2x BK Double Gems vs 1 BK P12-300SB-PR??

Jester1066

Active Member
Hi all looking for some advice/thoughts. I currently own a P12-300SB-PR - great sub too.... But, following a room re-gig, I'm debating whether to sell the P12 & get 2x Double Gems. These would be placed roughly at the 1/4 wall mark on the front wall (see pic)....

Now I've spoken (at length! 🤣😉) to Tom @ BK regarding whether this would be considered an "Upgrade" on the single P12... He believed it would be. Although he did say I'll lose some bottom end grunt the the Passive Radiator in the P12 provides, but this would essentially be compensated somewhat as I'd effectively be running "quad subs"!....

Anyone done this upgrade - or run 2x Double Gems? What do they sound like? I'll add that my usage is 50/50 music to movies. And I plan.on high level connecting all subs to my Audiolab 6000A, while using the low level to the AVR.

What I don't want to do is sell the P12 and regret it.

Cheers all
 

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MI55ION

Distinguished Member
What do you feel is "missing": low end grunt, spl, even response, speed?

Their specs seem a little vague but they both claim: "In your front room -3dB lower than 20Hz !!!"

Depending on the answer you provide it would seem to be more a lateral move than an "upgrade".

If you're happy with the performance of your current sub I'd just add a second one.
 

Gasp3621

Distinguished Member
@Digriz runs dual double Gems in music system! See post #14:

 

Jester1066

Active Member
Depending on the answer you provide it would seem to be more a lateral move than an "upgrade".
This was my initial thought.

If you're happy with the performance of your current sub I'd just add a second one.
Space "may" proof to be the stumbling block here. I say may, as I'm getting a custom AV Cabinet built, so maybe able to tweak the design a little.

What do you feel is "missing": low end grunt, spl, even response, speed?
Definitely not low end grunt, but have been told that as the Gem's are sealed subs (P12 is ported), they have more speed than their ported cousins - which is "better" as far as music is concerned.
 

Jester1066

Active Member
@Digriz runs dual double Gems in music system! See post #14:

Thanks @Gasp3621

It was actually this post that got me thinking about the change to double gems! 😂😂
 

MI55ION

Distinguished Member
This was my initial thought.


Space "may" proof to be the stumbling block here. I say may, as I'm getting a custom AV Cabinet built, so maybe able to tweak the design a little.


Definitely not low end grunt, but have been told that as the Gem's are sealed subs (P12 is ported), they have more speed than their ported cousins - which is "better" as far as music is concerned.
I was under the impression the P12 is a passive radiator design, not ported?

If it's speed you're after I don't think the difference between these two subs would warrant the changeover although as Tom suggested there may be a marginal advantage with the sealed design.

Have you dialed in the sub properly with room EQ, more specifically for the bass region as this often has a far greater effect on your perception of speed and timing.

You mention above that you're using high level for music. This defeats any room/bass EQ you might have in the AVR so you are sacrificing better bottom end response in favor of higher fidelity bypassing the AVR and using a dedicated stereo amp.
 

Gasp3621

Distinguished Member
Not really ported, but these two are not far from each other.

REL uses passive radiator design in their T7i and T9i which are clearly toward hifi systems and reportedly they sound fantastic! I think there is other brands aswell which suite great on music with PR design.

There is no reviews or measurements for Double Gem which is bit shame. Have you downloaded REW and tried the Room Simulator? It´s fairly easy to use and you could get some idea what kind of response you get with that placement you planned for dual subwoofers. You just add room dimensions there and the listener. Assuming you have fairly normal shaped room. Such a great tool to give some basic idea. :)
 

Jester1066

Active Member
I was under the impression the P12 is a passive radiator design, not ported?
It was Tom who said the P12 was ported & gem was sealed! Lol

Have you dialed in the sub properly with room EQ, more specifically for the bass region as this often has a far greater effect on your perception of speed and timing.
Nope as I've not actually got my speakers set up at present, as I'm waiting on the cabinet build and finishing some room decorating etc. But I did have the Sub EQ using Audrssey to the AVR before. I haven't connected the sub to high level yet at all, but plan to once the rooms finished etc.


You mention above that you're using high level for music. This defeats any room/bass EQ you might have in the AVR so you are sacrificing better bottom end response in favor of higher fidelity bypassing the AVR and using a dedicated stereo amp.
All BK subs allow you to simultaneously connect both a high level (to stereo amp) & low level (to AVR) feed. There are seperate high & low level controls on the subs too, so setting one has no effect on the other.

The Audiolab 6000A has HT Bypass. This is connected to my x4500h AVR front L&R pre-outs. My stereo speakers are connected to the Audiolab, as will be any (sub(s)) via high level. Any stereo (mainly music) will go directly through the Audiolab. I'll then duel connect the subs to the X4500H's duel sub outputs at low level via RCA. This will then be used for movies and in my 5.1.4 setup.

Hope that explains my intention and end setup goals
 

Jester1066

Active Member
REL uses passive radiator design in their T7i and T9i which are clearly toward hifi systems and reportedly they sound fantastic! I think there is other brands aswell which suite great on music with PR design.
I'll definitely look at these subs too. I'm a very demanding consumer & guess I'm looking for subs that can handle both music & movies well with no trade off!
There is no reviews or measurements for Double Gem which is bit shame. Have you downloaded REW and tried the Room Simulator? It´s fairly easy to use and you could get some idea what kind of response you get with that placement you planned for dual subwoofers. You just add room dimensions there and the listener. Assuming you have fairly normal shaped room. Such a great tool to give some basic idea. :)
Didn't know REW had a Room Simulator! Will definitely try it. I Was gonna REW the room so to speak, but was put off by potentially having to buy an expensive mic for a possible one off use! So the simulation sounds ideal 👍🏼
 

MI55ION

Distinguished Member
All BK subs allow you to simultaneously connect both a high level (to stereo amp) & low level (to AVR) feed. There are seperate high & low level controls on the subs too, so setting one has no effect on the other.

The Audiolab 6000A has HT Bypass. This is connected to my x4500h AVR front L&R pre-outs. My stereo speakers are connected to the Audiolab, as will be any (sub(s)) via high level. Any stereo (mainly music) will go directly through the Audiolab. I'll then duel connect the subs to the X4500H's duel sub outputs at low level via RCA. This will then be used for movies and in my 5.1.4 setup.

Hope that explains my intention and end setup goals
I understand how the high and low level connections work in your setup, I had similar some time ago.

What I'm trying to explain is that in this setup, when listening to music via the stereo amp, your subs will be active without the benefit of bass eq. Usually this means a more erratic low end response with dominating room modes that'll drown out much of the subtleties in the bass region. This often has a negative effect on what you hear in the full audio spectrum.

As Gasp3621 suggested above see if you can familiarise yourself with REW as it'll help create a better picture of what's happening particularly in the lower end.
 

Gasp3621

Distinguished Member
Yeah mate download the REW. It will look like this. Fairly easy to use. Left side is your room dimensions and if sealed/closed room. Then you can move the listener to exact spot where your head is at MLP, measure it. Then add Sub 1 and Sub1 put them sealed and the LF -3db figure. That`s about it. You can move the subs front to back and it shows you how much it is from side/front/rear wall so quite nice.





Personally i wouldn´t consider the small T-serie for movie use, unless it´s lot less important than music listening and no special crawings for strong low end.
 

TB Rich

Active Member
Talking music here, as you're running your mains full range and then high-level to sub, as Mi55on says you'll get no bass eq, and potentially issues therefore with phase cancelations etc unless you spend time setting it all up, ideally with a mic and REW.

I use an AVR+HT-bypass, and have come up with a great way to share a sub.
Use an RCA switch (Schiit Sys), AVR/LFE goes to Input A, pre-outs from your stereo amp go to Input B. This avoids any sort of double bass when using Input A for movies, and of course the AVR uses all it's usual EQ etc.
But the real advantage is you can slide a miniDSP in on the input B side, so you can then get all the PEQ, gain, crossover, timing and therefore accurate control for good integration into your music. You can also sport a few configs based on how much bass you want.

Also means you don't have to mess with the back of the sub(s) at all, and you just simply have to remember to select either Input A or Input B on the Sys based on what you're doing (Movie or Music).
 

Jester1066

Active Member
Talking music here, as you're running your mains full range and then high-level to sub, as Mi55on says you'll get no bass eq, and potentially issues therefore with phase cancelations etc unless you spend time setting it all up, ideally with a mic and REW.

I use an AVR+HT-bypass, and have come up with a great way to share a sub.
Use an RCA switch (Schiit Sys), AVR/LFE goes to Input A, pre-outs from your stereo amp go to Input B. This avoids any sort of double bass when using Input A for movies, and of course the AVR uses all it's usual EQ etc.
But the real advantage is you can slide a miniDSP in on the input B side, so you can then get all the PEQ, gain, crossover, timing and therefore accurate control for good integration into your music. You can also sport a few configs based on how much bass you want.

Also means you don't have to mess with the back of the sub(s) at all, and you just simply have to remember to select either Input A or Input B on the Sys based on what you're doing (Movie or Music).
I assume if I were wanting to connect 2 subs to the RCA switch, I could get a RCA splitter cable?
 

TB Rich

Active Member
I assume if I were wanting to connect 2 subs to the RCA switch, I could get a RCA splitter cable?
If you want the subs playing mono, yep, and you would on the stereo side ('B') use the miniDSP to sum it's output to mono too. Would be like this, purple being mono:
Screenshot 2020-09-24 at 16.43.29.png



However you can do stereo bass if you swap the position of the Sys and miniDSP.
I actually do it this way myself, but you have an extra step in that you need to also switch configs on the miniDSP based on what you're doing. Essentially run the miniDSP in a blank config to allow the AVR to do it's thing (although nothing stopping you from doing PEQ on the miniDSP still - and I have to because my AVR is old and has no room correction).

So,
Movie use = Sys in position A, Config 1/2 on miniDSP (1 could be blank, 2 could be bass boost)
Music use = Sys in position B, Config 3/4 on miniDSP (again depending how much bass you want).

I've also bought the WiFi module for the miniDSP so I can switch configs via the iOS/Android app on the fly. Which means I personally find it very easy to just click an input on a switch, and choose a respective DSP mode - but if you have family I can fully appreciate that sort of setup would be confusing and likely piss them off!!! :D

Screenshot 2020-09-24 at 16.40.51.png


The AVR you'd still want mono I guess and you just sum the input to both subs with in the miniDSP (just a bit messy to try and depict that on the diag).
 

Jester1066

Active Member
If you want the subs playing mono, yep, and you would on the stereo side ('B') use the miniDSP to sum it's output to mono too. Would be like this, purple being mono:
View attachment 1371366


However you can do stereo bass if you swap the position of the Sys and miniDSP.
I actually do it this way myself, but you have an extra step in that you need to also switch configs on the miniDSP based on what you're doing. Essentially run the miniDSP in a blank config to allow the AVR to do it's thing (although nothing stopping you from doing PEQ on the miniDSP still - and I have to because my AVR is old and has no room correction).

So,
Movie use = Sys in position A, Config 1/2 on miniDSP (1 could be blank, 2 could be bass boost)
Music use = Sys in position B, Config 3/4 on miniDSP (again depending how much bass you want).

I've also bought the WiFi module for the miniDSP so I can switch configs via the iOS/Android app on the fly. Which means I personally find it very easy to just click an input on a switch, and choose a respective DSP mode - but if you have family I can fully appreciate that sort of setup would be confusing and likely piss them off!!! :D

View attachment 1371370

The AVR you'd still want mono I guess and you just sum the input to both subs with in the miniDSP (just a bit messy to try and depict that on the diag).
Can I ask what DSP do you use?
 

TB Rich

Active Member
Depending on how you have the subs positioned, you may actually wan't them mono in all cases anyway.
I've seen it mentioned (including the Arendal setup manual) that unless you have the subs setup exactly like an equidistant stereo pair and next to the mains, then run them mono:

Screenshot 2020-09-24 at 17.07.05.png


That above is how mine is, L/R summed in the DSP and out to 2 subs..... well, it will be 2 subs when my 2nd XXLS400 turns up which I'm assuming will be next week now.
But they will both be off to the left side of my mains and so mono avoids a lot of potential timing issues I'm told.

Can I ask what DSP do you use?
miniDSP 2x4 HD
 

Jester1066

Active Member
@TB Rich

Thanks for the help/advice... I'm hoping my subs will be equidistant as you describe. On this basis if I were to go down the Switch/DSP route, I'd likely go mono all round.

Think I'll have a play with the REW Room simulator too as these results will tell me if it's worth going duel sub in terms of room placement etc.

Where are (will) your 2 subs be in terms of placement? I'm hoping mine can go approx 1/4 placement on front wall see pic on my 1st post - assuming this helps with base response etc.

Edit: just realised that I'd actually want to run them in stereo based on them being equidistant.
 
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TB Rich

Active Member
Ha after typing that I've literally just had the DPD notification to say 2nd BK arrives tomorrow :D

Thanks for the help/advice... I'm hoping my subs will be equidistant as you describe. On this basis if I were to go down the Switch/DSP route, I'd likely go mono all round.
Where are (will) your 2 subs be in terms of placement? I'm hoping mine can go approx 1/4 placement on front wall see pic on my 1st post - assuming this helps with base response etc
Can likely run stereo just fine then but you can experiment with mono or stereo as it's an easy input/output mapping in the config off the miniDSP - you won't have to touch the back of the subs or touch the cabling to do so.

I've got them just off to the left of main bit like this, so best to run them mono:
Screenshot 2020-09-24 at 18.00.29.png


I can create enough room for the 2nd one in the right corner for stereo sub usage, and moving the R speaker out it's response is fine, But, to get the left to positionally match then it really ruins the response - and I just couldn't get something I has happy with other than the position they are in now.

In all honesty I might sell a sub, but I needed a colour change hence ordering a 2nd. In theory I'll get 6dB of boost and I have a nice response for a single sub anyway. See how it pans out! But more is always more when it comes to bass :D

Think I'll have a play with the REW Room simulator too as these results will tell me if it's worth going duel sub in terms of room placement etc.
It's normally accurate enough I believe but doesn't work too well in my room, I have stairs that cut in to the room and must be throwing the results. So YMMV but most people seem to think it's worth doing, especially in a classic square or rectangular room.
 

Jester1066

Active Member
It's normally accurate enough I believe but doesn't work too well in my room, I have stairs that cut in to the room and must be throwing the results. So YMMV but most people seem to think it's worth doing, especially in a classic square or rectangular room.
Mine is indeed a classic rectangular room. Time to send the OH out with the youngest, drag my laptop out and have a play with REW me thinks! 😁
 

TB Rich

Active Member
Never a bad plan!! :laugh:
 

Jester1066

Active Member
This is a quick knock up of how I could layout a dual sub system using 2x P12's....

My only concern is that the l&r speakers are close to the centre speaker. There's approx 4ft between the L&R speaker. With the 2 P12's placed under the 2 tall cabinets. It's a very crude drawing, but what are peoples thoughts? The MLP Is on the wall directly opposite to this.

Edit: the left hand tall cabinet represents a fish-tank that the OH says "cannot be moved"...
If Muhammed can't move the tank, he shall build his AV gear into/around it 🤣🤣

Oh and anything in Green is obviously a speaker. I plan on the LCR being Monitor Audio Silver 100's (on atacama Moseco 6 stands) & a Silver C350 Centre (raised on a custom built stand).

@MI55ION - This is how I could accommodate 2x P12's - what your thoughts on this layout?
 

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Conrad.

Well-known Member
For the minidsp connection, why wouldn't you just use a 2-to-1 RCA cable from the stereo amp, and a sub cable from the AVR, both into the minidsp. Then use config and routings in the minidsp to push either input to both outputs? Removes a device from the chain.

Also, I found this very funny:

Was gonna REW the room so to speak, but was put off by potentially having to buy an expensive mic for a possible one off use!
One off. Good one 🤣
 

Jester1066

Active Member
For the minidsp connection, why wouldn't you just use a 2-to-1 RCA cable from the stereo amp, and a sub cable from the AVR, both into the minidsp. Then use config and routings in the minidsp to push either input to both outputs? Removes a device from the chain.

Also, I found this very funny:



One off. Good one 🤣
I assumed (clearly wrongly! 🤣😄), that once you'd "REW'd" a room, unless you changed your room layout, speaker positions etc, there would be no further need to REW again.

Re MiniDSP - I also think this is possible, but wasn't sure due to my limited knowledge on the technology.
 

Conrad.

Well-known Member
The minidsp is a great addition. You can use it just as routing, but the real value comes with a mic and REW. It's an investment, sure, but it might be enough for you to not to need replacing your sub? No promises, but poor bass is often the result of EQ and integration.

Something to think about if you want other options.
 

Jester1066

Active Member
For the minidsp connection, why wouldn't you just use a 2-to-1 RCA cable from the stereo amp, and a sub cable from the AVR, both into the minidsp. Then use config and routings in the minidsp to push either input to both outputs? Removes a device from the chain.
So the connection for running a dual sub setup for both home cinema & stereo use would in my situation be as follows:

2-1 RCA Cable - From Audiolab 6000A Pre-out ➡ "In 1" on miniDSP
Single RCA Cable - From X4500H Sub Out 1 ➡ "In 2" on miniDSP

Then an RCA from each Sub to "Out 1 & 2" on MiniDSP
Then configure the DSP to push either input to both outputs like you said!

Have I got that right?

Oh and looks like I'm saving up for that mic investment 😂😉
 

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