Speaker Impedence

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tallevan
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Speaker Impedence

#1 Post by tallevan » Sun Nov 17, 2019 12:05 pm

I'm considering the Omni 15 Tallboy plans.

Bill points out that the Kappalite 3015LF speaker has a volume displacement (vd) of 846cm2, whereby two Kappalite 3012LF speakers have a combined vd of 992cm2.

One 15 inch driver is almost half the price of two 12 inch drivers, lighter and not much less vd. So far so good.

My modestly powered but beautiful sounding solid-state amp delivers more power to a 4 Ohm speaker than to an 8 Ohm speaker.
I understand that the speaker's RMS power rating refers to the amount of energy it can soak up, rather than it's loudness.

So my first question is:
How much does speaker impedence affect loudness?

Of course, the Kappalite 3015LF has different TS parameters than the 3012LF, so other factors will come into play.
So let me ask a bonus question:
Is the Kappalite 3015LF-4 driver (the 4 Ohm version) suitable for the Omni 15?

Data sheet for the 3015LF-4 is here: https://www.eminence.com/pdf/Kappalite_3015LF_4.pdf

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Bill Fitzmaurice
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Re: Speaker Impedence

#2 Post by Bill Fitzmaurice » Sun Nov 17, 2019 1:06 pm

tallevan wrote:
Sun Nov 17, 2019 12:05 pm
So my first question is:
How much does speaker impedence affect loudness?
It doesn't, at least where maximum output is concerned. That's determined by driver displacement. Impedance affects sensitivity, how many dB you get per volt input. Halving impedance gives 3dB higher output per volt input. That can be somewhat significant if you have an amp that's seriously underpowered, otherwise it's not.
The 3015LF-4 isn't a 4 ohm driver. With a DC resistance of 3.85 ohms it's closer to 6 ohms. The DCR of the 3015LF-8 is 5.3 ohms, so the 3015LF-4 might have 2dB/volt higher sensitivity. A pair of 3012LF wired parallel has a DCR of 2.8 ohms, so they would have higher sensitivity than a 3015LF-4

Grant Bunter
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Re: Speaker Impedence

#3 Post by Grant Bunter » Sun Nov 17, 2019 3:07 pm

tallevan wrote:
Sun Nov 17, 2019 12:05 pm
My modestly powered but beautiful sounding solid-state amp delivers more power to a 4 Ohm speaker than to an 8 Ohm speaker.
This is true.
It comes to the heart of the matter as well.
I'll make a short assumption that 4 ohms on your amp is the lowest recommended impedance load.
While it is designed to do so, running your amp constantly at 4 ohms at maximum power is not good for it long term.
And while the amp puts out more power at 4 ohms than 8, it also uses more power doing so in terms of power supply.

2 x 16ohm drivers in parallel would be 8 ohms.
2 x 4 ohms drivers in series would be 8 ohms...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

tallevan
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Location: London, England

Re: Speaker Impedence

#4 Post by tallevan » Sun Jan 26, 2020 7:23 am

Thanks for the extra info, Peeps.

If anyone is interested, Avatar is no longer making 15" cabinets.
Consequently, they have a bunch of Eminence 3015LF-4 speakers (made for them) that they are selling on their website for $139:
https://avatarspeakers.com/shop/speaker ... ite3015lf/

Oddly, the TS and other parameters are different from the Eminence website:
https://www.eminence.com/speakers/speak ... e_3015LF_4

These are specified nominally 4 Ohms, but Bill points out above that they are closer to 6 Ohms.
In turn, the parameters for the 3015LF-4 (as specified by Eminence) are somewhat different from the 8 Ohm version (as specified by Eminence), but never mind that for now.

What is interesting to me is that the specs on the Avatar site indicate "Program Power", (that spurious parameter) as 300W. A quarter of what Eminence says for their usual version.

It's the same magnet size and coil diameter, Avatar doesn't state the xlim or xmax.

What do you reckon? Could Avatar's version of the 3015LF-4 really vary that much from the stock Eminence version?
I'm considering using it in an Omni 15 Tallboy for electric bass.

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Bill Fitzmaurice
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Re: Speaker Impedence

#5 Post by Bill Fitzmaurice » Sun Jan 26, 2020 9:13 am

The Avatar spec sheet shows pre-production data, so it doesn't look like a regular spec sheet. Xmax is seen as coil overhang, 8.06 mm, but that's not quite the same as a Klippel measured figure, which is likely at least 9mm. The 300 watt rating is also conservative, it's more likely the same 450w as the stock version. It's not a 4 ohm driver, if it was the Re would be close to 3 ohms. That's not unusual, most 4 ohm rated drivers are more like 5 to 6 ohms.

tallevan
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Re: Speaker Impedence

#6 Post by tallevan » Sun Jan 26, 2020 9:51 am

Thanks Bill. Very helpful.

I have one of the Avatar 3015LF-4 speakers on the way. I hope with poplar ply it will make a nice Tallboy, inexpensive, light and loud.

If the impedence is closer to 6 Ohms, should I modify the component values for your low pass filter?
I was thinking 47uF for the capacitor and either 1.5mH or 1.8mH for the choke.

tallevan
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Re: Speaker Impedence

#7 Post by tallevan » Sun Jan 26, 2020 9:58 am

.. or did you already bake that in to your design for the 4 Ohm version of the low pass filter specified in the plans?

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Bill Fitzmaurice
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Re: Speaker Impedence

#8 Post by Bill Fitzmaurice » Sun Jan 26, 2020 11:19 am

It wouldn't hurt to have the coil in the 1.5-1.8 mH range and the cap in the vicinity of 50uF. The filter in the plans assumes closer to an actual 4 ohm impedance that you get with a pair of 8 ohm drivers paralleled.

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