what determines the cut off for khorn woofers?

[D-MAN]

Shawn, it is an undeniable fact that an enclosed space (such as a room) can only support undistorted soundwaves whose wavelengths "fit" within its proportions. And what is not absorbed is reflected. Fact.

Accent on the word UNDISTORTED.

Also the operation of the ear, being that it CANNOT BE RELIABLY TESTED is not the determinant factor in this case.

The ear is sensing changes at a molecular levels in the local atmospheric pressure being caused by the pressure changes of soundwaves. If the soundwave is NOT a complete 40Hz waveform, which it CANNOT be in a fore-shortened space, then WHAT are you hearing that you would consider a 40Hz waveform? It is a mismash of sound and is resolved by the ear as "being somewhat low". But described by a frequency analyser, it is a combination of many permutations of waveforms caused by modulations of the air as the result of mainly, reflections, none of which form a true 40Hz sine wave.

To further check this out, and to possibly believe what I am saying is true, get ahold of Everest's "Handbook of Acoustics" that I heard about from artto's posts.

It is somewhat readable in that it is not overly reliant on formulas alone, yet is complicated enough to make my head hurt. But the main emphasis is on the listening environment.

Interesting chapter on the human ear and perception, too.

DM

[sfogg]

DM,

"it is an undeniable fact that an enclosed space (such as a room) can only support undistorted soundwaves whose wavelengths "fit" within its proportions. And what is not absorbed is reflected. Fact."

This happens well above a wavelengths space too. Music isn't a single wave in length... it is multiple waves.... they bounce around and interact with each other. No arguments there.

"If the soundwave is NOT a complete 40Hz waveform, which it CANNOT be in a fore-shortened space, then WHAT are you hearing that you would consider a 40Hz waveform?"

It IS a complete 40hz waveform, one that is in effect 'folded' (bouncing) around within the room.

"But described by a frequency analyser, it is a combination of many permutations of waveforms caused by modulations of the air as the result of mainly, reflections, none of which form a true 40Hz sine wave."

Wrong, it shows up as a 40hz sine wave. Not theory, fact... I've measured my various rooms many times.

Have you ever measured your room or are you just applying misunderstood theory?

All you will see when you play the 40hz tone in the room is a 40hz reading and as you move around the room the amplitude of the 40hz tone will change from the interference patterns setup in the room. It will still read as a 40hz tone though.

As an example of this I just went down to my 17' long room and played a 75' long wave (15hz) in it.... something you have said can't happen. See the attached for how it is 'described by a frequency analyzer.'

"To further check this out, and to possibly believe what I am saying is true, get ahold of Everest's "Handbook of Acoustics" that I heard about from artto's posts."

Get some test equipment and see the reality of what happens when you play a wave that is longer then your rooms length. You are misunderstanding what the book says.

Shawn

[DRBILL]

O, WOW, this has gotten to be fun!

Sometimes it is good to return our thoughts to the ancient Greek philosophers.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

F\6@<`:@F: (economy). "Regardless of all other proofs or arguments, that which has been done is not impossible".

My home is always open to forum members. COME AND SEE!

The ear is a remarkable device. There is a prehensile quality that allows us to hear the fundamental of any complex tone no matter how weak. Organbuilders use this in many inventive ways and some of their art is awfully (awefully) exciting.

On any occasion, I can demonstrate a mix of two Klipschorns and two Heresies faithfully reproducing 16Hz. You can feel it in your guts or feel it in the walls.

Put up your calculators and your formulae and COME AND SEE!

We are in Fort Worth. If you come this way, get in touch. You will be welcome. You will leave a believer. Chances are that you will get something good to eat and drink (after Great Lent).

Here endeth the second lesson.

DR BILL

[Marvel]

Shawn,

The chapel at the college where I work is a huge!!! cavern. It was built this way to hold a large pipe organ. Alas, like many Protestant endeavors (oops, sorry), the money for the organ wasn't forthcoming. The room was made this size so that the lowest notes (32ft pipes) could be reproduced undistorted.

Yes, we can still hear those low frequencies. No doubt about it. Fr. Bill doesn't need to make a believer out of me, I already am. But the larger tuned room will still sound better. OTOH, the room stinks for most everything else. The reverberant field is too large and again, for lack of money, isn't going to be fixed anytime soon.

It is a miracle that those small diaphragm mics can catch the music at all isn't it?

Marvel

[DRBILL]

Just for fun.

DR BILL

[homemade]

DAX616, the flutter you're hearing might be an air leak at the joints of the box. I had to add some more screws to my woofer cover to control the vibration and consequent air leaks on my homemade khorns. Remember, the bass rolls off fast below 40hz or so and that's why your low bass isn't as powerful as it could be. A little help from an eq. (here we go again) will balance things out wonderfully. How loud do you listen to your music? What's the freq. and power level of the bass in the music? Can you run a freq. analysis in a program to find out what kind of energy there is down low? According to my khorn literature from the mid 90's or earlier, the response is down 10db at 30hz compared to 40hz and 40hz is down 4db from 200hz. What did you think of the impact of the bass at high levels?

[michael hurd]

I am going to have to agree with Shawn, that even though a wavelength is longer that the rooms longest dimention, does not mean that it could not be reproduced. If that were the case, in a car or truck, you would not be able to reproduce low frequencies.

The point that the wavelength gets larger than the room is where room gain starts to occur. This is why we can have very loud low bass in a car. Has anyone else felt a 20hz-100 sweep in a car? I have, where the lowest frequencies are perceived as a terrific shaking, rather than heard.

[colterphoto1]

Perhaps I've missed this in scanning this thread, but there is a lot that goes into the equation for manufacturing a speaker assembly. All that tuning, port, and horn stuff aside (although very critical), the speaker cabinet must be aesthically pleasing, be saleable, able to be manufactured and shipped, priced for the market, etc.

Also, consider that when the Heritage line-up was invented, there was no Home THeatre per so, certainly not with the type of soundtracks we have today. And music was what was coming out of orchestras and traditional instruments. Hence the partial reliance on 40Hz being the lowest fundamental note that needed to be supported. How was PWK to realize that 40 years later his designs would be pumping out Eminem, Hunt for Red October, etc. ONly recently has the need for a solid 20Hz foundation been necessary.

Hope this helps, just get the sub, you'll be happy.

Michael

[DAX616]

Wow all this science and I just want to say my cats breath smells like cat food. Yes it is inevitable I need a sub. I believe the human ear is most sensitive to the voice range and less to the lower freq's. Most equipment as well tends to drop off towards the nether regions.Does anyone know where to get a velodyne hgs -18 for around $1500.00? Of course just for medicinal purpouses.

dax

[Frzninvt]

This ought to do the trick. The F and FSR series are the equivalent of the HGS series subwoofers. The servo's keep the bass clean and deep! Real deep!

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3275&item=5764013631&rd=1

[DAX616]

What's the difference between the two? I have to admit I get confused between the different models.It looks like the same thing except people eat thos hgs's as soon as they hit the used market like cabbage patch dolls or tickle me elmo's.

[ZAKO]

Just for the record you wont hear 20Hz. Just feel it. Any thing audible is its harmonic.

[sfogg]

"Just for the record you wont hear 20Hz. Just feel it. Any thing audible is its harmonic."

That isn't really true. Human hearing doesn't have a hard cutoff at any specific frequency... it varies with frequency and level. Certainly much of very low bass is tactile in presence but you can hear it too if it is loud enough.

I felt I could sort of 'hear' that 15hz tone last night... and there weren't harmonics showing up on the RTA.

I totally agree that harmonics can fool people, that is why I mentioned earlier that just an SPL meter isn't a good way to measure deep bass response. The meter only tells overall level, it doesn't show the frequency. So if a system wasn't capable of reproducing the fundamental but was 'doubling' (second harmonic) it would show up on a SPL meter but the user might not realize that what is being heard is the harmonic. On an RTA (or better) the listener would see what frequency is being reproduced and could tell if it was a fundamental or a harmonic.

Shawn

[D-MAN]

Hey, you guys, I said UNDISTORTED. More than once.

Like I said, the ROOM is an enclosure with its own frequency response values. Just get up and walk around and see how the bass notes change in the room.

Don't ignore the facts, or you might accidently start buying Bose.

DM

[sfogg]

"Like I said, the ROOM is an enclosure with its own frequency response values. Just get up and walk around and see how the bass notes change in the room."

That is a lot different then what you said earlier in that it wasn't possible to reproduce a wave in a room that is physically smaller then the wavelength. Fact: That isn't correct. The room gain makes it easier to get deep response in a smaller room then in a bigger room.

Of course a room has resonances at certain frequencies. No denying that. That will change the amplitude of the wave at different points within the room. This happens for waves that have wavelengths much smaller then the rooms dimensions too. After all if you face the reality that 1 second of a 10hz wave is 1130 feet long... just like 1 second of a 100hz wave is ALSO 1130 feet long. Neither will 'fit' in most anyones room without reflection. You have been fixating on a single waves length... music is very very rarely just a single wave in duration.

Those waves will bounce around in your room and interact with each other to setup standing waves at specific frequencies which will alter the amplitude at those points. It does not change the frequency of the wave as demonstrated by the RTA of the 75' wave in my 17' room I already posted. Don't ignore that fact.

Download the program listed here:

http://users.rcn.com/jimmuller/modes.zip

And it will model your room (assuming it is rectangular) to show you what resonances you will have. It takes awhile for it to calculate be patient.

Shawn

[Deang]

Good thread, I wish I knew what in the hell you guys were talking about.

[D-MAN]

Well, regardless of what I THOUGHT I said, DID say, or whatever, the point I am trying to make is that EVEN if you are using brute force to attain a DIRECT wave to the ear, sitting in the far field, if the room is too small (let's say less than or equal to 1/2 of the proposed 40Hz wavelength), you are also going to be hearing the reflection coming back OUT of phase at the same time and THAT is going to distort the direct wave which is still coming out and flying by your head and this doesn't even refer to any other modal discontinuities that may occur. Room gain doesn't effect the frequency, and is technically not part of this issue, unless it is considered as part of the brute force portion of the above (not by me, anyway). It reinforces in "loudness", but has no other effect on the frequency response.

To avoid this problem, a larger room is required with enough distance to offset the reflection timing and reduce the energy of the reflection to the point that it becomes a non-interfering factor as distance usually does, or I suppose that special room treatments can be used to absorb the energy at the reflecting surface (usually the back wall) to the point that the reflected energy is low enough that it does not influence (or distort) the directly propagating waveform to an audible degree. We have all experienced the point at where it can be said that the "speakers are too large for the room". Part and parcel of the point I was/am trying to make.

But I am not recanting; only "clarifying". Yeah, that's it - "clarifying".

DM

[sfogg]

I asked you directly:

Please tell me you aren't suggesting that a wave must be able to 'fit' into a room for it to be able to be reproduced in it.

To which you responded:

"That's EXACTLY what I'm saying."

No one here is putting words in your mouth. You have 'refined' your position since that post.

", if the room is too small (let's say less than or equal to 1/2 of the proposed 40Hz wavelength), you are also going to be hearing the reflection coming back OUT of phase at the same time..... Room gain doesn't effect the frequency, and is technically not part of this issue "

Room gain is absolutely part of the issue. You are basically describing why we get room gain. Only you are missing the point that when the wave lengths get big enough the reflection from the same cycle of the wave become more and more in phase with itself. That is where the room pressurization/gain really gets going.

"We have all experienced the point at where it can be said that the "speakers are too large for the room". Part and parcel of the point I was/am trying to make."

That is only because the bass response of the speakers when added with the room gain gets over bearing and the speaker becomes very bass heavy at low frequencies which make the whole thing sound muddy. If the response of the speakers was better balanced for the effects of room gain that isn't an issue. This is all the more reason to have flexibility in setting bass levels through powered subwoofers, EQ, autoformers on the woofer (ala AR LST) or even a high pass filter for the speaker that is more or less the inverse of the room gain. Wanna put a pair of K'Horns in a tiny room.... as a starting point try high passing them first or second order starting around 60hz and see if they don't sound better balanced.

I have what is basically an extremely potent array of subwoofers in what is a very tiny room... and they are well balanced with the rest of the system and don't let themselves be known until they are meant to.

Shawn

[michael hurd]

Question: How many degrees out of phase before it would start to affect the amplitude of a 40 hz wave, in a room that is technically too small? A 40 hz wavelength is 28 feet long, I would assume that once you get close to 180 degrees out of phase, then the output would start to drop off considerably.

[sfogg]

"I would assume that once you get close to 180 degrees out of phase, then the output would start to drop off considerably.      "

Not really since the waves are moving in opposite directions. Remember... even above this point waves bounce off the walls and can be out of phase with the direct sound. In fact this happens all the way up the frequency band.

The place the output will drop considerably is in the null point of a standing wave. Those will occur at specific points in the room at specific frequencies and if you move into one of them there will be a dramatic decrease in bass at that frequency at that point. On the flip side if you move into a standing wave point at a peak the amplitude jumps way up at that point.

This will occur even in large rooms... again because if you play a test tone you aren't only producing one cycle of the wave but are producing that wave continually. That bounces around and interacts with itself.

Shawn