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 Post subject: 1x 4" sub or 2x 3" sub?
PostPosted: 08 Feb 2011, 20:13 
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Joined: 18 Sep 2010, 18:43
Posts: 73
Well,

I stupidly ordered an 8ohm speaker for my 4ohm amp. I sent the seller and email and hopefully they'll be able to cancel the order...

That aside. For loudness and quality of sound, would it be better to have 1x 4" 4Ohm subwoofer or 2x "3 8ohm subwoofers? So 1 sub that's 4 inches and with a 4ohm impedance...or 2 subs that are 3 inches each with 8ohm impedances?

Any ideas?
Thanks.


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PostPosted: 08 Feb 2011, 21:26 
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Joined: 24 Jun 2010, 00:48
Posts: 788
Location: Christchurch, NZ
Hi,

For loudness and dynamics and power handling, the 2X 3'' subs will be better as the cone area will be larger.
For deeper bass and sound quality, the larger 4'' will win.
May I ask, why do you choose such a small driver for subs ?

I'd personally go for a driver no smaller than 8''.

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PostPosted: 08 Feb 2011, 23:29 
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Ah yes sorry. I'm essentially just replacing the really really junky 4" sub on my computer speakers. The amp for the sub is really only capable of 7.5W which isn't very much. I damaged the junk stock 4" somehow so I need to replace them.

While I'm at it, I'm also recapping some of the shoddy capacitors on the board and reheatsinking the amp chips.


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PostPosted: 08 Feb 2011, 23:32 
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May I ask you this. Should I buy 2x 3" subs or 2x4" subs if the source is only 7.5W? Since the nominal power handling of the subs are 15W, would it make sense to use 2x 4"s as I would never be able to use its full potential?

Would 2 x 4" sound better than 2 x 3" on the same amplifier with the same output?

The only reason I am suggesting two speakers is because the amp is stable at 4ohms and these speakers are 8ohms. So 8ohms/2 = 4ohms.

Any suggestions for cheap 4ohm woofers?


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PostPosted: 09 Feb 2011, 00:08 
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Joined: 24 Jun 2010, 00:48
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Location: Christchurch, NZ
For the same output, 2X 4'' subs will go louder and deeper than 2X 3'' subs as they are more efficient. However you must ensure that the drivers suit the enclosures...I guess you are building a small box for them ?
Sorry I don't know of any 4'' subwoofer drivers.

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PostPosted: 09 Feb 2011, 01:17 
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Joined: 08 May 2009, 08:20
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Location: Duesseldorf, Germany
TangBand has a wide range of nearly all size drivers. AFAIK - They also produce drivers for PC speaker systems and subwoofers.

Link:
http://www.tb-speaker.com/tbp.htm

Have fun ;-).

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 09 Feb 2011, 16:17 
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Joined: 18 Sep 2010, 18:43
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Thank you for all of the replies. I really appreciate it.

Well, my order was unable to be cancelled. :( ...It shipped already. It's a HiVi M4N 4" Midbass....Since it is an 8ohm speaker and my amp is stable at 4ohms, I decided to order ANOTHER M4N.

I am going to run the subs in parallel to give me an impedance of roughly 4ohms. The sepakers were $17 each I believe. So the total investment was around $40. A little bit more than I want to pay, but still a good price for such good speakers.


I'm a bit confused as to calculating the size of box for the two speakers. I suppose Google will help me with that.

Oh and Tom, I saw those Tang Bands. If I was able to cancel the order, I would have bought one, but since returning an M4N would cost me about $15 in shipping, I decided it wasn't really worth it. I think these HiVi's might be better, though I'm not expert.

Here's the website and picture: http://www.swanspeaker.com/product/htm/view.asp?id=83

Image


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PostPosted: 09 Feb 2011, 17:46 
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I think I'll be building a sealed enclosure for these as I actually don't really listen to my speakers that loud and I don't especially like how ported subs sound....

But, now since I'll be having two speakers in a box, I'm confused as to how big the box has to be. Correct me if I am wrong, but since the power of each sub is technically cut in half (because they are 8ohm subs and the amp is stable at 4), so 2 x 1/2 would = 1.

There's also another issue. The amp is only rated for 7.5W, which is half of the nominal handling of the sub (15W rated by HiVi). The rated size for the enclosure from HiVi is 4L (0.125ft cubed).

We have two factors. Two 8ohm subs are running in parallel @ 4ohms with a max of 7.5W between the subs (which is half the power that HiVi says they can handle).

So, technically, you can say that the 2x 8ohm subs are equivalent to 1x 4ohm sub running at 50% of the power that the amp is capable of. But we have to keep in mind that the because sub can only use 50% of the wattage that it can nominally handle. So, its only going to move about half the amount of air that HiVi is factoring in. HiVi says it can run at 15W at all times...and if it's only running at 7.5W, then it's really only moving half the air.

So now I need to change 4ohm back to 8ohm. (sort of). So technically isn't a 4ohm sub running at 50% of its nominal wattage handling roughly equivalent to a 8ohm sub running at 100% of its nominal handling.

Therefore, two 8ohm subs running at half their rated handling is equivalent to one 8ohm sub running at 100% of its rated handling???

Sorry if I made that so confusing. I don't know how else to explain it...

Am I wrong?

I'm sorry to blabber. It's hard to explain this in words....Is it alright to have the box a little bigger than what it needs to be?


Last edited by TheLaw on 09 Feb 2011, 17:58, edited 1 time in total.

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PostPosted: 09 Feb 2011, 17:58 
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Joined: 18 Sep 2010, 18:43
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Shoot I forgot the total power handling is 30W now between the two...Hopefully that doesnt matter....AHHH....SO confused.


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PostPosted: 11 Feb 2011, 13:39 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
With your amp being stable at 4ohms, it means that it can drive 4ohm speaker without issues. An 8 ohm speaker will also be fine for use with that amp. The only difference is that with an 8ohm speaker, the output power will be about half. If the drivers are the same sensitivity that equates to about 3dB less of maximum output which is not much at all. Two 8 ohms drivers in parallel (net 4ohm load) is also a good approach.

Post the datasheet for that driver and we can help you with a simulation for the enclosure.

Cheers

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