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Old 19th March 2013, 08:14 PM   #1
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Default 18" woofer for H-frame

I was toying with the idea of building a large H-frame dipole woofer using a 18" woofer.
I intend to build the H-frame 75cm deep which would allow a 80hz crossover and intend to have a lower cut off of 20Hz.

I have narrowed driver choice to either the Dayton RSS460HO or Stereo Integrity HT18.
Excursion being the limiting factor the max SPL at the cut off FQ would be 92dB and 97dB respectively.

Both these woofers have a Qts of 0.39 and low FS and large Xmax, they both have fairly open baskets which I am led to believe is important when used open baffle/dipole due to reduce chuffing.

Anyone know if these drivers are any good?

Last edited by rich31td; 19th March 2013 at 08:24 PM. Reason: Didn't finish typing!
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Old 19th March 2013, 10:48 PM   #2
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"Excursion being the limiting factor the max SPL at the cut off FQ (of 20 Hz) would be 92dB and 97dB respectively."

92dB and 97dB at 20 Hz is equivalent to a sound level of 41 dB and 52 dB at 1000Hz respectively, a good deal less than the sound of a whisper at one meter.

I don't know of any sub driver that is any good when used in an enclosure where it can't be heard.
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Old 20th March 2013, 12:38 AM   #3
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I'm not convinced this is a good idea.

Calling a H-frame a subwoofer is like calling a 4" driver in a 100Hz-tuned boombox a subwoofer.
Sure, you can force it to do LF, but its gonna distort like crazy just trying.

Use the same 18" driver, put it in a nice sealed or ported box, and get the performance you ought to from it.

Chris
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Old 20th March 2013, 10:49 AM   #4
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Perhaps I posted this thread in the wrong section then, they are going to be the woofers in an open baffle speaker I am building, rather than two 10" woofers in H/W/M-frames per side like an Orion, LX521 or Nao Note, I had the idea of one large 18" woofer in H-frame per side.

The two 10" have a total Vd of 880cm3 whereas the SI-HT18 has around 2651cm3, that coupled with a deeper H-frame should give a vast improvement.

I was after any personal experience with these drivers more than anything.

Last edited by rich31td; 20th March 2013 at 10:53 AM.
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Old 20th March 2013, 02:33 PM   #5
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by rich31td View Post
Perhaps I posted this thread in the wrong section then, they are going to be the woofers in an open baffle speaker I am building, rather than two 10" woofers in H/W/M-frames per side like an Orion, LX521 or Nao Note, I had the idea of one large 18" woofer in H-frame per side.

The two 10" have a total Vd of 880cm3 whereas the SI-HT18 has around 2651cm3, that coupled with a deeper H-frame should give a vast improvement.

I was after any personal experience with these drivers more than anything.
Hi,

You are right..If you place a H-frame (~53.5 x 53.5 x 75 cm^3) using the SI-HT18 close to a side-wall and ~5 ft from a corner: Max SPL would be ^122dB if you add an series resistor(1.7Ohm) to push up the Qts to about 0.7 and the passband BW would be from ~32Hz to ~120Hz if a 100Hz LR4 LPF at is added and the entire system is excursion protected if adding a 12 dB/octave HPF at ~10 Hz.

What size is the open baffle and which OB drivers do you intend to use?

b
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Old 20th March 2013, 02:48 PM   #6
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Quote:
Originally Posted by chris661 View Post
Use the same 18" driver, put it in a nice sealed or ported box, and get the performance you ought to from it.
Big cones act very good as microphones, superimposing what the cone picks up
from the pressure inside the box ( intermodulation )
Maybe it's not a good idea ( for home sized boxes )
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Old 20th March 2013, 04:31 PM   #7
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Originally Posted by picowallspeaker View Post
Big cones act very good as microphones, superimposing what the cone picks up
from the pressure inside the box ( intermodulation )
Microphones, regardless of diaphragm size are normally hooked up to mixers, subs are normally used as loudspeakers and are hooked up to amplifiers.

Amplifiers have damping factors sufficient to reduce intermodulation distortion to a level that is quite low on loudspeakers with decent Bl.
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Old 20th March 2013, 04:37 PM   #8
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Indeed, it's quite low
Just for the report ...
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