AVS › AVS Forum › Audio › DIY Speakers and Subs › Help ordering amps for 8 21's
New Posts  All Forums:Forum Nav:

Help ordering amps for 8 21's

post #1 of 54
4/23/12 at 11:58pm
Thread Starter 
Ok, I'm going to go with the LG Clones for my 8 mach 5 21's but would like to max out the subs when playing music and not blow them when watching movies with 2-3hz frequencies.

My first thought was to buy two LG FP14000 ran at 8 ohms stereo (4 subs/amp) for 9400 watts with 55 cuft enclosures. This would put xmax at 2.5hz (what I really want!). I want to be able to watch movies without ever being worried about reaching xmax at full tilt.

But here is where I'm just as confused as many others when it comes to gains on amps. What if I were to buy 4 FP14000s and run them 8 ohms bridged (2 subs/amp) for a claimed 35200 watts in the same 55 cuft enclosures. This would put xmax at 30 hz. Is there any way to really turn down the gain way I could still watch movies at full tilt or would I really need to do all that with EQ like the mini? I didnt know if there was a way to measure the watts coming out at max volume of the system and make it match the lower amount of watts (9400) way all I'd have to do is mark the gain positions on each amp when switching between music and watching movies?

Thanks if anyone can help me here as I'd really like the extra 6dbs from 30hz on up for music!!!
Reply
Reply

AVS Top Picks

post #2 of 54
4/24/12 at 12:09am
If you size your enclosures correctly, these FTW-21 will take a full 4400w each without Xmax concerns. If the listed specs are correct... you'd be good at ~4cuft for each driver. This is the best way to maximize power input and SPL output all while allowing you to never have to worry about overexcursion or needing to use limiters.

Otherwise you will have to use limiters, highpass filters or less power per driver. My approach is the maximum route with no real compromise other than needing to buy enough amps to supply 4400w times eight. You'd get maximum output, 2hz extension and no worries of overexcursion....ever.
Reply
Reply
post #3 of 54
4/24/12 at 1:05am
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

If you size your enclosures correctly, these FTW-21 will take a full 4400w each without Xmax concerns. If the listed specs are correct... you'd be good at ~4cuft for each driver. This is the best way to maximize power input and SPL output all while allowing you to never have to worry about overexcursion or needing to use limiters.

Otherwise you will have to use limiters, highpass filters or less power per driver. My approach is the maximum route with no real compromise other than needing to buy enough amps to supply 4400w times eight. You'd get maximum output, 2hz extension and no worries of overexcursion....ever.


Yeah but what about thermal limits? And on my sims it shows xmax at 5.2hz with that much power in 4cuft.

And if I did that then I deff would be wasting my time building horns for 30hz on up!!!! That increased the max spl to 146.7. That just gave me an idea! If I did that then I could still build my horns but have them ported through the garage with the mouths facing the pool. I could have mega bass outside lol.
Reply
Reply
post #4 of 54
4/24/12 at 1:37am
If you want 2hz and maximum output, there are no alternatives to what I proposed. You could limit bandwidth and not have 2hz extension if you want more SPL up high and would prefer to build larger, more complicated enclosures.

Thermal limits would be a non-issue with HT content. Music? Eh... do you plan on running all eight 21's at full tilt all the time? How large a space are you trying to energize? My models show output in excess of 130dB ~20hz before room and boundary gains and more than likely hitting the 140dB range in the upper bass.
Reply
Reply
post #5 of 54
4/24/12 at 2:09am
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

If you want 2hz and maximum output, there are no alternatives to what I proposed. You could limit bandwidth and not have 2hz extension if you want more SPL up high and would prefer to build larger, more complicated enclosures.

Thermal limits would be a non-issue with HT content. Music? Eh... do you plan on running all eight 21's at full tilt all the time? How large a space are you trying to energize? My models show output in excess of 130dB ~20hz before room and boundary gains and more than likely hitting the 140dB range in the upper bass.

I just dont see where you are coming up with 2hz being under xmax. My numbers could be wrong in winisd but put them straight in from mach 5 website. Its showing 5hz when I model them.

The room is right at 5000cuft and music will be played about 5% of the time. When music is played it will be at full tilt. Maybe like 2 songs at a time or so I would guess.
Reply
Reply
post #6 of 54
4/24/12 at 5:18am
Has anyone verified the low frequency corner and single digit stability of these LabClones?
Reply
Reply
post #7 of 54
4/24/12 at 7:13am
Quote:
Originally Posted by WiSounds View Post

Has anyone verified the low frequency corner and single digit stability of these LabClones?

Early on in not's clone thread he posted some graphs showing the difference between his old amps (can't remember which ones. Think they were 5050s but I'm on my iPhone so finding that will be a pain) and his clones. Though he uses filters using a minidsp to keep excursion from going crazy below (again if I recall correctly) 5hz.

I am assuming by single digit stability you're referring to frequency and not impedance because it's been stated a few times by sanway that they aren't stable with a load of less than 2.7 ohms

Matt
Reply
Reply
post #8 of 54
4/24/12 at 9:13am
Quote:
Originally Posted by audiovideoholic View Post

I just dont see where you are coming up with 2hz being under xmax. My numbers could be wrong in winisd but put them straight in from mach 5 website. Its showing 5hz when I model them.

The room is right at 5000cuft and music will be played about 5% of the time. When music is played it will be at full tilt. Maybe like 2 songs at a time or so I would guess.

WinISD does not account for the signal chain of rolloffs you're going to have in reality.

Nothing is perfectly flat to 2hz.

Quote:
Originally Posted by WiSounds View Post

Has anyone verified the low frequency corner and single digit stability of these LabClones?

Bosso's measurement's have shown that the Lab clones only start to roll off below 5hz.
Reply
Reply
post #9 of 54
4/24/12 at 9:36am
Quote:
Originally Posted by Scott Simonian View Post

WinISD does not account for the signal chain of rolloffs you're going to have in reality.

Nothing is perfectly flat to 2hz.



Bosso's measurement's have shown that the Lab clones only start to roll off below 5hz.

That is why I went with clones, both Notnyt and Bosso have verified their power down low and these seems like the only option to use without spending more on amps than subs. I can tell you I have used the EP-2500/4000, dayton, samson, ashly, Ada, crown, you name it and these clones are killers! My ada was great down low but they were made for speakers not high powered subs.
Reply
Reply
post #10 of 54
4/24/12 at 9:53am
I spoke with Ashly engineering and the KLR series corners at 3hz. I wonder if Bosso would measure one for verification if I sent him one.
Reply
Reply
post #11 of 54
4/24/12 at 9:54am
Quote:
Originally Posted by WiSounds View Post

I spoke with Ashly engineering and the KLR series corners at 3hz. I wonder if Bosso would measure one for verification if I sent him one.

Wicked.
Reply
Reply
post #12 of 54
4/24/12 at 10:08am
Thread Starter 
[quote=Scott Simonian;21945208]WinISD does not account for the signal chain of rolloffs you're going to have in reality.

Nothing is perfectly flat to 2hz.

So 4 cuft enclosures with 4400 watts will be safe at 2hz even though winisd says they will reach xmax? I understand that these amps to roll off but its not my much at all.

If I went with 4 amps that would defeat the purpose of having the two mal 21 FLHs so what would be the optimal enclosure for them to match the mach 5s?

I have all the mdf sitting here just waiting for me to make a decision but its hard! Sorry guys.

QUOTE]
Reply
Reply
post #13 of 54
4/24/12 at 10:13am
Is your program saying they will just barely hitting Xmax with 4,400w? Or are you modelling for Xmech?

First of all, you're not going to get more than 4,400w out of these and chances are you may never see that full power anyway but I won't say that's definite. Second, if you're modelling for Xmax then you still have safe throw before any kind of damage. Xmax is typically rated as 70% BL and at that point there is a drop in motor power and this can be quite a bit before any damage will come to be. Xmax for the FTW-21 is ~34mm. I'll be you $100 that the Xmech is over 40mm and maybe in the mid 40's. Model that up and see how much more power it takes to get there at 2hz.

None of this factors that your AVR, amp and whatever else you have in between your Blu-ray player and the driver itself will be limiting power down below 5-10hz.

You'll be fine.
Reply
Reply
post #14 of 54
4/24/12 at 10:24am
Quote:
Originally Posted by Scott Simonian View Post

If you size your enclosures correctly, these FTW-21 will take a full 4400w each without Xmax concerns.

IMO "sizing enclosures correctly" = turning power into heat.

With 8 21's, it's possible that if you limit amp power to what the subs can handle at the very low end that you'll still have eardrum-shredding SPL capability in the audible freq range.

av, what SPL do you expect at 2 Hz?

Even with 8 21's, it may not be worth the trouble.

How many DVD's even have anything there?

Just going from 2 to 5 Hz reduces Vd requirement by 6X for a given SPL.
Reply
Reply
post #15 of 54
4/24/12 at 10:25am
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

Is your program saying they will just barely hitting Xmax with 4,400w? Or are you modelling for Xmech?

First of all, you're not going to get more than 4,400w out of these and chances are you may never see that full power anyway but I won't say that's definite. Second, if you're modelling for Xmax then you still have safe throw before any kind of damage. Xmax is typically rated as 70% BL and at that point there is a drop in motor power and this can be quite a bit before any damage will come to be. Xmax for the FTW-21 is ~34mm. I'll be you $100 that the Xmech is over 40mm and maybe in the mid 40's. Model that up and see how much more power it takes to get there at 2hz.

None of this factors that your AVR, amp and whatever else you have in between your Blu-ray player and the driver itself will be limiting power down below 5-10hz.

You'll be fine.

Its showing excursion at 2hz it way way over 60mm. 3hz is at 45mm.

I'm just totally changing what I had originally planned so dont want to screw up here! Was going with large enclosures and using horns for upper FR but if can really use small and be safe from thermal and overexcursion then that would be best since I've always prefered small enclosures.

Would you add two extra mal x 21s into the mix or just save them for another project?

Thanks for helping here as I am needing to make saw dust tonight!
Reply
Reply
post #16 of 54
4/24/12 at 10:27am
Quote:
Originally Posted by noah katz View Post

IMO "sizing enclosures correctly" = turning power into heat.

av, what SPL do you expect at 2 Hz?

Even with 8 21's, it may not be worth the trouble.

How many DVD's even have anything there?

Just going from 2 to 5 Hz reduces Vd requirement by 6X for a given SPL.

Not necessarily. He doesn't have to input that much power but he wants to.

The method of "sizing correctly" just removes the requirement for using a highpass filter or any other limiters.

Quote:
Originally Posted by audiovideoholic View Post

Its showing excursion at 2hz it way way over 60mm. 3hz is at 45mm.

I'm just totally changing what I had originally planned so dont want to screw up here! Was going with large enclosures and using horns for upper FR but if can really use small and be safe from thermal and overexcursion then that would be best since I've always prefered small enclosures.

Would you add two extra mal x 21s into the mix or just save them for another project?

Thanks for helping here as I am needing to make saw dust tonight!

Again, WinISD has no way of seeing that you will have some electronic rolloff in the signal chain to help protect you from going into overexcursion ~2hz. If it's something you're really concerned about, remove .5cuft of net space inside the enclosure for more protection.

The overall design is up to you but if you want 2hz and maximum output, this is how you do it. Add in more subs for effect. Wow... 10 21's. I am envy.
Reply
Reply
post #17 of 54
4/24/12 at 10:28am
Thread Starter 
Quote:
Originally Posted by noah katz View Post

IMO "sizing enclosures correctly" = turning power into heat.

av, what SPL do you expect at 2 Hz?

Even with 8 21's, it may not be worth the trouble.

How many DVD's even have anything there?

Just going from 2 to 5 Hz reduces Vd requirement by 6X for a given SPL.

Yeah Noah heat is what I'm worried about most!

And at 5hz there will be enough spl to REALLY feel it! 108db without room gain.
Reply
Reply
post #18 of 54
4/24/12 at 10:29am
Quote:
Originally Posted by Scott Simonian View Post

If you size your enclosures correctly, these FTW-21 will take a full 4400w each without Xmax concerns.

IMO "sizing enclosures correctly" = turning power into heat; might as well just roll off the input drive to get the same net SPL.

av, what SPL do you expect at 2 Hz?

Even with 8 21's, it may not be worth the trouble.

How many DVD's even have anything there?

Just going from 2 to 5 Hz reduces Vd requirement by 6X for a given SPL.
Reply
Reply
post #19 of 54
4/24/12 at 10:33am
Thread Starter 
Quote:
Originally Posted by noah katz View Post

IMO "sizing enclosures correctly" = turning power into heat; might as well just roll off the input drive to get the same net SPL.

av, what SPL do you expect at 2 Hz?

Even with 8 21's, it may not be worth the trouble.

How many DVD's even have anything there?

Just going from 2 to 5 Hz reduces Vd requirement by 6X for a given SPL.

I know there arent many that do have anything at 2hz but when playing the ones that do I dont want to add filters to leave it out if enclosure size will protect me. At 2hz the spl would still be at 99db without gain.
Reply
Reply
post #20 of 54
4/24/12 at 10:33am
Quote:
Originally Posted by audiovideoholic View Post

Yeah Noah heat is what I'm worried about most!

And at 5hz there will be enough spl to REALLY feel it! 108db without room gain.

Down low in the deep bass is where you'll get the most cooling.

It's up high above 40-50hz where you'll burn out a voice coil. Not down low.

Reply
Reply
post #21 of 54
4/24/12 at 10:39am
Thread Starter 
Just to throw this out there. Model shows 15000 watts total to reach 2hz at xmax safely with 4cuft enclosures. So if had 35200 watts total would they really roll off by more than 50%?
Reply
Reply
post #22 of 54
4/24/12 at 10:42am
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

Down low in the deep bass is where you'll get the most cooling.

It's up high above 40-50hz where you'll burn out a voice coil. Not down low.


lol Yeah I am ignorant here thats why am turning to you guys!
Reply
Reply
post #23 of 54
4/24/12 at 10:50am
Lol, sorry. I wasn't trying to come off like you're ignorant or anything. Just saw a teachable moment.

It's really stuff like listening to music at crazy high levels where you'd have to worry about thermal build up and burning a coil. With eight 21's, I cannot fathom how you'd get to those kind of levels anyway. Movie content is different. It's very dynamic and the actual duty cycle is much lower than music.

Take for example that Notnyt with his eight 18's says that it becomes physically uncomfortable to sit in his room at full tilt listening to bass heavy music. You'd have the same power but even more displacement. That equals even more SPL. Again, I can't see how you could physically tolerate that for long. Thermal issues would be low on my list of things to worry about. I'd be more concerned about the house you're in or your neighbors hating you.
Reply
Reply
post #24 of 54
4/24/12 at 11:12am
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

Lol, sorry. I wasn't trying to come off like you're ignorant or anything. Just saw a teachable moment.

It's really stuff like listening to music at crazy high levels where you'd have to worry about thermal build up and burning a coil. With eight 21's, I cannot fathom how you'd get to those kind of levels anyway. Movie content is different. It's very dynamic and the actual duty cycle is much lower than music.

Take for example that Notnyt with his eight 18's says that it becomes physically uncomfortable to sit in his room at full tilt listening to bass heavy music. You'd have the same power but even more displacement. That equals even more SPL. Again, I can't see how you could physically tolerate that for long. Thermal issues would be low on my list of things to worry about. I'd be more concerned about the house you're in or your neighbors hating you.

LOL no its all good I had no idea that the upper FR of the subs would build up heat more than when its close to xmax. I just dont see how the 35200 watts could roll off to 15000 watts down under 3-4hz but if it does then thats what I shall build. I think sanway says their roll off is at 3hz if remember correctly is why I am worried about that so much. And, building 3.5cuft enclosures wouldnt be worth the hassle of trying to figure out how to build them and brace them to even worry with.
Reply
Reply
post #25 of 54
4/24/12 at 11:26am
Most consumer equipment has rolloff below 10hz and sometimes lower. Let's just pretend they are all 12dB/oct. I'm not sure what your AVR is but let's say it doesn't roll off until 5hz @ 12dB/oct. Then your amp has 5hz roll off @ 12db/oct. Now you're already doing 24db/oct rolloff from 5hz down. Then let's say you'd like to use a DCX for sub control or whatever. That device may rolloff 12db/oct @ 10hz. Now you're prolly get more than 36dB of rolloff below 5hz.

Not sure if that makes sense but each piece of equipment you have between your BD player and the driver itself will cascade with one another and add to the over rolloff of the entire system. There is no way to fix that other than to use equipment that doesn't rolloff.
Reply
Reply
post #26 of 54
4/24/12 at 2:17pm
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

Most consumer equipment has rolloff below 10hz and sometimes lower. Let's just pretend they are all 12dB/oct. I'm not sure what your AVR is but let's say it doesn't roll off until 5hz @ 12dB/oct. Then your amp has 5hz roll off @ 12db/oct. Now you're already doing 24db/oct rolloff from 5hz down. Then let's say you'd like to use a DCX for sub control or whatever. That device may rolloff 12db/oct @ 10hz. Now you're prolly get more than 36dB of rolloff below 5hz.

Not sure if that makes sense but each piece of equipment you have between your BD player and the driver itself will cascade with one another and add to the over rolloff of the entire system. There is no way to fix that other than to use equipment that doesn't rolloff.

AH! OK I gotcha. Well, I guess the plan is to build the 4 cuft enclosures. I might as well do away with the horns since putting 4400 watts to these will out perform them in the upper FRs. Tonight will get one enclosure for four subs built or atleast partially built.

Will running these at say 75-85% with music by ok for extended periods? Or will they need breaks?
Reply
Reply
post #27 of 54
4/24/12 at 2:25pm
Somehow I think it will be you that will need the breaks.

75% power will still have you in excess of 130dB throughout most the 'musical' range. Good luck!
Reply
Reply
post #28 of 54
4/24/12 at 3:17pm
Quote:
Originally Posted by audiovideoholic View Post

Model shows 15000 watts total to reach 2hz at xmax safely with 4cuft enclosures. So if had 35200 watts total would they really roll off by more than 50%?

Unless box size is an issue (you mentioned 55 cf so I assume it's not), I don't understand why you wouldn't use half the amp power and twice the box.

Saves stress on the driver too; 4 cf seems awfully small for a 21 with that displacement.

You only need to increase each dimension by 1.26X to double the volume.
Reply
Reply
post #29 of 54
4/24/12 at 3:21pm
I believe he orginally had plans to build a large horn loaded system with these 21's. Anyway, he said he wanted the most SPL possible and 2-3hz extension so cutting power in half won't allow for that. Twice the box won't give much extra over using more power. Just an extra dB or so below 15hz.

I also think that 4cuft sounds way small but I modeled it up in Unibox many times using the specs posted publically from IST and it looks fine to me.
Reply
Reply
post #30 of 54
4/24/12 at 4:06pm
Quote:
Originally Posted by Scott Simonian View Post

Anyway, he said he wanted the most SPL possible and 2-3hz extension so cutting power in half won't allow for that.

It will if it allows the same excursion.

I forget how it scales, but the point remains for whatever box volume gives the same excursion at the same freq.

I think it's linear to first order; twice the box volume gives half the air spring stiffness, and I suspect is still way stiffer than the driver siuspension.
Reply
Reply
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: DIY Speakers and Subs

AVS Top Picks

AVS › AVS Forum › Audio › DIY Speakers and Subs › Help ordering amps for 8 21's