Whether you use 12dB/oct or 24dB/oct depends on your main speakers. Sealed required 12dB/oct to match them, vented 24dB/oct.
What I did was use 2 dual gang pots. I also put one output socket after the first stage to give me a 12dB/oct connection if I wanted it. I mostly use the output socket after the second stage though as my speakers are vented and the steeper cutoff also sounds better to me.
What I did was use 2 dual gang pots. I also put one output socket after the first stage to give me a 12dB/oct connection if I wanted it. I mostly use the output socket after the second stage though as my speakers are vented and the steeper cutoff also sounds better to me.
What you need in the way of a crossover is entirely dependent on the *actual* response of both your mains and your subs as well as the xover frequency.
It is impossible to make a general rule for the slope.
One method to arrive at the proper relationships is to measure the mains and the subs - subs without any xover. Then look at the response. Then listen to the mains.
Are you going to permit the mains to roll off "naturally" or are you going to select a high pass filter? (you might do well like this with a small sealed box "mini-monitor on top, for example)
If it is going to roll off "naturally" the the Q of the mains near F3 plays a role in the overall sound and xover choices.
Many people feel that an electronic highpass degrades the sound sufficiently to want to avoid that. Ymmv.
Add the proposed high pass filter, listen again. Measure the resulting response.
Why go through all this, you may be asking? Speakers are non-flat devices and what counts is the *acoustic* response, not the imagined "text book" response...
Now you can start to add the subwoofer in... is the subwoofer's response *flat* from your selected F3 xover point? Did your main speaker's response end up down 3dB and then 12 or 24 dB where you expected it to be? Does your subwoofer's response *rise* as it goes higher in frequency, does it have any peaks?
(most do)
After you answer all these questions and find solutions, you can try to make a crossover that yields a reasonably flat transition through the xover region. Probably more important is the "Q" of the resulting sub woofer system, especially near the xover point... that's what will help it appear to blend seamlessly - along with the choice of xover frequency...
In general the *higher* in frequency the xover is the more critical the subwoofer becomes... lower in frequency, the less critical overall, but the mains have to work harder, have higher distortion and if headroom is also an issue, that is reduced compared to a higher xover...
Stated simply, applying a 12 dB/oct xover at say 100Hz. doesn't assure that you will *get* any roll off at all at 100 Hz. - if for example the driver is climbing at 6dB/oct in that region... and if it is, then applying a 24dB/oct xover will get you an 18dB/oct result.
Of course you can argue that a first order xover is sonically and electrically the best as far as the seamless recombination of the two...
Good idea to measure and select the xover slope and frequency, and any compensation elements (as desired) based on the actual frequency and phase response.
_-_-bear
It is impossible to make a general rule for the slope.
One method to arrive at the proper relationships is to measure the mains and the subs - subs without any xover. Then look at the response. Then listen to the mains.
Are you going to permit the mains to roll off "naturally" or are you going to select a high pass filter? (you might do well like this with a small sealed box "mini-monitor on top, for example)
If it is going to roll off "naturally" the the Q of the mains near F3 plays a role in the overall sound and xover choices.
Many people feel that an electronic highpass degrades the sound sufficiently to want to avoid that. Ymmv.
Add the proposed high pass filter, listen again. Measure the resulting response.
Why go through all this, you may be asking? Speakers are non-flat devices and what counts is the *acoustic* response, not the imagined "text book" response...
Now you can start to add the subwoofer in... is the subwoofer's response *flat* from your selected F3 xover point? Did your main speaker's response end up down 3dB and then 12 or 24 dB where you expected it to be? Does your subwoofer's response *rise* as it goes higher in frequency, does it have any peaks?
(most do)
After you answer all these questions and find solutions, you can try to make a crossover that yields a reasonably flat transition through the xover region. Probably more important is the "Q" of the resulting sub woofer system, especially near the xover point... that's what will help it appear to blend seamlessly - along with the choice of xover frequency...
In general the *higher* in frequency the xover is the more critical the subwoofer becomes... lower in frequency, the less critical overall, but the mains have to work harder, have higher distortion and if headroom is also an issue, that is reduced compared to a higher xover...
Stated simply, applying a 12 dB/oct xover at say 100Hz. doesn't assure that you will *get* any roll off at all at 100 Hz. - if for example the driver is climbing at 6dB/oct in that region... and if it is, then applying a 24dB/oct xover will get you an 18dB/oct result.
Of course you can argue that a first order xover is sonically and electrically the best as far as the seamless recombination of the two...
Good idea to measure and select the xover slope and frequency, and any compensation elements (as desired) based on the actual frequency and phase response.
_-_-bear
Undoubtedly, to get the best results, one would measure the actual system and design a custom crossover. For some of us simple folk (or busy folk), that's not really an option. What we do is buy a sub amp or an HT system with a built-in electronic crossover and then alternate guessing and tweaking. If one uses the G&T method, a 24dB/octave lowpass filter on the sub is a Good Thing.
Below is what Darren Kuzma of PartsExpress wrote in his review of the 300-804 plate amp, which has a 24dB/octave lowpass filter. Interestingly, PE does not advertize the feature in their catalog blurb for the 804, probably because their more expensive plate amps have a 12 dB/octave filter.
<QUOTE>
There are several problems associated with the common 12dB/octave filters found on other amplifiers. The shallow slope does not allow good integration with mid-sized main speakers. It is difficult to achieve a good transition without getting overlap in the lower midbass region, which can cause a tubby or boxy sound. Also, many subwoofers have large response peaks in the 800Hz-2kHz region. If not attenuated enough, these peaks can "bleed through" into the output from the subwoofer, causing what could be described as "ringing" sound. Not only is this annoying, but it can result in a fatiguing system and a subwoofer that does not "disappear" into the room.
Below is what Darren Kuzma of PartsExpress wrote in his review of the 300-804 plate amp, which has a 24dB/octave lowpass filter. Interestingly, PE does not advertize the feature in their catalog blurb for the 804, probably because their more expensive plate amps have a 12 dB/octave filter.
<QUOTE>
There are several problems associated with the common 12dB/octave filters found on other amplifiers. The shallow slope does not allow good integration with mid-sized main speakers. It is difficult to achieve a good transition without getting overlap in the lower midbass region, which can cause a tubby or boxy sound. Also, many subwoofers have large response peaks in the 800Hz-2kHz region. If not attenuated enough, these peaks can "bleed through" into the output from the subwoofer, causing what could be described as "ringing" sound. Not only is this annoying, but it can result in a fatiguing system and a subwoofer that does not "disappear" into the room.
Thanks for the detailed answer, gentleman.
Got a few questions I want to clarify:
From what I understood, the woofer and box design will determine the lower freq roll-off, and basically the crossover will take care of the upper freq roll-off, right?
And the most important thing is to make sure the sub upper roll-off matches the mains lower roll-off in order to blend seamlessly? And that is why 24dB/o is required when my mains are ported?
Got a few questions I want to clarify:
Why would my driver want to do that? typically subwoofers(in a box) are flat from their tuned frequency to their upper limit before it naturally rolls off. If it starts climbing at certain upper frequencies, that wouldnt be a woofer driver anymore right?
From what I understood, the woofer and box design will determine the lower freq roll-off, and basically the crossover will take care of the upper freq roll-off, right?
And the most important thing is to make sure the sub upper roll-off matches the mains lower roll-off in order to blend seamlessly? And that is why 24dB/o is required when my mains are ported?
skyraider said:Thanks for the detailed answer, gentleman.
Got a few questions I want to clarify:
Why would my driver want to do that? typically subwoofers(in a box) are flat from their tuned frequency to their upper limit before it naturally rolls off. If it starts climbing at certain upper frequencies, that wouldnt be a woofer driver anymore right?
From what I understood, the woofer and box design will determine the lower freq roll-off, and basically the crossover will take care of the upper freq roll-off, right?
And the most important thing is to make sure the sub upper roll-off matches the mains lower roll-off in order to blend seamlessly? And that is why 24dB/o is required when my mains are ported?
None of the above. Well, not much of the above.
A closed box speaker system will usually be rolled off significantly at its "tuned frequency," typically between 3dB (Qtc=.707) and 6dB (Qtc=.5), but it could be more or less. The passive radiator system I designed for my office has an "EBS" tuning, and rolls off throughout its entire "subwoofer range." I compensate for that with bass boost in the plate amp. With the help of people on this BBS, I wrote software to show me what the boosted FR response would look like.
Unless you have sophisticated equipment and knowledge, you probably can't assure that the "upper roll-off matches the mains' lower roll-off." It is not just a matter of matching the Q's. There are phase issues to deal with, and stuff I admittedly don't know anything about. Probably the best solution for a simple country robotics engineer such as myself is to use a 24 dB/octave filter on the bass, to keep it from overlapping with the mains any more than it has to. The 24dB/octave filter will also attenuate he nasty resonances that a lot of subwoofers have in the 800Hz+ range.
Finally, if your mains are ported, you will probably do best by sealing the ports or stuffing rags in them when you use a subwoofer. A ported system has violent phase swings at its tuned frequency that will make it difficult to match up with the sub.
The mains in my office system are MLTL's that go to about 65Hz. With the sub, the system sounds better when I stuff the ports and cross the sub over at 125Hz rather than leaving the ports open and crossing it over at 65Hz.
For my purpose, the subs will only be used for movies and boom music. At this stage I dont think I will be building a hi-fi, even though I wanted it to sound as nice as possible. I dont think I will go as far as stuffing socks because I wont be using subs for 'proper' music.
After much convincing from the members here, I will go for 24dB/o filter. Since my problem is to locate 4-gang pot, Im wondering where to source for it?
Is it ok if 12dB is adjustable, and 12dB is fixed at certain freq to take care of the upper freq response peaks?
After much convincing from the members here, I will go for 24dB/o filter. Since my problem is to locate 4-gang pot, Im wondering where to source for it?
Is it ok if 12dB is adjustable, and 12dB is fixed at certain freq to take care of the upper freq response peaks?
Four gang pots are available from the usual suppliers... mouser, digikey.
I'd suggest looking at some of Marchand's xovers... if you don't have the experience in this sort of thing, his boards work and take the guesswork out of the project. I think he has adjustable 24/db/oct xovers there. You can buy the PCB alone or the complete kit, or built, iirc.
Keep in mind that you cannot just take two 12/db/oct xovers and run them into each other and get a 24db/oct xover that is flat.
Forget about "Linkwitz" transfer function, or any other. You're only going to get that IF and only if you can adjust, tweak and measure your drivers/system and pick the xover point very carefully.
I also use a 24dB/oct xover for my subs, and usually can let the mains run "free" without finding much audible problem in the xover region... of course clever selection of the xover freq helps here.
I would not stuff the ports of most speakers, the results are unpredictable in terms of getting a hump in the lower midbass... ymmv.
If this isn't "hi-fi" then why not just buy a prefab or used subwoofer and not worry too much about all this??
_-_-bear
I'd suggest looking at some of Marchand's xovers... if you don't have the experience in this sort of thing, his boards work and take the guesswork out of the project. I think he has adjustable 24/db/oct xovers there. You can buy the PCB alone or the complete kit, or built, iirc.
Keep in mind that you cannot just take two 12/db/oct xovers and run them into each other and get a 24db/oct xover that is flat.
Forget about "Linkwitz" transfer function, or any other. You're only going to get that IF and only if you can adjust, tweak and measure your drivers/system and pick the xover point very carefully.
I also use a 24dB/oct xover for my subs, and usually can let the mains run "free" without finding much audible problem in the xover region... of course clever selection of the xover freq helps here.
I would not stuff the ports of most speakers, the results are unpredictable in terms of getting a hump in the lower midbass... ymmv.
If this isn't "hi-fi" then why not just buy a prefab or used subwoofer and not worry too much about all this??
_-_-bear
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