H-Frame High Frequency roll-off? - diyAudio
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Old 9th September 2005, 05:14 AM   #1
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Join Date: May 2004
Location: Dallas, TX
Default H-Frame High Frequency roll-off?

I've assembled my h-frames for my bass drivers and noticed that they appear to roll off on the top around 160hz. I can equalize this dip out and it sounds fine, but it takes about 6-9 db of boost from 160 hz to the 250 hz cross over point..

Is this normal?

Is there a way to calculate this roll off based on dimensions?

FYI: The frame is 18" wide, 30" tall and 24" deep....

--Chris
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Old 9th September 2005, 05:07 PM   #2
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Come on Dipole experts, somebody has to know?

--Chris
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Old 9th September 2005, 06:08 PM   #3
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I have never heard of a midbass dip due to an H-frame, sorry.
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Old 9th September 2005, 06:33 PM   #4
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Yeah, I've never heard of anything like it either...

I was wondering if the front/rear cavities could be resonating? Could it be acting like a very short transmission line???

I'm going to try to run them full-range tonight to see if its a "dip" or a true "roll-off" ...

Comments, ideas, would be greatly apreciated...

--Chris
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Old 9th September 2005, 07:39 PM   #5
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Quote:
Originally posted by DIY_newbie
I was wondering if the front/rear cavities could be resonating? Could it be acting like a very short transmission line???
Yep, you get pipe resonance effects. SL covers the theory on his page but he acknowledges that the simplified theory falls short of predicting everything. You just have to measure and EQ it flat. In the Orion, he uses shallower side panels and a lower crossover frequency, moving the problem frequencies out of the passband.
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Old 10th September 2005, 12:15 AM   #6
AJinFLA is offline AJinFLA  United States
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Join Date: Feb 2005
Location: Tampa
Hi Newbie,

how are you measuring this dip? What setup are you using (software,etc.)? Where are you measuring from (distance)? Inside, outside? What drivers are you using? Let's start there.
BTW, does newbie mean new to building dipoles, or just speakers in general? Welcome aboard either case.

cheers,

AJ
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Old 12th September 2005, 05:46 AM   #7
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Join Date: May 2004
Location: Dallas, TX
Just wanted to update everyone:

I dismantled the entire frame, covored all the joints with TONS of gorrila glue and re-assembled. After drying over night I removed all the excess glue which had leaked out of the joints (there was a lot of it everywhere).

Remounted the speakers and now the frame plays flat from 20hz to 250... I'm guessing I had an airleak in one of the joints...

Thanks for all the responses guys

--Chris
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Old 13th September 2005, 04:06 AM   #8
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Location: Puget Sound
If I had seen this before you reglued I would have suggested ensuring that the distance between the H-frame and the wall behind it was equal to the distance between your head (measuring position) and the wall behind it.

Due to the funny layout of my room, this type of placement is difficult as there is a stairwell behind my couch keeping me 5-6 feet from the rear wall. Once I pulled the speakers out to this distance, my ~5dB suckout between 100 and 200Hz disappeared.

Using this placement, my H-framed woofers measured better than +/- 3dB from 25Hz to 300Hz (1/6th octave smoothing / 8kHz input sampling).
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