Cross-over Question

[j_garcia]

You don't want a steeper slope, you DO want a more gradual one for the mains. You want the steeper slope on the low pass so the sub doesn't get up into the lower midrange as much (which is why many receivers have a 12dB/octave HP and a 18dB or 24dB LP). The sub should not be trying to cover what the mains are having filtered; rather it's the opposite, the way I see it - the mains should be more gradually blending with the sub, with a slight overlap even, in the lower midrange to cover what is being filtered from the sub. So by having the 12dB filter come into play above the natural roll off of the speaker, you allow it to blend more seemlessly.

 

[mulester7]

with a slight overlap even

.....there's where we part thoughts, JGarcia....as seamless as possible is best, period, and sure, that's my opinion, based on "down with mud"....the tweeters in my mains rolloff at -60 db....chop-chop......

.....I don't want the sub blending with the woofers of my mains, nor, do I want the woofer of my mains blending with the tweeter....I want sharp, distinct, and defined rolloffs at EVERY opportunity....

 

[j_garcia]

That's a pretty steep slope. That's internal to the speaker via passive x-over though, yes? That's not out of the question at all, depending on the design of the x-over and combination of drivers. I can totally see using a tweeter that handles well into the midrange and cutting it very quickly once it reaches it's usefulness, while also allowing the mid to operate in a narrower band. What type of network is that? I've read that many speakers that are popular with audio tweakers often use the simplest 1st order 6dB/octave x-overs. My 902s use this type of simple x-over and I think they do come close to what they claim - "they work as if they were one driver." The blend is very good, with the speaker being fairly neutral for all metal drivers, but still on the metalic side. That is not to say that a 1st order is the best for every application, but I tend to like to gravitate towards the simplest method that can be used, and the x-over is probably the single most important factor in a speaker after the drivers - part of what Vance Dickason lighlyt referred to as "black arts"

I'm pretty sure that's not what we're talking about in this particular thread though, if I am not mistaken (I hope not, since I am questioning a moderator ), we are talking about using a crossover external to the speakers to create a blend between the main speakers and the sub. It would seem like a simple matter, but it isn't always and room modes can definitely have an effect on how well a given x-over works in a particular setup.

 

[annunaki]

Steeper slopes are good things. They help detract from speaker localization, and aid in more uniform frequency response when using separate speakers for bass and for midrange/high. When using low crossover points such as 60hz/40hz having a steeper slope would be of great benefit. Especially if you were a midbass driver.

Crossover slopes can be somewhat subjective as well. I myself prefer a steeper slope, as I do not want first and second order harmonics possibly coloring the sound.

If using an 80hz crossover point (at 100db w/pink noise) the speaker would still be at 100db at 80hz. However, at 40hz (first harmonic) the speaker is still at 88db (without it's natural rolloff figured in) with a -12db/oct slope. With a 24db/oct slope it would only be at 76db at 40hz.

Now, if our speaker starts rolling off, natually (24db/oct w/ported enclosure), at 60hz, it would be down about 14db or so at 40hz naturally. So, with a 12db/oct slope at 80hz the speaker would be at about -26db down at 40hz or 74db.

With the steeper slope of 24db/oct (at 80hz) we would be down roughly -38db at 40hz or 62db. There would be much less of a chance of hearing any harmonic information (or distortion) using the steeper slope.

As you previously stated this becomes very important with subwoofers as well. I do not see how you could contradict yourself there by saying it is good for subwooofers but not midrange speakers. I am not picking on you, I promise, but that philosiphy just does not make much sense.

Cheers

 

[mulester7]

.....I don't know how I missed these previous two until 20 minutes ago, but I honestly did.....

....JGarcia, my mains are two-way floorstanders....there is no mid element....I said I didn't want the woofer blending with the tweeter....those two "possible phase lapovers", are side by side.....-60 per octave roll-off on the tweeter, and -24 on the woofer, attained by the internally mounted two-way crossover....it makes the two elements speak seamlessly as one voice....hello imaging at decent cranking, and the speakers are rated 300 rms at 8....but they're six ohm, and about to be 3....gone to ride....post of the week to Annunaki......

 

[j_garcia]

The reason I say that is a larger driver in a sub, generally 10" or 12" typically do not reproduce lower midbass as well as a smaller midbass driver of say, 6.5", so rolling off the sub a little sooner and letting the mains be a little more gradual to account for the higher roll off of the sub can make for a clean blend, as long as that overlap isn't too much. I do understand and agree that it is more worth while with a lower x-over point too, I just wanted to present my feelings with respect to the discussion.

The guy that builds my speakers recommended setting them to large, and adjusting the sub manually to blend best with the natural roll off of the mains.

 

[annunaki]

J Garcia,

Your point is well taken. What are your speakers capable to +/-3db on the low end? Have you tried setting them to small with a lower crossover point? I have always have very favorable results in using sharper slopes. Everyone is different though.

 

[mulester7]

The reason I say that is a larger driver in a sub, generally 10" or 12" typically do not reproduce lower midbass as well as a smaller midbass driver of say, 6.5", so rolling off the sub a little sooner and letting the mains be a little more gradual to account for the higher roll off of the sub can make for a clean blend, as long as that overlap isn't too much. I do understand and agree that it is more worth while with a lower x-over point too, I just wanted to present my feelings with respect to the discussion.

The guy that builds my speakers recommended setting them to large, and adjusting the sub manually to blend best with the natural roll off of the mains.

.....JGarcia, a thousand pardons if you read sharpness in any of my responses....sometimes, with only typed words as representation, the correct demeanor doesn't reflect....I just sit here and sip coffee....bravo, you are a thinker, and want to know why.....

.....and JGarcia, QUIT!!, haha, I was out of the bath and dressed to roll the sickle out....just kidding....phase overlap goes against clean....gone......

 

[j_garcia]

Unfortunately, my receiver's lowest x-over option is 80Hz, one of the few things that I might consider worthy for me to upgrade for, but 80Hz seems to work extremely well with the speakers I've chosen. My mains are -3dB at 55Hz, with a very gradual natural roll off. I don't notice a considerable difference between setting them to large or small with 80Hz, except the addition or removal of the sub's added extension.

My former speakers were actually rated at -3dB at 33Hz in room, and did not exhibit as much midrange as my current speakers in the same setup. I guess that's why I upgraded....

It's personal preferences, which is essenitally what audio is all about, hmmm? No two people will react the same way to a particular system/setup. There are a lot of factors that come into play, and may affect each particular installation too, so what works well in one, may not work the same in another.