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Subwoofer and Firstwatt F1
Subwoofer and Firstwatt F1
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Old 1st June 2009, 06:52 PM   #1
tgrauss is offline tgrauss  France
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Default Subwoofer and Firstwatt F1


I am building my homecinema 5.1 hifi, mostly focused on sound quality rather than the power.

So, I am building 3 clones of the Firstwatt F1 (so 6 channels) for the power amps.
All of my 5 speakers are DIY made, the main speakers are 2 D37 Backhorn Nagaoka. All off these speakers are based on Fostex.

This system will have a 6 channels (1 of the channel is for the sub) DIY preamp, based on UGS clones modules from Nelson PASS. I call this preamp the "HC UGS"

Until now, everything is fine, but what about the subwoofer?
I have 1 channel of spare in the F1 for the subwoofer, so 10W of power.
I was thinking using the Project P48A from Elliott Sound Page (modified so that it is symetric) for the filter of the sub.
I like the idea of the sealed box for the sub, because of the high quality of the sound coming from them.

My wish is more on a hifi sub rather than a pure HC sub.

Here are my requiriements :
  • Passive subwoofer
  • Symetric amplifier for the sub as the preamp is symetric
  • The filter of the sub will be in the preamp
  • Everything has to be full symetric (the preamp convert all signals to a symetric signal, thanks to the UGS modules)

I have one spare channel on the F1, 10W, so it would be nice if I can use it. Is there a way for this?
FIY, from what I have found, the D37 goes from 50Hz to 20kHz.
Maybe with my D37, it is not that useful to invest in a sub, and it is better to use this spare channel as a back center channel (so creating a 6.0 system)?

What do you think?
What would be the better choice using this spare channel?


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Old 1st June 2009, 10:56 PM   #2
cyclotronguy is offline cyclotronguy  United States
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Default F1 subwoofer

You would need a very efficient subwoofer to get much out of 10 watts. Something like an oversize Jensen Imperial with twin high sensitivity drivers.

If you wish a small sealed box woofer, I'm afraid 10 watts just isn't going to work.

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Old 2nd June 2009, 08:03 AM   #3
chris661 is offline chris661  United Kingdom
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For the sub, a decent horn should do the trick.

I know little about these, except you get some serious efficiency, and your woodworking skills need to be up to scratch.

What's the budget for this?
How big can you realistically have this sub?
Could you get hold of a higher power plate amp? - this would increase the number of sub designs you could use.

We can't really help until you answer some of these....
My work: www.grimshawaudio.com
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Old 2nd June 2009, 10:43 AM   #4
David_Web is offline David_Web  Sweden
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200L TH with a 15" midbass driver. (proper loading regarding fs, but a good sub driver will also do) Goes from 32Hz to 90-100Hz
Should be scary at 10W.
Although I agree with extra speaker instead.
TH also NEEDS subsonic filter.
100dB at 2pi with headroom to spare. (10W)
110dB in a corner with rooms to spare. (10W)
So a small class A will be enough for a sub if you are willing to accept the size.
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Old 2nd June 2009, 03:02 PM   #5
tgrauss is offline tgrauss  France
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Thank you for your reply.
Well, I was thinking adding only a little bit of bass, just adding what the d37 can't reproduce
But from what you say it will be difficult...

My 2 D37 are already quite big, so I don't think my wife will agree to add something too big anymore in the living room
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Old 2nd June 2009, 03:02 PM   #6
tgrauss is offline tgrauss  France
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To think about it again, if I am lucky enough to be able to build my house, I can integrate the sub in the house itself (integrate in the wall, to make it invisible).
What do you think of the idea?
Is there anything which can go wrong with this idea?


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Old 2nd June 2009, 03:02 PM   #7
tgrauss is offline tgrauss  France
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Hmmm, a big sub in the living room is not possible for WAF reason.
But, when I will build my house in a few year (hope so at least), I might be able to use the wall behind the frame of the videoprojector's screen.
The end of the horn can then be big as it is hidden by the screen (say 1.5 meter wide or more). And the total volume of the speaker can be huge as it is inside the wall (I can make a wall a little bit thicker compared to the standard).

If the driver is inside the horn (and not in front), can this horn be considered as a sealed enclosure?
For such a sub, is the sub filter from Elliott sound page good for it? Or is it better to use a 1st order low pass passive filter?

If I build this, the budget won't be too much a problem as it will be included in the loan of the house
Also, the decoration is not important as it is the wall itself, hence it will be painted as the other walls. The biggest cost will be the speaker itself as the MDF wood is not that expensive.

What do you think of the idea?
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Old 2nd June 2009, 11:28 PM   #8
steve71 is offline steve71  Australia
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Here's a pic of a bass horn built into a riser - don't know what the cut off is..


If you're going to build it into your wall I'd use quality ply - MDF is too easy to damage.

Another thought - why not just use a better suited amp? 10 watts is nothing for a sub for home theater use. At close to reference levels I use 80watts on my ~100db/w/m tapped horn in a small room.

Amp qualify isn't as much of a concern for subs.
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Old 3rd June 2009, 06:19 AM   #9
tgrauss is offline tgrauss  France
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Join Date: Apr 2009
Why do you say that MDF is to easy to damage? My speakers are made of MDF and no problem...
What is nice with MDF is the density

The sub won't be only for HC, it will also be for hifi.

Here is an Incredible subwoofer I have found It is build in the basement.
I don't think I will go that extreme
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Old 3rd June 2009, 02:57 PM   #10
steve71 is offline steve71  Australia
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If you can seal the MDF before you install it that might be OK. But it's very easy to damage MDF with water and if your sub is a permanent, built in arrangement then your up the creak without a paddle if you ever you get water damage. Baltic Birch Ply is a great material to build subs out of - there are plenty of MDF vs PLY threads you can read up on.

I use my horns for both Hi-Fi and HT and I wouldn't want a 10 watt amp unless I had 115db/w/m bass horns.

That's the great thing about multi amps with active crossovers - you can pick the right tool for the job.

Good luck with the project, it sounds very interesting!
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