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12" passive radiator replacement?

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Old January 6th 20, 08:05 AM posted to rec.audio.pro
Don Pearce[_3_]
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Default 12" passive radiator replacement?

On Mon, 06 Jan 2020 08:05:27 +0100 (CET), "Mat Nieuwenhoven"
> wrote:

>On Sun, 05 Jan 2020 14:12:19 GMT, Don Pearce wrote:
>>On Sat, 4 Jan 2020 18:21:29 -0800 (PST), nickbatz
> wrote:
>>>Happy New Year.
>>>So I just dumpster-dived a pair of mid-'80s (guessing) RS Sierra tower speakers from a neighbor.
>>>This is a premature question because I haven't hooked them up yet, but they have 12" rear-firing passive radiators with totally shot foam surrounds.
>>>Assuming it's worth fixing them - if only to trade someone for something else - is it likely to make any serious difference what round 12" cone-shaped thing I put back there? Serious = commensurate with the quality of these speakers.
>>>My guess is that these are hyped speakers, because I know Rogersound Labs and other stereo stores used to compare speakers to JBL L100s in those days. But the tweeter, midrange, and woofer are outwardly in good shape. The cabinets are in reasonable shape, but because I've been doing a lot of woodworking* recently I can easily replace some of the walnut veneer if it's necessary.
>>>* By the way, if anyone knows anyone in the market for custom studio furniture, especially a unique composer's desk, let me know and and I'll send you some pictures. This has become a serious side business - I just shipped a desk to Paris, another to Florida - and I'm truly enjoying it.

>>If you have the TS parameters for the main driver, you can probably
>>design a port that will allow you to do away with the stupid passive
>>radiator. They are no more than a spring and a mass, just the same as
>>air in a port tube, but suffer added non-linearity due to the
>>suspension. Any subwoofer design software will let you do this.

>A passive radiator is designed to match the main driver and do away
>with the port. A port works fine at low volumes, but if a lot of air
>needs to move it suffers from compression problems, especially if the
>port is longer. Plus mid-range leakage if it is at the front. A
>passive radiator does not have distortion problem any more than the
>matching main driver, and can be the only solution if the port would
>otherwise become too long.
>Mat Nieuwenhoven

None of those "problems" is actually a problem. The passive driver is
just another piece of stuff to introduce its own problems.


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