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time-aligned speakers: stepped fronts vs. sloping fronts

Let me first say my understanding of these things is rudimentary.

But I was thinking about manufacturers who used stepped back fronts (several vertical planes) to achieve so-called time-alignment, vs. those who slope back the whole front baffle at a certain angle/rake.

Thinking about, for instance, the tweeter driver mounted on a sloped baffle, won't its axis of radiation be shooting at a corresponding angle upward, meaning that a listener located directly in front of the speaker and with ears at tweeter height would already be listening off-axis?  Or am I missing something?  Or is that the point?

128x128twoleftears
andy2
1,545 posts
 
There are two ways to time align the drivers - sloping the baffle or stepped baffle : both achieve the same thing.  The advantage of sloping is to minimize diffraction caused by the stepped baffle.

Sloping baffle is also used in first order/time-phase coherence design to further adjust the phase of the tweeter and mid (among other things).  

As for listening off axis on a slope baffle, that is true but it gets complicated beyond this as there are other variables that come to play besides sloping baffle.  And everything besides sloping has to be considered on a case by case basis and difficult to make a general conclusion.  
jaytor's avatar
jaytor
761 posts
 
@bdp24 +1

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I've read/seen so many articles and videos over the years where the author/commentator was clearly just speaking some marketing drivel that didn't make any sense. Danny's videos are a breath of fresh air. He does a great job of presenting the science and engineering behind various aspects of loudspeaker design and the trade-offs where they exist. 

Watching these videos convinced me to build some of his designs. I've been building the NX-Oticas for the past several weeks. Open baffle subs come next. 
twoleftears's avatar
twoleftears OP
5,318 posts
 
These musings were in part a response to a recent review of the NSMT model 100 speaker and a reply by the reviewer to a question I posed.  He assured me he could hear no difference whatsoever when a felt mat was present or absent, a mat that sits under the tweeter box and on top of the main box and is clearly designed to absorb early reflections.  Hmmm.

Also after noting a fairly extreme rake on the upper units of some older models of Von Schweikert speakers.
bdp24's avatar
bdp24
9,746 posts
 

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erik_squires
16,021 posts
 
You are correct, but a lot of tweeters sound better off-axis.


It's up to the designer to balance the off-axis response, with the crossover, to yield the best tonal balance.

As Graveson has noted, sometimes we design speakers for listening at the tweeter axis and find we prefer listening one driver down.  Some speakers are deliberately designed with mid-woofer over tweeter, and designed to be llistened on mid-woofer axis.


This is a good experiment with most speakers, try listening below the tweeter. :)
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