John Curl's Blowtorch preamplifier part II

Status
Not open for further replies.
Jump to Latest
3

31697B

Disabled Account
Joined 2012
As we are not going into design and causes of distortions in drivers ----

To keep to the point --- this part is relevant to critical listening and accurate reproduction:

View attachment Spkr IM.pdf


I think if others want to go into it deeper, there is plenty of information available on the subject of distortions in drivers.... and it should not be poo-poo'ed as minimal..... except in the most narrow discussion of a specific condition.

WE should get driver distortion data at other than small signal levels. From available data and my own measurements even small signal isnt good enough in typical drivers. Medium and large signal distortions are relevant, also.


Thx-RNMarsh
 
Last edited:
PMA

PMA

Member
Joined 2002
pmacura.cz/audiopage.html
Paid Member
Attached is the 7" woofer 100Hz distortion at 4Vrms. Room and microphone noise not removed, as it would need too long file and noise pattern to be removed successfully at LF.

CCIF IM speaker audibility test:

http://pmacura.cz/speaker10+12k.zip

Pure twin tone vs. recorded at 5.66Vp. Room and microphone noise removed.
 

Attachments

  • woofer 4Vrms 100Hz.PNG
    woofer 4Vrms 100Hz.PNG
    106.3 KB · Views: 186
3

31697B

Disabled Account
Joined 2012
Not exactly what i was looking for. But I'll find it. I wanted to see graph of thd in applied voltage steps.

I can do the measurement at home when I am back. But I already know the distortions are high.

Nice to see the multitone as applied to speakers. Look at that distortion !! at 15 volts.


THx-RNMarsh
 
3

31697B

Disabled Account
Joined 2012
Hahaha. I always do. Then I drop a bottom line here without any data.

Then the arguing starts.

:)


THx-RNMarsh

I have that AP-2722 just sitting there --- think I'll see how good this M2 system is with multi Tones.

I was staying in warm sunny Thailand until Feb. Just changed it to DEC 5 so I can work on my projects.

Sara will be done with embassy interview in 10 days. No need to hang around after that. I can come to my condo any time - have a retirement visa - good any time and can stay forever if I want to.
 
Last edited:
gpapag

gpapag

Member
Joined 2002
Paid Member
billshurv said:
George: once again thanks for the link.
Click to expand...

Credits go to Klippel (Richard functions as an agitator here)

Out of context that graph seems to be a case of 'no sh*t sherlock'. Below 100Hz we all know that distortion goes up if the driver is operating outside it's core parameters?
Click to expand...

It is shown that most of the large signal distortion is due to force factor (Bl(x)).
It seems that the combination of a high BL and a small overhang is the root of the step increase of distortion with cone displacement. (I see that with 8V signal level, the max specified displacement has been achieved at freq lower than Fs (30Hz)).
I quote some paragraphs:

--------------------------------------------------

The example driver is an 8 inch woofer with a relatively high force factor as shown in Table 1. This corresponds with a short voice coil overhang causing an early decay of the Bl-product at small displacement as shown in Fig. 5.

(Fig.18) Both the measurement and the prediction agree in substantial distortion which is constant at about 40%. This is typical for motor distortion caused by an asymmetry in the Bl(x)-curve. Intermodulation distortion of this magnitude is clear audible as a roughness of the high-frequency component. The intermodulation due to the Le(x) nonlinearity are at a constant level of 1 % at higher frequency. The Doppler distortion increase by 6dB/octave to higher frequencies and come up to 10 % for f1= 2kHz. The intermodulation distortion from Cms(x) are less than 0.1% at very low frequencies and may be neglected at higher frequencies.

(Fig.19) There is an almost constant distance of about 15 dB between fundamentals and distortion components for the example speaker shown in Fig. 19. Again we see that the asymmetry of the force factor generates high amount of distortion ( > 20 %) when a low frequency bass tone with high displacement modulates any high frequency voice tone. It is typical for this kind of speaker distortion that the intermodulation are close to the voice tone. Above 5 kHz where the multi-tone signal provides no excitation the driver produces much less distortion ( < 1 %) because only harmonics and summed-tone intermodulation between high-frequency fundamentals are generated. Again we see that the harmonics are not the most critical distortion in loudspeakers.

Fig. 22 shows the contribution of each nonlinearity as the ratio of the peak value of the distortion referred to the total sound pressure output. Clearly, the force factor is the dominant source of distortion for all the three music examples. It exceeds 60 % in the first piece where the peak displacement is about 10 mm. The distortion from the voice coil inductance are about 20 % in first and third music piece but less than 10 % for the second piece. The nonlinear suspension produces more than 15 % distortion in during the first piece, less than 0.1 % during voice section and about 2 % distortion during the last music piece.

----------------------------------------------------

Notice in section 6 and in Fig 24 what a dramatic change in D2 would be achieved by correcting the voice coil offset (Fig. 23 shows the problem of this driver).

Perhaps Richard could arrange with Klippel for having his loudspeaker drivers tested with the Auralization technique.

George
 
3

31697B

Disabled Account
Joined 2012
you jogged my memory --- a couple decades ago -- a guy showed me how he used a DC supply to adjust offset and null the distortion to a large degree. Then he played his music.

He didnt show me his arrangement for doing this.... but i throw it out there for someone to think about and try.

I guess he cap-coupled to the speaker?? Maybe adjust PA output -- without dc servo --to provide needed offset?
Adjust offset while looking at distortion?


THx-Richard
 
Last edited:
Status
Not open for further replies.
Top Bottom