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diyAudio Member

Join Date: Jun 2007
Quote:
 Originally Posted by dirkwright Is that because he made a mistake in the spreadsheet? The mouth areas are the same, the throat areas are close, but only the length is different. I used the system designer tool in Hornresp to build the horn there.
Hi dirkwright,

It seems that there may be an error in the spreadsheet methodology.

For Placement = 4, the mouth area is divided by 4 as expected, but the new length is calculated assuming that the truncated mouth is fully formed, which is not really the case. This questionable assumption means that the profile cutoff frequency becomes 120 hertz rather than the required 60 hertz - which explains why the spreadsheet horn is shorter than it should be.

Fc = 60 Hz
Placement = 4
At = 178.8 sq cm
Am = 6539.5 sq cm
Length = 68.43 cm

Hornresp:

S1 = 178.80 sq cm
S2 = 6539.49 sq cm
L12 = 68.42 cm
F12 = 120 hertz

Note that when Fc is changed to 120 hertz in Hornresp, the results become the same - allowing for the slight differences in mouth area and length due to rounding, as mentioned previously.

Kind regards,

David
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www.hornresp.net

diyAudio Member

Join Date: May 2011
Location: Virginia
Quote:
 Originally Posted by David McBean Hi dirkwright, Have a look at the formula in the spreadsheet used to calculate Rm (mouth radius). The velocity of sound value used here is 340 m/sec. Change this to 344 m/sec and you will now get effectively the same results as those calculated by Hornresp - allowing for the very slight differences in mouth area and length due to rounding. Spreadsheet: Fc = 60 Hz Placement = 1 At = 178.8 sq cm Am = 26158.0 sq cm Length = 199.63 cm Hornresp: S1 = 178.80 sq cm S2 = 26157.99 sq cm L12 = 199.62 cm F12 = 60 hertz Kind regards, David
Holy Crap!!!!! Thank you thank you thank you!!!!

Mark Kravchenko
diyAudio Member

Join Date: Jan 2002
Quote:
THem who make no things make no mistakes!
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Mark
www.kravchenko-audio.com

diyAudio Member

Join Date: May 2011
Location: Virginia
Quote:
 Originally Posted by David McBean Hi dirkwright, It seems that there may be an error in the spreadsheet methodology. For Placement = 4, the mouth area is divided by 4 as expected, but the new length is calculated assuming that the truncated mouth is fully formed, which is not really the case. This questionable assumption means that the profile cutoff frequency becomes 120 hertz rather than the required 60 hertz - which explains why the spreadsheet horn is shorter than it should be. Spreadsheet: Fc = 60 Hz Placement = 4 At = 178.8 sq cm Am = 6539.5 sq cm Length = 68.43 cm Hornresp: S1 = 178.80 sq cm S2 = 6539.49 sq cm L12 = 68.42 cm F12 = 120 hertz Note that when Fc is changed to 120 hertz in Hornresp, the results become the same - allowing for the slight differences in mouth area and length due to rounding, as mentioned previously. Kind regards, David
Thanks again David! You've been very helpful. I still can't believe this software is free!

diyAudio Member

Join Date: Jun 2007
Quote:
 Originally Posted by dirkwright Thanks again David! You've been very helpful.
Hi dirkwright,

You're welcome :-).

It is interesting how the (corrected) spreadsheet assumes that a tractrix horn having S1 = 178.80, S2 = 6539.49 and L12 = 68.42 radiating into 1Pi space will have a performance comparable to a tractrix horn having S1 = 178.80, S2 = 26157.99 and L12 = 199.62 radiating into 4Pi space.

As can be seen from the attachment, a quick check in Hornresp shows that this is clearly not the case - the black trace shows the response for the 1Pi horn and the gray trace shows the response for the 4Pi horn.

Kind regards,

David
Attached Images
 Compare.png (25.5 KB, 130 views)
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www.hornresp.net

 28th August 2011, 02:34 PM #2186 diyAudio Member     Join Date: May 2011 Location: Virginia Thanks again for your analysis David. I'm very impressed with your enthusiasm. I just have one question about your program. Why is it not possible to increase the window size? I assume this is intentional, but don't know why. Once I get some other projects out of the way, I'll be building a 1/2 size 100Hz hyp-ex straight horn using data from your program. You've made a huge contribution to horn loudspeaker design. You should be very proud of your accomplishment.
diyAudio Member

Join Date: May 2011
Location: Virginia
Does anyone know what causes this ringing in the impulse response? How do I get rid of it? Suppressing rear chamber resonance doesn't take it away. Thanks.
Attached Images
 12PE32 100Hz impulse.JPG (32.0 KB, 112 views)

Last edited by dirkwright; 28th August 2011 at 02:47 PM.

 28th August 2011, 08:49 PM #2188 diyAudio Member   Join Date: Jun 2004 Location: Indiana I was modeling a TL enclosure and wanted to mess around with multiple drivers so I changed the number of drivers but nothing changed. In the same size line I got the same response and the same max SPL. Increasing the size of the line (cross section) changed the response in the same way as for a single driver. What am I neglecting? I wanted to model 8 10" drivers connected in series (there is a reason for this). I would think "n" drivers would require a cross section "n" times that of a single driver no? __________________ Generic Signature
 28th August 2011, 09:38 PM #2189 diyAudio Member     Join Date: Jun 2003 Location: Chamblee, Ga. Hmm, when I double up drivers it dramatically changes the response, turning a highly under-damped TL to over-damped and increasing its Xmax limited BW +6 dB at its minimum frequency just as it should. Correct, to maintain the same response the cab's net Vb must increase by however many drivers there are, so if one driver requires 100 cm^2, then eight require 800 cm^2, though you have to manually change the values in the appropriate fields as it won't auto add like some programs. GM __________________ Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
 28th August 2011, 10:27 PM #2190 diyAudio Member   Join Date: Jun 2004 Location: Indiana Yes, that is how I expected it to act however in my case the only thing that changes is the grey 8s shows up in the ND field. No change in the results when I run the sim though. Maybe I should try with just two drivers and see what happens. Maybe I am just exceeding some internal limit. __________________ Generic Signature

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