Multiple drivers affecting thiele-small?

[t3031999]

I want to try to build my own multi-driver speaker and I have a few questions

I know that if 2 drivers are wired in parallel it halves the impedance, and doubles in when they are in series.

My question is what happens to the other Thiele-Small parameters. Like sensitivity,
I would think 2 drivers would increase the sensitivity as well as the Vas.
I would also think drivers in parallel would double the power handling.
But what about the Q parameters (Qes, Qts, Qms).

Please help me out.

 

[Rip Van Woofer]

I'm less than expert but multiple drivers will certainly give more SPL than single. How much more I don't know. Don't know if it's a simple doubling of the figure. From what little I know of speaker design things are rarely that simple!

Don't know about the effect on the various Q characteristics.

Remember that when you lower the impedance by wiring drivers in parallel, you create a more difficult load for the amp driving the system. The impedance could of course drop well below the "nominal" calculated impedance at some frequencies getting dangerously low unless you have a ballsy amp that will be stable into very low impedance loads at least for short periods. (This is why I am driving the two woofers in my actively crossed-over Orion system with separate amps for each driver). So you'll need to add impedance compensation to the crossover. This in turn will probably decrease the sensitivity of the paralled drivers due to higher insertion loss for the crossover (assuming a passive crossover of course). Calculating all of this will be fun.

This is why I don't design my own speakers!

Questions like these could probably be answered by a book like the ones by Vance Dickason et al.

Speaker/crossover design software would be a big help, too.

Also try the Madisound speaker building forum at madisound.com.

 

[HowY]

Actually I'm uncertain if the TS param's would change at all
since they are based on "ideal" conditions anyway...

the motor charistitics of the driver are really fixed
so the motion of the cone and sensitivity are spec'd
against a known condition.... (1w/1m for spl) so the
box and volume will remain the same anyway....

The trouble is really the xover...

with the inductor's and cap's basically reducing
final voltage as well as filtering particular waves.

In addition any cap and inductor combination sets
the x-over in some harmonic (3x 5x) of the source...

There is also the phase relationship typical in LW
style filters that in effect swaps the polarity
of the hi pass section.

So your back to where you started the TS parameters are an
ideal - used best for enclosure design. Speakers have a natural
roll off and have some "order" of dynamic range. All these used
in conjunction to design an enclosure & x-over for a particular driver.

Volumetrics with the drivers Xmax or it's volume displacement
determining the box size. Dynamic range for the use of X-over
design.

Hi-Pass
Band Pass (if you use a midrange)
Low-Pass

Now then the hardest of which IS determining the final
load (in ohms) that your DIY speaker presents it's amplifier
(especially if notch filters are used...)

Now what was the question again?

 

[rosarian]

These Thiele/Small parameters are not affected by using multiple drivers:

Fs, Qes, Qms, Qts, Xmax

These are increased for each additional driver:

Vas, Pe, Sd

so that 2 drivers doubles the values, 3 drivers triples the values, etc.

Sensitivity is affected differently. Putting 2 drivers in series has no effect, but putting 2 drivers in parallel adds 3 dB to the value.

 

[monkish54]

Connecting 2 drivers on the same output naturally results in a doubling of the sensitivity, meaning a +3dB gain. It doesn't matter whether you connect the speakers in series or parallel, the impact on sensitivity is the same.

However, when you parallel connect 2 driver you halve the impedance which means that for the same voltage output of the amplifier the power will also double, meaning another +3dB gain.

And naturally the opposite is true if you series connect 2 drivers and thereby double the impedance and halve the power on the same voltage output, meaning a -3dB loss.

The difference between series and parallel connections only come into play if your measuring equipment measures in volts and not in watts.

What it really means is that the same amplifier can produce 6dB higher SPL, or 4 times as loud, on 2 drivers connected in parallel as on a single driver or 2 drivers connected in series.

The differences when you calculate crossovers should be obvious. If you have a working system with a tweeter and woofer which is balanced for sensitivity, and you suddenly decide to add another woofer then you will firstly add +3dB for having 2 drivers on the woofers output. Now depending on whether you series or parallel connect you will either get a -3dB loss or a +3dB gain (or top of those +3dB from before, remember).

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