Hi-
It is very unpleasant, although often useful, to read something that completely contradicts your understanding of something. For the past 2 days I have been modeling a sealed enclosure using two Volt BM2500.4 drivers in WINisd. I was very pleased with myself to have found a pair of drivers, which based on WINisd, worked really well in only 80 liters of space. It is true that I would need 2 of these expensive drivers to have a decent bass response, however in this configuration they rivaled some of the best subs within the same space constraints. I put them up vs Eton 11 inch, several PHL 10 and 12 inch units, Peerless XLS and many more. Of course some of these drivers could accomplish the same thing using 1 unit, and at a fraction of the price, but I think the BM2500 would work great with an ATC dome midrange. And I though it would be compact and simple to mate 2 of these midbasses with the ATC and a tweeter in a sealed full range 3-way config... After all, the BM2500 is designed for 2-way nearfield configurations, so it can go low enough. Then I read the following "snippet" from Sonic Craft. What he is saying makes sense, but WINisd is showing that bass extension will not be all too bad, for a sealed box that is. Please help me sort this out.
From Sonic Craft:
"The BM2500.4 10" is described as a "bass midrange" driver. Despite its 32 Hz Fs, this unusual low-Q design is pretty much useless in a sealed box below 100 Hz or a reasonably-sized vented box below 60 Hz. However, it has been highly recommended as an extremely neutral, uncolored driver. With an Xmax of 8 mm, it is well suited to a sealed system designed to be used with a separate sub woofer, or even in a TL design."
It is very unpleasant, although often useful, to read something that completely contradicts your understanding of something. For the past 2 days I have been modeling a sealed enclosure using two Volt BM2500.4 drivers in WINisd. I was very pleased with myself to have found a pair of drivers, which based on WINisd, worked really well in only 80 liters of space. It is true that I would need 2 of these expensive drivers to have a decent bass response, however in this configuration they rivaled some of the best subs within the same space constraints. I put them up vs Eton 11 inch, several PHL 10 and 12 inch units, Peerless XLS and many more. Of course some of these drivers could accomplish the same thing using 1 unit, and at a fraction of the price, but I think the BM2500 would work great with an ATC dome midrange. And I though it would be compact and simple to mate 2 of these midbasses with the ATC and a tweeter in a sealed full range 3-way config... After all, the BM2500 is designed for 2-way nearfield configurations, so it can go low enough. Then I read the following "snippet" from Sonic Craft. What he is saying makes sense, but WINisd is showing that bass extension will not be all too bad, for a sealed box that is. Please help me sort this out.
From Sonic Craft:
"The BM2500.4 10" is described as a "bass midrange" driver. Despite its 32 Hz Fs, this unusual low-Q design is pretty much useless in a sealed box below 100 Hz or a reasonably-sized vented box below 60 Hz. However, it has been highly recommended as an extremely neutral, uncolored driver. With an Xmax of 8 mm, it is well suited to a sealed system designed to be used with a separate sub woofer, or even in a TL design."
Amo:
I was unable to check Volt's numbers against Win ISD's listed numbers, since Volt's website is all messed up . Text is overflowing the parameters, etc.
Anyway, here is my own WinISD simulation, using WinISD's parameters for the Volt BM2500.4
They seem to bear out Sonic Craft's review.
This for 2 Volt BM2500.4 loudspeakers in an 80 liter sealed box.
I was unable to check Volt's numbers against Win ISD's listed numbers, since Volt's website is all messed up . Text is overflowing the parameters, etc.
Anyway, here is my own WinISD simulation, using WinISD's parameters for the Volt BM2500.4
They seem to bear out Sonic Craft's review.
This for 2 Volt BM2500.4 loudspeakers in an 80 liter sealed box.
Attachments
Amo:
Don't know what to tell you. I'm not a big fan of sealed for subs myself. I know that they are supposed to splice into room gain, but in this instance, you are 15 dB or so down at 30 Hz.
One thing I will point out. These Volts are 92 dB sensitive and rated at 8 ohms. Parallel two and hook up a 4 ohm amp, (like most subwoofer crossover/amps are) and your sensitivity goes up either 3 dB or 6 dB, depending on your amp.
So if, at the least, you are going to go up to 95 dB, then you really are only about 8 dB down at 30 Hz compared to an 88 dB efficient sub with flat response. Room gain should bring it up even closer to flat frquency response.
Just a thought.
Don't know what to tell you. I'm not a big fan of sealed for subs myself. I know that they are supposed to splice into room gain, but in this instance, you are 15 dB or so down at 30 Hz.
One thing I will point out. These Volts are 92 dB sensitive and rated at 8 ohms. Parallel two and hook up a 4 ohm amp, (like most subwoofer crossover/amps are) and your sensitivity goes up either 3 dB or 6 dB, depending on your amp.
So if, at the least, you are going to go up to 95 dB, then you really are only about 8 dB down at 30 Hz compared to an 88 dB efficient sub with flat response. Room gain should bring it up even closer to flat frquency response.
Just a thought.
amo,
Hi, put an Adire Shiva or Tempest into WinISD and then you'll see what *can* happen in a sealed box, with the right specs. A Shiva (12") f3 is something rather lower than that! And would work in that sized box iirc. I'm not at home so I cant do it myself, but have a look. Even the Tempest (15") sounds good in a 90l box, I tried this for a short time, and probably wasted my time moving to a 250l vented box
-Simon
Hi, put an Adire Shiva or Tempest into WinISD and then you'll see what *can* happen in a sealed box, with the right specs. A Shiva (12") f3 is something rather lower than that! And would work in that sized box iirc. I'm not at home so I cant do it myself, but have a look. Even the Tempest (15") sounds good in a 90l box, I tried this for a short time, and probably wasted my time moving to a 250l vented box
-Simon
Here is a difference between two BM2500.4 in 80 liters and one Sheeva in 80 liters:
40 Hz - 1.2 dB
30 Hz - 2.0 dB
20 Hz - 1.8 dB
And $1k USD
The only thing that I am not sure about, is if it is acceptable to have a sealed box with Qtc of 0.35. This will be the case here.
kelticwizard, you hit it right on the head! The Volts are so sensitive, and doubling up on them doesn't hurt either. The good thing is that the sensitivity of 2 Volts is that it is very close to that of the ATC dome, and also close to many good tweeters! Thank you guys for your help, I just wanted to make sure that I was not going crazy...
40 Hz - 1.2 dB
30 Hz - 2.0 dB
20 Hz - 1.8 dB
And $1k USD
The only thing that I am not sure about, is if it is acceptable to have a sealed box with Qtc of 0.35. This will be the case here.
kelticwizard, you hit it right on the head! The Volts are so sensitive, and doubling up on them doesn't hurt either. The good thing is that the sensitivity of 2 Volts is that it is very close to that of the ATC dome, and also close to many good tweeters! Thank you guys for your help, I just wanted to make sure that I was not going crazy...
Amo:
The problem is the extremely low Q of the Volt driver.
There is an enclosure type called a Daline you might wish to investigate. I have never built one. Not yet.
It's major contribution seems to be that it takes a driver with an extremely low Qts and allows it to be put into a larger box than you could with either a sealed or ported enclosure, with correspondingly low F3, and yet give a smooth response. Since your problem here is a Qts too low for the box you wish to design, it would seem to be a good choice.
It is sort of a combo Transmission Line and ported box.
There appears to be a very successful design which uses it.
I have never built one. Martin J. King, a member here, (MJK), has written downloadable freeware, based on a freeware MathCAD demo, which will model one. I am having slow progress getting through the MathCAD demo, but others here seem to pick it right up.
Somebody designed a Daline for a Peerless XLS, no doubt because of the low Qts.
I am inclined to believe that since the Qts is very low of the drivers involved, the rolloff rate might be more gradual than your average ported box, but I have never checked this.
If you are in the mood for experimentation, it might be rewarding.
Martin J. King's website with downloadable freeware:
www.quarter-wave.com
The problem is the extremely low Q of the Volt driver.
There is an enclosure type called a Daline you might wish to investigate. I have never built one. Not yet.
It's major contribution seems to be that it takes a driver with an extremely low Qts and allows it to be put into a larger box than you could with either a sealed or ported enclosure, with correspondingly low F3, and yet give a smooth response. Since your problem here is a Qts too low for the box you wish to design, it would seem to be a good choice.
It is sort of a combo Transmission Line and ported box.
There appears to be a very successful design which uses it.
I have never built one. Martin J. King, a member here, (MJK), has written downloadable freeware, based on a freeware MathCAD demo, which will model one. I am having slow progress getting through the MathCAD demo, but others here seem to pick it right up.
Somebody designed a Daline for a Peerless XLS, no doubt because of the low Qts.
I am inclined to believe that since the Qts is very low of the drivers involved, the rolloff rate might be more gradual than your average ported box, but I have never checked this.
If you are in the mood for experimentation, it might be rewarding.
Martin J. King's website with downloadable freeware:
www.quarter-wave.com
The low Q of this driver points to a bass reflex alignment being
the optimum choice, Q=0.35 is too low for a sealed box, I'd say
0.5 is the minimum, 0.6 good, 0.7 maximum.
Even so an overdamped bass reflex alignment is required for
good bass extension. To get a flat bass reflex alignment you'll
need a high port frequency and low bass goes out of the window
- its probably this the comments refer to.
Due to 'baffle step diffraction' the bass unit sensistivity needs to
be 6dB higher than the midrange and treble drivers. BSD also
complicates the crossover to the midrange considerably.
An overdamped bass reflex alignment with a low port frequency
and an active adjustable underdamped 2nd order high pass
filter with f = port frequency will give oustanding results.
/sreten.
the optimum choice, Q=0.35 is too low for a sealed box, I'd say
0.5 is the minimum, 0.6 good, 0.7 maximum.
Even so an overdamped bass reflex alignment is required for
good bass extension. To get a flat bass reflex alignment you'll
need a high port frequency and low bass goes out of the window
- its probably this the comments refer to.
Due to 'baffle step diffraction' the bass unit sensistivity needs to
be 6dB higher than the midrange and treble drivers. BSD also
complicates the crossover to the midrange considerably.
An overdamped bass reflex alignment with a low port frequency
and an active adjustable underdamped 2nd order high pass
filter with f = port frequency will give oustanding results.
/sreten.Ok now I understand... I have been modeling it wrong. The two Volts seem ok because of their high sensitivity. All this means is that it will take more power for the other driver to perform on the same level. When you do give the other driver more power, so that the "before drop-off point" level is the same, then you can see how many other drivers outperform these two in the first few octaves.
What you guys are saying about the low Q makes sense as well. I think this one is best left for midbass duties.
What you guys are saying about the low Q makes sense as well. I think this one is best left for midbass duties.
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