Spectral Content of Music

Ash,

The peaks above are around -40dB.

Are these very quiet tracks or is it something in your graphing package?

It most certainly does and also calls into question the wisdom of putting crossovers as in big three-ways or elderly monster two-ways in this region.

Ash

Regarding choice of x-over point(s), why would a company like PMC build these
new ( very expensive FWTW ) two-way actives with the x-over at 1.4 khz?
I'm assuming there must be trade-offs involved with decisions like this?
What would they gain by the relatively low x-over point?

http://www.pmc-speakers.com/product.php … ;show=spec

But then in one of their three-ways, x-overs at 380 hz and 3.8 khz ...

http://www.pmc-speakers.com/product.php … ;show=spec

I would think that since they have decided to partner the LF unit with a 34mm HF unit it is because the LF unit response falls off around 2kHz so they have to cross over lower, the downside is that the HF unit will still be providing audible output around middle C, not good.

The cross over frequencies in the 3 way are 'industry standard'

So assuming I understand Rod Elliot's commentary ( big if ), is he not saying finally,
that active x-overs are a whole different deal, where x-over points are concerned? ...

"It is not at all uncommon to see systems where the crossover frequency is set right in the middle of what I call the "intelligence band". This is the range of frequencies from 300Hz to 3600Hz, and is extremely important from a psycho-acoustic point of view. ..   It contains nearly all the "intelligence" of the sound, which is to say that if this band is "corrupted", intelligibility is greatly reduced.

Should a crossover be unavoidable in this region - due (for example) to available loudspeaker drivers - then the manufacturer must go to great lengths to ensure that "artefacts" created by the crossover are not audible. This often causes greater problems with amplifier loading at the crossover frequency, since impedance dips seem a common problem with many speakers. It will be found that these almost invariably occur at the crossover frequency.

By using an active crossover network, it should be possible to get excellent performance almost regardless of what the crossover frequency may be. The final setup will still have to be carefully aligned to make sure that there are no major issues with either driver at the selected frequency. In the course of many experiments and tests, it is safe to say that a properly set up active crossover gives one far more flexibility than almost any passive version, with the great advantage that no loudspeaker impedance correction is needed."

Two very important - and in my view often misunderstood - points here.

Larry

Sort of depends which of them were actually playing at the time of this quivk sample.  Frequency extremes may not be used often, but they are usually critical when they are being played.  Given the roll-offs in the music, all the more critical that a speaker be able to reproduce them as well as possible, IMO.

Last edited by BruceSeattle (2010-03-05 23:47:03)