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THX speaker specs (1 Viewer)

Patrick_T

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Ok,

I have browsed several speaker lines that have THX certification. The M&K S150 speakers are -2 db at 77Hz and the Atlantic Technology 450 system mains are -3db at 80Hz. Now, I am not buying a THX system, but the speakers I will be using (M&K S-125's) have the same 3db point as the S-150's...77Hz. Now, it seems the THX speakers have a fairly high -3db point for being crossed over at 80Hz (per THX processor spec). The only thing I can come up with is that THX processors must have a very high order crossover to facilitate the transition from satellite to sub over such a small frequency range. Now, if I will not be using a THX processor (I will be using the outlaw 950) , then will I have problems crossing over at 80Hz, or should I consider moving up to 100 Hz? I'd try for myself but none of the system is purchased and this is basically just something that piqued my curiosity. Thanks.
 

Patrick_T

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The slopes of the high-pass and low-pass (subwoofer-output) filters are determined from the slanting portions of the response graph curves. Knowing whether the rolloff is steep or gradual is of less practical value than knowing the crossover frequency, but these numbers may prove useful in ultra-critical applications. In theory — and when it comes to playing low frequencies with real speakers in real rooms, theoretical considerations must be taken with mountains of salt — an ideal crossover network will have unequal high-pass and low-pass slopes. That’s because the main speakers will naturally roll off at the low end of their frequency range, usually at 12 dB per octave below their –3-dB point, and this rate must be added to the high-pass filter’s rolloff rate, which is often 12 dB per octave also. The result in this case (24 dB per octave) should equal the low-pass rolloff rate at the subwoofer output.

Besides the speaker responses at the crossover frequency, the relative phases of the main-channel and subwoofer outputs have to match for the blend to be as smooth as possible. All these conditions are fulfilled only when the subwoofer is down 6 dB at the crossover frequency and rolling off at 24 dB per octave, and the high-pass filters and main-channel speakers are both down 3 dB at the crossover point and rolling off at 12 dB per octave below that (this is the situation, minus a speaker-response curve, shown in Figure 2). These are also, by no accident, the basic requirements for the bass-management filtering system used in THX-certified products. Lately we’ve seen such behavior in non-THX-certified receivers too — a welcome development.
Which products are implementing the crossover network mentioned above? Does the outlaw 950 do this? Does the Denon AVR-4802 do this even when not in THX mode? Thanks
 

Patrick_T

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Which products are implementing the crossover network mentioned above? Does the outlaw 950 do this? Does the Denon AVR-4802 do this even when not in THX mode? Thanks

Does nobody know if the 4802 uses the 12db/octave high pass filter and 24db/octave low pass filter even when not using the THX mode? I am curious because I am considering M&K S-125's which have very THX like specs, but would like to run without the THX mode engaged....thus the desire for a THX like crossover.
 

Patrick_T

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Maybe I answered my own question, though i would appreciate any verification. The 4802 manual has a section where is goes over setting the crossover. One of the option for setting the crossover frequency is "THX 80 Hz". This seems it will do what I want...the only question is if it really is a THX 80Hz...meaning the slopes match the THX spec. Maybe and email to denon will clear things up.
 

Greg_R

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Patrick,

If they call the crossover "THX 80" then it should meet the spec. If it's just "80" then you may want to call Denon and verify. I have a 5700 and it meets the spec (80Hz, appropriate roll-off).
 

RichardH

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I don't see why they (Denon) would use a different slope when not in THX mode. I'm guessing it's the same whether it's THX or not.
 

Lewis Besze

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I don't see why they (Denon) would use a different slope when not in THX mode. I'm guessing it's the same whether it's THX or not.
Your guess ir right.Denon using the THX mandated crossover section on it's non THX models as well[3802/2802,not sure on the 1801/2 though].

Also many manufacturers using the same slopes as well, including non THX licencees,since those aren't patented by THX,nor they "invented" it but surely "championed" it.
 

Paul_Saul

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Nov 6, 2001
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THX speaker spec have more to them than just

a low frequency role off point. The M&K

S-125s and S-150s are very different speakers.
 

Patrick_T

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Dec 14, 2001
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THX speaker spec have more to them than just

a low frequency role off point. The M&K

S-125s and S-150s are very different speakers.
Yes, this is exactly why I want to run the speakers at the THX crossover settings, but without any additional THX processing done. The S-125, as you said, is not designed for THX...the S-150 is. The only thing is that is seems M&K has designed many of the speakers similarly. The S-150 has multiple tweeters to satisfy dispersion THX spec, whereas the S-125 doesn't....but the S-125 and S-150 share many characteristics in terms of frequency response and crossover slopes. So, as long as their frequency response and crossover designs are similar I would like to employ the THX crossover...as I think they had this philosophy (at least crossover whise) in mind while designing both sets of speakers.
 

Paul_Saul

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Both the S-125 and S-150 are fine systems (I have

owned both of them). To my ear the S-150 has

stronger mid-bass.
 

Lewis Besze

Senior HTF Member
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Jul 28, 1999
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THX speaker spec have more to them than justa low frequency role off point. The M&K

S-125s and S-150s are very different speakers
Yep.

THX mandates vertical dispersion limits on the the main speakers to minimize celling reflections,however this can hamper the speakers music reproduction,to compare to "conventional"[I.E. non THX]designs.However more and more companies overcome on this obsticles,and able to deliver a speaker that THX certified yet exells with music as well.
 

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