Loudspeaker perception

[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]

Originally posted by 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.

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]

Originally posted by 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

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]

Originally posted by Lynn Olson


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: Why "Flat" is Inaccurate


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.