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Old 28th February 2014, 07:31 PM   #21
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Moonshine? And here was me growing up wishing I was one of the Duke boys! the car, Jessie, jessie and moonshine.

I digress - at one point we turned the speakers around to assess the bass with a little less of the 10KHZ sparkle, it was surprising how much of the HF came out of the upper port, you would have been forgiven for not believing that the speaker was rear facing.

Do you think that a front facing port, from the lower chamber would run the risk of canceling out LF response due to phase, or add a little? The rooms we were in were damped acoustically so that rear facing ports were throwing the signal into absorbing material. This was still an improvement on my lounge and its bass hungry floor, but perhaps front facing would help even out the rsponse a little?

Any thoughts most welcome.
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Old 28th February 2014, 08:22 PM   #22
xrk971 is online now xrk971  United States
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Scottmoose,
Thanks for taking the time to respond to my post in detail - I understand the nuances if your design much better now. You are right - I have been running dual Vifa drivers for sometime now and like them very much. Apart from a little sensitivity to standing up and sitting down impacting how the sound varies they are great. I run them in parallel to get the boost in efficiency so accept the limitations that come with it. Seeing how your design is in series and with a cap got me curious so I ask from a standpoint of wanting to learn more - not from standpoint of pouring water on your design. If it came across like that - I am sorry. No offense intended. I am running some sims of my dual Vifa's in series with and without the cap to see the effect and it is interesting how the lower cone and upper cone diverge. Above 2 kHz the cap essentially shorts to ground and the speaker sort of reverts back a single driver as freq goes higher. An interesting cross over.
Cheers,
X
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Old 28th February 2014, 08:45 PM   #23
BYRTT is offline BYRTT  Denmark
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Comment post #17: Think it is natural member xrk971 asked deeper questions.
Because of suddenly it was not only a good diy home speaker, but a speaker to do the art in studio and beat others (ultimate winner against Genelec, ATC and the dynaudio). This done with setup of two drivers box and a cap. I am only diy but think it needs further correction to be a reference producer, oposit use at home do as you like. This is friendly meant, and read i use Alpair dayly (10.2M) and very satisfied.

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..........I have requested that the tech man does some measurements for me, so I hope to be able to post some results soonish...........
......
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Old 28th February 2014, 10:32 PM   #24
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Quote:
Originally Posted by xrk971 View Post
Scottmoose,
Thanks for taking the time to respond to my post in detail - I understand the nuances if your design much better now. You are right - I have been running dual Vifa drivers for sometime now and like them very much. Apart from a little sensitivity to standing up and sitting down impacting how the sound varies they are great. I run them in parallel to get the boost in efficiency so accept the limitations that come with it. Seeing how your design is in series and with a cap got me curious so I ask from a standpoint of wanting to learn more - not from standpoint of pouring water on your design. If it came across like that - I am sorry. No offense intended. I am running some sims of my dual Vifa's in series with and without the cap to see the effect and it is interesting how the lower cone and upper cone diverge. Above 2 kHz the cap essentially shorts to ground and the speaker sort of reverts back a single driver as freq goes higher. An interesting cross over.
Cheers,
X
Not at all. Please accept my apologies if my original post seemed a little 'strong' -re-reading it, it didn't come over as very polite at all. Not intended that way; I'm shooting about between different things so much at the moment I don't get as much time as I'd like to write & edit. Which is no excuse for rudeness.

Anyway, right, the main changes are of course on the vertical axis (assuming they're disposed vertically of course!); extent varies with the driver, partly diameter but also innate dispersion characteristics. The 7.3 is as large as I'd go for twin drivers.

Spot on. For some reason it's not seen all that often, presumably because series crossovers aren't as popular as parallel -essentially it's a variation thereof. By (very) general analogy, a distant relation is the cascaded 2.5 way parallel filter Jeff Bagby popularised, where you have the large baffle-step inductor after the low-pass for the top woofer. Where they score is that you've got a reasonable level of control over what the low-passed driver is doing, and the phase relationship remains good. And of course, in the case of the series wired drivers, if you're starting with a unit that already has a slightly low impedance, you don't end up with something that's a nightmare to drive. < 3ohms gets very awkward (see the Apogee Scintilla for the genuine 1ohm amplifier killer -Krells quaked at their name. The Linn Isobarik wasn't much better). A couple higher than normal? Not too much of a problem providing it's not over-reactive. This is relative of course -large increases & you'll run into the problems you mention, unless you've a specialist amp.

Cheers
Scott
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Old 28th February 2014, 10:37 PM   #25
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Quote:
Originally Posted by BYRTT View Post
Comment post #17: Think it is natural member xrk971 asked deeper questions.
Because of suddenly it was not only a good diy home speaker, but a speaker to do the art in studio and beat others (ultimate winner against Genelec, ATC and the dynaudio). This done with setup of two drivers box and a cap. I am only diy but think it needs further correction to be a reference producer, oposit use at home do as you like. This is friendly meant, and read i use Alpair dayly (10.2M) and very satisfied.
Right. Wideband based speakers of various types are used in studios, especially smaller ones, more often than many realise & they can be a very good solution. But, as noted, it depends on what it is that's wanted & what they'll be used for. As with any speaker, it needs to be appropriate for the requirements.
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Old 28th February 2014, 11:27 PM   #26
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Putting the drivers in series with a 70uF cap across the bottom one effectively makes it a low pass filter that rolls off at 6 dB/decade above 2kHz.
Closer to 300 Hz.Making part of your later prose moot.

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This is why I was saying it is kind of a waste to use an A7.3, renowned for its high frequency ability as a woofer in a 1.5 way speaker.
But it is a perfect match. And as things go, not all that expensive.

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Also, putting the drivers in series makes the speaker an effective 16 ohm load below 2kHz - which will not be good from standpoint of getting enough power to the speaker using conventional 8 ohm rated amps with limited drive voltage.
Blow 300 Hz. Typically half the amp distortion, and likely the case that the studio already has amps that even at half the power are big enuff for the A7. Ampsare more likely current limited, and the higher impedance helps.

dave
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Old 28th February 2014, 11:30 PM   #27
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Originally Posted by xrk971 View Post
... that rolls off at 6 dB/decade above 2kHz.
octave, not decade.

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Old 1st March 2014, 01:02 AM   #28
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by planet10 View Post
octave, not decade.

dave
Good catch, octave I mean...

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Closer to 300 Hz.Making part of your later prose moot.
Maybe I should be more terse
And present my comments in verse?

When I modeled the dual A7.3 in a sealed cabinet wired in series with a 70uF cap across the lower driver, I get a response that falls off starting at 2 kHz. How did you get 300 Hz?
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Old 1st March 2014, 01:17 AM   #29
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I used standrd XO calculations to get in the ballpark.

Something is screwy with your sim. Would take about 10 uF to roll off at 2k.

dave
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Old 1st March 2014, 03:24 AM   #30
xrk971 is online now xrk971  United States
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Quote:
Something is screwy with your sim. Would take about 10 uF to roll off at 2k.
Scottmoose will know but I suspect it is because the cap is in parallel to the driver rather than something wrong with the sim. It is a pretty straightforward addition of a cap across the driver nodes - one line of code. The RC time constant for 5 ohms x 70 uF is = 0.7*5*70E-6 = 0.245 ms or about 4kHz.
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