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Old 08-28-2013, 11:50 AM
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Originally Posted by LTD02 View Post

"Near field for infrasound content makes a huge difference!"

? at 10hz the wavelength is 113 feet long, so you are in the nearfield from about 56 feet away (or is it 28?)! :-)

Lol! Yeah. Although I agree with Popa that nearfield does indeed make a large difference. Especially in the tactile feeling department. However, yes, I'm not so sure the <25hz stuff is really improved being up close. Unless of course if you have wood floors or using a riser.

I've actually taken some serious consideration to getting all my seats off my concrete carpeted floor and making a riser and having my nearfield subs on that. Maybe later. Lol.

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Old 08-28-2013, 01:09 PM
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Quote:
Originally Posted by LTD02 View Post

"Near field for infrasound content makes a huge difference!"

? at 10hz the wavelength is 113 feet long, so you are in the nearfield from about 56 feet away (or is it 28?)! :-)

My nearfield is 21".

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Old 08-28-2013, 01:52 PM
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Quote:
Originally Posted by Aaron Smith View Post

I totally agree 2.97 liters Vd is not an accurate assessment of the HO, but that is what the factory numbers calculate out to. wink.gif

Despite Josh's test, Bosso (stubbornly?) likes to keep referencing the factory numbers:

Or even worse -- at 22.5 liters Vd / 8 drivers, it seems he may be using the lower 1090 cm2 Sd # published on Data-Bass along with the 12.75mm one-way xmax. smile.gif

I'd sure like to see the data from Josh'd "test" of the dayton driver that confirms a different Xmax number. confused.gif

I see high 88dB with 16% THD (which exceeds Xmax as most define it) at 10 Hz in the compression test. The burst test shows 87dB with 20% THD @ 10 Hz. That seems in line with the PE stated Xmax figure to me, unless you see something I'm missing.

Xmax is Maximum Linear Excursion

We have 3 well known methods to determine this parameter:

1) VC length minus gap height divided by 2

2) 10% THD

3) When Bl drops to 70%

As far as I read from Josh, he didn't cite any of the 3. He said:
Quote:
The driver does not have a huge amount of displacement but it is certainly has more powerful low bass output than the geometric 12.75mm xmax rating might suggest. An effective useful excursion rating would likely be more like 18-20mm.

The online excursion calculator uses 1130 CM^2 for a single 18" driver (PE lists Sd as 1164 CM^2) and calculates 91.45dB for 12.75 Xmax.

If I missed Josh's Xmax test, please LMK where to find it?
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Old 08-28-2013, 01:58 PM
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Quote:
Originally Posted by Scott Simonian View Post


I've actually taken some serious consideration to getting all my seats off my concrete carpeted floor and making a riser and having my nearfield subs on that. Maybe later. Lol.

Do it. You won't regret it. I'd rather have the actual pressure wave rippling the floor than a tactile transducer vibrating the floor. cool.gif

I've set up basement HTs where the ULF was house curve room gained due to the reduction in transmission losses vs my HT, but when the floor and riser moves, it's far more realistic an experience, IMO.
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Old 08-28-2013, 02:14 PM
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Quote:
Originally Posted by bossobass View Post

Do it. You won't regret it. I'd rather have the actual pressure wave rippling the floor than a tactile transducer vibrating the floor. cool.gif

I've set up basement HTs where the ULF was house curve room gained due to the reduction in transmission losses vs my HT, but when the floor and riser moves, it's far more realistic an experience, IMO.

This.

It is a wonderful thing to feel the floor moving under your feet, and the couch beneath your seat. I love that I have a system that can create a realistic earthquake.

 


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Old 08-28-2013, 04:27 PM
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I get a better tactile feel (and it's obvious) in my second row that I recently built and that's WITHOUT having any subs on it. Just getting the couch off the ground on the riser made a difference. If I had a sub on that thing it would be crazy!! Someday I need to build a 2 level riser, a lower level for the front row, and have them extend the full width of the room. Then I could fit some subs on the riser and shake away to my hearts content.

I'm not sure how high the first row part of the riser would have to be, my current 2nd row riser is 10 inches and like I said that is plenty to get more shake even with no subs on it.
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Old 08-28-2013, 06:24 PM
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Quote:
Originally Posted by bossobass View Post

I'd sure like to see the data from Josh'd "test" of the dayton driver that confirms a different Xmax number. confused.gif

the long term sweeps show about where it starts to run out of gas and begin to compress.

somewhere between the green and the gold is the "useful" excursion. not sure exactly what distortion figure that is (edit: I found it, ~12%), but I think that is what josh is referring to.

it does 18mm excursion with less than 1 db of compression and that is considering power compression as well, so useable is at least 18mm. just eyeballing the data, i'd call it right about where josh called it at about 20mm or so, but xlim is up around 30 so there is a little extra running room. tough to know though how much of that is power compression because the chart just under it on data-bass.com suggests that most of the compression is actually power related.

http://www.data-bass.com/data?page=system&id=89&mset=96



also, the 110db distortion measurement shows about 12% distortion or so for 18mm excursion at 20hz.

http://www.data-bass.com/data?page=system&id=89&mset=96

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Old 08-28-2013, 07:24 PM
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Quote:
Originally Posted by LTD02 View Post

the long term sweeps show about where it starts to run out of gas and begin to compress.

somewhere between the green and the gold is the "useful" excursion. not sure exactly what distortion figure that is (edit: I found it, ~12%), but I think that is what josh is referring to.

it does 18mm excursion with less than 1 db of compression and that is considering power compression as well, so useable is at least 18mm. just eyeballing the data, i'd call it right about where josh called it at about 20mm or so, but xlim is up around 30 so there is a little extra running room. tough to know though how much of that is power compression because the chart just under it on data-bass.com suggests that most of the compression is actually power related.

http://www.data-bass.com/data?page=system&id=89&mset=96



also, the 110db distortion measurement shows about 12% distortion or so for 18mm excursion at 20hz.

http://www.data-bass.com/data?page=system&id=89&mset=96

How do you arrive at 18mm for 100dB (more like 98dB with 10% limit) @ 20 Hz? And, if 10% is the limit, how does 18 turn into 20mm with 12%? I'm after Xmax, not a subjective interpretation of "usable excursion".
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Old 08-28-2013, 08:55 PM
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Quote:
Originally Posted by bossobass View Post

How do you arrive at 18mm for 100dB (more like 98dB with 10% limit) @ 20 Hz? And, if 10% is the limit, how does 18 turn into 20mm with 12%? I'm after Xmax, not a subjective interpretation of "usable excursion".

xmax itself is subjective in that there is no agreed upon definition.

the equation for displacement limited spl in 2pi space is empirical:

spl = 94.3 + 20*LOG(excursion/500) + 40*LOG(frequency) + 40*LOG(diameter/1000) + 6 dB

where,
excursion is in mm
frequency is in hz
diameter is in mm (effective piston diameter of driver)

this is for 1 meter 2 pi space, so add 6db to josh's measurements to back out excursion.

rearranging gives:

excursion = 500 * 10^ ((spl - 100.3 - 40*LOG(frequency) - 40*LOG(diameter/1000)) /20)

be careful with the parentheses.

for the Dayton ho, I'm using diameter of 373mm.

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Old 08-28-2013, 09:19 PM
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also, I mentioned this before, but the distortion in the sweep may be partly power related. it is obviously starting to compress based on power from the series below the frequency response sweeps that shows the compression. since there is little compression around the impedance peak, we know that most of that is power related compression. so the excursion related distortion is probably a little better than what is shown in the charts. in other words, if the same sub were tested in a very large sealed enclosure, the distortion would likely be lower for the same amount of excursion.

I suppose that you could coordinate with josh to test one of your drivers in a small sealed enclosure in order to see how distortion scales with drive level. in a small sealed enclosure with a ton of power, you may be way over 10% distortion long before the official xmax is reached for the drivers that you employ.

then again, 10% distortion is only partially meaningful in some sense because it is unclear if that level of distortion is even audible in a controlled setting with experienced listeners in the sub bass. as such, we end up with new metrics such as "usable excursion" which represents some mixture of the point where the driver starts to get noisy mechanically or the distortion really starts to explode.

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Old 08-29-2013, 05:16 AM
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when somebody uses more than 4 subs with different drivers sizes (ie 4 x 12" + 2 x 18") ,
do you also need bandpass/HPF filters or all the subs output the same frequencies?
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Old 08-29-2013, 08:43 AM
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Quote:
Originally Posted by Tony_Montana View Post

when somebody uses more than 4 subs with different drivers sizes (ie 4 x 12" + 2 x 18") ,
do you also need bandpass/HPF filters or all the subs output the same frequencies?

No. Not unless you specifically want to HPF for another reason. Just because one sub will play lower doesn't mean you should nuter it because your other little guys can keep up.

Lots of variables to consider when mixing multiple subs...but size alone is not one of them.
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Old 08-29-2013, 08:59 AM
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Originally Posted by popalock View Post

No. Not unless you specifically want to HPF for another reason. Just because one sub will play lower doesn't mean you should nuter it because your other little guys can keep up.

Lots of variables to consider when mixing multiple subs...but size alone is not one of them.

The answer can also be yes. If one sub can't play as low as the other subs, then filtering the low response out on that sub and letting the others go deeper would be a good thing. Each situation is different.

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Old 08-29-2013, 10:02 AM
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Quote:
Originally Posted by LTD02 View Post

also, I mentioned this before, but the distortion in the sweep may be partly power related. it is obviously starting to compress based on power from the series below the frequency response sweeps that shows the compression. since there is little compression around the impedance peak, we know that most of that is power related compression. so the excursion related distortion is probably a little better than what is shown in the charts. in other words, if the same sub were tested in a very large sealed enclosure, the distortion would likely be lower for the same amount of excursion.

I suppose that you could coordinate with josh to test one of your drivers in a small sealed enclosure in order to see how distortion scales with drive level. in a small sealed enclosure with a ton of power, you may be way over 10% distortion long before the official xmax is reached for the drivers that you employ.

then again, 10% distortion is only partially meaningful in some sense because it is unclear if that level of distortion is even audible in a controlled setting with experienced listeners in the sub bass. as such, we end up with new metrics such as "usable excursion" which represents some mixture of the point where the driver starts to get noisy mechanically or the distortion really starts to explode.

Yeah, you're getting into gross misinterpretation of the data and philosophizing about sealed subwoofer design. This is where you cross the line in most of our discussions on the subject.

Xmax is defined as the point where Bl drops to 70% and the 10% THD limit is reached. I agree with that average and don't really care what anyone's neo-theory might be. Some have said that VC-gap divided by 2 isn't a good metric. I say prove it. It's a lot closer to reality than stretching 13 mm to 20 mm.

Have a look at the FR of the Dayton in the small box. Does it look like it will benefit from a lower Q (larger box) in actual use? You can put it in an IB for efficiencies sake. The curve will sound like crap and the Xmax won't change.

A K10 on a 220V/50A line is so far beyond any Dayton driver-based DIY system builder's reach I don't know what to tell you. That amp, IMHO, and I've said so before, skews the results of all of the DIY systems tested. In any case, if you see power compression in that test, be prepared to drastically lower the actual results for any end user. There's no way you see power compression. When you pump 2KW long term into a 900W rated driver, It's thermal up top and thermal/Xmax limit on the bottom. And, the amp was certainly not out of power at that point.

If you define Xmax as "some point where the driver starts to get noisy mechanically or the distortion really starts to explode", then the Xmax for the drivers I compared the Dayton to will scale accordingly.

Your formula is foreign to me. I don't have the time or desire to wade into it. It might be simpler to just compare the LMS-U results and draw a conclusion. You might conclude that the Dayton has 55% the Xmax of the LMS-U or some such baloney, and that's fine. Delusion has always ruled in these forums, generally speaking. What I'm debating here is the claim that the Dayton driver has 55% more Xmax than the designer/manufacturer claims it has based on some test Josh never performed.
You're just throwing out insane postulations instead of pointing me to the actual Xmax tests Josh performed.
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Old 08-29-2013, 10:42 AM
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Quote:
Originally Posted by AV Science Sales 5 View Post

The answer can also be yes. If one sub can't play as low as the other subs, then filtering the low response out on that sub and letting the others go deeper would be a good thing. Each situation is different.

+1

I totally agree. Didn't look at it from that perspective before i responded.

Good point.
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Old 08-29-2013, 11:06 AM
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Originally Posted by popalock View Post

No. Not unless you specifically want to HPF for another reason. Just because one sub will play lower doesn't mean you should nuter it because your other little guys can keep up.

Lots of variables to consider when mixing multiple subs...but size alone is not one of them.

Quote:
Originally Posted by AV Science Sales 5 View Post

The answer can also be yes. If one sub can't play as low as the other subs, then filtering the low response out on that sub and letting the others go deeper would be a good thing. Each situation is different.

Each situation is different, absolutely. But... lol.... if all these supposed smaller and larger subs are all sealed (and lack any dynamic limiter) then they will all extend equally as long as the electronic signal path is identical or nearly at least. The only difference should be is total output capability. The larger drivers will have more output over the smaller driver, obviously. wink.gif

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Old 08-29-2013, 01:14 PM
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I don't know much about the results, but SI has the klippel tested dayton showing 16.1 mm xmax.
http://stereointegrity.com/index.php?id=50
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Old 08-29-2013, 03:52 PM
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Quote:
Originally Posted by Tony_Montana View Post

when somebody uses more than 4 subs with different drivers sizes (ie 4 x 12" + 2 x 18") ,
do you also need bandpass/HPF filters or all the subs output the same frequencies?

This has been done in Velo's flagship DD 1812.

A half dozen years ago when it hit the streets CJ Whitehouse, AKA Slartibartfast, AVTalk's version of Ilkka, showed a phase problem between the 2 dissimilarly sized drivers at their crossover point.

Using filters of any kind in a so-called 2-way sub will alter group delay where it matters, causing more problems than it's worth.

If all the subs output the same frequencies, then you'd immediately have to question why use different sized subs.

If it's a case of just already having the 12s and wanting to keep them and add 18s, I say why not? Nothing to lose if you give it a go and see what happens.

But, it's just not a good plan to design it that way from the start.
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Old 08-29-2013, 04:00 PM
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Quote:
Originally Posted by bossobass View Post

Do it. You won't regret it. I'd rather have the actual pressure wave rippling the floor than a tactile transducer vibrating the floor. cool.gif

I've set up basement HTs where the ULF was house curve room gained due to the reduction in transmission losses vs my HT, but when the floor and riser moves, it's far more realistic an experience, IMO.

Quote:
Originally Posted by Spanglo View Post

This.

It is a wonderful thing to feel the floor moving under your feet, and the couch beneath your seat. I love that I have a system that can create a realistic earthquake.

Quote:
Originally Posted by carp View Post

I get a better tactile feel (and it's obvious) in my second row that I recently built and that's WITHOUT having any subs on it. Just getting the couch off the ground on the riser made a difference. If I had a sub on that thing it would be crazy!! Someday I need to build a 2 level riser, a lower level for the front row, and have them extend the full width of the room. Then I could fit some subs on the riser and shake away to my hearts content.

I'm not sure how high the first row part of the riser would have to be, my current 2nd row riser is 10 inches and like I said that is plenty to get more shake even with no subs on it.

Very well. That settles it then. I'll work on a riser after the uber mains and subs are installed and all dialed in. Project for 2014. biggrin.gif

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Old 08-29-2013, 04:05 PM
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Very well. That settles it then. I'll work on a riser after the uber mains and subs are installed and all dialed in. Project for 2014. biggrin.gif

It's always good to have a future project to look forward too, where would we be if we were perfectly happy with our setup? No, no, that simply won't do! biggrin.gif

That said I did get some good advice from Luke Kamp; he said we will have a life time enjoying this hobby so we don't need to be in a rush all the time to get the room perfect immediately.
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Old 08-29-2013, 04:24 PM
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It's always good to have a future project to look forward too, where would we be if we were perfectly happy with our setup? No, no, that simply won't do! biggrin.gif

That said I did get some good advice from Luke Kamp; he said we will have a life time enjoying this hobby so we don't need to be in a rush all the time to get the room perfect immediately.

That's very true! No rush.

I'm really trying to get mine all 'finalized' and all, if possible. I haven't been happy with my HT for a while and I hope to have that fixed. tongue.gif For one thing, the room is a mess. I'd like to pretty it up a bit.

The two big next things I need is a new projector. It's time. I've also thought about better seating. I'll have to plan that out with the addition of this riser. Sounds like a good plan.

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Old 08-29-2013, 08:35 PM
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Quote:
Originally Posted by Scott Simonian View Post


Each situation is different, absolutely. But... lol.... if all these supposed smaller and larger subs are all sealed (and lack any dynamic limiter) then they will all extend equally as long as the electronic signal path is identical or nearly at least. The only difference should be is total output capability. The larger drivers will have more output over the smaller driver, obviously. wink.gif

What if you are providing boost down low? If the 18's have the required xmas and the 12's do not have the needed xmas, then you can have over excursion. That is the situation that I was thinking about.

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Old 08-29-2013, 08:38 PM
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What if you are providing boost down low? If the 18's have the required xmas and the 12's do not have the needed xmas, then you can have over excursion. That is the situation that I was thinking about.

You are absolutely right about this. That's why I said the smaller drivers, in this case a 12", will have less overall output capability compared to their larger 18" bass brothers. smile.gif

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Old 08-29-2013, 08:40 PM
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Quote:
Originally Posted by Scott Simonian View Post

That's very true! No rush.

I'm really trying to get mine all 'finalized' and all, if possible. I haven't been happy with my HT for a while and I hope to have that fixed. tongue.gif For one thing, the room is a mess. I'd like to pretty it up a bit.

The two big next things I need is a new projector. It's time. I've also thought about better seating. I'll have to plan that out with the addition of this riser. Sounds like a good plan.

We have good b-stock deals that come up from time to time. Let me know your budget and what you are looking for and I will let you know when something that might interest you comes available.

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Old 08-29-2013, 08:46 PM
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You are absolutely right about this. That's why I said the smaller drivers, in this case a 12", will have less overall output capability compared to their larger 18" bass brothers. smile.gif

I guess I just was not very clear from the beginning. Because this was what I was getting at with my first post regarding filtering the smaller subs, so they do not go into over excursion. This only applies if you are boosting the low end on the subs.

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Old 08-29-2013, 08:56 PM
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One can boost their sub 100dB down low if they want. As long as the amplifier isn't capable of outputting enough voltage to destroy the driver in the first place (and preferably good use of an acoustic highpass), the user will not make the smaller sub go into overexcursion using any amounts of low end boost.

My Dual 18" LLT subs 120dB down to 10hz

 

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Old 08-29-2013, 09:03 PM
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What if you are providing boost down low? If the 18's have the required xmas and the 12's do not have the needed xmas, then you can have over excursion. That is the situation that I was thinking about.

I swear I've seen you mention xmas in the past...lol
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Old 08-29-2013, 10:02 PM
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"Yeah, you're getting into gross misinterpretation of the data and philosophizing about sealed subwoofer design."

nah. spl is just physics and it is fairly well understood.

"Xmax is defined as the point where Bl drops to 70% and the 10% THD limit is reached."

they are two different concepts, which is why it is subjective. those two things don't occur at the same excursion point in many drivers.

some manufacturers add back 1/3 of the gap, others add back 1/4 as well, so there are at least 4 different accepted definitions of xmax.

different designs such as xbl^2, underhung, differential drive, split coil, etc. all behave differently which is why, in part, there is not a simple standard.

"Your formula is foreign to me. I don't have the time or desire to wade into it."

understandable. if you choose to dig into it, the source is linkwitz.

"You're just throwing out insane postulations..."

ok.

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Old 08-29-2013, 10:09 PM
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here is the lms for comparison...so using the same method, this would seem to put the lms xmax somewhere around 40mm or so.


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Old 08-30-2013, 07:13 AM
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Quote:
Originally Posted by Scott Simonian View Post

One can boost their sub 100dB down low if they want. As long as the amplifier isn't capable of outputting enough voltage to destroy the driver in the first place (and preferably good use of an acoustic highpass), the user will not make the smaller sub go into overexcursion using any amounts of low end boost.

Adding a high pass filter was the original question and why I said some situations could require you to high pass a smaller sub. See Tony's question in post 101.

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