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 Post subject: DIY flush mount speakers
PostPosted: Fri Sep 02, 2011 9:01 am 
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This forum hasn't been active for a while. I have been away for about 5 years with the speakerbuilding crowd at the parts-express forum. There I have learned quite about speaker design, and designed and built a few of my own. There is some incredible software available for free to design phase coherent flat speakers (if that is what you want).

Most of the designs that people do include flush mount speakers. The problem is that most speakers are not designed to be flush mounted because the crossovers have what is called "baffle step compensation" designed into them. This is a 6db increase built into the crossover at a frequency determined by the width of the baffle. Barefoot designed a filter to compensate for this when a speaker is flush mounted.

I found that there are a lot of people DIYing a lot of very good speakers so I decided to take the plunge. I have now decided that the way for me to go, is to measure the drivers after they are in their baffles and mounted in the wall of the studio. There is very accurate software to do the simulations of how the different speakers will work together.

These are the drivers that I am using.

2 Dayton RS225s-8http://www.parts-express.com/pdf/295-366s.pdf
2 Tang Band W4-1337 http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-848&FTR=1337%20tang%20band
1 SB-Acoustics SB29RDC-C000-4 Ring Dome tweeter
http://www.madisoundspeakerstore.com/ring-radiator-tweeters/sb-acoustics-sb29rdc-c000-4-ring-dome-tweeter

These speakers all match very well together. The system has an efficiency of 93dB it is flat to 1.5db from 40hz to 20khz. There is no padding in the crossover design! (some of the filters have done a little padding). This design is based on the manufactures frequency response graphs (except the midranges which were done by a very respected speaker designer).
The low end is simulated based on T/S parameters.

If you want to know how some typical studio monitors measure, you can go here for a reference.
http://www.gearslutz.com/board/low-end-theory/453697-interesting-testing-adam-s2a-krk-dynaudio-jbl-genelec.html

Here are my simulated graphs.


Here is one that has a 1dB scale
Attachment:
zoomed response.JPG


Here is one that shows the crossover response, the phase correlation and the nulls caused by a revers polarity that shows how well the phase tracks on the speakers.
Attachment:
response with phase and nulls.JPG

This is the crossover schematic.
Attachment:
Crossover schematic.JPG


Since the manufacturer's testing is done on an "infinite baffle" the measurements will hopefully match fairly well with what I end up with when I measure. But at least now I know well that these drivers will play well together.


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Last edited by Eric Best on Sat Apr 15, 2017 3:43 am, edited 1 time in total.

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PostPosted: Fri Sep 02, 2011 9:09 am 
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I forgot, this is what it will look like.

Image

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PostPosted: Sat Sep 03, 2011 3:31 am 
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By the way, DON'T BUILD THIS! This is just a computer simulation and it probably won't be built for about a year. These computer simulations are VERY accurate and it will probably be a very good speaker, but I will let you know after I've built it. I already have all of the drivers, but I don't have a wall to mount it in yet! It kind of reminds me of the Beatles song Drive My Car. "I've got no wall and it's breakin' my heart, but I've got the drivers and that's a start."

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PostPosted: Sat Sep 03, 2011 4:38 am 
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Quote:
There is some incredible software available for free to design phase coherent flat speakers (if that is what you want).


Any chance you could provide some links to that free software? It sure sounds like something that folks here would be interested in (like me, for example! :) ).

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PostPosted: Sat Sep 03, 2011 8:30 am 
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Jeff Bagby is the King. Here is a link to his stuff.

http://audio.claub.net/software/jbabgy/jbagby.html

Jeff has a guide for PCD but Paul Carmody has written a very comprehensive guide to using Jeff's response modeler software and a few other freeware programs to get manufacturers spec sheets to responses ready in Jeff's Passive Crossover Design software.

http://sites.google.com/site/undefinition/simulated-measurements

I've just been thinking about seeing if I can design a fairly good somewhat inexpensive 2-way design that would do the same or better job than the monitors that most people are flush mounting. Give an inexpensive option for flushmounting and use their nearfields where they should be used.

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PostPosted: Sat Sep 03, 2011 9:35 am 
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Wooohooo!!! New stuff to learn! :) Cool! :yahoo:

Thanks very much, Eric!

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PostPosted: Mon Dec 19, 2011 4:40 pm 
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Eric, how is the loudspeaker project going on, I'm very curious about it...
Good tip about modeling SW.
If you need help regarding measurements i can help, locally...


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PostPosted: Tue Dec 20, 2011 5:29 am 
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Good to see someone else close.

I haven't had the chance to do anyting else with it. I figure that I'm going to finish the room that I'm building, measure the drivers in their boxes in the wall, then make the crossovers.

I coach at MSU (I live in DeWitt) and this is our busy season until the end of March so not much construction is going on in the studio right now. I figure that I won't get around to building the speakers until next summer when the room is closer to being finished.

One project that I would really like to do is design an inexpensive flush mount DIY that people could use instead of flush mounting their nearfield monitors and use them the way that they are supposed to be built, but I can't do that until I have a wall to test them in!

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PostPosted: Wed Dec 21, 2011 2:44 pm 
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First few questions/suggestions.

Are you going to use subwoofer?
I think that 2x8" per unit is inadequate for studio, 2x12" or at least 2x10" is my sugesstion, especially regarding your mid choice, you won't have problem matching them.
Take a look at this post of mine on DIYaudio
It is my $ per liter of air volume displacement idea as woofer selection mechanism, it can help when you already have few woofer to choose from, regarding your desired setup...
Regarding woofers, other that i think they are too small, and has metal membrane, motor is not of anything special, Le impedance rise rise suggest there is no shorting rings in the motor or any similar method of reducing distortions in the bass region where their impact is largest (and curve of the ear sensitivity is not helping there-loudness(Fletcher-Munson curves)) really suggests to read that article.
I think there is many better choices there...
Edit here, i checked the woofer data sheet more in detail, and they claim the use of : "two short-circuit paths" although impedance curve does not reveal that?!

Now why all the obsession with metal cone drivers, i try to avoid them as a rule of thumb, let me explain.
The good cone/dome material is supposedly to have high inner dumping and high stiffness, since both requirements are not on the same team, you got to compromise there, and metal is worst there...
If you check the response curve both have very nasty ringing above its usable range that heavily overshoots (it is even worse when you point the mic at it when you compare it to manufacturers datasheet).
That ringing you can represent yourself as bell effect, with stimulus like Dirac impulse (kicks, some drums, claps...) it will ring that you wil able to hear it with your own ears, it will introduce its own acoustic signature, "timbre" and it is not a good one, especially for studio where you try to avoid any sound coloration like plague!
The crossower helps BUT you can still hear it unless you are going with "brickwall" filter (active, eliptic).

Over 10 years ago i purchased good sound card (Midiman delta audiophile) that can do 96Khz Fs in order to do bunch of measurements on loudspeakers (now have 24bit/192Khz), but first reaction of my collegues was: why do you need that high Fs, we do not hear above 20K anyways?
Well widespread use od metal domes in tweeters was bugging me, so i wanted to investigate that little bit more in detail, and found out that ringing peak in tweet is the worst above 20K where we don't hear it, but, due to the non linear distortion mechanism involved in loudspeaker drivers as a normal thing, IMD type distortions with some help of normal program above 10K will create enhanced ALIASES in audible part, like in bad DAC!
Your tweeter choice is ok, no objections there (although we can debate better choices if you wish) but the point was more on other drivers, in tweeter you can hear it (metal membrane resonance), but in bass and mid it is even worse because it is in audible portion of the reproduced spectra.

So the same story regarding membrane works for mid (the underhung motor is great there) but the overall ringing effect is worse...

I do like the WMTMW 90deg arrangement, reminds me of some Dynaudio flushed studio monitors very nice.
In you drawing representation and real speaker you should try to put mids as close to the tweet, and then find space for woofers.
With MTM it is common that Comb filter effect that should be minimized and pushed higher in freq outside of operating range of the drivers in that arrangement if possible (hardly)!

Did you consider going active?
With Behringer :D
At least in the beginning to get the real transfer curves and when sound sits properly, can do dedicated active filter fitting in SPICE (better then that DCX2496 crossover solution, just DCX front end is worse then good custom filter, permanent one with higher quality, except for time delay issues, but you can always offset acoustic centers of the drivers since you're the one who is designing that loudspeaker so i do not see a problem there, i have already done some passive impulse cooherent, phase exact speakers in the past) together with some decent amps...
And there is more (5way?)...
IDK, i see potential in that speaker project and studio stuff should be top notch anyways, just my 2c

Regards


Last edited by zega on Wed Dec 21, 2011 3:40 pm, edited 1 time in total.

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PostPosted: Wed Dec 21, 2011 3:04 pm 
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Quote:
Over 10 years ago i purchased good sound card (Midiman delta audiophile) that can do 96Khz Fs in order to do bunch of measurements on loudspeakers (now have 24bit/192Khz), but first reaction of my collegues was: why do you need that high Fs, we do not hear above 20K anyways?
You seem to be confusing sample rate with frequency response! :shock: A 24/192 interface does not mean that it can digitize a tone of 192 kHz. It just means that the interface takes 192,000 samples per second of whatever is on the input. That is very, very different from being able to digitize or create 192 kHz tones...

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PostPosted: Wed Dec 21, 2011 3:43 pm 
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Soundman2020 wrote:
Quote:
Over 10 years ago i purchased good sound card (Midiman delta audiophile) that can do 96Khz Fs in order to do bunch of measurements on loudspeakers (now have 24bit/192Khz), but first reaction of my collegues was: why do you need that high Fs, we do not hear above 20K anyways?
You seem to be confusing sample rate with frequency response! :shock: A 24/192 interface does not mean that it can digitize a tone of 192 kHz. It just means that the interface takes 192,000 samples per second of whatever is on the input. That is very, very different from being able to digitize or create 192 kHz tones...

- Stuart -

Why do you think that i am not aware of Nuquist theorem for about 20 years now?
Hint, note the term Fs (as for sampling frequency) in my text you quoted above, twice. (enhanced for clarity)


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PostPosted: Wed Dec 21, 2011 4:05 pm 
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Quote:
Why do you think that i am not aware of Nuquist theorem for about 20 years now?
I've never heard of any "Nuquist theorem", actually. Personally, I reckon Nyquist is pretty accurate... (and no, that isn't splitting hairs: People who actually do know what they are talking about generally know how to spell key terms correctly, explain clearly, and can use at least half-decent grammar too).

And you still seem to be missing the point, using terms that you don't understand. Last time I checked, in the digital world "FS" refers to "Full Scale", as in the highest possible measurement LEVEL, in decibels. It has nothing at all to do with frequencies. Saying that your card measures "96 kHz FS" is sort of like saying the top speed of your car is "180 mph gallons"... :)

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PostPosted: Wed Dec 21, 2011 4:45 pm 
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Sharp eye i must say, how come that you missed Fs then?
I did not re-check that (Eng. not being my native did not help either, as pronounciation in my native has u in it (we don't use y), and we write as we speak :? that is where confusion comes from, and regarding that, logically do not expect decent grammar from me, i'm heavy on spellchecker.)
If you don't like bad grammar feel free to filter me and do not read my posts, you cannot learn anything from my posts anyways (last part would be your interpretation?)
edit: darn you're admin, your job is to read all that annoying stuff...
Sorry dude, you do not ban because of bad grammar do you? :cop:


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PostPosted: Thu Dec 22, 2011 2:22 am 
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:D

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PostPosted: Wed Dec 28, 2011 10:13 am 
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Hey Zega,

The choice of drivers were made based on speakers that I have previously listened to and had purchased the parts to build. I decided to adapt them to flush mount and change the tweeter to one that is a little less expensive, and that I liked the sound better.

40hz is plenty low for me.

I had thought about going active for the lower crossover, but decided to design it passive as an exercise.

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