Bi-amp vs 2.1

[xeclipse]

Which one sounds better:bi-amp with two smaller woofers or the infamous 2.1 with a large woofer?
What are the cut frequencies and power ratios for the two for a really loud hi-fi system?

[Moondog55]

This is better answered in "Multi-way"

[T101]

It is always better to have full stereo sound including to have stereo bass.

Depending on many things including speaker efficiency the difference in power demand for equal loudness level might be 250:1!
For instance a midrange operating at 1 kHz at 1W and with sensitivity of 96 db/w will produce 96 db spl @ 1 m to match the subjective loudness level the woofer will have to produce 110 db spl @ 1 m at 40 Hz and 117 db spl at 30 hz...

With a woofer with sensitivity of 88 db/w it would take 200 w at 40 Hz and 800 watts (that was a surprise) at 30 Hz to match a 96 db/w midrange operating at 1w at 1 khz...
If you are not trying to match the loudness level, but only the spl level it would take only 7 watts for the 88 db/w woofer to match the highly sensitive midrange. And it would be 1:1 if the sensitivity of both drivers is the same... which is never so with systems designed for high SPL.

So the answer vastly varies. Typically a healthy 200w amp will be able to satisfy you pretty much and a 500w amp with speakers effective over 90 db/w will be a handful.

[xeclipse]

Thanks T101!
ESP suggest a crossover frequency of around 300 to 350hz,how is that compared to 80-120hz?

[sangram]

@300-350Hz XO, power level for the lower and upper drivers is equal. Below that you need to increase power to the woofer or lower half.

Also at 300Hz there are some issues with phase shift if you use large drivers. I have a pretty big problem with that exact crossover frequency. In spite of lots of EQ I am unable to correct the response at listening position. These are large OB line arrays with a pair of 12" in a sealed box, firing sideways to the main array. I will be dropping the frequency to 120Hz in the second version of the concept, obviously after adding more grunt to the bottom.

[T101]

Originally Posted by xeclipse

Thanks T101!
ESP suggest a crossover frequency of around 300 to 350hz,how is that compared to 80-120hz?

Who or what is ESP?

You could pretty easily find the minimum crossover frequency if you look at the response curve of your midrange or if you calculate the excursion limited SPL of the midrange.
So it depends on the midrange, for my taste the lower the better, but it depends on baffle step and the low range response too.

Sorry, but I don't have a larger graph for the correlation between the displaced volume per cycle and the frequency and SPL, you should find one extending at least to 500 hz or 1 kHz and it'd be good if you post it as i don't have such too.

Here below is a graph that will orientate you a little.

Generally you should take the effective area of the membrane of the midrange and multiply it with the peak effective excursion, if it is 200 cm2 and 5mm you should always multiply equal units (cm with cm) so it would be 200X0.5=100 cm3 maximal displacement per cycle.

Then you find how low can you go with 100 cm3 at the desired SPL
Have in mind to consider one octave below the cut off point - for instance if you use 12 db/oct and aim to 100 db SPL, you should check if the midrange has enough displacement to cope with the demands of 88 db @ 1 oct lower
For instance if it has enough displacement for 100 db @ 200 hz, is it able to reproduce 88db spl @ 100 hz....

I have that kind of problems with an OB mounted midrange with first order crossover at about 200-250 hz... it just goes out of excursion at high levels because with 6 db/oct crossover it does 125 hz at -6 and 62.5@ -12 db - which would be 88 db total at 100 db mean system level... which is quite allot for a 6.5 inch midrange (actually it's allot for some 12 inch drivers too...)

Best Regards!

[Cal Weldon]

Moved to Multi way

[xeclipse]

Originally Posted by T101

Who or what is ESP?
Rod Elliot in Elliot Sound Products: Elliott Sound Products - The Audio Pages (Main Index)