H frame subwoofers - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 7 Old 01-26-13, 10:02 AM Thread Starter
vinod valiveti
Join Date: Sep 2008
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H frame subwoofers

I am really intrigued by IB subs, more specifically H frame subs. Is there a place where I can find more basic info about these subs & how to build them & proper dimensions of frame? I am looking at perhaps two 15" or 18' driver in separate H frame's for my theater room that's approx 2600 cuft dedicated room. Would these provide enough low end extension for HT use? I am looking at SI HT drivers to use & wondering how much power to use. Do these subs need low pass filter to protect them from over excursion?
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post #2 of 7 Old 01-26-13, 10:44 AM Thread Starter
vinod valiveti
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Re: H frame subwoofers

I an contemplating using either 2 Dayton audio IB 15" driver's or 2 Fi IB 315 or 318 driver's in 2 separate H frame's.
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post #3 of 7 Old 01-26-13, 08:56 PM
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Re: H frame subwoofers

Not sure about H-frames, and I haven't modeled the Dayton's or the Fi 15's, but the Fi IB318's don't need HPF with 300w per driver or less in an IB configuration anyway. They stay under max excursion all the way to zero hz in winISD.

I'm assuming you meant high pass filter for low end cut, not low pass filter which cuts the upper end of the subwoofer's range..
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post #4 of 7 Old 01-27-13, 12:16 AM
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Re: H frame subwoofers

One could drive either series to damage with low frequency but the Fi drivers handle more power with their natural attenuation at ultra low frequency. They have much more Xmax and are more optimized for IB installation than the Daytons.

I'm not familiar with an "H frame" installation however. Could you enlighten me?

In any case, the Fi IB driver is far superior...
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post #5 of 7 Old 01-27-13, 09:39 AM Thread Starter
vinod valiveti
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Re: H frame subwoofers

H frame is essentially an open baffle design with four sides but no front or back with the baffle in the middle of the box with driver firing into a short cavity. I will try to attach some pics.
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post #6 of 7 Old 01-27-13, 02:32 PM
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Keep in mind an H frame or W frame OPEN baffle speaker is very different from an infinite baffle. With an IB the baffle is infinite because it surrounds you. It is all four walls of your room so there is no way for the pressure wave from the back of the speaker to mix with the pressure wave from the front of the speaker.
Many rave about the natural sound of open baffle speakers and I too want to try them at some point. With that said I do not think it is feasible or even possible to create the earth shaking deep extension that everyone speaks if when designing a HT sub.
If the wave from the back of the speaker is allowed to mix with the front wave they cancel each other out. This is why any open baffle speaker looses output when you stand next to it. An IB sub does not have this problem because the two waves never mix. This problem is averted if the path separating the two waves is longer than a certain portion of the wavelength. A quarter of the wave length I believe. In the sub frequencies the wavelengths are many feet long. That ends up with a baffle many feet long, now blocking the reflection of the back wave that makes open baffle so natural sounding. Open baffle proponents will tell you to boost the lower frequencies to make up for it as you would with a small sealed box but it takes so much air movement to make up for the cancelation effect that you quickly run out of cone excursion. Like build something real big and the output down low would be sufficient to play at a level my grandmother would be comfortable with.
Make sure to do a lot of research and fully understand before commuting to a build. I used one source to model the 12"Titanics I had o use as upper subs like 70-120hz and was excited when they modeled to 120db with a 15" square H-frame but I must have done something wrong because all other modeling software put it well short of that. So short I abandoned the project.
I am on my phone now so giving you research sources is difficult but Linkwitz's site has a lot of info on open baffle speakers.

Last edited by gottavtr; 01-29-13 at 07:39 AM.
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post #7 of 7 Old 06-14-13, 12:40 PM
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Re: H frame subwoofers

Try this out. Or here.

As has been said, below a certain frequency determined by your baffle size, you will have a 6dB/octave drop in an OB speaker. This makes it hard to have crushing lows. OTOH, people say they are far less susceptable to room modes and they certainly have less box coloration than any other design (except maybe IB). IMHO, they are good for music but poor for HT.

Driver selection is different than what you'd look for in a sealed or ported box. Typically you aren't looking for super low Fs and I think you want Qts to be between .7 and 1. xmax is always good as you will likely be EQ'ing the low end.

Last edited by BoomieMCT; 06-14-13 at 12:49 PM.
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