12" subs; 1x100W or 2x50w?

[Slate8]

Hi all,

Bit of car audio advice needed.

I have fitted my oldskool Denon DCA-800 amplifier to the Surf this weekend. It's a 300w 6 channel amp with 50W per channel. I currently have 4 channels running the front and rear speakers, and two left over for sub(s).

My question is, which should sound better; running one 12" sub with 100W (in bridged mode) or getting two 12"s running at 50W?

Any suggestions?

[Slate8]

I have also asked this question on avforums.com. Here's the thread:

http://www.avforums.com/forums/showthread.php?t=231377

[AndyLala]

Two questions here.

1) is the amp twice as efficient in bridged mode than in stereo?
2) are two speakers twice as efficient as one?

Answer to both, probably not.
Bridged amps usually generate more heat than audio output. Pairs of subwoofer speakers create larger peaks and troughs than singular drivers, and rely greatly on placement within the vehicle to generate the 'right' amount of output in the desired location within the vehicle...

More detail is required to understand how the amplifier behaves in stereo and bridged. Also more details on the speakers, their alignment in relation to the enclosure, and enclosures alignment in relation to the cabin space in the vehicle.

That has probably confused more than answered...

[truckarms]

2*100W
Andylala think you have confused me:thick:

[Slate8]

That has probably confused more than answered...

No confusion, ok well maybe just a little

1) I'm not sure what you mean by efficient. Currently my limited knowledge on this amp is... Bridged mode pumps 100w at the sub, in "normal" mode it would be 50w to each. There is a switch on the amp for 2ohms or 4. It recommends 4 when bridged.

2) No idea. I thought 2 might be better. My logic is two subs = twice the surface area = more air moved, but I'm not sure how less watts would affect this. Having said that, I've also noticed that removing one speaker from a stereo home hi-fi seems to produce better bass (probably due to lower frequency sound waves not cancelling each other out?)

Also more details on the speakers, their alignment in relation to the enclosure, and enclosures alignment in relation to the cabin space in the vehicle.

As I haven't bought the speakers yet I'm not sure I can answer this one. I'm pretty much half way through building this system, so any advice on enclosures and alignment would be welcome

[dirtydog]

Id probably bridge one sub myself to get some half decent power going through it...
I take it the amps ratings are RMS?

[AndyLala]

I'll post a more in depth response when it is a little quieter.

[Slate8]

Id probably bridge one sub myself to get some half decent power going through it...
I take it the amps ratings are RMS?

Yes, thge amp is 300W RMS / 50W RMS per channel.

[Dog_Book]

Yes, thge amp is 300W RMS / 50W RMS per channel.

I'd go for the 100w rms diving a 12" sub, at least a 300w rated one at that

[AndyLala]

If you haven't brought the speakers yet... good timing.

300w RMS into 4 ohms will be enough (just) if you only have 50w RMS to 4 other channels.

Next question is, do you want sound quality, or sound pressure...

Do you want to be as clear as a bell, or be able to feel it 300 yds away.

More importantly, do you want to be deaf inside of three weeks, and are you quite happy to keep replace speaker cones every couple of months.


Sound Quality would give you a sealed or an isobaric alignment.
Sound pressure would give you a ported or dual ported alignment.
300 yds away would give you a sealed/ported or series ported.
And the killer box would be a combination of Vented and series vented enclosures.

I have a lot of fun with these... 'make me a box thats real loud'... Oh ok... EXCUSE ME, BUT ITS TOO LOUD.... sorry mate that is what you asked for.

So quite a can of worms.

If you are going to settle for two loudspeakers on the bridged channel, then you want to end up with a 4 ohm load at the frequency it is going to play at.

That could be two 2 ohm drivers in series, or two 8 ohm drives in parallel... it shouldn't make too much difference which. The trick comes if giving them enough power to play flat out without too much power (or distortion) to cause them any damage. Also the frequency curve / output curve improves to a point just about before the driver is about to fail when it will play at its best.

More 'clean' power would give you more headroom and consequently more control over the drivers excursion.
It might even be worth trying to pickup another amp just to run the subs and bridging four channels into two to run mid-bass drivers up front. (another thought to confuse matters.)

It all depends on how you listen to music in your vehicle.

[Chillitt]

dave, he said its a bit loud

[Slate8]

If you haven't brought the speakers yet... good timing. (etc....)

Wow, excellent reply!

I have had sealed boxes in the past and have always been happy with them. I didn't really understand the difference between sealed and ported (sound wise) until doing a bit of research yesterday.

From what you’re saying, if I get a sealed box the sound should be of a better quality and not as deafening. This sounds perfect to me and may well be the option I got for, so thanks for your advice.

I am still learning about getting the right ohm rating of sub. If you have a read of the thread linked from my second post you'll see that "MGDisco" has the same amp as me and seems to think one 4 ohm sub bridged with 200W would be the way to go. This would mean running the amp in 2 ohm mode apparently with the sub bridged.

So it sounds as if I may be going for a 4 ohm sub bridged in a sealed box.
What do you reckon Andy?

Thanks again for the advice!

[AndyLala]

I personally prefer the sound of sealed enclosures, they usually have a more controlled extension of the lower registers. This is of course easier in 'open' environments, but as always there is a bit of experimentation required.


I currently have an aperiodic enclosure at home for my home stereo setup, and have been pleasantly surprised with aperiodic enclosures in vehicles. The only problem is that they require tremendous amounts of power to drive them well.

The whole point of the enclosure is to control the excursion characteristics of the speaker. So if you are going to buy a sub, buy one specifically for a sealed enclosure. That being said, the build of the enclosure and the cabin volume of where you are going to place the speaker will have an effect on how the sub enclosure will sound.

You want to get a clear progression from the lowest note to its highest note will the least amount of output level variation (within 3db - 6db)... This then needs to tonally balance with your mid-bass speakers so that the progression up the frequency becomes transparent to the speakers reproducing those sounds. As the freqeuncy increases you will get a certain amount of frequency steering and ideally this needs to be minimised (or masked) as much as possible.

When that has been accomplished, you should end up with a full response (ideally 20hz to 20khz with as little as a 3db variation)... or as close as you can manage.

This will reproduce as close to the sounds mixers rendition of the recording...

Sealed enclosures should really be sealed. Remember that MDF, what most people build their boxes out of, is porous... coat the inside of the enclosures with fibreglass resin to completely seal it. When that has fully cured (upto a week), you can install the speaker. I have also had some success with stuffing the enclosures with various media (wool, acoustastuff, wadding) to ellicit a drop in enclosure volume and a change in tonality (to match it to mid-bass drivers).
Standard cushion wadding will, for example, give you approximately a 30% reduction in internal volume for exactly the same response characteristics, as opposed to a non-filled enclosure.

[Slate8]

Thanks for the info...

I'm going to pop down to my local car audio specilists and show them my current setup. I plan to print out this thread for them to see too then see what they suggest.

I'll probably get them to build the box and suggest a sub etc using the advice you've given, so thanks again.

[marky.b]

you might struggle with 100w for a 12, but have a look at www.talkaudio.co.uk
look in the FAQ's or used the search facility.

Try different dealers too, they may try and sell you the sub which they make the biggest margins on rather than the one best suited for your system.