Philips DH415 Pm 20W 8ohm speakers -- is this RMS or Peak Mu

[veek]

Hi, I have some really old speakers Phillips DH415 that were
gathering dust. I want to re-purpose them and use them with my
TV/computer - i got to buy an Amplifier for them.

(here's an image: subwoofer+bass reflex+tweeter is what i suspect)
http://imgur.com/a/Mt9Hw

I can't figure out what rating amp to buy.

If that's 20W PMPO x 2-speakers, then I need to buy: 30W RMS amp?
That seems like not a lot of power and I don't remember this set
being very loud. So is my assumption correct?

Are there any modern features I could look for in an amp. My TV is a
Samsung 4003 720p and it has Component Ports for audio/video.

 

[Phil Allison]

veek wrote:

Hi, I have some really old speakers Phillips DH415 that were
gathering dust. I want to re-purpose them and use them with my
TV/computer - i got to buy an Amplifier for them.

(here's an image: subwoofer+bass reflex+tweeter is what i suspect)
http://imgur.com/a/Mt9Hw

I can't figure out what rating amp to buy.

If that's 20W PMPO x 2-speakers,

** I reckon " Pm 20W " means "Power max 20 watts" .

then I need to buy: 30W RMS amp?

** That should be more than enough for TV and PC use.


.... Phil

 

[veek]

I measured the case resistance (resistance at the jacks) using a
multimeter and it shows 9 ohm, so i'm guessing these are 12 ohm
speakers. I really need to figure out how much power I need to feed
them.

 

It ain't that critical. Thirty watts will bee fine. Whether it is PMPO, PMPILS, RMS or average doesn't matter. An old Marantz receiver maybe, or some small Sansui or something from the 1970s or so. They are out there for reasonable money. some have been restored and go for big bucks but most of them will run alright for a long time without a restore. They are all of ever eBay, as long as the seller says that it is tested and working. If you don't fix shit obviously do not go for the ones that say "for parts or repair".

And Craigslist. If the guy says "You can hear it run at my house" it is not a robbery. When you first walk in there, leave your money in your car. And if you buy tell the guy the money is in our car, he can walk out there with you if he wants but you will be right back cash in hand. But all that shit is for high end items, you want a 30 watt amp you should spend, on an unrestored but working mid fi amp maybe fifty bucks.

There are makes and models that command alot more bucks but most people do not need them.

In the audiophile realm, there are 30 watt amps that go for five figures. If you were looking for that, you would not have asked the question you asked. So I am thinking of those mid end fi things that me and my "rich" friends shunned, but really did sound good. You would probably be happy with an MCS, which was a JCPenny house brand with some of them maybe being built by Rotel or whatever. Or a Radioshack, which seem to be gaining popularity among mid audiophiles.

Really, 30, 40, 50, even 100 watt amp, when you hear it start to stress out, back of the volume or you fry the speakers.

 

[Phil Allison]

veek wrote:

I measured the case resistance (resistance at the jacks) using a
multimeter and it shows 9 ohm, so i'm guessing these are 12 ohm
speakers.

** Says " 8 ohms " on the back of he twin cone speaker/woofer.

Try measuring right on the speaker terminal and check you meter.


..... Phil


I really need to figure out how much power I need to feed
> them.

 

[asdf]

On Sat, 10 Oct 2015 22:08:18 -0700, Phil Allison wrote:

> ** I reckon " Pm 20W " means "Power max 20 watts" .

Yup, PMPO is a marketing name which has no formal definition
and only serves the purpose of inflating numbers in advertising.
It's not that uncommon to see a 20 Watt RMS amplifier advertised
as a 600 Watt PMPO.

 

[pfjw@aol.com]

On Sunday, October 11, 2015 at 12:45:31 AM UTC-4, veek wrote:

Hi, I have some really old speakers Phillips DH415 that were
gathering dust. I want to re-purpose them and use them with my
TV/computer - i got to buy an Amplifier for them.

(here's an image: subwoofer+bass reflex+tweeter is what i suspect)
http://imgur.com/a/Mt9Hw

I can't figure out what rating amp to buy.

If that's 20W PMPO x 2-speakers, then I need to buy: 30W RMS amp?
That seems like not a lot of power and I don't remember this set
being very loud. So is my assumption correct?

Are there any modern features I could look for in an amp. My TV is a
Samsung 4003 720p and it has Component Ports for audio/video.

OK - a few basics on speakers - at least as they were sold in the US under FTC regulations (sit on your fingers, Phil!):

a) Rated power is based on CONTINUOUS power into the speaker. So, a "20-watt" speaker should be designed to accept 20 watts of continuous power at some mix of frequencies, usually specified, for some specific period of time, also usually specified.

b) Rated Power is not Average Power. Assuming a speaker that produces 90dB of noise at 1 watt at one meter on-axis. Assume a normal peak-to-average of 20dB on the incoming signal, and assume it is running at one watt average (quite loud). Then the speaker will be getting momentary peaks of up to 100 watts (assuming the amp is capable of such). This will do NO damage to the speakers whatsoever as-described.

c) Low cost, low-wattage amplifiers are much more likely to cause speaker damage than large amplifiers. What can happen with some solid-state designs is that when the amplifier clips (called to produce more power than it can), it may send straight DC into the speaker - which will destroy voice coils in short order. So, the larger the amp, the less this may be an issue. As one example, I run 30-watt rated speakers with a 200-watt-per-channel amp, and have done so for years with no issues at all.

So, unless you wish to listen at ear-bleeding volume with an audio-quality source with full-orchestral signal (none of which are likely from a computer source), 30 watts is far more than enough. Another exampleL I run 86dB speakers from a 60 watt-per-channel amp at moderate levels, no problems and no clipping. The speakers are rated at 100 watts, as it happens. The key is *moderate levels*.

This issue is far less so from a tube amp - the simplistic explanation is that it is harder for a transformer to pass DC, so tube amps clip softly. There is much more too it, but for this situation, that is enough.

Peter Wieck
Melrose Park, PA

 

[Phil Allison]

pf...@aol.com wrote:

OK - a few basics on speakers - at least as they were sold in the
US under FTC regulations (sit on your fingers, Phil!):

** The are simply no FTC rules for published speaker power ratings. The rules you seem to be alluding to are for *amplifers* used in home entertainment.

c) Low cost, low-wattage amplifiers are much more likely to cause speaker damage than large amplifiers.

** Depends a lot who is using the amplifer - but in general the risk of speaker damage goes up with more amp power.

What can happen with some solid-state designs is that when the
amplifier clips (called to produce more power than it can),
it may send straight DC into the speaker

** Absurd.

Clipping does not cause DC, the main effect is to compress the dynamic range of the music so there is more average power going to the speaker - which eventually overheats the voice coil.

This issue is far less so from a tube amp - the simplistic explanation is >that it is harder for a transformer to pass DC,

** Impossible in fact, but clipping wave peaks is just what tube guitar amps do most of all the time and blown speakers are very common - due again to high average power levels.


.... Phil

 

[Cursitor Doom]

On Wed, 14 Oct 2015 20:11:26 -0700, Phil Allison wrote:

pf...@aol.com wrote:



OK - a few basics on speakers - at least as they were sold in the US
under FTC regulations (sit on your fingers, Phil!):


** The are simply no FTC rules for published speaker power ratings. The
rules you seem to be alluding to are for *amplifers* used in home
entertainment.


c) Low cost, low-wattage amplifiers are much more likely to cause
speaker damage than large amplifiers.


** Depends a lot who is using the amplifer - but in general the risk of
speaker damage goes up with more amp power.


What can happen with some solid-state designs is that when the
amplifier clips (called to produce more power than it can),
it may send straight DC into the speaker

** Absurd.

Clipping does not cause DC, the main effect is to compress the dynamic
range of the music so there is more average power going to the speaker -
which eventually overheats the voice coil.


This issue is far less so from a tube amp - the simplistic explanation
is >that it is harder for a transformer to pass DC,


** Impossible in fact, but clipping wave peaks is just what tube guitar
amps do most of all the time and blown speakers are very common - due
again to high average power levels.

Makes sense the way you've explained it, Phil. I had a Technics amp one
time that just ate through speakers for some reason; all top quality KEF
units as well. The only thing I could come up with for a cause was
that the amp sound was very 'cold' - typical of Technics amps - so may
have been producing transients the speakers couldn't handle. But that's
no more than a hunch.
The other thing the OP seems to be unaware of is that the term 'RMS
power' is really indefinable anyway. You can't take the product of RMS
voltage and RMS current (which are both valid measurements) and derive
'RMS power' from them. We should drop the use of this non-sensical term
and adopt 'average power' instead. And as for 'total peak music power' -
bah! Don't get me started! ;->

 

pf...@aol.com wrote:
"- show quoted text -
OK - a few basics on speakers - at least as they were sold in the US under FTC regulations
(sit on your fingers, Phil!): "


Additionally, correct me if I'm wrong, but the "sticker"
impedance(ohms) is the lowest reading for a speaker,
across the audio spectrum.

 

[Phil Allison]

Cursitor Doom wrote:

Phil Allison wrote:


** The are simply no FTC rules for published speaker power ratings. The
rules you seem to be alluding to are for *amplifers* used in home
entertainment.

Clipping does not cause DC, the main effect is to compress the dynamic
range of the music so there is more average power going to the speaker -
which eventually overheats the voice coil.



Makes sense the way you've explained it, Phil. I had a Technics amp one
time that just ate through speakers for some reason; all top quality KEF
units as well. The only thing I could come up with for a cause was
that the amp sound was very 'cold' - typical of Technics amps - so may
have been producing transients the speakers couldn't handle. But that's
no more than a hunch.

** Not much of a one.

People like to blame the amplifier when a speaker fails - but if it still works fine, it is almost certainly blameless.

The other thing the OP seems to be unaware of is that the term 'RMS
power' is really indefinable anyway.

** The term simply refers to "watts rms" which has always meant the power rating is based on the rms value of the sine wave used for the test.

A much clearer term is "continuous sine wave power", but that is inconveniently long.


..... Phil

 

[Phil Allison]

thekma...@gmail.com wrote:

Additionally, correct me if I'm wrong, but the "sticker"
impedance(ohms) is the lowest reading for a speaker,
across the audio spectrum.

** For individual woofers and full range drivers that is normally so - a woofer labelled "8ohms" has about 6.5 ohms of resistance and tests 8 ohms only around 250 to 400Hz.

But it's not generally true for speaker systems where the crossover network can introduce impedance variations both above and below the nominal figure.



..... Phil

 

[pfjw@aol.com]

On Wednesday, October 14, 2015 at 11:11:32 PM UTC-4, Phil Allison wrote:

pf...@aol.com wrote:



OK - a few basics on speakers - at least as they were sold in the
US under FTC regulations (sit on your fingers, Phil!):


** The are simply no FTC rules for published speaker power ratings. The rules you seem to be alluding to are for *amplifers* used in home entertainment.

Let's clarify, then. US speaker manufacturers very rapidly adapted to the FTC rules when publishing their ratings. Prior to these rules, IPP was the way amp makers would fool their buyers, and speaker makers would do their ratings similarly. As things equalized, their ratings became much more realistic.

c) Low cost, low-wattage amplifiers are much more likely to cause speaker damage than large amplifiers.


** Depends a lot who is using the amplifer - but in general the risk of speaker damage goes up with more amp power.


What can happen with some solid-state designs is that when the
amplifier clips (called to produce more power than it can),
it may send straight DC into the speaker

** Absurd.

Clipping does not cause DC, the main effect is to compress the dynamic range of the music so there is more average power going to the speaker - which eventually overheats the voice coil.

If you can, next time you are out on the street, see if you can borrow either of a Dynaco ST80, ST120, AR amplifier, any of several Scott/Fisher/Sherwood solid-state designs, any any of many pacific-rim solid-state designs that used discrete output transistors, a Revox B722 - the list goes on. Drive it to clipping. At clipping you will see serious DC at the outputs. This will 'freeze' the VC(s) in one position with lots-O-energy at the same time. Not generally a good idea.

This issue is far less so from a tube amp - the simplistic explanation is >that it is harder for a transformer to pass DC,


** Impossible in fact, but clipping wave peaks is just what tube guitar amps do most of all the time and blown speakers are very common - due again to high average power levels. Instrument amps blow speakers for many different reasons - and even a transformer will transfer chopped DC. Hence the term "simplistic". But instrument amps are a balance of many things. I have always wondered why the makers do not use much heavier speakers than they do - I guess it is a cost/benefit thing. But musicians using such devices seldom care much about fidelity - being more interested in noise and effects. And they generally operate at the bleeding edge.

A well-designed amplifier not driven to clipping into well-designed speakers not driven at ear-bleed levels will generally be safe forever, or at least until the one or the other device fails for other reasons than being over-driven. But I betcha I could do more damage to my AR3a or Maggie speakers with the 40-watt solid state amp than with the 17-watt or 75-watt tube amp - these representing my most rugged speakers being rated at 100 and 200 watts respectively.

Point being that not all devices are safe across the board. And many legacy/vintage devices are flatly unsafe if abused. The typical user these days believes that decent sound can come from a highly compressed source into computer speakers and/or earbuds, and have probably never heard a decent system under decent conditions with decent signal. Nor do they have a clue about Clipping, and what it actually means, nor its relationship to perceived volume and power requirements to achieve it. So, off they go trying to shake the floor or rattle the windows with a 4" speaker...

Peter Wieck
Melrose Park, PA

 

[Phil Allison]

pf...@aol.com wrote:

OK - a few basics on speakers - at least as they were sold in the
US under FTC regulations (sit on your fingers, Phil!):


** The are simply no FTC rules for published speaker power ratings.
The rules you seem to be alluding to are for *amplifers* used in
home entertainment.


Let's clarify, then. US speaker manufacturers very rapidly adapted to the FTC rules when publishing their ratings. Prior to these rules, IPP was the way amp makers would fool their buyers, and speaker makers would do their ratings similarly. As things equalized, their ratings became much more realistic.

** Entirely different to the nonsense you posted before.

The "rated power" of a hi-fi speaker is generally the largest amplifier power rating that it is acceptable to use with music program. This number is however many times greater than the continuous (ie sine wave) power handling of the same speaker.

What can happen with some solid-state designs is that when the
amplifier clips (called to produce more power than it can),
it may send straight DC into the speaker

** Absurd.

Clipping does not cause DC, the main effect is to compress the
dynamic range of the music so there is more average power going
to the speaker - which eventually overheats the voice coil.



If you can, next time you are out on the street, see if you can borrow either of a Dynaco ST80, ST120, AR amplifier, any of several Scott/Fisher/Sherwood solid-state designs, any any of many pacific-rim solid-state designs that used discrete output transistors, a Revox B722 - the list goes on. Drive it to clipping. At clipping you will see serious DC at the outputs. This will 'freeze' the VC(s) in one position with lots-O-energy at the same time.

** You are still equating peak clipping with steady DC, which is bizarre nonsense.

" Clipping does not cause DC, the main effect is to compress the dynamic range of the music so there is more average power going to the speaker - which eventually overheats the voice coil. "

Instrument amps blow speakers for many different reasons -
and even a transformer will transfer chopped DC.

** Chopped DC has both DC and AC components.

Transformers can only "transform" AC current while any DC current is converted to heat in the primary winding and magnetises the iron core.
No DC appears at the secondary.



.... Phil

 

[pfjw@aol.com]

On Monday, October 19, 2015 at 10:16:12 PM UTC-4, Phil Allison wrote:

** You are still equating peak clipping with steady DC, which is bizarre nonsense.

Phil:

If you are sufficiently curious, just try and find one of the amps I listed and drive it to clipping - say, with a 1000hz sine wave. Measure what comes out. It will (at least) get you to raise your eyebrows...

Peter Wieck
Melrose Park, PA