crossover/attenuation guidance?

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Joined 2007
alrighty, I'll be making some speaker boxes for my brother for christmas, using these tweeters:


and TWO of these woofers per box, in an isobaric setup:


I plan on crossing them over at 3500Hz, 12dB per octave, but how much will the tweeter need to be attenuated?

keeping in mind, that the two woofers will be wired in parallel, to give 4 ohms, however, they will be loaded isobarically...

does this mean the sensitivity of the woofers, with 2.83 volts will be the same as a single woofer?

thanks for your help people!
Isobaric is not recommended:

Using Synrta to plot the CW2135 FR, they're only good up to ~1600Hz (Don't have the plot handy, it's on my other computer).

In a 54L box tuned to the low 30's, a pair aren't bad as part of a 3 way system.....but it seems you're trying to make something smaller???
I tried then in a 2 way using a SEAS tweeter crossed at 1400, worked pretty well, but not as clean as my Peerless speakers.

If you don't have the drivers already, Altronics has a tweeter at a similar price that has a lower Fs than the Jaycar one. (& a 5" driver that may go higher yet give a similar low end response)

They will be same sensitivity but half the impedance.

Quite frankly you will waste a lot of box volume going isobaric,
(cannot use clamshell arrangement) and whatever the midrange
response is like likely it will get worse with the isobaric chamber.

Slapping unmeasured drivers in configurations not really suitable
with a "cookbook" crossover that will be certainly wrong is not
the way to do it. Unknown responses = unknown problems.

FWIW after implementing baffle step the allegedly 94dB tweeter
will need attenuating 12dB or so to match the BSC equalised
82dB or so sensitivity (from 87dB) of the isobaric array.

Disabled Account
Joined 2007
PeteMcK said:

and thats just awesome how that thread has nothing to do with isobaric loading....

ok, so, if I have two woofers, in an isobaric setup, but wired in parallel, how is the overall sensitivity of the woofers effected,

I believe you lose 3dB by isobaric loading, correct?, but seeing as the woofers are now at 4 ohms, each woofer is getting the same power, so, at 2.83 volts, I have twice the power of a single driver, so, at 2.83 volts, wont the sensitivity be the same?

I need to know how much the tweeter needs attenuating....
Disabled Account
Joined 2007
its twice the power, so, while the 8ohm tweeter is getting 1 watt, the 4 ohm woofer is getting 2 watts, and is therefore 3dB higher when designing crossovers,

so, Im working to the assumption, that the woofers, in an isobaric setup, loose 3dB 1w/1m, but at 2.83 volts (same as the tweeters 1 watt measure) they are back up to the original 1 watt efficiency (~87dB) so, I will be attenuating the tweeter by 7dBs
Thawach said:
Hi! Twojz

When two woofers will be wired in parallel or series the sensitivity be the same. But 4 ohm, The sound level is higher than 8 ohm. I don't know how much. I think of it's not over than 3 db.



No. For isobaric :
Parallel the same sensitivity. In series sensitivity is - 6dB.
Efficiency in both cases is - 3dB compared to a single.

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