# Should the mid driver have less sensivity than the bass driver (Harman curve in mind) ?

#### diyiggy

Hi,

How to choose the sensivity of the mid driver when having already the bass driver and wanting a sligthy diving spl magnitude à la Hartmann (Toole book) ?

There is the baffle step to think about. OK. But at seing such measurement -look at the picture with the overlapp of the 3 drivers- The midrange seen to need less spl orat least needs atenuation vis à vis of the bass driver overlapp : look at the green mid curve which seems to be circa 7 to 8 dB less than the end of the bass driver !

Here it is a Pida's member design just for illustration.
For the discussion : imagine I have for instance a Bass driver measured on its baffle around 91 dB/2.8V around 300 hz where I want cross over with a mid ! Which sensivity at minima should I select the mid driver ? Around + 3dB for the bafle step compensation or less than the bass driver in that 300 hz aera like in the picture number 4 above in order to have a sligthy diving curve and/or maybe try to avoid serie resistors ?

Forget it all and choose the mid sensivity sligthy equal to the 300 hz bass aera measurement at 1 m ?

#### YSDR

You can start with the datasheet frequency and impedance responses, put these into e.g. Vituixcad, simulate the enclosure, the baffle, the placement of the drivers and the crossover and you will get the answer.
The charecteristic sensitivity values of the drivers are not enough for this if you want accurate results/answers.

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#### PKAudio

Few points to give you a directions:
1. when you look at datasheet and drivers FRs and sensitivities, make sure you compare same numbers, which means dB/2.83V/1m, and you can forget about impedance
2. simulate bass driver alignment in Vituix, and subtract ~3-4dB bafflestep. You will get estimated system sensitivity.
3. Midrange drivers usually need at least some coils in the path. To avoid heavy low Rdc coils expect >2ohms in the series path, which means 1-2dB sensitivity loss
4. if all LR4 filter, then no sideband gain for the midrange, if all LR2 then you can expect 1-2dB sideband gain for midrange
5. midrange FR in the actual baffle will get 1-2dB gain in 1kHz area
6. doing SPL calibrated measurements helps a lot. Without SPL calibration, gated measurements with ~5ms window are harder to determine the value of primary filter coil, as this one basically realizes bafflestep compensation. Gated measurement can create bump below 500Hz, it looks that this is characteristic sensitivity, and you will end up with less then optimal bafflestep compensation, elevated are around 500-1000Hz, and issues with the sound. This is the reason why I started looking at the measurements also without gating, just 1/12smoothing. Of course, larger room, high ceiling helps a lot, or outdoor measurement.

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#### GM

In short, there's no such thing as too much efficiency, just a point of diminishing returns, so historically it's best to use the highest available and some form of frequency shaping EQ as required to ensure sufficient high SQ dynamic headroom.

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#### Scottmoose

+1.

As GM says, at the end of the day it's like most things: if you have too much, you can always get rid of what you don't need, so assuming all other things are equal, better to have a high efficiency / sensitivity & attenuate as necessary.

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#### YSDR

"assuming all other things are equal"
Yeah but this is not often happens. For example: if one of two of the same sized driver have higher efficiency, this probably comes at the expense of bandwidth. This can be problematic or beneficial, it depends. But for a midrange driver, the bandwidth loss from high efficiency is usually not a big problem, but that depends on the mating woofer, tweeter etc.
Anyway, higher sensitivity compared the woofer(s) is much better than a too low.

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#### Scottmoose

Agreed; that's why I stressed the point. The underlying principle still holds good though.

#### YSDR

Anyway, if we start with flat frequency response drivers, it is possible to get a flat anechoic frequency response loudspeaker (that resulting in a slightly sloped down aka Harman curve in-room response when the directivity is close to uniform) with a lower sensitivity (than the woofer) midrange driver because of baffle step loss towards lower frequencies and band-pass gain of the baffle response ripple.