Troels Gravesen and stepped baffles, good or bad?

Troels Gravesen seems to like stepped baffles and uses them a lot in his designs,

DIY Loudspeaker Projects Troels Gravesen

He is a prolific speaker designer and has designed speakers for Janzen and other companies.

Many of his designs incorporate a stepped baffle in order to time align the drivers.

Is this good or bad?

Doesn't time aligning the drivers on a stepped baffle mess up the off axis response? In other words, they are only time aligned face on and the more off axis you go, the less time aligned they are?

Isn't it best to compensate for the Z alignment of the drivers with the crossover on a flat baffle and therefore retain that time alignment off axis?

And then there are the diffraction problems that a stepped baffle introduces...

Thoughts?
 

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eriksquires

Member
2013-05-10 4:11 pm
It works the opposite. Imagine you draw a line through the acoustic centers. In a time-aligned, stepped baffle system, no matter the angle, that line is straight, vertical.



If you used DSP to time align a pair of drivers in a flat baffle, you'd only have a straight line in front and behind. to the sides, the time alignment would no longer hold.



To be complete though, I think his designs use a combination of stepped baffle and crossover alignment. As far as I know, most of his stepped baffle designs are not also time coincident.



Maybe some one can correct me, I'm too tired to do the research.
 

ScottG

Member
2003-02-04 12:23 am
US
I think Dave is thinking of horizontally off-set driver's with horizontal axial differences.

Diffraction can be a problem, but that's true for a normal baffle as well - it's really all about the end-result. ..and yes, you can get differences in the vertical axis.
 

kimmosto

Member
2005-10-06 10:37 am
Doesn't time aligning the drivers on a stepped baffle mess up the off axis response? In other words, they are only time aligned face on and the more off axis you go, the less time aligned they are?

Isn't it best to compensate for the Z alignment of the drivers with the crossover on a flat baffle and therefore retain that time alignment off axis?

Correct. Basically common Z-position of radiators' mouth and compensation of radiators' depth with delays by XO is better approach for off-axis timing. But that applies usually to horizontal plane only with multi-way so mechanical offset is not that terrible with quite flat radiators. Simplifies passive XO.
 

Lojzek

Member
2012-02-10 12:12 pm
Croatia
Troels Gravesen seems to like stepped baffles and uses them a lot in his designs...Is this good or bad? Thoughts?


It is his private decision for the reasons probably mentioned many times.
When you are a novice DIYer, you can't do much about it, either build as is or don't.

I could not do that for 3 reasons. It is ugly looking, produces diffraction effects and prevents me from building a higher order tweeter HP for protection and phase alignment purposes.
 
I have built his SEAS Classic 3-Ways, and they are musically communicative, easy to drive and very easy to listen to. The stepped baffles make sense to me, and - as has been mentioned above - should ideally put the acoustic radiating centres of the mid and tweeter on the same vertical axis (you are sure your head is at the right height, of course?).

On the other hand, I don't like the aesthetics of the stepped baffle, and, like Lojzek, find the thought of diffraction effects in the vertical axis from the step subliminally distracting. I'm at an advanced stage right now of building Troels' MUN-17, and find this design a lot more intuitively appealing (if also a lot more expensive!).

Alex
 
...find the thought of diffraction effects in the vertical axis from the step subliminally distracting.

Compared to the baffle edges, the small step (20mm or so) does hardly nothing in terms of differaction. You might be able to see some tiny effects in the measured response from 10 kHz and up, but that's about it.

I am certainly in the "the step is good" camp!
 
Compared to the baffle edges, the small step (20mm or so) does hardly nothing in terms of differaction. You might be able to see some tiny effects in the measured response from 10 kHz and up, but that's about it.

I am certainly in the "the step is good" camp!

I know the step works as intended - my objections are aesthetic and instinctive!

As you say, a step of 20mm is a half-wavelength at 8.5kHz, so indeed can't have much effect on a musical signal. All the same, our perception of positional clues is acute, and any contribution to diffraction at high frequencies can't be a good thing, given the choice.

Alex
 

Daihedz

Member
2010-01-20 6:44 am
Neither good nor bad, Troels lists all the alternatives in this article:
18W-8434G00
I prefer to deal with the issue in the crossover, the step looks ugly to me....
In this example and for the tweeter, the diffraction effects caused by the stepped baffle is smeared over a time span of roughly 1:3 ... 1:4, time needed for the wavefront to travel from the dome to the step. This welcome and useful repartition of the diffraction's effects energy over time will minimize the effects on audibility in terms of early echoes (=erratic psychoacoustic directional clues) and also in terms of frequency response.

I could imagine some further optimization potential in terms of time smearing, a more evenly spread of diffractions intensity departing from the circular shape of this step, in order to provide the best possible, energy-even repartition over time. This would certainly call for a modification of the geometry of the baffle contour/rim, no more necessarily and optically harmonically following the shape of a circle as is in these published pictures. Also in search of most harmonic dispersion of effects over time, the steepnes of the step could certainly be modified into a more "wedgy" geometry where suitable, e.g. in the proximity of the tweeter and even obturating some of it's faceplate. But this kind of rather radical "form follows function"-approach could/woould definitely offend some subject's aesthetical preferences. Not good for sales to some acoustically unware clients, loving to look at fancy faceplates...

In this respect in the oppisite direction, a tweeter buried in a circular hole in the baffle, without any waveguide to match the transition, is worst-case nightmare.
 
I like the CSD of MT section:

Yes - that is a sign of high quality drivers.

What I think is more attributable to Troels' design skills in this case is the horizontal off-axis response (10-degree intervals, up to 40 degrees off axis):

hor-disp-0-10-20-30-40-1000.png


I think that is quite beautiful, and it was one of the clinchers that decided me in favour of this project.

Alex