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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
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millercarbon's avatar
millercarbon
12,531 posts
 
No, you got it right. Which of course the effects of this radiation pattern is just another in a whole long list of things they try and use to get the sound they want.

The slope by the way is used so often because its a whole lot more cost-effective. Cabinetry already accounts for a large share of total speaker cost, and stepped-front is a lot more expensive to build than a single sloping baffle. 
bdp24's avatar
bdp24
9,788 posts
 

Watch the series of videos posted by Dannie Richie of GR Research on You Tube (actually, the videos are made by Danny and posted by Ron of New Record Day). Danny is a speaker designer who does a lot of cross-over work for other companies, and offers his own DIY speaker kits.

Anyway, on the videos Danny explains in great detail the questions involved in the arrival times from multiple drivers, how different x/o slopes are used to get the drivers in phase with each other (where their outputs combine, rather than cancel) over as wide a frequency range as possible. The off-axis response of each driver is a major consideration in all loudspeaker design. If the off-axis response of a speaker is significantly different from it’s on-axis response, the sidewall, ceiling, and floor reflections will sound like another, different sounding loudspeaker (one defined by the off-axis response) is playing along with the direct sound of the real one. Not good.

The idea that time aligned drivers and 1st-order crossovers automatically great a great loudspeaker, and that in and of itself is all that is required, is an over-simplification of a complex situation. Watch the videos; Danny explains it all in a way that technically-unschooled audiophiles/music lovers can easily understand

kijanki's avatar
kijanki
4,428 posts
 
My speaker's have slopped front with speakers pointing a little higher than listening position.  I've read in one of the reviews that it was done to avoid "closed" sound - so called "cupped hands" effect.
andy2
1,549 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
765 posts
 
@bdp24 +1

Love Danny's videos.

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
9,788 posts
 

@jaytor, you’re gonna love the OB/Dipole Sub! I installed mine in a pair of W-frames I had, but one of the contributors to the GR Research Forum on AudioCircle (a woodworker) is making a really good H-frame and selling it for a reasonable price ($600/pr, I believe), cut out of 1.5" thick MDF on a CNC machine. The frames are shipped as flat packs; the panels having rabbets cut into them, along with alignment dowel pins, making assembly relatively easy. The only tools required are wood glue and a few clamps. Paint or veneer to taste

The world’s only OB/Dipole sub with servo-feedback woofers (the Rythmik system)---State Of The Art bass! No fat, no box resonance, no overhang---"stop-on-a-dime" transient response. Lean and clean, it reproduces upright bass, piano lower registers, and my Gretsch 24" bass drum (recorded by myself with a pair of small diaphragm condenser mics straight into a Revox A77) like nothing else I’ve heard.

erik_squires
16,057 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. :)
twoleftears's avatar
twoleftears OP
5,318 posts
 

So many variables!

So when listening to speakers with tweeters mounted on sloping baffles, perhaps best to start listening to them pointing directly at you; if not, you'll be hearing the tweeters doubly off-axis (which admittedly, may be still be the design intent).

andy2
1,549 posts
 
if not, you'll be hearing the tweeters doubly off-axis
Although I know what you meant, I don't think the word "doubly off-axis" is a proper characterization.  It's either exactly on-axis or off-axis at certain degree angle in a 3-dimensional space.  The tweeter may be angled upward and the listening position at a lateral angle, overall it's still just off-axis at some angle in a 3D environment.  

The difference with angled baffle is probably more about aligning the phase of the tweeter and the mid driver.  


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