Hi,
Firstly great forum - it has helped me a lot!
I have a probably dumb question. Have an mth30 tapped horn sub running off a bridged crown xls1502- 1050w 8 ohm available.
The driver is p.d 12sb30. 400w rms 7mm xmax 8 ohm. Ive never hammered it but have set a brickwall limiter on ui24 at point when i heard a tiny bit of distress. Its hi passed at 45hz and low passed at 120hz via dsp on amp.
Using an online calculator gives around 56v. So I guess feed pink noise and set to 56v max?
But the figure given by precision devices is rms - not sure what is safe to set for this driver in this cab... Music is live reggae generally.
Any advice gratefully received!
In future hope to build another mth30 and hope to run 2 bridged from the same crown amp ( at 4 ohm is rated1550w). Does this sound doable or even sensible?!
Cheers!
Al
Firstly great forum - it has helped me a lot!
I have a probably dumb question. Have an mth30 tapped horn sub running off a bridged crown xls1502- 1050w 8 ohm available.
The driver is p.d 12sb30. 400w rms 7mm xmax 8 ohm. Ive never hammered it but have set a brickwall limiter on ui24 at point when i heard a tiny bit of distress. Its hi passed at 45hz and low passed at 120hz via dsp on amp.
Using an online calculator gives around 56v. So I guess feed pink noise and set to 56v max?
But the figure given by precision devices is rms - not sure what is safe to set for this driver in this cab... Music is live reggae generally.
Any advice gratefully received!
In future hope to build another mth30 and hope to run 2 bridged from the same crown amp ( at 4 ohm is rated1550w). Does this sound doable or even sensible?!
Cheers!
Al
Last edited:
It's not clear to me exactly what you are asking. Sorry if any of the following is a misinterpretation of what you have going on.
Are you suggesting playing pink noise and measuring voltage with another device to set the power level at 400 watts, then setting the limiter there? Without an oscilloscope, I don't think this is a good approach. It's far simpler to just use a sine wave at 60 Hz. Any decent multimeter can measure that signal/frequency accurately. And I would disconnect the speaker for this, obviously.
You implied this in your post, but I'm going to state it more plainly: the 400 watt specification for the driver is a thermal rating. In practice, excursion is often the limiting factor on woofers, and that is heavily influenced by the cabinet.
You don't plainly say how/where the limiter is set currently. Looks like there's a compressor function in the UI24, and I'm assuming that's what you are referring to, but I'm not familiar with it, so I don't know how it behaves with various settings. Were you anywhere near its limit when you heard the distress? If not, what kind of power level do you think you were at when you had trouble?
Another approach to all this is just to play the song that gave you trouble and set the limiter/compressor to just below the level that causes distress.
There's some talk at the following links about power levels, excursion, etc. for your cabinet. I don't know the posters on speakerplans, so I'm not sure whose answers are most right there. If the quoted table below is correct, another way to approach the issue may be to increase the frequency a bit on your high pass.
https://forum.speakerplans.com/mth30-excursion-limit_topic42345_page1.html
If I sim the mth-30 (2Pi) with the pd 12sb30 then I reach/exeed xmax at:
100w 40hz
200w 48hz
300w 52hz
400w 54hz
500w 55hz
600w 55,5hz
700w 56hz
. . .
With typical program material and a suitable high-pass, 400W should be OK.
Sine-wave sweeps may be a problem.
https://techtalk.parts-express.com/...5268-thinking-about-making-mth-30-sub-drivers
with no measured SPL charts that I can find, a reference by the designer that the f3 is 52Hz, and some sims that show it to have a 60-65Hz Fc, it appears not to be a subwoofer
Are you suggesting playing pink noise and measuring voltage with another device to set the power level at 400 watts, then setting the limiter there? Without an oscilloscope, I don't think this is a good approach. It's far simpler to just use a sine wave at 60 Hz. Any decent multimeter can measure that signal/frequency accurately. And I would disconnect the speaker for this, obviously.
You implied this in your post, but I'm going to state it more plainly: the 400 watt specification for the driver is a thermal rating. In practice, excursion is often the limiting factor on woofers, and that is heavily influenced by the cabinet.
You don't plainly say how/where the limiter is set currently. Looks like there's a compressor function in the UI24, and I'm assuming that's what you are referring to, but I'm not familiar with it, so I don't know how it behaves with various settings. Were you anywhere near its limit when you heard the distress? If not, what kind of power level do you think you were at when you had trouble?
Another approach to all this is just to play the song that gave you trouble and set the limiter/compressor to just below the level that causes distress.
There's some talk at the following links about power levels, excursion, etc. for your cabinet. I don't know the posters on speakerplans, so I'm not sure whose answers are most right there. If the quoted table below is correct, another way to approach the issue may be to increase the frequency a bit on your high pass.
https://forum.speakerplans.com/mth30-excursion-limit_topic42345_page1.html
If I sim the mth-30 (2Pi) with the pd 12sb30 then I reach/exeed xmax at:
100w 40hz
200w 48hz
300w 52hz
400w 54hz
500w 55hz
600w 55,5hz
700w 56hz
. . .
With typical program material and a suitable high-pass, 400W should be OK.
Sine-wave sweeps may be a problem.
https://techtalk.parts-express.com/...5268-thinking-about-making-mth-30-sub-drivers
with no measured SPL charts that I can find, a reference by the designer that the f3 is 52Hz, and some sims that show it to have a 60-65Hz Fc, it appears not to be a subwoofer
Hi,
Thanks very much for the comprehensive reply. Sorry I wasnt so clear in what I was saying- I see- Reading what you have replied I think that the best bet might be to play the most bass heavy track I use and listen to the driver as I crank it up til I hear any issues and limit to just before that point- or is that too simplistic ?
. I set the compressor in the UI24 as a brickwall limiter - Fastest attack and fast(ish) release with infinnity ratio. I just then turned up the music til I heard what I thought was the start of distress (!) and set the threshold to kick in about a 1db before. No idea of this is the right way to do it - but I now understand the cabinet has a part to play in what is possible- not just a wattage figure - so thanks for the knowledge!
I was a bit concerened that I read that folded horns can destroy the drivers unless limiters in place - and you dont hear any distress til its too late - not sure if this is case with tapped horns and hance a bit nervous of blowing my Precsion Device driver through ignorance to be honest!
I think I'll do some measuring with REW of the sub to see what mine is actually doing SPL and frequency response wise:-
Just awaiting a measurement mic- Is it best to measure with mic on ground about 3-4 meatres away do you think?
Was planing to bulid another one for our wedding band - don't laugh!- we have 2 EON615 as tops and I figured 2 MTH30 woudl make fro a resnobly discreet system - Audience size around 100 and dont really need huge volumes - cant really push the JBLs to hard before the top end starts getting harsh anyway- mainly just decent level on dance floor area and the MTH30 are an ok pack size for us- I havent noticed too much bass drop off playing tracks through mine but will have a good listen and test - and if its not up to it have a look at reflex 12 or 15 ,with a decent long excursion driver instead. Not surfe if we can afford BMS sadly!
Reading about tapped horns there seems to be those that love them and those that think other designs leave them dead in the water - I guess size of box, drivers and impentation are all key.
Dont hoenstly know if the 2 MTH30s will suffice til I do some more measuring - but its wedding volumes not concert levels we're after and killing Grannies with too much volume isnt our plan 🙂 Was kinda hoping that having a bit of a power alley woudlnt be a bad thing in this case with subs either side?
Any way cheers for the information - very much appreciated-
Cheers!
Al
Thanks very much for the comprehensive reply. Sorry I wasnt so clear in what I was saying- I see- Reading what you have replied I think that the best bet might be to play the most bass heavy track I use and listen to the driver as I crank it up til I hear any issues and limit to just before that point- or is that too simplistic ?
. I set the compressor in the UI24 as a brickwall limiter - Fastest attack and fast(ish) release with infinnity ratio. I just then turned up the music til I heard what I thought was the start of distress (!) and set the threshold to kick in about a 1db before. No idea of this is the right way to do it - but I now understand the cabinet has a part to play in what is possible- not just a wattage figure - so thanks for the knowledge!
I was a bit concerened that I read that folded horns can destroy the drivers unless limiters in place - and you dont hear any distress til its too late - not sure if this is case with tapped horns and hance a bit nervous of blowing my Precsion Device driver through ignorance to be honest!
I think I'll do some measuring with REW of the sub to see what mine is actually doing SPL and frequency response wise:-
Just awaiting a measurement mic- Is it best to measure with mic on ground about 3-4 meatres away do you think?
Was planing to bulid another one for our wedding band - don't laugh!- we have 2 EON615 as tops and I figured 2 MTH30 woudl make fro a resnobly discreet system - Audience size around 100 and dont really need huge volumes - cant really push the JBLs to hard before the top end starts getting harsh anyway- mainly just decent level on dance floor area and the MTH30 are an ok pack size for us- I havent noticed too much bass drop off playing tracks through mine but will have a good listen and test - and if its not up to it have a look at reflex 12 or 15 ,with a decent long excursion driver instead. Not surfe if we can afford BMS sadly!
Reading about tapped horns there seems to be those that love them and those that think other designs leave them dead in the water - I guess size of box, drivers and impentation are all key.
Dont hoenstly know if the 2 MTH30s will suffice til I do some more measuring - but its wedding volumes not concert levels we're after and killing Grannies with too much volume isnt our plan 🙂 Was kinda hoping that having a bit of a power alley woudlnt be a bad thing in this case with subs either side?
Any way cheers for the information - very much appreciated-
Cheers!
Al
Yes.
2 meters is enough distance for a sub the size of yours if your mic can handle the SPL without clipping.
"Power Alley" is generally not a problem, and Grannie and Gramps are going to have more problems with the SPL of the rest of the system than sub frequencies.
Thermal protection of your subs really requires separate peak and RMS limiting, a description can be found at the bottom of the first page of this thread:
https://www.diyaudio.com/community/threads/keystone-sub-using-18-15-12-inch-speakers.185588/
The Crown XLS1502 limiters are peak only from what I read in the manual, you may be able to use an RMS limiter on an aux send of the UI24 driving the subs to provide the long term thermal management.
Art
Do you mind me asking, what would the oscilloscope be used for in the limiter setting process? Checking for amp distortion, or other?
Just measuring the voltage accurately. Since pink noise is a complex, rapidly changing signal, some multimeters could have trouble giving an accurate reading. An oscilloscope is typically fast enough that it can accurately measure most anything in the audio range.
Some true RMS meters with enough bandwidth are likely OK with pink noise too, but I prefer something easier to measure, like a sine wave near mains frequency. It's a nice, steady signal that most any multimeter can read without significant error.
https://billfitzmaurice.info/forum/viewtopic.php?t=14333
"If you measure a pink noise source the voltage won't be constant, it will continuously flutter about. To a great extent that flutter will be stabilized when reading a limited signal, as the limiter reduces the signal peaks. But it's still a lot easier to get a good reading with a sine wave source. Technically the pink noise is closer to actual program material, so the reading is more 'accurate', but if the reading keeps jumping about to the extent that you can't tell at what voltage it's actually clamped then you're just spinning your wheels."
Some true RMS meters with enough bandwidth are likely OK with pink noise too, but I prefer something easier to measure, like a sine wave near mains frequency. It's a nice, steady signal that most any multimeter can read without significant error.
https://billfitzmaurice.info/forum/viewtopic.php?t=14333
"If you measure a pink noise source the voltage won't be constant, it will continuously flutter about. To a great extent that flutter will be stabilized when reading a limited signal, as the limiter reduces the signal peaks. But it's still a lot easier to get a good reading with a sine wave source. Technically the pink noise is closer to actual program material, so the reading is more 'accurate', but if the reading keeps jumping about to the extent that you can't tell at what voltage it's actually clamped then you're just spinning your wheels."
