Thoughts on 12" Full-Range EV's for Open Baffles

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SuperTzar

  • Jr. Member
  • Posts: 6
Thoughts on 12" Full-Range EV's for Open Baffles
« on: 4 Mar 2018, 03:44 am »
Hi everyone,

Here goes my second foray into open baffle speakers. I have just finished reconing and modifying a pair of Electro-Voice SP12C speakers. I took some inspiration from the Eminence Beta 12LTA mods I've seen by adding a wooden craft egg for a phase plug. I also treated the cones with mod-podge glue and left off the whizzer cones.



After running the speakers in free air with no baffles, it's obvious that they'll be suited open baffles. The sound is a little harsh, but they have bass even on their own.



I've drawn up a design for a simple open baffle. My space isn't too big, 11'x14' or thereabouts, so the baffles can't be too big. I'll run the EV's on their own first, but will probably end up using a super-tweeter. I'm thinking the new Eminence APT-30 would be a good choice. Similar sensitivity to the EV's, so I can probably just use a 1 or 2 uf cap for a crossover.

These are my thoughts and ideas on implementing 12" full range drivers for open baffle use. Hopefully it's on the right track, feel free to comment or critique.


richidoo

Re: Thoughts on 12" Full-Range EV's for Open Baffles
« Reply #1 on: 4 Mar 2018, 06:27 am »
Welcome to AudioCircle!

Qts of the original SP12C was .67, which by itself is good for OB use, but the Xmax is only .13", so while it should play pretty low in OB, it can't play low and loud in OB. The TS specs suggest it is a good warm sounding fullrange driver relying on a vented box to make good bass. ymmv. It will probably do OK in OB as long as you don't push it to bottom out quickly at LF.

Consider time alignment between the two drivers when you design your baffle. The crossover frequency, filter slopes, baffle tilt and baffle position of the drivers all affect the time alignment. You want the sound from both drivers playing at the same frequencies to arrive at your ears at the same time. The APT30 tweeter is probably about same acoustic length as the woofer, so maybe the baffle at the center point between the 2 drivers can be angled to be normal (perpendicular) to your listening angle. But whether tweeter is longer or shorter you'll want to tilt the baffle or position the tweeter so that the waveforms from both drivers stay aligned thru the entire xo band.

The necessarily large center to center distance between the woofer and the tweeter will cause frequency response lobing cancellation at mid and high frequencies. You'll hear a change in tone as you move your head position around. Can't be avoided with these drivers, no way to make their centers more coaxial because of woofer's large diameter. Ideally they would be spaced within 1/2 wavelength of the xo freq. to avoid the perception of lobing. If you crossover very high, like 5k or higher, then the lobes will be very small in size, maybe not so noticeable, or maybe even more noticeable depending on how deep the FR cancellations and other acoustic factors like wall reflections.

The APT 30 is only 93dB sensitivity, while the EV woofer is 100db sensitive. You want to avoid using resistors on the woofer as that will ruin the electrical damping of the woofer (amplifier's control of the cone) which reduces the detail you hear. You may prefer using the APT80, which has 102dB sensitivity, easily matched to the woofer with a resistor network, which will not harm the woofers damping.  But APT80 is twice as deep as APT30, so it will be more difficult to achieve time alignment. You could move the tweeter forward up off of the baffle to align with woofer. Or maybe there are other tweeter horns you can check out to find a shallow tweeter with 100dB sensitivity. There are many listed at usspeaker.com, and on partsexpress.com. 

Because of these issues, you are wise to try listening to just the woofer at first. It's supposed to play up to 10kHz, but at that freq the treble will be a laser thin beam. The new recone and surround may not play that high anyway unless the replacement parts are specifically made for this driver. The link above provides details on how to build a reflex box for these drivers, in case you decide to try that in addition to trying OB.

Good luck!
Rich

SuperTzar

  • Jr. Member
  • Posts: 6
Re: Thoughts on 12" Full-Range EV's for Open Baffles
« Reply #2 on: 4 Mar 2018, 07:32 pm »
Welcome to AudioCircle!

Qts of the original SP12C was .67, which by itself is good for OB use, but the Xmax is only .13", so while it should play pretty low in OB, it can't play low and loud in OB. The TS specs suggest it is a good warm sounding fullrange driver relying on a vented box to make good bass. ymmv. It will probably do OK in OB as long as you don't push it to bottom out quickly at LF.

Consider time alignment between the two drivers when you design your baffle. The crossover frequency, filter slopes, baffle tilt and baffle position of the drivers all affect the time alignment. You want the sound from both drivers playing at the same frequencies to arrive at your ears at the same time. The APT30 tweeter is probably about same acoustic length as the woofer, so maybe the baffle at the center point between the 2 drivers can be angled to be normal (perpendicular) to your listening angle. But whether tweeter is longer or shorter you'll want to tilt the baffle or position the tweeter so that the waveforms from both drivers stay aligned thru the entire xo band.

The necessarily large center to center distance between the woofer and the tweeter will cause frequency response lobing cancellation at mid and high frequencies. You'll hear a change in tone as you move your head position around. Can't be avoided with these drivers, no way to make their centers more coaxial because of woofer's large diameter. Ideally they would be spaced within 1/2 wavelength of the xo freq. to avoid the perception of lobing. If you crossover very high, like 5k or higher, then the lobes will be very small in size, maybe not so noticeable, or maybe even more noticeable depending on how deep the FR cancellations and other acoustic factors like wall reflections.

The APT 30 is only 93dB sensitivity, while the EV woofer is 100db sensitive. You want to avoid using resistors on the woofer as that will ruin the electrical damping of the woofer (amplifier's control of the cone) which reduces the detail you hear. You may prefer using the APT80, which has 102dB sensitivity, easily matched to the woofer with a resistor network, which will not harm the woofers damping.  But APT80 is twice as deep as APT30, so it will be more difficult to achieve time alignment. You could move the tweeter forward up off of the baffle to align with woofer. Or maybe there are other tweeter horns you can check out to find a shallow tweeter with 100dB sensitivity. There are many listed at usspeaker.com, and on partsexpress.com. 

Because of these issues, you are wise to try listening to just the woofer at first. It's supposed to play up to 10kHz, but at that freq the treble will be a laser thin beam. The new recone and surround may not play that high anyway unless the replacement parts are specifically made for this driver. The link above provides details on how to build a reflex box for these drivers, in case you decide to try that in addition to trying OB.

Good luck!
Rich

Thanks Rich, you've made some very good points.

Unfortunately the T/S specs supplied by EV don't really apply to my speakers as I used recone kits for the earlier SP12B, plus I made some modifications. I suspect their Qts is somewhere between 0.7 and 1.0, due to my cone treatment adding mass and lowering the fs. These modifications may have also lowered the sensitivity somewhat.

My plan is to listen to them full-range on their own in the open baffles, and then add some kind of baffle step compensation if they're too bright. A super tweeter is a last resort option, and I was hoping that by crossing it over fairly high that I would avoid issues with lobing.

richidoo

Re: Thoughts on 12" Full-Range EV's for Open Baffles
« Reply #3 on: 5 Mar 2018, 01:08 am »
I think you have the right approach. They are what they are, and they will sound good, so just listen and see what happens, then make adjustments from there, just like with any new system. The fun never ends. :)

The upward angle of the baffle may serve you well if it shoots the treble beam over your head.

The woofer center is very low, and that's where the treble comes from, so that's where the sonic picture will appear. I like treble to come from 40-45" high, a little above my ears while I'm seated. But putting the woofer near the ground prevents floor bounce cancellation in mid bass frequencies and also provides some EQ support to the bass frequencies in general. Maybe you can design the baffle so it can be inverted to raise the center up a little higher while baffle still touches the ground, to enable experimentation.

The side panels will provide good bracing against baffle vibration, but angle them outward slightly, or use some absorbent material on the inside surfaces to prevent them slap echoing in midrange wavelengths. Or make it an open triangle instead of solid panel.

Try mounting the woofer off center so the baffle diffraction step will be less pronounced in the FR. 3" either way can smooth out the FR nicely. A nice trick is to size the baffle and place the woofer so that the distance from woofer center to each baffle edge differs by 3", spreading out the diffraction frequencies to smooth the FR compared to all edges falling off at same freq and seeing a more pronounced edge effect in the FR. An example I would do is to increase the height of the baffle by 1", then move the driver left by 3" and down by 1" and you will have perp. distances from driver center to the edges of 6", 9" 12" and 15" from center of driver to the edge. The points of the rectangular baffle further vary the distance to edge and smooth the FR. An app you can use to simulate and fine tune the offset of your driver position for flattest FR is The Edge.

You probably won't need any baffle step correction with such high Q.

SuperTzar

  • Jr. Member
  • Posts: 6
Re: Thoughts on 12" Full-Range EV's for Open Baffles
« Reply #4 on: 5 Mar 2018, 07:13 am »
I think you have the right approach. They are what they are, and they will sound good, so just listen and see what happens, then make adjustments from there, just like with any new system. The fun never ends. :)

The upward angle of the baffle may serve you well if it shoots the treble beam over your head.

The woofer center is very low, and that's where the treble comes from, so that's where the sonic picture will appear. I like treble to come from 40-45" high, a little above my ears while I'm seated. But putting the woofer near the ground prevents floor bounce cancellation in mid bass frequencies and also provides some EQ support to the bass frequencies in general. Maybe you can design the baffle so it can be inverted to raise the center up a little higher while baffle still touches the ground, to enable experimentation.

The side panels will provide good bracing against baffle vibration, but angle them outward slightly, or use some absorbent material on the inside surfaces to prevent them slap echoing in midrange wavelengths. Or make it an open triangle instead of solid panel.

Try mounting the woofer off center so the baffle diffraction step will be less pronounced in the FR. 3" either way can smooth out the FR nicely. A nice trick is to size the baffle and place the woofer so that the distance from woofer center to each baffle edge differs by 3", spreading out the diffraction frequencies to smooth the FR compared to all edges falling off at same freq and seeing a more pronounced edge effect in the FR. An example I would do is to increase the height of the baffle by 1", then move the driver left by 3" and down by 1" and you will have perp. distances from driver center to the edges of 6", 9" 12" and 15" from center of driver to the edge. The points of the rectangular baffle further vary the distance to edge and smooth the FR. An app you can use to simulate and fine tune the offset of your driver position for flattest FR is The Edge.

You probably won't need any baffle step correction with such high Q.

Ah good idea on putting absorbent material on the wings. I've also considered adding a shelf to the top edge of the baffle above the driver, similar to the JE Labs open baffle. Something that might help  prevent early reflections. I may also make the wings flush with the sides of the baffle, so I can offset the driver. I didn't really leave myself enough room to do that. I'm hoping that the angle of the baffle will raise the sound stage, but I wanted to keep the driver low to reinforce the bass response as much as possible.

Another thought I've had is how much high extension do we really need? As far as most music is concerned, there is little going on above 10Khz. So if these EV speakers are solid up to 8 or 9Khz, then am I really missing that much?

JohnR

Re: Thoughts on 12" Full-Range EV's for Open Baffles
« Reply #5 on: 5 Mar 2018, 09:53 am »
There may not be "much" over 10k but you will miss it if it's not there.

Still, I think you should just build it and see. I think you will end up adding a sub/woofer and a tweeter, and possibly a midrange, but you have to start to start  :thumb:

SuperTzar

  • Jr. Member
  • Posts: 6
Re: Thoughts on 12" Full-Range EV's for Open Baffles
« Reply #6 on: 9 Mar 2018, 03:30 am »
I've also considered adding a top panel to the baffle similar to what is used on the JE Labs open baffles. Something like an 11" wide by 6" deep panel mounted to the top edge of the baffle above the driver.

It is said to focus the midrange and bass, and prevent early reflection. I don't know if it's worth adding, but I could try it with and without to hear if it really does make a noticeable difference in the sound.

Also, I've been listening to the drivers on their own with no baffle, just sitting on the floor, and I've really fallen in love with them. Hopefully I'll get the baffles made up next week, I'm really looking forward to hearing these speakers reach their full potential.