@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
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....
InDIYana Event Website
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: