1 sub, 1000 questions - placement and so on

[Flash]

will addition pr passive radiators help reducing the size?

Yes it will reduce the size. But the biggest advantage is eliminating port noise without sacrificing output

Sealed subs are usually more accurate than ported ones however the trade off is Sound pressure levels.

Ported Subwoofers have the advantage of SPL over accuracy. However problems arise due to cabinet size / Port noise etc

A Subwoofer with Passive radiators gives you the best of both worlds.

 

[anm]

I also need to understand the "2 subs smoothen the response" thing.

=> What is "smoothening of response"?

=> Should the subs be identical for this?

=> will it be better if one plays 80-30 Hz while another 30-15 Hz?

 

[Flash]

I also need to understand the "2 subs smoothen the response" thing.

=> What is "smoothening of response"?

2 subs are always better than 1, purely because of Room modes. every room has a null or peak and by by adding 2 subs in opposing corners of the room helps eliminate the null or peak in the room . So irrespective where you are in the room . the bass will sound even . So basically smoothening the sound in the room irrespective which part of the room you are in . In fact 4 sub would be even better . But that's going over the top.
Adding the second sub does not double the output- the overall output will increase by 3db

=> Should the subs be identical for this?

Preferably identical, reason being no 2 subs perform the same. Some play faster / some slower / some have peaks at 80 hz region etc etc.
When the subs are identical . the subs play the same frequencies at the same speed with the same output. so integration would be seamless.

I have tried 2 using 2 subs from different manufactures in the same room JBLES250PW and Rythmik .... after playing around with tweaking for over 3 days. I still could not get it right . I decided to disconnect the JBL's and connected them in a different room for HT. However if 2 Rythmik's or 2 JBL were placed in the ssame room . integration would be seamless

=> will it be better if one plays 80-30 Hz while another 30-15 Hz?

No - again the point having 2 subs is not to have them play different frequencies. it is to take care of room modes. let both play the same fq range lets say 80hz down.
Again overall increase will be only 3b in output. but you will have a linear response in the room .

 

[anm]

but doesn't PEQ help in smoothening the response?

 

[Flash]

but doesn't PEQ help in smoothening the response?

Yes it does . However using parametric EQ will rarely eliminate a null in a room .Yes it will eliminate a null or peak at your sitting position. However let say if you move away from your listening position your room null would still come into play.

having 2 subs eliminates nulls in the room as well as in the listening position. Parametric EQ will help only at the listening position.

Try this out ... have your sub on and walk around in the room . there will be a point in the room where there is absolutely no bass. that's the null in the room . how do you eliminate the null , by adding a second sub.

The PEQ will not help resolve the null at the particular part of the room.
Let say at your sitting position, you hear that there is absolutely no bass impact at 60hz, using the PEQ, would can increase the gain at 60hz and widen the bandwidth to eliminate this null, same goes for a peak . lets say there is a inherent peak in spl at 80hz and it sounds too pronounced compared to 60 - 70hz. In this case you use the PEQ to reduce the gain at 80hz to match the output of the other freq.

 

[anm]

thanks Flash for the gyaan. Feeling better now
still to decide on 12" gr research paper vs 15" rythmik aluminium. GR research has ready stock, rythmik doesn't have the high power ones.
GR Research goes up to 200 Hz so even with small bookshelves they will integrate better it seems.

 

[Flash]

thanks Flash for the gyaan. Feeling better now
still to decide on 12" gr research paper vs 15" rythmik aluminium. GR research has ready stock, rythmik doesn't have the high power ones.
GR Research goes up to 200 Hz so even with small bookshelves they will integrate better it seems.

Happy to Help !!!!


Yes the Paper cone drivers can go up to 200 hz, Rythmik subs are best suited to be played under 90 hz. and are recommended to play with Bookshelves which atleast have 6.5 inch drivers.

You can't go wrong with either.

 

[Flash]

PS
Your Eminence drivers are pretty good as well. They just require a proper ported cabinet and a plate amp to extract the best out of them

 

[manoj.p]

anm,

Excellent info by Flash. Just to add bit more. Here is some more gyan, especially the part where you can see the graphs about how it smoothens out the bass.
Low Frequency Room Acoustic Optimization

Ultimately it will come to this - One excellent/expensive sub or 4 cheaper subs. some food for thought.

 

[anm]

One more question - how much SPL (assuming flat freq curve) is decent for movie listening - at the listening position?
I sit 12 ft from the front wall. Is 100 db peak at listening position (accounting for loss in SPL due to distance) sufficient? Or peak needs to be higher to have headroom for louder scenes, while average loud listening is 100db? I am assuming high bass is not going to make me deaf, but only unsettle the foundation of the house and throw stuff out of the almirahs.

 

[anm]

lol ..yeah you can't measure by filling water....well air volume in cubic feet ...... same way you measure cubic feet of a room .

No would not need to take the cabinet apart for damping ....it may not be required to damp, if the cabinet is well braced and it surely looks that way

Plate amp ..... - well the plate amp, the reverse side of it usualy has a transformer etc / depending of the topology of the amp .. and without a cut out. there would be practically no way of puttng it ..

However you can try this .. keep the plate amp separate from the Sub cabinet .
Allow the plate amp leads to go in the cab thats it .
Build a small little box for the plate amp and let it rest on the floor besides the sub or on top of the sub .

I have an idea how to measure the volume of an existing cabinet.

Let us assume volume to be 1 cubic feet. And max diameter of the port I can afford on the sub is 2 inches.
Now there are two variables - tuning frequency, and port length. Let us fix a length of 6 inches and put it in the existing cabinet.
Run a frequency sweep and using an SPL meter figure out the actual tuning frequency. I am ASSUMING the SPL will drop drastically below the tuning frequency. So we have
D, Fb, L - we can get the actual volume from the following formula.

Length of port L = ((14630000*(D/2)*(D/2))/((Fb*Fb*Vb*1728)-(1463*(D/2)))) - source - Subwoofer Enclosure Calculators, Fraction to Decimal, Parallel, Series, Port Length and Volume Calculators

Now I recalculate the desired length by putting actual volume, and desired tuning frequency in the above formula.

What say?

 

[manoj.p]

One more question - how much SPL (assuming flat freq curve) is decent for movie listening - at the listening position?
I sit 12 ft from the front wall. Is 100 db peak at listening position (accounting for loss in SPL due to distance) sufficient? Or peak needs to be higher to have headroom for louder scenes, while average loud listening is 100db? I am assuming high bass is not going to make me deaf, but only unsettle the foundation of the house and throw stuff out of the almirahs.

THX recommends 85 db + 20 db headroom at listening position. But its too loud. Many people listen to 75 db in their dedicated theater rooms. I find that tiring too. I listen at 72 db.

But your subs, speakers and amp should be able to do +20db more comfortably. That's the headroom and it shows off how effective the system is when more spl is demanded, like in case explosions etc.

 

[Flash]

anm - port tuning frequency should also be dependent on the driver parameters as well.

Remember in a ported design there is a big possibility of over excursion of the driver and it risks bottoming out. So tune your ports accordingly. Too high port tuning wlll cause a one note bass. Too low and port chuffing will come into play.

 

[anm]

but what about the idea of finding volume. koi to subhaan-allah bolo.

 

[Flash]

but what about the idea of finding volume. koi to subhaan-allah bolo.

Wah Wah Subhaan - Allah ... Subhaan - Allah ...

 

[anm]

so should I make downfiring port or a front firing? I want a chest hitting bass for movies.
Downfiring port - lot of surface area available, so can make one broad port. For fronts, I would be limited to several 1.5 inch dia ports.

What should be the diameter of the ports? Where can I find flared ports?

 

[Flash]

so should I make downfiring port or a front firing? I want a chest hitting bass for movies.
Downfiring port - lot of surface area available, so can make one broad port. For fronts, I would be limited to several 1.5 inch dia ports.

What should be the diameter of the ports? Where can I find flared ports?

Well go with downfiring , it will be less forgiving that a badly constructed front firing design.
You will not hear port noise etc.

Flared ports in India are a little difficult to find.
I have called for some 2.5inch x 4 inch flaredports. If i don't require it will give it to you

 

[anm]

you mean downfiring would be "more" forgiving?

 

[manniraj]

Hi

Sorry to ask my queries in this thread..

I have recently brought the Jamo Sub200 which is a down firing/down ported sub. Currently I have placed this on the floor with 2 carpets. My question is can I place the sub with the carpets on my wooden show case. I have the custom built show case with MDF double thickness for the layer and it is about 12 ft length 2 & 1/2 ft in width. I have placed my tv and other speakers on this. I felt the sub sound was pretty good on this spot but was worried would it create a problem to my wooden showcase/sub.

Thanks

 

[anm]

pls share a photo, only then you will be forgiven for posting in this thread