Crossover Observation (Question?)

[Jabez Scratch]

For a long time, I set my crossover to 80Hz and turned the frequency cut-off setting on my sub to its highest frequency (or about 150Hz). I switched subs about a month ago and, for some reason, put the sub cut-off to about 80Hz. It sounded good, but not great. Yesterday, I wondered why I had ever lowered the sub cut-off and turned it back to its maximum (or highest frequency) w/ extraordinarily positive results. I changed no other settings.

Here is my observation (question): I know that changing the frequency cut-off on the sub does not technically affect the sound coming from the speakers, only the output of the sub. Yet the speakers sound incredibly fuller, imaging is enhanced dramatically, the surround effect is improved vastly, and the speaker project much better (so much so that I need to turn the volume down from what I normally have it at). How can this be? I'm certainly not complaining, I'm just miffed as to a reaslistic explanation.

[hwatkins]

First - may apologies to all that can state the following better, but here goes:

By their nature - highpass (or lowpass for that matter) filters are only able to 'reduce' the amount of electron flow that creates the frequency. This is best done (at least partially for the harmonics influence) in orders of magnitude. A very gradual slope filtering may be along -6db with a steeper slope being -24db. In all cases a speaker is presented information to produce a frequency above the designated crossover point. What this means is that when filters are made for a smaller slope - quite abit of action above the Xover point is presented to the speaker. Interestingly - the speakers production beyond the Xover point influences the overall sound and is usually a primary consideration in designing a Xover.

So what is happening with your set up? If you implement a filter on the amp and a further filter on the Subwoofer amp you have (in effect) increased the percieved slope of the Xover, so the sub is not producing the same SPL above the 80 hz range as you are used to or that is even what is best.

Most suggest using the bass management on the primary amp or pre and do not filter the woofer at all. I agree

[yromj]

I think Henry said it pretty well. Cross-over are slopes, not brick walls. Many people prefer to set their cross-overs an octave above the lowest frequency of the mains. The reason is just because of what you stated in the original post. It eliminates the "hole" in the frequency response.

There is also another factor which comes into play here. X-overs on subs are notoriously inaccurate. Whenever a sub's cross-over must be used, it is always recommended to set the cross-over frequency with an SPL. (From what I've seen about that method some chicken bones and some of eye of newt could be helpful as well.)

John

[Grand11]

In addition to the above, you should also note that the LFE channels is designated to cover a range from 20hz-120hz. So even if the crossover on the reciever/pre-amp is set to 40hz you're still going to get information well above that being sent to the subwoofer, depending on how it was mixed on the DVD. VERY few DVD tracks have no LFE recorded.

So if you use a highpass setting on your sub, even though it does technically rolloff, by tuning it down you risk cutting out some of the sound information (assuming you don't set LFE+Main). Technically you should only ever be using the crossover on one of the devices, not both, otherwise that risk will always exist.

Use the reciever's if you plan on feeding the sub via LFE, or feed the mains through your sub and use it's highpass. Don't set both.