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Multi-Way Conventional loudspeakers with crossovers

Drop In replacement for seas woofer
Drop In replacement for seas woofer
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Old 1st December 2019, 10:51 AM   #1
vassilis1984 is offline vassilis1984
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Default Drop In replacement for seas woofer

Hi everyone!.

I want to replace a seas p21rf and I already own a p21rex pair (new old stock, never used before) so I am tempted to change the 20 years old drivers for the new one.

Crossover wise, will the new driver work with old crossover? They share many similar specs and Seas states that p21rf is a further development of the p21rex but with 2inch voice coil, also I like the sound of p21rex, it is more sensitive speaker so it works better for me
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Old 1st December 2019, 01:57 PM   #2
BradH is offline BradH
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Curious to know the answer to this as well. I have a pair of p21re and they are such great drivers. Wish they still made them.
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Old 1st December 2019, 03:23 PM   #3
boswald is offline boswald  United States
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Drop In replacement for seas woofer
No.
You will need a new crossover.
Once you make a new low pass, you will at least have to change the attenuation on the high pass, probably more, probably enough more that you are better off starting with a clean sheet, rather than add more bandaids.


Of course, you could throw one in and see if you don't hate it.
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Old 1st December 2019, 06:04 PM   #4
system7 is offline system7  United Kingdom
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I would just try it!

A few old SEAS drivers still around: Seas P21RE/P H0942-08 Woofer. H0313 2015 remake

You might make some guesses about acoustic loading. The above is more of a closed box driver around 0.51 Qts. Reflex is nearer 0.38 Qts usually.

Adjusting tweeter level is usually a question of adjusting an ohm or two at the tweeter input crossover. But I have swapped 8" bass units often enough. They usually work OK.
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Last edited by system7; 1st December 2019 at 06:06 PM.
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Old 1st December 2019, 06:16 PM   #5
vassilis1984 is offline vassilis1984
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I am a noob at crossover designs, and I've never seen a design like this. This is the Tweeter crossover design. Too many resistors...
Six resistors 10w 10.7ohm
Attached Images
File Type: jpg IMG_20191113_191809.jpg (597.3 KB, 146 views)
File Type: jpg IMG_20191113_191749.jpg (291.6 KB, 143 views)

Last edited by vassilis1984; 1st December 2019 at 06:21 PM.
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Old 1st December 2019, 07:06 PM   #6
PeteMcK is offline PeteMcK
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They look similar enough to me, the only item of concern is that the rex is ~ 3dB more efficient
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Old 1st December 2019, 07:08 PM   #7
Dave Bullet is offline Dave Bullet  New Zealand
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Well you won't do any harm swapping woofers (replacing RFP with REX) as they have very similar impedance profiles.

However, the REX looks to be ~ 2 - 3dB more sensitive? and has cone breakup to deal with?

You might find the midbass / lower midrange a bit bloated and there could be some nasal / forwardness in the lower treble without attenuating the breakup.

I'm guessing the tweeter is probably crossed higher? so the breakup will likely need to be dealt with.

Best thing to do is plug your current speaker crossover and factory curves (traced) into a simulator. It doesn't matter that they don't include the actual measured drivers, since what you are trying to do is alter the crossover to replicate the FR response with the REX in place. That's what I'd do.
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Old 1st December 2019, 07:10 PM   #8
system7 is offline system7  United Kingdom
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You'll have to roll your sleeves up and draw the schematic to figure out what to adjust!

You might find this thread helpful:
Restoring Monitor Audio R300 bookshelf speakers.

These things usually end up like this:

Click the image to open in full size.

Click the image to open in full size.
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Old 1st December 2019, 07:45 PM   #9
system7 is offline system7  United Kingdom
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Looking at SEAS here:

http://www.seas.no/images/stories/vi...511_p21rfp.pdf
http://www.seas.no/images/stories/vi...282_p21rex.pdf

Not much in it! Both reflex drivers. REX a bit louder and brighter at the top than the old RFP one. That won't be hard to correct. Maybe a bigger bafflestep coil, or maybe a bigger shunt capacitor. Maybe reduce resistance at the tweeter input to make tweeter louder.

Have a go. Nothing will break!
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Old 4th December 2019, 08:36 AM   #10
vassilis1984 is offline vassilis1984
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Thanx for the responses!. As soon as I have time, I will draw the schematics!.
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