Skybuck Flying <skybuckflying@gmail.com> wrote:
>
>At 7.46 Hertz the Denon Receiver 1909 would shut down ! and it's power ligh=
>t would start blinking RED.

You bet. It's going into protection to prevent it from blowing itself up.
Those speakers can hardly drive 75 Hz, let alone 7.5 Hz. Be glad you have
protection logic in your amp instead of a bunch of ruined hardware.

You're trying to drive those speakers more than ten times out of their
operating range. You wouldn't expect your car to behave very well if you
tried to drive it at 800 miles an hour instead of 80 either.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On 7/27/22 07:11, Scott Dorsey wrote:
> Skybuck Flying <skybuckflying@gmail.com> wrote:
>>
>> At 7.46 Hertz the Denon Receiver 1909 would shut down ! and it's power ligh=
>> t would start blinking RED.
>
> You bet. It's going into protection to prevent it from blowing itself up.
> Those speakers can hardly drive 75 Hz, let alone 7.5 Hz. Be glad you have
> protection logic in your amp instead of a bunch of ruined hardware.
>
> You're trying to drive those speakers more than ten times out of their
> operating range. You wouldn't expect your car to behave very well if you
> tried to drive it at 800 miles an hour instead of 80 either.
> --scott
>
When I first got an FM synth (80's) I experimented with low
frequency sine waves. I was able to play frequencies lower
then 7.5hz without a problem. I could see the woofer of my
rather ordinary speakers dutifully pushing in and out in
accordance with the signal. I never had any problems doing
that.

It seems that your car comparison would play better if
we were talking about the amplitude of the signal.
What is it in an amplifier circuit that is under stress
at 7.5Hz? I could imagine that capacitors would fill up
which I could see causing problems.

Tobiah

On 27/07/2022 15:53, Tobiah wrote:
> On 7/27/22 07:11, Scott Dorsey wrote:
>> Skybuck Flying <skybuckflying@gmail.com> wrote:
>>>
>>> At 7.46 Hertz the Denon Receiver 1909 would shut down ! and it's
>>> power ligh=
>>> t would start blinking RED.
>>
>> You bet. It's going into protection to prevent it from blowing itself
>> up.
>> Those speakers can hardly drive 75 Hz, let alone 7.5 Hz. Be glad you
>> have
>> protection logic in your amp instead of a bunch of ruined hardware.
>>
>> You're trying to drive those speakers more than ten times out of their
>> operating range. You wouldn't expect your car to behave very well if you
>> tried to drive it at 800 miles an hour instead of 80 either.
>> --scott
>>
> When I first got an FM synth (80's) I experimented with low
> frequency sine waves. I was able to play frequencies lower
> then 7.5hz without a problem. I could see the woofer of my
> rather ordinary speakers dutifully pushing in and out in
> accordance with the signal. I never had any problems doing
> that.
>
> It seems that your car comparison would play better if
> we were talking about the amplitude of the signal.
> What is it in an amplifier circuit that is under stress
> at 7.5Hz? I could imagine that capacitors would fill up
> which I could see causing problems.
>
>
Loud signals at low frequencies need a lot of power to be fed into the
speaker, and speaker impedances tend to reduce at low frequencies, as
they are mainly inductive devices as far as the amplifier is concerned.

Add the two together, and it is easy to trip the protection or blow the
fuses. Most commercial amplifiers are designed to reduce the output
levels below about 20 Hz, which avoids the problem.

--
Tciao for Now!

John.

In article <tbrjhj$1hni$1@gioia.aioe.org>, Tobiah <toby@tobiah.org> wrote:
>When I first got an FM synth (80's) I experimented with low
>frequency sine waves. I was able to play frequencies lower
>then 7.5hz without a problem. I could see the woofer of my
>rather ordinary speakers dutifully pushing in and out in
>accordance with the signal. I never had any problems doing
>that.

First of all, measure the DC resistance of your speakers. An eight ohm
speaker is likely around 2 to 3 ohms resistance, and at 7.5 Hz you are
pretty close to DC. Your amp won't like driving much power into that load.
And what is worse, most of the energy is going into resistive losses in
the voice coil, which will get pretty hot.

You can see the cones moving in and out, but you won't actually move very
much air either.

>It seems that your car comparison would play better if
>we were talking about the amplitude of the signal.
>What is it in an amplifier circuit that is under stress
>at 7.5Hz? I could imagine that capacitors would fill up
>which I could see causing problems.

The amplifier is under stress because it's got a very low impedance load
on the output. It might be fine putting out a couple watts, but it will
go into protection if you try and put much power out. Unless it's an amp
designed for very low-Z loads in which case the speaker will vaporize long
before the amp.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:
================
> Skybuck Flying
> >
> >At 7.46 Hertz the Denon Receiver 1909 would shut down ! and it's power ligh=
> >t would start blinking RED.
>
> You bet. It's going into protection to prevent it from blowing itself up.

** Nearly all stereo amps and receivers from Asia have switch on delay, plus DC offset & low frequency protection.
This usually consists of one or more a speaker relays driven by a special IC that monitors the output from each channel and will hold the relay/s open if a fault condition is sensed.
The switch on delay is for "anti thump" and there is also a fast fast off when AC power is removed for the same reason.

IME, low frequency detection operates from about 5 to 10 Hz downwards at level of about 10V peak at the output.
This is mainly to save woofers from damage due to over excursion, plus it sounds horrible.
How do these high level sub sonics ever arise in normal use?
From rough handing of a turntable with the volume advanced.
FYI 1
the standard test of such protection schemes is to feed in a sine wave of about 5Hz from a bench generator with NO load connected.
The relays typically react by cycling on and off ( ie clicking audibly ) or locking out until the test signal is removed.

FYI 2

" Skybuck Flying" does not inhabit the same planet as you and I.

...... Phil

palli...@gmail.com <pallison49@gmail.com> wrote:
> Scott Dorsey wrote:
> ================
>> Skybuck Flying
>>>
>>> At 7.46 Hertz the Denon Receiver 1909 would shut down ! and it's power ligh=
>>> t would start blinking RED.
>>
>> You bet. It's going into protection to prevent it from blowing itself up.
>
> ** Nearly all stereo amps and receivers from Asia have switch on delay,
> plus DC offset & low frequency protection.
> This usually consists of one or more a speaker relays driven by a special
> IC that monitors the output from each channel and will hold the relay/s
> open if a fault condition is sensed.
> The switch on delay is for "anti thump" and there is also a fast fast off
> when AC power is removed for the same reason.
>
> IME, low frequency detection operates from about 5 to 10 Hz downwards at
> level of about 10V peak at the output.
> This is mainly to save woofers from damage due to over excursion, plus it sounds horrible.
> How do these high level sub sonics ever arise in normal use?
> From rough handing of a turntable with the volume advanced.
>
> FYI 1
> the standard test of such protection schemes is to feed in a sine wave of
> about 5Hz from a bench generator with NO load connected.
> The relays typically react by cycling on and off ( ie clicking audibly )
> or locking out until the test signal is removed.
>
> FYI 2
>
> " Skybuck Flying" does not inhabit the same planet as you and I.
>
>
> ..... Phil
>
>

Not to mention he probably couldn’t hear anything, so turned up the volume.