Tiny ground-effect omnidirectional biamped system

trevmar

Member
2011-01-10 8:36 pm
How small can you make a set of HiFi speakers?
A few months ago I realized that I was going to be traveling a lot over the next few years, and I started to explore how tiny I could design a HiFi system without losing fidelity. My goal was to produce a set of small speakers, with a tiny matching amp, that could travel in a suitcase with me, my laptop, and my FLAC collection. What I developed is the 8" high black speaker you can see in the photo. It uses the magnificent Peerless Tymphany 83093 widerange driver.

However, in all but the smallest rooms, the 2" widerange needed a little more deep bass, so I added a woofer, using the SEAS driver from my Linkwitz Pluto (the white tube) to boost output power below 200Hz. Suddenly I found I had not only a portable system, but a top-notch set of HiFi speakers capable (IMO) of holding their own in any 'average living living room'.

The amplifier modules are described over at the Class-D forum:
http://www.diyaudio.com/forums/clas...tput-filter-designs-sure-tda7498-example.html

Photo below. You can find the detailed stuff at my website:
Trevor Marshall - Ground Effect Omnidirectional HiFi Loudspeakers
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trevmar

Member
2011-01-10 8:36 pm
Neato ! If you could find a wider range for the woofer tube, (negating the tweeter tube) It would be even more elegant :)

It's not really a tweeter'. The crossover is at 200Hz. The tiny speaker covers 200Hz-20KHz. All the woofer tube really does is increase the amount of air which can be pushed around at low frequencies. The smaller speaker tube does have an extended bass (down really low) on its own, it just can't push around a lot of air :)
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Hi Trevor,
very interesting design.
The Peerless FR on the response graph is omni only upto 4Khz. So does the the smaller tube also need to be kept at ground level.

BTW, any reason you preferred to use the Peerless FR instead of the Aurasound NSW2 used in the Pluto :confused:
Did you also experiment with the idea that perhaps bipole FRs could also possibly give near omnipolar radiation :rolleyes:
Thanks.:p
 

trevmar

Member
2011-01-10 8:36 pm
Hi Trevor,
very interesting design.
The Peerless FR on the response graph is omni only upto 4Khz. So does the the smaller tube also need to be kept at ground level

The smaller tube is better at ground level. It relies on the ground effect for its lows, and you will find that the HF response is pretty flat at 45 degrees off-axis). In practice, the (omnidirectional) sound field fills the room and the location of the speakers becomes less obvious.

BTW, any reason you preferred to use the Peerless FR instead of the Aurasound NSW2 used in the Pluto :confused:
Did you also experiment with the idea that perhaps bipole FRs could also possibly give near omnipolar radiation :rolleyes:

Yes, the Peerless is a nice, clean speaker with an excellent transient response. I never really warmed to the 'icy' sound of the Aurasound. Try the Peerless - you will be surprised :) But don't just listen to them on-axis, let them give you an omnidirectional sound field :)

ps: I tried a lot of drivers. I used these Peerless because they sounded cleanest. Even the 8 ohm version of the Peerless drivers was not as crisp...
 
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Ive been messing around with something similar, (albeit using seperate satellites, and presently minus the Sub) using Tangband W2-800SL in ~50cc tea-light holders (40x40x50mm truncated cuboid).

They sound fairly good, to my ears. Actually the graphs looked better than the Peerless, which is why I got the TBs, but the results dont always concur with specs :rolleyes: so Im not critising in the slightest. Interestingly, the cube's F3 is around 450Hz (low Qts ~0.24) so 2 subs are in the pipeline, to avoid localisation as much as possible.

Out of interest what F3 do the Peerless have in the small tube enclosure?
 

trevmar

Member
2011-01-10 8:36 pm
Out of interest what F3 do the Peerless have in the small tube enclosure?

Details attached (P980983 in 8 inches of 2 inch pipe)
First is response, then Power handling vs frequency.

Let's see .. your 90dB limits us to 200Hz and above :) Guess where I put my crossover :) Great ears must think alike:)
 

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:D Haha!

The Qts and lower Fs of the Peerless makes a big difference here, with a Qt=0.24, Vas=0.23, and Fs=160, the TB fits into a Sixth of the volume (sealed)

Had I gone vented instead, my F3 would be better (~265Hz).

With such a small 'baffle' BSC is a big issue. So I came up with a multipurpose baffle. An A4 paper sized piece of PU foam, 1 inch thick. Hole cut into the middle and cube shoved in there. Ta da! Multipurpose diffraction reducing, baffle step reducing baffle which doubles as transit protection!

:wchair: More than 90dB? Hahaha, neither the peerless or TB would take much more than 90dB anyway....Did a Badger hide the x-over? I certainly didnt have room for mine inside the cube!

Just as well ;)
 
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trevmar

Member
2011-01-10 8:36 pm
:D Did a Badger hide the x-over? I certainly didnt have room for mine inside the cube!

I use a MiniDSP as an active crossover/compensator. And Bi-Amping... That is one of the reasons the design works so well :) Did you look at how many poles and zeroes were in my compensation DSP coefficients?

I am quite happy putting up with the huge size of 8 inches of 2" pipe for my HF enclosure. After all, what good is an enclosure if it does not take up floorspace? :) :)

Mind you, the Seas woofers are huge! 16 inches of 6 inch pipe! It is tough to find space for them. But fortunately they can be a foot or so from the HF drivers, since the xover is at 200Hz...
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trevmar

Member
2011-01-10 8:36 pm
I like this. Looks like flooder now has a proper scientific name

True, Elias. But in my case there is emphasis on the omnidirectional, point-source, design. As in -- no multiple arrays of horizontally facing drivers :) The choice of suitable drivers is, of course, key :)

And the drivers I chose do come from Scandinavia :) Where the flooder became popular :) Probably not coincidence :)
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I have to admit I havent seen the DSP bits, on the site I presume:) Ill have a look, but Im a DSP virgin ;)

The Tangbands could work well in a similar 8inch pipe, vented rather than sealed. I think the Peerless have the edge in low end reach though, thats sure. I remember looking at the Peerless, I dont recall which model, I think it was the inverted surround version, and it had a peak that put me off. Instead I got the Tangband, sacrificed some low end extension for the smooth rise which would be easier to deal with (passively, or at least in analogue domain)
 
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feeshywow

Member
2018-09-24 9:07 am
tiny speakers - would be great to have!

Dear TrevMar,
I got here from your website. Your "click here to send an email" doesn't appear to be working. Copying the link to view the hyperlink only results in a dead end. I love the speakers you made, and wish I had the background to make some for my house! But, my true reason for posting here is so I can get in touch with you to ask some questions about wavelengths. Is there a way to send a private message with your email address, so I can send some questions? Sincerely, Feeshywow.