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Multi-Way Conventional loudspeakers with crossovers

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Old 25th January 2012, 03:33 PM   #601
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Built up the crossovers, installed, and finished wiring them up. Just using zip cord right now to make sure everything works. I used a terminal strip as a temporary thing. I bought a few extra resistors to experiment with the tone. When all is done I will solder point to point. I stained and then finished with Polycrylic. Installed the speakers. I guess they turned out ok. I laughed at myself when I tried to drive them with the Tubelab SSE I built. I ended gabbing a chip amp I build't about two years ago. It puts out about 65 watts. I thought I had a problem with a crossover after the right channel dropped out after about five minutes. Traced it to a crappy interconnect on the negative side. A 5 cent wire nut fixed the problem. I then listened trouble free for about three hours.
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Old 25th January 2012, 03:43 PM   #602
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Great! Looks very nice. Yes, you will need at least a 30W amp with these.
Let us know what you think once you've listened a bit.
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Old 25th January 2012, 05:23 PM   #603
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Quote:
Originally Posted by shortwave View Post
Built up the crossovers, installed, and finished wiring them up. Just using zip cord right now to make sure everything works. I used a terminal strip as a temporary thing. I bought a few extra resistors to experiment with the tone. When all is done I will solder point to point. I stained and then finished with Polycrylic. Installed the speakers. I guess they turned out ok. I laughed at myself when I tried to drive them with the Tubelab SSE I built. I ended gabbing a chip amp I build't about two years ago. It puts out about 65 watts. I thought I had a problem with a crossover after the right channel dropped out after about five minutes. Traced it to a crappy interconnect on the negative side. A 5 cent wire nut fixed the problem. I then listened trouble free for about three hours.
And... what'd 'ya think?
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Old 25th January 2012, 05:34 PM   #604
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What are the effects of absorbent material behind an OB? Like curtains and such?

Can you use foam/felt etc on the walls behind an OB to control the sound, or should it be reflected.

I'm a noob to OB.
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Old 25th January 2012, 05:44 PM   #605
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Originally Posted by Pano View Post
Well John, it looks like we about 1/2 agree. From my point of view, it pretty much all comes out the same. True, with the active filter you don't have the big inductive load, but most amps don't seem to mind it.

OK, then were does the power go? You say it's not dissipated by the crossover and the current and voltage at the driver are the same. Where is the extra power dissipated?


What I said was that efficiency is probably not a good usage here. There is a difference between the power dissapated in the VC and the reactive power the amp must supply. Energy is stored in caps and inductors, and released. But the energy needed to charge the reactive element must come form somewhere and that is the amp, placing greater current and voltage demands aon the amp than an active eq does.

Anyway, look at my page on hybrid design and you might get an idea of why active eq yeidls improved headroom:

Hybrid Design

The argument applies to baffle step in box spakers as well as dipole eq.
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Old 25th January 2012, 06:17 PM   #606
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Thanks John, I'll have a look.
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Old 25th January 2012, 08:26 PM   #607
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With EQ ahead of the poweramp (active or not), the voltage swing at the output of the power amp would in this case (OB) only be high for the lowest frequencies. If a wideband signal is sent through the poweramp, although the power dissipation may not be substantially different, the total voltage swing would be a bit higher, due to the full amplitude presence of the higher frequency energies. Most poweramps are more limited by voltage swing than power dissipation, so I would expect better headroom in the poweramp when the EQ is ahead of the poweramp.

A slightly different subject is the reactive nature of the load with the passive EQ (12 - 20mH inductor). High feedback amplifiers sometimes have tantrums when they drive highly reactive loads (the reactive load shifts in time ("phase-shift") the feedback signal in the amp circuit). Most speakers are relatively resistive in their intended passband, but if they've got 15mH of coil in series with them, some high feedback poweramps might get mad.

The other thing that one could argue is that with EQ ahead of the poweramp, the amps output Z as seen by the driver is very controlling (usually a good thing), since the source impedance of a high feedback amp is measured in milliohms across frequency. With the giant inductor in between the amp and the speaker, damping of the speaker by the amplifier rolls off dramatically as you go up in frequency; as soon as the frequency response is rolled off by the inductor, which starts in at about 60HZ in this case.

To be fair, low damping doesn't necessarily sound bad. The high end low feedback tube poweramps have low damping (1 to 8 ohm output impedance), and many people like that sound (not me, I like tight accurate bass).

I'd be a bit concerned about "cavity effect" on the rear radiation with side boards that are 4 inches deep. I limited mine to 3 inch total, 1.5 inch extended beyond the back side of the 1.5 inch thick front baffle board, and put a 45 degree corner brace made of oak (high density and very stiff) in there to help "waveguide" the acoustic energy out into the room with minimal frequency selective acoustic reactance.
Scroll down about an inch to see a photo of what I just described.
http://www.spiritone.com/~rob_369/audio/AuriumWaveguide2010.htm
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Old 25th January 2012, 09:45 PM   #608
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Originally the wings were asymmetric, with a diagonal wing on 1 side. (see post #1)
John changed that to shallow, symmetrical wings. I doubt there is much cavity resonance with wings this short, but John will know.
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Old 25th January 2012, 09:47 PM   #609
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Quote:
Originally Posted by kec View Post
What are the effects of absorbent material behind an OB? Like curtains and such?
IMO they do two things. Help the sense of depth (but a little less "space") - and reduce the level of mid bass. Trade-offs, as always.
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Old 25th January 2012, 09:51 PM   #610
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Originally Posted by Bob Richards View Post
With EQ ahead of the poweramp (active or not), the voltage swing at the output of the power amp would in this case (OB) only be high for the lowest frequencies. If a wideband signal is sent through the poweramp, although the power dissipation may not be substantially different, the total voltage swing would be a bit higher, due to the full amplitude presence of the higher frequency energies. Most poweramps are more limited by voltage swing than power dissipation, so I would expect better headroom in the poweramp when the EQ is ahead of the poweramp.
Exactly.

Quote:

The other thing that one could argue is that with EQ ahead of the poweramp, the amps output Z as seen by the driver is very controlling (usually a good thing), since the source impedance of a high feedback amp is measured in milliohms across frequency. With the giant inductor in between the amp and the speaker, damping of the speaker by the amplifier rolls off dramatically as you go up in frequency; as soon as the frequency response is rolled off by the inductor, which starts in at about 60HZ in this case.
Much is often made of this but electromotive damping really is only significant around the driver's resonance. Above and below resonance damping the decreases quickly. Above resonance it's mass controlled. Below it's compliance controlled.
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