from the A/B terminals of my Rotel RA-1062.

What this has allowed me to do is listen to the HF & LF independently. I've found that the problem of harshness that I'm experiencing seems to be down to the tweeter's inability to reproduce distorted guitar, without doing an impression of a duck with larygitis! Playing further with some test tones, I'm very surprised to hear the tweeter doing it's best to reproduce tones as low as 500Hz. I'm not at all surprised to find a 1" speaker struggling with tones this low.

My (very limited) understanding of the crossover is that it should prevent anything below the crossover frequency (2.4KHz in this case) from reaching the tweeter. I would expect to hear near silence from the tweeter until approaching the crossover point - or have I misunderstood completely?

Crocodile,

You have touched on a very interesting point - the audibility of a drive unit beyond the crossover point.

Drive units do not cut-off immediately at the crossover point, but they are filtered out. The steepness of the filter is referred to as 2nd order, 4th order, etc.

 

[Anonymous]

The crossover point is where the Bass and Tweeter intersect and the rate of roll off is described in dB per Octave. The best compromise in passive designs is 2nd order or 12 dB/Octave which means your speakers will be 12dB less loud at 1.2 kHz and 24 dB down at 600 Hz, which isn't enough in our experience, or yours by the sound of it.

We've been trying to explain that problem to the subjective side of Audio for a couple of years now. If you design and active crossover it will have 1/100th of the distortion of the passive one and you can have much steeper filters than is practical in passive designs. These shut the tweeter down more quickly and dramatically improve the mid band.

You'll also find another dramatic improvement in the low end because connecting a decent quality, low output impedance power amp to the bass driver gets rid of boom and improves clarity as well.

Please also bear in mind that guitars can have a massive dynamic range and may push your amp to clip. A Maplins Scope for £80 is a great help in checking all this out.

In our opinion this is an area of hi fi that set to improve over the coming years as manufacturers which to better performing and more cost effective Active speakers.

Ash

 

[Crocodile]

Cheers guys.

Just been reading a bit more on how they actually work.

I'm awaiting a call back from Mission to see what they have to say about the crossover fitted to the M34i.

 

[Crocodile]

The call back never came, nor did a reply to an earlier e-mail. Seems Mission subscribe to the Ryanair school of customer service, ie "we've had you money so you can <insert expletive of choice> off".

The specs say it's a stage two & in the absence of Mission wanting to talk to me, I'll have to draw my own conclusions:

• The crossover is poorly designed with low grade components.
• The tweeter is more sensitive than the bass units but hasn't been attenuated in the crossover.
• The tweeter is simply rubbish.
• Mission (under IAG are rubbish).
• All of the above.

There's a pair of AE Neo 3s due for delivery today so I'll see how they go.