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|7th March 2007, 02:18 AM||#1|
Join Date: Jul 2004
David: Small vented loudspeaker with bass boost
having had that idea over a year ago,
I finally want to finish my (1st set of) small speakers.
As they're intended to be about the smallest that can produce some "bass" ( everyone will probably jugde differently on what is "bass" ), I call that loudspeaker David. Any objections? Are there any "Davids" already? ...Registered trademarks or the like?
When I thought about this a year ago, I already asked here and I want to mention Sreten, who helped me big time!
Initial thread on David:
Bass boost in portable active speakers?
Thread about active high pass filters with gain and "bump":
high gain 2nd order high pass active filter topology
Unfortunately I have too many hobbies and then, David only came to my mind again this winter...
What I did recently:
* More simulations (still with Boxsim, which is said to give good results, at least with the already impemented Visaton chassis)
* mounting that Visaton FR10-8 I had lying here into an enclosure of another loudspeaker which fitted quite well.
I took off the tweeter of that (2-way) loudspeaker and mounted a quickly built cardboard bass reflex tube instead.
* Measured impedance afterwards to assure the tube's resonance was alright.
* Remarked that a 10" FR speaker isn't that nice off-axis...
OK, maybe others are better than mine, I could only get a pleasing sound at one angle, moving my head the sound wasn't only more dull, but rather unpleasing!
* So I cut-off the FR at 5kHz and added a CP13-4 tweeter (that sphere in the image below) (Luckily I bought those along with the FR drivers "in case of")
Now both drivers play along very well, in the coaxial configuration, the sound is pretty much the same from all angles, also the FR and tweeter sound integrate very well... "they're together as one".
Still everything is simulation:
I listen to one speaker only, playing music in mono (to both channels the same signal) from the computer, with one channel eq'ed for the FR, the other for the tweeter, then run through a standard power amp into both chassis.
So it's an active setup with the filter via software for now...
Sounds quite good, but I have to EQ the FR at two frequencies at the moment.
And I think that another, better driver would make that job better than the FR10-8, which I bought because I didn't want to spend a lot on my very first loudspeaker project and because it modeled well in Boxsim. It's only now that I realize that all the time spent on thinking, reading, simulationg, measuring, the enclosure and the (still to do) power amp with the filters implemented is quite "more expensive" than if I used a "better" driver instead of the Visaton FR10-8 (but well, it's definitely not bad after all!).
And finally, the Simulation was pretty near to what I get now. But I have to add that my measurements are taken in a "normal" listening room, so no quiet measuring room.
Going to bed now...
Reporting more soon.
|9th March 2007, 02:41 PM||#2|
Join Date: Nov 2003
Location: Brighton UK
Re: David: Small vented loudspeaker with bass boost
So what is your plan to finalise ? Better drivers ? box size ? power ?
|10th March 2007, 10:06 PM||#3|
Join Date: Jul 2004
Hi, nice to see you, sreten!
Oh yes, it seems I forgot to mention important parameters...
* Volume is 3l (though the volume of the actual testing enclosure is 3,8l).
* Tuning frequency and the highpass with 6dB bump frequency are both 58Hz. That's what seemed best in the simulation program I used, Boxsim.
* F(-3dB) is about 52Hz
What I'm planning to do?
Atm, I'm searching for 10 to 13cm drivers costing up to 25 Euro which could fit in my project (small Vas, Fs below 90Hz, Xmax (max linear excursion) bigger than those 1,5mm of the Vistaon FR10, Qts between 0.4 and 0.7 (should be ok, shouldn't it?) and rather flat frequency response up to at least 3kHz.
Sensitivity isn't a problem, because the setup is active, but a big sensitivity wouldn't harm
In case that the 10/13cm driver doesn't go up to 5kHz, I'm keeping my eyes open for a nice/cheap tweeter.
Also I still have to finish the active stage.
I wasn't sure if I could add the lowpass to the highpass/6dB bump filter without needing another op-amp.
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