Omni-stereo speaker for a small room

In one of my previous articles I mentioned that I enjoy sound that travels some distance, before arriving to listener's ears. I'm not going to write long boring article how I arrived to final design. In short- I found out that in small room, single speaker with stereo channels firing from one point sounds better than a pair of stereo speakers. My goal was to make a speaker which I would place nearby and still have an illusion of distant spacious sound. For large rooms typical pair of speaker does adequate job.

Trying different ways of mixing stereo channels.

In terms of sound precision, nothing beats mono coaxial speaker.

What do I mean by sound precision?

It is difficult to put into words, it has to be heard. 

Analogy would be a photo in focus (coaxial mono)

and photo not quite in focus (all other configurations)

 

Final result is below.

Sub-woofers are in isobaric configuration.

I am happy with this speaker, although I'd rather split it

in 5-6 ways for greater dynamics. But that would be another project.

 

Green graph is frequency response at listening position

(both channels playing )

 Crossover is pretty basic, but works well.

Paintings-speakers

Some recent experimentations with parts-express tactile transducers and stretched canvas allowed
me to create a very interesting product.
FR can be fine-tuned by strategically adding acrylic paste to certain areas of canvas.
Sound is surprisingly good, similar to an unfiltered full range driver, which many people like.
Here is an example of fine sounding painting I made after Joshua Reynold's "Strawberry girl" 20"x24"
Sample FR shows a transducer attached to canvas. Final product's FR will be smoothed out by adding more transducers and acrylic paste.
One downside is that painting can not be wall mounted, it has to be set on an easel.
I am working on wall-mountable prototypes of boogie-paintings.

Update August 14, 2016 : www.boogiepaintings.com project has evolved into an art gallery. Above described concept will be utilized only for fine art applications, as it is clearly not suitable for high fidelity sound reproduction

Crossover for E0057-08/06 C18EN001/M

This is an experimental crossover for new Seas E0057-08/06 C18EN001/M coaxial driver.
I don't have actual drivers, I just modeled crossover that I would use with these drivers.
If someone tries it, let me know how it sounds.
There are resistances of regular air core inductors were used for simulation.
Tweeter must be wired with reversed polarity.

Crossover for Dayton Audio B652 speakers

Dayton Audio B652 are hugely popular speakers.
I'd purchase a pair for evaluation, but I don't have space for any new projects.
Nevertheless I designed crossover for these speakers. It is based on measurements
provided by other people. I traced graphs from Zaphaudio site. He has the most helpful set of measurements.
Here is my crossover and parts list:

 

6.2uF capacitor (2)
http://www.parts-express.com/pe/showdetl.cfm?partnumber=027-427
22uF capacitor (2)
http://www.parts-express.com/pe/showdetl.cfm?partnumber=027-348
3Ohm resistor (2)
http://www.parts-express.com/pe/showdetl.cfm?partnumber=016-3
1.2mH inductor (2)
http://www.parts-express.com/pe/showdetl.cfm?partnumber=255-050

It is important to flip tweeter's polarity, otherwise you'll get this FR (yellow line)

White lines represent unfiltered response of the drivers.
The biggest expense in this upgrade are inductors. You could save some money by using piece of
foam to filter out woofer's high frequencies. But it would require you to have a sound measurement setup.
This version of crossover should provide nice laid-back sound.

How to improve sound of speakers you already have

I'd like to share with everyone how I set up my speakers for improved sound-stage, imaging and overall spaciousness of sound. Firstly and very importantly, speakers must be equalized to flat or slightly downward frequency response. Most commercially available speakers have very bright sound (too much treble ) It is easily remedied by turning down treble control on your amplifier. But, if you use a receiver which does not support treble adjustment (sometimes there are presets without individual controls), you can attach pieces of foam in front of your speakers. One way to do it would be by increasing length of grill's legs.

Now, when speakers don't have that annoying boosted treble, we need to place them for a best possible sound reproduction. Usually people adjust their speakers for their listening position "sweet spot". But then they can't share their music enjoyment with anyone else. Person sitting next to a person in a "sweet spot" won't have the same listening experience.

The solution for this narrow "sweet spot" problem is to physically separate both speakers.Another problem is how to make it aesthetically acceptable. I think, placing big piece of thick glass between speakers is a good idea, if one can afford such a large piece of glass. Another solution would be a piece of big furniture between speakers.

For computer speakers best placement would be on sides of the table, provided that table has enclosed sides. I personally used this setup for a long time, it creates very three dimensional sound on some recordings.

If you have fancy designer's table with open sides, speakers can be left on a table, separated by a piece of board.

That's it. Key to a great spacious sound is normalization of treble and physical separation of stereo channels. Of course, speakers themselves also matter. 2in computer multimedia speakers probably won't sound good no matter what you do. Something with larger radiating surface is needed.
And you will need multiple sub-woofers. It's very difficult to achieve good bass with only one subwoofer.
I know that many people will object to my proposed layout. But, I have tried it and it works for me an it costs almost nothing, except if you decide to use that fancy piece of glass.

4 way speakers

I was working on this project during last summer. It was an experiment, where I tried to make a speaker with very simple crossover. Lower frequencies were filtered out with capacitors and higher frequencies were filtered with foam of varied thickness. The benefits of this design are low cost(no expensive inductors) and flat impedance (easy load for an amplifier).
This speaker still needs a separate powered subwoofer, because lower woofer is in bandpass enclosure and it's frequency response drops sharply at around 100hz.
I don't have photos of finished speakers yet.

.

Car Audio

I've been playing with different car audio setups for a few years. Here is where I am at now.
For tweeters I use modified  Aurasound NSW2 drivers (cone is slit and coated with damping spray and rear chamber is staffed with foam)  attached to small horns. they cover ~1khz-15khz
For midbass I use modified Dayton Audio PA165-8.
Subwoofer is 15in driver from diycable.com (very nice sub)

Foam acts as lowpass filter and provides smooth high frequencies roll off.

I use a single inductor for woofer's crossover. if you use metal drivers, notch filter has to be implemented, foam won't filter out metallic resonances.

This is frequency response(red) at driver's sitting position. It looks like high frequencies are recessed too much, in reality tonal balance is just right.

nearfield measurements of woofer and tweeter (system is playing pink noise)

frequency response on tweeter axis, mic is 8in away

So, my conclusion is that car system needs to be calibrated on tweeter axis, no matter where tweeter is installed. If I tried to achieve flat frequency response at drivers position, sound would be very bright and unnatural.

Of course there are still some problems in my install, particularly that hump at ~300hz

boombox, ghetto blaster

Here is my new project with drivers mentioned in previous post.
I used amp6 for woofers and t-amp for tweeters. Crossovers are passive (I didn't have time to design and build active ones). Crossover point is at around 1khz. Woofers' 7khz resonance is about 30db down, which is apparently not low enough, because at high volume sound becomes "crisp" It should be tested with higher power amp, because that sound could be caused by clipping amplifier. Anyway, it plays loud and sounds quite good for a boombox.
For power supply I use 10 rechargeable AA batteries.

Sunflower is not part of the boombox, it's just sitting behind.
Back of the boombox looks exactly the same as front(tweeter and two woofers)
Calculated frequency response.

Update, August 2013
I've tried to listen to this speaker through my UCD180 amplifier for a few days.
And I came to conclusion that notch filter must be used with metal woofers.
That spike you see around 7khz, 35db down is a big problem. It is not immediately apparent, but over time it develops into an unpleasant listening experience. If you are building speakers with metal drivers based on someone else's designs, I suggest you choose only those crossovers  that use notch filters.

aluminum woofers' cone treatment experiment

These modifications were done a few years ago. I'm just reusing these dayton DA175-8 woofers for a new boombox project. Cones were slit an covered with automotive damping spray. Small copper caps are glued on top of pole pieces.

Blue line in the graph below shows modified woofer's FR, measured on axis(in box).

Yellow line is FR measured with thick foam placed in front of the woofer.

Manufacturers' supplied FR

I was doing these modifications to reduce resonance above 5khz. As you can see resonance is still there. Unfortunately aluminum cones do not benefit from this kind of modifications.

Neo8 planar transducer in a waveguide

I just found photos of my unfinished project. Neo8 in a waveguide.
Animated  .gif picture illustrates effect of an acoustic filter (foam).
I don't remember FR's measuring distance.