Size of manifold (bandpass effect)

[kimtherkelsen]

Hi,
I want to mount two IB15s right above each of my front speakers and I am going to install them in the configuration where they point against each other to cancel out wall vibrations.

Each driver has an area of 830cm2, so I guess the opening should be 1660cm2 to completely avoid the bandpass effect. I have tried using WinISD and some other loudspeaker design software to see how small an opening area I can make without really seing the bandpass effect. The problem is that when I model the system as a bandpass system I do not get the correct results.
What software should I use/which model should I use to generate correct frequency response curves?

/Kim

[ThomasW]

It's a little tricky to do theses models since the bandpass programs don't easily deal with an infinitely large space. The opening has to be overly small for it to be a problem. Look at the "infamous installs" section of the photo gallery to see bandpass examples

What's the joist spacing? If it's a standard 16" studbay, thats plenty wide an opening for a pair of 15"s

[kimtherkelsen]

Hi,
Look at:
therkelsen.info/temp/ib_install.JPG
to see how I am going to install a IB15 pair above each main speaker.

I wanted to place the speakers as close to the opening as possible but I guess I does not matter at all if they are two inches or 6 inches from the opening since the wavelength at for instance a 100Hz is about 3 meters / 9 feet.

Is an opening of 16"x16" not the optimum size for a IB15 pair because it matches the membrane area?

/Kim

[carvernut]

kimtherkelsen said:

Hi,
Look at:
therkelsen.info/temp/ib_install.JPG
to see how I am going to install a IB15 pair above each main speaker.

I wanted to place the speakers as close to the opening as possible but I guess I does not matter at all if they are two inches or 6 inches from the opening since the wavelength at for instance a 100Hz is about 3 meters / 9 feet.

Is an opening of 16"x16" not the optimum size for a IB15 pair because it matches the membrane area?

/Kim

your manifolds will be fine sitting on top of the joists like that... thats how mine is... it rests on top of the joists and comes down into the room and it works great

this is my manifold


and 16" x 16" willl work fine even for 2 15"s

[kimtherkelsen]

Hi,

Yes, it is about the same, I am going to do. There will be a joist on each side of the opening. In the place where the first subwoofer is going to be installed there is 45,5 cm / 18 inches between the joists. There is about 22 inches between the joists where the second subwoofer is going to be installed.

At what frequency are you crossing over to the IB subwoofer? Are you using a third order filter?

[ThomasW]

kimtherkelsen said:

At what frequency are you crossing over to the IB subwoofer? Are you using a third order filter?

Most use the sub-out from a receiver or pre-pro. Usually those are 4th order and around 80Hz.

[carvernut]

kimtherkelsen said:

At what frequency are you crossing over to the IB subwoofer? Are you using a third order filter?

actually it depends, if it's for movies or games yes 80hz... but for music i run it around 120-140hz through the Behringer FBQ6200 Ultragraph
www.samedaymusic.com/product--BEHFBQ6200

then from the FBQ6200 into the DSP1124
www.samedaymusic.com/product--BEHDSP1124P

i use the DSP 1124 to fine tune the lower bass octaves with it's fine tuning up to 1/60th of selectable octaves and frequencies

[rickf325]

carvernut said:

this is my manifold
<<picture deleted >>
and 16" x 16" willl work fine even for 2 15"s

Interesting. I may be looking at your installation wrong, but it appears to me that the opening you show is the opening into the room. If that is the case, it changes things for me in my design!

Let me ask a question directly:

Is it okay for joists/studs to "interrupt" the airflow from a manifold into the room provided the opening remains at least as big as the sum of the Sds?