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Old 17th September 2005, 04:18 PM   #21
JinMTVT is offline JinMTVT  Canada
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Retsel : i'll be seriously inerested in knowing the results of your W 18" system!!

what will u be using at 100hz + ?
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Old 19th September 2005, 12:33 PM   #22
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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."
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Old 21st September 2005, 12:45 AM   #23
Retsel is offline Retsel  United States
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Default 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
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Old 21st September 2005, 09:14 AM   #24
qi is offline qi
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Retsel

Quote:
I was rolling the Genesis sub off at about 40 hz to Hedlund Horns, which used a Lowther DX4. The midbass of the Lowther driver in a back horn is also something to behold. The very flexible crossover provided by Genesis allowed me to provide a seamless crossover, which I am convinced is the reason why most don't get great bass.
Nice!

Overall, how would you rate this system?

For example, is this your "best system yet"?

Have you considered a supertweeter (e.g., ribbon)?
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Old 21st September 2005, 09:58 AM   #25
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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?
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Old 21st September 2005, 12:18 PM   #26
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Box Q's

The scan 10" drivers I used were in a Q~0.72 box, with the tempests in a Q~0.61 box. The scans sounded much tighter / faster etc than the tempests.



Rob.
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Old 21st September 2005, 02:45 PM   #27
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Rob, how are the lab horns going and how do you think they compare to the scan speak, excluding the obvious difference with output? When played at a volume that is comfortable for the Scan Speaks, that is. Are your tempests vented?
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Old 21st September 2005, 05:07 PM   #28
Retsel is offline Retsel  United States
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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
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Old 21st September 2005, 06:50 PM   #29
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Quote:
Originally posted by paulspencer
Rob, how are the lab horns going and how do you think they compare to the scan speak, excluding the obvious difference with output? When played at a volume that is comfortable for the Scan Speaks, that is. Are your tempests vented?

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.
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Old 21st September 2005, 07:05 PM   #30
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Default Re: Retsel

Quote:
Originally posted by 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
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.
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