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Discussion Starter · #1 ·
Hi there

I'm thinking of building a sealed sub - and I want to get your oppinion - for a sealed sub (I have plenty of roomgain in my 1950 cubic feet room) should I get the LMS 5400 18" or B&C 21SW152-4 21" - (5400 is 925$ and 21SW152 is only 669$)? The 18" would probably be in a 3 cubic feet cab and the 21" in a 5,75 cubic feet
Is there actually a difference in sound quality between such drivers? or is it just about making a good cabinet, a powerfull amp and eq?

I've attached graph from Winisd - regarding spl-output - at both subs at 1000 watts - I can give the lms55400 2000 watts (+3 db) using a more expensive amp - but if I do that to the B&C-driver I exceed the xmax at 28,5hz....:dontknow:

Any thoughts?
 

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Discussion Starter · #2 ·
Here is the winisd SPL output graph - yellow is LMS 5400 18" - 3 cubic feet (internal) - 1000 watts, red is B&C 21" - 5,75 cubic feet (internal) - 1000 watts (BTW - I can't see how I can make the 21" cabinet much smaller)
 

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I see little to no benefit of the 21" sub based on those graphs. You're in a pretty small room! Sealed will be easier to tweak to a flat response in a small room. For the same price or less you could go with a smaller sub and some nice EQ. Get flat response to 20Hz, or lower, in room as a priority. Why not?
 

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Discussion Starter · #6 ·
It might be a stupid question, but is xmax what I should look out for - more than the drivers stated power handling - cause I looked at the lms5400 18 inch - and it states 2000 rms or 8000 peak... and if I put one in a sealed 2,4 cubic feet cab and connect it to (of the upcomming) Behringer Inuke DSP at 6000 watts - this is how it appears compared to the above mentioned designs.
 

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IMO - The LMS Ultra is much better of a design for a small-ish room, and even a large one.

The xmax is significantly better, And that helps way down low. Both are pretty close in output in sealed boxes on the same amount of power, but the LMS uses a box thats about 40% smaller. Apples to apples, you're getting more for less space, and only about 1-2 db less output total. The big difference is that you're going from average levels of distortion to very low distortion with the LMS.

You can also cheat when using a driver like the LMS, Eq the low end, I'tll take away a small amount of head room, but you've got plenty left over with the 1000w model. Use some of that massive xmax to your advantage. I don't think that even with EQ you would hit xmax at 1000w. This gives you the best output, in the smallest package. As long as you've got the amps to drive it.
 

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^ +1. Add some EQ and you should get great results with that shallow sealed roll-off. Not to mention the smaller footprint box will probably help in a moderately small room.

The rule of thumb is to NOT make something that exceeds Xmax by design. There are various ways that manufacturers calculate Xmax, one way I think is when 10% distortion is present. Another way I think is when the voicecoil is so far out of the magnetic gap. The big mystery and danger about exceeding Xmax is when the driver will bottom out, Xlim being the excursion limit of the suspension. Few manufacturers publish an Xlim number, and to my experience some drivers bottom out not far after Xmax whereas others (e.g. car audio subs with weak motors and way overbuilt limits of travel) can go far beyond before they start slapping. Undoubtedely if you powered the sub as your 6000W graph shows, it'd destroy the driver and probably sound terrible long before you ever gave it that much power.
 

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Xlim on the LMS Ultra is about 44mm one way, (maybe slightly higher than this)
Xlim on the 21" is about 30mm one way. (60mm peak to peak before damage)

The LMS wins for safety. And with the aluminum cone, just looks too pretty.
 

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Xlim on the LMS Ultra is about 44mm one way, (maybe slightly higher than this)
LOL! Nevermind then, looks like the LMS would chug right along at 6000W in a tiny sealed box. Maybe higher distortion but according to that plot up there, it wouldn't exceed Xlim. What a monster...

I still don't recommend overpowering it :)
 

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I think the B&C is a good driver, but I never came up with a HT design that made it practical. Either because of the huge cabinet or the poorer LF response.

The LMS is known for consistent performance.
 

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LOL! Nevermind then, looks like the LMS would chug right along at 6000W in a tiny sealed box. Maybe higher distortion but according to that plot up there, it wouldn't exceed Xlim. What a monster...

I still don't recommend overpowering it :)
This is exactly what the sub was designed for, Its a displacement leader in any box. Large boxes help max output, Small boxes eat headroom, but when they can take 6000w, they make up for headroom. lol, You just need an amp that can drive that beast. and don't melt the voice-coils.
 

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The big difference is that you're going from average levels of distortion to very low distortion with the LMS.

Data-bass has done measurements of both 1x LMS 5400 and 2x B&C 21SW152 woofers in a closed box, however I cannot post a direct link to the site. Google.

In ultimate sound quality application, I would go for multiple low inductance, low THD woofers and minimize the cone excursion (=minimizing THD, IMD and Doppler distortion) in all listening levels with huge cone area.
 

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Discussion Starter · #16 ·
This is exactly what the sub was designed for, Its a displacement leader in any box. Large boxes help max output, Small boxes eat headroom, but when they can take 6000w, they make up for headroom. lol, You just need an amp that can drive that beast. and don't melt the voice-coils.
LOL! Nevermind then, looks like the LMS would chug right along at 6000W in a tiny sealed box. Maybe higher distortion but according to that plot up there, it wouldn't exceed Xlim. What a monster...

I still don't recommend overpowering it :)
Thanks for all the fantastic input -
Fear of overpowering and melting voicecoils doesn't sound that good - so when are you overpowering - it's specs suggest max 2000 rms and 8000 peak - so is 2000 or 8000 what I should look for, or is it not exceeding xmas - and when can/does a voicecoil melt?

In regards to THD, is there any way to simulate this? - I'm using Winisd
 

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Specs say max 2000W rms, so don't give it more than 2000W rms! haha. Can you post an excursion graph in the box you want and 2000W? I've always thought that peak power ratings were kind of silly.

Stuff like THD and IMD need to be measured from the actual speaker as far as I know. You might be able to find some tests out there on the interweb.
 

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Discussion Starter · #18 ·
Here's the lms 5400 in two different cabinet sizes - one is 3 cubic feet internally and the other is 5.75, but I figured the driver would limit it about .5 cubic feet. So the yellow lines are the 2,5 cubic feet cab, and the red is the 5,25 cubic feet. I've added 3 amp sizes at 2,5 - 1000, 2000 and 3000 watts, but only 1000 & 2000 watts at 5,25 because of excesive cone excursion.
 

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Discussion Starter · #19 ·
The two cabinet sizes are derived from two cabinet kits I've seen at parts express - the black 4 cubic feet at 3 cubic feet and 200$ and the bare baltic birk at 5,75 cubic feet at 130$. - It has to go in the livingroom and I have teen thumbs - so I need help...

I've figured that both cabinets should be ok (the small black should also fit the driver) if there reinforced with additional bracing and an extra layer on the front plate.
 

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Go for the small one. Buy some fiber fill and use it. The cabinet will be stiffer and its less work to finish it off.
 
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