[guest60106]

Hello fellow audiophiles and greetings from a new guy.

I have been designing and building high fidelity loudspeakers for about 30 years. I have had experience in sealed, bass reflex, TL QW, and in-wall. I have some drivers laying around in my shop that I have had for a few years that I initially bought for an in wall application. I have since lost interest in that project. I have run models on the 10” drivers and I can’t find reasonable “Box” alignment (read huge) partly because of the specs but mostly because I have eight of them and I want to run 4 per side in stereo. This was my original intent with the IB in-wall arrangement.

Everything about this driver says OB so why not. I have always kepth track of developments in OB DIY for pleasurable reading and interest. This is what brought me to this forum. I have zero practical experience with OB design. I am thinking a 2-way with a full range to cover the mid to high section. Bi-amping and an electronic crossover with the point set in the neighborhood of 200-800 Hz. The crossover is a 24db slope (I have a few of these laying around). Power is not a problem. I have 3 Adcom 555 amps in surplus (a luxury of being an audiophile for many years). I will run each bank of 4 10” drivers with a dedicated 555 bridged and run the full range with a 555 in stereo. Both channels from the pre-amp driven in full stereo. Here are the specs on the 10” drivers.

Exodus Audio DPL-10

Re:  6.5
Fs: 23Hz
Qms: 4.7
Qes: .91
Qts: .76
mms: 99g
cms: .47 mm/N
Vas: 73L
Sd:  333 cm^2
BL: 10.2
SPL: 81.7
X-max:  19mm

As can be seen from the efficiency of the 10, I will need the power although running 4 per side in series and parallel to get me back the 6.5 ohms will get me about 6-8 more db (roughly). This does not take into account the OB configuration. This also led me to the selection of the full range, a Visaton SC 8 N 8 OHM. These are the specs for it:

Rated power 30 W
Maximum power 50 W
Nominal impedance Z 8 Ohm
Frequency response 70–20000 Hz
Mean sound pressure level 81 dB (1 W/1 m)
Opening angle (-6 dB) 150°/4000 Hz
Excursion limit +/−3 mm
Resonance frequency fs 91 Hz
Magnetic induction 0,9 T
Magnetic flux 170 µWb
Height of front pole-plate 3 mm
Voice coil diameter 20 mm
Height of winding 4 mm
Cutout diameter 73 mm
Net weight 0,28 kg
D.C. resistance Rdc 7,0 Ohm
Mechanical Q factor Qms 3,68
Electrical Q factor Qes 1,31
Total Q factor Qts 0,97
Equivalent volume Vas 1,5 l
Effective piston area Sd 26 cm²
Dynamically moved mass Mms 1,9 g
Force factor Bxl 2,4 Tm
Inductance of the voice coil L 0,3 mH
Temperature range −25 ... 70 °C

This driver was selected primarily because the efficiency is as close a match for the 10 as I could find but also because of the price and a fairly flat response. The original plan (may change with design constraints) is to run 4 of the full range in a mini line array next to the line of 4 10s. This is an initial thought. Again this is why I am here. I am a BSME CAD designer so modeling is second nature. I am here for opinions and constructive criticism on my initial design thoughts. If I have time this weekend I will throw a few CAD model ideas up here for debate as well

Any thoughts?

MLC

[JohnR]

Hi, with an active crossover the sensitivities shouldn't matter. With 4 DPL10s per side you should have ample output down to around 30 Hz with not too much eq required. I'd be inclined to try keeping the crossover point down to the lower end though. I think I'd suggest using a single larger full-ranger rather than an array of smaller ones - then you could fold the four DPLs in a "W" type of arrangement and put the fullrange driver up top.

Another option would be to use just 2 DPLs in the baffle itself, and another two as dedicated subs (would need a three-way crossover of course).

[JBspeakerman]

OK, you have what you need driver and motivation wise. 

What you need to determine first is the largest baffle width you can stand.  This will set your OB bass sections efficiency and F =.  Once you have that nailed down, the rest is much easier to handle.  Assume you have visited Mr. Linkwitz's site, Linkwitz lab?  A great technical info source.  A must read.  So, let us know about the baffle, wings (if any) and the group can chime in and head you toward a great OB system.

[guest60106]

I banged out a quick CAD model today. Here are a few jpgs of the idea I have been thinking about for a baffle layout. This idea has a BG RD48 for The mid-high section, however, I can utilize a line array of the Visaton SC 8 N 8 as well. I haven’t gotten that far in the design yet. Notice that I have the mid-high panel angled back by 30 degrees. I have used this technique in the past with good success for imaging because I don’t like to toe the speakers in when they are placed in the room. I am contemplating putting sides and top and bottom on the panels about 7.5 inches (?) deep to create a U-Baffle. Again, I haven’t gotten that far in the design process yet. I am very familiar with the Linkwitz Lab sight. I have been on and off there for the last few years out of interest but am now reading the modeling material in great depth. I have also downloaded the EDGE software and am getting to know that as well. Right now, the DOL-10 Baffle is 12 inches wide and 50 inches tall and the ribbon baffle is 6 inches wide and the same height. With the 30 degree angle included this yields a total baffle width of 17.5 inches.

[JohnR]

Hi, nice work. Haven't heard much about the RD ribbons lately.

You'll get upper-end rolloff with the arrays of FRs. Not that it's necessarily unworkable. You might like to try the line array simulator (Excel spreadsheet) from FRD consortium.

[guest60106]

Good Lord! Now that I have started studying the Linkwitz material in depth and playing with EDGE I have a plethora of ideas floating around in my head. So many ideas….so little time! The MJK stuff is really good reading. I thought I knew about speaker design. I think I know just enough to get myself in trouble. I really like the H baffle design principal for the bass section.

[guest60106]

After studying the MJK whitepaper (and other sources) and working with EDGE, the basic (read subject to modification) design I have chosen is the U- Frame shown here. I am still studying the design aspects of U-Frame mounting. The set-up still has some short comings that I am working through but all in all it seams to show promise. As stated earlier, the bass drivers which I already own are DPL-10s. The 8” full range is a Visaton B200. The main reason for the DPL-10s is first cost ($35 ea) and second, in my room I am limited to a fairly narrow baffle width (no more than 13-14 inches). I wanted more cone area for the OB set-up than I could get with one larger driver do the baffle width constraints. The combined Sd for the 4 10s is about 1332 cm^2. Sd average for an 18” driver from what I have looked at is approximately 1160 c^2. So as far as that goes I am in the ball park. I have chosen the Visaton B200 for more than one reason not the least being that I like the dynamics better than the large planer options (shown in the first model) that I have listened to. Also, the first model reminds me of a Carver Amazing Clone. I wanted to avoid that. The placement of the B200 on the baffle cam about mostly through the use of EDGE. When I started I had a pseudo D’Applolito array with the B200 in the center. According to EDGE this was less than optimal as far a baffle step is concerned. I still have more to do with this. It is a bit high (42”), but this may or my not help with the beaming aspect of the B200 as it will place the driver just above seated listening position and just below standing. I will have to try it to find out whether placing the driver at that height is detrimental to imaging. I have also toyed with the idea of designing an acoustic lens for the B200, something I have done successfully in the past with smaller Fostex full range drivers. The sides are 7” deep. I still haven’t found relevant information on specifying total baffle width for dictating a suitable f3. The Bass driver Qts is specified @ .76 and I have little information on the actual roll off. I will break the drivers in and measure the specs before I have numbers I can depend on. For the roll off, I will have to get this information from measurements with test baffles.

Discussion welcome.









Matthew

[mcgsxr]

In my experience with the b200 Visaton (over 5 years on OB now), they benefit from a number of things.  One is being slightly higher or lower than your listening position, I think that will help with beaming.

Moreso, are the Planet 10 mods to use the wooden phase plugs.  They made a dramatic difference in high frequency linearity in my system, they are here to stay for sure.  http://www.planet10-hifi.com/pp-info.html

The use of many 10's should work out fine.

I am the wrong guy to comment on anything else in your design, the U shaped baffle will draw both praise and criticism, but for my enjoyment, it is in the experimentation.  I would draft up some baffles in mdf, to test it out and see how it gels with your ears.

Have fun, thanks for sharing!

[canzld]

In my experience, using the 7inch u frame with the B200 will not maximize imaging

[ebag4]

In my experience, using the 7inch u frame with the B200 will not maximize imaging

That was my experience as well while testing the B200 in various baffles.  The wings always seemed to mudy the midrange beauty of the B200.

Best,
Ed

[guest60106]

In my experience, using the 7inch u frame with the B200 will not maximize imaging

That may very well be the case. I have no experience in design with the B200. I will know more after I build test baffles. Thank you for the heads up.

[Angaria]

maybe you could eliminate the U-baffle just in the area around the b200 and get the best of both worlds.

[guest60106]

Yet another iteration,

I really like preliminary design work. The problem for me has always been committing to a design. Once I do, I just go for it and make it work.

I picked up this idea from looking at other projects here on the forum. It is 6 pieces of ¾ MDF laminated together. It has obvious vibration advantages, especially if I mount it on Mcmaster-Carr rubber isolation feet. I have had good luck using those in the past. They seem to sound better to me than spikes. Much more tolerant of floor surfaces too. I can get all the wood I need out of 3 4x8 sheets of MDF so the design is fairly efficient to build. I own all of the drivers so I don’t have to buy anything but the wood. The rear tweeter (both tweeters are Focal TI-21s) will be driven out of phase with the front. The mid is an Arum-Cantus 180F1D DVC. I believe this can lend flexibility to crossover options but from the response graph, that diver could be a little complicated crossing to the Focal. The only major concern I have is the deep cylindrical insets on the back of the drivers. This may add slight U-frame (those with experience feel free to chime in) loading? Not sure. It is possible this may help or hurt. If it is an issue I may be able to step the cutouts larger in diameter as I laminate the MDF panels to the rear, then smooth them with filler and sandpaper yielding a conical shape. The design lends itself well to finish options. I like the radius edge painted contemporary look shown in the last 3 pics. My wife prefers a more conventional look by doing a wood edge surround frame and a grill to cover the drivers.

Critiques welcome.

[ttan98]

Hi,

At one stage I was trying to build speakers similar9not the say) to yours, I was told the configuration is very difficult to get the horizontal and vertical dispersion correctly hence will affect your sound image. Also the x-over is fairly complex.

It is much easier to get the vert. & Hor. dispersion correctly if you line up the drivers vertically, there is much to say about this principle is because you can seldom find speakers with your speakers orientation.