F3 too close to XOVER?? Help!

[birkinshawc]

I am designing a satellite/sub combo using a pair of Peerless HDS 164 drivers that I have. Using a 8.7 L box gives a Qtc of 0.707 and an F3 of 76.96 Hz. I wanted to crossover the speakers to a sub at less than 120Hz for imaging reasons, but would prefer this frequency to be nearer 80Hz. However, I am am concerned the F3 will then be too close to the XOver frequency... can anyone advise?

Cheers,

chris

[Volenti]

I can't see the problem? You'll simply end up with a steeper acoustical x-over slope than you would get with just the electrical side alone.

[birkinshawc]

So wouldn't this mean that if I crossover at 80Hz and the mid has rolled off too far there will be a dip in the frequency response?

This would be bad!

[sreten]

your satellites will roll off at 80Hz with a classic Butterworth
second order roll off.

Further electrical crossover is difficult to achieve passively,
the box resonance thoroughly interfering with the filter.

for 120Hz you'll need an active arrangement, or just
use the bass management feature in an AV amplifier.

sreten.

[birkinshawc]

I was going to use an active 80Hz 24db/octave LR crossover, will this be too low?

[5th element]

Not a problem at all, I use the 12db natural roll off in the bass coupled with a 12db xover to get a 24db roll off in my speakers midrange cabinet. This is active though so passive may present more problems.

[5th element]

Passive is exaclty sreten said it creates problems.

I just ran a few things thru LSPcad and came up with a passive network you could use however it would cost, due to large caps and inductors.

With just a simple 2nd order added you get the target 24db roll off but high Q so you get a substantial peak prior to this. So to compensate I added a series notch filter (L+C+R).

This worked like a charm and you get the desired response, 24db roll off linkwitz riley topology at 80hz

Xover as follows

[birkinshawc]

Thanks very much for the passive xover advice, however I already have an active crossover with selectable xover points and 24db slopes and wanted to use this... I guess this should make things easier anyway?

[5th element]

Right appologies I made a few errors!

Anyway the other post was for a butterworth at 80hz
and its a shunt or paralell branch not series DOH!

Anyway here is the correct network

[5th element]

Right and here just for completeness is an Active version!