What Measurement Shows an Amps Low Frequency Capability?

[SimpleTheater]

I’ve read the garbage What HiFi reviews, but one that caught my attention said the amp didn’t have good low end extension. What measurement, other than frequency response (which is almost always 20-20,000 0.1 to 0.3 dB) would show an amps ability to produce good low end power into a speaker (assuming the amp is within the speakers power requirements and ohm ratings)?

 

[Deleted member 46664]

You would need to know the below 20hz frequency response, which is rarely published.
A good amplifier will be -3db at about 3hz ... the bad ones run out of steam at about 15hz.

Also you need to know it's maximum output current, also rarely published.

 

[Aerith Gainsborough]

You would need to know the below 20hz frequency response, which is rarely published.
A good amplifier will be -3db at about 3hz ... the bad ones run out of steam at about 15hz.

Unless you are trying to DIY subwoofers or drive passive subwoofers, that is completely irrelevant though.

I think the What HiFi review was simply that: garbage.

 

[RHO]

You need to know the clipping point at 20Hz, compared to the clipping point at higher frequencies. If it's not lower at 20Hz you should be fine. Or you need a more powerful amp for your application.

 

[Deleted member 46664]

You need to know the clipping point at 20Hz, compared to the clipping point at higher frequencies. If it's not lower at 20Hz you should be fine. Or you need a more powerful amp for your application.

That would be a frequency response measurement.

 

[RHO]

That would be a frequency response measurement.

No. It can be perfectly flat from 1Hz to 100Khz below clipping at any frequency. But when you test max capabilities it could be lower at bass frequencies than at higher frequencies.

 

[Deleted member 46664]

No. It can be perfectly flat from 1Hz to 100Khz below clipping at any frequency. But when you test max capabilities it could be lower at bass frequencies than at higher frequencies.

Good point .... thank you.

 

[Vini darko]

Output impeadance is a factor too I think.

 

[Speedskater]

Output impeadance is a factor too I think.

With Vintage & Legacy tube amps, maybe.
With modern design solid-state amps, no.
But the low-frequency impedance of woofers, might be a big factor.

 

[Jukka]

Powercube tells power into different loads and phase angles. Low impedance with steep phase angle is generally considered the worst case for an amp to drive.

Remember that power into any Hz is load dependant, so you need details of the load (speaker) you're putting it to drive. There are some speakers that have impedance of less than 1 Ohm at specific frequency range, those would really difficult to drive. 8 Ohms and more and generally regarded as easy loads.

Some say that higher Ohm version of a speaker element sounds better than lower Ohm version of the same element. I'm into DIY and I used 16 Ohm elements. And they do sound good.

 

[DVDdoug]

If you're trying to go subsonic you might have to contact the amplifier manufacturer. And assuming you also want high-power you're probably going to be buying a "specialty" amp or "pro" amp and in that case you are more-likely to get an answer.

Most amps are deliberately high-passed... If you accidently get DC (zero Hz) the amp or speakers could burn-up (without making any sound). Sometimes there is also low-pass filtering to keep-out radio frequencies.

Most amplifiers could be modified for lower frequencies (probably by just increasing the value of one or two capacitors) but I'm not recommending that you attempt it.

P.S.
There is a Rotary Woofer that they claim goes down to 1Hz. But If it goes to 1Hz it seems like you could "pressurize" a room at 0Hz... I don't know what kind of amplifier they are recommending. Apparently, it doesn't require much (amplifier) power because it has a motor (it's an electro-mechanical amplifier).

On the other hand, most big subwoofers used for live sound or in dance clubs only go down to about 40Hz. That's about the lowest note on a standard electric bass and it's low-enough to get bass you can feel in your body. As you go lower it takes more energy and bigger woofers to get the same "impact" so they try to put the electrical & acoustic energy where it really counts.

 

[Chromatischism]

On the other hand, most big subwoofers used for live sound or in dance clubs only go down to about 40Hz. That's about the lowest note on a standard electric bass and it's low-enough to get bass you can feel in your body. As you go lower it takes more energy and bigger woofers to get the same "impact" so they try to put the electrical & acoustic energy where it really counts.

There's a lot of rumble down lower than 40 Hz, but along with taking excursion and power, the sound will travel very long distances. That may be undesirable.

 

[Blumlein 88]

Power at low THD into low frequencies and low impedance should tell you plenty. Like here on a recent review look at the orange line for 20 hz into 4 ohms. Other factors might be damping factor (almost never a problem other than tube amps) and current beyond what is needed for a 4 ohm load because some ported speakers have a low impedance and are not resistive across some range of lower frequencies. Non-resistive loads can require additional current which some amps may struggle to deliver. Even this isn't usually a problem with a fairly powerful amp.

Here is an example where this speaker has a 5 ohm impedance with -40 degrees phase angle. This will require more current than if it were just a 5 ohm resistive load around the 30 hz range in this particular case. This one isn't particularly awful as some speakers might have 2 or 3 ohms here and significant phase angles which would require much more current in this particular frequency range. So one amp might run out of current if signal is in this range and another with more current capability would do better.

The power cube type measurement mentioned is one of the best ways to measure, but usually not necessary. Here are a couple of web pages that explain and illustrate how that works. It is a graphical display of an amps capabilities into various non-resistive loads.

Technical Library

www.ap.com

https://www.audiograph.se/wp-content/uploads/2018/10/PowerCube_12p_brochure_complete.pdf