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| Date: |
August 08, 2003 at 20:14:27 |
| From: |
Adrian Mack, [dialup-196-238.wasp.net.au] |
| Subject: |
Waveguides, Ports and Peerless XLS 10 |
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URL: My website, Peerless XLS 12 Dual PR Sub Project, 18LW1400 vented sub, Horns, etc..... |
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Hi guys!
[about what Mike said]
> see the response?its droppy, down 4.5db at 40hz
> this is crap! needs EQ!which is just a waste of
> power to compensate for a dodgy system response.
There is nothing bad whatsoever about this driver. You've simply chosen the wrong alignment. We can use EQ on this alignment, which is available in plate amps, like the Parts Expres 250W amp. And thats no bigger than the amps people use with Shiva and the such, so theres no disadvantage there. Or we can use SPICE or the such and build a circuit which exactly compliments the rising response characteristic - this is easy to do. Thats what I've done on my HF horns.
> Flare the ends like they say,but who knows how long
> the port will be when u flare them! perhaps the
> same length,perhaps not.
Thats right, it will be somewhere inbetween. But having a flared port does not change the fact the system is forming a Helmholtz resonator - It just makes the tuned frequency indicated by the formulas less reliable because we dont know the exact length of the port. Buts its still a resonator, and tuned to some frequency. If we choose a distance thats somewhere between the end of the port and the end of the flare, then we can get a pretty good approximation of its real length. And an inch off either side wont matter all that much - and thats all it will really be.
> if you want a 1metre long port and enjoy the fun of
> trying to fit it into a box,you can :)
One other thing to consider is that it can form a waveguide, and this can happen when one cabinet dimension or the port is long in comparison to the others. Either of these can form standing wave problems and might add unexpected audible resonances in the passband.
> i tuned 33hz,and im not get a sub that tunes any
> lower,its a waste of time.
I wouldn't say that, unless you know everyones listening preferences. Some people have applications or listen to various styles of music such as organs which have lots of low bass energy.
> dont forget youl need a HUGE amp to use its full
> potential
Same thing goes for Shiva, AV12, Tempest, Tumult, Brahma, Titanic, SV12..... and more. The XLS series are very well built drivers, and I'd reccomend it to just about anyone whoes after low distortion, true 20Hz operation in very small boxes.
[about what Derek said]
> I know you recommend PR but for what i am tryign to
> do i want to go ported and just rap the port around
> inside the box.
Well, we can use a port I guess, its more of a pain though. One thing to notice when using a shelf type port, for long ports that cover two or more walls, the entire internal volume of the enclosure is usually going to be bigger too - and then you have to remove that volume using filler blocks, which is pretty annoying, but it can be done. It also makes the cabinet physically larger - and small cabinets may be one of your design aims.
> the 10" requires a 1.24 cu ft enclosure with a 3"
> port that is 31.5 inches long.
I would use a 30L box (1.08ft^3) and tune at 18.9Hz, which is the drivers resonance. I'd also enable EQ in the plate amp - so set it for about +3db at 23Hz, I can tell you the resistor values that need to be changed for this. Dont forget to use it in eigth space conditions (corner loaded). See my website for a 30L passive radiator box using Peerless XLS 10" driver, and also, the 12" XLS box is up there too.
Adrian
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