Monopole vs Dipole bass in small room - The battle continues - Wavelets to the rescue

[Elias]

Hello !

The comparison analysis between dipole and monopole bass loudspeakers in a small listening room continues !

I give emphasis on temporal fidelity of the reproduced signal. Real music signal contains time domain energy variations that must be reproduced accourately before high fidelity is achieved. This is also true for bass.

Temporal variations are best seen in the time varying envelope. I created modulated wavelet for this purpose. (Inspired by Linkwitz Dipole vs Monopole woofer)

[IMGDEAD]http://dl.dropbox.com/u/2400456/diyaudio/modulation3_wavelet5_50Hz_ideal.PNG[/IMGDEAD]

In the time-frequency domain it looks like this for ideal impulse response (20Hz-100Hz, 40dB scale):
[IMGDEAD]http://dl.dropbox.com/u/2400456/diyaudio/ideal-impulse_modulation3_wavelet5_20-100Hz_40dB.PNG[/IMGDEAD]


Then I measured monopole and dipole bass loudspeakers in a small room at the listening position. Here are the results.

Monopole (normalised, 40dB scale):
[IMGDEAD]http://dl.dropbox.com/u/2400456/diyaudio/100-1_2m5_modulation3_wavelet5_20-100Hz_norm40dB.PNG[/IMGDEAD]


Dipole (normalised, 40dB scale):
[IMGDEAD]http://dl.dropbox.com/u/2400456/diyaudio/Vuage1-Hbasso_2m5_modulation3_wavelet5_20-100Hz_norm40dB.PNG[/IMGDEAD]


Ideal impulse response (10dB scale):
[IMGDEAD]http://dl.dropbox.com/u/2400456/diyaudio/ideal-impulse_modulation3_wavelet5_20-100Hz_10dB.PNG[/IMGDEAD]


Monopole (normalised, 10dB scale):
[IMGDEAD]http://dl.dropbox.com/u/2400456/diyaudio/100-1_2m5_modulation3_wavelet5_20-100Hz_norm10dB.PNG[/IMGDEAD]


Dipole (normalised, 10dB scale):
[IMGDEAD]http://dl.dropbox.com/u/2400456/diyaudio/Vuage1-Hbasso_2m5_modulation3_wavelet5_20-100Hz_norm10dB.PNG[/IMGDEAD]


It appears that in a small room a dipole is superior over a monopole in it's ability to reproduce temporal finesse at bass frequencies.

Full report:
http://dl.dropbox.com/u/2400456/html/Elias_Pekonen/main.html


- Elias

 

[RockLeeEV]

When you say "monopole" are you factoring in

- enclosure (was it sealed? transmission line? vented? horn?)
- cabinet bracing (what kind of bracing, cabinet construction etc)
- driver damping (what is the QTC of the speaker?)
- multiple (2 simultaneous) monopoles (as is recommended by toole et al)

You're calling it a monopole, but you haven't really described it. Surely I could take a driver poorly suited to OB, shove it in a bad location,g and get poor impulse results in the same way.

Not arguing with your results, but they just seem to be pushing an agenda without clarification of variables.

 

[SL08]

Very nice work.

You should present this at an AES Convention and write an AES paper about constant Q periodic wavelets.

Your data displays and measurements could also illustrate the Modulation Transfer Function of multiple monopole woofers in an acoustically small room. A wider understanding of what contributes to accurate bass reproduction is badly needed.

SL

 

[gainphile]

Wonderful analysis Elias.

Did you try other frequencies as well and were they consistent?

 

[LineArray]

Hello Elias,

very interesting results, thank you for posting.

Cheers

 

[Rudolf]

Elias,

I see results that look detailed and convincing - as usually . But I don't yet understand the reasons behind. Differences really start just below 40 Hz. What significance has that frequency for the room (or the speakers)? And I am wondering if rotating the dipole 90° would have led to another diagram. Did you have a chance to test that too?

Rudolf

 

[dantheman]

My question would be "do these have any perceptual relevance?"

I'd be interested in others thoughts on this preferably with some pertinent data.

Dan

 

[thoriated]

Oh noes! I see no images!

 

[LineArray]

My question would be "do these have any perceptual relevance?"

...
Dan

I can see you are providing some information in your blog ...

audio blog: Hearing Beyond Haas

Human hearing has poor time resolution for artificial modes etc. ...

So do you think, time resolution below 100Hz is irrelevant ?

What about masking effects possibly caused by LF "burst smearing",
which could be detrimental for the perception of detail from upper
bass to lower midrange ?

Cheers

 

[Radugazon]

Good job Elias (and damned good tools !) , but the subject is so wide that this is only the top of the iceberg.

The measured differences of dipole vs monopole would be more explicit when using the same drivers, because here we dunno what part of this difference can be imputed to the dipole radiation pattern or to the dynamic characteristics of each driver, the dampening from the sealed load and so and on...

A very subjective POV : I was happy with my dipoles subs, but now I use an Infinite Baffle line array.
This very primitive load is absolutely a great option to consider for those who have enough space.

 

[Robh3606]

I have a couple of questions. Where the speakers measured from the same location and where the speakers in the same location when measured. More importantly how do you correlate how audible a wavelet artifact is. The two may look very different but is it audible??

Rob

 

[LineArray]

These masking patterns are for simultaneous masking,
which is not the only auditory masking effect low frequency
maskers can have on the perception of higher frequencies,
because there is also a pre- and a postmasking.

Picture shows maskers down to 200 Hz, that was the lowest
i could find so far.

Source: http://www.medialab.fh-osnabrueck.de/~kamo/intern/06ws/av/pdf/21_av5_audcomp2.pdf

That paper is on audio coding, where masking effects are exploited
consequently in data reduction formats like mp3 ...

At first glance it seems to me that low frequency content resulting from
long decay in a room is well suited for masking higher frequency content
if loud enough.

 

[john k...]

Of course, unless the frequency response at the measurement point is the same... well you get the idea. Nice work, but just cracking the shell. Different modal excitment yields different results. A lot more has to be done here.

 

[dantheman]

Oliver, the best "data" I have has 8 data points. I have theory with some support, not close to thorough.

Dan

 

[6.283]

Impressive, Elias !
As SL points out, multiple monos would be interesting and imo a cardioid as well.

Differences really start just below 40 Hz.

Rudolf,
aren't the biggest differences between 40Hz and 60Hz and then again below 30Hz ?

 

[LineArray]

Oliver, the best "data" I have has 8 data points. I have theory with some support, not close to thorough.

Dan

Dan,

well german wikipedia e.g. offers an approximation formula
for simultaneus masking, where Sl is the lower slope of the
masking curve and Sr is the upper slope.


Gross approximation of masking slopes:

Maskierungseffekt ? Wikipedia


The lower slope is assumed independent from frequency
(on bark scale) in that formula, while the upper slope is
frequency dependent.

I do not know how close that approximation is for maskers
in the lowest say 3-4 octaves of the hearing spectrum.

But nevertheless auditory masking seems a rather well
studied effect. Very close approximation of masking curves
seems to be a kind of science of its own e.g.

http://www.acoustics.bseeber.de/tun/da.pdf
(e.g. Picture 2.5 in Chapter 2.6)

But for our purposes of discussion here, it seems not
necessary IMO to approximate masking curves very closely.

 

[markusA]

Without details of the setup it bears no relevance.
Pretty pictures but it doesn't really say anything unless you provide the needed information to interpret them correctly.

 

[LineArray]

Well Markus i'd like to put it like this:

1) The correct interpretation for one share of members
will probably be that dipole speakers have advantages in temporal
resolution of "music like" signals in small rooms.

That opinion will most probably turn out independent from any future
efforts to make the above measurements of dipole vs monopole "more comparable".

2) The correct interpretation for a different share of members
will probably be that monopole speakers have advantages in temporal
resolution of "music like" signals in small rooms.

That opinion will most probably turn out independent from any future
efforts to make the above measurements of dipole vs monopole "more
comparable".

---
So please Elias, give us some more information to make the measurements
more comparable and could you provide a measurement please, making the
dipole looking real bad ?

Maybe i can give some hints, how to achieve this:

Modify the room into a square and place the dipole in the middle
of the room, radiation axis of the dipole exactly aligned with the
rooms edges.

Listening (microphone) position should be on axis, directly at the
rear wall, middle of the room ...


Cheers

 

[john k...]

Certainly if you sit a dipole, a monopole and a cardioid down at a single position in a room you would expect different results. But, is this simple due to the different modal behavior which carries over to frequency response, or is there more? Is any one format turly superior? How do the results variy with the position of the source and measurement position. What happens with multiple sources of any type or mixed format sources. What happens if the (amplitude) response is eqed to a similar referece (doesn't have to be flat). What about alignment of the sources (rotation of the axis).

My simulated transient data shows very significant differences for dipoles when rotated (see impulse response near bottom of page). What about Welti's setup? Or the double bass aray?

It's a great start. Go the mile....

 

[AllenB]

1) The correct interpretation for one share of members will probably be that dipole speakers have advantages in temporal
resolution of "music like" signals in small rooms.

I can believe this, and yet I choose monopoles. It stands to reason that dipoles would have superior temporal performance as a result of their reduced room interaction. I am not convinced that this is what is important, and the in room steady frequency response seems important enough to me.