Hi Sardon,
Well the circuit does not exactly the same. The LW transform is not an exact inverse of the 2nd order speaker response, although when properly dimensioned it comes very close and can give stunning performance.
I actually started with the LW transform but it has its limitations. It is nearly impossible to adjust without recalculating the whole thing and rebuilding it. Further it is quite sensitive to component tolerances and put a lot of demand on the single op-amp.
I came to the more complex circuit to have more design freedom and for the ease of calculating it. And it is by far less critical than the LW transform. Just changing a few resistors for instance can change Qt, one of the things I wanted to experiment with regarding room response. I have chosen Fliege filters because of the wide range of Q they can handle and the frequency tuning components are for the 3 branches exactly the same. Fliege filters are kind of simplified GIC filters that to my ears perform the best. Fliege filters are by themselves more complex than standard S & K filers. But to work best both opa’s in a filter branch need to be matched. I used BB OPA2604 dual opa’s for the filters.
For me complexity by itself is not a problem if it makes life easier and considering the total effort needed of a whole project ...
Cheers 😉
Well the circuit does not exactly the same. The LW transform is not an exact inverse of the 2nd order speaker response, although when properly dimensioned it comes very close and can give stunning performance.
I actually started with the LW transform but it has its limitations. It is nearly impossible to adjust without recalculating the whole thing and rebuilding it. Further it is quite sensitive to component tolerances and put a lot of demand on the single op-amp.
I came to the more complex circuit to have more design freedom and for the ease of calculating it. And it is by far less critical than the LW transform. Just changing a few resistors for instance can change Qt, one of the things I wanted to experiment with regarding room response. I have chosen Fliege filters because of the wide range of Q they can handle and the frequency tuning components are for the 3 branches exactly the same. Fliege filters are kind of simplified GIC filters that to my ears perform the best. Fliege filters are by themselves more complex than standard S & K filers. But to work best both opa’s in a filter branch need to be matched. I used BB OPA2604 dual opa’s for the filters.
For me complexity by itself is not a problem if it makes life easier and considering the total effort needed of a whole project ...
Cheers 😉
Pjotr
I see what you're saying. Complexity is not a problem for me either. But soldering is!! The less joints i have to make the beeeetttterr! I desperately need to practise more soldering. So in this case.. this simpler the better.
I see what you're saying. Complexity is not a problem for me either. But soldering is!! The less joints i have to make the beeeetttterr! I desperately need to practise more soldering. So in this case.. this simpler the better.
choosing Q = 0.6
I chose 0.6 because this is probably the best low Q value
for an overdamped sealed box sub woofer - the practical
range is 0.5 to 0.6.
0.5 needs a bigger box and doesn't give much advantage.
With an overdamped alignment you can simply EQ it with
a second order high pass set to the bass cut-off frequency
you want, the lower the frequency the higher the Q you
need - practical range is a Q between 1 and 3.
Paper calculations can be very misleading - but I suspect
a filter set to 30Hz and a Q of 2 to 3 will give good results
for free space postioning - i.e. not rear wall postioning.
If your 'mains' rolloff at 150Hz IMO we are not in subwoofer
territory - you should build two enclosures with twin units
as a 'stand' for the left and right mains - effectively we are
talking about a 3-way speaker - but if its active you don't
need to worry about sensisitivity issues - you've plenty
enough to worry about to get your bass / mid transition
to work well.
What is your mid unit ? this could be critical.
🙂/sreten.
I chose 0.6 because this is probably the best low Q value
for an overdamped sealed box sub woofer - the practical
range is 0.5 to 0.6.
0.5 needs a bigger box and doesn't give much advantage.
With an overdamped alignment you can simply EQ it with
a second order high pass set to the bass cut-off frequency
you want, the lower the frequency the higher the Q you
need - practical range is a Q between 1 and 3.
Paper calculations can be very misleading - but I suspect
a filter set to 30Hz and a Q of 2 to 3 will give good results
for free space postioning - i.e. not rear wall postioning.
If your 'mains' rolloff at 150Hz IMO we are not in subwoofer
territory - you should build two enclosures with twin units
as a 'stand' for the left and right mains - effectively we are
talking about a 3-way speaker - but if its active you don't
need to worry about sensisitivity issues - you've plenty
enough to worry about to get your bass / mid transition
to work well.
What is your mid unit ? this could be critical.
🙂/sreten.
Hi Sreten,
Actually the Q depends also on room size and lower –3dB point. I’ve even experimented with a Q of 0.4 in a small room (4m x 4m). That gave a rather thin yet powerful, tight and relaxed total bass response.
Dunno if you looked at the link I posted but I did use the filter also for de mid to give it a neat 2nd order hp function at 125 Hz with a Q of 0.5 (LW alignment). The actual mid had its fb at 65 Hz with a Qb of 0.34 and was thus largely over damped. However this much to large box reduced distortion a lot.
😉
Actually the Q depends also on room size and lower –3dB point. I’ve even experimented with a Q of 0.4 in a small room (4m x 4m). That gave a rather thin yet powerful, tight and relaxed total bass response.
Dunno if you looked at the link I posted but I did use the filter also for de mid to give it a neat 2nd order hp function at 125 Hz with a Q of 0.5 (LW alignment). The actual mid had its fb at 65 Hz with a Qb of 0.34 and was thus largely over damped. However this much to large box reduced distortion a lot.
😉
That's what i planned on doing all along 🙂 I guess i kinda forgot to mention that. i'm gonna use either 3 or 4 per side. I'm thinking 3, that way i can have a cute little standmounted speaker around 7" wide (i'm gonna trim the sides of the woofer) and around 35 inches high that goes down to i'm hoping 20 hz. if they can't handle that then i'll have to adjust the filter for maybe 30hz or so.
OK,
there are better ways to deal with small rooms than a Q=0.4
alignment, especially given sx's concerns about enclosure volume.
Q=0.6 and a mild 2nd order notch filter for example.
sx :
If want to go for 20Hz IMO an overdamped reflex alignment
with the port tuned to around 26Hz is a better idea.
If the speaker software your playing with can show excursion
requirements you will soon see why a reflex will help.
If you play around you'll find a two unit reflex will equal a 4 unit
sealed box and be around the same volume as a 4 unit box.
🙂 /sreten.
there are better ways to deal with small rooms than a Q=0.4
alignment, especially given sx's concerns about enclosure volume.
Q=0.6 and a mild 2nd order notch filter for example.
sx :
If want to go for 20Hz IMO an overdamped reflex alignment
with the port tuned to around 26Hz is a better idea.
If the speaker software your playing with can show excursion
requirements you will soon see why a reflex will help.
If you play around you'll find a two unit reflex will equal a 4 unit
sealed box and be around the same volume as a 4 unit box.
🙂 /sreten.
sreten, i'm just using loudspeakers101 to get rough numbers, I'm not using any software. I doubt excursion will be a problem, each one of the TB 8" drivers has an excursion of 12 mm one way. Impressive eh??
I'm going to try sealed enclosure first - better transient responce. If it doesn't work out i can always punch a hole.
I'm going to try sealed enclosure first - better transient responce. If it doesn't work out i can always punch a hole.
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