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CMac, you have a wonderful ambitious project you are taking on, but I'm very very worried about your speaker/XO decisions. I get the strong impression that you have never built and modeled drivers/XOs. It is a very complicated process and you can't just slap a pre-fabricated XO onto speakers or you will have horrific results. I hate to discourage you, but you really need to put in a lot of research time into planning the driver/XO/enclosure part. Even something as simple as a 2 way can be quite complicated and challenging for people with a fair bit of experience.

I have slapped together speakers and crossovers before <grin> I have never modeled a system. True. I have been in sound re-enforcement for years (which means I have a somewhat trained ear for quality sound). I can tell the difference between a Bryston and a Crown and much prefer ribbon speakers over cones. I guess my fault may be that the speakers that I slapped together in the past have always sounded pretty good. Granted this is the first time that I have gone off the beaten path as far as keeping one speaker in the box;) Perhaps others have experienced "horrific" systems at their own hand - I can't say. If this configuration doesn't cut the mustard I guess I will be the first to know.

Thanks for the word and I understand where you are coming from and I appreciate the sentiment. I have a friend who owns $45,000 worth of stereo equipment in his basement. I purchased a used Bryston 3B and a pair of MMG's for under $1000 and apart from the lowest bass response the systems would sound comparable to the "average" person. I would be willing to bet that most people wouldn't be able to notice a 300 hz gap (down 5 db) in the midrange of a speaker system at around 3k. I guess I am questioning the degree to which "horrific" is noticed. Put the gap on a graph and people would see it but ask them to go to that spot on a 31 band eq to fix it and I think you would have mostly hit and miss.

I dunno, just my two cents. I don't mind opening up my project again if its a dud.

A few tips that I can offer which will do no more then point you in the right direction on a few aspects :-D

1)Keep the tweeter-woofer spacing identical for each set and minimize that distance as much as possible
2) flush mount tweeter
3) woofer and subwoofer in separate enclosures (all woofers can share an encloser. most tweeters are sealed, but not all. Check it)
4) don't use rock wool, especially if you plan on porting
5) until you get the XO nailed, keep them either external or very easily accessable for tweeking
6) Use a 1" dome tweeter and not a planar/ribbon since you are doing off axis stuff
7) read about baffle step compensation. Very hard to model with your implimentation.
8) have a beer


If you can afford it, you can get an uncalibrated mic for about $50 from partsexpress and a simple phantom powered pre-amp. and I believe there is free basic measurement software (I use Soundeasy, but it isn't exactly free)

PS, MMGs are awesome speakers!

I can tell the difference between a Bryston and a Crown ...

Amplifiers? You can tell the difference between amplifiers? That's extraordinary.

Ya, I tried to overlook that :P

If you can hear the difference, IMO one of the following has happened
1) one is a really old digital (like the Crown K1/2) being used for high frequencies
2) the volumes aren't matched
3) one is really really crappy or broke
4) Filtering is implemented on one

Not really. Things like slew rate can make a large difference when all else is equal - even among expensive amps. Not to mention that most amplifiers cannot handle a 4 ohm load like in the Magnepans. At first I was amazed that I could tell the difference - but after a while you realize that not all amps are created equal.

Only if all drivers are identical. Otherwise you'll have the larger coned ones pushing the smaller coned ones around. Even if for some reason this didn't hurt the smaller coned ones, the backwave on them would really increase intermodulation distortion.


The real question is why do this at all? You should use something that more resembles a proper sub to do the lows (with good thick enclosure walls) and cross that over around 100Hz or so to your other woofers (and tweeters) so that they are relieved of the low bass burden. The result will sound much cleaner. From the pic in that AG article it appears Yamaha is doing just that and for many good reasons. I don't know, but I wouldn't be surprised if their "soundboard" is so thick and rigid that it doesn't add anything in the way of sound radiation.


Stuffing is more to absorb the midrange backwave and to make the box appear acoustically larger via thermodynamics (adiabatic vs. isothermal IIRC). It won't really help you here, bass waves go right through the stuff.

A port only functions at very low frequencies, above that the port mass acts more like a rigid barrier (though some midrange could radiate from it, hence box stuffing and/or internal wall foam treatments).

Speaker design is within the grasp of almost anyone that is interested enough to study it and learn from example, through both your own experiences and those of others. It is engineering though, with various tradeoffs and pitfalls traceable back to the construction of the universe itself. It's one of those areas where you're way better off knowing how to play the game somewhat before you attempt to seriously break the rules.

Hello all,

I don't even have a piano (still looking for the right soon, hopefully I'll get one, someday) and your project idea is absolutely friggin AWESOME!!!! I am kicking myself in the butt becuase a few months ago I saw a (beautiful) upright player piano was a "haul it for free" item. The interior of the piano was shot which would have cost a tremendous amount of money to fix. This idea of gutting the internal parts out to install a keyboard on the bed is BRILLIANT. Had I heard of something like this, I would have kept the damn thing. The color of the piano was exactly the color of the room that we would have kept it in. ughhhhhh.

Can't wait to see the finish product. Gotta to keep my eyes open for the next "free" piano.

Mac

Update: With the weather turning cooler now I decided to bring the piano inside the house. The smell of the paint and finish have for the most part left. I still have a fair bit of work to do mounting the lid, attaching the pedals to an electronic sustain, fabricating a music stand (the piano didn't come with one) etc. The walnut veneer took the black paint and varathane amazingly well so the finish looks practically professional. What a joy to sit at an instrument that is starting to resemble a grand piano

Wow, it's really starting to come together - great job!

James
x

Are those big holes for potted plants?

We all have to do our part to keep the planet green

coming along nicely. I still think you should have minimized the center to center distance and lept it constant. Far apart with the XO points you indicated will have substantial lobing issues.

really cool project!

Agreed. Something Yamaha clearly does on the AG:



I wonder if the down-facing bass drivers are underneath those black panels?

Yesterday I attached the speakers and the lid. I just had to see how it sounded

The "Wall of Sound".

What an interesting afternoon I had today. With everyone out of the house I had a chance to "play". The first thing I did was to hook up the four sets of speakers on the soundboard without the bottom cover to the box in place. The amp can simulate 6 channel sound with 2 inputs so I hooked up right, left, surround front and surround back. WOW. I was surprised at how the downward firing sound waves enhanced the sound. Next I selected the stereo setting on the amp so just left and right were firing. Wow again. It suddenly sounded like it was no longer a piano but a stereo playing a piano. (I don't know how else to describe it).


Now that the top speakers were in place and I had an idea how the whole setup sounded I could start to tackle the bottom of the instrument. First of all I screwed the 2 larger woofers in place and attached the bottom cover. In this configuration the larger speakers acted like passive radiators. I was not powering them yet. The sound from the 4 smaller woofers up top would no longer travel directly out the bottom of the piano. As expected the bass was extended but the efficiency of the piano dropped dramatically. The sound was a bit more punchy but somehow the "life" of the instrument vanished. The speakers did a pretty good job generating the sound but the special something just wasn't there.


Next I removed the larger woofers and allowed the sound to protrude through the empty holes left behind. The volume increased as expected, and the sound had somewhat more of a tameness to it, but still lacked the presence that I first heard.

Finally I removed the bottom piece entirely again so it was just like it was at the beginning. Wow. Ok - so this is it. Now time to play music. I went back and forth through these configurations a few times over the course of the next couple of hours while I played various songs and came to a few very interesting conclusions:

1) 4 speakers are WAY better than 2
2) An open piano soundboard is WAY better than any stereo setup I have ever played my digital pianos through
3) A "wall of sound" is far more than just recreating the frequencies of a grand piano. The stereo configuration recreated all the frequencies but when the 4 speakers were active with the reverse wave from the soundboard speakers pointing down the instrument comes "alive". I don't know how many more speakers on the soundboard are realistic to have (probably not much) but when multiple signals interact all around the instrument it so feels like playing a "real" piano. The NW (New Wood) keys on the Yamaha CP5 are very expressive to begin with but when coupled with a hollow shell of a grand piano filled with speakers the dynamics are enormous.

Conclusions:
I am going to trash the idea of the big 12 inch woofers on the bottom of the cabinet. The 6 1/2 inch woofers on the soundboard do a very good job generating the low frequencies required. Perhaps they are getting a boost from the shape of the piano or the soundboard or perhaps some other form of constructive interference I don't know. That was a bit of a surprise for me . I thought for sure I would need a bit more bottom register punch. I really only notice the tweeters when I play sounds that are synthy. The CP5 has a 5 band EQ and I can practically roll the top end all the way down without much change to a clean piano sound. I didn't really know how so many speakers were going to play out. There was a very real possibility that the surround front and back channels were going to "confuse" the sound. That isn't the case. They actually enhance the piano experience very much. (Big grin).


OK. I think I'll keep it

Wow is right! Looks like you have done a great job with that. As an amateur woodworker myself I can really appreciate what you have done there. I wish I could hear it live. Congrats on a fine job and let us know how it "plays" out in the days to come, and if you need to make any more changes.

Also, can you feel the vibrations on the bass notes? I find that just with the BX5A speakers I have on my Celviano I can feel the vibes in the bass end almost like I could with my old upright. Again, congrats!

To be honest I thought that I was going to feel the vibrations of the lower notes more than I do. They are there but are not prominent. To get the digital piano to sit as low as possible to the old key bed I removed the bottom rubber pads from the CP5. There are a number of screws in the bottom of it that make good contact with the baby grand body. I guess not enough though. The vibrations may also be lessened by foam and rubber strip that I placed on all the ribs and sound board surround to keep any buzzing or rattling down. Surprising the number of design decisions that are made that can effect the sound. I chose to go with screws to hold the soundboard down at first too just because it was easy to undo if I needed to.

Freakin' awesome!