My experience with my AV12 subs is similar to Rob's - they don't do so well up that high compared to midbass woofers, even when calibrated flat. Exactly why is a mystery to me as well.
I've heard high end speakers with the XLS running up to 80 Hz with a steep crossover, and didn't notice any ill effects of crossing that high. This was with a 100db/octave slope! (yes you heard that right)
I also hear many that claim that the bass from Phoenix and Orions dipole woofers is the best bass they have heard, and this uses the XLS crossing as high as 80 or 120 Hz IIRC. Perhaps it is just a matter of getting subs which have low distortion on their "top end." Or perhaps it is "stored energy."
I've heard high end speakers with the XLS running up to 80 Hz with a steep crossover, and didn't notice any ill effects of crossing that high. This was with a 100db/octave slope! (yes you heard that right)
I also hear many that claim that the bass from Phoenix and Orions dipole woofers is the best bass they have heard, and this uses the XLS crossing as high as 80 or 120 Hz IIRC. Perhaps it is just a matter of getting subs which have low distortion on their "top end." Or perhaps it is "stored energy."
Retsel
More about open baffle (dipole) bass.
I played around with my Gensis 900 subwoofer in different configurations. One was to use the Genesis amp without the Servo. It was amazing how "slow" (high in distortion) the bass was. The woofer was not very adept at reproducing the bass signals even when rolling the woofer at 40 hz. I have heard that what the servo does is essentially reduce the Qts of the system to a very low Qts value, which is perhaps the reason why the bass sounded so tight with the servo operating. The upgrade to the accelerometer attachment by Genesis I referred to above probable lowered the Qts even lower, thus lowering distortion even lower.
Once when the servo was not wired up (thus giving "slow" sounding bass) I unscrewed and removed the woofer while the subwoofer was playing. I was amazed at how much tighter the bass (the bass that was there) sounded with the woofer in my hand or laying on the floor. The conclusion I reached is that the box raises the Qts of the woofer substantially thus increasing distortion.
Thus, if you take a fairly low Qts driver and put it into an open baffle, there should be very good bass even up to higher frequencies because there is no box that will increase the Qts of the system.
To answer an earlier question, the pair of Avalanche Audio 18 inch drivers will be crossovered to a pair of Lowther DX4s in open baffle. I am doing a very modified Basszilla speaker with the woofers also on open baffle. The Lowthers are apparently providing bass down to around 100 hz.
Retsel
More about open baffle (dipole) bass.
I played around with my Gensis 900 subwoofer in different configurations. One was to use the Genesis amp without the Servo. It was amazing how "slow" (high in distortion) the bass was. The woofer was not very adept at reproducing the bass signals even when rolling the woofer at 40 hz. I have heard that what the servo does is essentially reduce the Qts of the system to a very low Qts value, which is perhaps the reason why the bass sounded so tight with the servo operating. The upgrade to the accelerometer attachment by Genesis I referred to above probable lowered the Qts even lower, thus lowering distortion even lower.
Once when the servo was not wired up (thus giving "slow" sounding bass) I unscrewed and removed the woofer while the subwoofer was playing. I was amazed at how much tighter the bass (the bass that was there) sounded with the woofer in my hand or laying on the floor. The conclusion I reached is that the box raises the Qts of the woofer substantially thus increasing distortion.
Thus, if you take a fairly low Qts driver and put it into an open baffle, there should be very good bass even up to higher frequencies because there is no box that will increase the Qts of the system.
To answer an earlier question, the pair of Avalanche Audio 18 inch drivers will be crossovered to a pair of Lowther DX4s in open baffle. I am doing a very modified Basszilla speaker with the woofers also on open baffle. The Lowthers are apparently providing bass down to around 100 hz.
Retsel
Retsel, it's interesting to hear your comments on the servo sub. It's a pity that there is only one diy servo sub option currently available, and that it is only a 12" driver with fairly limited output (compared to current high excursion drivers).
You made some interesting observations. I've also noticed how much more articulate bass is when the driver is out of the box. I found this with my AV12s even when they weren't broken in. In their (pretty ordinary) prototype boxes they aren't as articulate as my mains in the upper bass, but soon I plan to put them in a H frame dipole and compare. I'm curious to see if with a dipole arrangement, they actually can do a good job of upper bass.
I tend to disagree when you equate distortion and subjective speed with Qts. I doubt there is any direct relationship, and suspect they are in fact totally unrelated. Qts describes damping, and affects rolloff. The XLS with its high Qts, large motor and low fs has very early rolloff, and hence requires eq, more so than drivers with a higher Qts. I think what you think is related to Qts is actually things like box coloration and transient response. Were you suggesting distortion is also related to Qts?
You made some interesting observations. I've also noticed how much more articulate bass is when the driver is out of the box. I found this with my AV12s even when they weren't broken in. In their (pretty ordinary) prototype boxes they aren't as articulate as my mains in the upper bass, but soon I plan to put them in a H frame dipole and compare. I'm curious to see if with a dipole arrangement, they actually can do a good job of upper bass.
I tend to disagree when you equate distortion and subjective speed with Qts. I doubt there is any direct relationship, and suspect they are in fact totally unrelated. Qts describes damping, and affects rolloff. The XLS with its high Qts, large motor and low fs has very early rolloff, and hence requires eq, more so than drivers with a higher Qts. I think what you think is related to Qts is actually things like box coloration and transient response. Were you suggesting distortion is also related to Qts?
Retsel
I cannot say that I know a lot about creating great bass, but I have been successful at it using a servo modulated subwoofer. I have made observations based on my experiences and I am trying to understand why I heard what I have heard.
My experience with the Genesis woofer can be molded into a theory by the Qts of the driver and of the system. What changed from the same woofer being able to reproduce mid bass well or not was whether the woofer was in the cabinet or not which affects the Qts. I believe that the only parameter associated with the woofer that changes whether it is in the box (and potentially overdamped) or not is the Q. Thus, I formulated a theory that the Q has an important affect on the driver's ability to reproduce midbass with low distortion. I think that it is a viable theory.
If the system Q does not describe why the woofer reproduces bass with low distortion, then what other reason makes sense? What I am looking for are alternative theories. I am more than happy to change my theory.
Retsel
I cannot say that I know a lot about creating great bass, but I have been successful at it using a servo modulated subwoofer. I have made observations based on my experiences and I am trying to understand why I heard what I have heard.
My experience with the Genesis woofer can be molded into a theory by the Qts of the driver and of the system. What changed from the same woofer being able to reproduce mid bass well or not was whether the woofer was in the cabinet or not which affects the Qts. I believe that the only parameter associated with the woofer that changes whether it is in the box (and potentially overdamped) or not is the Q. Thus, I formulated a theory that the Q has an important affect on the driver's ability to reproduce midbass with low distortion. I think that it is a viable theory.
If the system Q does not describe why the woofer reproduces bass with low distortion, then what other reason makes sense? What I am looking for are alternative theories. I am more than happy to change my theory.
Retsel
paulspencer said:
Hi Paul,
One lab is finished and painted, one is waiting for the last side to be glued on and paint. Both will be finished by Sunday. Am waiting for the aluminium plate to make the access plates. Will get that Friday hopefully. So haven't heard one yet....will let you know.
Cheers,
Rob.
Re: Retsel
Hi Retsel,
When you take the driver out you also change its acoustic response. I've noticed with subs that as you lower the subbass, midbass seems to 'tighten / get faster'. Could it be that the midbass quality of your speaker is the same, but sounds tighter due to the lack of lower bass masking it ?
Reason I ask is that with my scans I could have the subbass flat with the mains and they'd sound tight. With the tempests it would sound a bit slow, a bit boomy. If I drop the tempests by 5 or 6 dB the tightness returns, but the overall sound is colder, weaker.
I'm pretty sure it's just the driver quality difference between the scans and the tempests though.
Cheers,
Rob.
Retsel said:
Hi Retsel,
When you take the driver out you also change its acoustic response. I've noticed with subs that as you lower the subbass, midbass seems to 'tighten / get faster'. Could it be that the midbass quality of your speaker is the same, but sounds tighter due to the lack of lower bass masking it ?
Reason I ask is that with my scans I could have the subbass flat with the mains and they'd sound tight. With the tempests it would sound a bit slow, a bit boomy. If I drop the tempests by 5 or 6 dB the tightness returns, but the overall sound is colder, weaker.
I'm pretty sure it's just the driver quality difference between the scans and the tempests though.
Cheers,
Rob.
Retsel
I agree that removing the woofer from the box will cause a roll off in frequency response at the lower frequencies which does affect the sound of the bass being produced. But what I am noticing is the abiliity of the driver to reproduce the midbass (not the frequency response. Even though the deepest frequencies are not being heard (they are not anyways, they are felt) the woofer is still trying to reproduce them. However, what I am comparing when the woofer is in the box or not is the upper frequency bass because that is what was so poor when the woofer was mounted in the box without the servo hooked up to it (it could not "keep up" with the mains). When removed from the box the woofer suddenly had a dramatically improved ability to reproduce the midbass and improved ability to match the mains.
The driver is likely being affected in other ways when it is mounted in the box. For example, the pressure or vacumn created by the woofer as it moves forward or backwards in the box will cause the driver to distort (become more concave or convex). But again, the problem that I am hearing with the woofer in the box is not that the midbass is slightly distorted by these cone movement artifacts, it just cannot track the signal being given to it. Now in this case the woofer is likely a fairly high Q driver mounted in a fairly small box thus raising the Q to very high levels. So it is an extreme example of what happens when a woofer is placed in a box. But this does not matter in this application as designed because the engineers at Genesis designed the woofer to be used with a servo device thus lowering (dramatically so) the Q of the system.
So what is Q. I have read that it is the ability of a speaker reproduce versus dampen (store) the input energy provided to it. Placing a woofer into a box decreases the damping (increases the Q). As I understand it, a desired Q would result in a flat frequency response to provide deep bass without the need to have to roll off the higher frequencies. So if a driver is underdamped (high Q) it will produce deeper bass at a higher output than the higher frequencies. If a driver is a lower Q, it will produce the higher frequencies at a higher output than the lower frequencies.
However, isn't it also logical that damping also affect the ability for the driver to follow the input signal? A well damped driver will reproduce the input signal particularly well while a poorly damped driver (heavy cone/small magnet) will flop around at the same frequencies. These drivers can reproduce lower frequencies OK because the response needed is "slow" (i.e., 20 to 40 cycles). But as the frequency needing to be reproduced increases (100 to 200 hz), the lack of damping takes its toll.
Another issue may be at play for woofers in general. I know that Adire has stated that the high inductance of a woofer can contribute to a poorer frequency response by woofers at higher frequencies. However, in my case, removing a woofer from a box should not affect the inductance of the woofer. So I doubt that inductance is the cause of this effect. However, it perhaps could be a combination of inductance and lack of damping which causes woofers to be "slow" at the higher frequencies.
Well, this is more musing on my part....
Retsel
I agree that removing the woofer from the box will cause a roll off in frequency response at the lower frequencies which does affect the sound of the bass being produced. But what I am noticing is the abiliity of the driver to reproduce the midbass (not the frequency response. Even though the deepest frequencies are not being heard (they are not anyways, they are felt) the woofer is still trying to reproduce them. However, what I am comparing when the woofer is in the box or not is the upper frequency bass because that is what was so poor when the woofer was mounted in the box without the servo hooked up to it (it could not "keep up" with the mains). When removed from the box the woofer suddenly had a dramatically improved ability to reproduce the midbass and improved ability to match the mains.
The driver is likely being affected in other ways when it is mounted in the box. For example, the pressure or vacumn created by the woofer as it moves forward or backwards in the box will cause the driver to distort (become more concave or convex). But again, the problem that I am hearing with the woofer in the box is not that the midbass is slightly distorted by these cone movement artifacts, it just cannot track the signal being given to it. Now in this case the woofer is likely a fairly high Q driver mounted in a fairly small box thus raising the Q to very high levels. So it is an extreme example of what happens when a woofer is placed in a box. But this does not matter in this application as designed because the engineers at Genesis designed the woofer to be used with a servo device thus lowering (dramatically so) the Q of the system.
So what is Q. I have read that it is the ability of a speaker reproduce versus dampen (store) the input energy provided to it. Placing a woofer into a box decreases the damping (increases the Q). As I understand it, a desired Q would result in a flat frequency response to provide deep bass without the need to have to roll off the higher frequencies. So if a driver is underdamped (high Q) it will produce deeper bass at a higher output than the higher frequencies. If a driver is a lower Q, it will produce the higher frequencies at a higher output than the lower frequencies.
However, isn't it also logical that damping also affect the ability for the driver to follow the input signal? A well damped driver will reproduce the input signal particularly well while a poorly damped driver (heavy cone/small magnet) will flop around at the same frequencies. These drivers can reproduce lower frequencies OK because the response needed is "slow" (i.e., 20 to 40 cycles). But as the frequency needing to be reproduced increases (100 to 200 hz), the lack of damping takes its toll.
Another issue may be at play for woofers in general. I know that Adire has stated that the high inductance of a woofer can contribute to a poorer frequency response by woofers at higher frequencies. However, in my case, removing a woofer from a box should not affect the inductance of the woofer. So I doubt that inductance is the cause of this effect. However, it perhaps could be a combination of inductance and lack of damping which causes woofers to be "slow" at the higher frequencies.
Well, this is more musing on my part....
Retsel
I just re-calibrated my system for use without the subwoofer with eq to get it flat down to 25 Hz in room. Then I played the Dianna Krall live in Paris music DVD which is an excellent bass test DVD as it has a lot of acoustic double bass. When the double bass plays low, most of its deep output seems to be 50 - 100 Hz, and I noticed that when just my TL speakers, the sound is noticeably more articulate than with my subs supplementing the bottom end, even when crossed low! 
The sound is fantastic with just the TLs, but now dynamics are gone
The sound is fantastic with just the TLs, but now dynamics are gone
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