I don't think your speakers will struggle or get damaged by 60Hz. By definition, sub sonic is below 20Hz. If your speaker isn't capable of handling it, you simply won't hear that lower frequencies. But the speakers won't get damaged.
That's a very good point. More specifically, if the crossover is set at 60Hz, the speakers wont be receiving bass any lower than 60Hz as those signals will be sent to the sub.
60Hz isn't a particularly low frequency though is it?
That still leaves the sub a 40Hz range to handle.
Would you consider that changing my 685s for 684s would be an upgrade (in a system used exclusively for home cinema/ tv)?
Yes and no.
Yes, because obviously the 684's are going to be more capable in that they will handle higher SPL's with less distortion as you'll have two mid/bass drivers sharing the load that one would be dealing with on the 685's.
No, because big floorstanders aren't needed for AV systems. Using a sub to cover up to 80Hz means that only small speakers are needed, in which case, the 685's will do fine. I tend to find that floorstanders (when used in the traditional way of being allowed to utilise their entire useful frequency range before asking the sub to join in) can sound "heavy" and bloated in an AV system, which smothers detail. A standmount or satellite speaker sounds "faster" in comparison.
It would be sensible to assume you'll get the same from a standmount speaker and a floorstander if they're both set to an 80Hz crossover point, although this isn't true. You will get a slightly different sound from the two. The floorstander, due to its larger cabinet volume, will sound a little fuller than the standmount, but again, a fuller sound is smothering detail. The floorstander will also deal with a 60Hz crossover better, as its dual mid/bass drivers and cabinet volume will allow it to reach deeper more effortlessly.
There would be no real need for a floorstander if THX guidelines were being followed. Many people will though, mainly if they prefer their music reproduction via the more conventional 2.0 type speaker system.
David @Frank Harvey Hi-Fi, Coventry
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60Hz isn't particularly low, but remember that the lower the frequency goes, the more cone movement is needed to reproduce that frequency at the same level as the higher bass frequencies (hence why hi-fi speakers can't do sub frequencies). During movies that have a lot of bass, there could be very strong 60Hz energy going on, and played at higher volumes, this could become an issue for some speakers. I've used smaller satellite speakers (which were designed to roll off at 80Hz that have had their mid/bass drivers bottom out when set as they should do, basically because the volume was too high fr them to handle. Setting the crossover point higher at something like 100Hz cures this, so crossover points for speakers are all based on the speaker's capabilities. The size of the speaker isn't really an issue, its what the drive units are capable of.
Thanks David, your posts have helped to improving my understanding.
I've been experimenting with different crossovers and have found that a consistent crossover all round really improves integration too. I had previously experimented with the fronts at 60Hz and 80Hz whilst keeping the rears (B&W DS3s) at 90Hz. Having them all at 80Hz makes the system sound more open and coherent.
I think I will stick with 80Hz all round.
My system is sounding great.
Cheers for your help and advice.
My "floorstanders" (which are all actually on stands or on raised surfaces), both front and surround pairs, are designated as "Large" by the receiver calibration in all my rooms. I have tried setting them as "Small" with a crossover frequency of 80Hz, as the THX guidlines and David recommend. However, I personally prefer the sound, for both 2.0 inputs like most TV and 5.1 Blu-Rays, with the speakers set as Large (with no crossover frequency and thus handling the full range of frequencies), supported by the LFE effects being sent to the subwoofer when playing Blu-Rays. If others prefer to set speakers to "Small" with a crossover frequency of 80Hz when playing Blu-Rays, I'm happy with that, for them. But certainly for 2.0 inputs, like the television, I can't believe that putting that through a full-range speaker is not better than using a smaller speaker, all other things being equal, of course. Last night, for instance, I was quite struck by some of the deep noises that were broadcast during CSI on channel 5 USA, which surely a smaller loudspeaker would not do as well, no?
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