Been working on the xovers for a few days to replace the woofers with RS270P-8's. I ran up a new set of measurements for these woofers and have come up with the below revised schematic (6 changes highlighted in yellow). Everything else is the same. I'll attach the new 6 pack model and then some of the individual 25dB/decade graphs for clarity. It's hard to see the detail in the 6 pack model alone.
Revised xover:
Revised 6 pack model:
On-axis FR and Listening window (25dB/decade aspect ratio). Crossovers are now 750 and approx 4kHz. The upper xover is probably a little bit too high, as this is causing a very narrow vertical lobe in the presence region. Also, the woofer breakup at 2-3kHz is only about 15dB down. On the positive side, the on-axis FR is plus or minus 1dB from 50 to 20,000Hz!
Power & DI screen at 25dB/decade. Nice, smooth downward sloping power response and PIR curves. Smooth gentle upward slope on the bottom most ERDI curve.
Horizontal directivity looks very smooth all the way out to 90 degrees. The first graph is the line chart and the 2nd graph is the heat map version:
Now for the bad news: Here is the vertical directivity out to 45 degrees. The first graph is the line chart and the 2nd graph is the heat map version. Notice how narrow the vertical becomes in the presence region. This is due to the driver spacing (approx 5.5" ctr to ctr) and the high xover frequency (4kHz). I think I need to do something about this.
Finally, here is the Group Delay and Phase chart. Very good phase tracking between drivers. Group delay is very low, 0.5ms or less down to 300Hz, then bumps up to 1ms at 200Hz, 3ms at 100Hz, and 10ms at 50Hz. Looks OK to me for a standard bass reflex type design.
@Steve_Lee said:
Is the room causing any of these abrupt vertical dispersion dips @10 & 20* off-axis or just driver spacing on the MT section (as you suggest)?
Everything else looks incredibly good to me as a casual observer.
Thanks, Steve. No, these dips would not be the room. The modeled vertical curves are quasi-anechoic. Room reflections have been gated out. I think this is simply a function of driver spacing and the high xover frequency of 4kHz. One half wavelength at 4kHz is 1.69 inches. That is probably the difference to the tweeter and midrange driver cones from a distance of 2.5 meters at 10 degrees vertical.
I still have the old xover installed in the speaker, so I have been listening to this problem to see how bad (or good) it sounds. You can definitely hear the highs roll off when you stand up from a seated position. I did some "high flying" type vertical sweeps with OmniMic and discovered that the lobe tilts down by 5 degrees or so. So if I tilt the speakers back by 5 degrees, there is no difference in the sound or the measurement between the seated and standing positions. I really like the way it sounds, the tweeter and mid blend together very well. So I may just leave the xover the way it is and modify my stands to tilt the speaker back by 5 degrees.
Great looking speakers Bill and it looks like you've almost got the xo's nailed (sans the woofer break up which I'm sure you'll address).
Question: My RS270P-4 woofers have the typical "Dayton RS" extended pole pieces. Your RS270P-8 appear to have dust caps. Did I miss where you knocked out the extended pole pieces and glued on dust caps?
@PWRRYD said:
Great looking speakers Bill and it looks like you've almost got the xo's nailed (sans the woofer break up which I'm sure you'll address).
Question: My RS270P-4 woofers have the typical "Dayton RS" extended pole pieces. Your RS270P-8 appear to have dust caps. Did I miss where you knocked out the extended pole pieces and glued on dust caps?
Thanks, Craig! You have a very sharp eye! Caught me in another one of my many speaker building mistakes! I was wondering if anyone was going to catch this. You didn't miss anything. I used these woofers in my Kowaxial speakers and, several years ago, I was having trouble getting the bass reflex alignment to match my WinISD model. Thinking that perhaps I had an air leak through the phase plug, I knocked out the plugs and silicone glued two dust caps, with added mass, onto the cones. EDIT: This reduced the SPL somewhat so they did not sound as boomy, but made no improvement in the low frequency extension. I did not have time to re-measure them before loading up the speakers for the long trip to MWAF. Then, after I got back from MWAF, I completely forgot about the problem and never bothered to re-measuring them.
Fast forward to a few days ago. I mounted the RS270P-8's in my Retro speakers and tried to run up a new set of measurements. But I was getting a huge FR notch, of about 10dB, that ran from 200 to 400Hz. Like something was out of phase in the center of the cone and really messing up the response. So, I very carefully removed the dust caps and re-installed the phase plugs. Problem solved. Nice, smooth response out to about 1kHz or so. That phase plug was in there for a reason. Luckily, the RS270P's paper cones are treated and sealed, so the silicone did not soak into the paper. The silicone pealed away from the cone with no damage. In the pic below, you can see a little scuffing where the dusk cap was glued, but the cone is still in excellent shape. So, I was able to successfully restore both woofer phase plugs. Sorry for the long explanation.
I wonder if the siliconed dust cap was resonating out of phase because it wasn't tightly coupled to the cone? Maybe if it were preped and epoxied it might not have had that issue? Just seems odd as most dust capped drivers don't automatically have an issue.
@6thplanet said:
I wonder if the siliconed dust cap was resonating out of phase because it wasn't tightly coupled to the cone? Maybe if it were preped and epoxied it might not have had that issue? Just seems odd as most dust capped drivers don't automatically have an issue.
I think you are correct. I can't believe that I actually did this, but I also siliconed a steel washer to the underside of the 2.5" diameter dust caps in an effort to increase the mass of the cone and "improve" the alignment. With the steel washers, the dust caps weigh 36 grams each (see pic). Mms for these woofers is only 72 grams, so that amounts to a 35% increase in the total mass of the cone! No wonder my measurements came out so bad! Below is an overlay comparing NF with dust cap verses NF with phase plug. Wow! Egg on face!
Note: The green NF curve for the restored woofer still shows a smaller glitch at 700Hz, but this glitch does not show up in the FF gated measurement for the same woofer. So I don't think this is real. NF measurements for 10 woofers are not accurate above about 500Hz or so. The red curve's larger glitch at 400Hz is real and shows up in both the NF and FF curves for the same woofer.
I'm getting ready to register for SDC and am considering changing the name to "Retrolaspeak" This would be a merging of "retro" + "motorola" + "loudspeaker" Motorola was originally a car radio company back in the 40's. So they merged "Motor" + "Victrola" to get Motorola. So, the "retro" would refer to the Morel MDT33 and Vifa D75MX speakers. The "motorola" would refer to the idea of moving down the road to the more modern Dayton RS270P-8 (only about 7 or 8 years old). What do you think? Or would you go with something different?
I messed up the angle cuts when attempting to mod my original 9" high stands for a 5 degree tilt back. So, I cut my 13" stands down to 9" and gave them a 5 degree tilt back. I salvaged most of the mahogany/maple boards from the original stands by wrapping it around the center sections. Didn't turn out too bad.
Comments
Been working on the xovers for a few days to replace the woofers with RS270P-8's. I ran up a new set of measurements for these woofers and have come up with the below revised schematic (6 changes highlighted in yellow). Everything else is the same. I'll attach the new 6 pack model and then some of the individual 25dB/decade graphs for clarity. It's hard to see the detail in the 6 pack model alone.
Revised xover:
Revised 6 pack model:
On-axis FR and Listening window (25dB/decade aspect ratio). Crossovers are now 750 and approx 4kHz. The upper xover is probably a little bit too high, as this is causing a very narrow vertical lobe in the presence region. Also, the woofer breakup at 2-3kHz is only about 15dB down. On the positive side, the on-axis FR is plus or minus 1dB from 50 to 20,000Hz!
Power & DI screen at 25dB/decade. Nice, smooth downward sloping power response and PIR curves. Smooth gentle upward slope on the bottom most ERDI curve.
Horizontal directivity looks very smooth all the way out to 90 degrees. The first graph is the line chart and the 2nd graph is the heat map version:
Now for the bad news: Here is the vertical directivity out to 45 degrees. The first graph is the line chart and the 2nd graph is the heat map version. Notice how narrow the vertical becomes in the presence region. This is due to the driver spacing (approx 5.5" ctr to ctr) and the high xover frequency (4kHz). I think I need to do something about this.
Finally, here is the Group Delay and Phase chart. Very good phase tracking between drivers. Group delay is very low, 0.5ms or less down to 300Hz, then bumps up to 1ms at 200Hz, 3ms at 100Hz, and 10ms at 50Hz. Looks OK to me for a standard bass reflex type design.
Is the room causing any of these abrupt vertical dispersion dips @10 & 20* off-axis or just driver spacing on the MT section (as you suggest)?
Everything else looks incredibly good to me as a casual observer.
This is one where I definitely want to spend time listening to hear what's going on at 4K up
Thanks, Steve. No, these dips would not be the room. The modeled vertical curves are quasi-anechoic. Room reflections have been gated out. I think this is simply a function of driver spacing and the high xover frequency of 4kHz. One half wavelength at 4kHz is 1.69 inches. That is probably the difference to the tweeter and midrange driver cones from a distance of 2.5 meters at 10 degrees vertical.
I still have the old xover installed in the speaker, so I have been listening to this problem to see how bad (or good) it sounds. You can definitely hear the highs roll off when you stand up from a seated position. I did some "high flying" type vertical sweeps with OmniMic and discovered that the lobe tilts down by 5 degrees or so. So if I tilt the speakers back by 5 degrees, there is no difference in the sound or the measurement between the seated and standing positions. I really like the way it sounds, the tweeter and mid blend together very well. So I may just leave the xover the way it is and modify my stands to tilt the speaker back by 5 degrees.
Great looking speakers Bill and it looks like you've almost got the xo's nailed (sans the woofer break up which I'm sure you'll address).
Question: My RS270P-4 woofers have the typical "Dayton RS" extended pole pieces. Your RS270P-8 appear to have dust caps. Did I miss where you knocked out the extended pole pieces and glued on dust caps?
Thanks, Craig! You have a very sharp eye! Caught me in another one of my many speaker building mistakes! I was wondering if anyone was going to catch this. You didn't miss anything. I used these woofers in my Kowaxial speakers and, several years ago, I was having trouble getting the bass reflex alignment to match my WinISD model. Thinking that perhaps I had an air leak through the phase plug, I knocked out the plugs and silicone glued two dust caps, with added mass, onto the cones. EDIT: This reduced the SPL somewhat so they did not sound as boomy, but made no improvement in the low frequency extension. I did not have time to re-measure them before loading up the speakers for the long trip to MWAF. Then, after I got back from MWAF, I completely forgot about the problem and never bothered to re-measuring them.
Fast forward to a few days ago. I mounted the RS270P-8's in my Retro speakers and tried to run up a new set of measurements. But I was getting a huge FR notch, of about 10dB, that ran from 200 to 400Hz. Like something was out of phase in the center of the cone and really messing up the response. So, I very carefully removed the dust caps and re-installed the phase plugs. Problem solved. Nice, smooth response out to about 1kHz or so. That phase plug was in there for a reason. Luckily, the RS270P's paper cones are treated and sealed, so the silicone did not soak into the paper. The silicone pealed away from the cone with no damage. In the pic below, you can see a little scuffing where the dusk cap was glued, but the cone is still in excellent shape. So, I was able to successfully restore both woofer phase plugs. Sorry for the long explanation.
I wonder if the siliconed dust cap was resonating out of phase because it wasn't tightly coupled to the cone? Maybe if it were preped and epoxied it might not have had that issue? Just seems odd as most dust capped drivers don't automatically have an issue.
I think you are correct. I can't believe that I actually did this, but I also siliconed a steel washer to the underside of the 2.5" diameter dust caps in an effort to increase the mass of the cone and "improve" the alignment. With the steel washers, the dust caps weigh 36 grams each (see pic). Mms for these woofers is only 72 grams, so that amounts to a 35% increase in the total mass of the cone! No wonder my measurements came out so bad! Below is an overlay comparing NF with dust cap verses NF with phase plug. Wow! Egg on face!
Note: The green NF curve for the restored woofer still shows a smaller glitch at 700Hz, but this glitch does not show up in the FF gated measurement for the same woofer. So I don't think this is real. NF measurements for 10 woofers are not accurate above about 500Hz or so. The red curve's larger glitch at 400Hz is real and shows up in both the NF and FF curves for the same woofer.
Right on.
Hey, +1 for trying stuff, I freaking dig that!
I'm getting ready to register for SDC and am considering changing the name to "Retrolaspeak" This would be a merging of "retro" + "motorola" + "loudspeaker" Motorola was originally a car radio company back in the 40's. So they merged "Motor" + "Victrola" to get Motorola. So, the "retro" would refer to the Morel MDT33 and Vifa D75MX speakers. The "motorola" would refer to the idea of moving down the road to the more modern Dayton RS270P-8 (only about 7 or 8 years old). What do you think? Or would you go with something different?
I like it, Bill. It really isn't the previous project any longer anyway....
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Not too bad. The bulge in 3rd harmonic @ 600Hz is 0.4%. Typically 0.2% to 0.3% elsewhere for 2nd and 3rd harmonic.
I messed up the angle cuts when attempting to mod my original 9" high stands for a 5 degree tilt back. So, I cut my 13" stands down to 9" and gave them a 5 degree tilt back. I salvaged most of the mahogany/maple boards from the original stands by wrapping it around the center sections. Didn't turn out too bad.
Original stands:
New stands: