Matching an amplifier to a speaker

[Hayato]

I think that the stiffness of the cone/suspension is crucial.
When you have soft materials like some sort of silicone and other polymeters, they act like "low-pass filters" due their low hardness (soft materials tend to have low ressonant frequency).

 

[audioguru]

I have woofers with a very loose suspension and their resonant frequency is very low. They use the air inside their sealed enclosure for "air suspension".

 

[Sceadwian]

Ag/Hyato, either of you have suggestions on further reading?
In the speakers I've seen, especially subs the cone is very stiff and the suspension is very soft.

 

[Hayato]

If you have a very stiff cone, the coil positioning must be very precise so that the cone does not vibrate transversely.

Long long time ago I read a very antique book, Audio System, from Sir. Douglas. It was very nice, it showed how to "translate" every mechanical thing in a audio system to electrical models.
For example, a speaker enclosure inner volume would represent capacitor... And so on.

But I believe that, due the books age, you'll won't find it to buy, just in some libraries.

 

[Sceadwian]

We have a good library system here, I'll have to look it up, is that exact title/author? I've seen LTspice models that some people in the yahoo group use to simulate speaker enclosures and calculate frequency response based on models like that. A book would be nice.

 

[Hayato]

The title is "Audio Systems", the autor is Julian Lawrence Bernstein, I believe.
It's an old book, only tubes were shown in the amps chapters, but it is good.

 

[miro_gt]

I'd use 2 times more powerful speaker than the amp itself (in RMS terms)

 

[audioguru]

I'd use 2 times more powerful speaker than the amp itself (in RMS terms)

Why?
Do you listen to sounds that are continuous and always at more than full volume? No.
Music has occasional peaks which might be at full volume but the average power is 1/10th the full volume.

 

[miro_gt]

Why?
Do you listen to sounds that are continuous and always at more than full volume? No.
Music has occasional peaks which might be at full volume but the average power is 1/10th the full volume.

you cant listen to sound that is more than full volume, that can not happen.

music has peaks all over the place. As long as the amp will not clip the signal, the sound would be of better quality with more powerful speaker then the output of the amp than with matched powers speaker - amp. The reason is within the speaker itself, not the amp. Todays amps produce very low distortion over their output range (freq and power). The speaker however has frequency/db output chart that is far from linear.

I tend to listen on high volume when the song is good though

anyways, I'm not fine when my high and mid frequencies are produced fine, but when the base hit and fade it's a big no no. Quality FTW

but then of course there are bunch of other factors as well, such as type of the speaker, diameter of the cone, coil used, space between the coil and the magnet, el.characteristics of the coil, cooling of the coil, size of the magnet .. and others that define quality.

on the amp side, the lower part of the power output graph has lower distortion and therefore provides better quality. But as I said above, the difference is not that big with the volume going up, as long as no clipping occurs.

 

[audioguru]

you cant listen to sound that is more than full volume, that can not happen.

Some people turn up the volume so high that the output is severely clipped square-waves that have double the RMS power of the amplifiers.
so the sound level is more than full volume.

 

[Nigel Goodwin]

My new PA speakers advise you to use an amplifier up to twice the RMS rating of the speakers, it's far worse driving the amplifier into clipping than having too large an amplifier.

 

[Sceadwian]

Just don't turn it all the way up on accident =)

 

[BuffaloEngineer]

My new PA speakers advise you to use an amplifier up to twice the RMS rating of the speakers, it's far worse driving the amplifier into clipping than having too large an amplifier.

I'd use 2 times more powerful speaker than the amp itself (in RMS terms) ... As long as the amp will not clip the signal, the sound would be of better quality with more powerful speaker...

I think these comments get to the heart of the question - is it better to have a low power amp so the speaker can't be blown from cranking the volume or is it better to have a higher power amp to prevent clipping?

I was hoping the easy answer was just to use matched RMS power levels. If a higher power amp is used, the input voltage to the amp needs to be limited to prevent too much power from going to the speaker, right?

 

[Nigel Goodwin]

Nothing is that simple - BUT - most damage is caused by running the amplifier into clipping, both to the amplifier and the speaker.

So a smaller amplifier is fine, as long as you don't turn it up too loud, likewise a larger amplifier is fine, again as long as you don't turn it up too loud.

Notice there's a theme here? - DON'T TURN IT UP TOO LOUD!.

 

[miro_gt]

^ see that can not happen. Everybody wants volume up when the good song comes

and with your suggestion I see they change speakers every week.

however, todays nice amps have power limiting (protective) circuits so in case the load gets too big, the amp lowers the volume by itself. Or shuts down (like the JL audio ones do, lol). But not all have that feature though.

on the other hand, even if the amp would start clipping, one can always hear it with "bigger" speakers and lower the volume thereafter.

thinking more about it, even if an amp start clipping, this is not a sign that it will burn out. As long as it's heaving the necessary cooling abilities, it can run even if it starts clipping, said that the parts can withstand current at the clipping voltage. Clipping is just the unability of the amp to raise voltage high enough to sustain the gain of the amp and therefore to drive the load at the wanted levels. What burns out stuff is the high current flow.

 

[Nigel Goodwin]

^ see that can not happen. Everybody wants volume up when the good song comes

and with your suggestion I see they change speakers every week.

however, todays nice amps have power limiting (protective) circuits so in case the load gets too big, the amp lowers the volume by itself. Or shuts down (like the JL audio ones do, lol). But not all have that feature though.

My PA amp is class-D, and limits before it clips, I suspect this is probably pretty important on a class-D design.

on the other hand, even if the amp would start clipping, one can always hear it with "bigger" speakers and lower the volume thereafter.

thinking more about it, even if an amp start clipping, this is not a sign that it will burn out. As long as it's heaving the necessary cooling abilities, it can run even if it starts clipping. Clipping is just the unability of the amp to raise voltage high enough to sustain the gain of the amp and therefore to drive the load at the wanted levels. What burns out stuff is the high current flow.

You need to think further, clipping greatly increases the current flow, and also generates high levels of high frequency harmonics, which can kill the tweeters in the speaker.