Open baffle VERY close to back wall? - diyAudio
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Old 2nd April 2009, 09:47 PM   #1
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Default Open baffle VERY close to back wall?

I am doing an unorthodox install in my car (sedan) and I had a question about open baffle. I was originally going to run all my full range drivers from 150hz-20khz in small sealed enclosures. Its good to note that I am doing a matrix surround setup (halfler stereo with a center channel) and the center voice and left/right information will be discretely separated via an external processor.

Im starting to consider an open baffle setup for the front three channels.

Obviously, the boundaries will be VERY close to the speakers. Essentially we have the dash which is angled down about 15 degrees from the horizontal axis. We have the A-pillars on the sides, and finally the nasty windshield which is about 40 degrees from the horizontal axis. The L/R channels will have a bit less than 1/3 of a meter spacing from the corner made by the windshield, dash, and A-Pillar. The center will have about the same amount of spacing. The listening position is almost a meter away from the closest channel.

How bad of a response could I expect from this kind of setup? Obviously it is difficult to determine how well this will work, but Im looking for experiences with cramped open baffle near field setups.

I am not at all opposed to adding diffusers/absorbing materials to the dash, for example. I LOVE the effortless sound of open baffle, so a trade off between tonality and that sound may be worth it to me.

I forgot to mention, I have 5 bands of parametric equalization available for the L/R channels and another 5 parametric bands for the center channel (Q =0.5-5).

From what I can gather, since the windshield and dash are at weird angles, the resulting reflections may not be so bad. Any help would be greatly appreciated.
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Old 3rd April 2009, 02:33 PM   #2
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ANY input would be appreciated. I may just suck it up and try it
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Old 3rd April 2009, 03:16 PM   #3
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Default Re: Open baffle VERY close to back wall?

Quote:
Originally posted by Fast1one
. . . . Im starting to consider an open baffle setup for the front three channels.
. . . Obviously, the boundaries will be VERY close to the speakers. How bad of a response could I expect from this kind of setup?
By any audiophile standard, It's gonna be bad.
EQ won't work, because in addition to peaks, you'll have serious boundary nulls in the midrange. -- The kinda actual nulls that EQ can't fix.

Damping/absorption won't really fix things either, as the space is too limited to allow for sufficient absorption in the frequency range needed.

I suppose you could build a really dense 'enclosure' of absorption materials, so that the drivers are aperiodically loaded/damped without actually being "boxed". That would be the only option (besides traditional enclosure) I would even consider.

Open baffle simply must have significant distance to reflecting boundaries, (or an anechoic space --no reflecting boundaries), in order to work.

My 2 cents.
--Mark
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Old 3rd April 2009, 10:16 PM   #4
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Default Re: Re: Open baffle VERY close to back wall?

Quote:
Originally posted by Tubamark


By any audiophile standard, It's gonna be bad.
EQ won't work, because in addition to peaks, you'll have serious boundary nulls in the midrange. -- The kinda actual nulls that EQ can't fix.

Damping/absorption won't really fix things either, as the space is too limited to allow for sufficient absorption in the frequency range needed.

I suppose you could build a really dense 'enclosure' of absorption materials, so that the drivers are aperiodically loaded/damped without actually being "boxed". That would be the only option (besides traditional enclosure) I would even consider.

Open baffle simply must have significant distance to reflecting boundaries, (or an anechoic space --no reflecting boundaries), in order to work.

My 2 cents.
--Mark
Thank you for your response! Since its difficult do build an enclosure with such a small space (I hate fiberglass, too much work for it to be "dead") I was thinking of simply adding a section of PVC (or ABS) tube behind the driver and simply adding heavy fiberglass stuffing behind the driver. So basically what I am trying to ask is, how crucial is the volume behind the driver? I was thinking if simply adding stuffing behind the driver until I can kill the impedance peak...
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Old 4th April 2009, 12:33 AM   #5
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Default Re: Re: Re: Open baffle VERY close to back wall?

Quote:
Originally posted by Fast1one

Thank you for your response! Since its difficult do build an enclosure with such a small space (I hate fiberglass, too much work for it to be "dead") I was thinking of simply adding a section of PVC (or ABS) tube behind the driver and simply adding heavy fiberglass stuffing behind the driver. So basically what I am trying to ask is, how crucial is the volume behind the driver? I was thinking if simply adding stuffing behind the driver until I can kill the impedance peak...
That could work, but it depends on the specs of the driver; if the Qts or Vas of the driver are high (like a driver intended for in-door/infinite baffle mounting), it might be a challenge. If the driver has a lowish Qts and Vas (one intended for small sealed or ported box), you should be able to achieve what you describe.

If you know the driver specs, or have the means to measure the impedance curve (in the tube w/damping), you should be able to figure it out before you commit to mounting in the vehicle. As you increase stuffing density, the impedance will decrease, and at some point when density becomes too great, the trend will reverse. The optimum is just before that point. Avoid packing stuffing too close to the driver - this will actually INCREASE Qts/impedance - not good.
If you can't get good results, then the tube is just too limited in volume for that particular driver.
Be aware (if testing/listening outside the vehicle) that midbass efficiency will increase inside the vehicle.
Let us know how it turns out!

--Mark
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Old 4th April 2009, 01:38 AM   #6
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Default Re: Re: Re: Re: Open baffle VERY close to back wall?

Quote:
Originally posted by Tubamark


That could work, but it depends on the specs of the driver; if the Qts or Vas of the driver are high (like a driver intended for in-door/infinite baffle mounting), it might be a challenge. If the driver has a lowish Qts and Vas (one intended for small sealed or ported box), you should be able to achieve what you describe.

If you know the driver specs, or have the means to measure the impedance curve (in the tube w/damping), you should be able to figure it out before you commit to mounting in the vehicle. As you increase stuffing density, the impedance will decrease, and at some point when density becomes too great, the trend will reverse. The optimum is just before that point. Avoid packing stuffing too close to the driver - this will actually INCREASE Qts/impedance - not good.
If you can't get good results, then the tube is just too limited in volume for that particular driver.
Be aware (if testing/listening outside the vehicle) that midbass efficiency will increase inside the vehicle.
Let us know how it turns out!

--Mark
Ahh I forgot to add the driver specs! Silly me... They are 4 ohm Dayton RS100s

http://www.parts-express.com/pe/show...TOKEN=37874369

I just modeled them and they seem to perform well in 0.02-0.03 cubes sealed. I am limited to using 4 inch ABS tubing because of space so a 3-4 inch depth gives me that value. Looks like I may go that route instead.

I will update this thread with pictures when its done. These will only be payed to about 150hz where the dedicated midbass drivers will take over. Thank you for the help!
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Old 4th April 2009, 07:01 PM   #7
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Cool! Please let us know how it goes.
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