Help required in Choosing sub & room acoustic

[CnS]

Hi All,


i am about to start build my dedicated Dolby Atmos home theater room in my new ongoing constructed house, the size of the room is L-16.5 ft x B-13ft x H-9ft. i already have following equipment on board with me

Polk audio Rti A7 for front ,
Polk CSi A6 as a center channel ,
Bose dual cube as a surround,
Pioneer VSX 922K AV ( only using surround section of this amp)
Velodyne 15" Sub CHT 15 750 watt RMS,
Marantz MM9000 THX ultra 2 Certified 5 channel power amp rated 170 watt rms/ channel,
Pioneer BDP 170 Bluray Player
LG PA77u 720p Projector

i will upgrade to matching polk surround and dolby atmos amp later ,

i have separate stereo setup of wharfedale diamond 8.4 paired with NAD 319

this is room is for movies only not for music

now i have few queries related to equipment and acoustic

1. i am getting a good deal on JBL Pro Cinema Sub Model 4642A dual 18 inch drivers which will be pair with Crown CL2 amp, my query is this monster sub is a right choice for the room size i have or it is a over kill for this room, as of now am not able to decide. what in my mind is in moderate volume it will give depth to movie sound, following are the specs of subwoofer and crowm amp.

JBL Sub Specs

1200 Watts Continuous Pink Noise, 2400 Watts Continuous Program Power Handling
Usable response to 22 Hz (-10 dB, no EQ), flat to 22 Hz (-3 dB) with External EQ

Rated Impedance 4 ohms
Minimum Impedance 3.2 ohms
Power Handling Capability -
Continuous Pink Noise 1200 Watts
Continuous Program 2400 Watts
Peak Power 4800 Watts
Output Capability -
Axial Sensitivity 50 Hz to 500 Hz; 101 dB, 1W @ 1m
40 Hz to 100 Hz; 100 dB, 1W @ 1m
Net Weight 98 kg (216 lbs.)
Dimensions H x W x D 762 mm x 1219 mm x 610 mm
30 in x 48 in x 24 in

Crown CL2

CL2
*1 kHz Power: refers to max

8 ohm Stereo (per channel)-400W
4 ohm Stereo (per channel)-660W
2 ohm Stereo (per channel)-975W

4 ohm Bridge-Mono 1,950W
8 ohm Bridge-Mono 1,320W

*1 kHz Power: refers to maximum average power in watts
at 1 kHz with 0.5% THD.

CL2
*1 kHz Power: refers to max

2. My 2nd query if Expert FM answer is "yes" for above querry, than how will i can connect AV sub pre out to this crown amp because the connection types are completely different.

3. am not doing complete wall acoustic in my room rather covering main sound reflection points which i learned through available youtube video and room build threads,though i want to know is it important to do acoustic/ defuse area/wall behind screen.

i will ask few more questions as an when.

would request FM to answer my queries asap.

thanks in advance

 

[efernand1]

Hi

Two 18 inch subs would be overkill for the room unless you are intending a DISCO!

12 inch subs work quite well.....all depends on placement and type of subs used....

There are a variety of cables available which you can use....XLR to RCA or Jacks etc.....

I think there is a post somewhere available on the forum where a couple of members have made dedicated rooms and have shared good insights....check forums on Home Theatre

 

[CnS]

Thanks for the prompt response, i already have 15 inch velodyne with me , but i have seen people using pro speakers in there dedicated rooms with good results, if i add this dual 18 inch sub to my room will it give depth and space to overall movie sound

 

[sdurani]

my query is this monster sub is a right choice for the room size i have or it is a over kill for this room

Additional subs are never overkill. Keep in mind that during initial calibration, the combined output of ALL your subs will be set to the same exact volume level as EACH speaker. So, more subs doesn't mean louder bass or overkill for small rooms. Instead, more subs mean less distortion (amp AND driver) and smoother bass.

The more subs you have, the less each subwoofer amp has to work in order for all your subs to hit the same volume level. For example: imagine if you had three more of your same Velodyne sub, then the amp on each one would have to work 1/4 as much as your current subwoofer amp is working to hit the same volume level. Since they'll be loafing along instead of straining, the distortion will be much lower. Plus, you'll have lots of headroom for sudden loud sounds.

Same with the larger JBL drivers. One 18-inch driver has to vibrate with less excursion in order to move the same amount of air as the 15-inch driver in your Velo. Two 18-inch drivers will barely have to vibrate to do the same. Less excursion means less chance of the drivers straining and going into distortion.

Spreading the three subs around the room (rather than stacking them in the same location) will result in smoother bass. There is very little chance that the peaks & dips from each sub will line up perfectly with the peaks & dips from the other subs. Instead, it's more likely they will mis-align and cancel some of each others' peaks & dips, resulting in flatter/smoother bass.

So that's two different ways that adding the JBL subs will improve the bass in your room: lower amp & driver distortion AND fewer/smaller peaks & dips.

 

[CnS]

Thanks Sanjay your response gave me a more courage to go ahead and buy this jbl sub....just to clarify these are not separate sub instead 2 of this 18 inch sub mounted in one box weight around 98kg....in my next post i will share the rough drawing of my room and where i want to put them.