Accidental Manzanita Ultra Plus

After building a pair of Decware DNA rear loaded horns, I became enamored by the sound of the Alpair 10P speakers. So clear, so coherent. If only they had the bass to go with that sound. Don’t get me wrong, they’re impressive in the DNA horns, but they won’t shake the house. After coming across the Manzanita thread, I thought two GRS woofers in parallel should bring the efficiency up to about the same level as the Alpairs and make the crossover a piece of cake. Long story short, built a set of open baffles similar to the Manzanita Ultra Plus but using the Alpair 10Ps. I could get them to sound wonderful using an active crossover but just could not get a passive put together that didn’t sound like crap. The Alpairs went back into the DNAs and the Ultras into a corner of the basement.
While on a trip to Walmart I found a Blaupunkt touch screen stereo on clearance for $35 with two 6.5” speakers. Since my old truck needed a stereo, this was a no brainer. I tried out the speakers and they sounded amazingly good for something you can buy for about $25 a pair but were lacking in the bass department. They didn’t go into the truck but I tried them in a transmission line alignment that I had and was very impressed by them. I almost stopped there but happened to notice the frames with the two GRS sitting in the corner. Cut the ears off the 6.5” Blaupunkts and into the frames they went. A Parts Express 4 ohm 100hz crossover was wired in as a simple first order and a pot used to pad down the Blaupunkts. Amazing sound out of a total of about $200 of parts! I’ve replaced the pot with 8ohm resistors and may have to do a little shaping but it is damn close as is. The Blaupunkts are basically operating full range and naturally fall off in the lower octaves. The 9mh inductor of the crossover tunes 4ohms to 47hz but the slow rise of the GRS woofers combined with the inductor ends up pretty flat to 200hz before tapering off. It just works.
 
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Here they are;
 

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Here is the crossover, if you look close, you can see where I ground the foil off to let the resistor work. Woofers are only using the inductor, Blaupunkts are through the cap and 8 ohm. Basically full range.
 

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Parts list;
4 GRS 15PF-8 x $24.70 = $98.80 Parts Express
Blaupunkt GTX 650 coax = $22.68 Walmart
2 x Parts Express 100 Hz Low Pass 4 Ohm Crossover = $33.90
2 x 8 Ohm 20W Resistor Wire Wound = $2.08
1 4x8 Sheet Baltic Birch $70
$227.46 Total

Considerable money could be saved by using Big Box Store Birch bringing this to an under $200 build but I wouldn’t recommend it. Good wood sounds good.
 
Here is the measured FR at about 12 feet. Pretty severe dip at 80HZ but I'm pretty sure that it is due to the rear reflection. As I walk through the room I can plainly detect low frequency lobing. Obviously the distance from rear walls is going to have a marked effect on sound quality. I don't have cables and space enough to do much experimenting. The rise from 10khz up is something that I may have to address. Even my old ears can hear it.
 

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Update: after playing around with these for a couple weeks, I decided to try the Alpair 10p’s again with what I’ve learned. First thing I’ve found is that quite contrary to what seems to be the common consensus, a $23 15” speaker really doesn’t sound that good. They seem to be perfectly acceptable in the subwoofer range, a kettle drum sounds like a kettle drum, but vocals coming out of the GRS woofers make me cringe. What I’ve ended up with is a second order 100hz low pass on the woofers. This rolls them pretty well out of the way by 200hz. Getting the Alpair to blend was a much bigger challenge, though in the end, very few parts were used. Mark Fenlon is pretty adamant about not playing his speakers through crossover components but I found some hints from Curt Campbell’s Halcyon design. Curt crossed his speakers over at 400hz but I was focusing on 200. I originally tried to use a voltage divider to pad down the Alpairs so that impedance would stay but found that it really ruined the FR of the speakers. Curt used series resistance to pad his and when I tried that, the sound quality came back. I’m using a 30uF capacitor rather than Curts 10uF and that let them reach down to where they cross flat. The rise in impedance of the Alpairs at low frequencies results in some unusual values of components to get the result you want. As Curt found, a pricey cap sounds much better than a cheap one with these speakers. I’m now more than thrilled with these, being my first open baffle. The Alpairs are handling 90% of the content, most importantly the vocals, while being protected from the lowest frequencies, allowing very high SPL without bottoming. As I mentioned, the GRS woofers seem pretty accurate with the lows. When I play “Chant” the drum hits sound like you are standing next to the big drums and “Cosmic Hippo” will rumble your chest. Combine that with the clarity of the Alpairs and I’m in audio nirvana. I was rather concerned about 4ohm lows and 16 ohm highs but my amp doesn’t seem to mind at all.
 
Fun in OB land

Fourears, it has been interesting to read your post(s) and the sonic discoveries your project has provided you. For the UP to work as intended (as you have worked it out via trial and error) is to use a full range capable of reaching down into the 250 Hz area. My original used the good, but expensive Seas FA22RCZ 8" full range. To clean up the GRS woofer, I added an appropriate trap to control the cone break up and left the large single inductor with its 6 db electrical roll off. This provides smooth driver integration without an overly complicated crossover. The UP is one of those rare speakers that can fill the rolls of audiophile and home theater duties for an amazing low material cost.

However there are two negatives, size and distance requirements out from the rear wall. Thank you for sharing your experience. John
 
Wow, John! Didn’t expect to hear from you. I can’t thank you enough for sharing your Ultra with the community. Reading the thread about it is what inspired me to build these. I’m really happy with the way these are performing now but there is still some tweaking to do. I think some felt around the back of the full rangers to silence the reflections might be in order and some minor shaping of the woofers response. Thanks again!
 
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Very Nice!

How do the Blaupunkt's ($22.70 + shipping,etc pr USD) compare to the Alpair 6P ($220 + shipping, etc USD)?

This is the first time I've seen measurements of a car speaker used for a home system.

Is there anyway to bring down the top end?

https://www.walmart.com/ip/Blaupunkt-6-5-360W-4-Way-Coaxial-Speakers-GTX650/54964475

Markaudio Alpair-10P Paper Cone 6" Full Range: Madisound Speaker Components


Years ago I bought a TV from Visions Electronics, got the price down & asked the sales manager to throw in a pair of Polk MC60 ceiling speakers, nice guy, he did.
I built a pair of Polk MC60 Open Baffle, easist speakers I've built, nice sounding too!
Inspired by:

6moons audio reviews: Polking fun at DIY speakers

TIA-Chris
 
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Chris, the Blaupunkts sound better than they have any right to for the $$. In my opinion, however, they do not hold a candle to the Alpairs. The coax tweeters look like they are made out of tin foil but very clear highs are emitted from them. The bottom end is lacking, forcing fill in from the big GRS speakers up into the 500hz range and I’ve mentioned that I don’t like the vocals out of the big GRS. Overall, though, I was amazed at how good these sounded with the Blaupunkts. If you are looking for something low buck that will wow your friends with the bass they are capable of, these are worth a shot. I don’t think you will be disappointed. To tame the Blaupunkts top end I would try putting a 4ohm resistor and a 2-4uF cap in series across speaker terminals. Using the Alpairs takes them to the next level. They are factory flat down to 125 hz and I love how clear and articulate they are. Right now I have an 8ohm resistor and 45uF cap in series on the Alpairs and this pretty much evens them out with the GRS volume wise. Could maybe be just a touch louder. 45uF into a total of 16 ohm starts to roll them off at 200hz but they are still providing a significant level of sound down to 50hz. This seems to combine well with the second order low pass on the GRS. (9mH inductor and 280uF capacitor) The GRS have a rising output and a second order filter results in an output similar to first order in the theoretical world. Polarity is reversed on the Alpairs. I know next to nothing about Open Baffle design and built the cabinets as a sort of modified U frame, with the primary consideration being that both of the speakers be made from a single 4x8 sheet of plywood. Mine are narrower than Johns but have deeper sides so about the same distance around the baffle. Around back there is a full partition between the two GRS and a smaller partition above the top GRS. I really doubt that I will ever build more cabinets to experiment with design, just enjoy what I have. I do, however, intend to play with the crossover more, there are improvements to be made, I’m sure.
 
Location, location

I’ve been playing around with these for several weeks now and getting them closer and closer to what I think sounds good but there were a few things that were bugging me. The openness of the sound was almost overwhelming, bordering on fatiguing. Echoes and cancellations were readily apparent and annoying. Some music would sound amazing and other music disappointing. I just assumed this was the trade off for the live sound of an open baffle. I was getting ready to beg for help from the forum to solve these issues. I totally realized that I was not in an ideal listening room with concrete floors, hard walls and bare joists for a ceiling but was also totally unprepared for the difference when I finally carried them up to my normal listening room. All of a sudden there was imaging instead of diffusion, depth instead of echoes, solid bass instead of booming, focus in place of dispersion. I’m no stranger to good sound, having moved a pair of Jim Holtz and Curt Campbell’s Anthologies out of the way to make room for these. My comparison? Bigger, more alive, just as detailed. I’m ecstatic. They also seem to integrate better with the rear surrounds on also.
 

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Sold

Ok, Now I’m sold on this whole open baffle deal. You’ll never guess what it was that did it. John *******’ Denver singing “Leaving on a Jet Plane”. I swear he was sitting in my living room with a denim jacket on, in an old press back chair that was painted a weathered light blue color, strumming his guitar. You just don’t get that out of a Sony speaker. I have a long way to go with these yet, they are no where near as accurate as my Anthologies, which are likely THE most accurate speakers I have ever heard, but there is something about them that have me up at midnight on a work night relistening to familiar music. I just hope they aren’t like my foray into vinyl. Bought a 70s pioneer PL-518, music on it seemed to have more “presence” than digital. Bought an Ortofon cartridge, did a careful alignment, finally changed all the cables to eliminate any hum and interference, carefully cleaned my albums and now it sounds exactly like a 24/96 flac recording. Just hoping the magic doesn’t go away when I get them “perfect”.
 

svobodin

Member
2020-12-04 12:00 pm
Mel
Update: after playing around with these for a couple weeks, I decided to try the Alpair 10p’s again with what I’ve learned. First thing I’ve found is that quite contrary to what seems to be the common consensus, a $23 15” speaker really doesn’t sound that good. They seem to be perfectly acceptable in the subwoofer range, a kettle drum sounds like a kettle drum, but vocals coming out of the GRS woofers make me cringe. What I’ve ended up with is a second order 100hz low pass on the woofers. This rolls them pretty well out of the way by 200hz. Getting the Alpair to blend was a much bigger challenge, though in the end, very few parts were used. Mark Fenlon is pretty adamant about not playing his speakers through crossover components but I found some hints from Curt Campbell’s Halcyon design. Curt crossed his speakers over at 400hz but I was focusing on 200. I originally tried to use a voltage divider to pad down the Alpairs so that impedance would stay but found that it really ruined the FR of the speakers. Curt used series resistance to pad his and when I tried that, the sound quality came back. I’m using a 30uF capacitor rather than Curts 10uF and that let them reach down to where they cross flat. The rise in impedance of the Alpairs at low frequencies results in some unusual values of components to get the result you want. As Curt found, a pricey cap sounds much better than a cheap one with these speakers. I’m now more than thrilled with these, being my first open baffle. The Alpairs are handling 90% of the content, most importantly the vocals, while being protected from the lowest frequencies, allowing very high SPL without bottoming. As I mentioned, the GRS woofers seem pretty accurate with the lows. When I play “Chant” the drum hits sound like you are standing next to the big drums and “Cosmic Hippo” will rumble your chest. Combine that with the clarity of the Alpairs and I’m in audio nirvana. I was rather concerned about 4ohm lows and 16 ohm highs but my amp doesn’t seem to mind at all.

I have the Aplair 10.3 and GRS woofers and hope to put them together like you did. Can you please share the crossover schematic?
 
I have the Aplair 10.3 and GRS woofers and hope to put them together like you did. Can you please share the crossover schematic?
Svobodin, where I’m at with the crossover is very simple at this time and sounds about as good as I’ve tried yet. I have no real good way of showing you a schematic other than taking a picture of a pencil drawing but it is so simple that I’ll just try to describe it. I’m using the parts express 100hz 4ohm low pass crossover as a series crossover. Amp positive on the inductor side, amp negative on the capacitor side. Woofers in parallel for 4ohms load positives connected between the inductor and capacitor, negatives on the capacitor end. Full range is connected positive between inductor and capacitor, negative to the inductor end. This is reversed polarity for the full range but I see a dip at 120hz when connected normal polarity. I’m also using a

Parts Express Speaker L-Pad Attenuator 50W Mono 1" Shaft 8 Ohm​

to adjust the balance of the full-range speakers. Just wire it in to the full range circuit according to their instructions. I’ve found this setup to work acceptably with a number of different full range speakers as long as the speaker sounds good on it’s own. Most fall off below 200hz and this is the range the GRS woofers start to come in. The crossover does very little to the sound of the full range since the resistance is higher than the crossover parts were designed for. Some slight attenuation starting at 100hz. Natural roll off of the speaker does most of the work.