Loudspeaker perception

[graaf]

Or with the electronics?

clearly electronics was various, different in different rooms with different OB's

best!
graaf

 

[markus76]

Originally posted by ScottG As for the meter, its a standard 2-setting "weighted" meter. Note that you aren't looking for extreme accuracy, what you ARE looking for is a substantial change. Something that *is* within the means of these cheap toys.

What kind of weighting? How big in dB was the "substantial" change you measured?

 

[HiFiNutNut]

Thanks guys. It has been a pleasure to read your discussions.

There has been a strong support here for OB directivity at low frequencies using dipole or cardiod. I have cardiod bass which sounds clean.

However, John K has a paper which shows power response suffers using OB bass when mating with OB midrange - For a flat on-axis response, due to 2 Pi radiation of the woofers placed near the floor, monopole provides better power response comparing to OB. This can easily be understood with simple maths.

Which do you think more important: directivity or power response at low frequencies?

Regards,
Bill

 

[Elias]

Hello,

There still will be ringing as active absorption can't dissipate energy. This can only be done with passive absorption.

I think DBA can be seen in the light of the same principle like active noise cancellation. In DBA the wave reflected from the back wall can be seen as an 'intruder' that's entering the room through back wall, but it will not propagate because the wave pressure is cancelled on the spot. 1-1=0, no?

If there is no wave pressure where has the energy gone? So we put in two times the original energy and got zero wave pressure out

Why is a plane wave desirable? I don't see a reason to assume that.

Then open your eyes.

Plane wave is the natural sound appearing practically in all the real sound events.

With plane waves we can have low freq ITD, thus low freq phantom imaging comes possible.

With plane waves we have low freq interaural differences, thus we can have low freq envelopment.

With plane waves we can externalize bass out of inside the head.

And as already mentioned, no room resonance issues.


- Elias

 

[markus76]

Originally posted by Elias I think DBA can be seen in the light of the same principle like active noise cancellation. In DBA the wave reflected from the back wall can be seen as an 'intruder' that's entering the room through back wall, but it will not propagate because the wave pressure is cancelled on the spot. 1-1=0, no?

No. http://www.kettering.edu/~drussell/Demos/superposition/superposition.html
Read more and write less.

Generally you guys should really step back before treating a PhD with a thesis "Low Frequency Sound Field Statistics in Non-rectangular Rooms" like you did in the last posts. You make a fool of yourselves.

 

[Elias]

Hello,

I have cardiod bass which sounds clean.

How did you implement you cardioid bass, if I may ask? Interesting

Which do you think more important: directivity or power response at low frequencies?

Power response is measured in steady state, so for music signal which is not steady state it's usefulness can be questioned.

More important is temporal aspects of response at low freqs. Directivity helps in this regard.

- Elias

 

[Elias]

No. http://www.kettering.edu/~drussell/Demos/superposition/superposition.html
Read more and write less.

You can read it right there, under destructive interference.

 

[ScottG]

What kind of weighting? How big in dB was the "substantial" change you measured?

"C" weighting. Substantial - in the worst areas with certain placement for the sub, more than 3 db. I'm not sure it matters though, a change is a change unless the meter registers a change with no "input". Of course it would be nice to go in with a laptop, some real-time software, calibrated hardware - and do some "mapping", but we aren't talking about anything particularly rigorous for this example ..just effect or no effect.

 

[markus76]

"C" weighting. Substantial - in the worst areas with certain placement for the sub, more than 3 db. I'm not sure it matters though, a change is a change unless the meter registers a change with no "input". Of course it would be nice to go in with a laptop, some real-time software, calibrated hardware - and do some "mapping", but we aren't talking about anything particularly rigorous for this example ..just effect or no effect.

So you say that you didn't move the SPL meter between the connected and the unconnected situation and found a difference of 3dB? No way. And how do you perform a measurement of the modal field using a SPL meter with a swept sine signal?

I guess when connecting the sub it DID emit sound. Why should there be any change by connecting a cable that doesn't carry any signal?

 

[ScottG]

So you say that you didn't move the SPL meter between the connected and the unconnected situation and found a difference of 3dB? No way. And how do you perform a measurement of the modal field using a SPL meter with a swept sine signal?

I guess when connecting the sub it DID emit sound. Why should there be any change by connecting a cable that doesn't carry any signal?

Believe what you want, experiment as you like. As for the rest, try going back and rereading, it may answer some questions you have posed here. I am however done with this.

 

[markus76]

You're just trying to avoid that I show that all you said about "active absorption" is complete nonsense. Sorry, it's the truth.

 

[ScottG]

You're just trying to avoid that I show that all you said about "active absorption" is complete nonsense. Sorry, it's the truth.

Now why would I do that, for any subject?

Have you ever seen drivers (in other loudspeakers/subs) that were in the same room but were not "on" and were moving? If not, I'm sure you would say that it was impossible.

 

[mige0]

Thanks guys. It has been a pleasure to read your discussions.

There has been a strong support here for OB directivity at low frequencies using dipole or cardiod. I have cardiod bass which sounds clean.

However, John K has a paper which shows power response suffers using OB bass when mating with OB midrange - For a flat on-axis response, due to 2 Pi radiation of the woofers placed near the floor, monopole provides better power response comparing to OB. This can easily be understood with simple maths.

Which do you think more important: directivity or power response at low frequencies?

Regards,
Bill

Hi Bill

I guess you are referring to that paper of John Kreskovsky :

http://www.musicanddesign.com/PowerMatching.html

Though OT, I guess Johns suggestion is to use a combination of a monopole *and* a dipole

"Clearly, somewhere between the cardioid
and the monopole there exists a situation where the relative strength of the
monopole and dipole are such that DF = 1.5 can be obtained on axis. "



The solution I find working fine is to use two dipole woofer at 90° which sum to the desired 45°

I use the "split power approach" actually intended / implemented to reduce excursion - to gently turn the axis from 0 (at roughly 300Hz) to 45deg around 100Hz and below – as a positive side effect.

I found that to be an even more elegant solution.

As for your question – no clue.
But it works – most important for me.


Michael

 

[markus76]

Originally posted by ScottG Have you ever seen drivers (in other loudspeakers/subs) that were in the same room but were not "on" and were moving? If not, I'm sure you would say that it was impossible.

You said that the sub was in the room before but when connecting it without transmitting a signal, it worked as "active absorption" which is nonsense (e.g. a Helmholtz resonator needs a volume of 100 l or more to have a substantial impact on the modal field). Then you said that this was measured with a SPL meter using a swept sine signal, which is nonsense too.

 

[markus76]

Originally posted by Elias You can read it right there, under destructive interference.

What can I read there? "it will not propagate because the wave pressure is cancelled on the spot. 1-1=0" or "we put in two times the original energy and got zero wave pressure out"? There's no absorption - the energy you put in the room stays there. You should re-read your physics textbook.

This whole DBA discussion is only academic because in a real-world situation there is no room that has perfect symmetry and rigid walls that allow for the wave to stay planar while it's travelling.

 

[HiFiNutNut]

Michael,

Yes that is the paper. I built John K's NaO that has an U-frame (sub) woofer. I am far from as advanced as you guys.

Dipole or monopole, the biggest problem I have is room modes in my small room with rather odd dimensions (2.5m height x 5.1m width x 6.3m long). My basic measurements indicates that it is ruler flat nearfield but in farfield a 6dB peak at 80Hz and a broadband 6dB dip between 200Hz - 500Hz (which is a mystery). Although base directivity may arguably reduce room modes, I think I will adopt Dr. Gedlee's multiple monopole sub approach which appears to have been proven to work.

So my next pair of speakers have a removable back on the woofers, and I will first try monopole, and if not successful, remove the back and try cardiod (a lot more complicated measurements and EQ).

Regards,
Bill

 

[PB2]

Not many - I'd guess maybe four or five or so out of the scores of audiophiles and designers I've known over the last thirty-five years. They frequently have elaborate mono systems, unusual locations for the stereo speakers, and will go on at some length about how mono recordings sound so much better than stereo. It took me a while to realize this was a perceptual thing - like a partially colorblind person not being able to fine-tune a color TV or adjust the colors in Photoshop, while by contrast, a professional in a color-print lab can see subtle color variations most of us don't see.

This is an intersting subject, the phantom center image and mono listening. There is this thread also, and I discussed this years ago with DDF: http://www.diyaudio.com/forums/showthread.php?s=&threadid=103978


We have a highly regarded member (an EE) of our local audio society who not too long ago was still running mono. I didn't know him in his mono years! He does design speakers and dislikes most; his own do image quite well and he says he worked hard to get it including a dedicated room in his home.

He also designed and fabricated a turntable nearly from scratch with some impressive and unique features.

I sometimes think that a stereo system that does not produce a good center image is certainly a step backwards.

Pete B.