Impedance rise in hons [message #51712] |
Sat, 12 January 2008 20:34 ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Bob Coley
Messages: 4 Registered: May 2009
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Esquire |
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I'm hoping to build a horn with a large peak right at about 52hz. If I'm successful, would I get a substantial impedance rise at 52hz like I would with a ported box? Is it possible to design a horn with a large peak at 52hz? From my experience most horns are pretty flat, but that's not what I'm looking for. This horn will be striclty for competition. That's why the 52hz is so critical as is knowing the impedance rise. Does anyone know how to calculate the impedance rise?
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Re: Impedance rise in horns [message #51714 is a reply to message #51713] |
Sun, 13 January 2008 18:47 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Bob Coley
Messages: 4 Registered: May 2009
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Esquire |
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![](http://www.wisconsinrapids.com/splhorn.gif)
Hello and thanks for the great reply. I learned a lot from you Wayne. Here's where I'm at with design. I building this enclosure arounds a TC Sounds TC3000. QMS 6.1 Res 4.63 BL 27.1 Mms (grams) 373.00 Cms uN/M 136.00 Sd (m^2) .0820 Vas 127.60 Fs 22.35 Qes .330 Qts .313 nO 4.16E-03 SPL (dB) 88.19 This driver has quad 1.4 ohm voice coils that I plan on wiring for a .35 ohm load. That's why impedance rise is so critical. I want to a play one tone and one tone only (51 hz). I know that if I use 2 1000 watt RMS amps and wire it that way I will likely cause more than just hearing damage if I miss that target frequency. Anyway, below there should be a basic diagram of what I'm looking at building. All the dimensions are outside dimensions. The depth will be 17". I'm planning on using 3/4" MDF, but would open to doubling the outside wall thickness if needed. Some of your thought would be great. Thanks again and have a great day.
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Re: Impedance rise in horns [message #51715 is a reply to message #51714] |
Sun, 13 January 2008 20:23 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18756 Registered: January 2001
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Illuminati (33rd Degree) |
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Some people call that a rear-loaded horn, others call it a scoop. Either name you give it, the front of the speaker radiates directly from the cone and the rear through the pipe. Only bass gets through the pipe but full range is radiated out the front. The front wave and rear wave sum together, so of the overlap range of bass and misbass frequencies, some combine constructively and others cancel. You can model this with Hornresp.You might also try a traditional front-loaded horn and see what you come up with. Since you only need one frequency, you don't have to care as much about mouth area so the horn might not have to be all that big. You'll want the length to support 1/4λ resonance at your target frequency of 51Hz, so I can see why you chose 66". Pipe area and environment offset this some though, so you may find a slightly different length gives you an edge. You can play with that some in Hornresp and afterwards when you make a physical model. Also try different rear chamber volumes to set it for the biggest peak at 51Hz. Making the rear chamber smaller will raise the mechanical resonant frequency of the woofer cone, so you will want to set that for the biggest peak at 51Hz. Too large will increase output below 51Hz and too small will increase output above 51Hz. The throat area and front chamber volume will also have an effect on response, so play with those values. Smaller throats give higher compression ratios but be careful because too much compression will bend or tear your woofer cone at high excursion levels. The front chamber volume will act as a low-pass filter. Finally, the shape of the pipe will have an effect on response so try different taper angles. Since you are only trying to generate a single frequency my gut feeling is a straight pipe will be fine but try tapered pipes as well.
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