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I’ll start this off by saying that I will never build another system without a wave guide. If there are any downsides, I don’t see them.
This system uses 2 RS180 midbass and one XT25tg60 (double magnet) in a wave guide crossed actively at 1700hz. The XT25/60 is superior to the single magnet XT25/30. It more efficient, has a cleaner measuring low end, and its only a few dollars difference. I used a cap on the tweeter at around 5000hz passive and a coil on the lower RS180 to cut it off early in addition to the active cross over. The cap lowers distortion because it keeps operating lower and lower in frequency in comparison to simply EQ'ing the response flat. Since higher order distortion is based on what is happening far lower in freq, the cap lowers F4 and F5 up top too. The lower crossed RS180 eliminates baffle step cross over inefficiencies and increases system efficiency. Using two RS180's also lowers the distortion at a given SPL. I imagine system efficiency is near 93db with two paralelled RS180's and the XT25/60 is also 93db. Being active, the drivers didnt really have to be that close in efficiiency but the match will help those trying a passive cross. I also placed a notch actively at the tweeter resonance and lowQ at the twin peaks average on 7500hz.
Wave guides lower distortion by using a cap to counter the rising low end lifted by the wave guide. I dont have measurement equipment but the way the XT25 is used here counters any statement about its low end distortion.
To illustrate for others who aren't aware of wave guides' effects added to a tweeter..............
This is the Seas 27-TDFC bare response (Not this system)
Image not available
This is the lift with a small 6" wave guide (I used a 8" wide for the XT25 = more low end lift)
Image not available
This is the response with a 3.3 cap on it:
Image not available
Here is the bare tweeter distortion plot
Image not available
Here is the distortion plot with guide and cap. The F2 distortion is down by 25db at 2000hz and the response is again flat on the tweeter. Since the harmonics generate the noise up top that they're based on, the F2 is down 15db from 6-10k Hz compared to the bare tweeter. Whats really interesting is that the higher order distortion is based on whats happening from the low end (500hz) hiccups and thus the F4 and F5 is sent to the floor on the top of the range. Active crossover uses can use any slope they want countering the phase issues electronically. The roll off approximates an LR2. I dont know how to build passives but if you can then increase the crossover to LR4 from 1800 or so, the low end issues are off the map including the res freq ringing like a bell.
Image not available
As you can see the resulting response once back to flat has lower distortion by 25db around 2000hz. Once back to flat from the cap (also protects my active speaker from DC), I can apply any active slope crossover to the lower distortion XT25 as its an active system. The resonant frequency ringing is also lowered over 30db. The dispersion with a wave guide is now wall to wall as the off axis response is not falling off much even at 45 degrees off axis. It also moves the acoustic center back to match your midbass. This post is to show how wave guides improve just about everything.
Since I already owned a DCX2496 for the sub cross, adding another amp for active 2 way mains was pretty cheap taking into account how much higher order crossover costs to build especially when they don’t come out good which is most of mine. For me it’s a matter of pushing buttons and turning a knob. Having the ability of 8th order electrical with phase/time alignment is priceless to me. I can shift frequency and try many slopes so have at it.
These two unlikely driver mates can work quite well together if you add in one more ingredient: a wave guide. I have so wanted to use the XT25 with a wave guide because it seems to like them. One man who made wave guides more reasonable to use is Dave Pellegrene. His website is located at:
acoustic waveguides
I chose the 8x5 unit for limited vertical but excellent improved horizontal dispersion although I hear no drop in highs standing up as I did with the bare XT25. Horizontal dispersion is wall to wall. I lived with the XT25 for quite some time. Its night and day.
The rear mounting plate that Dave makes which makes it so easy.
The tweeter with its faceplate removed with the Dave supplied studs to bolt up the guide. Make sure you get studs that bottom out in the tweeter body or you will have the stud turn as you try to tighten the nut. You can use loc-tite on the studs if they arent bottomed out but you have to wait for that to cure before you try to tighten nuts on them. Dave sent me out longer ones when I brought the problem to his attention. He was great to deal with.
Image not available
All together and a little bit of sealant to assure an airtight fit. I know I have one because its a sealed box with movement on one mid bass as I push the other. This is essentially now a $70 tweeter with industry leading dispersion and low disrtion on the low end. The tweeter is 35 as is the wave guide. Its worth every penny.
Image not available
A secondary benefit is that the wave guide allows a lower crossover point with the same power handling but lower distortion. Moving the crossover point to 1700hz LR4 with a notch on the 600hz res frequency allows a better utilization of the RS180’s abilities within its limitations. The speaker is an active unit but I’m sure others can develop a passive crossover that will make it usable to many. I also use a notch up at the twin peaks. Feel free to comment on the crossover and other areas of improvement if you think it will help others. I’m no guru in this department. I was initiallt worried about the 1700hz cross for the RS180 but I saw that Zaph used these 7" drivers with an 850hz 2nd order cross. Thats down 24db at 3400 and so is mine. By 6000 its down >40db and >50db by 9000. Its 4th order electrical. When I had the DCX time align/phase correct, it only saw a 4mm difference from mid to tweeter so the wave guide moved it back near perfectly to match the acoustic center back to be near perfect with the RS180. This is a bigger benefit to passive crossovers.
The response with the XT25 and this waveguide. It looks to be about an 10db lift at 2000 so a cap at 6k or so brings it back down along with the distortion. I always use a cap anyway to protect from DC from the amps being active. I still had a slight 3db peak around 3500-4000 so I may try a smaller cap. For now, I just have EQ. This is the Pellegrene Acoustics supplied freq response graph and polar response graph.
Image not available
The enclosures are standard MDF units that are ¾” thick on the sides and 1.25” thick on the front and rear to allow for counter sinking.
I usually over do the thickness on my cabinets so this time I’m trying to keep it down to a mild 100lbs. The dimensions are 45.5” high counting the granite bases I had made, 10.5" x 10.5". My home theater has a 16’ diag screen and I need a higher perspective than some applications of others. I sit about 12 feet from the speakers and vertical dispersion is fine with the tweeters actual position at 38”.
The finish of the cabinets use Dave Pellegrene’s trench method for making butt joints in MDF disappear. The original article for the trench method is here: https://plus.google.com/photos/10403...609?banner=pwa
Autobody filler on the trenched seams. I put a beveled edge on so the filler will go to the new routed edge afterward.
Image not available
Image not available
Bottom plate to make the speaker appear to be floating over the granite bases. Note the beveled edges and how the trench method moved the seam into the bevel.
Image not available
Trial fit for counter sinking and here you see my grills that have cutouts for the drivers just behind them. The grills are not very invasive on the sound. I can't hear a difference.
The finish was initially going to be an auto paint finish. In my case I used the trench method to get the seams blended with Rage auto body filler. Its pretty creamy to use compared to others. Avoid Bondo brand. After Rage sets for about 10 mins start getting the big stuff off with 60-80 grit paper. Work on one side at a time. If you let the filler sit for too long it will be a week of sanding to get it smooth. Ignore people telling you to use the softer filler as the main filler. After the trenches are filled I completely covered the entire surface of the speaker with the Rage body filler for a skim coat. It creates a seamless finish more likely to resist showing through the auto quality paint job I planned to do to it. It’s a ton of work but you will get out of it what you put into it. I wasn’t looking to cut corners. Ultimately I decided to use Duratex instead of paint. In a front projection home theater, the reflective paint would be too much light. My next project already underway will be painted with auto paint. I can tell at the primer stage that this finish trench method will be seamless.
A warning on Duratex. It doesnt stick to Zinsser 123 shellac primer well during application. Once dried its fine but it spreads differently and looks like a seam where is none. I used the Zinsser because it was initially going to get an automotive paint finish.
Drivers mounted in finished cabinets
Complete with grills on. I had name plates made up for them. I named my 'speaker company' when I was 12...Axis. Do they look stare bought? Go easy on me.
Granite bases:
Rear shot showing seamless edges. This was the side with all the seams. Once primered, you cant tell its a seam. The trench method works.
Sound: The tweeter dispersion is unreal. The sweet spot is anywhere in the room for highs. It doesn’t seem to roll off even at 60 degrees off axis. Standing anywhere in the room is the same too. Height doesn’t seem to affect dispersion in my application. I have 600 watts for the tweeters. It used to fry the bare XT25 at 2K LR4. Now I see clip lights at 1700hz LR4. Even at 1500hz, theres no strain. The cap filters quite a bit. I figure its 10db headroom since thats the boost from the WG.
Crossover:
I tried 4th order electrical and 8th order electrical. Once I have the DCX2496 adjust the time alignment/phase, I cant tell a difference 4th/8th at 1700hz. An 8" wide guide would work down to 1700 so I chose that frequency (13560/8). I vary it from 1500 to 2000 and there is no real difference. I stayed wth 4th for the power handling. To cut the top end of the lower midbass, I used a 4.0 iron core inductor and the tweeter has a 4.7 clarity cap on it to level off the rising low end of the waveguide. The width of the baffle really calls for a 450hz cut off for the lower midbass but there was a peak there so I used a bigger inductor. I guess that’s then 5th order electrical on the tweeter? I had non-inverting polarity on the drivers and there was a deep null at the cross that would move if I turned the knob to change the cross freq. Once I had the DCX auto adjust for phase, it was gone. I would have been lost on the build without the Behringer. Before the auto adjust for phase/time, it sounded unfocused, not a pin point image.
My Home theater with a 16 foot diag screen. My subs are 4 15" TC sounds powered by two bridged Peavey 4080hz amps which bench test to 4400watts @ 8ohms.
I’m really happy with the results. I would like to replace all my other speakers in my house with wave guide systems. I already ordered another pair from Dave. He really made the experience easy and fun. Once EQ'd there are no honky sounds or other harshness so many claim horns produce. Each wave guide is different as is every tweeter. I imagine combos of both are different too. As it sits, I have a state of the art tweeter that plays low in freq with lower distortion than most any bare tweeter, plays louder, and has all the attributes the XT25 with a clean decay but with excellent off axis response even at 50 degrees. Does it get any better?;x(
Thanks for reading.
This system uses 2 RS180 midbass and one XT25tg60 (double magnet) in a wave guide crossed actively at 1700hz. The XT25/60 is superior to the single magnet XT25/30. It more efficient, has a cleaner measuring low end, and its only a few dollars difference. I used a cap on the tweeter at around 5000hz passive and a coil on the lower RS180 to cut it off early in addition to the active cross over. The cap lowers distortion because it keeps operating lower and lower in frequency in comparison to simply EQ'ing the response flat. Since higher order distortion is based on what is happening far lower in freq, the cap lowers F4 and F5 up top too. The lower crossed RS180 eliminates baffle step cross over inefficiencies and increases system efficiency. Using two RS180's also lowers the distortion at a given SPL. I imagine system efficiency is near 93db with two paralelled RS180's and the XT25/60 is also 93db. Being active, the drivers didnt really have to be that close in efficiiency but the match will help those trying a passive cross. I also placed a notch actively at the tweeter resonance and lowQ at the twin peaks average on 7500hz.
Wave guides lower distortion by using a cap to counter the rising low end lifted by the wave guide. I dont have measurement equipment but the way the XT25 is used here counters any statement about its low end distortion.
To illustrate for others who aren't aware of wave guides' effects added to a tweeter..............
This is the Seas 27-TDFC bare response (Not this system)
Image not available
This is the lift with a small 6" wave guide (I used a 8" wide for the XT25 = more low end lift)
Image not available
This is the response with a 3.3 cap on it:
Image not available
Here is the bare tweeter distortion plot
Image not available
Here is the distortion plot with guide and cap. The F2 distortion is down by 25db at 2000hz and the response is again flat on the tweeter. Since the harmonics generate the noise up top that they're based on, the F2 is down 15db from 6-10k Hz compared to the bare tweeter. Whats really interesting is that the higher order distortion is based on whats happening from the low end (500hz) hiccups and thus the F4 and F5 is sent to the floor on the top of the range. Active crossover uses can use any slope they want countering the phase issues electronically. The roll off approximates an LR2. I dont know how to build passives but if you can then increase the crossover to LR4 from 1800 or so, the low end issues are off the map including the res freq ringing like a bell.
Image not available
As you can see the resulting response once back to flat has lower distortion by 25db around 2000hz. Once back to flat from the cap (also protects my active speaker from DC), I can apply any active slope crossover to the lower distortion XT25 as its an active system. The resonant frequency ringing is also lowered over 30db. The dispersion with a wave guide is now wall to wall as the off axis response is not falling off much even at 45 degrees off axis. It also moves the acoustic center back to match your midbass. This post is to show how wave guides improve just about everything.
Since I already owned a DCX2496 for the sub cross, adding another amp for active 2 way mains was pretty cheap taking into account how much higher order crossover costs to build especially when they don’t come out good which is most of mine. For me it’s a matter of pushing buttons and turning a knob. Having the ability of 8th order electrical with phase/time alignment is priceless to me. I can shift frequency and try many slopes so have at it.
These two unlikely driver mates can work quite well together if you add in one more ingredient: a wave guide. I have so wanted to use the XT25 with a wave guide because it seems to like them. One man who made wave guides more reasonable to use is Dave Pellegrene. His website is located at:
acoustic waveguides
I chose the 8x5 unit for limited vertical but excellent improved horizontal dispersion although I hear no drop in highs standing up as I did with the bare XT25. Horizontal dispersion is wall to wall. I lived with the XT25 for quite some time. Its night and day.
The rear mounting plate that Dave makes which makes it so easy.
The tweeter with its faceplate removed with the Dave supplied studs to bolt up the guide. Make sure you get studs that bottom out in the tweeter body or you will have the stud turn as you try to tighten the nut. You can use loc-tite on the studs if they arent bottomed out but you have to wait for that to cure before you try to tighten nuts on them. Dave sent me out longer ones when I brought the problem to his attention. He was great to deal with.
Image not available
All together and a little bit of sealant to assure an airtight fit. I know I have one because its a sealed box with movement on one mid bass as I push the other. This is essentially now a $70 tweeter with industry leading dispersion and low disrtion on the low end. The tweeter is 35 as is the wave guide. Its worth every penny.
Image not available
A secondary benefit is that the wave guide allows a lower crossover point with the same power handling but lower distortion. Moving the crossover point to 1700hz LR4 with a notch on the 600hz res frequency allows a better utilization of the RS180’s abilities within its limitations. The speaker is an active unit but I’m sure others can develop a passive crossover that will make it usable to many. I also use a notch up at the twin peaks. Feel free to comment on the crossover and other areas of improvement if you think it will help others. I’m no guru in this department. I was initiallt worried about the 1700hz cross for the RS180 but I saw that Zaph used these 7" drivers with an 850hz 2nd order cross. Thats down 24db at 3400 and so is mine. By 6000 its down >40db and >50db by 9000. Its 4th order electrical. When I had the DCX time align/phase correct, it only saw a 4mm difference from mid to tweeter so the wave guide moved it back near perfectly to match the acoustic center back to be near perfect with the RS180. This is a bigger benefit to passive crossovers.
The response with the XT25 and this waveguide. It looks to be about an 10db lift at 2000 so a cap at 6k or so brings it back down along with the distortion. I always use a cap anyway to protect from DC from the amps being active. I still had a slight 3db peak around 3500-4000 so I may try a smaller cap. For now, I just have EQ. This is the Pellegrene Acoustics supplied freq response graph and polar response graph.
Image not available
The enclosures are standard MDF units that are ¾” thick on the sides and 1.25” thick on the front and rear to allow for counter sinking.
I usually over do the thickness on my cabinets so this time I’m trying to keep it down to a mild 100lbs. The dimensions are 45.5” high counting the granite bases I had made, 10.5" x 10.5". My home theater has a 16’ diag screen and I need a higher perspective than some applications of others. I sit about 12 feet from the speakers and vertical dispersion is fine with the tweeters actual position at 38”.
The finish of the cabinets use Dave Pellegrene’s trench method for making butt joints in MDF disappear. The original article for the trench method is here: https://plus.google.com/photos/10403...609?banner=pwa
Autobody filler on the trenched seams. I put a beveled edge on so the filler will go to the new routed edge afterward.
Image not available
Image not available
Bottom plate to make the speaker appear to be floating over the granite bases. Note the beveled edges and how the trench method moved the seam into the bevel.
Image not available
Trial fit for counter sinking and here you see my grills that have cutouts for the drivers just behind them. The grills are not very invasive on the sound. I can't hear a difference.
The finish was initially going to be an auto paint finish. In my case I used the trench method to get the seams blended with Rage auto body filler. Its pretty creamy to use compared to others. Avoid Bondo brand. After Rage sets for about 10 mins start getting the big stuff off with 60-80 grit paper. Work on one side at a time. If you let the filler sit for too long it will be a week of sanding to get it smooth. Ignore people telling you to use the softer filler as the main filler. After the trenches are filled I completely covered the entire surface of the speaker with the Rage body filler for a skim coat. It creates a seamless finish more likely to resist showing through the auto quality paint job I planned to do to it. It’s a ton of work but you will get out of it what you put into it. I wasn’t looking to cut corners. Ultimately I decided to use Duratex instead of paint. In a front projection home theater, the reflective paint would be too much light. My next project already underway will be painted with auto paint. I can tell at the primer stage that this finish trench method will be seamless.
A warning on Duratex. It doesnt stick to Zinsser 123 shellac primer well during application. Once dried its fine but it spreads differently and looks like a seam where is none. I used the Zinsser because it was initially going to get an automotive paint finish.
Drivers mounted in finished cabinets
Complete with grills on. I had name plates made up for them. I named my 'speaker company' when I was 12...Axis. Do they look stare bought? Go easy on me.
Granite bases:
Rear shot showing seamless edges. This was the side with all the seams. Once primered, you cant tell its a seam. The trench method works.
Sound: The tweeter dispersion is unreal. The sweet spot is anywhere in the room for highs. It doesn’t seem to roll off even at 60 degrees off axis. Standing anywhere in the room is the same too. Height doesn’t seem to affect dispersion in my application. I have 600 watts for the tweeters. It used to fry the bare XT25 at 2K LR4. Now I see clip lights at 1700hz LR4. Even at 1500hz, theres no strain. The cap filters quite a bit. I figure its 10db headroom since thats the boost from the WG.
Crossover:
I tried 4th order electrical and 8th order electrical. Once I have the DCX2496 adjust the time alignment/phase, I cant tell a difference 4th/8th at 1700hz. An 8" wide guide would work down to 1700 so I chose that frequency (13560/8). I vary it from 1500 to 2000 and there is no real difference. I stayed wth 4th for the power handling. To cut the top end of the lower midbass, I used a 4.0 iron core inductor and the tweeter has a 4.7 clarity cap on it to level off the rising low end of the waveguide. The width of the baffle really calls for a 450hz cut off for the lower midbass but there was a peak there so I used a bigger inductor. I guess that’s then 5th order electrical on the tweeter? I had non-inverting polarity on the drivers and there was a deep null at the cross that would move if I turned the knob to change the cross freq. Once I had the DCX auto adjust for phase, it was gone. I would have been lost on the build without the Behringer. Before the auto adjust for phase/time, it sounded unfocused, not a pin point image.
My Home theater with a 16 foot diag screen. My subs are 4 15" TC sounds powered by two bridged Peavey 4080hz amps which bench test to 4400watts @ 8ohms.
I’m really happy with the results. I would like to replace all my other speakers in my house with wave guide systems. I already ordered another pair from Dave. He really made the experience easy and fun. Once EQ'd there are no honky sounds or other harshness so many claim horns produce. Each wave guide is different as is every tweeter. I imagine combos of both are different too. As it sits, I have a state of the art tweeter that plays low in freq with lower distortion than most any bare tweeter, plays louder, and has all the attributes the XT25 with a clean decay but with excellent off axis response even at 50 degrees. Does it get any better?;x(
Thanks for reading.