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Old 11th June 2012, 10:43 PM   #1
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Default bass reflex tuning compensated by wall ?

I know that a speaker positionned against a wall does have a +3dB boost in its bass frequencies, but do you know at which frequencies this boost occurs ? Is it the low part of the baffle-step effect ? (so if my baffle step frequency is about 1khz all frequencies below will be accentuated ?)

Depending on the answer [if only lowest frequencies are boosted], since the speaker I want to make will be set against a wall, I like the idea of tuning my bass reflex a bit low :
Click the image to open in full size.
Is it a good idea, and for those who already made vented speakers, what type of tuning do you prefer ? (peak at tuning frequency / linear / slow falloff). Do you consider room gain when designing your speakers ?

Last edited by gougigaga; 11th June 2012 at 10:47 PM.
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Old 11th June 2012, 11:18 PM   #2
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Without knowing anything about your drivers, I appears that the box is too big tuned too low. Are you sure that your driver is suitable for a vented box?

Bob
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Old 12th June 2012, 08:40 AM   #3
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The EBP is about 240 and qts about 0.4 (from what I've measured), it looks good for vented (they were used vented in multimedia speakers - but I want to make a better enclosure for them, since the box is leaky and quite ugly)

I can tune it to 95hz in a 2 liter box to have a nearly flat response, but the aim was to tune it a bit below the 0dB to anticipate the bass boost given by the wall. Power handling / xmax is not an issue since I listen at low volume
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Old 12th June 2012, 07:24 PM   #4
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Download winISD Pro. Follow the help file to re-input your speaker, and then try the simulation again.

The Pro version gives you more graphs (like excursion) which can be useful.

IMHO, the simulation looks okay, but I'd consider (after building) adding some light stuffing to the port - you tend to get more gain at lower frequencies, so you may end up with a one-note bass sound.
You could also try tuning it even lower (contrary to what Bob has said) to try to match it better to the room - there's always some experimentation needed to get speakers sounding "right" subjectively.

Chris
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Old 12th June 2012, 09:56 PM   #5
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Well, I did some simulations in WinISD Pro (and re-meased my driver with Arta), I noticed I have to keep it in a small 2L box tuned to 115Hz if I don't want a peak at tuning frequency.
I noticed I can use a bigger enclosure tuned lower, without a big peak if I add mass to the cone. Is it a good idea ? I noticed some people here who paint and do strange things to their cones, but I wonder what effect it has on the mid and high range. No problem if it just decrease efficiency, but I dont wan't to loose sound quality for bass extension.
My driver parameters are :
Qts=0.33
Qes=0.38
Qms=2.63
Fs=108 Hz
Vas=1.84 L
Mms=1.61 grams
Re=3.6 ohm
Sd=31.17 cm^2
BL=3.21 Tm
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Old 12th June 2012, 10:27 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

Forget about bass, its not a bass driver, and won't ever do bass without
it sounding like mud. Don't what the driver is, and your not saying but I
don't trust the specs. Adding mass won't help at all.

rgds, sreten.
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Old 12th June 2012, 10:44 PM   #7
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Quote:
Originally Posted by gougigaga View Post
Well, I did some simulations in WinISD Pro (and re-meased my driver with Arta), I noticed I have to keep it in a small 2L box tuned to 115Hz if I don't want a peak at tuning frequency.
Yes, and?

Bob
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Old 12th June 2012, 10:52 PM   #8
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Yes I don't want them to make real bass, I meant more the "mid-bass", like 80Hz @ -3dB to sound ok when used alone (I'm not a bass addict)

I will experiment also with adding a resistor in series with the speaker to see what happens. I read that it rises the qts
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Old 12th June 2012, 11:04 PM   #9
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by gougigaga View Post
Yes I don't want them to make real bass, I meant more the "mid-bass", like 80Hz @ -3dB to sound ok when used alone (I'm not a bass addict)

I will experiment also with adding a resistor in series with the speaker to see what happens. I read that it rises the qts
Hi,

The latter does raise Qts and will make it worse.

Post full driver details, I suspect it can't remotely do bass
with the specified combination of Mms, Vas, Fs and Qts.
Given those, probably decent efficiency but no excursion.

rgds, sreten.
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Last edited by sreten; 12th June 2012 at 11:09 PM.
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Old 13th June 2012, 08:09 AM   #10
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For the parameters:

Qts=0.33
Qes=0.38
Qms=2.63
Fs=108 Hz
Vas=1.84 L
Mms=1.61 grams
Re=3.6 ohm
Sd=31.17 cm^2
BL=3.21 Tm

diameter=3" (6.3 cm)
impedance=4ohms

I doesn't have xmax, all I know is the suspension is quite soft/loose, the voice coil is short and yes it has quite good efficiency compared to my other drivers of the same size. I found pictures of them on the net:
Click the image to open in full size.Click the image to open in full size.
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