A new pair of computer speakers for the heavy user

[yggdrasil]

The past year or so I have been spending gradually more time in the office. There is no one close to disturb, so the standard computer speakers was exchanged for a micro stereo during the winter. A huge upgrade, but of course they fell very short...

A month or so ago a friend donated a pair of potato mashers (2410's with 2301). In storage I had a pair of 2215A's.

Here's a shot of the result.

[yggdrasil]

Obviously the footprint needed to be very small, so the inside of the box leaves less than 1 cm on each side of the drivers and between them. The box is only 28 cm deep.

It is designed as a modified U baffle. The last year or so I have been reading up on open baffles and wanted to try out a variation of a concept Nelson Pass wrote http://www.enjoythemusic.com/diy/0911/slot_loaded_open_baffle_speaker.htm with the accompanying diyaudio thread http://www.diyaudio.com/forums/multi-way/195734-nelson-pass-slot-loaded-open-baffle-project.html

The baffle is actually 22mm chipboard, with 20mm pine glued onto it. The sides and top are also pine.

The cutout in the baffle for the 2215 is approximately 1/3 of the area of the 2215.

Here's a shot of my work desk.

[yggdrasil]

The design started with building the raw U baffle without the slot.

Actually the design started with some rather anxious measurements of the 2410/2301 combo. The slot loaded ob does not have much hf extention, so the crossover point would have to be a stretch for both drivers.
56426

Equipped with that measurement there was time to build a U frame and mount a 2215. First a measurement on the ob.
56427

Then the 2215 was covered leaving a vertical 10cm wide slot.
56428

Finally I covered the 2215 with a circular opening with d=21cm.
56429

Given these results I went for the latter.

[yggdrasil]

It was time to look at crossovers. Given the measurements I aimed at 650Hz, 12dB/octave, passive.

First the high-pass showed this impedance curve:
56430

I didn't particularly like the impedance peaks in and around the crossover region. Since the 2410/2301 needed to be padded I placed a 15 Ohm resistor in parallell with the driver and measured the impedance again:
56431

Which was much more pleasing...

Speaker workshop suggested this high-pass filter:
56432

I had a 3mH inductor lying around, so the network ended up like this:
56433

[yggdrasil]

Then I run an impedance plot on the the 2215 in the baffle with the circular slot:
56434

The low pass network with compensation network ended up like this:
56435

[yggdrasil]

First in place measurements:
56437

There's way too little in the bottom. Which led me to add the following passive circuit between the preamp and poweramp:
56438

The low frequency improved, but not enough. As a bonus the 2410's now got far too much low frequencies... Due to this I decided to redo the passive circuit. Routing the HF outside the low frequency compensation. The HF leg was built with a 10K pot for easy adjustments. Meaning I needed another poweramp for the HF. The low frequency compensation have also been made steeper.
56439

No measurements of this setup yet.

[pos]

Nice build, with up to 10dB boost from the slot loading! Albeit it forces you to cross the woofer lower...
Can we have a picture of the rear?

[yggdrasil]

Here's a picture of the rear.56476

[Hoerninger]

Nice project, indeed. :cool:
Do you know the trick to CC without a batterie?
___________
Peter

[yggdrasil]

Nice project, indeed. :cool:
Do you know the trick to CC without a batterie?
___________
Peter
Thank you. Sounds quite nice too. The OB bass is quite intriguing.

I know about the diode CC, but I got a bag of 50 battery clips for this purpose, so why not use them...

[Mr. Widget]

Computer speakers? :D

Very interesting indeed... thanks for sharing, and for sharing all of the details!


Widget

[Alien_Shore]

Computer speakers? :D

Very interesting indeed... thanks for sharing, and for sharing all of the details!


Widget

+!
Yes!
Thanks for sharing. This is a great educational thread.

(and I now have computer speaker envy) :)

[pengesluk]

Steike!