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Multi-Way Conventional loudspeakers with crossovers

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Old 7th May 2012, 12:24 PM   #21
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It's very hard to tune a hole! That's how many vented enclosures were made in the past, before we knew what we know today, and they sounded pretty terrible. You need a long enough port so that end effects don't swamp out what you're trying to accomplish. The port works because of the mass of the air within it. One way to get more mass is to use a passive radiator, but that comes with its own problems. Small speakers are often problematic because you don't have room in the box for a port of sensible dimensions. In that case you typically have to stop worrying about port noise and reduce the diameter. I use a set of KEF "Q" speakers for the TV and they have flared ports a little over an inch in diameter. They have surprisingly good LF response, but you'll never feel it in the chest like a larger speaker. IMO, with a small bookshelf speaker you won't be moving enough air to worry much about port noise.
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Old 7th May 2012, 12:41 PM   #22
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Quote:
Originally Posted by Conrad Hoffman View Post
I use a set of KEF "Q" speakers for the TV and they have flared ports a little over an inch in diameter. They have surprisingly good LF response, but you'll never feel it in the chest like a larger speaker. IMO, with a small bookshelf speaker you won't be moving enough air to worry much about port noise.
I like the way you think and I also like flared ports. The one I used is from jentzen and I just looked and there is a smaller version. Will do some testing whit lower tuning and see whats happens.
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Old 7th May 2012, 05:38 PM   #23
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The resistance curve for closed box gives the Qts approximately near 0.6 and itís like the resistor isnít the case.
Tuned 75 Hz is really high for this speaker and, definitely, 5-6 excessive decibels come from this tuning. Modeling software suggests 55Hz.
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Old 8th May 2012, 06:48 AM   #24
mdocod is offline mdocod  United States
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As far as I know the surface of port should be equal or at least half of surface of driver. This is to avoid any noise created by port itself.
There's more than Sd to take into consideration. Sd by itself doesn't paint a large enough picture to make any determinations about necessary port cross section.

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I know that because of limitations of design this is rearly used, but I think I can use that size of a port and live with this design.
The current tuning results in a bass response that people point and laugh and joke about as a typical max-SPL one-note-wonder cheap car stereo sub. I wouldn't be able to live with that at all....

[emphasis added to the following quote...]
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The reason for high tuning frequency is as said before to be able to get out more from this driver in relation to cone displacment.
A proper tuning would provide useful extension to down around 50hz. IMO, that would be more.

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The idea is to have port tuned at Fs of the driver. The simulation didn't look that problematic.
I can't get my head wrapped around the idea of a 10dB spike in response being less problematic than a 7dB dip

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Thanks, will try diffrent port and see or rather hear what happens
I'm excited to hear your impression of the change!

Regards,
Eric
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Old 8th May 2012, 02:01 PM   #25
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Here is picture of simulation, and from this I was thinking that a few dB peak as seen here 3 dB would be nice and add to that a perfect impedance curve I just had to try it

I have already tryed a longer port and it is much better, will post mesurment when I will done it.
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File Type: jpg HX 10 br simulation.jpg (218.5 KB, 54 views)
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Old 8th May 2012, 06:19 PM   #26
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I like a slight peak with smaller sealed systems and usually go for a Q of 0.9, but I'm wary of doing the same thing with vented systems. See how it sounds, but watch for "one note bass". Errors of omission are usually preferable to peaks.
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Old 8th May 2012, 06:57 PM   #27
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This one (vented) doesnt't sound good.

What do you think about this driver, seales box for q 0,9 the calculations says 2,4 liters and fs of system 125 Hz. Would this be way too high?

Some time ago I did a lot of band pass push pull sub with center frequency around 80 Hz and always loved sound.
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Old 8th May 2012, 07:31 PM   #28
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Originally Posted by pk2carlos View Post
In theory the port should be as big as loudspeaker and since there is enought space I decided to use this one. I don't think that smaller diameter would make any differenc or would it?
Wouldn't it be only shorter for the same tuning?
I think your "theory" is a bit confused.

Vent cross section area does matter, but only insofar as vent velocity is kept under 17m/s
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Old 8th May 2012, 08:05 PM   #29
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Originally Posted by RockLeeEV View Post
I think your "theory" is a bit confused.

Vent cross section area does matter, but only insofar as vent velocity is kept under 17m/s
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"
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Old 10th May 2012, 09:31 AM   #30
mdocod is offline mdocod  United States
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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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Eric
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