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Old 14th April 2013, 08:43 PM   #1
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Join Date: Jun 2012
Default Confused help needed

Hey guys

I'm am pretty new to the hole speaker science. I am currently making a system to a festival. The sound will be provided by two p.Audio Hp-15w http://www.discopro.ro/files/HP-15W-12S.pdf and two tweeters. My amplifier is a Ta2020 to save power.
The next move is building the box. I want to try a vented box.

My questions are following-

When using two vents, where on the box should they be placed?

What tuning frequence should the box be? (considering we are playing outside)

How to decide how many vents?


Your help is much needed and I thank you in advance

From Virumflame - Simon
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Old 15th April 2013, 12:22 AM   #2
Zero D is offline Zero D  United Kingdom
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Join Date: Aug 2009
Hi,

Quote:
When using two vents, where on the box should they be placed?
Front & anywhere you like. But why 2 ?

Quote:
What tuning frequence should the box be? (considering we are playing outside)
It depends on the volume of the box & how low you want/need to go & how much power you feed them with & what kind of music you will be playing.

Quote:
How to decide how many vents?
Sometimes people can only get certain size tubes/pipes etc, so they use 2 smaller ones. One bigger is best. The larger the diameter the longer they will be, compared to a smaller diameter @ the same tuning frequency.

It would be better if you experimented with something like WinISD. Here's a thread i made which should help How to correctly use WinISD
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Old 15th April 2013, 12:45 AM   #3
OscarS is offline OscarS  United States
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unless for some weird reason, you absolutely need "multiple" vents, use one single larger one. The cross-sectional area is determined by viewing the vent air velocity graph and noting the peak velocity. Ideally, you want to stay below 5% the speed of sound if at all possible. Flaring the ends of the ports helps out.

Model your particular driver with WinISD or any other suitable simulation program and play around with port tuning frequency. See which one gets you the frequency response graph that you are looking for.
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Old 15th April 2013, 01:03 AM   #4
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Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
After running some quick calculations, this driver(Assuming it is the one pictured here) really doesn't "need" to be a ported type. The Efficiency Bandwidth Product is at 48.863...... it kinda splits the difference between ported or sealed. Being as it has a rather limited Xmax, or cone travel limits, it is best suited to a sealed enclosure. I calculated an eight cubic foot box for each driver will work fine.......Getting you a Qtc a tad over .8 A very small boomy effect but it will keep the cone "in check" when frequencies go way down.


_________________________________________________R ick.........
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File Type: jpg IMF driver.jpg (42.9 KB, 99 views)
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Old 15th April 2013, 03:02 AM   #5
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1. How many people are expected to be at this festival?
2. Why did you choose that specific 15" driver?
3. What will be using to provide power to these speakers?
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Old 15th April 2013, 09:50 PM   #6
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I'ts a huge festival called Roskilde. The reason why I would like to build a vented box is because we would like a feel that boom everytime the bass drops. But I don't know anything about tuning frequensy and what our tuning frequency should be. Any suggestions ?

I have tried both WinISD beta and alpha, but I can't determine what tuning I should set it to.
I thank you for the advice on the vents by the way

My main question is tuning frequency?

By the way Richard Ellis driver is the one I linked

Brian Steelse - We are using a car battery to power a Lepai Ta2020 wired to two of the before mentioned driver. This is only a part of our setup but needless to say a vital part
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Old 15th April 2013, 10:00 PM   #7
OscarS is offline OscarS  United States
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you need to simultaneously look at the normalized frequency response, cone excursion, and vent air velocity while you vary the enclosure volume and tuning frequency. If you want a flat frequency response, then adjust the volume and tuning to do so, if you want a to sacrifice some low-end for a higher bump at a single frequency do the same, if you want an extended bass response at the expense of some dBs, then do the same.

Lets see screenshots of what you have come up with so far.
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Old 16th April 2013, 10:31 PM   #8
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I have tried WinISD for some time. I understand how the size, tuning and port affects each other. So there is no confusion the third is my driver https://www.intertechnik.de/Shop/Lau...e32960513efd13 .

I set the tuning frequens to 33 and the pictures is only 1 driver in a box.
My question are following -

1. What is cone excursion and transfer function magnitude exactly? (attachhed pictures)

2. Why is the only possibility a rear port? What about a front port?

3. Where should the driver be placed when a tweeter will be in the box as well?

4. Does WinISD subtract the volume of the port in the box?


Once again thank you
Attached Images
File Type: jpg Kasse cone.jpg (172.1 KB, 62 views)
File Type: jpg Kasse mach.jpg (182.4 KB, 62 views)
File Type: jpg Kasse magnitude.jpg (181.2 KB, 63 views)
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Old 23rd April 2013, 06:51 PM   #9
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Location: Dahlonega, Ga
Hi VF, it's good to be want to build your own cabinets BUT. If you're pushing them with 12 volt powered amps, you're not going to get chest pounding bass. It takes lots of watts to do that in a live sound situation. By the time you spend money on wood, speakers, finish, wire, jack plates, etc. and ending up with a marginal cabinet that won't do what you want, you could buy a couple of efficient commercial subs that will make you happy. I've used and built a lot of subs and I recommend a Yamaha SW218V or CW218V. Same speaker, just different finishes. They're real cheap for the output, especially if you can find a used pair.
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Old 23rd April 2013, 09:19 PM   #10
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Quote:
Originally Posted by Virumflame View Post
1. What is cone excursion and transfer function magnitude exactly? (attachhed pictures)
2. Why is the only possibility a rear port? What about a front port?
3. Where should the driver be placed when a tweeter will be in the box as well?
4. Does WinISD subtract the volume of the port in the box?
Once again thank you
1. Cone excursion is the distance (one way) that the cone travels from it's resting position. Xmax is the maximum linear excursion the speaker is capable of, more power over Xmax makes more distortion, but not much more "good" bass.
"Transfer function" is the same as frequency response, how loud at a given frequency.
2. A port can be put on any side of the cabinet.
3. The tweeter in general should be as close to the woofer as possible.
4. Net volume does not include driver, port, or bracing volume.
5. A car battery's life will be short if used for power without an alternator.
They are designed to give up power quickly, then be immediately brought back to 12.6 volts.
Marine batteries are designed for deeper discharge, they have heavier plates.
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