How low do does a subwoofer really need to go?

[KEW]

Ok, what are your thoughts on the center channel and using a bookshelf speaker? Or do you solve any lobing effect with a concentric driver like Kef uses?

Obviously, the first consideration is whether the bookshelf in the upright position is too tall. The main reason to have a specific "center" speaker was to provide a low profile speaker to fit under the TV.
After that, it depends on he speaker and how the center is made and how the bookshelf compares with the mains.
If you are using the same bookshelf for all three across the front, it is hard to argue against it!
A traditional MTM center (on its side) presents some compromises. The beauty of the MTM design when it sits vertically is the waves from the mids block the tweeter from reflecting off of the floor and the ceiling. When you lay it on side, you are restricting the horizontal dispersion. Whether this is a problem depends how far off axis your listening positions get.
For towers as your mains, the choice between a center and a bookshelf as center depends on which is most similar to the tower.

 

[William Lemmerhirt]

Obviously, the first consideration is whether the bookshelf in the upright position is too tall. The main reason to have a specific "center" speaker was to provide a low profile speaker to fit under the TV.
After that, it depends on he speaker and how the center is made and how the bookshelf compares with the mains.
If you are using the same bookshelf for all three across the front, it is hard to argue against it!
A traditional MTM center on its presents some compromises. The beauty of the MTM design when it sits vertically is the waves from the mids block the tweeter from reflecting off of the floor and the ceiling. When you lay it on side, you are restricting the horizontal dispersion. Whether this is a problem depends how far off axis your listening positions get.
For towers as your mains, the choice between a center and a bookshelf as center depends on which is most similar to the tower.

Agreed. And as @panteragstk IMO 3 matching towers up front as ideal, the matching BS to the towers usually makes a great alternative to the tower as a center. I’m a believer in timber matching across all speakers when possible but certainly across the front.

 

[yepimonfire]

Agreed. And as @panteragstk IMO 3 matching towers up front as ideal, the matching BS to the towers usually makes a great alternative to the tower as a center. I’m a believer in timber matching across all speakers when possible but certainly across the front.

Also important to consider that so much of the soundtrack is anchored to the center as well. It's stupid to pair big towers with a small bookshelf that can't keep up.

Sent from my LGMP260 using Tapatalk

 

[Steve81]

Or do you solve any lobing effect with a concentric driver like Kef uses?

A traditional MTM center on its presents some compromises.

FWIW, the KEF centers aren't traditional MTM designs, given that the UniQ acts as both the T and the M. From the vertical dispersion measurements I've seen of their towers at Stereophile (like the R700), lobing shouldn't present a problem.

 

[snakeeyes]

Was looking at Kef Q950 vs R500. Either way would you go R200c? Or Q650c? Does q have to be with a q center?

Also like the idea of 3 SVS ultra Books.

Thoughts?

 

[Steve81]

Was looking at Kef Q950 vs R500. Either way would you go R200c? Or Q650c? Does q have to be with a q center?

I'm generally a fan of the R-series over the Q's: better cabinets, better XOs, actual 3-way design vs 2.5 way, etc. The SVS Ultra's are also pretty nice too IME.

 

[snakeeyes]

I'm generally a fan of the R-series over the Q's: better cabinets, better XOs, actual 3-way design vs 2.5 way, etc. The SVS Ultra's are also pretty nice too IME.

I thought the Q950 was better than Q900 possibly and perhaps close to the quality of the R500 but I haven’t heard any of them. Just read some reviews.

The SVS they let you upgrade if you wish during a limited period. So could change to towers later...

 

[shadyJ]

If you are using the same bookshelf for all three across the front, it is hard to argue against it!
A traditional MTM center (on its side) presents some compromises. The beauty of the MTM design when it sits vertically is the waves from the mids block the tweeter from reflecting off of the floor and the ceiling. When you lay it on side, you are restricting the horizontal dispersion. Whether this is a problem depends how far off axis your listening positions get.

The pressure waves from the mids in a upright MTM do not block the tweeter's dispersion; they partially restrict their own dispersion through lobing patterns. They wouldn't interfere much with the tweeter's output except around the crossover point.

FWIW, the KEF centers aren't traditional MTM designs, given that the UniQ acts as both the T and the M. From the vertical dispersion measurements I've seen of their towers at Stereophile (like the R700), lobing shouldn't present a problem.

Agreed, the coaxial midrange/tweeter in the KEF center speakers should do a lot to address problems with conventional MTM center speakers. The closer a center speaker can push the crossover point of the bass drivers to the transition frequency of the room, the better it will be.

 

[KEW]

Also important to consider that so much of the soundtrack is anchored to the center as well. It's stupid to pair big towers with a small bookshelf that can't keep up.

Sent from my LGMP260 using Tapatalk

It certainly depends on the specific bookshelf.
Most bookshelf speakers with a 6" mid-woofer will do well if bass is off-loaded with a 80-100Hz XO (typical for a center channel).
For many speakers, the towers, center, and bookshelf all use the same tweeter and after removing the bass demand, I think it is safe to say the tweeter is normally the weakest link for max SPL, but I am sure there are exceptions!

 

[KEW]

The pressure waves from the mids in a upright MTM do not block the tweeter's dispersion; they partially restrict their own dispersion through lobing patterns. They wouldn't interfere much with the tweeter's output except around the crossover point.

Yeah, I over-simplified what happens (in my understanding as well as what I just stated). I went back to test data on my Focal Twin6 Be (which TLSGuy advised me to never lay on their side) and the issue is not so much specific to the tweeter.
If you compare Fig. 2 - Horizontal off-axis response graph vs Fig. 3 - Vertical off-axis response chart, you see bad things happening starting at the 30 degree off axis measurement!
https://www.focal.com/sites/www.focal.fr/files/shared/catalog/presse/resolution-2.pdf
For this measurement, the speaker was laying on its side, but by standing it up, I reverse these two measurements to get good horizontal off-axis performance (and poor vertical off-axis response, which is not much concern).

Am I correct in attributing this to the MTM layout? I know the Focals are not a traditional MTM layout, as the tweeter is not truly centered between the mid-woofers.

 

[William Lemmerhirt]

Also important to consider that so much of the soundtrack is anchored to the center as well. It's stupid to pair big towers with a small bookshelf that can't keep up.

Sent from my LGMP260 using Tapatalk

That’s fair. I can only say then, a person would have to either go for the tower, or be reasonable with the volume knob.

 

[William Lemmerhirt]

Was looking at Kef Q950 vs R500. Either way would you go R200c? Or Q650c? Does q have to be with a q center?

Also like the idea of 3 SVS ultra Books.

Thoughts?

Fwiw @Pogre first built his system with 3 ultra BS speakers. He really loved that setup. I feel partially responsible for him upgrading to ultra towers which he found to be NOT might and day but still worthy. Iirc...
My 5.2 Setup 2
https://r.tapatalk.com/shareLink?share_fid=59414&share_tid=108072&url=https://forums.audioholics.com/forums/index.php?threads/My-5.2-Setup-2.108072/&share_type=t

 

[shadyJ]

Yeah, I over-simplified what happens (in my understanding as well as what I just stated). I went back to test data on my Focal Twin6 Be (which TLSGuy advised me to never lay on their side) and the issue is not so much specific to the tweeter.
If you compare Fig. 2 - Horizontal off-axis response graph vs Fig. 3 - Vertical off-axis response chart, you see bad things happening starting at the 30 degree off axis measurement!
https://www.focal.com/sites/www.focal.fr/files/shared/catalog/presse/resolution-2.pdf
For this measurement, the speaker was laying on its side, but by standing it up, I reverse these two measurements to get good horizontal off-axis performance (and poor vertical off-axis response, which is not much concern).

Am I correct in attributing this to the MTM layout? I know the Focals are not a traditional MTM layout, as the tweeter is not truly centered between the mid-woofers.

Yes, those measurements show how the two woofers interfere with each other. The off-center tweeter does not effect that. The only thing the off-center tweeter does is improve diffraction at one side at the expense of the other side.

A really good way to handle this is what Atlantic Technology does with their THX center speakers like this one:

See how close those woofers are? When they that close, they can act as a single woofer up to frequencies that do not surpass the wavelength distance of the center-to-center driver spacing. That means they don't lobe up to to treble frequencies, since those are not large woofers. But of course, the tweeter takes over by the time they would start interfering with each other. This is basically the only good way to make a 2-way horizontal MTM that uses a dome tweeter. The Focal speaker doesn't have that kind of spacing or design.

It should be said though, that the audibility of lobing patterns in-room can be overstated depending on the acoustic conditions of the room.

 

[Steve81]

I thought the Q950 was better than Q900 possibly and perhaps close to the quality of the R500 but I haven’t heard any of them. Just read some reviews.

I'd want to see a detailed review of the Q950 before I recommended it over the R series. The Q900 had its flaws in cabinet resonance and the simple XO being insufficient to tame the UniQ midwoofer's breakup:
https://www.stereophile.com/content/kef-q900-loudspeaker-measurements

Those ridges on the UniQ cones of the new series may help with breakup a little, but I have my doubts that it will compare well with the much smaller dedicated midrange unit on the R's coupled with a higher order XO. Stereophile's measurements of the Q350 suggest that the cabinets are still as crappy as ever though.

 

[shadyJ]

I'd want to see a detailed review of the Q950 before I recommended it over the R series. The Q900 had its flaws in cabinet resonance and the simple XO being insufficient to tame the UniQ midwoofer's breakup:
https://www.stereophile.com/content/kef-q900-loudspeaker-measurements

Cabinet resonance has been talked about a lot but I have never seen any study that gauges its audibility. Everything I have ever read about the audibility of cabinet resonance has been anecdotal. While its better to have an inert cabinet, I would say the jury is still out as to its importance.

 

[snakeeyes]

Fwiw @Pogre first built his system with 3 ultra BS speakers. He really loved that setup. I feel partially responsible for him upgrading to ultra towers which he found to be NOT might and day but still worthy. Iirc...
My 5.2 Setup 2
https://r.tapatalk.com/shareLink?share_fid=59414&share_tid=108072&url=https://forums.audioholics.com/forums/index.php?threads/My-5.2-Setup-2.108072/&share_type=t

Ya I bet the dual HSU subs were making the Ultra Books shine just fine. But I don’t know how loud he cranks the movies. I love a good action movie cranked up loud.

 

[William Lemmerhirt]

Ya I bet the dual HSU subs were making the Ultra Books shine just fine. But I don’t know how loud he cranks the movies. I love a good action movie cranked up loud.

He’s more a music guy, but iirc in his movie reports, the volume was definitely up there. He has nothing but love for his “shoes”

 

[Steve81]

Cabinet resonance has been talked about a lot but I have never seen any study that gauges its audibility.

I'd presume that's because it's not a static target. Variances in frequency, amplitude, Q, what panels are resonating, etc. can have an impact on the outcome.

 

[KEW]

Cabinet resonance has been talked about a lot but I have never seen any study that gauges its audibility. Everything I have ever read about the audibility of cabinet resonance has been anecdotal. While its better to have an inert cabinet, I would say the jury is still out as to its importance.

This is curious, I always assumed this was a given! I would think it would be easy enough to measure/verify!

I know the Infinity Primus 363 (maybe 362?) towers I had sounded pretty good until I increased the volume after which the bass would start to get boomy/heavy.
I guess either cabinet or port resonance could have been responsible. Are there other sources of a "non-linear additive" response aside from resonance? What I mean by "non-linear additive" is where increasing the volume by double (on average) results in a significantly larger than double increase at the (resonance) frequency.
Seems like it would be easy to measure FR at one SPL and again at higher (very loud) SPL to determine what frequency it is and if it was around the port tuning.

Actually, I think @Dennis Murphy measured some FR data when he was developing the "Quarter Pounder" speaker prototypes. These speakers had very thin walls, and he added a brace inside the cabinet. IIRC, it was to tame resonance. I would be very surprised if he did not measure the difference in the FR and if it was not audible! Maybe he can comment on whether he has seen measurements to validate concerns over cabinet resonance!

 

[shadyJ]

This is curious, I always assumed this was a given! I would think it would be easy enough to measure/verify!

I know the Infinity Primus 363 (maybe 362?) towers I had sounded pretty good until I increased the volume after which the bass would start to get boomy/heavy.
I guess either cabinet or port resonance could have been responsible. Are there other sources of a "non-linear additive" response aside from resonance? What I mean by "non-linear additive" is where increasing the volume by double (on average) results in a significantly larger than double increase at the (resonance) frequency.
Seems like it would be easy to measure FR at one SPL and again at higher (very loud) SPL to determine what frequency it is and if it was around the port tuning.

Three could be a few things occur that could cause the effect your are talking about. It could be port artifacts, it could be the drivers were being driven into distortion, there could be some kind of room mode that you didn't notice until loud volumes. Cabinet resonance would increase at a linear rate with volume. Something else to remember is that bass gets louder more quickly than midrange frequencies once it is above the hearing threshold.