Hi everyone, and thanks to the mods for authorising my account....
My first post is a plea for help. I have bought some twin 15 inch sub woofers for my PAsystem. They are a tapped horn design. Unfortunately I have an issue with them. They have uncontrolled cone excursion at twice the resonant frequency of the drivers.This is a huge issue as it is about 74Hz which is not useful . It means that the speaker suddenly seems to not be able to handle much bass with certain types of music content. I can dramatically increase the power handling of the speaker by notching 74Hz out using a parametric equaliser on my mixing console...Has anyone hear of this sort of issue before with this design of enclosure I am new to these as I have only used bass reflex designs before and they have never had an issue like this. I can provide more pics and dimensions if anyone is willing to help me.
My first post is a plea for help. I have bought some twin 15 inch sub woofers for my PAsystem. They are a tapped horn design. Unfortunately I have an issue with them. They have uncontrolled cone excursion at twice the resonant frequency of the drivers.This is a huge issue as it is about 74Hz which is not useful . It means that the speaker suddenly seems to not be able to handle much bass with certain types of music content. I can dramatically increase the power handling of the speaker by notching 74Hz out using a parametric equaliser on my mixing console...Has anyone hear of this sort of issue before with this design of enclosure I am new to these as I have only used bass reflex designs before and they have never had an issue like this. I can provide more pics and dimensions if anyone is willing to help me.
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They look like ported cabinets
If you can, measure the impedance Vs frequency to find out what they are tuned to.
You could use REW with a soundcard and a resistor setup, or even whatever frequency generator you can find and a DVM in line with the amplifier out to measure the current at differing frequencies.
If you can, measure the impedance Vs frequency to find out what they are tuned to.
You could use REW with a soundcard and a resistor setup, or even whatever frequency generator you can find and a DVM in line with the amplifier out to measure the current at differing frequencies.
Just a thought.
It may be a out of phase cancelation (acoustic short circuit) cased by the upper range of the port or horn path contribution (which ever it is), scoops sometimes suffer from the same but more pronounced due to more output from the horn, but the driver arrangement in this case might cause a similar effect?
Again, this is guesswork, so don't take it to seriously, hopefully it can spark some ideas.
It may be a out of phase cancelation (acoustic short circuit) cased by the upper range of the port or horn path contribution (which ever it is), scoops sometimes suffer from the same but more pronounced due to more output from the horn, but the driver arrangement in this case might cause a similar effect?
Again, this is guesswork, so don't take it to seriously, hopefully it can spark some ideas.
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Many thanks for the replies, I will make full measurements of the cabs and post it up, they are indeed celestion drivers, I will post up there specs as well.
Sorry about saying they are tapped horns when they are not. they are certainly not just ported though as the porting flares out like a horn.
As for using REW I don't have the skills to do this....I have used REW to do simple frequency response measurements but that's it sorry.
Sorry about saying they are tapped horns when they are not. they are certainly not just ported though as the porting flares out like a horn.
As for using REW I don't have the skills to do this....I have used REW to do simple frequency response measurements but that's it sorry.
For sure, you want to see what the cones are doing, as Xoc1 suggested above.
All methods start by having a resistance in series with the voice coil, like 150-Ohms minimum. You might even find a very small incandescent light bulb works like 1-watt if there is such a thing.
Then you can use REW or any other source, swept or static tones.
1. Just having a mic almost touching the dust cap will give you a very helpful notion of cone motion even if not quite proportional.
2. using any old voltmeter across the VC works nicely too but much more effort.
B.
It may be a coincidence, normally a drivers free air resonance frequency (fs) as specified in the T/S parameters is changed (lowered) as soon as it gets loaded, and a fresh drivers fs is usually higher then what is specified in the T/S parameters, but it will settle in around the specified frequency once it gets broken in (suspensions get softer).
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In a vented enclosure, maximum excursion in the passband usually occurs about 1.4*Fb, where Fb is the resonant frequency of the enclosure. If this is happening at 2*Fs, it could mean that enclosure is tuned too low for those drivers. What is their rated Xmax?
I will measure the cabs and post up the design.
You have got me thinking about the amplifier situation, I initially tested them with a chevin research A3000 analogue amp. Then I tried a Class D amp (behringer Nuke) ...the chevin seemed to work better with less of the severe resonance at about 70Hz. Don't know why that would be.
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