I finally started building my first OBs.
The drivers are vintage Seas paper cone alnicos from early 70s.
4 ways:
1 x 2"
1 x 4"
1 x 8" mid (fabric surround)
3 x 8" woofers (rubber surround)
For the first experiment, I used a 3 way Seas crossover for the upper 3 drivers (2000-5000). This CO works fine for the same drivers in a box. But on OB, upper mids are a bit too pronounced. Can anyone guess or explain why?
However, the bigger problem is the bass.
The woofers are 15ohm each, wired in parallel to give about a 5ohm load. Each woofer should be around 89-90db efficient with Fs=30Hz and Qts of 0.4-0.5
The 8" mid driver should be about 92-93db, and Qts~0.7
I have just a 10mH coil on the woofers and no high pass on the mid.
I don't have any measurement gear, but purely by ear I do not think there is much going on under 100hz at the listening position (more bass as you get closer though). I even tried adding a 4th woofer, but still weak bass.
I have another eight 10" woofers from the same series (these were used in the famous Dynaco A-25). My original idea was to build separate H frame subs with the 10" woofers. Now I am in doubt. The bass might never be to my liking. Plus they will probably take too much space in my living room.
Any comments on the CO of the main speaker and the idea of H frame subs?
I think I probably should put the woofers on the main speaker in a closed box instead of adding subs.
The drivers are vintage Seas paper cone alnicos from early 70s.
4 ways:
1 x 2"
1 x 4"
1 x 8" mid (fabric surround)
3 x 8" woofers (rubber surround)
For the first experiment, I used a 3 way Seas crossover for the upper 3 drivers (2000-5000). This CO works fine for the same drivers in a box. But on OB, upper mids are a bit too pronounced. Can anyone guess or explain why?
However, the bigger problem is the bass.
The woofers are 15ohm each, wired in parallel to give about a 5ohm load. Each woofer should be around 89-90db efficient with Fs=30Hz and Qts of 0.4-0.5
The 8" mid driver should be about 92-93db, and Qts~0.7
I have just a 10mH coil on the woofers and no high pass on the mid.
I don't have any measurement gear, but purely by ear I do not think there is much going on under 100hz at the listening position (more bass as you get closer though). I even tried adding a 4th woofer, but still weak bass.
I have another eight 10" woofers from the same series (these were used in the famous Dynaco A-25). My original idea was to build separate H frame subs with the 10" woofers. Now I am in doubt. The bass might never be to my liking. Plus they will probably take too much space in my living room.
Any comments on the CO of the main speaker and the idea of H frame subs?
I think I probably should put the woofers on the main speaker in a closed box instead of adding subs.
Attachments
There is a 12 to 18db/octave bass roll off on an OB depending on the baffle size. The corner frequency depends on how far the rear wave has to travel before it starts cancelling the front wave. A bigger baffle will push the cancellation frequency downwards, and your bass will start rolling off later than that on a small baffle.
To counter this loss, you must add a big coil to the crossover, such that the falling bass is compensated by a rolled off mid. You can simulate this in Edge. Another way to counter the loss is to get lots of cone area, something like twin 15" woofers will do it. Higher efficiency units also work better, because you have efficiency to throw away in the bass.
At the end of the day, you are trading off efficiency. To get a flat response, you must EQ your mid and midbass to the bass, which has that steep rolloff due to the OB.
To counter this loss, you must add a big coil to the crossover, such that the falling bass is compensated by a rolled off mid. You can simulate this in Edge. Another way to counter the loss is to get lots of cone area, something like twin 15" woofers will do it. Higher efficiency units also work better, because you have efficiency to throw away in the bass.
At the end of the day, you are trading off efficiency. To get a flat response, you must EQ your mid and midbass to the bass, which has that steep rolloff due to the OB.
See the crossover design and explanation in this one:
http://www.diyaudio.com/forums/multi-way/110583-fast-fun-inexpensive-ob-project.html
http://www.diyaudio.com/forums/multi-way/110583-fast-fun-inexpensive-ob-project.html
Yes - what ra7 said. OB crossovers are different. You will be fighting the rising response of the woofer(s). To get the proper tonal balance you need to set the woofer crossover much, much lower than you would in a box. Electrically it may be very low, but acoustically it will be right.
You've gone in the right direction with the 10mH coil on a 5 ohm load, but you may still need a big cap in there (second order) to fight the rise. If the load really is 5 ohms, you should have about an 80Hz low pass now. You'll loose a lot of SPL doing that, but it's the trade off you have to make.
You can also try some shallow side wings to help the bass. Making them asymmetrical will help.
You've gone in the right direction with the 10mH coil on a 5 ohm load, but you may still need a big cap in there (second order) to fight the rise. If the load really is 5 ohms, you should have about an 80Hz low pass now. You'll loose a lot of SPL doing that, but it's the trade off you have to make.
You can also try some shallow side wings to help the bass. Making them asymmetrical will help.
Member
Joined 2009
Paid Member
You will need some baffle step compensation for any resonably sized baffle. With such narrow baffle more than a wide baffle such as OBL11.
With no mean of measure it is really hard to get things right. If you have an other one of the 4" units you can use (BLACKCONES) and then you have the midrange and tweeter range set. I am thinking about building something along with the OBL11 using four Seas 10" high Q drivers and then the 8" and 4" units of the black cone.
With no mean of measure it is really hard to get things right. If you have an other one of the 4" units you can use (BLACKCONES) and then you have the midrange and tweeter range set. I am thinking about building something along with the OBL11 using four Seas 10" high Q drivers and then the 8" and 4" units of the black cone.
I think you have to reduce the output of the top 8" driver. at least the 4 Ohm version of Seas 21 TV-G is about 96 dB and actually about 100 dB for 2.83 Volt in the 1.5-4 kHz range. I assume that the orginal box was wider than the open baffle. A 30 cm wide baffle drop up to 6 dB below about 450 Hz the original design with a wider baffle would have support to a lower frequency. A reduction in output 450 to say 300-200 Hz compared to previous design would explain part of the lean sound.
10 mH gives a crossover at about 80 Hz. Here and below the woofers are into cancelation between front and back so there is no way you are getting 92 dB. I would try to mute all 3 top drivers by 6 dB and see if you like the balance better
10 mH gives a crossover at about 80 Hz. Here and below the woofers are into cancelation between front and back so there is no way you are getting 92 dB. I would try to mute all 3 top drivers by 6 dB and see if you like the balance better
my amp is an integrated digital amp with digital input and no pre-out.
so going active is complicated.
i was eyeing digital plate amps with line level input but those are expensive and hard to get in the UK.
i was also hoping to avoid wings on main baffle (hence the idea of separate H frame subs).
experimenting with cardboard extensions to the baffle is a very good idea. thank you.
Okay, this is what I am listening now (see pic).
(Well I am actually listening to Molvaer's Solid Ether)
I used to boxes to increase baffle size and now there is a lot of bass, everything seems balanced. It is lovely actually. I have this brace in the middle of the open baffle in the back and because of that there is a bit of resonance.
I have been thinking about way forward:
1. adding subs won't be practical; i am short of space
2. because i am using 4 woofers the cones hardly move: there is potential to get more out of them
3. i am still liking the idea of using a very low 1st order on the woofers to flatten the rising open baffle bass response (as in Manzanitas and OB project on Supravox website)
So here is my plan:
Instead of current 8" woofers I will use the 10 inchers which I already have (4 on each side). On a flat baffle 4x10" would be too high. So I am thinking of an M frame (MM in this case). And most importantly I will try to go active on the woofers. With the low crossover the main problem is SPL. And going active can solve this without adding new problems (such as wings and resonance).
I think the woofers can be pushed much further in this set up.
I am looking into Behringer Inuke DSP pro digital amps for this purpose. If only I can figure out how to integrate volume control.
Thoughts? Does anyone have experience with Inuke DSPs?
BTW I was sceptical on OB bass after the first impression but I am loving what I am hearing right now. OB shines on vocals too.
(Well I am actually listening to Molvaer's Solid Ether)
I used to boxes to increase baffle size and now there is a lot of bass, everything seems balanced. It is lovely actually. I have this brace in the middle of the open baffle in the back and because of that there is a bit of resonance.
I have been thinking about way forward:
1. adding subs won't be practical; i am short of space
2. because i am using 4 woofers the cones hardly move: there is potential to get more out of them
3. i am still liking the idea of using a very low 1st order on the woofers to flatten the rising open baffle bass response (as in Manzanitas and OB project on Supravox website)
So here is my plan:
Instead of current 8" woofers I will use the 10 inchers which I already have (4 on each side). On a flat baffle 4x10" would be too high. So I am thinking of an M frame (MM in this case). And most importantly I will try to go active on the woofers. With the low crossover the main problem is SPL. And going active can solve this without adding new problems (such as wings and resonance).
I think the woofers can be pushed much further in this set up.
I am looking into Behringer Inuke DSP pro digital amps for this purpose. If only I can figure out how to integrate volume control.
Thoughts? Does anyone have experience with Inuke DSPs?
BTW I was sceptical on OB bass after the first impression but I am loving what I am hearing right now. OB shines on vocals too.
Attachments
Okay here is the next step.
I will keep the mids and up as it is: open baffle.
And put the woofers in a separate closed box.
I will chop the woofer section of the open baffles and they will sit on top of the bass box isolated by sorbothane feet.
Bass section will be using two 10" vintage SEAS woofers per side.
At 8ohm each and wired parallel, it will be a 4ohm load.
This should give about 96db efficiency in the bass region, hopefully.
Bass box will be with no vents and about 3 1/3 cubic feet of internal volume.
I am thinking of lining the interior with wool carpet, and the walls except the front baffle will be filled with sand and supported by a single brace in the middle.
Front baffle will be 2 layers of 18mm plywood.
Rest of the walls will be a sandwich of 18mm mdf, 15mm sand, and 9mm mdf.
I bought the wood and sand last weekend and am ready to roll with my jigsaw.
Any comments before I start?
*yes, I wish I had a router...
I will keep the mids and up as it is: open baffle.
And put the woofers in a separate closed box.
I will chop the woofer section of the open baffles and they will sit on top of the bass box isolated by sorbothane feet.
Bass section will be using two 10" vintage SEAS woofers per side.
At 8ohm each and wired parallel, it will be a 4ohm load.
This should give about 96db efficiency in the bass region, hopefully.
Bass box will be with no vents and about 3 1/3 cubic feet of internal volume.
I am thinking of lining the interior with wool carpet, and the walls except the front baffle will be filled with sand and supported by a single brace in the middle.
Front baffle will be 2 layers of 18mm plywood.
Rest of the walls will be a sandwich of 18mm mdf, 15mm sand, and 9mm mdf.
I bought the wood and sand last weekend and am ready to roll with my jigsaw.
Any comments before I start?
*yes, I wish I had a router...
Yes, the Eminence works great for the $!
Also in just plain Open Baffle. Have a look at what can be done with the Eminence and the DaytonPS220.... granted, I'm extensively using DSP and using some very complex combinations of filters to effect Timbral Correction on the system, but this gives an idea of what can be achieved.
Attachments
Here is my latest experiment:
An H-frame with 4 Seas alnico 10"ers (same woofer used in the legendary Dynaco A25). Low passed 2nd order with 10mH and 100uF.
Lets first talk about the bass.
It is still somewhat weak. But very clean too. My biggest complaint: lack of dynamics compared to mids.
At higher volumes bass becomes visceral - you start feeling it in your body - which is very promising to stick to OB. Dynamics improve a bit too.
For next step to improve bass dynamics, what should I do?
- keep current driver set up and switch to active CO/biamp on bass section
- or keep passive and switch to 2 15" pro audio woofers (high eff, cloth surround + light paper cone)
Now more info on the upper section:
3 way with
Seas 8"
Seas 4"
B&G Neo3 PDR
Cross over is a very old 3 way Seas board (2000/5000) to be updated later on
An H-frame with 4 Seas alnico 10"ers (same woofer used in the legendary Dynaco A25). Low passed 2nd order with 10mH and 100uF.
Lets first talk about the bass.
It is still somewhat weak. But very clean too. My biggest complaint: lack of dynamics compared to mids.
At higher volumes bass becomes visceral - you start feeling it in your body - which is very promising to stick to OB. Dynamics improve a bit too.
For next step to improve bass dynamics, what should I do?
- keep current driver set up and switch to active CO/biamp on bass section
- or keep passive and switch to 2 15" pro audio woofers (high eff, cloth surround + light paper cone)
Now more info on the upper section:
3 way with
Seas 8"
Seas 4"
B&G Neo3 PDR
Cross over is a very old 3 way Seas board (2000/5000) to be updated later on
Attachments
Probably you haven't fully exploited the potential of that H frame yet. Before investing in another set of drivers you should biamp your dipole, but keep the passive crossover for the H frame. Reverse two of the woofers (diagonally) on the baffle, looking at their baskets. And put massive vertical and horizontal bracing between the drivers to stabilize the baffle and the frame walls. The bracing you show in your picture doesn't deserve its name 
.
Put a MASSIVE weight on top of the H frame to keep it from moving back and forth. I think about one or two 40x40 cm concrete slabs.
Rudolf
.Put a MASSIVE weight on top of the H frame to keep it from moving back and forth. I think about one or two 40x40 cm concrete slabs.
Rudolf
Thank you Rudolf.
There is more robust bracing in the back actually
But adding mass is very good idea.
Sand, concrete or plasticine I am thinking.
Buying a new amp would cost me more than new PA drivers though.
I am thinking of buying the drivers for one side to test first.
These Chinese drivers are very cheap here:
SoundLab :: SoundLAB 15" Black High Quality 400 W Bass Speaker (8 Ohm) 35.39 IN STOCK (18 Oct 2012)
Two of those per side should be more efficient than the current set up.
I have a suspicion that rubber surround drivers can never be as dynamic as fabric ones.
There is more robust bracing in the back actually
But adding mass is very good idea.
Sand, concrete or plasticine I am thinking.
Buying a new amp would cost me more than new PA drivers though.
I am thinking of buying the drivers for one side to test first.
These Chinese drivers are very cheap here:
SoundLab :: SoundLAB 15" Black High Quality 400 W Bass Speaker (8 Ohm) 35.39 IN STOCK (18 Oct 2012)
Two of those per side should be more efficient than the current set up.
I have a suspicion that rubber surround drivers can never be as dynamic as fabric ones.
An other trick is to suspend the box/h-frame. Either by hanging it by wires from the ceiling, or use a very soft suspension between the floor and the box. I use small tire tubes with light air pressure, it works very well.
The point is to lower the pendulum resonance frequency of the box itself. The lower it get, the less will the box move.
The point is to lower the pendulum resonance frequency of the box itself. The lower it get, the less will the box move.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.