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Multi-Way Conventional loudspeakers with crossovers

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Old 18th February 2009, 05:05 PM   #11
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my behringer A500 goes close to clipping when running 12in woofers on dipole without high pass filter. well I guess it all depends on SPL required. I like it to play night club loud, occasionally.
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Old 19th February 2009, 02:09 AM   #12
CLS is offline CLS  Taiwan
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In my application, these OB woofers eat not much.

Now with T-bass circuit, the impedance is approaching 1 Ohm in particular range, so I use SS amp. Before I tried T-bass circuit, I used tube amps for the OB bass, even with SE 300B for quite some time

At that time, the SE 300B could also made some room-filling and window-rattling bass. (Not so tight and controlled as present SS amp with T-bass, though) I've never clipped any of the amps, even on that 6W SE tube power which was dealing with several 18"ers.

OK, maybe my apartment is small and the window frames are in bad shape... :lol:

Well, fine with me anyway.

When I hooked up the 1 Ohm load (thanks to T-bass) to my old SS Hafler, I worried a little, as the user manual says "do not connect to loads much lower than 8 Ohm". Hmm... I thought to myself, what the xxxx, just give it a try.

Then it turned out very well. The cheap old little SS amp is doing just fine with that 1 Ohm load. No problem at all. Playing pretty loud for several hours, it's still only warm on the heatsinks. (It's only rated as 60W x 2 output @ 8 Ohm load, no data for other load impedances. Its power transformer is maybe 300VA or so, and with tiny filter caps. A totally no-looker for low impedance loads. No internal photo should be published in reviews for such amp, if any.)

I think, the cones must pump out specific amount of air to produce particular SPL. And the speaker drivers need that particular 'power' to do it. When in normal condition, high impedance peaks commonly seen in the bass range need very high voltage to get enough power.

With helps of T-bass, the impedance peak drops dramatically so the woofer can draw a lot more current (power) in the working range. Compared with the ordinary combinations of [high gain (EQ) + high driving voltage + high load impedance ], I prefer the performance of lower impedance + high current of T-bass.

As to the inevitable OB loss, I guess it's somewhat averaged out by the 'unloaded' cones which are much easier to move. Overall, I never feel OB speakers hunger for power. They are easily driven and pretty loud in my usage.
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Old 19th February 2009, 02:34 AM   #13
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CLS,

Have you exchanged your right and left speakers so the tweeter and midrange are on the inside of the sound stage? This arrangement often sounds better to my ears. I design 3-way speakers and put the woofers in a separate bottom structure to avoid transfering vibration to the upper mid-tweet structure, and to allow me to angle the mid-tweet inward toward the listener and angle the woofers outward toward the walls to adjust room effects.
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Old 19th February 2009, 02:50 AM   #14
CLS is offline CLS  Taiwan
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Never tried that actually. (did that before with other boxed speakers, though)

I thought, with such large toe-in (and the needs of near-wall positioning for practical reason), the inside arrangement would make the back of midrange even closer to the wall and the sides of TV (the previous TV was much larger and deeper). By the 3' width of the baffle, the difference is quite large. By this reason I keep them on the outside.

The separate mid-high and bass parts is a good idea. Will do in the near future.
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Old 19th February 2009, 02:01 PM   #15
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Quote:
Originally posted by CLS
I think of other problems on this. Even if the phase knob is "properly working", it's still questionable. Reflecting to the 23cm difference of path lengths, the phase angle at 40Hz and 30Hz and even 20Hz are all different! Which point should I aim for? In the end, I probably converge them in one frequency and miss all others. So, what I need should be a constant time delay instead of a phase angle. Am I right? (or wrong?)
You are right. Phase and delay are two different things. You could try something, when your wife is not at home. Move the sub 23 cm and see, where it gets you. Then you will probably still need to adjust the phase. If it helps, add a delay correction to the sub.

One thing that could also be helpful is to put something on the floor that absorbs, like a thick carpet. And maybe as well on the wall behind the speakers, so that the reflected out-of-phase waves do not cancel out the in-phase waves from the front.
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Old 20th February 2009, 09:07 AM   #16
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I found an interesting phenomenon, touching the cones when playing, the cone motions on main baffle and center sub are sometimes different in timing and amplitude. (I kept attentions on those drum hits and bass plunks, and felt the cone motions simultaneously. )

The woofer on main baffle works up to higher frequency, so it feels 'faster' and reacts to more notes, quite a lot of transient response coming along with music. While the woofers on center sub work only in the bottom octave, so the motions are slower and react to less notes. (no low bass contents on many of them)

For most of the bass notes, their "major initial attack" seem quite coherent -- they push my fingers simultaneously (I might say almost, with the unknown 'resolution' of my touching feel). The woofer on main baffle pushes with sharper edges and shorter movement, while the one on center pushes gentler and with slightly longer strokes. In spite of somewhat different 'feels', I do sense the 'starting time' of their motions is almost the same.

But in some particular notes, I can obviously feel their initial attacks not at the same timing. The one on main baffle takes the lead all the time in such case. And when this happened, the motions of the center sub would often be even slower and softer start with even longer strokes, and also stop the motions in longer time. That is, the center sub delays its whole action and produces lower frequency with higher amplitudes.

Back to the listening position, my ears can not distinguish all these detail differences among all three baffles anymore. They are blent into a big sound. Sometimes there'd be very short period of low bass 'tails' coming behind the initial attacks, which are mostly a sense of vibration or blowing of air. Fortunately they don't make things muddy or blurred because they are very different 'sound', so I can tell which is which.

I can only guess it's the complex overtone structures in the low frequncy music notes.

As to that 23cm path length difference, I decided to forget it. For such low frequencies with so long wave lengths, it's just too small to be considered. I have other things to worry about...


PS. I can move everything in the house whenever I want. My major 'problem' is that the wife and kid are just too noisy. I can enjoy my time only after I drive them into the bedroom, but that's usually too late to play loud, or I'm simply too tired to do so. Sigh...
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Old 20th February 2009, 05:08 PM   #17
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Are you using T-Bass on the main speakers as well or only on the subwoofer?

Did you check with Graham Maynard about the T-Bass circuit in combination with the active filter of the plate amp? As far as I remember the T-Bass provides some boost to counter the natural roll-off at very low frequencies. With an active low-pass set to 40 Hz you probably render that useless.
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Old 21st February 2009, 12:38 AM   #18
CLS is offline CLS  Taiwan
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I use T-bass on all three of them.

My previous xover setting on main baffle was also very low, while the T-bass still overwhelmed the whole thing -- drawing extra current on the very low frequency makes it very different.

Although the xover on plate amp is set at 40Hz, T-bass still works. (The level on plate amp is set very low) Of course I can skip the T-bass and turn up the volume to get the simular response, but they just "sound" different. I've also tried playing with the xover point on the plate amp, when it's set higher then a point, I saw a dip occured at around 80Hz -- that's another 'proof' of T-bass's work.
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Old 21st February 2009, 05:50 AM   #19
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Yes, the T-Bass works. There is little else it can do. And it will still have its positive effect on the ring in. It is just such a pity to boost the bass with it and then attenuate it again with a cross-over.

Could the dip at 80 Hz be due to phases adding up wrongly due to the cross-over's influence?
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Old 22nd February 2009, 12:10 AM   #20
CLS is offline CLS  Taiwan
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I should've described it the other way around.

I need the sub to handle only 40Hz and down. The bottom octave filling is all I need. In such case, T-bass is still working good.

I don't attenuate anything I need.

Above 40Hz (upto about 160Hz), the woofers on main baffles are already more than enough.

I can recheck the 80Hz dip to see if it is the cancelling or the T-bass. Maybe later....

By the way, I didn't check the impedance of this center sub until just now. It drops below 1 Ohm in the 30~50Hz range!!

This is what it looks like:
Click the image to open in full size.
(Note the unusual scale)


If I made the scale of vertial axis for impedance peaks of normal woofers (200 Ohm full scale), then it would look like this:
Click the image to open in full size.



edit: I'll update here if the plate amp is blown.
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