• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Understanding a Speaker's Recommended Amp Spec.

ash87

Member
Joined
Feb 1, 2022
Messages
31
Likes
9
Hi ASR,

I’m interested in getting a 2 channel amp for some Chora 826 speakers I’m planning to buy and I don’t quite understand the speaker's amp recommendations.

The Chora is 8 Ohm nominal and 2.9 Ohm minimum with a amp recommendation of 40/250W.

I am considering a Buckeye amp, but don't understand how to reference the buckeye amp specs to the Chora 40/250W recommendation

Without sounding totally clueless, I understand that under powering speakers will cause the amp to feed heavily distorted signals that will screw up the drivers (hence 40W minimum recommended amp). And I understand that giving a speaker more juice that it can handle will cause severe excursion and damage the drivers (Don't need any amp that will blow up your speakers at 12:00 on the dial). What I don't understand is how to calculate that sweet spot and determine what is appropriate "headroom".

Thanks in advance for offering an help to a newb.

- Alex


p.s Is the Chora amp rec. of 40/250W assuming at 8 ohm (like the amp rec. always is at nominal impedance)?
 

AudioStudies

Addicted to Fun and Learning
Joined
May 3, 2020
Messages
642
Likes
328
The amp power recommendation would not be restricted to the nominal impedance, the speaker manufacturer knows full well that the impedance will vary. My guess is that all of those amp power specs are RMS (root mean square) power, and not peak or instantaneous power. If that is the case, the HPEX may very well be capable of more than 250 watts for peak power. I would also assume that the Chora recommendations for amp power are RMS. Most of the time during playback the amps are not at peak power. I am no expert, and I hope some experts will weigh in. But I don't have the sense that any of these amps would be harmful to your speakers., unless you cranked up the volume way beyond listenable levels (and you have no reason to do so).
 

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
16,446
Likes
28,341
I would feel pretty sure Focal means RMS 40 wpc @ 8 ohms minimum and 250 wpc @ 8 ohms maximum. The difference between those by the way is only 8 db SPL. So you don't have to nail it exactly.

So any of the amps you listed should be fine.

Many amps can put out more power into 4 ohms than 8 ohms, and some even more into 2 ohms than 4 ohms. If there is an amp I like, I wouldn't worry if it were a bit over like say 300 watts. Watt ratings on speakers is not an exact science, and music is so variable those are general guidelines to keep you from having too few watts, and enough not to be on the edge of blowing things up. I could delve into it in more details, but basically any amp rated for 250 or less at 8 ohms should be safe for you.
 

tomtoo

Major Contributor
Joined
Nov 20, 2019
Messages
3,146
Likes
3,829
Location
Germany
The low power recomend makes no sense, couse this depends just how loud you like to listen.

The max. Power is tricky and depends on so many things that you could write books about.

To finde the sweet spot for you. You need to know the efficince of the speakers.
How far you sit away.
And how loud you like to listen at that place.
 

AudioStudies

Addicted to Fun and Learning
Joined
May 3, 2020
Messages
642
Likes
328
In the old days, when most amps were Class AB, one way of evaluating an amp was to look at the power specs for various impedances and see if they go up or down as the impedance goes lower. For example, if an amp could deliver 100 W at 8 ohms, then 150 W at 4 ohms, that is a good thing. But any amp that delivered less power as the impedance went down was not considered as high a quality of an amp. With all these new classes of amps now, beyond traditional AB, that kind of changed the landscape. My understanding is some of these newer classes of amps are just fine even though they may deliver the same power into 8 ohms as into 4 ohms.
 

AudioStudies

Addicted to Fun and Learning
Joined
May 3, 2020
Messages
642
Likes
328
I would feel pretty sure Focal means RMS 40 wpc @ 8 ohms minimum and 250 wpc @ 8 ohms maximum.
Only at 8 ohms? I am not saying you are wrong, just having trouble grasping why any manufacturer would recommend amp power based on only the nominal impedance, when we know that during playback the impedance will be all over the map.
 

AdamG247

Coadjutor Miscreant and general Scalawag
Moderator
Forum Donor
Joined
Jan 3, 2021
Messages
2,996
Likes
7,886
Hi ASR,

I’m interested in getting a 2 channel amp for some Chora 826 speakers I’m planning to buy and I don’t quite understand the speaker's amp recommendations.

The Chora is 8 Ohm nominal and 2.9 Ohm minimum with a amp recommendation of 40/250W.

I am considering a Buckeye amp, but don't understand how to reference the buckeye amp specs to the Chora 40/250W recommendation

Without sounding totally clueless, I understand that under powering speakers will cause the amp to feed heavily distorted signals that will screw up the drivers (hence 40W minimum recommended amp). And I understand that giving a speaker more juice that it can handle will cause severe excursion and damage the drivers (Don't need any amp that will blow up your speakers at 12:00 on the dial). What I don't understand is how to calculate that sweet spot and determine what is appropriate "headroom".

Thanks in advance for offering an help to a newb.

- Alex


p.s Is the Chora amp rec. of 40/250W assuming at 8 ohm (like the amp rec. always is at nominal impedance)?
When trying to determine Amp requirements for specific speakers. Just looking at the manufacturer specs is going to usually be misleading. These speakers have been tested by Sterophile and the results were far from the OEM specifications. These speakers drop down to below 3 ohms in some frequencies and I would say that they averaged more like 4 ohms than 8. Focal even lists the both these numbers. Min is listed at 2.8 ohm. This is the important number because it tells you the speaker becomes very powe hungry at certain frequencies. This is normally seen in the lower bass rages of the speakers. 100 hz and below.

So you need to look for an Amp that will be stable down to 4 ohms min and maybe consider amps that can handle sub 3 ohms loads. If it were me I would be looking for 4 ohms Amps. Focal’s recommended power of 40/250 watts is rated at what Ohms? Since they rate the speaker at 8 ohms. We can assume that this power spec is for 8 ohms load. You can safely double the power at 4 ohms. Making the power spec at 4 ohms to 80/500 watts. This puts you in the Hypex NC502MP category. Again this is just my opinion based on very limited data about these speakers. The NC252MP will not give you any head room for dynamic peaks.
 

DVDdoug

Major Contributor
Joined
May 27, 2021
Messages
1,363
Likes
1,731
Without sounding totally clueless, I understand that under powering speakers will cause the amp to feed heavily distorted signals that will screw up the drivers (hence 40W minimum recommended amp).
You can ignore the minimum rating. * You can check the sensitivity of the speaker to see how loud it will go with 1W, and make calculations from there...

The maximum rating is supposed to mean that it's safe to use a 250W amplifier hitting 250W peaks with regular program material with no clipping. It can't (necessarily) handle constant 250W test tones and the tweeter can't handle as much power as the woofer. It's the short-term average that burns-out speakers and highly-compressed music peaking at 250W is worse than highly-dynamic music peaking at 250W. So it's kind-of a fuzzy guideline.

But I don't trust most amplifier ratings or most speaker ratings. ;)




*Blowing drivers with low distorted power is "mostly false". You aren't going to fry a 250W speaker with a 40W amp unless you are playing constant high-frequency test-tones, and 250W test-tones would be worse!

It's true that you can get more power with clipping . A square wave (which can be a very-badly-clipped sine wave) has twice the power of a sine wave at the same voltage, and that additional power is all in the harmonics. But the lower harmonics are the strongest and most of the power is in the low frequencies so the additional power to the tweeter is limited by the harmonic content of a square wave. And the clipping can actually end-up reducing the regular musical high-frequencies and harmonics.
 
OP
A

ash87

Member
Joined
Feb 1, 2022
Messages
31
Likes
9
Thanks for all the replies. I asked Focal if their recommended amp spec was 8 ohm RMS and the response was basically, "Go listen at a dealer, we can't tell you anything more specific."

TBH I'm still not all that clear. I think this is my main takeaway here:
but basically any amp rated for 250 or less at 8 ohms should be safe for you.

But the above does contradict this:
We can assume that this power spec is for 8 ohms load. You can safely double the power at 4 ohms. Making the power spec at 4 ohms to 80/500 watts. This puts you in the Hypex NC502MP category. Again this is just my opinion based on very limited data about these speakers. The NC252MP will not give you any head room for dynamic peaks.

The NC252 is sub 250W @ 8 ohms, so "should be safe" but doesn't "give any headroom" for dynamic peaks?

But then this is telling me that I need to find an amp that will not output any more than 250W, meaning the NC252MP is the only option because the other amps peak higher than 250?

The maximum rating is supposed to mean that it's safe to use a 250W amplifier hitting 250W peaks

Always a fun time navigating the complexities of HiFi forums.

Thanks again for the replies.
 

AdamG247

Coadjutor Miscreant and general Scalawag
Moderator
Forum Donor
Joined
Jan 3, 2021
Messages
2,996
Likes
7,886
Your thinking in linear terms and amp/Spkr power is logarithmic. Think of this analogy. You have a heater that requires 250 watts to run at 100%. Do you get a power generator that can produce 250 watts at full throttle or do you get a generator that can produce 500 watts and run your heater at 50% throttle? Also keep in mind that with just about all power amps, the closer you get to their max power output you also start getting more distortion and noise generated. Go look at the power graphs for these amps. You will see as power output goes up so does the noise/distortion percentage. A more powerful amp will run easier and quieter driving the speakers. You in most cases, unless you’re outside, will be limited to how high you crank the volume by how loud the speaker will be in your room. You will know when they are too loud. Do some reading about dynamic range in music and movies. Then consider that a 3 dB increase in loudness requires a doubling of power. Each time. It doesn’t take many doublings for you to reach bigger numbers of power needed. Speakers power draw is constantly fluctuating from small amounts to large amounts for peaks and low frequency sound. The more Bass in music means more power is needed to produce that range of sound.

Here is a good video that explains how dynamic power from an amp to speakers works:

 

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
16,446
Likes
28,341
Only at 8 ohms? I am not saying you are wrong, just having trouble grasping why any manufacturer would recommend amp power based on only the nominal impedance, when we know that during playback the impedance will be all over the map.
Well amps are typically rated at 8 ohms. They can take as much of the complexity in answering the question for the consumer into account and give a suggestion that makes some sense. Nominal ratings give you some idea if the speaker generally is okay with an 8 ohm rating or 4 ohm or something else. The subject is quite complex to answer with any exactness. The impedance of nearly all speakers is a roller coaster ride, and you need to take into account reactance. One speaker's 2.9 ohm minimum might not be very taxing and one with a high amount of reactance could be nearly an amp killer.

For an over-simplified example, I have speakers that have a minimum impedance of .75 ohms. Do I have to find an amp rated at high power for that? No they suggest 100 watts to 250 watts, and note the speaker can handle up to 1000 watts. The same speakers have a very high impedance well over 30 ohms in the lower frequencies. In fact you don't even need an amp with much current capability. Because the high impedance is all lower frequencies and the 3/4 ohm is up at 20 khz where you have very little power in music.

The only speaker I know that is almost wholly resistive are the Magnepans. They are usually 3 or 4 ohms and need some current, but otherwise aren't really a difficult load.

So Focal has taken all this into account, and would know if most amps up to 250 watts will be okay with the load of their speakers. One review says in the low end the speaker can require quite an amp as the 2.9 ohm minimum comes with lots of reactance and quite a bit of current is needed. Suggesting it should be rated as 4 ohm nominal. Most good amps of 250 watts could handle at least a bit more than that at 4 ohms. Again these ratings are a craft almost as much as a science.

Is it possible to find a 40 watt amp that couldn't handle these speakers? Sure. These aren't cheap speakers and Focal likely expects decent amplification. None of the amps mentioned by the OP are junky amps and I don't expect a problem. The most likely occurance is someone with an AVR thinking it has 40 watts and it would be okay. It might not be. I mentioned in my other post it is a complex topic if you get into the picky details. I'd still say the simple answer to the OP's question is any of the three amps he listed will be fine.
 

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
16,446
Likes
28,341
About that dynamic power, how much is enough, how much is good? An amp with 6 db of dynamic power would be very good. It would mean 400% more power for peaks. Yet 6 db while not nothing isn't subjectively all that much louder. Does Focal know at more than 250 watt peaks the tweeter might burn out in a fraction of a second? I don't know. It could be so. Not very many tweeters can handle 50 watts at high levels for any length of time. Does it matter if you have a 100 watt amp with 400 watts of dynamic power or a 400 watt amp with zero additional dynamic power?

It really is a complicated subject if you try to get exact answers. Plus there are no completely exact answers if you don't know what signal is being played. Again I can almost guarantee you the tweeter would not take 50 watts for 1 minute, probably not for 10 seconds, quite possibly not 1 second. Fortunately such a thing in music would be incredibly rare.

The situation for power ratings of speakers is something of a mess. A number of things could be done to improve it, but all of them would be terribly confusing to regular consumers who don't know about electronics and speakers. So this is where we are.

For more pessimistic treatments of the topic:


 
Last edited:

AudioStudies

Addicted to Fun and Learning
Joined
May 3, 2020
Messages
642
Likes
328
Think of how often tweeters in car audio systems are fed signals from amps with much more power than the tweeter is rated for, in active crossover systems. Yet the tweeters for the most part are Ok. I am not sure how often the reason the tweeters are ok is because a blocking capacitor was used or that the music just wasn't played loud enough to hurt the tweeter.
 
OP
A

ash87

Member
Joined
Feb 1, 2022
Messages
31
Likes
9
Thanks again for more good info.
Here is a good video that explains how dynamic power from an amp to speakers works
If an amp doesn't come with meters like in the video, is there a way to add a meter to an amp or possibly see it digitally (in something like miniDSP)?


None of the amps mentioned by the OP are junky amps and I don't expect a problem. The most likely occurance is someone with an AVR thinking it has 40 watts and it would be okay. It might not be. I mentioned in my other post it is a complex topic if you get into the picky details. I'd still say the simple answer to the OP's question is any of the three amps he listed will be fine.

Just heard back from Buckeye on lead times. 9-10 weeks is testing my patience considering I just ordered the Chora's today. On the other side of the 40/250W spectrum, what would be the drawbacks of using an amp like Topping LA90 at 50W 8ohm? From everything said here, I understand it may be limited to lower volumes or risk not having enough wattage to produce dynamic peaks. It does appear to run without much distortion as it approaches it's max output (from how I read the review). I just don't see any specs saying whether or not it can dig deeper than 4 Ohm.

Maybe use the LA90 as a stop gap until the Buckeye comes in, then sell or find a new use for the LA90 down the line. It's 50W at 8 ohm into 91 db speakers in a 24x12' room *shrug emoji*. My selection criteria for audio products is unusual. I'm not buying made in China unless the company is Chinese. Don't ask...

@Blumlein 88 and @AdamG247, thanks for the reference links. I think Blumlein's are a bit too technical for my 2 semesters of community college electronics, but I may take a second look in a more ambitious mood.
 

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
16,446
Likes
28,341
Thanks again for more good info.

If an amp doesn't come with meters like in the video, is there a way to add a meter to an amp or possibly see it digitally (in something like miniDSP)?




Just heard back from Buckeye on lead times. 9-10 weeks is testing my patience considering I just ordered the Chora's today. On the other side of the 40/250W spectrum, what would be the drawbacks of using an amp like Topping LA90 at 50W 8ohm? From everything said here, I understand it may be limited to lower volumes or risk not having enough wattage to produce dynamic peaks. It does appear to run without much distortion as it approaches it's max output (from how I read the review). I just don't see any specs saying whether or not it can dig deeper than 4 Ohm.

Maybe use the LA90 as a stop gap until the Buckeye comes in, then sell or find a new use for the LA90 down the line. It's 50W at 8 ohm into 91 db speakers in a 24x12' room *shrug emoji*. My selection criteria for audio products is unusual. I'm not buying made in China unless the company is Chinese. Don't ask...

@Blumlein 88 and @AdamG247, thanks for the reference links. I think Blumlein's are a bit too technical for my 2 semesters of community college electronics, but I may take a second look in a more ambitious mood.
I'd say the LA90 is not a good choice. Only 36 watts at 8 ohms. And only 50 watts at 2 ohms according to Amir's review. So it doesn't have lots of current capability for the 2.9 impedance minimum and it is marginal on power for the higher impedance ranges. It might work out, but it would be marginal all the way around. So while not a science, this one is marginal in my opinion.
 

AdamG247

Coadjutor Miscreant and general Scalawag
Moderator
Forum Donor
Joined
Jan 3, 2021
Messages
2,996
Likes
7,886
If an amp doesn't come with meters like in the video, is there a way to add a meter to an amp or possibly see it digitally (in something like miniDSP)?
That Sir is an entirely different and much deeper rabbit hole. I have seen some variations but nothing that displays power in numbers in similar configuration. You could start reading up on the few VU Meter threads that we have here. Then there are LED strip meters and such. But I have found nothing that matches what is presented in the video except that amp. Which is of course the cost of a Car. If you do happen to discover a equivalent solution that won’t cost as much as a new Tesla please share. The video was more to demonstrate how dynamic the power fluctuations truly are. Very far from a static number. This is an incredibly complex process and trying to explain it in a few short paragraphs is never going to be successful. We are wetting your appetite hoping that you will be interested enough to start researching and reading to achieve your own deeper understanding.
 

AudioStudies

Addicted to Fun and Learning
Joined
May 3, 2020
Messages
642
Likes
328
I'd say the LA90 is not a good choice. Only 36 watts at 8 ohms. And only 50 watts at 2 ohms according to Amir's review. So it doesn't have lots of current capability for the 2.9 impedance minimum and it is marginal on power for the higher impedance ranges. It might work out, but it would be marginal all the way around. So while not a science, this one is marginal in my opinion.
The subject is so complex but one thing is pretty simple -- you want more than 50 watts anywhere near 2 ohms. Curious if the OP ever considered powered monitors (studio monitors)? Going that route, with a reputable manufacturer, all the amp to driver matching is done correctly for the consumer. With the added advantage of active crossovers rather than passive crossovers.
 

Koeitje

Major Contributor
Joined
Oct 10, 2019
Messages
1,899
Likes
3,134
In the old days, when most amps were Class AB, one way of evaluating an amp was to look at the power specs for various impedances and see if they go up or down as the impedance goes lower. For example, if an amp could deliver 100 W at 8 ohms, then 150 W at 4 ohms, that is a good thing. But any amp that delivered less power as the impedance went down was not considered as high a quality of an amp. With all these new classes of amps now, beyond traditional AB, that kind of changed the landscape. My understanding is some of these newer classes of amps are just fine even though they may deliver the same power into 8 ohms as into 4 ohms.
You can't rely on specs, a lot of amps provided more power at 8 ohm than the specifications told you just so they could show a doubling at 4 ohm.
 

AudioStudies

Addicted to Fun and Learning
Joined
May 3, 2020
Messages
642
Likes
328
You can't rely on specs, a lot of amps provided more power at 8 ohm than the specifications told you just so they could show a doubling at 4 ohm.
Indeed. We can't "rely" on specs, just "hope" they are providing some useful info, and take them with a grain of salt. Doesn't sound like the manufacturers were very reputable in the scenario you mentioned . . .
 
Top Bottom