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Multi-Way Conventional loudspeakers with crossovers

wiring parallel or series sensitivity rules?
wiring parallel or series sensitivity rules?
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Old 3rd January 2014, 04:06 PM   #21
Greebster is offline Greebster  United States
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Quote:
Originally Posted by zead View Post
interested in creating a woofer system to play up to 200hz... would like to combine SS 13inch (90db) with SS 10inch (88.5db) ... they have same 8ohm... what i want to do is have these in the same box connected in parallel, with a highpass on 10inch so that it works 60hz up to 200hz and have either a low pass on the 12 at 100hz or just let it also get the same 200hz upper cut-off. How difficult is that?
It's not difficult, just hook them up with proper crossover more or less. Be aware that driving two different drivers with completely different (mainly mechanical) specs will create two different sounds, a timbrel change coloring the true sound. There were several speakers in the late 70's that used this approach and have for the most part been abandoned for good. Today we do know that this causes issue and can be measured so is not normally done unless drivers are the same.
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Old 16th November 2016, 06:19 AM   #22
Bill poster is offline Bill poster  Thailand
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acoustic coupling- if using opposing, side mounted woofers, connected in series, how does this affect sensitivity? Do u lose a further 3db?
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Old 16th November 2016, 07:15 AM   #23
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Bill poster View Post
acoustic coupling-
if using opposing, side mounted woofers, connected in series,
how does this affect sensitivity? Do u lose a further 3db?
Hi,

No.

FWIW the sensitivity specification of a driver is dB/2.83V/1m/2pi
space. That is 1W into 8ohm, 2W into 4ohm, 0.5W into 16 ohm.
This is the figure used in design software and for level matching.

Sometimes sensitivity is specified as dB/1W/1m/2pi. What
this means is the nominal impedance is taken ito account
and is 3dB lower for 4 ohms and 3dB higher for 16 ohms.
You can call this the nominal efficiency of a driver
but you don't use that figure in design software.
(Its the same as sensitivity for a nominal 8 ohm driver.)

Two identical drivers in series or parallel have identical
efficiency, +3dB over one driver, but the proper design
sensitivities are +6dB for parallel and same for series.

Note that this is all into 2pi (half) space. Into 4pi (full)
space you lose 6dB sensitivity and efficiency at low
frequencies. At higher frequencies as the radiation
moves to 2pi due to the baffle size, it moves up 6dB.
This is the so-called baffle step, that usually needs
some form of compensation, often not the full 6dB.

So take a typical 88dB 6.5" 8 ohm driver. In a two
way the sensitivity will be 84dB with 4dB of BSC,
(baffle step correction) with a 8 ohm impredance.
In a 2.5 way you usually get the full BSC of 6dB
the sensitivity will be 88dB, but 4 ohm in the bass.

rgds, sreten.

Last edited by sreten; 16th November 2016 at 07:37 AM.
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Old 16th November 2016, 07:35 AM   #24
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by zead View Post
interested in creating a woofer system to play up to 200hz... would like to
combine SS 13inch (90db) with SS 10inch (88.5db) ... they have same 8ohm...
what i want to do is have these in the same box connected in parallel, with a
highpass on 10inch so that it works 60hz up to 200hz and have either a low
pass on the 12 at 100hz or just let it also get the same 200hz upper cut-off.
How difficult is that?
Hi,

Extremely difficult. Try high passing any woofer at
60Hz, it's impedance peak simply won't let you.

What you need to do is split the box volume and
/or arrange suitable driver parameters, such that
both drivers are effectively used, and reach their
limits moreorless at the same time. It can get
very complicated to model, lots of options.

rgds, sreten.
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Old 16th November 2016, 04:33 PM   #25
BlueWizard is offline BlueWizard  United States
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Quote:
Originally Posted by Toast_Master View Post
Hello ...


Now for my example, assuming you had an amp that put out 100 watts at 4, 8 and 16 ohms, and a woofer that had an spl or whatever it called at 100 db 8 ohms at 1 metre with 1 watt

Now say we wire one speaker to the amp, its sensitivity will remain 100db/8 ohms/1 meter

Now say we wire 2 of the speakers in parallel making a 4 ohm load, I assume the sensitivity now rises to 103 db because a doubling of cone area at the same watts

Now say we wire 2 in series causing a 16 ohm load, I assume again that the spl now rises to 103 again because of the doubling of cone area,


Based on that does parallel and series sensitivity go by what the amp can out put at certain ohm loads....

Thanks
Did anyone notice that this thread was STARTED in 2008?

The above suggestion is in error. In Parallel, both speakers get the same voltage and have the same output, but combining them should give you a roughly +3db boost.

However, in Series, each speaker gets HALF the voltage, you get more output because of two speakers, but with each getting half the voltage, the output drops back. So it is +3 -3 = 0db. The output for two speakers is the same as the output for one speaker (more or less).

However, each speaker will consume half the power and have half the excursion. Typically given a boost in sound quality and low distortion.


If we assume this is ultimately a 3-way with a Midrange, then there are two ways to do this.

1.) At the lowest of the low frequencies, both bass drivers run in parallel. That would be a 3.5-way system.

Click the image to open in full size.

2.) Build the equivalent of a 4-way system - Low-Bass, Mid-Bass, Midrange, tweeter.

Click the image to open in full size.

I've considered doing something similar with a 10" and a 8". Using not the same size drivers is unconventional, but it can be done.

Click the image to open in full size.

Now, I used 3-way and 4-way in my examples because I already had those graphics. The absents or presents of a Midrange is up to you.

Though I think the 60hz and 200hz crossovers are bit unrealistic. Though what the precises crossover would be would depend on the rest of your design.

In a 3-way, the Low-Bass crossover could be in the 100hz to 300hz range, and the Mid-Bass to Midrange crossover would likely be in the 500hz to 1000hz range, though 500hz and 800hz are common in a 3-way.

With a Parallel configuration you get more output but at the cost of lower impedance and higher current. Higher current means more heat in the amp.

In Series you get greater power handling, but less output.

Also, in a multi-way system, where each driver has its own individual selected range of frequencies, their impedance does not combine.

As an example, if the Low-Bass covers 0hz to 200hz, and the Mid-Bass covers 200hz to 800hz, those impedance are not combined. Each has the impedance of a single speaker in their Pass-Band.

In a 2.5-way or a 3.5-way the Low-Bass would cover, just as an example, 0hz to 200hz, and the Mid-Bass would cover 0hz to 800hz. So, both are in parallel between 0hz and 200hz with a combined parallel impedance of 4 ohms. Above 200hz, the speaker system would be 8 ohms.

So, to make any sense of this, we would not only need to know about the woofer, but the vision for the complete system.

Does he plan to overlap the speakers, or does he plan to give each bass driver its own personal frequency range to deal with?

The OP is saying that the speakers will be in Parallel or Series, that implies that they can only cover the same frequency range. That's not really good design.

So, if the Original Poster is still around, he would need to give us his overall vision for the full speakers system. Then we can evaluate the possibilities. But without that, he will get nothing but speculation about what we think his vision of the speaker system might be.

But to his basic question, 2 speakers in Parallel will have higher output but lower impedance. Two speakers in Series, will have the output of one speaker, but each speaker will have half the voltage and half the excursion boosting power handling and lowering distortion.

That said, as he stated it, I don't think this is a realistic design. Perhaps he has no design and was simply wondering about the possibility of combining two speakers, but my interpretation of what he described is unrealistic in a real speaker design.


Just a few thoughts.

Steve/bluewizard
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Last edited by BlueWizard; 16th November 2016 at 04:44 PM.
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Old 7th January 2018, 05:20 PM   #26
Vortex is offline Vortex  Hungary
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Last edited by Vortex; 7th January 2018 at 05:47 PM. Reason: got my answer sry..
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Old 8th January 2018, 02:40 AM   #27
Tweet is offline Tweet  Australia
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There is a difference between sensitivity and efficiency. Sensitivity does not change but power conversion changes (that is, efficiency) with how you connect drivers together.

In a series connection with 2 drivers of the same impedance.... efficiency remains the same. Power conversion to SPL is the same as a single driver but the dynamic range of the 2 driver combination has now doubled. With similar drivers of the same cone area (Sd) the two drivers in series have twice the surface area of a single driver but being in series the current (the motivating force) is only half of that for a single driver. So 2 x Sd (cone surface area) x 1/2 of I (current) = 1 x Sd x 1 x I (current) for a single driver. So the efficiency doesn't change thus the SPL doesn't change for a series combination over that of a single driver of the same make.
Of course the impedance does change and is now double for the series combination relation to that of a single driver, but, the series combination does preserve Xmax over that for the single driver. This is important if the loudspeaker is to be driven to high levels.

With the combination of parallel drivers, the Sd is doubled and the total current flowing via the both drivers combined is double that for a single driver. Consequently, 2 x Sd x 2 x I (current) is equal to 4 times that for a single driver. Now 4 times in efficiency equates to a 6 db increase in SPL but the overall impedance of the parallel combination is now halved which puts a greater load on the amplifier's output. In the parallel combination Xmax is not preserved but is used up with the greater efficiency provided by this combination.

C.M

Edit: This is an old thread !


Last edited by Tweet; 8th January 2018 at 02:48 AM.
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Old 8th January 2018, 10:06 AM   #28
Vortex is offline Vortex  Hungary
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Interesting.

- WinISD still calculates for my 2 midranges in parallel with +3dB (I'd like to believe you 'cause I plan with +6dB lift in mind. If +3dB is the reality I have to re-think..)

- preserving Xmax: I thought series connection halves Xmax and parallel retains it (seen for 1 driver of 2, compared to 1 single driver). It should behave like light bulbs in series: half the light in series, while both at full light in parallel. Or I'm really misunderstanding something.

Old thread but there was still no final consent about it, everybody told their assumptions and I was just wondering like hmm, either half of the guys don't know physics or physics is cheating on us. I'm not an engineer, so I was hoping for a reliable statement but lots of people here seemed to make a final statement , fully contradicting to eachother.

That's why I google'd a bit and then it showed me this topic here, hey I'm registered anyway, let's ask again..

This shouldn't be that much of a rocket science I assume and if your +6dB theory is right, we can say WinISD's box simulation is wrong at that point, especially the SPL curves. They lift for 2 parallel speakers by 3dB only.
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Old 8th January 2018, 11:22 AM   #29
AndrewT is offline AndrewT  Scotland
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+3dB because you have input twice as much power to the pair of speakers.

The extra +3dB due to coupling ONLY applies where you have constructive interference, i.e. where the listener is in line with the interference peak/s AND the frequency is low enough that the two drivers can be considered to be coupled (close together).
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Old 8th January 2018, 11:27 AM   #30
Vortex is offline Vortex  Hungary
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Thanks. What does "low enough" mean ? (They would be crossed at around 125Hz, going up to 2.5k, active LR4).
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