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Old 26th December 2001, 10:03 AM   #1
jteef is offline jteef  United States
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Default On the subject of subwoofers

I am planning on building some MTM's very similar to the Proteus by Tony Gee. (http://home.hetnet.nl/~geenius/Proteus.html) The next project on the docket is gonna be a subwoofer. It is still going to be quite a ways off. Being unemployed allows a great deal of simulation time but very little buying/building/testing time...

I am not sure what specifically I want. It will most likely be powered by a strapped leach amp...roughly 450-500 watts into 8 ohms.

The main design requirements should be something along the lines of

1) cleanest sound possible within budget.
2) doesn't need to be loud.
3) shouldn't be excessively large. ~4 cuft / channel stereo or 6 cu ft total for mono.
4) should play as low as possible
5) rough budget of 500-750 for the driver(s) and wood.
6) They need to last. I plan to keep the MTM's as the mains for a year or two, and then move them to surround duty and get a pair of nice electrostats. so 10 years is a minimum lifetime.

I am going to try to use at least 2 drivers. Comments on whether I should go with a pair of subs for stereo use or one mono sub with multiple drivers?

in the stereo setup, each enclosure would be getting only ~250 watts into 4 ohms instead of 500 into 8. They will probably be ported so I can overcome the Xmax limitation at the lower frequencies. I think this may be more important than any "loss of control" and with the low tuning frequencies the group delay is going to be most prevalent at the frequencies where it is least audible. I think I'll have more airspace to work with if I go with stereo subs because I'll be able to integrate them into the stands of the MTM's. This would be more desireable for me than to have a large extra box sitting in the room.

I really want to give the Audiomobile MASS 2012's a try. The underhung voice coil I think allows more linearity/less distortion. (Skaaning uses this config) They are pretty damn expensive though. $329 each. Would anybody like to comment on the FR graph and THD plots they have posted. (http://www.audiomobileinc.com/massspecs.htm). They dont provide test conditions for their plots which is annoying. I haven't heard of a single person having a bad experience with a home audio sub based on the mass, but I also haven't heard of many stories period (probably because it costs twice as much as most other drivers). They are "small sealed enclosure" drivers, but their projected vented FR in unibox looks quite nice. Almost a perfect B4 alignment to 18hz. What else out there should I be looking at for 300+/ driver?

Another sub that intrigues me are the Alumapro Alchemy's. I think they look really neat. They are cheaper than the MASS', but the 12mm xmax is a big turnoff. I am thinking that their cooling system will keep the impedance closer to where it should be. Especially compared to the MASS which I would imagine suffers from a big increase in RE due to heat buildup(biggest flaw in underhung designs). My relatively low input power will probably reduce this to where it isn't an issue though. I haven't seen any actual tests to back any of that up btw.

Alternatively, I could go with 4 shiva's(or 2 and save 300+ bucks), but I think the enclosures would be too large.

The different sonotube subs I have seen all turn out pretty well, so I will probably at least give it a try. My only worry is that it isn't stiff enough. To those who have a sonotube sub, when you are playing at a moderate to high level, does the tube vibrate much? I am worried about bracing as well. There isn't a good way to cross brace. Do they sell 20" sonotube? I am worried that 24" wont give me enough length for a low port tune, and 16" wont give me enough radius for the driver and the port. I would also have to have them up or forward firing unless I want amplifier heatsink fins sticking out of the top of my box (I don't). I guess I could lower the bias currents a little bit, try not to worry about it and hope my house doesn't burn down.

comments or ideas?

thanks

jt
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Old 26th December 2001, 03:18 PM   #2
Super is offline Super  United States
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Given your cost range, you'll likely be pleased with the output of 4 Shivas. If you don't want heatsinks sticking out of the top, you could just put the amp in a separate enclosure. I had to do this, because my SonoSub has the port top firing, and the driver downfiring (16 inch diameter).

Also, if you don't go for a sonotube enclosure, you could take a look at Thomas W's 4 shiva IB design.
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Old 26th December 2001, 09:05 PM   #3
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Tha AudioMobile MASS subs are really nice but too expensive.

Your post is confusing, you talk about not needing high SPL's then you say a 12mm Xmax as a turn off.

If you want deep then get Shiva's.

If you want small and loud get a pair of http://www.blueprintdrivers.com 1203's $199ea.

Here's a UniBox plot of one in a ported box

Click the image to open in full size.

BTW MTM's really don't work very well as effects speakers for ESL's. Get a pair of Maggie MMG's instead.
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Old 26th December 2001, 11:19 PM   #4
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If your goal is to end up with electrosatics then I feel you need to consentrate on paper and size or the sub will be too slow and your phasing will be off. Good drivers usually don't require massive amounts of power and your design should reflect what the main reason for the sub is. An enhancement for music or an effect for movies. No reason not to have both since the one for movies can be much smaller and cheaper. Make it a front firing with a DVC driver that has a large excurion so you can get thumped in the chest. To enhance the stats you have to go for quickness or your phasing will be off. Take a look at the Eminence line. High quality and very efficient and they make an 18"er that goes down to 25 Hz that could be easily run with 30 watts. Parts Express is closing out the line so you can get em cheap which will help pay for the lumber. Remember the length of soundwaves so you don't shell out extra $$ for Hz that are too low for your room to handle.
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Old 27th December 2001, 01:19 AM   #5
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I have a fairly large ESL array and the Shiva's have NO problem keeping up with them.

Quote:
"Remember the length of soundwaves so you don't shell out extra $$ for Hz that are too low for your room to handle."
One doesn't need a large room to reproduce low bass. My electrostatic headphones reproduce 20Hz. And I can measure 10Hz output nearfield ~12" from the outlet of my big IB
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Old 27th December 2001, 07:50 AM   #6
jteef is offline jteef  United States
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I re ran some of the simulations, and the Alchemy looks like it will be alright. xmax will be exceeded above ~200 watts / driver though. I can get an F3 of about 18.5hz with it, but might want to increase that a little to ensure the speaker doesn't exceed xmax between 25 and 40hz.

My goals in audio are largely music oriented. I watch a lot of movies, but I don't put much weight in the sound quality of them. As long as I can understand what people are saying and the distortion levels haven't reached the annoying level I am good to go. The MTM's will be moved to the surrounds out of convienience, nothing more.

I think I am going to skip the sonotube so i can brace the hell out of the enclosure.

I am a little skeptical of the shiva's. stamped basket and foam surrounds = cheap in my book. I haven't heard anybody complain about them, so I will reserve judgement until I can hear them for myself. I don't think using 4 shiva's is an option anymore, however. The enclosures would need to be around 250 L. That is about 100L too large. I could cope with 4 10"s maybe. I dont know if i'll be able to secure a sub 20hz f3 with that config though. Any recommendations on 10" subs suitable for this? The Peerless XLS doesn't appear to be a contender. The audiomobile evo 2210's look like they might work, but I don't think they offer anything i can't get elsewhere for their steep $170 price tag.

Are there any other drivers between $200 and $300 I should be looking at. I am considering the blueprint 1203, but I am not sure I like a response with 2+ dB's of dip. I do like the small enclosure though!.

thanks

jt
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Old 27th December 2001, 05:05 PM   #7
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Well ignoring Shiva's because of the looks of their construction is sort like of cutting off one's nose to spite one's face IMO. It's not the looks of the driver that matters its the performance. Shiva's do perform and perform well.

The idea behind a tube sub is that it doesn't need bracing because of the inherent characteristics of the cylinder.

My priorities are 'music' as well. And I have several subs. The 2 IB's use Shiva's and they are VERY good. I have a stand-alone sub that uses the HE-15. Its sounds pretty good, but isn't up to the sonic quality of either IB.

You can do all the 'bench racing' you want with software sims but they do not tell how the drivers perform in the real world.

Have you ever looked at Siegfried Linkwitz's website? He likes the Peerless and Shiva drivers alot. But perhaps his recommendations aren't up to your standards.


BTW, we build a little MTM that's similar to Tony's Proteus, but decided to use slightly better midwoofers (Eton Hexcone Kevlar) and put them on a proper stand

Click the image to open in full size.
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Old 27th December 2001, 06:21 PM   #8
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Speaking of the SLAMM klone... when can we expect to see a writeup of the project!

BTW, what bass drivers did you use in the SLAMM klone?
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Old 27th December 2001, 07:51 PM   #9
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Super

Ask and you shall receive Jon just won first prize in the ClioWin Grand-Prix design contest for the SLAMM klone design. Here a link to the write-up regarding the design. It's not complete but most of the pertnant data is there.

http://www.cliowin.com/FOTO/gpphoto/Hancock/slamm.htm
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Old 28th December 2001, 03:58 AM   #10
jteef is offline jteef  United States
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ThomasW:

I would love to build an X1/SLAMM clone but the economics aren't there, and neither are my tools.

The MTM's are rather temporary as mains and while i'd like to spend $3-400 more I dont think it is warranted.

I can certainly appreciate the success you and others have had with the Shiva and I think they are probably well worth their low price tag.

I am trying to convince a friend to let me build him a sub. If he agrees, I will try to use the shiva and maybe my impression will change. Right now, it just seems like they cut too many corners for my liking.

jt
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