I read something somewhere that said, "Thou shalt not tune below Fs or thou shalt reap droopy bass."
I was designing the box for my Definitive/Seas MTM and I have arrived at a slim mini-tower speaker that I can put on some shelves in my room. It has dual Definitive Tech 5.25" woofers, which have a Fs of 50.1 Hz. The F3 of the box is 47.8 and the tuning frequency is at 51.86 Hz.
So, can I expect my woofers to always be unloading and flopping around if I arrive at a F3 that is below the driver's stated frequency response of 50-3500 Hz? I don't want droopy bass from my mains.
I was just wondering...
~Rory
I was designing the box for my Definitive/Seas MTM and I have arrived at a slim mini-tower speaker that I can put on some shelves in my room. It has dual Definitive Tech 5.25" woofers, which have a Fs of 50.1 Hz. The F3 of the box is 47.8 and the tuning frequency is at 51.86 Hz.
So, can I expect my woofers to always be unloading and flopping around if I arrive at a F3 that is below the driver's stated frequency response of 50-3500 Hz? I don't want droopy bass from my mains.
I was just wondering...
~Rory
Hello,
for my common sense, tuning woofers of such size too
low won't do anything good.
Any more data on the drivers?
Greetz,
Spherion
for my common sense, tuning woofers of such size too
low won't do anything good.
Any more data on the drivers?
Greetz,
Spherion
Driver information
Woofer: Parts Express 299-706 -- Definitive Technology 5.25" cast-frame poly cone woofer with rubber surround
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=299-706
These woofers were part of Parts Express's Definitive Tech factory buyout. The drivers were on special for the holidays, and I saw them used in an Ariel clone that appeared at a DIY2002 event (the one held at KaiAudio). I have heard good things about their resolution (for the price) and bass output. That and the fact that they're handsome-looking.
Tweeter: Parts Express 279-312 -- Seas H537-06 1" Aluminum-dome tweeter with rear damping chamber as found in Definitive's BP3000TL units
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=279-312
This tweeter was also part of the Definitive Tech buyout at Parts Express. It, too, was also on holiday special. I decided if I was going to get an aluminum dome tweeter, I was going to get it from a reputable name. I was about to choose the Dayton tweeter, but a short time before I ordered these drivers, someone came on the Parts Express tech talk message board saying that they had used a variation of the Seas tweeter (the H534) that didn't have the rear damping chamber, and he said that it was a very smooth tweeter, especially for a metal dome, while retaining the precise detail of metal domes, and he was recommending the H537 to anyone looking for a great metal dome.
The drivers are arriving tomorrow (if the snowstorm doesn't stop UPS from delivering the package). I just wanted to get the drivers while they were available, before PE ran out of them. I have plenty of time to work out an enclosure, and I already have the crossover worked out, with a little guidance from Jason Andreasen, the man who built the Ariel clone using the 299-706 woofer and the matching Definitive tweeter.
Woofer: Parts Express 299-706 -- Definitive Technology 5.25" cast-frame poly cone woofer with rubber surround
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=299-706
These woofers were part of Parts Express's Definitive Tech factory buyout. The drivers were on special for the holidays, and I saw them used in an Ariel clone that appeared at a DIY2002 event (the one held at KaiAudio). I have heard good things about their resolution (for the price) and bass output. That and the fact that they're handsome-looking.
Tweeter: Parts Express 279-312 -- Seas H537-06 1" Aluminum-dome tweeter with rear damping chamber as found in Definitive's BP3000TL units
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=279-312
This tweeter was also part of the Definitive Tech buyout at Parts Express. It, too, was also on holiday special. I decided if I was going to get an aluminum dome tweeter, I was going to get it from a reputable name. I was about to choose the Dayton tweeter, but a short time before I ordered these drivers, someone came on the Parts Express tech talk message board saying that they had used a variation of the Seas tweeter (the H534) that didn't have the rear damping chamber, and he said that it was a very smooth tweeter, especially for a metal dome, while retaining the precise detail of metal domes, and he was recommending the H537 to anyone looking for a great metal dome.
The drivers are arriving tomorrow (if the snowstorm doesn't stop UPS from delivering the package). I just wanted to get the drivers while they were available, before PE ran out of them. I have plenty of time to work out an enclosure, and I already have the crossover worked out, with a little guidance from Jason Andreasen, the man who built the Ariel clone using the 299-706 woofer and the matching Definitive tweeter.
Rory,
The values you gave are close to a B4 alignment for a BR type enclosure. You’re within 5% of prefect alignment. For a realization of a speaker design to turn out this close is excellent. To give you an example, Keele in his paper “Sensitivity of Thiele’s Vented Loudspeaker Enclosure alignments to Parameter Variations”, show that fb variation of 10% high only produced a 1.5db bump in the response curve.
I have included a scan of a graph from Small’s paper on vented enclosures that shows diaphragm displacement vs frequency around fb. It shows the woofer cone displacement WRT the drivers maximum cone displacement (0db). This is in general terms, but it can be seen that music signals below f3 ~ fb will drive the cone to relatively high cone excursions regardless of a minor misalignment.
Rodd Yamashita
The values you gave are close to a B4 alignment for a BR type enclosure. You’re within 5% of prefect alignment. For a realization of a speaker design to turn out this close is excellent. To give you an example, Keele in his paper “Sensitivity of Thiele’s Vented Loudspeaker Enclosure alignments to Parameter Variations”, show that fb variation of 10% high only produced a 1.5db bump in the response curve.
I have included a scan of a graph from Small’s paper on vented enclosures that shows diaphragm displacement vs frequency around fb. It shows the woofer cone displacement WRT the drivers maximum cone displacement (0db). This is in general terms, but it can be seen that music signals below f3 ~ fb will drive the cone to relatively high cone excursions regardless of a minor misalignment.
Rodd Yamashita
Attachments
So I'm in good shape, then? Or should I try for a different alignment? I tweaked it so that the box would have its f3 at 51 Hz, which is better for the woofers, I think.
The woofers themselves seem pretty robust, so I think they could take some cone motion if they had to, but if there's something I need to do to protect my drivers (thus increasing their life span) I am open to suggestions.
First, let me see that I'm understanding you. So for frequencies below the tuning point of the box (51.86 Hz) but above the F3 (47.8 Hz) I can expect those cones to really move, right?
The CLIO-measured FR of the woofers is at the most +/-3dB between 50 Hz and 3500 Hz. The Fs of the woofers is 50.1 Hz. The tuning point of the box is 51.86 Hz so I have not tuned below Fs (which leads to droopy bass.) But the box still shows an F3 of 47.8 so there is the possibility of the cones unloading. The VC former is made of aluminum, but I don't build speakers just to hear them go pop-pop-popping along.
Forgive me if I have misunderstood - It's after midnight here and I usually go to bed at 10.
~Rory
The woofers themselves seem pretty robust, so I think they could take some cone motion if they had to, but if there's something I need to do to protect my drivers (thus increasing their life span) I am open to suggestions.
First, let me see that I'm understanding you. So for frequencies below the tuning point of the box (51.86 Hz) but above the F3 (47.8 Hz) I can expect those cones to really move, right?
The CLIO-measured FR of the woofers is at the most +/-3dB between 50 Hz and 3500 Hz. The Fs of the woofers is 50.1 Hz. The tuning point of the box is 51.86 Hz so I have not tuned below Fs (which leads to droopy bass.) But the box still shows an F3 of 47.8 so there is the possibility of the cones unloading. The VC former is made of aluminum, but I don't build speakers just to hear them go pop-pop-popping along.
Forgive me if I have misunderstood - It's after midnight here and I usually go to bed at 10.
~Rory
You will get an F3 below the tuning frequency of the box if the box is larger than the speaker's Vas.
There are perfectly satisfactory alignments that have an box volume larger than Vas. However, it is best not to overdue that too much.
With a Qts of .39, the box should be built with a volume of Vas, tuned to Fs and will have an F3 of Fs. That is the way the B4 alignment-also called the "classic bass reflex alignment"-works.
There are perfectly satisfactory alignments that have an box volume larger than Vas. However, it is best not to overdue that too much.
With a Qts of .39, the box should be built with a volume of Vas, tuned to Fs and will have an F3 of Fs. That is the way the B4 alignment-also called the "classic bass reflex alignment"-works.
Rory,
You’re in good shape right now. You will be able to tweak the box 5 or 10%, but it’s a lot easier if the box is too big rather than too small. The B4 alignment will work fine. Be sure to measure the speaker parameters when they come and than make the necessary adjustments in your alignment.
WRT the cone excursion, the speaker is made for a vented enclosure and if you’ve heard good things about it, I would assume you to pretty safe. It is not a bad idea to use a subsonic filter with small bass drivers. Bi-amping with a sub-woofer would solve that problem very nicely.
Rodd Yamashita
You’re in good shape right now. You will be able to tweak the box 5 or 10%, but it’s a lot easier if the box is too big rather than too small. The B4 alignment will work fine. Be sure to measure the speaker parameters when they come and than make the necessary adjustments in your alignment.
WRT the cone excursion, the speaker is made for a vented enclosure and if you’ve heard good things about it, I would assume you to pretty safe. It is not a bad idea to use a subsonic filter with small bass drivers. Bi-amping with a sub-woofer would solve that problem very nicely.
Rodd Yamashita
Good Bass
Yeah. These woofers have some pretty good woofage potential. I tested them in free air with 3 watts and I was getting a good deal of excursion. These have the potential for 6mm, I think.
Yeah. These woofers have some pretty good woofage potential. I tested them in free air with 3 watts and I was getting a good deal of excursion. These have the potential for 6mm, I think.
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