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Old 29th December 2005, 07:17 PM   #1
e-side is offline e-side  Netherlands
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Default Closed or vented?

Hello everyone,

I'm a but confused right now. This because I recently measured 4 drivers from Jamo (type EC 141 A), and according to the results these drivers should be mounted in a closed box:

Fs: 55.6 Hz
Qms: 4.05
Qes 0.89
Qts: 0.73
Vas: 18.2 L

However, I used two testboxes of about 50 L, one completely closed and one with a 'vent'. The closed box really sounded bad (no low end), the 'vented' box produced nice bass with these drivers.

I can hardly imagine that the measurement results aren't right, because I repeated them several times. However, I don't like building-a-box-and-hope-it-sounds-good, because i want to know what I'm doing.

Could anyone explain the difference between the measurement results and the 'soundcheck'-results? Or does anyone know what type of enclosure to use to get the most optimal results from these drivers?

best regards

Erwin
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Old 29th December 2005, 07:30 PM   #2
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Did you measure the drivers after you mounted them in your test boxes? That might give you more information.

Either way, your ears aren't lying to you - if vented sounds better, stick with it.
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Old 29th December 2005, 07:56 PM   #3
e-side is offline e-side  Netherlands
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Quote:
Originally posted by sdclc126
Did you measure the drivers after you mounted them in your test boxes?
No, I only measured them in free air (just for TSP). Thanks for the advice!

BTW, will a dipole with these (small) drivers sound nice?

best regards

Erwin
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Old 29th December 2005, 08:20 PM   #4
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Quote:
Originally posted by e-side


No, I only measured them in free air (just for TSP). Thanks for the advice!

BTW, will a dipole with these (small) drivers sound nice?

best regards

Erwin
To be honest I can't speak to those specific drivers in regards to a dipole/open baffle design, but consider these variables:

- Do the drivers have relatively open baskets, to allow breathing room for the rear wave?

- Is your listening room large enough to accomodate moving the speakers 3-4 feet out from the rear wall to achieve the dipole effect?

One thing for certain is, if you go open baffle with relatively small drivers you will lose the bass you are experiencing with the ported boxes you have now. So you will need to supplement with a sub or subs to get it back. You will also likely need to deal with crossover and equalization issues with open baffle. Have you read the Linkwitz site?

Since you have measuring equipment and test boxes it should be relatively easy to mount the drivers on an open baffle and see what happens, but definitely measure again. It can't hurt to try a few different designs before you find the one that sounds best to you, and use your measuring equipment to tweak it until it's "perfected."

Hope this helps!
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Old 29th December 2005, 09:35 PM   #5
Wizard of Kelts
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E-side:

You mounted all four woofers in a single box of 50 L?

Okay, for the vented box, can you please tell me:

A) The inside dimensions of the box. If not easily available, the outside dimensions plus the thickness of your building material.

B) The position of each woofer on the face of the box.

C) The position of the port on the box.

D) Diameter and length of the port.

The reason for all this is that I plan to run Martin J. King's software on your vented box and see what it looks like. I need this info, though, to do this.

Finally, I know this sounds elecmentary, but how is your wiring in each case? If you hooked all your woofers up in parallel on one of the boxes, you're going to strain your amp. I'm sure you know that, but it's worth it to check the wiring anyway.
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Old 30th December 2005, 04:20 PM   #6
e-side is offline e-side  Netherlands
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Quote:
Originally posted by sdclc126

- Do the drivers have relatively open baskets, to allow breathing room for the rear wave?

...

One thing for certain is, if you go open baffle with relatively small drivers you will lose the bass you are experiencing with the ported boxes you have now.
- Not really. I don't know exactly what should be considered as 'very open', but there isn't very much space left.

I agree that the low-end will be reduced much when mounted in an OB, so apparently it isn't the most ideal enclosure for these speakers.

Quote:
Originally posted by kelticwizard
E-side:

You mounted all four woofers in a single box of 50 L?

Okay, for the vented box, can you please tell me:

A) The inside dimensions of the box. If not easily available, the outside dimensions plus the thickness of your building material.

B) The position of each woofer on the face of the box.

C) The position of the port on the box.

D) Diameter and length of the port.
I'm sorry for my previous unclear explanation, but for the testboxes I used one woofer for each testbox (1 woofer for a single box)

A) The inside dimensions are 19.8 x 97.5 x 26.9 cm (WxHxD), or 7.92 x 39 x 10.76 inch

B) The woofer's center is positioned at 72 cm / 28.8" from the floor, and 9.9 cm / 3.96" from the side (vertically in the middle of the front panel)

C) The 'vent' is just a hole in the back panel of the box, positioned at 9.5 cm / 3.8" from the floor and 9.9 cm / 3.96" from the side (vertically in the middle of the back panel)

D) Diameter = 8.3 cm / 3.32", length=1.8 cm / 0.72"

Because there's only one woofer, the impedance for the amplifier is about 8 Ohms.

Thank you all very much for your help!

best regards

Erwin
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Old 30th December 2005, 04:33 PM   #7
Wizard of Kelts
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And, save for the port, the dimensions of the sealed box are the same?

If not, I would appreciate the dimensions on the sealed box as well. Also, could you approximate how much stuffing, if any, you used in each box?
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Old 30th December 2005, 07:01 PM   #8
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I believe your venting is giving you about 20Hz more bass extension. It is also probably giving you a bit of a hump around 80-100Hz which can sound "punchy". The sealed box works out to a system Q of roughly 0.85, if you driver params are correct.

Play around with this applet:
http://www.linearteam.dk/default.aspx?pageid=newdriver
(The site also has a vent calculator.)

This will give you some intuition about what is happening.
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Old 30th December 2005, 07:40 PM   #9
e-side is offline e-side  Netherlands
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Quote:
Originally posted by kelticwizard
And, save for the port, the dimensions of the sealed box are the same?

If not, I would appreciate the dimensions on the sealed box as well. Also, could you approximate how much stuffing, if any, you used in each box?
Dimensions are the same, and I didn't use any stuffing.

Quote:
Originally posted by Dumbass
I believe your venting is giving you about 20Hz more bass extension. It is also probably giving you a bit of a hump around 80-100Hz which can sound "punchy". The sealed box works out to a system Q of roughly 0.85, if you driver params are correct.

Play around with this applet:
http://www.linearteam.dk/default.aspx?pageid=newdriver
(The site also has a vent calculator.)
I'll have a look at that site. Thank you and kelticwizard for your kind replies.

regards

Erwin
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Old 31st December 2005, 12:42 AM   #10
Wizard of Kelts
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I forgot to ask-what size are these speakers? And what Bl, ( I might be able to figure that one out from the other specs).

In the tall skinny enclousre you have, I would think that box effects would be pronounced.

Can't find Jamo EC 141 A anywhere. Your box is 8" wide, suggesting an 8 inch, but the 141 suggests somwthing closer to a 6 inch. Hmmmm

I don't need the full Sd, (cone area), just the diameter of the speaker frame.
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