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In Reply to: Re: PPSL posted by bmar on May 16, 2003 at 19:26:45:
"Is the equal and oposite reaction limited to 2nd harmonics, and does it make the system less efficient"Yes, the equal and opposite reaction only reduces 2nd harmonics, it does not change the system efficency.
"With the drivers close together like this. Just how high can this system be used."
The closer the better seems to be the rule as far as HF response goes. A four 12 box I made could be crossed at 400hz, some dual 18 boxes were able to cross at 250hz. The majority that I have built are dual 15 and crossed far enough below where the plenum rolls off to use an off-the-shelf LR4 crossover.
"What kind of parameters do you use when calculating the rear chamber"
Use normal TS parameters and size like a regular box, I use low Qts drivers with a step-down tuning and equalization. Drivers with Qts=.312 give the deepest bass response from the smallest box size. Alternately one can seal the box and use a Linkwitz transform, or leave the back open like the Linkwitz dipole.
"and can you actually build the box so it would act like a low pass filter down to 80hz if needed."
Yes you can, but now you have a bandpass box. That may better suit your needs, and many modeling programs are available for those.
At the time I was looking at both the EV MTL4 and the KEF 104, both had their strengths and their weaknesses. My design had all their strengths and none of their weaknesses.
Follow Ups:
Thanks for the info, I appreciate it. I like the tower style speakers because the horn is more ear level. Using a design like the PPSL as the lower portion of a cabinet might come off like having a sub built in to each cabinet. That could leave me enough cabinet under a horn for a nice midrange driver.I was going to start working with a built in powered sub, but that begins a whole new story. The efficiency isn't necessarily there and the choice of built in amp will always be questionable.
Dont have any experience with the KEF you mention. I have thought about using two drivers and basically just use one with a linkwitz transform to augment the lower octaves to the other.
Hi Dennis!I've been thinking about this configuration since you brought it up, and it seems to me that it might reduce second harmonics whether they are caused by non-linearities in the suspension or the magnetic structure. Pretty cool idea, really, and I'm surprised it isn't more commonly used on systems that have multiple woofers. I never gave it much thought before now, because none of my stuff uses more than one woofer. But it does seem like a good configuration for dual woofer designs whether they be baffle loaded, plenium loaded or horn loaded.
Please do post more references if you know of any. I'd like to see more quantified data, if there is any that's available. Looks to me like you've found a good thing here.
Wayne
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