X-Over Bypass.... should I use it?

[geedee]

Hello All,

My "Vintage" sub (a Mirage LF 150) has 2 inputs.... one marked "Input" that the manual says is for Dolby Pro Logic, and the other is "X-Over Bypass" which is supposed to be for Dolby Digital.....

I've had it for years, and for some reason when I first rigged it up I had a Y connector fitted so that both inputs were used... not really sure why!

I now have a new receiver that uses Audyssey and have connected only the XOver Bypass. But, when setting up with Audyssey XT32, it asks me to reduce the volume of the sub to 75db, which I can't do because the output and frequency controls are bypassed.

Would I be better off using the normal input?

Any help appreciated.

 

[Adam]

Hi. If it were me, I'd use the normal input, set the crossover on the sub itself to the highest possible value (which looks like 120 Hz from the manual), and then adjust the gain on the sub itself until it works well with Audyssey.

What speakers are you using? I just want to make sure that 120 Hz isn't too low of a crossover. For most speakers, 80 Hz is a typical value, so I'm guessing that you'll be fine.

 

[geedee]

Thanks Adam, that was quick!
I'm using speakers that came with it... Mirage Omnisats. I no longer have the manual so am not sure what they can handle.... Audyssey has set them up as 100Hz for the fronts and centre, and 90 for the rears (I think...). It also has them as 6 ohm speakers, and I thought they were 8?

This is where I become confused.... if Audyssey is sending anything lower than 100 to the sub, but the sub is set to 120 (the max, as you pointed out) won't that cause a problem?

 

[Adam]

I'll see if I can find the manual for those speakers, and if I do, I'll give you the link.

As long as what you set the dial on the sub to is higher than what you want on the receiver, then you're set. What the 120 on the sub means is that the filter inside of the subwoofer will begin to filter out any frequencies above 120 Hz. So, if the receiver is filtering out frequencies above 100 Hz before it sends a signal to the sub, then the filter in the sub will never get used. (The filters aren't brick walls and there's a slope to the filtering, but your receiver should still be at a lower level at 120 Hz and above than the sub itself would do).

 

[Adam]

Stupid me...there's a number of Omnisats models. You wouldn't happen to know the model number(s), would you?

EDIT: Do you have the Omnisat 6 system? (That link shows the system.)

 

[geedee]

Stupid me...there's a number of Omnisats models. You wouldn't happen to know the model number(s), would you?

EDIT: Do you have the Omnisat 6 system? (That link shows the system.)

Yep, that looks like them!

So, in a nutshell, if I have the frequency on the sub wound to 120, it will accept anything coming in that's lower.... so if the receiver has set things up to send 90 / 100 to the sub, and anything higher to the sats, all will be well? This is preferable to bypassing the crossover in the sub?

 

[Adam]

Yep, that looks like them!

Cool - then here is another article with a frequency response graph on the third page.

So, in a nutshell, if I have the frequency on the sub wound to 120, it will accept anything coming in that's lower.... so if the receiver has set things up to send 90 / 100 to the sub, and anything higher to the sats, all will be well?

You got it!

This is preferable to bypassing the crossover in the sub?

Not preferable, but also not an issue in your case. What you really want is to be able to use the gain (volume) dial on the sub, and it sure seems that in order to do that, you need to also use the crossover on the sub.

 

[geedee]

Many thanks Adam.... it will actually be handy to use the gain control, so I'll set it up like that and see (hear) how it goes!