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james77 26th May 2010 04:34 PM

First DIY speaker project initial concept - thoughts?
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Hi, Im pretty new here, have been reading for a few weeks though and there seems to be a lot of knowledge here, so i thought id post my idea for my first project...

Basically im planning to build and active all in one 2.1 speaker dock for iphone etc use. I intend on using a pair of ~6" mids w/ tweeter and a single ~10" sub. I plan to drive these using LM3886's, one driving each stero channel (50W-60W ea i understand) and the sub using three for about 150W. I also intend to build a simple circuit to charge the iphone while docked also. I plan to put all the electronics in the compartment at the back of the box, and the actual speaker compartment volume should be 40-47L after the speakers and braces etc are in there. I thought about doing the backplate in aluminium to act as chip heat sink aswell.

Here are a few pictures of my initial design idea, please give any advise or opinions on the entire build.

br85 26th May 2010 04:50 PM

Looks like a good idea, but I'd highly recommend making sure that sub gets its own chamber, otherwise it's going to play havoc with the cones on the midrange. Even better, seal off the midranges and tweeters so the sub gets assigned more of the airspace in the box.

james77 26th May 2010 05:49 PM

Thanks, I did think that the sub may generate too much air pressure inside the box and damage the other speakers. So improvement 1 - seal off mid/tweeters.

Also can anyone suggest some decent drivers , I would like to spend 100-200 all up for the drivers (100 is probably dreaming for something of reasonable quality. Are the Dayton range of speakers good? Car speakers mb quart etc?


joe58 26th May 2010 06:28 PM

Are you taking inspiration from Geneva labs? If not you could always do a clone on on of these shown in the link. Do it professionally and style it well and you could have a quality product. For a lot less than they charge for theres anyway.

james77 27th May 2010 01:44 AM

Joe, im not sure what link your referring too, but i googled geneva labs, I have never heard of them before - i guess the design is quite similar though. I some how doubt my will be finished as nicely though :)

twest820 27th May 2010 03:37 AM


Originally Posted by james77 (Post 2199186)
I would like to spend 100-200 all up for the drivers (100 is probably dreaming for something of reasonable quality)

A lot of folks like the Daytons but I find I often end up shying away from them; they're not bad for the price but one can usually do better for around the same cost. Car stuff can be good, but most of it's not. You could pull off USD 100 if you can find some good buyouts but USD 200 is more realistic.

I'm coming up with USD 197.44 plus shipping for 2x Vifa BC25SC06, 2x SB Acoustics SB17NRXC35, 1x Peerless 830668; something like that should be a reasonable starting point; it's not hard to find decent tweeters on the cheap but if you want solid woofers (decent Qms and Rms, low distortion, reasonably flat SPL) you're generally into the USD 50-60 per driver range. Personally I'd opt for the Peerless 830667 over the 830668 for its higher Qms and lower Rms. If you can scrape up the extra USD 5.20 :p the Dayton PA255 is worth a look as well. I'm an open baffle guy so the subs may or may not be suitable for your box. But the 830667 looks close.

Consider LME49811+STD03s instead of 3886s; the 49811's a considerably better part, kits are available, the complexity's not too much higher, and the cost riser's not excessive. You'll find lots of threads in the chipamp forum. Also, check your SPL and power budgets; 50W into a single 90dB efficient driver will get you 105dB concert levels for nearfield listening. So the 300+W proposed may be be overkill. Also, work through the thermal maths; if you want to use the back of the box as a heatsink you'll likely need lower powers. Both to keep the die temperatures reasonable and to avoid the box becoming a fire hazard.

roger_lew 27th May 2010 05:07 AM

I should preface my post by saying I'm probably more lazy than you are. That is a complement to you! A large part of my planning actively involves figuring out how to not do actually work.

I've thought about doing something similar with a T-amp so I could use battery power. I would aim for optimizing sound quality over sound quantity. If you are going for quantity you might want to google "podzuma."

I would use a DVC sub like the Dayton SD215-88. Each stereo would drive one of voicecoil to mechanically sum the outputs. Or perhaps two SDX7s? They work in pretty small sealed enclosures and are crossover friendly. This would eliminate the need for a third amplifier to drive the sub.

As twest820 mentioned 300 watts is probably overkill. I think you could probably get away with 1 LM3886 per channel. 50 watts goes further than you would think. You will most likely be excursion limited not power limited.

If I were doing this I would also opt for widerange or fullrange drivers like the CSS FR125 or maybe the MarkAudio CHR-70 to avoid the hassle and expense of figuring out how to match the mid to the tweeter. The former has more cone area and more excursion but the gap between the phase plug and the voice coil makes me a little nervous for a portable system. The later would work in a smaller enclosure.

Just some ideas to ponder.


james77 27th May 2010 06:28 AM

Thanks for the input guys - gives me something to think about with the drivers.

For the amps, sry if I didn't make it clear I am only going to use 1 lm3886 per stereo channel and three for the sub. I already have the 3*lm3886 amp and will purchase the others. I'm quite capable with electronics I'm currently at advance diploma level of electronics engineering so if there are any good mods let me know :)

aswell quality is first preferabce over spl - but I still want to be able to go loud when needed


twest820 27th May 2010 06:47 AM


Originally Posted by james77 (Post 2199654)
if there are any good mods let me know

If you take a look at page 7 of the 3886 datasheet you'll see it's not actually an op amp. Modding the input stages is kinda hard, though; expect around 0.5% THD on the parts at typical volumes. The woofers I suggested will beat that but the tweeters will run around 1%. Investing more there wouldn't hurt but the system will still be fairly amp limited; you might also want to work through the PSRR and excess loop gain relative to other parts.

james77 27th May 2010 01:53 PM


Originally Posted by roger_lew (Post 2199622)
If I were doing this I would also opt for widerange or fullrange drivers

I havent really looked into them before, but it would certainly keep things simple, do they perform well? im a little skeptical of 'full range' drivers but that is probably just cause i never used a decent one before.


Originally Posted by twest820 (Post 2199575)
I'm coming up with USD 197.44 plus shipping for 2x Vifa BC25SC06, 2x SB Acoustics SB17NRXC35, 1x Peerless 830668

Can I ask where you got these prices, i really only know of partsexpress for decent prices for speakers.

Also i have a pair of ~2.5K 2-way crossovers i got from a pair of yamaha speakers (NS-C325 & NS-M325) these are orginally for 6 ohm speakers with 50watt nominal power handling - is there any reason i shouldn't use these? providing i use a tweeter that kicks in about 2k

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