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Old 10th May 2012, 02:31 PM   #31
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Quote:
Originally Posted by pk2carlos View Post
I'm no expert on the mater, but Loudspeaker design cookbook, which I think is a good reference says that port should be "nearly equal to the driver area as possible"
That's so wrong. Port dimensions can be derived from a formula and experience that confirms it as so many designers know. (Not many people know it for sure.)
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Old 10th May 2012, 02:32 PM   #32
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Originally Posted by mdocod View Post
Look at your simulation, compare it to my simulations, there is a major difference. Look at your response measurements, they more closely mirror my simulations than yours. I'm not sure how you are simulating, or what you are doing exactly, but there is obviously some error going on there. The measured response confirms the nasty peak in response predicted by hornresp when I estimated your port dimensions.

If the Loudspeaker Design Cookbook does actually say that, then it is in error for the vast majority of driver/box combinations that are rational. More importantly, even if you do want to have that enormous port diameter, it needs to be a LOT longer to achieve an appropriate tuning. I don't know how in-depth the book goes in regards to vented alignments (never read it), but I'd have to imagine that if the book discusses ported enclosures, it would cover appropriate tuning concepts. A port with a cross section equalling the driver Sd, is more akin to a transmission line build. A different animal for sure.

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That's such a good point and correction Eric.
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Old 12th May 2012, 07:33 AM   #33
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Quote:
Originally Posted by mdocod View Post
Look at your simulation, compare it to my simulations, there is a major difference. Look at your response measurements, they more closely mirror my simulations than yours. I'm not sure how you are simulating, or what you are doing exactly, but there is obviously some error going on there. The measured response confirms the nasty peak in response predicted by hornresp when I estimated your port dimensions.
You are right, will try to contact author of the program so he can have a look if I made some error whit the project. Tuning of the box is at 75 Hz.

Quote:
If the Loudspeaker Design Cookbook does actually say that, then it is in error for the vast majority of driver/box combinations that are rational.
Yes it says this I think somewhere around page 76 I had a look, but as I said it isn't practical in theory as you had writen because of large dimensiones of port.
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Old 12th May 2012, 07:50 AM   #34
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I'm not super up-n-up on the whole workings of room diffraction and such, however, considering the original 147hz dip issue, this corresponds to about a 90 inch round trip cancellation if I understand correctly. From your test position, are there many boundaries ~45" from your microphone? Or a number of boundaries that sort of average out to about a 45" distance?
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Old 12th May 2012, 07:58 AM   #35
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I think your calcualtion are spot on the hight of room is around 90"

Do you have any formula for calculating minimum port surface or any softwere so I don't neet to look all over te internet for it?

I would like to use flared port Aand I can get it from jantzen. The smalesta available is diameter 35 mm, would that be enought?
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Old 12th May 2012, 08:46 AM   #36
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WinISD Pro Alpha (free) is a box simulator that can calculate and graph port air velocity versus frequency for any particular design at any power level.

http://www.linearteam.dk/default.aspx?pageid=winisdpro

After entering the driver parameters and choosing the box size and port frequency to get the bass alignment you want you would enter a power level that corresponds with maximum expected output SPL and it will graph port air velocity. (To help determine the power level you can use the maximum SPL graph which shows maximum possible output based on excursion and power handling figures)

Keep the peak velocity near the port tuning below 17m/s for a non-flared port and you should be fine. If its above 17m/s increase the port diameter until it isn't and the app will recalculate the port length to keep the resonant frequency the same. Simple.

Well designed flared ports can go a bit above 17m/s but most software can't calculate or simulate them for you as it requires a full 3d model of the port and a complex fluid dynamics simulation - way in advance of what most (all?) box simulators do.

And yes, your notch at 147Hz will definitely be room modes and/or boundary cancellation. Nothing to worry about as there isn't anything you could do wrong in the speaker design to get an actual notch in the response like that. Doing a near field measurement will allow you to measure up to 200Hz or so without room effects, and you would see the notch disappear in that case.
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Last edited by DBMandrake; 12th May 2012 at 08:59 AM.
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Old 12th May 2012, 10:50 AM   #37
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I like hornresp personally, I used to use winISD pro exclusively because it was all I knew. Even after learning of hornresp, I continued using winISD for awhile because I was wading through the steeper learning curve of hornresp, however, I think it's well worth the effort to learn how to use the program. It can simulate the effects of far more complicated enclosures, far more accurately than winISD. A flared port simulation in hornresp will actually show the effects of a flared port, on response, excursion, and particle velocity. winISD can't do that.

Regards,
Eric
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Old 12th May 2012, 05:30 PM   #38
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Thanks, have downloaded horenresp and I alrady have instaled WinISD :-)
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Old 12th May 2012, 05:44 PM   #39
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Here are mesurments with frequency tuning at 55, 60, 65 and 75 Hz. My favorite is 60 Hz so thats the one on last picture, but the plot is combined mesurment of driver and port. On a first picture are mesurments made on axis of driver at closer range 0,36 meter and the resolution is 1/6 octave. For the last picture all is the same except I combined plot with port mesurment. On the second picture I mesured only port using same resolution, but close range around 10 cm away for the same frequency tuning as above.

Any idea what could be the source of peak at around 500 Hz?
Attached Images
File Type: jpg hx10 full variable BR.jpg (125.7 KB, 45 views)
File Type: jpg hx10-port only.jpg (144.2 KB, 46 views)
File Type: jpg hx10-final.jpg (97.8 KB, 47 views)
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Old 13th May 2012, 09:15 AM   #40
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Quote:
Originally Posted by pk2carlos View Post
Any idea what could be the source of peak at around 500 Hz?
Quarter wave box resonance would be my guess. I honestly don't even know if that is the correct terminology to describe it.

Last edited by mdocod; 13th May 2012 at 09:29 AM.
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