Looking for anyone who has done some FR measurements on the JBL M115-8 woofer for a project I'm working on. It came out of a JBL AC2115 cabinet and isn't in good shape, otherwise I'd be able to check this myself. Its the same driver used in many lower end JBL cabs like the JRX series and Mpro 215.
I just need to see if its worth using the OEM woofer or getting something better. I've heard from others the M115-8 LF driver is pretty decent despite having a stamped steel frame. I don't typically bother with a project like this but its for a friend. He's trying to upgrade the stock wimpy 2412H compression driver which keeps on failing and wants something better like a DE250 or similar HF driver. It would require crossover mods which I can't determine without measured LF response graphs. I do have TS parameters.
Anyone have any info on this?
I just need to see if its worth using the OEM woofer or getting something better. I've heard from others the M115-8 LF driver is pretty decent despite having a stamped steel frame. I don't typically bother with a project like this but its for a friend. He's trying to upgrade the stock wimpy 2412H compression driver which keeps on failing and wants something better like a DE250 or similar HF driver. It would require crossover mods which I can't determine without measured LF response graphs. I do have TS parameters.
Anyone have any info on this?
I don't think JBL publishes any data for budget drivers. Nor do they use this driver in any of their active (bi-amp) systems (they specify 4739LF instead).
However, if it's just for assessment, then you could use the curves/data from JRX115/215. The 3722 cinema speaker also has the same driver (twice, called 3739LF) in case you're looking for a network diagram. Hope that helps.
From the T/S parameters, the main highlight in case of this driver seems to be its 50g Mms. Expect all kinds of breakup-related issues along with the resulting mid-range extension of the paper cone.
However, if it's just for assessment, then you could use the curves/data from JRX115/215. The 3722 cinema speaker also has the same driver (twice, called 3739LF) in case you're looking for a network diagram. Hope that helps.
From the T/S parameters, the main highlight in case of this driver seems to be its 50g Mms. Expect all kinds of breakup-related issues along with the resulting mid-range extension of the paper cone.
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If JBL doesn't even publish data on this driver, it's probably not very hopeful. Judging by the original cossover, this driver requires quite a bit of shaping to correct FR, so i would say you're right about the expected results.
It was somewhere I read this driver was either considered or used in a version of the econowave speaker, but I can't find anything on it. I have some TS data from a good driver I took a while back. The estimated efficiency was around 100 dB/W with the smaller magnet and light cone, so I'm not very hopeful on getting good results from this thing. It looks like it would make a good guitar speaker which isn't what I had hoped. What's crazy is they made a dual 15 inch sub with this driver - I can't imagine it sounded that great.
I'm also considering a reasonably priced replacement driver like the Emjnence Delta Pro 15 which costs around $150. This guy is on a budget so I can't reach for the usual list of decent 15" drivers. By the time I replace both woofers and compression drivers, he could have bought something else, but would end up with more lousy ear bending top end.
It was somewhere I read this driver was either considered or used in a version of the econowave speaker, but I can't find anything on it. I have some TS data from a good driver I took a while back. The estimated efficiency was around 100 dB/W with the smaller magnet and light cone, so I'm not very hopeful on getting good results from this thing. It looks like it would make a good guitar speaker which isn't what I had hoped. What's crazy is they made a dual 15 inch sub with this driver - I can't imagine it sounded that great.
I'm also considering a reasonably priced replacement driver like the Emjnence Delta Pro 15 which costs around $150. This guy is on a budget so I can't reach for the usual list of decent 15" drivers. By the time I replace both woofers and compression drivers, he could have bought something else, but would end up with more lousy ear bending top end.
Thanks. Yes,, the driver I have is the same version - M115-8A
I came up with very close TS specs so it must be the same one.
If you have some FR measurement data, that would be helpful.
I came up with very close TS specs so it must be the same one.
If you have some FR measurement data, that would be helpful.
I have to decipher it from the assembled crossover. I'll get back to you on that...
Just reading your 1st post again, if your friend wants to upgrade the CD driver then you'd need the tweeter measurements, not the bass driver ?
I believe lots of people fitted a fairly cheap Selenium screw in driver as a direct replacement and were very happy with it.
Selenium D220TI
Cheers,
Rob.
I believe lots of people fitted a fairly cheap Selenium screw in driver as a direct replacement and were very happy with it.
Selenium D220TI
Cheers,
Rob.
Here's the schematic.
The 8.4mH inductor and 51 ohm resistor aren't a typo. I measured the inductors since their values weren't marked.
The two round symbols under the parallel 30 ohm resistors are protection lamps, so they should be around 1 ohm insertion resistance cold.
JBL states a 2100 Hz crossover point, which is high for a 15" LF driver, but the 2412H HF driver is so wimpy that it can't deal with a lower HP frequency.
A B&C DE 250 would work well here and even the cheaper Selenium D220TI. Both would be a massive upgrade to the 2412H and would need some amount of padding. I've run the D220TI in the JRX115 with good results but its definitely not a drop in replacement if you want a reasonably flat FR. The M115-8A doesn't sound half bad for a cheap woofer, but it lacks definition and clarity (sounds a bit fuzzy and veiled to me) compared to the middle of the road 15" drivers I'm accustomed to.
The 8.4mH inductor and 51 ohm resistor aren't a typo. I measured the inductors since their values weren't marked.
The two round symbols under the parallel 30 ohm resistors are protection lamps, so they should be around 1 ohm insertion resistance cold.
JBL states a 2100 Hz crossover point, which is high for a 15" LF driver, but the 2412H HF driver is so wimpy that it can't deal with a lower HP frequency.
A B&C DE 250 would work well here and even the cheaper Selenium D220TI. Both would be a massive upgrade to the 2412H and would need some amount of padding. I've run the D220TI in the JRX115 with good results but its definitely not a drop in replacement if you want a reasonably flat FR. The M115-8A doesn't sound half bad for a cheap woofer, but it lacks definition and clarity (sounds a bit fuzzy and veiled to me) compared to the middle of the road 15" drivers I'm accustomed to.
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You're probably right that it would be more logical to match the existing HF driver response, but that driver sounds so bad already and I'd rather match the LF response to get a better balanced sound.
Looking at the huge 8.4 mH inductor in the LF LP, I would think the woofer had some serious rise in response, requiring a lot of BSC to flatten it.
JRX in room with an 80Hz high pass. Measured at 3 positions across a couch, left speaker then right speaker.
The smooth line is the Harman curve.
Looks like the original just needs an L pad to bring down a bit if a little harsh.
Rob.
The smooth line is the Harman curve.
Looks like the original just needs an L pad to bring down a bit if a little harsh.
Rob.
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The crossover is really simple though. A 2nd order electrical low pass plus zobel. If a driver can be controlled with this then it's well behaved.
You need a primary inductor as large as that for baffle-step compensation when you've got a baffle as wide as a 15" driver requires. Not to mention the low crossover frequency that JBL will be using.
You need a primary inductor as large as that for baffle-step compensation when you've got a baffle as wide as a 15" driver requires. Not to mention the low crossover frequency that JBL will be using.
Yes, the main issue with the AC 2215 etc. is the high crossing above 2kHz, not the woofer itself. Using a better compression driver would easily prevent the woofer from wandering into the mid-range.
Besides, M115-8A, despite its PA reputation, is widely used in small format cinema speakers, which is indicative of a decent sound quality below 800 Hz. However, there is a big difference in cabinet volume, which is usually only half as much for PA when compared to cinema (~300L), which explains the more complicated crossover network (#10 vs #2).
Thus, on the whole, I think it's best to leave the woofer the way it is and focus on the HF instead, like others have already said.
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Well that does explain why this woofer is used in just about anything on the lower end that JBL sells, but it does look to have good potential if not expected to work outside of its comfort zone. Guess I'm just spoiled.
The main reason I wanted a response curve for the woofer was to fix the recessed dark sound. Most of the other 2 way cabs using this woofer have much smaller inductors. 8 plus mH is almost getting into 3 way corssover LP territory and I think they had to use that size I nductor to get the phase response correct so it somewhat mates with the HF driver directivity, which happens to make a big jump at the crossover frequency (as to be expected).
I'm going to try running the LP to 1000 Hz and adapt the upgraded HFdriver to follow suit. I'll have to be careful with the primary resonance of the HF driver and try compensating the impedance peak so it doesn't sound to shouty in the midrange.
Does anyone have crossover implementations for the DE250 running down to around 1 kHz?
The main reason I wanted a response curve for the woofer was to fix the recessed dark sound. Most of the other 2 way cabs using this woofer have much smaller inductors. 8 plus mH is almost getting into 3 way corssover LP territory and I think they had to use that size I nductor to get the phase response correct so it somewhat mates with the HF driver directivity, which happens to make a big jump at the crossover frequency (as to be expected).
I'm going to try running the LP to 1000 Hz and adapt the upgraded HFdriver to follow suit. I'll have to be careful with the primary resonance of the HF driver and try compensating the impedance peak so it doesn't sound to shouty in the midrange.
Does anyone have crossover implementations for the DE250 running down to around 1 kHz?
That's interesting as I find my JRX boxes a little harsh and bright without EQ.
Shows how 2 sets of ears hear totally different.
Rob.
Technically the DE250 isn't a cheap driver compared to others, but its the lowest price driver that I would consider which is readily available.
The D220TI isn't all that bad for the money, but it wouldn't satisfy my needs and I wouldn't expect other people to settle for it if they can afford to spend 120 buck more for significantly better than usual drivers.
For the performance you get from the DE250s, the price is cheap. I would use BMS if it were readily available. They are the most "hifi" sounding out of the modern 1 inch drivers IMO.