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Just so I got this right ... [message #50020 is a reply to message #50019] Tue, 12 September 2006 14:09 Go to previous messageGo to next message
GarMan is currently offline  GarMan
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Registered: May 2009
Illuminati (2nd Degree)
The front chamber attenuates harmonic distortions that's generated by LF signals, but sits in the HF spectrum?

That's brilliant!

Re: Just so I got this right ... [message #50021 is a reply to message #50020] Tue, 12 September 2006 14:32 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
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Registered: January 2001
Illuminati (33rd Degree)

In this case what I mean by "HF" is frequencies higher than the fundamentals. Looking back at it, I don't think "HF" was really the proper term since I'm talking lower midrange. But what I meant was the front chamber and folds attenuate signals that are above the passband. So, for example, a bandpass box or a folded basshorn tuned for 30Hz to 100Hz will actually attenuate signals above that range. So second and third harmonics (and all others above that) are reduced.

Without this kind of acoustic filter, whatever harmonics are generated by the speaker will be heard. Even if you low-pass electronically, the harmonics generated by the speaker are still there. But the acoustic low-pass filter formed by the folds of a basshorn or the front chamber of a bandpass box attenuate them.

When also using push-pull drive, you have another level of distortion reduction. The main feature of the push-pull drive is that it cancels even harmonics. So the second harmonic is greatly reduced. That's the one of lowest frequency, closest to the passband. The next one up is the third harmonic, which is not reduced by the push-pull drive, but is 3x the frequency of the fundamentals and on the edge (or completely outside) of the passband. By the fourth harmonic, push-pull cancellation plus the depth out of band ensures practically no distortion is heard. The combination of the push-pull drive and attenuation of out-of-band harmonics make distortion very low.


Re: Just so I got this right ... [message #50022 is a reply to message #50021] Tue, 12 September 2006 15:45 Go to previous messageGo to next message
GarMan is currently offline  GarMan
Messages: 960
Registered: May 2009
Illuminati (2nd Degree)
I think I see it now. Unfortunately, I'm getting scared off by the size of this thing. Back chamber will be doubled that of a single driver. Add the front chamber to the equation and you're looking a almost 10 cu ft!

Re: Just so I got this right ... [message #50023 is a reply to message #50022] Tue, 12 September 2006 16:54 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18783
Registered: January 2001
Illuminati (33rd Degree)

Yeah, you're right. Ten cubic feet isn't bad for prosound subs but for home hifi use, it's pretty big. The HL10 can be used in a smaller cabinet, so maybe it's worth looking into.

And don't dismiss using a single LAB12 in a bass-reflex or sealed box either. It sounds good. The LAB12 works very well in vented cabinets from 2.0ft3 to 6.0ft3 tuned to 22Hz. It also works well in a large sealed cabinet, particularly with boundary reinforcement. If out in the open, like placed as a coffee table, I'd run vented. If in the corner or near walls, either run an overdamped vented alignment or run sealed.


Re: Just so I got this right ... [message #50024 is a reply to message #50023] Tue, 12 September 2006 21:47 Go to previous messageGo to next message
GarMan is currently offline  GarMan
Messages: 960
Registered: May 2009
Illuminati (2nd Degree)
Yup. Back to my original plan I guess. I was fun exploring new ideas though.

Re: Just so I got this right ... [message #50063 is a reply to message #50021] Thu, 21 September 2006 17:30 Go to previous message
mollecon is currently offline  mollecon
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Registered: May 2009
Master
It deserves to be mentioned, that apart from horns, 4th order BP boxes are probably the best at handling power, + reducing diaphragm excursion, and hence distortion. The price one pays is the limited bandwith (though that in itself also gives some advantages, as pointed out by Wayne), and the fact that it can be difficult to design a correct port in smaller BP boxes.

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