speaker efficiency

speaker efficiency

A acquaintance of mine is wanting to upgrade his amplifier, an EL34-based
tube amp wired in ultralinear configuration. I'm considering buying it, but
am unsure if this amp's 20 wpc is enough to drive my Boston Acoustics T-830
speakers. Right now they're driven with a 50 wpc Harmon Kardon vintage
solid state amp, and that setup can be played LOUD. If I purchased the tube
amplifier, I'd likely want to rewire it in triode configuration which would
halve my power output to around 10 wpc.

Does anyone know the efficiency specs for the T-830 speakers, or any of the
T-series BA loudspeakers from the early 90's? I have the original cartons
but none of the literature that came with the speakers.

Thanks

Dave S.

Re: speaker efficiency

On Oct 23, 7:51 pm, "Dave" <dspear9...@yahoo,com > wrote:
> A acquaintance of mine is wanting to upgrade his amplifier, an EL34-based
> tube amp wired in ultralinear configuration. I'm considering buying it, but
> am unsure if this amp's 20 wpc is enough to drive my Boston Acoustics T-830
> speakers. Right now they're driven with a 50 wpc Harmon Kardon vintage
> solid state amp, and that setup can be played LOUD. If I purchased the tube
> amplifier, I'd likely want to rewire it in triode configuration which would
> halve my power output to around 10 wpc.
>
> Does anyone know the efficiency specs for the T-830 speakers, or any of the
> T-series BA loudspeakers from the early 90's? I have the original cartons
> but none of the literature that came with the speakers.
>
> Thanks
>
> Dave S.

Don't really need to know the efficiency. Going from 50 watts down to
10 is a gigantic loss of power. Every doubling of power raises the
volume output of a system by only about 3 db. Your tube amp will be
cranking at full rated power and be pushing the speakers at just above
conversation level. And since it's running at full power, distortion
will occur more readily for any slight increase in dynamics of the
music.

If you had some very effiicent horn speakers like Klipsh, then maybe.
But with regular cone speakers?

Don't do it.

CD

Re: speaker efficiency

codifus wrote:

> Don't really need to know the efficiency. Going from 50 watts down to
> 10 is a gigantic loss of power. Every doubling of power raises the
> volume output of a system by only about 3 db.

Uh huh. So a 50 watt amp will be capable of 7db more output than a 10
watt amp.

Is 7 db SPL too much to give up?

Also, since the lower power amp is a tube amp, it won't sound as nasty
if it's overdriven, so you can push it harder than a 10 watt solid state
amp.

//Walt

Re: speaker efficiency

Walt <walt_askier@yahoo,com > writes:

> codifus wrote:
>
>> Don't really need to know the efficiency. Going from 50 watts down to
>> 10 is a gigantic loss of power. Every doubling of power raises the
>> volume output of a system by only about 3 db.
>
> Uh huh. So a 50 watt amp will be capable of 7db more output than a 10
> watt amp.
>
> Is 7 db SPL too much to give up?
>
> Also, since the lower power amp is a tube amp, it won't sound as nasty
> if it's overdriven, so you can push it harder than a 10 watt solid
> state amp.

The problem is that 7 dB is in a gray area. It's a pretty big drop, but
it's not THAT big. How loud was "loud" in the original setup? If it was
just "barely loud" then 7 dB would probably drop that to "not loud."

In my opinion, 10 wpc on 88 dB SPL speakers is wimpie wimpie wimpie.
But then I'm a Klipschorn owner...
--
% Randy Yates % "How's life on earth?
%% Fuquay-Varina, NC % ... What is it worth?"
%%% 919-577-9882 % 'Mission (A World Record)',
%%%% <yates@ieee.org> % *A New World Record*, ELO
http :// www .digitalsignallabs,com

Re: speaker efficiency

On Oct 23, 6:51 pm, "Dave" <dspear9...@yahoo,com > wrote:
> A acquaintance of mine is wanting to upgrade his amplifier, an EL34-based
> tube amp wired in ultralinear configuration. I'm considering buying it, but
> am unsure if this amp's 20 wpc is enough to drive my Boston Acoustics T-830
> speakers. Right now they're driven with a 50 wpc Harmon Kardon vintage
> solid state amp, and that setup can be played LOUD. If I purchased the tube
> amplifier, I'd likely want to rewire it in triode configuration which would
> halve my power output to around 10 wpc.
>
> Does anyone know the efficiency specs for the T-830 speakers, or any of the
> T-series BA loudspeakers from the early 90's? I have the original cartons
> but none of the literature that came with the speakers.
>
> Thanks
>
> Dave S.

Hmmm.....

OK, let's do some basic math that is irrespective of speaker
efficiency. Assume that BA speakers are relatively inefficient. So,
let's figure say.... 86dB @ 1 watt. So, a 20-watt amp will be capable
of giving you 99dB without clipping. A 40-watt amp will give you
~102dB, and a 50-watt amp will not make any perceptable difference to
that 102.

A 50-watt amp will be capable of giving you ~102/3 dB without
clipping. 3dB is a very small increment relative to all things, one
that you can definitely hear with normal hearing but not earth-
shattering.

10 x the power = 2 x the volume perceived. So, 1 watt gives 86dB, 10
watts give 96dB, 100 watts gives 106dB.

The calculations for the dB relationships are: for a 10 to one
relationship, the log of 10 is 1, and ten times 1 is 10. For the 2 to
one relationship, the log of 2 is 0.3, and 10 times that is 3.

Put another way, after 20 watts, the next truly meaningful increment
as to headroom under normal conditions and normal listening levels is
roughly 100 watts. The value of headroom decreases with the efficiency
of the speaker. And it increases with the peak-to-average levels of
the source material.

Do a search on "watts to decibels" and you will get much useful
information. But it comes down to the fact that there is little actual
difference in capacity between amps say.... over 10 watts and under 50
watts under most conditions.

Peter Wieck
Wyncote, PA

Re: speaker efficiency

"Peter Wieck" <pfjw@aol,com > wrote in message
news:ffmdql02ip@news5.newsguy,com ...

Opinion #1:

> information. But it comes down to the fact that there is little actual
> difference in capacity between amps say.... over 10 watts and under 50
> watts under most conditions.

Opinion #2

> If you had some very effiicent horn speakers like Klipsh, then maybe.
> But with regular cone speakers?
>
> Don't do it.
>

I need a third opinion here to break the deadlock. BTW, I found out that
the efficiency is 88 db/w/m.

Dave S.

Re: speaker efficiency

Dave wrote:

> I need a third opinion here to break the deadlock. BTW, I found out that
> the efficiency is 88 db/w/m.

So, a ten watt amp will be capable of driving the speakers to 98 db SPL
at one meter.

A 50 watt amp, which has 7db more output than the ten watter, will be
capable of of driving the speakers to 105 db SPL at one meter.

Now, you're unlikely to be listening at a distance of one meter, so
you'd need to compensate for your actual listening distance. In an
anechoic chamber, you'd drop the db SPL 6db for each doubling of
distance. In a room with reflections it's more complicated, and without
knowing more about your listing room I can't tell you much beyond this:

For moderate listening levels in a small to medium sized room, no
problem. For rock concert levels or in a big room, 10 watts ain't enough.

Why not just wire the darn thing up and see what you think?

//Walt

Re: speaker efficiency

"Dave" <dspear99ca@yahoo,com > wrote in message
news:ffm1dd02nhi@news5.newsguy,com ...
>A acquaintance of mine is wanting to upgrade his amplifier, an EL34-based
> tube amp wired in ultralinear configuration. I'm considering buying it,
> but
> am unsure if this amp's 20 wpc is enough to drive my Boston Acoustics
> T-830
> speakers. Right now they're driven with a 50 wpc Harmon Kardon vintage
> solid state amp, and that setup can be played LOUD. If I purchased the
> tube
> amplifier, I'd likely want to rewire it in triode configuration which
> would
> halve my power output to around 10 wpc.
>
> Does anyone know the efficiency specs for the T-830 speakers, or any of
> the
> T-series BA loudspeakers from the early 90's? I have the original cartons
> but none of the literature that came with the speakers.
>
> Thanks
>
> Dave S.

1993 Audio Annual Equipment Buyer's Guide

Boston Acoustics T-830:

Frequency Response: 40Hz - 20kHz +/- 3dB
SPL: 1 watt/1 meter / 88dB
Recommended Min. amp power: 15 watts per channel

Re: speaker efficiency

snip
> > So, you
> > will get 88dB at 1 watt at 1 meter from your BA speakers.
> >
> > 88dB is not LOUD, but it is substantially above conversational level,
> > roughly 2x louder.
> >
> > 1 watt = 88dB
> > 10 watts = 98dB
> > 20 watts = 101dB
> > 50 watts = 104/5 dB
> >
> > All other things being equal on those speakers.

My understanding (and I'm always willing to keep learning) is that two
speakers (stereo) will provide 3db more volume than one if both are
driven to the same level at the same time. So this reduces the power
needed a bit.

We must also take into account that the 1 watt = 88dB does not account
for musical peaks, which may be up to 30 or more dB above the average
level and will therefore require much more power. IMO this is one reason
that very high power amps often sound better than low power ones of the
same quality.

Of course all calculations must include room size and absorbtion as
well, so at best without real room data, it is all a guess.

In the end, if it works, it works. Give it a try and see whether you
like it.

Greg

Re: speaker efficiency

On Fri, 26 Oct 2007 15:27:39 -0700, Arny Krueger wrote
(in article <fftpkr022ae@news1.newsguy,com >):

> "Peter Wieck" <pfjw@aol,com > wrote in message
> news:ffr5m50173f@news5.newsguy,com ...
>> On Oct 24, 6:51 pm, "Dave" <dspear9...@yahoo,com > wrote:
>>
>>> I need a third opinion here to break the deadlock. BTW, I found out that
>>> the efficiency is 88 db/w/m.
>>
>> Dave:
>>
>> Far be it from me to render a "third" opinion. Rather I would suggest
>> that you check an independent source or two on the relationship
>> between watts and decibels as it applies to your speakers. So, you
>> will get 88dB at 1 watt at 1 meter from your BA speakers.
>>
>> 88dB is not LOUD, but it is substantially above conversational level,
>> roughly 2x louder.
>>
>> 1 watt = 88dB
>> 10 watts = 98dB
>> 20 watts = 101dB
>> 50 watts = 104/5 dB
>>
>> All other things being equal on those speakers.
>>
>> You will not miss the increment between 20 and 50 watts for two
>> reasons one a bit esoteric, the other very practical:
>>
>> a) Tube amps clip softly.
>
> False claim. Tube amps plenty sharply if they have enough loop feedback to
> be usable for hi fi purposes.

I was taught in engineering school that tubes produced mostly even-order
harmonic distortion when they clipped and that the clipped waveform didn't
look as much like a square wave as does a transistor which, when fully "on"
acts like a switch and produces lots of odd-order distortion. Perhaps, since
even-order harmonic distortion is easier on the ear and more consonant with
music, that this is the source of the term "soft-clipping". Of course, driven
hard into clipping, no amplifying device is listenable, no matter what type
of distortion is being produced but momentary peaks are another matter.

> Some PR mileage has been made out of the fact that tubed amps often have
> relatively poorly-regulated power supplies, but once higher-voltage
> transistors became more available, lots of SS amps with relatively
> poorly-regulated power supplies have been built and sold.
>

Re: speaker efficiency

"Sonnova" <sonnova@audiosanatorium,com > wrote in message
news:ffvj1m01pp5@news1.newsguy,com ...

> I was taught in engineering school that tubes produced mostly even-order
> harmonic distortion

No even order distortion if those tubes are in a push-pull configuration,
which has been the standard for power amps since about 1933.

> when they clipped and that the clipped waveform didn't
> look as much like a square wave

Tubes cut off and saturate just like transistors. The edges of a clipped
signal are sharpened by inverse feedback, which has been the standard since
about 1938.

> as does a transistor which, when fully "on"
> acts like a switch

Tubes also act like switches. Just drive them hard enough.

> and produces lots of odd-order distortion.

Odd order distortion is a natural consequence of clipping of both the
negative and positve halves of the signal.

> Perhaps, since
> even-order harmonic distortion is easier on the ear and more consonant
> with
> music, that this is the source of the term "soft-clipping".

Repeat: push-pull amplifiers can't produce even order distortion whether
they are tubed or SS, because of the rule of half wave symmetry,

> Of course, driven
> hard into clipping, no amplifying device is listenable, no matter what
> type
> of distortion is being produced but momentary peaks are another matter.

Actually, if those momentary peaks are really short, they pretty well escape
the ear's notice if we're amplifying music.

Please name the engineering school that taught you all of these strange
things.

Re: speaker efficiency

On Sat, 27 Oct 2007 20:08:26 -0700, Arny Krueger wrote
(in article <fg0ufa0v89@news5.newsguy,com >):

> "Sonnova" <sonnova@audiosanatorium,com > wrote in message
> news:ffvj1m01pp5@news1.newsguy,com ...
>
>> I was taught in engineering school that tubes produced mostly even-order
>> harmonic distortion
>
> No even order distortion if those tubes are in a push-pull configuration,
> which has been the standard for power amps since about 1933.
>
>> when they clipped and that the clipped waveform didn't
>> look as much like a square wave
>
> Tubes cut off and saturate just like transistors. The edges of a clipped
> signal are sharpened by inverse feedback, which has been the standard since
> about 1938.
>
>> as does a transistor which, when fully "on"
>> acts like a switch
>
> Tubes also act like switches. Just drive them hard enough.
>
>> and produces lots of odd-order distortion.
>
> Odd order distortion is a natural consequence of clipping of both the
> negative and positve halves of the signal.
>
>> Perhaps, since
>> even-order harmonic distortion is easier on the ear and more consonant
>> with
>> music, that this is the source of the term "soft-clipping".
>
> Repeat: push-pull amplifiers can't produce even order distortion whether
> they are tubed or SS, because of the rule of half wave symmetry,
>
>> Of course, driven
>> hard into clipping, no amplifying device is listenable, no matter what
>> type
>> of distortion is being produced but momentary peaks are another matter.
>
> Actually, if those momentary peaks are really short, they pretty well escape
> the ear's notice if we're amplifying music.
>
> Please name the engineering school that taught you all of these strange
> things.
>

San Jose State University.

Re: speaker efficiency

On Sat, 27 Oct 2007 07:51:03 -0700, Arny Krueger wrote
(in article <ffvj8n01pvt@news1.newsguy,com >):

> "Peter Wieck" <pfjw@aol,com > wrote in message
> news:fftvl502gjv@news1.newsguy,com ...
>
>> On Oct 26, 5:27 pm, "Arny Krueger" <ar...@hotpop,com > wrote:
>
>>>> a) Tube amps clip softly.
>
>>> False claim. Tube amps plenty sharply if they have enough loop feedback
>>> to
>>> be usable for hi fi purposes.
>>
>>> Some PR mileage has been made out of the fact that tubed amps often have
>>> relatively poorly-regulated power supplies, but once higher-voltage
>>> transistors became more available, lots of SS amps with relatively
>>> poorly-regulated power supplies have been built and sold.- Hide quoted
>>> text -
>
>> Tube amps, at least those that use output tranformers do not pass DC
>> to the speakers.
>
> Neither do typical solid state amps. They are not DC-coupled. There at least
> one LF pole. So here we have yet another straw man argument.
>
>> Hence, they clip - SOFTLY - as compared to many/most
>> vintage SS amps of the same/slightly greater output capacity.
>
> DC coupling has nothing to do with soft clipping. That makes yet another
> straw man argument.
>
>> And, hence, they are less likely to damage speakers (or themselves) if
>> driven to clipping, assuming reasonable build quality in either case.
>
> The issue was soft clipping, not probability of damage. That makes three
> straw man arguments in just this one post. Or, is it a red herring? BTW, in
> the days of tubes we managed to destroy speakers quite nicely with tubed
> amps. Most speakers are destroyed by the application of excess power, and it
> matters not where that excess power comes from tube amp or SS amp, because
> regardless of source it is all turned into heat by the resistance of the
> voice coil & etc.

Actually, I think you'll find that just as many speaker systems are damaged
by too little power as by too much. Here's the scenario: Small amp is driven
into constant clipping by listener's desire for louder rock-n-roll. Clipped
high frequencies exceed the duty cycle of the tweeter's voice coil. Coil
heats-up, burns out.

Re: speaker efficiency

"Sonnova" <sonnova@audiosanatorium,com > wrote in message
news:fg0u8e0v0l@news5.newsguy,com ...
> On Sat, 27 Oct 2007 07:51:03 -0700, Arny Krueger wrote
> (in article <ffvj8n01pvt@news1.newsguy,com >):

>> BTW, in
>> the days of tubes we managed to destroy speakers quite nicely with tubed
>> amps. Most speakers are destroyed by the application of excess power, and
>> it
>> matters not where that excess power comes from tube amp or SS amp,
>> because
>> regardless of source it is all turned into heat by the resistance of the
>> voice coil & etc.

> Actually, I think you'll find that just as many speaker systems are
> damaged
> by too little power as by too much. Here's the scenario: Small amp is
> driven
> into constant clipping by listener's desire for louder rock-n-roll.
> Clipped
> high frequencies exceed the duty cycle of the tweeter's voice coil. Coil
> heats-up, burns out.

The fallacy here is the idea that clipped musical signals always have more
high frequencies than unclipped musical signals. Clipping does not
necessarily increase the high frequency content of musical signals. In fact,
in some cases, clipping decreases the high frequency content of musical
signals. That's one reason why clipping tends to make music sound muddy.

Re: speaker efficiency

On Sun, 28 Oct 2007 20:07:40 -0700, Arny Krueger wrote
(in article <fg3ips0dvd@news5.newsguy,com >):

> "Sonnova" <sonnova@audiosanatorium,com > wrote in message
> news:fg0u8e0v0l@news5.newsguy,com ...
>> On Sat, 27 Oct 2007 07:51:03 -0700, Arny Krueger wrote
>> (in article <ffvj8n01pvt@news1.newsguy,com >):
>
>>> BTW, in
>>> the days of tubes we managed to destroy speakers quite nicely with tubed
>>> amps. Most speakers are destroyed by the application of excess power, and
>>> it
>>> matters not where that excess power comes from tube amp or SS amp,
>>> because
>>> regardless of source it is all turned into heat by the resistance of the
>>> voice coil & etc.
>
>> Actually, I think you'll find that just as many speaker systems are
>> damaged
>> by too little power as by too much. Here's the scenario: Small amp is
>> driven
>> into constant clipping by listener's desire for louder rock-n-roll.
>> Clipped
>> high frequencies exceed the duty cycle of the tweeter's voice coil. Coil
>> heats-up, burns out.
>
> The fallacy here is the idea that clipped musical signals always have more
> high frequencies than unclipped musical signals. Clipping does not
> necessarily increase the high frequency content of musical signals. In fact,
> in some cases, clipping decreases the high frequency content of musical
> signals. That's one reason why clipping tends to make music sound muddy.
>

Seen too many burned-out tweeters associated with too-small amps to buy that.
Sorry.