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In Reply to: RE: Can a simple crossover (cap/inductor) achieve time alignment without a stepped baffle? posted by jupiterboy on July 18, 2014 at 06:29:34
My Boston A40's - only one Cap in series with tweeter "Upside Down" on a 20" stand have perfect time alignment measured through the crossover region at my listening position.
The upside down placement With tweeters below the ear did not seem to effect the sound stage.
Note- My MMG's with the standard crossover at a 45 degree tweeters in at the listening seat measured pretty dang close time alignment through the crossover - though panels are a little vague at a 2 meter distance.
Three most important things in Audio reproduction: Keep the noise levels low, the power high and the room diffuse.
Follow Ups:
...the woofers were probably designed to have a natural roll off at the required crossover frequency, so an inductor wasn't necessary. Also keep in mind that natural roll off was very possibly second order as with the tweeter as well. Placing a capacitor in series with the tweeter would increase that to 3rd order. Just because a woofer or a tweeter have only one component connected to them, they're most likely NOT first order crossovers.
Grammar: The difference between feeling your nuts, and feeling you're nuts.
Edits: 07/26/14 07/26/14
And this could me confirmed or measured by measuring the response of each driver by itself? Anyway, there is an inductor on the woofers.
I was referring to the previous poster's Boston A-40's lack of an inductor, not yours. And the only way to tell the crossover's actual acoustic order is to measure it. It's important to understand that regardless of the ELECTRICAL order of the filter, it's the ACOUSTIC result that defines the crossover.
Grammar: The difference between feeling your nuts, and feeling you're nuts.
Ah, good clarification. So a first order crossover could very well achieve second order or third order slopes with help from a cabinet design. What eludes me is what effect this has on phase.
You'll get second order from a sealed cabinet, 4th order from a ported one. It still doesn't seem like you're able to differentiate between electrical and acoustic crossover orders.
Grammar: The difference between feeling your nuts, and feeling you're nuts.
What do you get from a transmission line, 1/8th wave, which reportedly is not possible? I am not affecting some scholarly knowledge of acoustic engineering, I am trying to make some measurements and have a real look at a set of speakers that are sitting in my living space at the moment.
Let’s say, for arguments sake, that the tweeter is in a sealed box, as many are, then we have a technical marker for the designer’s claim that the design is transmission line/acoustic suspension hybrid. Beyond this, transmission line provides some of the back pressure of acoustic suspension, but is not acoustic suspension as the porting provides a momentary pressure that is dissipated through the transmission line.
What I would like to comprehend at the moment is how these design parameters influence phase.
Thanks for you input. Please keep it coming.
If you don’t mind my asking, how do you measure and how extensive is your test equipment?
I am trying to decide what measurement is worth using low end measurement methods.
FWIW, the step response look pretty good—comparing a 1M on tweeter axis vs. a listening position. It also looks almost identical to what my Vandersteens produce, and they are known to be one of few speakers to produce a good step response.
I suspect my level of error might disguise an early tweeter.
Jupiter-
Just a comment. The graph you show is not a step response, the time scale (horizontal) for a speaker's step graph would be maybe a few tens of milliseconds. And the vertical scale on that is dB (no polarity info). A good step response would drop in a straight sloped line like that only when shown on a linear scale. I'd guess that is a graph of decay of room refections, or possibly a nearfield of a very ringy speaker!
On some other discussions in this thread: an acoustic suspension woofer has a 2nd order highpass response, so can only approach time waveform coherence at frequencies much higher than the woofer's f3 cutoff. A very low Q alignment (sealed or OB) can approach linear phase but hard to get deep bass from.
Interesting. I don’t know how REW calculates impulse and step from a sweep. This is the actual step isolated in the window. The app. evidently looks for the response within this window.
I suspect you can turn the phase data on or off. Still, this is not what I see, for example, Stereophile listing as a step response.
I have used a different window to clear the noise around the wave form, but essentially, the REW measurement protocol for step response does use the same horizontal and vertical axis.
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