Jump to content

Under what conditions would you need more than 100 Watts per channel with Khorns


Guest " "

Recommended Posts

Heck, I didn't read this whole thing...but from what I understood from PWK and have experienced on my own you'd need 100 watts with K'horns if you wanted to listen at 100db well beyond any normal listening distance with power to spare and needed to light a 90 watt light bulb at the same time.

OK, I'll go back and read this tomorrow to see if something changed.

Dave

Link to comment
Share on other sites

Heck, I didn't read this whole thing...but from what I understood from PWK and have experienced on my own you'd need 100 watts with K'horns if you wanted to listen at 100db well beyond any normal listening distance with power to spare and needed to light a 90 watt light bulb at the same time.

I think a lot of people take PWK's comments out of context, which I'll try to describe below:

To help clarify, let's go back to my first comment about needing 100W:

If you were listening to music with 30dB of crest factor at 88dB on
speakers with 104dB sensitivity while sitting 2m away...

I'm not saying that you will be pushing 100W continuous out of the amplifier....what I'm saying is you need an amplifier with the same amount of voltage swing as a 100W amplifier, which is ~28Vrms. With 30dB of crest, you're talking only 0.9Vrms, or 0.1W continuous. Technically, that 28V for the crest is actualy 28Vpeak, so an amplifier capable of "only" 20Vrms, or about 50W would technically be sufficient.

An amplifier only capable of 10W can only swing 12.5Vrms (18Vpeak); so even though it is capable of delivering the 0.1W continuous, it won't have the voltage swing to accurately reproduce 28Vpeak transients. Sometimes this ~6dB of compression goes by unnoticed depending on the source material, or maybe the source material has less crest factor.

Anyways, PWK is concentrating on that 0.1W continuous number because it makes for good marketing.

And just another comment since we're on the topic...when an amplifier gets driven into the non-linear region of operation (clipping, and just before clipping), the intermodulation distortion will start to skyrocket. So even though the THD numbers might be decent, you can get into situations where you're creating tones that aren't tonally related to the source material. That's when you start getting into snare hits that sound smooshy, or gargling vocals during heavy bass passages and drum fills. The peak output of an amplifier is usually measured at about 1% THD, so it's not like you want to be running normal source material into that region....which is why I get loose on the extra 3dB of headroom when calculating for crest factor (picking the 100W amp instead of the 50W amp). Most well designed amplifiers have a very sharp distortion knee, so you don't need to be that much lower in level to get outta the distortion region.

For what it's worth, I was skeptical of my calculations until I actually sat down with an oscilloscope connected to the output of an amplifier. We designed a class D amplifier in college and hooked up a variac to change the power supply voltage so that we could set the bus voltage (and the ultimate clip point). Playing a single Chorus II at ~96dB as measured on a calibrated meter in the lab at a distance of about 1m, we needed something like +/-50V rails before the waveform wasn't squaring off on the output when listening to Blue Man Group, which would be the equivalent of a 150W amplifier (35Vrms). That correlates to a crest factor of about 26dB, but we heard cleaner transients when the rail voltage was increased to the equivalent of a 200W amplifier because it moved you further from the distortion knee. In other words, when changing the power supply voltage without the person knowing, they would start to notice distortion when we got below 200W, and it became progressively more noticeable as it was lowered. Listening with +/-15V rails (the lowest we could go) sounded like pure garbage when getting the SPL meter to register 96dB. That 14W is a whole heck of a lot more power than the 0.5W or so people here are claiming for a 101dB speaker to play at 96dB at 1m. Good music has way more than 10dB of crest...

Link to comment
Share on other sites

I'm a little surprised that no one here has discussed dynamic headroom of amplifiers Indifferent

Not relevent to this discussion. An amp rated 60 WPC with may in fact put out 100 W peak power. With that amp you can present the speaker with 100 W. So for the purposes of determining the peak SPL output of a speaker, you are powering it with 100 W. For a continuous loudspeaker SPL rating use the continuous power rating of the amp, or 60 W.

The amount of dynamic headroom varies between amplifiers, generally depending on the power supply. Power supplies that are tightly regulated result in a low dynamic headroom spec for that amplifier. A 60 W amp puts out about 60W and thats it.

Link to comment
Share on other sites

Not relevent to this discussion.

I believe that I was referring to Mike's "crest factor" discussion, not average SPL.

The amount of dynamic headroom varies between amplifiers, generally depending on the power supply.

Yes...it does...considerably.

Chris

Link to comment
Share on other sites

Mike, you are the engineer. I am just a listener. It was in PWK's lab at Hope listening to the Saint Saens "Organ" Symphony from an Ampex deck that I swallowed his "...what this country needs is a good 5 watt amplifier" whole. That room was very wide, and the sound totally filled it to the point I had to shout my question of "How much power are we hearing?" He glanced at the meters on the Marantz VT amps and said "Oh, about 5 watts."

I believe the maximum power of those amps was 30wpc and I am reasonably certain they were never pushed near there.

Perhaps the IM was through the roof...I certainly heard none.

Whilst I have some interest in specs and such, I've pretty much long since put my faith in ears...it's never failed.

Dave

Link to comment
Share on other sites

"All of that not withstanding, a Khorn will not output 104 dB SPL @ 100 feet with 100 watts input power. That is concert level SPL and would take something like a Turbosound or EAW pro rig with a lot more amplifier power to achieve that output @ 100 ft. "

Actually, the Khorn sensitivity is 105 @ 1 W. In the calculated senerio, at point source, it would be putting out about 112db's. The max spl of the khorn at point source is 121db. Way above what is needed to deleiver 104dbs at 100ft.

Due to power compression a stock Khorn will not do 121 dB continuous, but we will assume that it can to give your argument a best case scenario.

Per the inverse square law, 6 dB loss per doubling of distance:

4 ft. 121 dB

8 ft. 115 dB

16 ft. 109 dB

32 ft. 103 dB

64 ft. 97 dB

128 ft. 91 dB

For 2 Khorns, add 3 dB.

In the late 60s a friend and I hauled a Khorn to a gymnasium and put it into a corner on the floor. Powered by 60 watts of tube amplification (Golden Ear Laboratory Amplifier) we measured 90 dB with sine tones at an approximate 100 ft. distance. Past a certain distance the SPL did not follow the inverse square law (critical distance). Considering these measurements, and Pat Brown's article, I would conclude that the calculator you used would work better with less directional speakers. As the quoted article shows and as Pat Brown says, " Horns are immune from boundary effects"

A pair of motengators or a pair of KP-600 stacks will get you there.... [;)]
Link to comment
Share on other sites

""Due to power compression a stock Khorn will not do 121 dB continuous, but we will assume that it can to give your argument a best case scenario."""

This wasn't a question, look at the below website extract, under MAXIMUM ACOUSTIC POWER. If you don't agree with Klipsch, discuss with them. We do not know how their tests were done, equipment used, etc, etc, etc.

Link to comment
Share on other sites

Mike, you are the engineer. I am just a listener. It was in PWK's lab at Hope listening to the Saint Saens "Organ" Symphony from an Ampex deck that I swallowed his "...what this country needs is a good 5 watt amplifier" whole. That room was very wide, and the sound totally filled it to the point I had to shout my question of "How much power are we hearing?" He glanced at the meters on the Marantz VT amps and said "Oh, about 5 watts."

I believe the maximum power of those amps was 30wpc and I am reasonably certain they were never pushed near there.

Perhaps the IM was through the roof...I certainly heard none.

Whilst I have some interest in specs and such, I've pretty much long since put my faith in ears...it's never failed.

Dave

In the quest of science, do you know of a similar recording that we cohld measure? My hypothesis is that he was using a tube amp that had a pleasant compression sound to it.

Link to comment
Share on other sites

""Due to power compression a stock Khorn will not do 121 dB continuous, but we will assume that it can to give your argument a best case scenario."""



This wasn't a question, look at the below website extract, under MAXIMUM ACOUSTIC POWER. If you don't agree with Klipsch, discuss with them. We do not know how their tests were done, equipment used, etc, etc, etc.

From The Dope From Hope, Vol.16, No.1 Jan. 1977, it took 375 watts to achieve 120+ dB SPL from a Khorn. Not 100 watts.

A Khorn won't take 375 Watts for long. Around that time I had to assist a friend in replacing 1 woofer and 2 tweeters in a pair of Khorns hooked to a Phase Linear 700 amp.

The above referenced article fully describes the test, done with rock music with a 10 dB peak-to-average ratio. This is a best case test for max SPL, more dynamic music would require more than 375 WPC, ruining the Khorns even more quickly.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...