# One or Two Subs



## Tommy (Apr 20, 2006)

Ok NDawag convinced me to return the in-wall sub I purchased but I havent seen him online much since.

I've been hearing different things recently of whether I should do one larger sub for the room or two smaller size ones. Thoughts?

The basement room is 20' x 14' with cement floor and one riser.


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## Sonnie (Apr 11, 2006)

E has his hands full right now with a new baby boy. 

Remember your room is almost the size of mine and I have two SVS PB12-Plus/2's. I had just one hooked up for a night and then hooked the other up the next night... NO lookin' back! I can't figure out how I ever lived without two... and for those two subs you actually get 4 x 12" subs with about 1800 watts total power. 

But I forget... you were originally considering in-wall so you might opt for the cylinder subs... a pair of those would be awesome as well. 

Either way... whatever you get... go for two, one in each front corner and you'll never have to ask yourself, "what would two subs be like"... and I won't have to whoop you over and over about not going with two. :R


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## toecheese (May 3, 2006)

utstanding: 

Get an IB!


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## JCD (Apr 20, 2006)

An IB might not be a bad choice for you. If you drink the KoolAid (I love that metaphor) over at the Cult, then I think you have an ideal situation for an IB. It will give you the "in-wall unit" you were originally looking for, but also give you that ohmygawdthat'samazing kind of bass that I think was missing from your previous unit. Given the size of your room, you may need to get 4 or 6 15" drivers. 

If you're going to go with the stand alone sub, SVS is the way to go. I'd e-mail Tom V. with your room dimensions and ask for his opinion. He'll tell you what he thinks will work best in your space, with no bias towards the more expensive stuff. He'll also give you his honest opinion on whether or not a dual sub arrangement would be worth it. He'll also get back to you

_*The IB Pro's*_
Cleaner appearance-- they're in wall after all
Bass is supposed to be better
Figure ~$250 for the amp, ~$100 for the BFD, then the cost of the drivers. Depending on which way you go, you can spend between $100 and $300 per driver

*The SVS Sub Pro's*
Much easier to set up
SVS is a great product. I think the IB will be better overall, but the SVS is no slouch.
Great customer service
Cost for their subs run from $429 to ~$1200, well, they also have one over the top ridiculous sub for ~$2000


JCD


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## Sonnie (Apr 11, 2006)

If I'm not mistaken I think he decided he has no place for IB. Of course Tommy will know best and will certainly chime in. We discussed in one thread about using the Store room and I can't remember what the reasoning for not using that was... but he did decide he really didn't want to cut into the wall right in that location anyway.

Now that soffit he built on the front (if he leaves it up)... that might be an option for IB... not sure if that's enough volume though for four drivers.


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## JCD (Apr 20, 2006)

I missed the earlier thread where he decided he couldn't do the IB.. however, the soffit should have enough volume. The entire volume is supposed to be a minimum of 4 times the Vas of the drivers. I took a look at one of the Parts Express IB drivers. Its Vas was 9.92ft^3 per driver, so as long as the soffit has 160ft^3 he should have enough space in the soffit alone. More, of course, is better.

My main concern is if there is enough distance for the back sound wave. I don't know all of the physics involved, but seems to me that if he flush mounted the drivers on the front side of the front soffit, there would be enough space for the back sound wave. 

JCD


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## Josuah (Apr 26, 2006)

Sonnie, have you pushed your subs to the maximum to see if you actually need those four drivers? Just wondering. I've got a pair of SVS 16-46PC+ subs in the 12Hz tune, and I will hit 110dB maximum at my seating position, 105dB max at lower frequencies. My room is open to the rest of the house and over 5000 ft^3. So, I will need two more subs to hit 115dB maximum, which is my target for reference level playback.


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## Sonnie (Apr 11, 2006)

I could live with one sub (which would include 2 drivers)... but having two subs there is a noticeable difference in overall sound. Maybe less strain on each individual sub and more of a pressurized feeling. I had to cut down the volume on the subs after listening for a short while... it was just too much, but it still sounds better than just having one. Maybe it fills a void or something, I don't know. Somebody probably knows more about the technical advantages than I do. I'm just a hillbilly.


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## Phil M (Apr 19, 2006)

I asked the quetion to SVS 2 years ago when finalising (English spelling) my HT. I emailed a drawing and they recommended one sub.
Morale of the story - get in touch with Tom and he'll make an expert recommendation.
The air is different in Hillbilly land - that's why Sonnie needs 2!


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## Tommy (Apr 20, 2006)

Sonnie said:


> E has his hands full right now with a new baby boy.


:yes: I should have said I'm trying not to pester him because I know he's busy.

Anyway who is this Tom guy?

I havent thought much on it till the guy that came out to give an estimate suggested getting the two speakers instead of the one.

All I know is if I do finish it myself I still need to ask some wiring questions about it soon. Like whether I'm wiring for one or two speakers

what type of wire to get
should I get it with the connections already on the ends or not
and how to get it thru the wall so its not just popped out a hole in the sheet rock...


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## Josuah (Apr 26, 2006)

Two subs can certainly result in better overall response depending on placement. I used to have my pair of subs next to each other in the same place, and now I have them separate: one on each side outside of my left and right speakers. This placement got rid of a null and resulted in a flatter overall response.


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## Sonnie (Apr 11, 2006)

Tommy said:


> Anyway who is this Tom guy?


Tom is one of the owners of SVSound (SVSubwoofers). All of those guys are very helpful and you'll never hear them downgrade another company nor anyone who doesn't wish to buy their subs. Their customer service is literally second to none.

He is a member here and I'm sure he'll chime in... but I would recommend giving him a direct call... or email him.



Tommy said:


> All I know is if I do finish it myself I still need to ask some wiring questions about it soon. Like whether I'm wiring for one or two speakers
> 
> what type of wire to get
> should I get it with the connections already on the ends or not
> and how to get it thru the wall so its not just popped out a hole in the sheet rock...


If you are going to purchase a sub or subs like the SVS subs, then you will need to decide where you are going to locate them... generally as far into the front corners as possible. If you decide on this location then you can run some RCA cables in wall from where ever you will have your BFD located (don't think for a minute you aren't gonna own one  who knows... you may get lucky and win one... either way plan on a BFD) then run them to where you will locate the subs. You can get some good cable from Apature (link in Components forum up top). Or you could get some RCA plates (N-Dawg can probably help you there) and mount them ... have your installer terminal some cable for you. Then you'll need a short cable to go from the plate terminal to your sub. Or... if you want to eliminate that extra connection in the wall plate you can get a solid plate and drill a hole and run the cable through.


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## kingkip (Apr 20, 2006)

One sub, especially a SVS, will probably do, but two will almost always sound better. Subs are all about displacement, double the drivers and your subs no longer have to work as hard to put out the same spl and that means less distortion. ie an ib:R BTW if an ib is an option I will side with the other guys and say go for it.


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## JimP (May 18, 2006)

kingkip said:


> One sub, especially a SVS, will probably do, but two will almost always sound better. Subs are all about displacement, double the drivers and your subs no longer have to work as hard to put out the same spl and that means less distortion. ie an ib:R BTW if an ib is an option I will side with the other guys and say go for it.



....and if you check some of the test where the frequency response is plotted at various SPLs, you'll find that many subwoofers loose their bottom end the louder they're played. The workaround for this is to use multiple subs so that when you reach those sound levels, you're still at the flat part of the subs operations.


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## Josuah (Apr 26, 2006)

An infinite baffle supposedly requires double the drivers because you are throwing away the reverse excursion? This is what I've heard at least. It's supposed to sound cleaner also as a result, because you never deal with the reverse excursion, which is not going to be identical to the forward excursion.

As JimP mentioned, all drivers have a harder time reaching higher SPL at lower frequencies. So you either need a lot of surface area to move back and forth a little (multiple drivers) or less surface area to move back and forth a lot (greater excursion). Since drivers are physically limited in their excursion, multiple drivers is a simpler solution. 

If a driver attempts to move back and forth past their physical limit, that's called bottoming out and you'll hear clanks or clacks. That's okay if it happens once or twice, but if you keep pushing your sub that hard you can do permanent damage. I'm led to believe that a sealed subwoofer cannot bottom out because the sealed volume within the enclosure will prevent that, if properly matching the enclosure, driver, and amplifier. But I'm not entirely sure of that.


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## Tommy (Apr 20, 2006)

For 2 subs, how is it wired?


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## Sthrndream (Apr 21, 2006)

How many sub outs do you have? Many AVRs have 2. Otherwise a Y-splitter with each sub having their own EQ I would think gives the best results.


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## Josuah (Apr 26, 2006)

A lot of people seem to want to EQ each subwoofer independently. I haven't been convinced of any benefits to doing so instead of EQing all subs in aggregate.

Gene (I think) over at Audioholics indicated his preference would be to EQ a single sub to avoid introducing delay problems, but I'm still not sure what he was getting at there. An EQ in the path will certainly introduce some further delay, perhaps not constant across the modified bands, but I'd imagine it would be easier to deal with that if that delay was introduced to all subs rather than one.


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## JimP (May 18, 2006)

If you do that, you also benefit from using the exact same sub, which is probably not what most people are doing.


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## Josuah (Apr 26, 2006)

Why would using the exact same subwoofer matter? Phase differential as a function of frequency will be different between the two regardless. Unless by some magic the delay introduced by the EQ unit makes one sub's group delay function match the other sub's, except in amplitude. ???


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## Sonnie (Apr 11, 2006)

I have identical subs symmetrically placed in the two front corners. I eq them simultaneously with one channel of the BFD. I believe I added one foot to the distance setting to compensate for the delay (per brucek's instructions in his review and testing of the BFD).


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## Sthrndream (Apr 21, 2006)

My apologies, I should've said _most flexible_ instead of the more sbujective _best_. Obviously there are arguments for doing it either way.


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## rcarlton (Apr 29, 2006)

For an interesting take on two subs see: two subs


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## Sonnie (Apr 11, 2006)

Hey Ron.... he seems to recommend stereo subs... but this would be hard for most wouldn't it? Most sub pre-outs are mono I think aren't they?

I still question too how much stereo sub information is present in the LFE channel... I've always thought it was mono... :scratch: Maybe I'm confused... which wouldn't be a surprise.


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## rcarlton (Apr 29, 2006)

Next big thing in pre/pro's...stereo subwoofers! :R I also think LFE is mono:blush: . Not sure. Will do some googling.


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## Tommy (Apr 20, 2006)

pierrebnh said:


> How many sub outs do you have? Many AVRs have 2. Otherwise a Y-splitter with each sub having their own EQ I would think gives the best results.


01
I dont see anything on the back of this receiver marked exactly as sub-out, is it named or initialed somthing different? :huh: 

02
Also, I know your not supposed to mix speakers does the same go for the subwoofers, I sent the in-wall MTX sub back but when I buy a floor standing sub now does it still need to be from MTX?

03
Ok I know the subs get different type of wire then the speakers but exactly what of wire?

04 
I saw something about having it precut to lengths with the connectors already added. Can I order it like the speaker wire on a spool and cut it where I need it? Or do I need the fixed lengths?

05
If I am cutting it what type of connectors & tools do I need? 

06
Going thru the sheet rock, what type of boxes/plate covers do I need to either run the wire out of it or which would even look nicer is there someway to terminate it at the box and then on the outside screw it to a connection piece on the box plate?


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## rcarlton (Apr 29, 2006)

Sonnie said:


> I still question too how much stereo sub information is present in the LFE channel... I've always thought it was mono... :scratch: Maybe I'm confused... which wouldn't be a surprise.


Turns out the LFE channel is mono!:duh:


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## kingkip (Apr 20, 2006)

Tommy said:


> 02
> Also, I know your not supposed to mix speakers does the same go for the subwoofers, I sent the in-wall MTX sub back but when I buy a floor standing sub now does it still need to be from MTX?


No, that isn't necessary. The timbre matching usually has to do with the tweeter. Get a sub that can fill your room and sound good to you. Or whatever other qualities you need for it.



Tommy said:


> 03
> Ok I know the subs get different type of wire then the speakers but exactly what of wire?


Decent shielded rca




Tommy said:


> 04
> I saw something about having it precut to lengths with the connectors already added. Can I order it like the speaker wire on a spool and cut it where I need it? Or do I need the fixed lengths?


You can but then you have to terminate the cables yourself. Soldering skill, an iron and wire strippers, though not terribly difficult. You can get decent factory cables starting at around $20 or so.




Tommy said:


> 05
> If I am cutting it what type of connectors & tools do I need?


See above




Tommy said:


> 06
> Going thru the sheet rock, what type of boxes/plate covers do I need to either run the wire out of it or which would even look nicer is there someway to terminate it at the box and then on the outside screw it to a connection piece on the box plate?


Home Depot, Lowes etc sell RCA wall plates or speaker terminal wall plates and the like.


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## kingkip (Apr 20, 2006)

Sonnie said:


> Hey Ron.... he seems to recommend stereo subs... but this would be hard for most wouldn't it? Most sub pre-outs are mono I think aren't they?
> 
> I still question too how much stereo sub information is present in the LFE channel... I've always thought it was mono... :scratch: Maybe I'm confused... which wouldn't be a surprise.


Really only financially hard. All you have to do is use a y-cable to split the signal and then run it to both subs. With big enough subs I suppose it would be physically hard to position them though.


It absolutely is mono. However when you use the LFE out it sends all the signals (from all of the channels you are using ie 2, 5, 6, 7 whatever) below what you have the xover set at in the receiver to the sub. Since sound at those freqs are omnidirectional it doesn't matter that it only comes from one place. 

Where two subs usually help is with displacement and with good positioning can help cancel out some nulls.


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## kingkip (Apr 20, 2006)

Josuah said:


> An infinite baffle supposedly requires double the drivers because you are throwing away the reverse excursion? This is what I've heard at least. It's supposed to sound cleaner also as a result, because you never deal with the reverse excursion, which is not going to be identical to the forward excursion.


You aren't thowing away the back wave. If that were true a sealed subwoofer (which is what an IB is on a grand scale) would require double the drivers as well, as the back wave can't escape the box. Why you typically need more drivers in an IB is because you lose the accoustic suspension provided by having that sealed box. In a typical sealed box the air trapped in the box compresses as the driver move in and resists the driver, making it harder for the driver to bottom out. In an IB since the "box" is so large there is no air "shock absorber" and therefore it is easier to bottom out the spooks. More drivers mean more displacement which means more SPL for less movement from each driver and there is your protection.

BTW if you don't believe me about throwing away the back side, sit in the room on the back side of the IB during U-571:devil:


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## Fincave (Apr 20, 2006)

Tommy said:


> 01
> I dont see anything on the back of this receiver marked exactly as sub-out, is it named or initialed somthing different? :huh:


Page 13 of the manual reads something like "CONNECTING A SUBWOOFER. Use the PRE OUT SUBWOOFER jack to connect a powered subwoofer (powered amplifier built in)" On the rear panel of the SR 7500 it is marked as SW PRE OUT, am not meaning to be sarcastic but it really is worth taking the time to read the manual carefully. Receivers can be a bit complicated as they have a wide range of features and options.


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## Sonnie (Apr 11, 2006)

I can see Tommy now... :rant: :reading: :rant:


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## Steve Williamson (May 11, 2006)

You know I understand sub inputs :scratch: 

This a pic of the back of mine, left and right line in, left and right line out, left and right speaker in and left and right speaker out.

Now I'm confused, and I've buried my manual somewhere whilst we pack for moving.

My receiver only has one "subwoofer pre out" labelled on the back next to the pre out for the rear surrounds.


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## JimP (May 18, 2006)

Steve,

This can be confusing.

What you are seeing with all these ins and outs is where you are using the sub's crossover to seperate the frequencies that the sub is responsible for from the ones that go on to the speakers.

You basically have 3 different options.

1st. Use the receiver's crossover and send the sub out signal from the receiver to the line in input (either left or right will do). When you do this, you do want to turn the crossover on the sub to the highest setting to avoid the effects of a double crossover. This is probably the best setup for home theater.

2nd Use a preamp's stereo left right line level output to the sub's line level input and then route the sub's line level output to an amplifier. In this example, you'd want to disable the crossover in the preamp and use the crossover on the sub. This would work best when you're using the the sub for stereo as the low frequencies for the other channels in a home theater setup would not be routed to the sub.

3rd Last but not least, route the left right speaker output from the receiver or amplifier to the sub's left right speaker input and then route the left right speaker output to the speakers. This primarily works for stereo.

Thinking outside of the box here, I have a variation that you guys might be interested in. I have a 7.1 system where my front mains, center channel and side surrounds are set to small and the low frequency information is routed to a sub located at the front of the room between the TV and the right front channel through an equalizer (velodyne SMS-1). Now here is things get interesting. My back surrounds are set as "large" in the preamp and the speaker level out from the amplifier first goes to the "speaker in" on a subwoofer located at the back of the room then on to speakers. The sub in the back of the room crossover is set at 80 hz, the same as the preamp setting for the other speakers. What I gain with this is a more 3 D effect of the sub frequencies. Imagine a battle cruser fly by with the lower bass located at the front of the room and the rest of the sound going from the back of the room to the front of the room. Now imagine the same fly by when all the sound originates from the back of the room then all moves forward to the front of the room. Since I'm using fairly significant speakers all the way around (flat to around 50hz) and that I'm using them at roughly a 80 hz crossover, that many other options exist as to setup. Although I like what I'm hearing (after much experimentation) when the mad scientist gene kicks in again, who know what I'll try next.

Edit: One thing that I tried and did not like is where I ran both the front sub and the rear sub off of the sub output of the preamp. I also used the Velodyne SMS-1 equalizer for the front sub. I spent days getting everything calibrated and what I wound up with was having the sub frequencies always coming from the middle of my head. Cute at first, extremely annoying soon thereafter. In retrospect, this might have been better with a 50 hz crossover where there is less information going to the subs between 80 and 50, but with a 80 hz crossover, you constantly have this pounding going on that is overkill.


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## Tommy (Apr 20, 2006)

Sonnie said:


> I can see Tommy now... :rant: :reading: :rant:


hahaha sonnie, I'll get ya back for that one... :devil: 



Fincave said:


> Page 13 of the manual reads something like "CONNECTING A SUBWOOFER. Use the PRE OUT SUBWOOFER jack to connect a powered subwoofer (powered amplifier built in)" On the rear panel of the SR 7500 it is marked as SW PRE OUT, am not meaning to be sarcastic but it really is worth taking the time to read the manual carefully. Receivers can be a bit complicated as they have a wide range of features and options.


Ok I'm not that bad and will always fully read the manual before actually touching anything unlike most people. But for the quick reference of answering how many output jacks I have, I did not bother to open the manual as of yet.

BTW Fincave, thank you mentioning the Pre Out was what I was getting at as far as asking if it was named something else.


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## Tommy (Apr 20, 2006)

Thank you Kingkip this also answers some of my questions. 

I guess what I'll plan for then is behind the wall I will run pre-cut terminated wires, one wire to the far corner on the back wall and one wire to the front of the room (same side) and have both connected to there own wall plate.

Then I'll get a seperate wires that run from the wall plate to the subs after I figure where exactly they'll sit.

Does this sound right?



kingkip said:


> No, that isn't necessary. The timbre matching usually has to do with the tweeter. Get a sub that can fill your room and sound good to you. Or whatever other qualities you need for it.
> 
> Decent shielded rca
> 
> ...


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## kingkip (Apr 20, 2006)

Tommy said:


> Thank you Kingkip this also answers some of my questions.
> 
> I guess what I'll plan for then is behind the wall I will run pre-cut terminated wires, one wire to the far corner on the back wall and one wire to the front of the room (same side) and have both connected to there own wall plate.
> 
> ...



That should do it.:T


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## Tommy (Apr 20, 2006)

Sonnie said:


> Remember your room is almost the size of mine and I have two SVS PB12-Plus/2's. I had just one hooked up for a night and then hooked the other up the next night... NO lookin' back! I can't figure out how I ever lived without two... and for those two subs you actually get 4 x 12" subs with about 1800 watts total power.


Two of them, aint they like 1,200 each? [Filtered word here], I want the room to shake but not sure if I want to spend that much extra. 

I thought I was doing well bumping it up from one $500 speaker to maybe two or just getting one speaker that is better.


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## Tommy (Apr 20, 2006)

Sonnie said:


> Remember your room is almost the size of mine and I have two SVS PB12-Plus/2's. I had just one hooked up for a night and then hooked the other up the next night... NO lookin' back! I can't figure out how I ever lived without two... and for those two subs you actually get 4 x 12" subs with about 1800 watts total power.


Sonnie I ordered _one _SVS PB12-Plus/2's. :T 

Those things are expensive at $1,200 each. I'll see how I like the one and how the whole room is before deciding if I should get another one. 

I've heard different things saying whether or not Im gonna need a seperate amplifier. Is there a test I can run to show whether or not one will be needed?


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## Josuah (Apr 26, 2006)

Separate amp? The PB12+/2 has an amp built-in.


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## Sonnie (Apr 11, 2006)

Yeah... lol... where ever you heard you need a separate amp for that sub... you should stay far far away from... cause they stupid or ignorant or both.

What? :yikes: ... you paid how much? You didn't get the 25% discount... did you not give them the coupon code? What were you thinking? You could have saved 300 bucks man! :rolleyesno: Now it's too late. It was only good through 12 midnight 5/31/06. Oh well... live and learn I suppose. :dontknow:


Well congrats on the sub... you will be excited... and one might be enough. Two would look prettier. :R

Hey no fair... you got the new drivers in yours... :rant:


*Spoiler* 



Noooooo.... there is really no coupon code and there is really no 25% discount... you could not have saved 300 bucks. I'm just yankin' ya chain... :rofl:


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## Tommy (Apr 20, 2006)

:devil:


Sonnie said:


> Yeah... lol... where ever you heard you need a separate amp for that sub... you should stay far far away from... cause they stupid or ignorant or both.
> 
> What? :yikes: ... you paid how much? You didn't get the 25% discount... did you not give them the coupon code? What were you thinking? You could have saved 300 bucks man! :rolleyesno: Now it's too late. It was only good through 12 midnight 5/31/06. Oh well... live and learn I suppose. :dontknow:
> 
> ...



Hey sorry there was some miscommunication on my part. When suggested I get a seperate amp that was when I was trying to find a sub but didnt actually select or get this specific one yet. 

But I did want to know if there was some specific gauge/test or stat that shows if your running it on enough?

Oh and ya did have me cursing here about the 25% discount, I'll get ya back for that one... :rant: 

Let the prank wars begin... :devil:


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## Josuah (Apr 26, 2006)

You can tell if you're overdriving the sub if you increase the volume on your pre-pro or processor (the gain on the back of the sub doesn't matter) and it stops increasing the SPL coming out of the sub, or the sub starts clacking (bottoming out).

If that SPL or volume setting at which this happens is not loud enough for peaks in a movie (+30dB over dialogue) then you could use a second subwoofer, which will either give you +3dB or +6dB max SPL (I don't recall the correct number) if it is an identical subwoofer.


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