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Hey Mark,


Please correct me if I am wrong. Is the THX HPF (80Hz and up) not a 12dB/oct slope? Is the design not to work with the acoustic roll-off of THX speakers at 80Hz (typically 12dB/oct for sealed box) to become a 24dB slope?
Don’t know much about THX myself, but according to this site it’s 24 dB. Not saying that’s gospel; it’s just the first thing I hit when I Googled “thx high pass.”


Prof's room (like my own) is small. I am not sure how the difference between 80Hz (HPF'd) and a natural acoustic roll off is so night and day.
I think it probably would be at audible. Anytime you cascade two filters on top of each other, the roll-out slopes combine for a steeper slope. I don’t see how it could be any different if one of the “filters” is acoustic. After all, the speaker can’t “ignore” the effect of the electronic filter.

In any event, actual extension with the speakers set for small vs. large would be easy enough to check with a sine wave at something like 80 Hz or perhaps a bit lower, and an SPL meter. If there is no change in a small vs. large reading, then the filter is having no audible effect.


I wonder if Prof experimented with lowering the crossover from the THX 80Hz default back to 50Hz, rather than bi-pass HPF'ing altogether?
Theoretically, if move the crossover point far enough beyond the speaker’s actual bass output, the effect should be inaudible.

Regards,
Wayne
 

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Discussion Starter #22
I wonder if Prof experimented with lowering the crossover from the THX 80Hz default back to 50Hz, rather than bi-pass HPF'ing altogether?
Mark..I haven't tried dropping the xover down to 50Hz. but I don't understand the reasoning for that..
The front speaker roll-off starts around 75dB..so output is diminishing below that frequency..On the other hand the subs xover setting of 80Hz. leaves a gap between the two..
For a smooth transition of frequencies around the xover point..does there not need to be a reasonable overlap of frequencies between the two speakers like any speaker design?
I realise that the xover is not a brick wall and frequencies from fronts and sub are still within those xover points..
but obviously will have an effect on voices and instruments which fall within that gap..

If the sub xover is lowered further to 50Hz. then surely that gap is further increased..for frequencies in that range..:scratch:
 

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Discussion Starter #23
My Pioneer VSX23TXH has additional frequency shaping capability which I use depending on the mains that I use. I make changes to the EQ while in the MCACC setup particularly in the area of the SW crossover. In addition after MCACC has been completed I make pluses and minuses using the "tone" controls ie: bass treble + plus or - minus 6, settings. The frequency adjustments with the Pioneer receiver are almost limitless . . . . below 63Hz.
I presume you mean above 63Hz., because the 63Hz. adjustment is only operational if you have your speakers set to LARGE..
 

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Mark..I haven't tried dropping the xover down to 50Hz. but I don't understand the reasoning for that..
If you think that running a band limited satellite sounds better full range than HPF at 80Hz, then lowering that crossover means that your not feeding the 20Hz ~ 50Hz into a an LCRs that is clearly not designed to play full range signals. This way you should get the 'benefit' you believe your getting with risking overload to the drivers. All you will be doing is filtering frequencies to the LCR that you can't hear (because the speaker doesn't play them loud enough) anyway.

The front speaker roll-off starts around 75dB..so output is diminishing below that frequency..On the other hand the subs xover setting of 80Hz. leaves a gap between the two..
Not quite. SUB = 20~80. LCRs = 50(75)~20K. If anything, you have a slight overlap, not a hole. The result should be the same as the full range sound without the risk of feeding excessive deep bass to the LCRs.

For a smooth transition of frequencies around the xover point..does there not need to be a reasonable overlap of frequencies between the two speakers like any speaker design?
Not according to THX whose LCRs F3 point is 80Hz at 12dB/oct which is then combined with the 12dB active crossover providing a total 24dB slope. The fact that your speakers extend that bit below is trivial because there are some THX certified speakers that go to 50Hz.
I realise that the xover is not a brick wall and frequencies from fronts and sub are still within those xover points..
but obviously will have an effect on voices and instruments which fall within that gap..
It is not a gap, it a slight overlap, so if anything, it should behave as if the mid bass was pushed slightly.

If the sub xover is lowered further to 50Hz. then surely that gap is further increased..for frequencies in that range..:scratch:
If you lowered the SW LPF to 50Hz, then yes, you could create a "hole" because of the lower limit of the LCRs.

Question is, can you even select different frequencies?
 

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Discussion Starter #26
Not quite. SUB = 20~80. LCRs = 50(75)~20K. If anything, you have a slight overlap, not a hole. The result should be the same as the full range sound without the risk of feeding excessive deep bass to the LCRs.
Doh!..that was my stupid mistake..I was looking at it from the wrong direction..of course there is a slight overlap..:whistling:

It is not a gap, it a slight overlap, so if anything, it should behave as if the mid bass was pushed slightly.
And that push is further enhanced when I raise the xover to 100Hz..

Question is, can you even select different frequencies?
Only in MCACC..
 

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Is this thread name really correct? Should it not be "Setting Speakers Large Or Small - The Great Debate!" ? I am sure there would be many Audyssey owners out there that also argue the point.

I am a fan of BM and always have been. What is funny to me now is the look on a guys face that believed his sales guy when he bought his system. He had an Onkyo THX certified AVR and Krix D'Appolitos for the L and R fronts. The sales guys had set it up for him with the main speakers as large (as the Krix were floor standing) and he wondered why he could only ever turn the volume up to about -10dB without audible cone strain. I suggested that he use his bass management and of course he questioned that because it conflicted with the advice of the sales guy. So I went into his set up menu and set his speakers to small, then played back the same piece of video he'd just showed me. With speakers set to small, I was able to push the volume to 00dB reference with no issue and his jaw hit the ground. And it is purely a case of preventing the drivers in the L and R from having to deal with the huge excursions required to reproduce deep bass. Sending those signals to a purpose built bass speaker (AKA Sub-woofer) did exactly what it was supposed to do - lower distortion and increase dynamic range.
 

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Is this thread name really correct? Should it not be "Setting Speakers Large Or Small - The Great Debate!" ? I am sure there would be many Audyssey owners out there that also argue the point.
That's a good point Mark..I hadn't considered Audyssey owners being in the same situation..and I guess there are a lot more owners of Audyssey systems on this forum than MCACC systems..
I will change the thread title..
 

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Discussion Starter #30

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Yeah that was an interesting read.

Conclusions

In the meantime, you can either buy speakers that fit the crossover in your processor, or in the case of separates, you can add a 2nd order filter between processor and amplifier to give a full-range speaker the roll-off needed to fall in line with the standard THX crossover.
Or you do as I have done and custom build speakers to suit.
 

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Are huge cineplex front speakers also crossed at 80Hz?
In a THX certified cinema (or THX certified dubbing stage) yes. In a non certified cinema, usually not. The whole reason Tom Holman introduced the crossover in the Lucasfilm dubbing stages (now Skywalker Sound) when they were creating the standards was so the mixers could actually hear all of the low bass. The horn loaded speakers of a cinema in a baffle wall tend to roll off about 40Hz. So the question raised was then: How important is that first octave? The answer is very important. They discovered they could hear the low bass on a home HI FI system and not in the dubbing stage which film sound was mixed. Hence Bass management was born.

The system in this photo is impressive at 11.4 which I got to hear last night. It is fully bass managed even though the main speakers are as large as they are.
 

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And by mass managed you mean 80Hz HPF?
I do believe he does use 80Hz and heavily equalizes the bass to be flat - something MCACC can't do. It is interesting that once you take out the 50~60 "boom" in a room, how much deep bass a sound track has. of course, at first, it seems that the 'slam' is missing because he has Eq'ed that out. Flat to 14 using REW apparently. It is physical. It has made his in chair 'shakers' redundant. I had actually assumed they were still connected but he told me after the first demo that they were no longer in service.
 

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The amount of space available to you will determine the type of speakers you can set up within it. If you live in a tiny apartment, you’re not going to buy monstrous speakers that will take up the entire space. You’ll likely go with a much more conservatively sized set. Just remember that they won’t provide the same amount of power as a larger set of speakers would. Larger speakers will usually provide a better experience overall, but make sure you have the room for them.
 
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