Mixing high and low sensitivity

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Do people ever use very high and very low sensitivity drivers in the same speaker?

I've been playing around with Dayton RS125-4's and am thinking about using them in a 3-way. These have poor sensitivity (84.2), but are otherwise nice, especially for the price.

The natural choice seems to be Dayton's RS225-4, which is the same line and looks the same, only it is larger. These are much higher sensitivity (89). If I make a standard 3-way speaker uses 1 of each, I would need to burn 4.8db worth of power on a resister or l-pad to my woofer, which seems like a real shame.

I've seen a lot of posts asking about series and parallel wiring and sensitivity, and some of the information seems contradictory. Since the RS125-4 is 4ohms, I don't think I can use them in parallel. If I did series, would that give me approximately 3db more in output (from the same amplifier - not necessarily at the same watts, volts or amperes)?

Another idea is to use them with a non-standard crossover. The RS125 probably gets a first order highpass around 320Hz no matter what I do. Possibly I could then cross the RS225 in such a way that it gave the whole system a flat response. For example, if I had an F3 at 70Hz without a crossover, I could use a 1st order lowpass at 1kHz, with something like several notch filters between 80Hz and 1kHz. I'd have to be very creative to find a way to do it without a ton of high cost parts.
 
A woofer with up to 6dB more sensitivity can be a good thing to fight-off baffle-step. If the sensitivity mis-match is exact to do so, crossing-over to the midrange right in the area of the baffle-step frequency is then ideal, assuming the drivers can do it.

IG
 
This could be a happy coincidence for someone who doesn't need to place their speakers near a wall. Unfortunately, that isn't me.

I'd still like to know whether using 2 RS125's per speaker would help the relative levels. I am not sure whether I correctly understand how series wiring changes sensitivity.

One way to think about this is it doubles the resistance, which cuts the current in half for the same voltage, and therefore the circuit uses half the wattage for the same voltage. Each speaker is half as loud, but there are 2, so the volume is the same.

Another way to think about it is that all power used by a speaker either turns to sound or heat, and the ratio of the 2 stays relatively linear at all usable power levels (otherwise we couldn't have 'sensitivity' as a useful spec). Then if this ratio doesn't change, and the sound level doesn't change, you can't get any more efficiency without violating conservation of energy. You get less distortion, double the RMS, but the same sensitivity.
 
Do people ever use very high and very low sensitivity drivers in the same speaker?
Since the RS125-4 is 4ohms, I don't think I can use them in parallel. If I did series, would that give me approximately 3db more in output (from the same amplifier - not necessarily at the same watts, volts or amperes)?
Normally one wants the HF transducers to be more sensitive than LF so less power is wasted in resistors.

Doubling woofer area gives 3 dB more efficiency, and depending on the amplifier, when in series, half the power, a theoretical net result of the same level as one, given a constant voltage.

Few amplifiers are a perfect voltage source, so power does not cut in half at double the impedance, usually two four ohm speakers in series (a nominal 8 ohm load) will be louder than one, and given enough voltage, will be able to go 6 dB louder than one. Check the output power of the specific amplifier at different impedance, some current limit at 4 ohms and have hardly any more power than at 8.

By the way, it takes a 10 dB difference at 1000 Hz to sound twice or half as loud, a 3 dB difference is usually lost in the huge variations found in-room.
 
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Normally one wants the HF transducers to be more sensitive than LF so less power is wasted in resistors.

With the exceptions of baffle-step correction and using more than 1 of the same drivers, I'd think if everything had the same sensitivity you'd use a crossover without any resistors. Most designs I see have larger resistors for smaller drivers.

Do large sound waves take more power to create than small ones? I always thought that amplitude of the wave determined both its loudness and the power it takes to generate (ignoring that human hearing is not equally sensitive to all frequencies).

TA Speaker Topics: Loudspeaker Design Tradeoffs

Looking at their equation for maximum sensitivity, what was said here about doubling the woofer area, this would make sense.
 
Do large sound waves take more power to create than small ones?
If the reproducer is the same efficiency, the same amount of power is needed for LF production as HF production.

That said, producing a 40 Hz wave at the same SPL as a 4000 Hz wave at the same input power requires a far larger speaker system for the LF than the HF.

Given most domestic users dislike large portions of their real estate given over to huge speaker cabinets, for most the solution for loud low frequency is relatively small, low sensitivity, long excursion drivers with a lot of power behind them.

If one has the space available, like an attic or a basement to house woofer enclosures, sensitivity of around 111 dB one watt one meter down in the 30 Hz range is possible.

With just 2 watts input, such a system would be louder than an 84 dB sensitivity woofer using 1000 watts.

Makes the difference between CFL and incandescent light bulbs seem rather small.

Of course, in the winter, the heat radiated by low sensitivity speakers helps heat the room..
 
The Dayton site has the RS125-4 as 88dB...

How embarrassing! I've been talking about RS-100-4's.

84.2 is from PartsExpress and they are 82.65 on Zaph's!

The speakers being replaced are 88. I have my receiver set to raise the level of my right (test speaker) 5db. At the same distance on axis with a 1k test tone, they are the same volume level. Of course, I have no idea how accurately spec'd my original speakers are or the RS225-4 spec is.

I might end up with the RS180-4 instead, depending on the size of the toys my wife lets me play with. This gets me closer in sensitivity, but still might leave a hole between my sub at 80Hz and where they fall off. Parts express says sealed F3 of 69Hz, but the Dayton spec shows a fall off around 200Hz. I know the enclosure will have some effect, but a small sealed enclosure won't drop it more than an octave.
 
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