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Replacing sub drivers with a different model?
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Old 6th February 2018, 11:13 PM   #1
Cableaddict is offline Cableaddict
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Default Replacing sub drivers with a different model?

This is a tough one, but incredibly important for me.
I realize that critical data is missing, but I'm hoping to get even just some basic opinions from you guys.

It's a lot of reading, so thanks in advance, if anyone can help even a little bit.
================================================

BACKGROUND:

I have just replaced my live-performance subs with Line 6 L3s's. These a a dual 12",front-loaded design. For several important reasons (ergonomics, electronics, etc) these are absolutely perfect for me. Unfortunately, I'm not happy about the sound when they are pushed hard.

I didn't expect them to be loud, so that's not it. In fact, I'm very happy that whomever designed them kept the porting small, and so willingly sacrificed overall output for frequency response. (They're 3 db dow at 38 Hz! ) The only other company I know that has done this (in a non-touring cabinet) is Yorkville, also with a 2 X 12" design

And the sound at medium volume is fantastic. Almost as tight and punchy as my old, sealed Bag End subs, but about twice as loud.
----------------------------

The problem is when they are pushed to just under where the limiter kicks in.
The drivers start to "fart" quite badly. (A highly technical term, which I'm sure you understand!) They are not breaking up, just mildly distorting in a very annoying way. There is also no coil rubbing when mechanically tested.

These are just really cheap speakers. They have smallish magnets, very little surround area, (they look more like guitar speakers than subs) and simple, non-reinforced baskets. They either don't have enough magnet to control them at high excursion, or the baskets themselves are flexing. - Or maybe that minimal surround makes them too stiff at high excursion?

FWIW, they are 4 ohm, 12" Celestion T5850A (AKA L172-124 )

Sadly, I can't get any info on these, from any source. Even Celestion has been no help. I did read a supposed repair tech's report, from someone who felt the same way once and took them to see if they were defective. That tech said the speakers were rated for 350w rms.
=========================================

SO HERE ARE MY QUESTIONS;

I am considering replacing these with Eminence Lab 12C drivers. These are excellent sub drivers, with lots of surround material and beefy baskets. They are still 4 ohm, and are rated at 500w rms. There's no doubt that they are far superiro drivers.

- BUT WILL THEY THEORETICALLY WORK GOOD IN MY EXISTING CABINETS, with the existing ports and electronics?

1: The first, big question is cabinet tuning. I'm assuming that the cubic volume should be OK, as a 12" is a 12", at a given frequency range. - But what about the theil-Small parameters?

Again, I can't get any specs on the Celestions, as there are not a stock retail item. Should I be concerned that the porting could be slightly off, or can I safely assume that, again, any 12" in that frequency range should be about the same?

2: Electronics: These subs have the typical protection found in most self-powered speakers. protection from amp overload, thermal peaks, and driver excursion. None of these should be a factor with replacement drivers that take MORE power. What concerns me is if there might be some other circuitry, such as phase correction or damping control.

2: Phase Correction: As a general rule, am I right to assume this would NOT be found in a subwoofer?

Damping Control: Would you expect to find this is a fairly low-cost, powered speaker? I'm assuming no, especially since the tech sheet doesn't mention it, but what is your gut feeling?

3: Efficiency: Again, no specs for the stock Celestions.

Is there a way for me to actually test my current drivers for aproximate efficiency? (I have some basic electronics gear, though no scope.)

If not - The Eminence Lab 12C has an efficiency rating of 89.2 dB. Does that seem high, low, or average? (If it's high, then of course I'm more willing to take a chance & try them.)
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Old 6th February 2018, 11:33 PM   #2
Brian Steele is offline Brian Steele  Grenada
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Can you post a picture of the Celestion bass driver that you're talking about?
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Old 7th February 2018, 12:28 AM   #3
Cableaddict is offline Cableaddict
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Hey, Brian.
For now, very good pics of this speaker can be seen here:
12" Celestion T5850A Line-6 (L172-124) speaker 4 ohms | #1852542630
------------------------------
This is the replacement I'm considering:
http://www.eminence.com/pdf/LAB_12C.pdf
These will make my subs rather heavy, (44 bs / pair vs 18 lbs / pr for the stock Celestions) but if the sound is cleaner, and the frequency response doesn't change "significantly" then it will be worth it.

Last edited by Cableaddict; 7th February 2018 at 12:34 AM.
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Old 7th February 2018, 12:52 AM   #4
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More info:
internal volume of this cabinet: ~ 4.5 ft/3 (it's hard to measure exactly, due to internal bracing and the amp modules, but this is very close.)
Two Ports. Each: 3 7/8” diameter, and about 4” deep into the cabinet.
-------------------------
some specs from the Eminence LAB 12C spec sheet: (I don't understand most of this at all, though it appears that my enclosure volume, at least is near perfect.)
Recommended Enclosure Volume, Vented: 1.5 - 5 cu ft
Fs 23 Hz

Re 3.11 ohms

Le 1.09 mh
Qms 11.7
Qes 0.34
Qts 0.33

VAS 4.53 cu ft
VD 659 cc
CMS 0.36 mm/N
BL 13.36 T-M

Mms 13.36 T-M
EBP 67
Sd 506.7 cm2

Last edited by Cableaddict; 7th February 2018 at 01:02 AM.
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Old 7th February 2018, 07:34 AM   #5
chris661 is offline chris661  United Kingdom
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For those following along, this is an active subwoofer, with lots of DSP on-board.

For that reason, I wouldn't bother swapping the drivers. Here's why:

- The drivers currently installed will have a particular EQ curve applied to them to get them usefully flat in that box. A different driver will need a different EQ curve, so throwing them in at random will hurt the sound quality at lower levels.
- Cabinets like this usually have a variety of limiters available, including over-excursion, RMS limiting, and peak limiting. What applied to their drivers in their box will not apply to any other driver in that box. It might take 200w for their driver to hit Xmax at some frequency, while a different driver might need 500w. Their amplifier will still limit at 200w, so there really isn't much to be gained at high levels, either.
- A driver with more displacement needs bigger ports. A LAB12 would laugh at a single 4" port.

In my opinion, it might have been worth scouring the fora before buying those subs.
For example, the 15" PA sub that was designed between me and tb46 is excellent - Teeny tiny PA 15" subwoofer
Buying everything brand-new (with an NU6000DSP that could power four) would set you back about as much as one of those Line6 subs, and I'd bet money the 15" would go at least as loud, if not louder. Smaller box, too, at around 650x440x440mm.

If you're really set on dropping LAB12 drivers into those cabinets, I hope you've got some decent measurement gear to re-EQ them, and it won't go much/any louder, but the drivers probably won't distort until the amplifier limits.

Chris
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Old 7th February 2018, 07:45 AM   #6
globalplayer is offline globalplayer  Germany
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Those "woofers" look more like mids to me.

Like already mentioned the plate amp is most likely tailored to the speaker/enclosure combination with tons of processing.
Replacing just the speakers will get you nowhere really.
Also the labs need much more port area.

I would just replace the whole thing with a decent diy sub.
Less hassle and guaranteed to work.
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Last edited by globalplayer; 7th February 2018 at 08:05 AM.
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Old 7th February 2018, 08:33 AM   #7
Cableaddict is offline Cableaddict
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You guys are probably right about the corrective EQ.

regarding over-excursion & and peak limiting, that's not a factor, because the Eminence can take alot more power. The Line 6 electronics would simply kick in sooner than they need, but it would still match the amps.

About the porting: I figured I'd have to modify them, but I probably wouldn't have to change too much. I'm not looking for more output, I'm looking for bass extension. Doesn't a smaller port extend the LF, at the expense of output?

Well, it still won't work I guess, due to the corrective EQ.

Say, I just had a thought: Tomorrow I'll run a tone sweep through the amps, and see if there is, in fact any corrective EQ. If there is, and I can get some graphs from Eminence (or some kind soul here) MAYBE it wouldn't be such a mis-match after all.
I don't have high hopes, though.
-------------------------------------

I'm not going with custom subs, though. I need self-powered, with built-in crossovers. Not enough room in my truck, not enough time for the extra setup. Not with the kind of gigs I do these days. Also, the L3S is exactly the right height to serve as a keyboard stand, so it makes a very compact setup.

I'm just stunned at how crappy these things sound when pushed. They get incredible reviews from everyone who ever posted about them. Go figure...

Maybe I'll sell them and go back to my old QSC KW181's, but those kind of suck also, and they're harder to carry. (I'm a one man show.)

The best ever was my four non-ported 18" Bag Ends, driven by Lab Gruppen amps. Amazing sound, but horribly inefficient. I got tired of blowing $4,000 amps (I had three, kept in rotation as they melted.) and circuit breakers.

^ True story.

Sigh ....

Last edited by Cableaddict; 7th February 2018 at 08:42 AM.
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Old 7th February 2018, 09:12 AM   #8
globalplayer is offline globalplayer  Germany
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Maybe someone can make a suggestion if we would know max. price, max. size, min. power, min. db, crossover freq range, number of subs, location(s), type of music, low freq response, max. weight, and maybe some information about the tops, etc.

If you sweep just the amp you still won`t know about the enclosure tuning, response, also there is no fr graph of the celestion...

Here is the Eminence, but it is more of a car woofer than PA:

www.eminence.com/pdf/LAB_12.pdf
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Old 7th February 2018, 05:57 PM   #9
chris661 is offline chris661  United Kingdom
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Quote:
Originally Posted by Cableaddict View Post
You guys are probably right about the corrective EQ.

regarding over-excursion & and peak limiting, that's not a factor, because the Eminence can take alot more power. The Line 6 electronics would simply kick in sooner than they need, but it would still match the amps.

About the porting: I figured I'd have to modify them, but I probably wouldn't have to change too much. I'm not looking for more output, I'm looking for bass extension. Doesn't a smaller port extend the LF, at the expense of output?
The Line6 electronics would limit early, so you're not getting the most out of your drivers. The LAB12 drivers will probably take a lot more abuse than the ones installed, though, so if the unhappy noises are due to driver stress then the new drivers might well fix it. Assuming, of course, you can sort out the corrective EQ.

A smaller port area will drop the tuning (with any changes on the frequency response that would imply), and will "chuff" at higher volumes. A chuffing port is bad - there's so much turbulence that you're looking at serious changes to the frequency response (many dB loss around the port tuning), as well as the ugly noises associated with the turbulence itself.
Larger port areas will let more air through, so they don't chuff so easily.


On the Bag End subs, I'm not surprised you were struggling to get enough level out of them. 113dB maximum at 40Hz really isn't much (though IIRC the KW181 manages a similar number).
I ran sealed boxes for my PA system for a while, and found I needed a lot of cone area even at fairly small gigs. Swapped the drivers over to ported, and there's a new level of "grunt" available.
I'm surprised you were melting amplifiers, though - Lab make some good stuff. The 18" Bag End subs I pulled the datasheets for were rated for 400w AES, with a recommended amplifier power of up to 800w. 8ohm. Shouldn't be a problem driving a pile of those with most amplifiers.

Where abouts in the world are you?
In the unlikely event you're around Sheffield I'd be happy to let you try a couple of those 15"s.

Chris
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Old 7th February 2018, 08:56 PM   #10
Brian Steele is offline Brian Steele  Grenada
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Measure the t/s parameters for the driver, and replace it with a better one that has similar t/s parameters. Below 200 Hz they should give the same results at low levels no matter what EQ or limiting is built into the amp. At higher SPL levels, the better driver will give better results.
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