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Old 9th April 2004, 07:07 PM   #21
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Quote:
Originally posted by ozynigma
moving electron

Current plan is to go the 15" Adire Tempest driver in a 55 litre enclosure with the 110W amp and LT.

Instinctively, 55 litre sure seems tiny for the large Vas of the Tempest but it does appear you can get an F3 or 22Hz and a 99 dB SPL level with 130 watts via the LT.

Again enjoy your project and let us know how it goes!
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Old 9th April 2004, 10:02 PM   #22
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MikeB,

I want to keep the enclosure and driver arrangement really simple. Having seen what can be accomplished with an LT in a small sealed enclosure I am going to avoid passive radiators or vented systems.

I have modelled the Peerless XLS 12 and Adira Shiva as well, but not the XLS 10.

moving_electron,

The cabinet is open at the rear so no problem mounting and venting the amp. Yes the new sub replaces the old and takes up the bottom half the cabinet, being about twice the enclosure size.

Also managed to squeeze the final design up to 62litres.

Ozynigma
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Old 10th April 2004, 04:20 AM   #23
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What about stuffing my approximately 60litre enclosure that I am going to LT?

Stuffing will give me a larger effective volume to start with, would this mean less gain on the LT and less load on the amp?
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Old 10th April 2004, 12:27 PM   #24
michael is offline michael  Australia
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I have been modelling in WinISD and cannot recomend the Tempest in 62l, it simply has a vey limited low end, LT or no LT, the power it takes to reach a said SPL is the same.
I would not rely on electonics this much when there are much more practical solutions.
My suggestion is an adire DPL12, it will have slightly higher low end efficiency than the Tempest, though much less at 50hz up where it is not going to be used anyway.
With my suggestion you will not need as much power nor will you need a LT. Not to mention that the DPL is a more advanced and better constructed driver than the Tempest.
IMO an LT should only be used when a more economical solution can not be found.
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Old 10th April 2004, 12:48 PM   #25
Eva is offline Eva  Spain
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Contrary to the popular wisdon, I would recommend tuning the current box to about 25Hz, reducing the Qb to about 3-5 and then applying custum parametric equalisation to flatten the result [depending on room gain]

Low-Q too-low-tuned reflex enclosures have the same transient response as closed enclosures with moderate Q but higher SPL capability in the lower octave. Knowing this fact, it's nonsense to insist in using closed boxes and huge Xmax drivers with very low efficiency powered by 1KW amplifiers to get just 110dB SPL

To reduce the Qb of a reflex enclosure to make it more sealed-like simply add stuffing to the box or place the reflex mouth closer to the back wall and/or in a corner of the enclosure. Reducing the Qb widens the frequency range where the reflex resonates and thus reduces required cone excursion to half or less in that range
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Old 10th April 2004, 05:26 PM   #26
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Quote:
Originally posted by Eva

Low-Q too-low-tuned reflex enclosures have the same transient response as closed enclosures with moderate Q but higher SPL capability in the lower octave. Knowing this fact, it's nonsense to insist in using closed boxes and huge Xmax drivers with very low efficiency powered by 1KW amplifiers to get just 110dB SPL
Eva,

To clarify, is the following statement capture and extend what you are saying:

In the frequency range above the port tuning frequency the group delay etc. of the subwoofer is nearly the same as a closed box, so if you can tune the box low enough you get good transient response in the music range.

Group delay can get really "loose" around the port tuning area but there is a case for "who cares if rumble, avalanches etc. are not tight.

One consideration is that the excursion may be an issue as it rises dramatically below the port tuning frequency, but if it is below the interesting frequencies it may not be an issue.
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Old 10th April 2004, 06:04 PM   #27
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Quote:
Originally posted by michael

My suggestion is an adire DPL12, it will have slightly higher low end efficiency than the Tempest, though much less at 50hz up where it is not going to be used anyway.
With my suggestion you will not need as much power nor will you need a LT. Not to mention that the DPL is a more advanced and better constructed driver than the Tempest.
IMO an LT should only be used when a more economical solution can not be found.
The DPL12 does model nice in the 62l box. As you say although it is lower efficiency in general (could require twice the power in some situations) in this box size and desired frequency range it is more efficient, as is the Shiva. The Tempest in this small box size will require about 4 times more boost in the low 20-25 Hz range than the DPL12.

The DPL12 still rolls off less in this box as does the Shiva, but less so than the Tempest.

On the other hand all of these options (Tempest, Shiva, DPL12) work fo him as long as the SPL requirement is low.

Pretty much it depend on what he might want to do with this driver in the future, say in a bigger box.

It appears to me if he is listening to a movie and the level is say 94 dB for his mains (pretty loud), to match this with the Tempest/LT would take about 50 watts of power to be -3 dB at 22 Hz Q .8

I am considering a similar situation myself and this discussion has got me thinking about the DPL12 with LT. I perhaps would end up with the Shiva though because it is less expensive and I just think it would be fun to make one of those 7-8 ft Sonotube subs with it sometime.
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Old 10th April 2004, 08:46 PM   #28
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Group delay and cone excursion behavior below Fb are entirely dependent on Qb

Bass reflex systems with very low Qb [let's say 3] and small boxes can be tuned in the lowes part of the 'music range' without having much worse group delay than a sealed box or the cone excursion increasing too fast below Fb

The drawback of doing so is that there is no efficiency improvement over a sealed box, frequency response is almost the same [maybe 1dB boost] but SPL capability is increased and cone displacement distortion is reduced

This allows to extend the output from cheap drivers, high efficiency low Xmax drivers or even wideband drivers

I've used this technique very succesfully in custum-built car-audio systems with 6th order bandpass subwoofers and ports radiating into the cabin [formulas for tuning no longer work on these circumstances and it must be tuned empirically]. This kind of subwoofers have to be designed to have 12dB/oct rolloff below about 60Hz to get an acceptable respone inside the car. I use a small low Qb reflex rear chamber tuned to about 33-37Hz to maximize SPL capability and still get the 12dB rolloff below 60Hz. It's easy to get 120dB output [35-120Hz] from an old 8" driver with +-3.5mm Xmax with just 150W in that kind of enclosures and cone excursion tends to be really small

Same principle could be applied in a room using wall or corner loading with a 12" or bigger driver
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Old 10th April 2004, 10:07 PM   #29
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Quote:
Originally posted by michael
I have been modelling in WinISD and cannot recomend the Tempest in 62l, it simply has a vey limited low end, LT or no LT, the power it takes to reach a said SPL is the same.
I would not rely on electonics this much when there are much more practical solutions.
My suggestion is an adire DPL12, it will have slightly higher low end efficiency than the Tempest, though much less at 50hz up where it is not going to be used anyway.
With my suggestion you will not need as much power nor will you need a LT. Not to mention that the DPL is a more advanced and better constructed driver than the Tempest.
IMO an LT should only be used when a more economical solution can not be found.
Michael,

Thanks for your comments. Any idea on pricing and availability of the DPL12? Acoustic Concepts don't have it on the Adire price list they sent me.

I will do some more modelling of both 12" and 15" drivers. I agree that a 12" driver would work better in my box size with or without LT.

How could I model the effect of stuffing the box, I have heard or read the effective volume of a stuffed box is about 1.4 times the actual volume??

To put my SPL requirements in perspective, when watching "The Two Towers extended edition" last night the wife insisted on the volume being turned down to "what did he just say?" levels. Fortunately she is not always home when I use the HT/music system . I am looking for deep and accurate reproduction of bass, not necessarily very loud bass.

One alternative I am now considering is to build with a 12" driver tuned to deliver between 20 - 40hz which is below the response of my main speakers. If I find I don't get enough SPL I could build a second identical sub to boost the SPL's (by 6db I have read?). After all this is costing me alot less than buying a A$2500 commercial unit with the spec's I am looking for and the one I am building fits perfectly into my existing cabinets to integrate with other components.

Ozynigma
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Old 10th April 2004, 10:37 PM   #30
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the DPL is cheaper than the tempest, ast time i checked with john at AC it was 300 plus gst. so a very good price for a driver of its kind.
Some food for thought, my sub is capable of 105db of output from about 20hz and up and to me it does not seem all that loud at all.
The lower the frequency the louder it needs to be for it to have the same impact. i am currently designing a sub to be 112db capable from 25hz and up. this way i will be getting the low punch i am after, if this does not satisfy me i will build a horn, capable of nothing less than 130db.
My point is that you should not aim low, set your sights high otherwise you will not be satisfied, 95db is not as loud as it sounds.
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