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
Fast Bass, Slow Bass - Myth vs. Fact - DIYMA.com - Scientific Car Audio - Truth in Sound Quality
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
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.
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.
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
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
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
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
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.
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.
Attachments
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.
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.
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
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
Attachments
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
speaker design program
You’re going to want to find a speaker design program to download. I still use my old Perfect Box. However there are much better programs out there, I’m sure some of the more knowable fellows on here can point you in the right direction.
Incase you missed an earlier thread; I do have a little trick for a slot port:
semi build the box, to the point where the front baffle board and “slot” (glued together like an “L”) can be slid up and down, which changes the port’s volume - using a generator and volt meter you can tune the box with certainly and then do the final glue up (you’ll need a good number of clamps).
To answer your question about this box, I started with 1 8” woofer in a 2cf cabinet and tuned it to 30hz; great low, house shaking bass, however it did have some problems with bottoming out with high volume during action scenes (explosions, etc).
I decided to but two speakers in one box, to help handle the power. The design - I simply cut the volume in half and added of volume for the tunnel and extra speaker.
You’re going to want to find a speaker design program to download. I still use my old Perfect Box. However there are much better programs out there, I’m sure some of the more knowable fellows on here can point you in the right direction.
Incase you missed an earlier thread; I do have a little trick for a slot port:
semi build the box, to the point where the front baffle board and “slot” (glued together like an “L”) can be slid up and down, which changes the port’s volume - using a generator and volt meter you can tune the box with certainly and then do the final glue up (you’ll need a good number of clamps).
To answer your question about this box, I started with 1 8” woofer in a 2cf cabinet and tuned it to 30hz; great low, house shaking bass, however it did have some problems with bottoming out with high volume during action scenes (explosions, etc).
I decided to but two speakers in one box, to help handle the power. The design - I simply cut the volume in half and added of volume for the tunnel and extra speaker.
combinations
It was a bit of a story, a friend gave me 4 cabinets with the woofers. I had 4 chances to get something to work, so by trying 4 different combinations, tuning, seat-of-the-pants stuff, I came up with this. I did end up burning up and throwing away the other 3 boxes (I was on a roll).
Foster, that sounds familiar, I think I have a pair an old pair of 10” they’re 12 ohm right?
It was a bit of a story, a friend gave me 4 cabinets with the woofers. I had 4 chances to get something to work, so by trying 4 different combinations, tuning, seat-of-the-pants stuff, I came up with this. I did end up burning up and throwing away the other 3 boxes (I was on a roll).
Foster, that sounds familiar, I think I have a pair an old pair of 10” they’re 12 ohm right?
Foster is one of the largest speaker manufacturers in the world. They have likely built 1000s of different 10" drivers. Their Fostex subsidury is likely more recognizable.
dave
So you went from 2cf to 1? as well as adding the second 8, and it still preforms just as well?
Yes, that is the process, 2 speakers ~ face to face (clamshell) – Mag to Mag – front to back, you can make the cabinet half the size. Don’t forget to add some extra volume for the 2nd speaker and/or internal “tunnel”.
I’d like to know a little more about push pull, I have a few Rockford 8” P2s around here. I tried them for HT, but they only started sounding good at higher volume levels.
I’d like to know a little more about push pull, I have a few Rockford 8” P2s around here. I tried them for HT, but they only started sounding good at higher volume levels.
using this method, how do you calculate friction loss coefficients?
the .75/10 ratio is almost Aperiodic.
Odoubo’s no calculator method
Sound engineer, ohh….but I knew that before I looked at your profile. I do understand your question, to a point.
The sliding baffle idea; AKA Odoubo’s no calculator method.
[This probably won’t make any sense to people that never tuned a bass reflex speaker]
As mentioned I had the frequency generator and volt meter hooked up early on, I tried different versions (port lengths) and my measure was the amount of port air noise (keeping the high and low voltage peaks the same for each version).
I made adjustments to the length of the port (on the table saw, speakers and all) and also the height, before the final glue up.
With the experimentation, I set the port at the edge of the “wind noise” being noticeable, at same time setting the voltage swings where they looked good.
To expand on construction, the front/port, top, back, bottom need to cut at the same time; 10” wide for this project. You’ll want them all to be exactly the same for an air tight fit. The 17” x 19” sides can be cut oversized and trimmed with a router or belt sander. WATCH THE PORT, easy to forget and gouge it with a flush cut router.
Sound engineer, ohh….but I knew that before I looked at your profile. I do understand your question, to a point.
The sliding baffle idea; AKA Odoubo’s no calculator method.
[This probably won’t make any sense to people that never tuned a bass reflex speaker]
As mentioned I had the frequency generator and volt meter hooked up early on, I tried different versions (port lengths) and my measure was the amount of port air noise (keeping the high and low voltage peaks the same for each version).
I made adjustments to the length of the port (on the table saw, speakers and all) and also the height, before the final glue up.
With the experimentation, I set the port at the edge of the “wind noise” being noticeable, at same time setting the voltage swings where they looked good.
To expand on construction, the front/port, top, back, bottom need to cut at the same time; 10” wide for this project. You’ll want them all to be exactly the same for an air tight fit. The 17” x 19” sides can be cut oversized and trimmed with a router or belt sander. WATCH THE PORT, easy to forget and gouge it with a flush cut router.
If you are not going to mount isobaric drivers "clamshell" facing each other, you might want to consider shallow-profile drivers for the automotive market for mounting with a short tunnel. There are some that are flat and shallow yet achieve relatively extreme excursion. Some place the "motor" inside the cone, others place the voice coil at the surround, some have convoluted formers, etc. etc. but it's a new creative emerging area, ALL WONDERFUL FOR CLOSE-MOUNTING ISOBARICS. Mounting the drivers closer wastes less space, and can operate to higher frequencies.
Take two of these wonderful babies from JL Audio and isobaric them, and you could get away with a really small box, or perhaps scale it up with more isobaric drivers and/or more boxes:
JL Audio 13TW5 Subwoofers - Car Audio Subwoofers
If you can't afford that:
http://www.earthquakesound.com/sws.htm
The disadvantages nobody has mentioned is inefficiency and cost. Engineering is a compromise and if you are willing to buy big amps and spend money amazing things are possible.
Take two of these wonderful babies from JL Audio and isobaric them, and you could get away with a really small box, or perhaps scale it up with more isobaric drivers and/or more boxes:
JL Audio 13TW5 Subwoofers - Car Audio Subwoofers
If you can't afford that:
http://www.earthquakesound.com/sws.htm
The disadvantages nobody has mentioned is inefficiency and cost. Engineering is a compromise and if you are willing to buy big amps and spend money amazing things are possible.
Last edited:
Thanks, The JL speakers are tempting, hard to justify buying them unless you seen and heard them in a proven design. Always wanted to experiment with their 8” W7 line, $350 bucks each though.
I saw one fellow write, one is never enough; so that’s where I would probably end up, buying a second :-/
For this box, the tunnel is 5” x 7” and the magnet is so big (the front speaker) there is not much space left in there. I did think about making the 10” by 10” plates concentric, hour glass shaped, but didn’t. As mentioned earlier, I did build a couple of clamshell boxes (leave 5/8” to 3/4"space between woofers!), I do think they had a slight advantage over the front to back, but these are much easier to look at.
Big amp for these??? naaaaaa. I had them hooked up to a 60watt Rotel, tons of bass (car crossover set at 50hz), pounded the whole workshop.
Rockford has a new shallow woofer also. For those that don’t know, Rockford has a great web site for DIY, the box wizard is very handy.