John Curl's Blowtorch preamplifier part II

[vacuphile]

Of course you can, you can have subsonic sound even in automobiles.

Actually, it is the reverse of what you state. In rooms that are smaller than the wavelength of de frequency reproduced, you get 'cabin gain'. Which of course is not limited to cars but also applies to small rooms.

 

[SY]

Can you hear bass in headphones?

 

[marce]

Would not all recording and playback media have the same effect as all are based on 20Hz - 20KHz with digital having the widest dynamic range?

 

[billshurv]

Of course you can, you can have subsonic sound even in automobiles.

Actually, it is the reverse of what you state. In rooms that are smaller than the wavelength of de frequency reproduced, you get 'cabin gain'. Which of course is not limited to cars but also applies to small rooms.

You get room gain. You also get a complete mash of room nodes, windows shaking etc. I have a sub, just not built the crossover for it yet. As the room is a near cube and placement is limited by where there is space I do not hold out for flat to 20Hz so am in no great rush ! You could fit the whole ground floor of my current house into what I had as a den in the 90s. But those damn glass fronted fireplaces beloved of certain types of home in America rattle like b***ery with full range reproduction. It was a rental so nothing I could do about it.

 

[billshurv]

Of course you can, you can have subsonic sound even in automobiles.

like this? https://www.youtube.com/watch?v=GYWsQcmYWiI

 

[dvv]

Not just the music fundamentals, more importantly room ambience. Yes, it's worth reproducing such content if it's in the recording, for example greatly adds to realism for classical performances I find. Yes, this means a recording and playback chain that's intended for it, and not lopping off, which often crops up in digital transfers of analog recordings IME.

Not that it's essential, but a point of audio playback detail, a matter of the total experience. The recorded room is part of the performance.

It is essential for full fidelity playback, I think. My current speakers have their reflex port tuned at 35 Hz, system resonance is at 31 Hz, and clean and clear bass is available all the time. It hasn't been once I noticed the low registers doing their thing and it sounds good.

One of several very pleasant surprises my NAD C565EE served me is an excellent low end, beyond my expectations, thus all the more wellcome. And the power amp (H/K PA 2400, 2*170W/8) takes it in its stride. A joy to listen to.

 

[vacuphile]

You get room gain. You also get a complete mash of room nodes, windows shaking etc. I have a sub, just not built the crossover for it yet. As the room is a near cube and placement is limited by where there is space I do not hold out for flat to 20Hz so am in no great rush ! You could fit the whole ground floor of my current house into what I had as a den in the 90s. But those damn glass fronted fireplaces beloved of certain types of home in America rattle like b***ery with full range reproduction. It was a rental so nothing I could do about it.

As a matter of fact you can only have room modes above frequencies where at least half a wave fits into the largest dimension of the room.

American balloon frame houses are fickle. I used to occupy the -huge- basement of a house in Bethesda, Md, when we lived there. My speakers did a very nice 20 Hz, inaudible to me, but enough to set up vibrations of all sorts in the entire house. Walls, window panes, floors, sliding doors, the whole place would be dancing.

Btw, nice clip, lol!

 

[billshurv]

I'm British and used to American mini monitors. 100Hz IS bass to me

I should really measure my room. With an anechoic -6dB point of 43Hz on my speakers I would be interested to see how low it does go.

Did I mention I am daft enough to be going open baffle in my tiny cube at some point in the near future?

 

[Hiten]

Noob query. If we dont take of low frequencies like 20 hz at the source what happens to Harmonics of 20hz ? do they get emphasis in the phono peramplifier. Though I read somewhere that harmonics are usually at lower level than fundamental frequency.

 

[vacuphile]

Hiten,

Harmonics are usually at a lower level than the fundamental. However, if you look at the overtone structure of instruments such as saxophone, clarinet or violin, you will see that most of the energy typically is not so much in the fundamental, but rather in the overtone structure. https://www.google.nl/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCIQFjAA&url=https%3A%2F%2Fcourses.physics.illinois.edu%2Fphys193%2FStudent_Reports%2FFall03%2FTammy_Linne_Andy_Schurman_Ivy_Thomas%2FTammy_Linne_Andy_Schurman_Ivy_Thomas_Phys199pom_Final_Report.pdf&ei=buZlVfenNMrkUfTpgPgL&usg=AFQjCNFkbmLRuSOSTL-zaqzA3oQQ3CebAA&bvm=bv.93990622,d.d24&cad=rja.

In the lowest octave, tones would not be intelligible if it weren't for harmonics that are sometimes way above the fundamental.

I find it one of the miracles of the human auditory system that we can see the trees through all the wood, that is, distinguish the fundamental even in a forest of overtones. An even greater mystery is how you can hear playback distortion in signals that consist mainly of harmonics to begin with.

 

[marce]

Same with telephony, most fundamental vocal frequencies are outside of the Bel frequency range, just shows the phenomenal power of the mind in sorting out everything that's around us.....

 

[Esperado]

An even greater mystery is how you can hear playback distortion in signals that consist mainly of harmonics to begin with.

Culture and recognition ?

 

[hitsware]

> Did I mention I am daft enough to be going open baffle
> in my tiny cube at some point in the near future?

Wellcome to enlightenment .......

 

[bcarso]

For a change, something in the public domain, from a recent lecture at McGill. He ran out of time to discuss the use of multiple subwoofers for more uniform bass in rooms, but the basic frequency effects are there. The need for good off-axis response in the loudspeakers is emphasized.

https://www.youtube.com/watch?v=zrpUDuUtxPM

 

[31697B]

The unwanted infra-frequencies have a lot to do with causing low freq drivers (esp ported enclosures) to have increased cone displacements while music is being played and thus increased distortion for the audible recorded music. When these freqs <20Hz are removed, the over-all sound clears up.... from lowered speaker distortion(s). Not to mention large amounts of PA energy being consumed... which leads to poor bass quality in low freq music tones.... unless larger amounts of PS storage C is added to the PA to compensate.

The hard part is how to make a cost effective sub-audio filter which has low enough Group-Delay. [phase shift doesnt matter]. If you can not do that, then a HP filter will be audible and not used... and you are left with less than the best sound your system is capable of.

Because audio systems vary so greatly, I would have a suitable low group-delay <20Hz filter added to a preamp for LP's and let the user decide if it needs to be turned-on or not.



THx-RNMarsh

 

[john curl]

And how can we make this low group delay filter, Richard? I don't know how, but maybe somebody here has an answer.

 

[gpapag]

For a change, something in the public domain, from a recent lecture at McGill.

Thank you Brad.
The readable version:

http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/LoudspeakersandRoomsPt1.pdf

http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/LoudspeakersandRoomsPt2.pdf

http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/LoudspeakersandRoomsPt3.pdf

The hard part is how to make a cost effective sub-audio filter which has low enough Group-Delay. [phase shift doesn’t matter]. If you can not do that

Observe phase shift rate

Measurement of Distortion :

There is no problem if there is a linear phase characteristic, ie phase shift is directly proportional to frequency. The ratio of change in phase to change in frequency is given the name of Group Delay (Tg) which is expressed as follows:

Tg = A0/360Af

where AO = phase change in degrees
and Af = frequency change in Hertz

Variation in group delay over the signal passband is what causes signal distortion and this variation defines the phase distortion.
Using basic test equipment, phase shift can be measured at spot frequencies and a curve plotted of phase versus frequency. Ths slope of the curve (which is actually group delay) is scaled off around sections of the curve and a new curve, of group delay versus frequency, is then plotted.

George

 

[fas42]

An even greater mystery is how you can hear playback distortion in signals that consist mainly of harmonics to begin with.

Because one is familiar with the harmonic structure from a lifetime of exposure to the "real thing". The lower notes of acoustic piano very often are not rendered well on audio systems - they're just 'wrong', and one's ears know it straight away ...

 

[31697B]

Observe phase shift linearity --

Measurement of Distortion :



George[/QUOTE]


yes, group-delay is what i am talking about in regards to low freqs of the <20Hz filter.

Check AES for audible limits of GD at low freqs. and design filter accordingly.



THx-RNMarsh

 

[Binely]

RE: detection of sound using harmonics...

It always amazes me how we can train the senses. I remember even after a year from "quitting" the horn, I was playing with a group overseas and I was astounded how the memory comes back. The sense of "tune" get's locked in and you never forget the ear for it.

I can't imagine how strongly the sense would be trained for those without sight. Ever heard of the kid who taught himself echolocation?

https://www.youtube.com/watch?v=AiBeLoB6CKE