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Old 1st September 2011, 10:07 AM   #21
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Quote:
Originally Posted by ODougbo View Post
I did try wiring the woofers so they are pushing against each other, I didn’t get much sound output. I found that moving the cones in same directions works the best.
Wiring them to push together would just cause cancelation. If the speakers are mounted mag-2-mag or cone-2-cone with one driver out of phase you will get the best sound quality from them-as the opposite motions of the drivers will cancel some 2nd order harmonics

Quote:
Originally Posted by ODougbo View Post
Several years ago I had two pairs of Peerless 12” woofers, clamshell mounted (4 woofers total) in a 6cf cabinet; it worked but the bass was so slow to get going, a lot was lost, before it ever got started.

The 8’s are super quick, they have powerful bass and the sound stays in the room (not louder/deeper in the adjacent room). Typically the bass is strong without a lot of cone movement, but warning, they will bottom out!
Fast Bass, Slow Bass - Myth vs. Fact - DIYMA.com - Scientific Car Audio - Truth in Sound Quality

Quote:
Originally Posted by PressureFM View Post
It clearly stated that an isobaric alignment will have lower resonance because the air space between the woofers will act as a buffer of sorts.
?
The air volume between the isobaric woofers is irrelevent as the space is sealed, both drivers are the same so will move in and out together maintaining the same volume of air between them-it certainly does not act as a buffer
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Old 1st September 2011, 11:00 AM   #22
ODougbo is offline ODougbo  United States
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Default still going strong at 25hz

To tell the truth I don’t understand the mystery of why isobaric works, but it does and the results are amazing. There is some mechanical factor that couples the speakers and enables them to work harder (and protects them).
There are much better drivers out there, the point here was a low cost project with big results and is somewhat compact 11.5” x 17’ X 19”. I think the most interesting part is how low they go, they are still going strong at 25hz. The bass is tight and defined.
I did compare this sub to a friend’s $400 major manufacture's sub (hint, starts with a V). The home made $100 project blew it out of the water. The $100 is excluding the amplifier. I did find my notes today from when I tuned it: 14.5v @ 19hz – N/A, 31hz – 14.5v @40hz.
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Old 1st September 2011, 11:21 AM   #23
ODougbo is offline ODougbo  United States
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Default MDF vs. Plywood

Well I do see a lot of people using the plywood, let’s just say it’s not for me. I’ve never had a problem with MDF and some of my speakers were made in the mid 80s. They still look nice and work great, easy to freshen up with sanding and new paint if needed. I will admit MDF is not good if the speakers might end up in a flooded basement, but my house stays dry, so not worried. That said I did have a pair of MDF speakers outside for 10 years up inside a gazebo, all the cones went bad, but the boxes were in pretty good shape.
The BB grade I was referring to was not Baltic Birch, hey btw, thanks for all the info


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Originally Posted by planet10 View Post
Actually, BB is excellent material for a speaker project -- especially for woofers. Far better than MDF IMO. I won't use MDF for building a speaker (except some small amounts in some very specific areas).

There has been considerable dicussion on this subject already. Start here: Discussion on what materials to build speakers out of

... and what do you mean by over here in the US?

dave
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Old 6th September 2011, 11:04 AM   #24
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Odougbo,
You should head over to Exotic Lumber in either Annapolis or Gaithersburg and pick up some baltic birch. It is so far superior to MDF for speaker building, you'll never go back. It finishes easier, it actually holds a screw, and you don't have to worry that roundovers will break.

-Jim
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Old 6th September 2011, 12:34 PM   #25
ODougbo is offline ODougbo  United States
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Default 1” MDF

Jim,
Thanks for the advise, I’ll keep it in mind. We do have access to cabinet shop distributors in the area:
1) Harbor sales near Balt 2) A&M Supply Upper Marlboro (new location).
I do like the MDF however, for something out of the ordinary, buy 1” MDF and line the inside walls with lead sheet (available at roofing centers). I build all my satellite speakers with that method, they are awesome! (pic attached)
I know people are going to spill there coffee when I mention that I don’t use hardware (screws/nails) when building speakers. I cut carefully, glue heavily and clamp; sometimes I kerf cut the joint for added strength.
That said, every now and then I will add screws well after the box is constructed, just because some think it is a good idea. As mentioned, I have MDF boxes 20 years old, still using some of them.
Quote:
Originally Posted by Jim McPherson View Post
Odougbo,
You should head over to Exotic Lumber in either Annapolis or Gaithersburg and pick up some baltic birch. It is so far superior to MDF for speaker building, you'll never go back. It finishes easier, it actually holds a screw, and you don't have to worry that roundovers will break.

-Jim
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Old 6th September 2011, 07:43 PM   #26
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Originally Posted by ODougbo View Post
I do have a question for you, I have no idea, can a tapped horn box be tuned?
The "tuning" of a TH is mostly in the box design, which can be thought of as two ports that take up the entire box.

Changing the exit size of a TH will affect tuning, but it is best to get the overall size and path length correct, and only play with the the exit size over a relatively small range. The Fb of a BR box can be changed over octaves, the tuning of a TH box with very large exit size variation only changes by a matter of 1/3 octave or so.
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Old 8th September 2011, 07:49 PM   #27
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So what's the chance that the isobarick design works by having the moving mass of double the woofer? But it still has the same suspension setups giving it a lower FS, but it also has double the motor, giving it the light cone mass of the eight, and the suspension work against both cones. I could go on, but it seems like an excellent design, and I would really like to build one. Would you mind if I asked how you calculated the volume and port for the subwoofers? I have a pair of old drivers I'd like to build in a box like this.
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Old 8th September 2011, 08:18 PM   #28
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In the end, 2x the motor, 2 x the mass, ends you up with 1/2 the Vas. Qt, Fs remains the same. Most everything else stays the same. Impedance changes.

dave
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Old 8th September 2011, 08:41 PM   #29
ODougbo is offline ODougbo  United States
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Default second pair of woofers in one isobaric box

Dave, I have gone back and put a second pair of woofers in one isobaric box (cut it in half and then multiply by two) I found you can use 1 speaker OR 4 in the same size cabinet. I laugh every time I hear this creation, bass like outdoor concert – only using a rotel 60 watt per channel amp. The woofers are old 10” peerless,4 cf box, tuned to 27 hz



Quote:
Originally Posted by planet10 View Post
In the end, 2x the motor, 2 x the mass, ends you up with 1/2 the Vas. Qt, Fs remains the same. Most everything else stays the same. Impedance changes.

dave
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Old 8th September 2011, 08:51 PM   #30
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Quote:
Originally Posted by ODougbo View Post
I found you can use 1 speaker OR 4 in the same size cabinet.
To optimally take advantage of 4 woofers you need to take a few measures... i have a stereo pair of push-push pairs of push-pull Foster 12" in the works.

dave
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