Foro dedicado al mundo del SubWoofer HUM, construcción, configuración, ecualización, drivers, plate amplifiers ...
#1878 por atcing
Jue, 22 May 2014, 00:14
hemiutut escribió:Taboadax,esta es la medición hecha ayer de mis 2 Subs juntos.
El Car Audio de 15" lleva un filtro L-Riley 48dB.
Si pongo la distorsión del sub de 15" da yuyu verla :mrgreen:.
Creo que parte de la culpa es porque falta más watios ( amplifico con 300w ) aparte del volumen
de la caja ( 40-45 litros ),pero a oido y al volumen que veo las
películas no noto nada raro.
Imagen
A 20,09 Hz hay un THD de 7.18%.
A 23,66 Hz hay un THD de 2%.
Haber si la ve atcing y nos puede orientar que tanto % de distorsión es admisible
para las frecuencias más graves.

Saludos.................


7.18% en 20hz es irrisoriamente baja THD ;)

En 20hz en cajas tienes que rondar el 100% ( el clap, clap de peligro de rotura) para que sea audible (incluso con tonos puros y en auriculares que es dodne más fácilmente se detectan),Con señal musical todavía cuesta más.]



Echadle un vistazo a los estudios de Axiom, de Earl Geddes y del grupo Harman.:

se conoce perectamente la detectabilidad deTHD según frecuencia (en graves profundos SOMOS SORDOS PERDIDOS, tanto con tonos puros como con señal musical)[/B]:


Imagen

The Results

While it is has been recognized for years that human hearing is not very sensitive to low bass frequencies, which must be reproduced with much more power and intensity in order to be heard, what these results show is that our detection threshold for “noise” (made up of harmonically related and non-harmonically related test tones) is practically non-existent at low frequencies. (The “noise” test tones are noise in the sense that they are not musically related to tones commonly found in musical instruments.) In fact, the “noise” tones at 20 Hz and 40 Hz had to be increased to levels louder than the music itself before we even noticed them. Put another way, our ability to hear the test frequency “noise” tones at frequencies of 40 Hz and below is extremely crude. Indeed, the results show we are virtually deaf to these distortions at those frequencies. Even in the mid-bass at 280 Hz and lower, the “noise” can be around -14 dB (20% distortion), about half as loud as the music itself, before we hear it. Conclusion

Axiom's tests of a wide range of male and female listeners of various ages with normal hearing showed that low-frequency distortion from a subwoofer or wide-range speaker with music signals is undetectable until it reaches gross levels approaching or exceeding the music playback levels. Only in the midrange does our hearing threshold for distortion detection become more acute. For detecting distortion at levels of less than 10%, the test frequencies had to be greater than 500 Hz. At 40 Hz, listeners accepted 100% distortion before they complained. The noise test tones had to reach 8,000 Hz and above before 1% distortion became audible, such is the masking effect of music. Anecdotal reports of listeners' ability to hear low frequency distortion with music programming are unsupported by the Axiom tests, at least until the distortion meets or exceeds the actual music playback level. These results indicate that the “where” of distortion—at what frequency it occurs—is at least as important as the “how much” or overall level of distortion. For the designer, this presents an interesting paradox to beware of: Audible distortion may increase if distortion is lowered at the price of raising its occurrence frequency




Experimental Study : Distortion - Axiom Audio


Y es que a SPL promedio de entre 86dB y 92dB (SPL donde detectamos cualquier anomalía en graves con mucha más facilidad que por ejemplo a 100dB), ya somos sordos perdidos)... sólo un buen chute de sugestión y una prueba mal realizada nos puede hacer creer lo contrario. Sería el mismito error que afirmar falazmente que unas 8040A tienen menor THD que unas B2031 comparando THD sin que nos llegue de cada caja la mismo SPL en frecuencia en toda la banda ;)



Y es que de 250hz hacia abajo a esos SPL (ni siquiera con tonos puros somos capaces de detectar una THD a -14dB de la señal): -14dB equivalen aproximadamente a un nivel de distorsión del 20%.
A 80Hz a mismo SPL para detectarla nos tenemos que ir a -10dB de la señal: -10dB de la señal equivale a una THD de 31.6%.
De 40hz hacia abajo a ese mismo nivel de SPL aceptamos ya el 100% de la THD: Hablando claro, hasta que no clipea el driver no nos enteramos... así de claro
;)


Un saludete


http://www.forodvd.com/tema/120905-comp ... ndex4.html



Sobre la audibilidad de la THD e IMD quizás también os puede interesar esto:


Originally posted by smellygas


Woh, these were some very interesting papers from Geddes. Thanks for the link! I don't fully understand the math, but he basically showed that there is only a very weak correlation between IMD/THD and listener perception. He didn't include the actual % or dB levels of distortion, which makes it difficult for me to interpret. However, what this likely means is that simple measurement of IMD or THD levels does NOT correlate very well with audible problems with the sound. He does, however, create his own composite formula for quanitfying the amount of distortion present (not strictly HD or IMD) that correlates VERY well with listener preference (we're talking R^2 of 0.9). This tells me that increasing distortion is definitely objectionable, but increasing HD or IMD does NOT necessariliy correlate with objectioable sound. Maybe someone else can interpret the article better than me. Interesting.

SG

Gedlee:

Let me interpret since I did the work. The "weak correlation" of THD and IMD to perception was NEGATIVE - you forgot to mention that. This means that, as a metric of perception, one should increase the THD to make it sound better. This is of course absurd, but it's the absurdity of THD and IMD measures that is the culprit not the results of the test.

The THD and IMD numbers are indeed shown in all the graphs. They are the X-axis.

Its NOT the level of the harmonics that matter but where the nonlinearity occurs - at low levels or high levels and the order, 2nd, sixth, etc. Low level nonlinearity is by far the most insidious especially if high order - like crossover distortion in an amp. This is why an amp with extremely low levels of THD can still sound terrible. But loudspeakers, on the other hand, tend to have nonlinearities that increase with level and are likely very low level like second or third. This makes them fairly benign. In fact, for the most part, nonlinearity in a loudspeaker (as long as its not broke) is a non-issue. In a test of compression drivers we had twenty five people evaluate distortion levels up to 25% and statistically noone could detect it at those levels.

Its hard to make blanket statements about the audibility of nonlinearities in specific cases, but for the most part nonlinearity is a major concern in electronics, but so much so in loudspeakers.
There are, of course, going to be exceptions to this
.


How much tweeter distortion is audible? - diyAudio


Este otro:

Geddes:

Actually modeling the nonlinearity curve is the only way to do this. Thats because THD and IMD are only symptoms of the problem which occur when precise waveforms are used. To hear the effects of these same nonlinearities on an actual music waveform you have to model the underlying root caues nonlinearity. Thats what my MathCAD program does. You can use any wave file. Lets decide on an example wav file and nonlinear characteristic and I'll post the results. First would obviously be a strong third order soft clip, because you will be amazed that at 50% THD the effect is completely inaudible. Then a .1% example of crossover distortion which will sound terrible.


http://www.diyaudio.com/forums/multi-way/139046-how-much-tweeter-distortion-audible-2.html





-Éste que mola más:


Gedlee:

THD on a compression driver was measured at 25% and it was not audible when compared to the direct fed signal. Compression drivers ARE NOT low THD devices.

The Summa speakers are not PA monitors, they have almost never been used for that purpose (although they do work quite well). They are almost exclusivley used for Stereo and HT critical listening. They were designed to be audiophile loudspeakers not Pro loudspeakers. I use Pro drivers because they are better drivers.

My point is that I don't care about nonlinear distortion anymore. I don't study it, I don't measure it and I don't look at THD levels in the drivers. Low THD, high THD, it doesn't matter. What matters is polar response, low diffraction and thermal capability. Smooth response is desirable, but ruler flat on any one axis is also irrelavent. THD and IMD are meaningless.

So did I or will I do the tests that you suggest - no. If you want to "prove the validity of THD" then you do it. I'm simply not interested. I did enough tests to make up my mind and if I have not convinced others then so be it. Let them think what they will. I made my case and I'll rest on the evidence presented.

And I am not the only one of this opinion - there is Floyd Toole, Laurie Fincham, Alex Voishvillo and many many other people who spent their lives looking at sound quality.





O este otro también bastante interesante:


Audibility of Non-Linear Distortion: A Practicum


I'm a real measurements person, but I like to keep things practical. After looking at enough graphs of harmonic distortion for different drivers, I decided to try a simple experiment - can I actually hear a 5th harmonic at -xxdB down from the fundamental?

I devised a relatively simple method of doing this. Using a digital audio 'workstation' (Cocko's Reaper), I set up a series of pitch shifters, one each producing a 2nd, 3rd, 4th, 5th and 7th harmonic. I patched in a stereo input (from my CD player), and also sent out the unprocessed 'fundamental'. I then patched everything out on one channel to my amplifier. I checked that the results with a FFT and a microphone, to make sure I was on target for my harmonics.

I also created an 'IMD' test, but taking two pitch shifters, and setting their output to +15% and -15% of the fundamental frequency. For a single tone, this produces a warble tone, often used in speaker testing. Watching a FFT of the output of a speaker, it was obvious this induces a lot of IMD.

Here is a screenshot of my setup:

Imagen


So using the volume control on the various harmonics/IMD tracks, and the 'solo' buttons, I could listen to specific levels of each harmonic/IMD. The volume slider lets you set a specific -dB relative to the fundamental/source signal.

The results were surprising. Here is a chart of the point where I could no longer hear a difference between just the original, and the original plus the harmonic/IMD:

Imagen


All listening was done on a single Pluto loudspeaker, my head 18" from the speaker, at a 90dB SPL level.

The warble tone was of a 100Hz sine wave. All other tests were done with music. I can provide reference to the specific albums if people really want.

A few things were surprising - the biggest was that with music, for the most part, I couldn't hear differences below -40dB down. Particularly with the IMD test, which was particularly noxious at high levels, below -30dB, it was basically inaudible
.

I noticed that music with lot of HF content made it easier to hear (Vivaldi). Music with lots of bass, and/or lots of compression made is harder to hear differences (Nujabes). Contrary to 'common knowledge', complex music (orchestral) masked differences while simple (singer/acoustic guitar) made it easier to hear differences. So the point at which difference could be heard changed depending on the music, but still within what I would call a small window- ie, somewhere between -30 and -40dB.

I've zipped up the file I made to do these sort of examinations, so other people can try it. Reaper can be downloaded for free, and then use the file I've attached. People will have to route their hardware I/O (on each track), but other than that, it should be relatively straightforward. Use the solo button of the harmonics/imd to turn them on or off. Keep the 'fundamental' solo on. Change the level of the harmonics/imd with the track's respective volume sliders. Don't change the level of the track labeled 'fundamental'. To change the volume of the IMD tracks, use the volume slider and solo button of 'IMD1' - 'IMD2' is slaved to it. Be careful where you click, you may disrupt some of the internal routing.

Feedback? I, for one, am less worried about non-linear distortion now.


Audibility of Non-Linear Distortion: A Practicum - diyAudio


Y es que todos van en la misma línea... no me extraña que suenen tan bien las Supreme 100 a SPL medio tras la EQ con su respuesta polar impecable, verdad juluska!? ;D


Un saludete


http://www.forodvd.com/tema/132374-prim ... ndex9.html







A parte de que influye con el SPL... y no debemos emocionarnos con el mismo para evitar quedarnos "sordos": ;)



... Para el que le interese un poco el tema del peligro de tan alto SPL:
Imagen

http://hrpinero.files.wordpress.com/2008/01/decibees-y-frecuencias.ppt#279,6,Sound Pressure Level Niveles de Presión del Sonido

De hecho siendo preciso:

Imagen


Y claro, es un pez que se muerde la cola... pues cuanto más oido perdemos más tenemos que enroscar y al final resulta que cuando medimos 90dB no estamos ni escuchando el equivalente de 80 y volvemos a enroscarle al pote :D ...



http://www.forodvd.com/tema/132374-prim ... ndex7.html







A 100dB incluso el oído genera [u]tanta THD propia al autoprotegerse que estamos literalmente sordos a poder aprieciarla:[/u] :rofl:


... Fíjate como aumenta nuestra sordera conforme aumenta el nivel de SPL:

Imagen

A 100dB ya estamos sordos perdidos!!! ;D

... pero como en la AES lo saben, realizan las pruebas a 75-80dB, ya que es un nivel de SPL mucho más apropiado para detectar cualquier diferencia por pequeña que ésta sea; de hecho para la zona de graves es el IDEAL ;)


Un saludete



http://www.forodvd.com/tema/120905-comp ... ndex4.html

Un saludete
#1879 por hemiutut
Jue, 22 May 2014, 00:27
Gracias atcing por la información,la iré leyendo poco a poco.
Mira que THD más alta en el Sub Car Audio 15",por eso lo preguntaba.
LLeva Filtro L-Riley activado.
Imagen

Saludos..........
#1880 por atcing
Jue, 22 May 2014, 00:39
hemiutut escribió:Gracias atcing por la información,la iré leyendo poco a poco.
Mira que THD más alta en el Sub Car Audio 15",por eso lo preguntaba.
LLeva Filtro L-Riley activado.
Imagen

Saludos..........


eso qe ves en 20hz es un valle "engañosos". Seguramente la THD en esa zona en realidad estará (por la forma de la curva de la señal y de la tendencia de la de los armónicos) entre -10 y -15dB de la señal... y no debería ser audible (al menos la THD; otro tema es que se notara otra anomalía diferente). :)


Un saludete
#1885 por hemiutut
Jue, 22 May 2014, 19:29
Este es el Sub Car Audio 15" por el que viene la consulta de la THD ( Distorsión ).
Imagen
Y esta su respuesta en Frecuencias.
Linea Azul respuesta previo a la EQ.
Imagen
EQ aplicada NU1000DSP.
Imagen
¿ Amplificando con más watios de los 300 y con la misma caja,bajaría más
previo a la EQ o es indespensable la caja con más volumen y más watios ?.
La de ahora hará 40-45 litros.
Lo digo por no forzar tanto la EQ,tengo 2 filtros en 20Hz cuya suma son 17dBs
tal como se ve en la captura del menú de la etapa.

Saludos y pido disculpas a Taboadax por estas reflexiones en su hilo.
#1887 por atcing
Jue, 22 May 2014, 21:02
hemiutut escribió:Este es el Sub Car Audio 15" por el que viene la consulta de la THD ( Distorsión ).
Imagen
Y esta su respuesta en Frecuencias.
Linea Azul respuesta previo a la EQ.
Imagen
EQ aplicada NU1000DSP.
Imagen
¿ Amplificando con más watios de los 300 y con la misma caja,bajaría más
previo a la EQ o es indespensable la caja con más volumen y más watios ?.
La de ahora hará 40-45 litros.
Lo digo por no forzar tanto la EQ,tengo 2 filtros en 20Hz cuya suma son 17dBs
tal como se ve en la captura del menú de la etapa.

Saludos y pido disculpas a Taboadax por estas reflexiones en su hilo.



No lo he calculado con este driver pero me da que está capado de SPL por abajo porque seguramente el recinto se quede MUY pequeño y esté en compresión. Los diseños para car están calculados para bajar adrede "poco", y qe sea el maletero (una sala enana) el que le de ganancia por abajo :)

Meter +17dB en 20hz es una barbaridad; Seguro que optimizando el diseño y/o colocándolo mejor obtienes respuesta no muy distante de la de los GT01514

Un saludete

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