A horn throat distortion question, and eficiency Vs dynamics?

[toddalin]

This is true. As mentioned before, decibels are measures of relative power levels, so doubling the input power from 1 watt to 2 watts is a 3 dB increase, and so is the difference between 250 and 500 watts. However, doubling the input power does not double the acoustic energy produced by the loudspeaker. Adding a second identical system also receiving the same level of input signal would produce an actual doubling of energy--more in cases of acoustic coupling, as when assymetric folded horn mouths are arranged in mirror-imaged pairs. Simply applying a 3 dB increase in input power will not produce this magnitude of effect.
Nor are decibels absolute measures of sound level. John L. Murphy, of the True Audio Loudspeaker Design Center, states that if a loudspeaker were 100% efficient, an electrical input of 1 watt would produce an output of 1 acoustic watt, which, measured at 1 meter, would be 112.1 dB SPL (radiating into half space). The question ought to be, "112.1 dB above what?" The baseline level cannot be silence, for any multiple of no sound is still no sound. If we use the measurement of one loudspeaker's output that is produced by a 1 watt electrical input and, for instance, call it 85 dB, then how many times can we double the acoustic energy produced by that loudspeaker before it becomes burned out junk? If, on the other hand, if we measure the output of a system the same way, using the same equipment, and find a reading of 95 dB, we may double that acoustic energy perhaps the same number of times before destroying the transducer, but the ultimate output will be much greater. Now, obviously, either system will play softly enough to produce sounds that are barely audible, but the more efficient one will play far more loudly, thus its dynamic range is wider. Finally, listening to music at the same average level, the more efficient system with the wider dynamic range will, by allowing the amplifier greater reserves for reproducing transient peaks, simply sound "more dynamic."

Have to disagree with you on a few levels. Whizzer

First off, as long as the speaker is operating within is linear excursion and electrical parameters, doubling the power will in fact double the cone excursion thereby moving twice the air mass raising the sound by 3 dB increase. Bringing in a second sound system may result in further increase if various room nodes are able to interact further increasing the wave amplitude. On the other hand, you could get cancellation reducing the amplitude.

Second, YES DECIBELS ARE AN ABSOLUTE MEASURE OF SOUND LEVEL. The dB scale does have a zero dB reference point of a pressure level of 20 micropascals per square meter. Therefore, 3 dB = 40 micropascals per square meter and 6 dB = 80 micropascals per square meter, etc.

"The question ought to be, "112.1 dB above what?"
BTW, 112.1 dB = 3.2436E12 micropascals per square meter. The equation is

10^(desired level in dB/10) x 20 micropascals/m^2

And, to answer your anticipated question, yes, thre can be values less than ZERO dB. For example 10 micropascals per square meter = -3 dB.

[Mr. Widget]

First off, as long as the speaker is operating within is linear excursion and electrical parameters, doubling the power will in fact double the cone excursion thereby moving twice the air mass raising the sound by 3 dB increase.

This is true at low power levels, but as the voice coil heats up the coil inductance and other parameters change so it isn't linear... I think this is what whizzer was getting at.

[QUOTE=whizzer]

A mechanical and/or electrically-induced restriction of dynamic range is exactly what "power compression" is.

Sure... I guess what I was trying to say was that your earlier post seemed to imply that a sensitive speaker helped the amp loaf and therefore increased the system's dynamics... my point was that while true, I feel the loudspeaker's characteristics are more important. For example, a pair of AR3as being driven with a pair of kilowatt Mac mono blocks... That system still won't sound dynamic even though there is no shortage of amplifier headroom.

Widget

[Akira]

Unless physics have changed since I was in engineering school...

double power = an increase of 3db
double power plus double speaker = an increase of 6db
preceived acoustical doubling is stated at 10db.

the definition of 1db is the smallest increase in SPL that the human ear can detect 50% of the time.
0db is the threshold of hearing that the human ear can detect 50% of the time

the speed of sound is xxxxx at sea level @ 70degrees CAN'T REMEMBER...I FLUNKED THAT PART OF THE COURSE!!!!

all quotes from Modern Recording Techniques, Robert E. Runstein (Recording Institute of America)

[Mr. Widget]

Unless physics have changed since I was in engineering school...

Still the same, but I think you'd agree that school is an idealized environment.

Widget

[Akira]

Still the same, but I think you'd agree that school is an idealized environment.

Widget

Damn right. My education started when I left school and the 'industry' quickly showed me that I new nothing of the real world.
BUT I USED TO KNOW WHAT THE SPEED OF SOUND WAS!!!!

[Earl K]

BUT I USED TO KNOW WHAT THE SPEED OF SOUND WAS!!!!

FWIW : I usually use 1130 ft per second . This figure works well enough in other equations .

[toddalin]

Damn right. My education started when I left school and the 'industry' quickly showed me that I new nothing of the real world.
BUT I USED TO KNOW WHAT THE SPEED OF SOUND WAS!!!!

1,116 feet per second at sea level.

BTW, 1,130 feet per second would put Toronto about 3,250 feet BELOW sea level.

[whizzer]

First off, thanks to Mr. Widget for clarifying what I was trying to say. Sometimes teaching English just gets in the way. While it's true, at least in theory, that doubling the input power will result in moving twice the air mass, that's rarely actually true in the real world--not that it can't be, mind you--it's just rare that physical conditions are so ideal as to produce results that are identical with theory. I guess the real point is that a 3 dB increase in electrical input power is a far cry from a doubling of acoustic energy in that one watt of acoustic energy is measured as an output of 112.1 dB @ 1 meter on axis, which, in the real world, would, with most loudspeakers, require far more than a one watt input. That is, the energy measures are not 1-1 linear. Apparent "twice as loud" is not a simple 3 dB increase in input watts, but is a true doubling of output in terms of acoustic energy-- not in terms of theory, but in terms of human hearing. The purpose of the whole SPL-efficiency rating thing is to differentiate between the output of various drivers with a standard input. If System A produces a measurement of 85 dB with this input while System B produces 95 dB, then we know that system B does more with one watt than does System A, thus, it would seem to me that we have no reason to assume that System A will respond just as vigorously to a doubling of the input as System B, as it has already been shown to be less efficient at converting electrical energy to sound. If, for instance, in actuality, the rate of increase in the output falls as the input level increases, as in "power compression," then a simple formula of x dB in = x dB out becomes increasingly out of touch with physical reality.

On a related note, regardless of the dynamic capabilities of the driver itself, if there is not a sufficient reserve of amplifier power capable of reproducing transients 15-20 dB above the average content, then clipping and dynamic compression will be the result.

[pangea]

First I wanted to tell you that today I was listening to one of Mike Oldfields CD's "Amarok" and although I must admit that I have set my Behringer Ultracurve to add a few dB of expander on the midbass section, I noticed the dynamic range on the CD spanned from 40dBC to 97dBC!!! Isn't that amazing?

Talk about dynamics!!! How many speakers other than JBL's do you think are up to the task???

One other thing I would like to ask, is why those yellow kevlar type of cones have become so popular.

I read this article from Passlab on the project Rushmore, where it said that many speaker driver manufacturer who really succeeded and excelled, were those who used their ears when choosing materials and designs and the best sounding cones were those made of paper, the article said.
So, why are there so many kevlar cones out there?

Is this also the main reason for JBL staying with paper cones?

EDIT: Follow up question if that IS the case. Why do paper cones sound better?

Anyone know?

BR
Roland

[toddalin]

First I wanted to tell you that today I was listening to one of Mike Oldfields CD's "Amarok" and although I must admit that I have set my Behringer Ultracurve to add a few dB of expander on the midbass section, I noticed the dynamic range on the CD spanned from 40dBC to 97dBC!!! Isn't that amazing?

Talk about dynamics!!! How many speakers other than JBL's do you think are up to the task???

One other thing I would like to ask, is why those yellow kevlar type of cones have become so popular.

I read this article from Passlab on the project Rushmore, where it said that many speaker driver manufacturer who really succeeded and excelled, were those who used their ears when choosing materials and designs and the best sounding cones were those made of paper, the article said.
So, why are there so many kevlar cones out there?

Is this also the main reason for JBL staying with paper cones?

EDIT: Follow up question if that IS the case. Why do paper cones sound better?

Anyone know?

BR
Roland

What makes you think that JBL doesn't use kevlar in the paper cones???

W15GTI
15" Differential Drive® Design Subwoofer
If you are in search of the ultimate woofer, this is it! JBL has leveraged all engineering resources to develop quite simply the best subwoofer money can buy. Symmetrical Field Geometry ensures linear cone travel and low distortion at virtually any level by creating a uniform magnetic field around the coil. Die-Cast basket
• Suggested Retail Price: $699.00

• Differential Drive® Design (DDD) motor

• Die-cast vented basket

• Kevlar®-impregnated paper woofer cone

• Nitrile-butylene surround

• Power handling RMS: 800 watts

• Power handling Peak: 5,000 watts

• Mounting depth: 10-1/4"

• Cut-out diameter: 13-7/8"

• Dual 6-ohm voice coils

• Sensitivity: 92dB

[pangea]

What makes you think that JBL doesn't use kevlar in the paper cones???

W15GTI
15" Differential Drive® Design Subwoofer
If you are in search of the ultimate woofer, this is it! JBL has leveraged all engineering resources to develop quite simply the best subwoofer money can buy. Symmetrical Field Geometry ensures linear cone travel and low distortion at virtually any level by creating a uniform magnetic field around the coil. Die-Cast basket
• Suggested Retail Price: $699.00

• Differential Drive® Design (DDD) motor

• Die-cast vented basket

• Kevlar®-impregnated paper woofer cone

• Nitrile-butylene surround

• Power handling RMS: 800 watts

• Power handling Peak: 5,000 watts

• Mounting depth: 10-1/4"

• Cut-out diameter: 13-7/8"

• Dual 6-ohm voice coils

• Sensitivity: 92dB

Yeah yeah, but those should hardly be counted, since they're mainly intended for car use, where they have to endure various weather conditions, am I right?

I was talking about sonic excellence here, or do they qualify in this respect too?

Besides, isn't the sensitivity a bit low?

Hmmm, dual voice coils, does that mean, you can parallel them if the amp can handle a 3 Ohm load, or that they can be coupled with a stereo signal to each coil?

BR
Roland

[toddalin]

Yeah yeah, but those should hardly be counted, since they're mainly intended for car use, where they have to endure various weather conditions, am I right?

I was talking about sonic excellence here, or do they qualify in this respect too?

Besides, isn't the sensitivity a bit low?

Hmmm, dual voice coils, does that mean, you can parallel them if the amp can handle a 3 Ohm load, or that they can be coupled with a stereo signal to each coil?

BR
Roland

It would appear from other posts on this forum, that the W15GTI is similar to the new sub for pro use.

Hey, they're JBL! One would not expect anything less than sonic excellance regardless of the venue!

At 92 dB their are only 1 dB less efficient than the 2235, and way more efficient than an LE15.

To make the speaker work as designed, the coils MUST be wired in parallel or series and were not designed to be used coupled for stereo.

[Mr. Widget]

At 92 dB their are only 1 dB less efficient than the 2235, and way more efficient than an LE15.

The LE15 is a few dB more sensitive than the 2235....

Paper or plastic?
While plastic, kevlar, carbon fiber, etc. allow certain benefits, I have preferred the sonic quality of paper myself. Typically the doped, aquaplas coated, carbon or kevlar impregnated paper cones are also great, but there is just something about paper...


Widget

[Alex Lancaster]

How about the hemp ones?

[toddalin]

The LE15 is a few dB more sensitive than the 2235....

Paper or plastic?
While plastic, kevlar, carbon fiber, etc. allow certain benefits, I have preferred the sonic quality of paper myself. Typically the doped, aquaplas coated, carbon or kevlar impregnated paper cones are also great, but there is just something about paper...


Widget

Almost right. My catalog says LE15 does 45 dB SPL at 1 mW at 9.1 meters and when I do the calcs, it comes out to 94 dB at 1 meter. Like the 2235, the 136A comes in at 93 dB at 1 meter. But a 124A only comes in at 89 dB at a meter, so at 92 dB at 1 meter the W15GTI is still not bad!

I guess efficiency is the price you pay (at least in part) for that massive surround.