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Old 1st May 2006, 10:50 PM   #1
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Default Need help designing a horn

I have a pair of JBL 10" GT1000 woofers that I would like to design a horn for. The horns would be used for music only so sound quality is important. I have a normal sized room and would like extension down in the 30's Hertz region. Would these be good woofers to do it?

Xmax 7.15 mm
Re 3.23 ohms
Le 2.13 mH
Sd 355 cm squared
Bl 11.48 TM
Vas 61.73 liters
Fs 28.64 Hertz
Qts 0.38
Qms 10.20
Qes 0.40
Pe 260 Wrms
SPL 94 dB
Z 4 ohm

I have built several boxes before, both sealed and bass reflex.
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Old 2nd May 2006, 07:24 PM   #2
e-side is offline e-side  Netherlands
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Default Re: Need help designing a horn

Quote:
Originally posted by Nichol1997
I have a pair of JBL 10" GT1000 woofers that I would like to design a horn for. The horns would be used for music only so sound quality is important. I have a normal sized room and would like extension down in the 30's Hertz region.
The horns will be vert large when you want them to go that low. Corner placement will be necessary to get reasonable enclosure dimensions.

Anyway, your woofers could go that low when horn-loaded. I quickly simulated a possible alignment (see attachment). I reduced the mouth area somewhat to keep the size down.
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File Type: gif hornresp3.gif (32.4 KB, 385 views)
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Old 2nd May 2006, 07:28 PM   #3
e-side is offline e-side  Netherlands
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Resulting frequency response:
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File Type: gif hornresp4.gif (24.7 KB, 410 views)
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Old 3rd May 2006, 12:52 AM   #4
tinitus is offline tinitus  Europe
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Maybe you can use this as inspiration....mind you, things can change a lot when drawing in real size on cardboard
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File Type: png corner bass horn.png (10.4 KB, 426 views)
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Old 3rd May 2006, 02:10 AM   #5
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Wow, I did'nt realize it would have to be so big. Thank you for simulating it. Does HornResp also do folded horn designs? I think this might be a better option for me.
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Old 3rd May 2006, 09:08 AM   #6
e-side is offline e-side  Netherlands
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Quote:
Originally posted by Nichol1997
Wow, I did'nt realize it would have to be so big. Thank you for simulating it. Does HornResp also do folded horn designs? I think this might be a better option for me.
If the horn's still too large, you could reduce the mouth area some more. However, if you want 'flat' frequency response you should increase the horn's cutoff (higher F3), because a horn reproducing the 30 Hz region simply needs to be very large.

You could take the calculated values for throat area (St or S1), compression chamber volume (Vb or VRC), the length of the horn etc. as a starting point. Then you could design a folding pattern to fit the horn into a cabinet. It's important to maintain the horn's expansion through the bends.
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Old 3rd May 2006, 09:55 AM   #7
AndrewT is offline AndrewT  Scotland
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Hi Eside,
you chose a 3:1 ratio for Sd:St. Why?
It seemed to result in very low ripple in the passband. Can I assume that is not coincidence?

For 30Hz you have chosen quite a short horn at 2.72m, resulting in -12db @30Hz. Is the bass roll more due to horn length or Vtc?

What is ATC?

Nichol,
just to give you a feel for some numbers expect a speaker volume of at least half a Labhorn (350litres) for mediocre performance and equal to Labhorn (700litres) for adequate performance, for good performance you may need Tannoy Westminster volume (1000litres). Corner loading can and should be used to reduce the Tannoy target. Corner loading will be mandatory for the 350L cabinet and advised for the 700L cabinet. The Labhorn needs 12cabinets in free space, 6cabinets in single boundary space and 3cabinets in 2 boundary space (floor and wall loading). 1.5cabinets are needed for corner loading but a mouth extender will reduce this requirement to 1cabinet.
Corner loading simulates a mouth area equal to 8times the actual mouth area and can approach 16times when the corner is used to continue the expansion of the actual horn flare.
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Old 3rd May 2006, 10:01 AM   #8
hm is offline hm  Europe
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Default 10" Basshorn

what you think about that:
http://www.hm-moreart.de/5.htm
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Old 3rd May 2006, 10:08 AM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
just to confirm some numbers that horn in post8 is 330litres and the mouth area of 0.16sqm cannot possibly do justice to 30Hz music signals. The floor loading from a back loaded horn can only simulate an effective mouth area of 0.32sqm, that's what I mean by mediocre.
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Old 3rd May 2006, 10:15 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi,
a thought just occured, below the horn loading passband the speaker sees a loading of just the rear chamber and starts to perform as a sealed box design at these low frequencies.

If your system could overload the driver in this situation of high drive voltage at below passband frequency then you need to add a high pass filter to protect the driver.

But you may be able to adjust the rear chamber resistance to give the protection you need but at the expense of raising the low frequency cut off frequency.
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