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Multi-Way Conventional loudspeakers with crossovers

Matching amplifier to loudspeaker question(s)
Matching amplifier to loudspeaker question(s)
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Old 29th December 2017, 09:05 PM   #1
montana1 is offline montana1  United States
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Default Matching amplifier to loudspeaker question(s)

Hi To All,
This is very much a newbie question and one that's probably been answered before elsewhere on this forum. But here goes, what virtues should a person look for in selecting an amplifier that will have the least amount on altering the x over and frequency response? I read somewhere that high output impedance is to be avoided. Is that correct? I'm looking for suggestions as to what amplifier specifications to look for in properly matching loudspeakers. It's time to work upstream in the signal chain and rather then make blind purchases; I thought asking a few questions here might save me some coin and buyers remorse.

Best Regards,
Rich
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Old 29th December 2017, 09:28 PM   #2
Joshcpct is offline Joshcpct  Germany
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Hi Rich

Yes, low output impedance / high damping factor = smallest amplitude/ xo changes.
But, i wouldn’t connect it to = better sound. I think most will agree.
Its always complex, but if you desire simple values: SNR, THDN, low-impedance-stability, cost-no-objective-outut-relais (!), load stability, lowend bandwidth, balanced inputs, no switches/potis/vu-meter/toys, .... are way more important.
Talking bout SS amps only ...

Cheers
Josh
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Old 29th December 2017, 09:35 PM   #3
montana1 is offline montana1  United States
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Josh,
Thanks for your input! That gives me some ideas when making an amplifier selection.

Best Regards,
Rich
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Old 30th December 2017, 09:27 PM   #4
AllenB is offline AllenB  Australia
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I don't use very low output impedance amps. Matching adjustments can be made between the amp and speaker.
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Old 30th December 2017, 09:39 PM   #5
montana1 is offline montana1  United States
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AllenB,
Thanks for your reply! Could you elaborate some on your methods used to match amp to speakers?

Best Regards,
Rich
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Old 30th December 2017, 11:20 PM   #6
eriksquires is offline eriksquires  United States
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Hi Montana1,

In theory, a perfect amp has zero output impedance. That is, the output frequency is load invariant. Most solid state amps behave like this above the rated minimum impedance.

However, it is also true a lot of very good amps are not so great, especially tube amplifiers that use transformer coupled outputs. The best way to illustrate this is to use the Stereophile simulated speaker load and compare a couple of amps.

First lets look at a good tube amplifier, reviewed here: Stereophile Audio Research Reference 75:

Click the image to open in full size.

Notice the black squiggly line. That +- 1 dB variance in FR is the interaction between the simulated speaker load, and the amplifier. Compare the same test to a solid state amplifier the Pass Labs XA605:

Click the image to open in full size.

Notice the variation is now much much smaller, +- about 0.1 dB

I am picking these amps at random, btw, haven't heard either of them. So, from a specmanship, speakers with higher and more even impedance perform better with tube amps.

Speakers with more variation in impedance, or very low impedance (i.e. ESL) perform poorly with tube amps.

However, this is somewhat of an exaggeration in the sense that your own ears matter a lot more than these charts. You should listen, but be prepared to hear this principle hold more-or-less true.

Also, it IS possible to design speakers specifically for tube amps, so that they have much more steady impedance profiles than normal. You'll read about this in reviews, I'm sure.

Best,


E
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Last edited by eriksquires; 30th December 2017 at 11:29 PM.
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Old 30th December 2017, 11:25 PM   #7
eriksquires is offline eriksquires  United States
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FYI, a long time ago I actually built the Stereophile simulated speaker load in XSim and posted it in another thread:

Simulated Speakers and Amp Z

For brevity, it may help to just take a look at the impedance of a typical 2-way system to understand what the amps are usually battling. These two lines are of the same 2-way speaker, with the port open (green) and closed (blue):

Click the image to open in full size.

While the impedance remains relatively high (>4 Ohms) at all frequencies, those peaks may induce some FR variance.

Also, almost forgot, the amplifier does not change XO behavior in terms of crossover frequency, but they do interact due to the final speaker impedance, as seen in this chart.

Best,

E
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Last edited by eriksquires; 30th December 2017 at 11:28 PM.
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Old 30th December 2017, 11:29 PM   #8
globalplayer is offline globalplayer  Germany
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Most important never use a lower impedance speaker than your amp impedance rating. This is asking for trouble.

If you use a speaker with higher impedance rating than your amp you won't be able to extract the max. power out of the amp.

Therefore it is generally best to match speaker and amp impedance.

If the amp has sufficient power you can use a higher impedance speaker, this will result in a higher damping factor and more cone control although less maximum power.

Because of the low damping factor of tube amps they generally like high impedance/high sensivity speakers.

If possible I choose amp wattage=1.5-2x speaker wattage.
You can never have enough clean headroom.
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Old 31st December 2017, 12:51 AM   #9
montana1 is offline montana1  United States
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Hi Erik,
Thanks for your very detailed explanation! I will study the thread you referenced on simulated speakers and amp z. Just another frontier to explore.

Best Regards,
Rich
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Old 31st December 2017, 12:59 AM   #10
montana1 is offline montana1  United States
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Hi globalplayer,
Thanks for your suggestions! I will be looking at purchasing an amp this coming year and will keep your recommendations in mind when making a selection. So for review, lets say the 3 way speakers I have are nominal 4 ohm; should I look for an amp with a higher damping factor (say 80-100)?

Best Regards,
Rich
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