Refurb/Rebuild passive subwoofer?

blownrx7

blownrx7

Audioholic
I have a pair of ACI Saturn subwoofers that I purchased/assembled in 1990. I initially used them with a pair of Dahlquist DQ-10's and a Audio Control Richter Scale Series III crossover/equalizer. Each sub has 2-12" drivers arranged in a push-pull arrangement at the bottom of a tall (~4 ft) column . They were great for music but recently got a little out of sorts when I pressed them into service for the HT stuff. Lo and behold I discovered that the woofer surrounds were laying at the bottom - disintegrated. :eek:
Right now, I am going the cheapest route possible and refoaming the surrounds. But, longer term, I was wondering if I could reuse the cabinets and replace the drivers or even make them active subs....
The cabinets are approximately 13.5x14.5x 35" tall! They are extremely well-built (1" walls) so I feel "re-using" them is a viable option.
I was hoping some of you knowledgeable types might make a suggestion for my next step?
Stay with the refoamed woofers?
Put in new drivers? What are the popular/desired/best for low freq etc?
Stay with the push/pull configuration or go with std single driver?
Go active? Of course that opens up a whole buch of options.
My budget? Hmmm. I guess about $1000 to redo both units.
Thanks in advance for your help!
 
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WmAx

WmAx

Audioholic Samurai
Using the parameter limitations of your cabinets, use a program such as WinISD to plug-in the T/S parameters of different woofers and find one that meets your preferences. A push/pull configuration provides for a decrease in linear distortion as is cuased by assymetrical behaviour of the drivers motor as it incurses vs. excurses. The operation of both driver motors in opposite states simultaneously serves to balance the non-linearities at moderate to hi incursion/excursions. However, the effectivness of such an execution is pointless with many of the premium drivers available today that feature fine quality motors that produce distortion products that are well below human detection thresholds even at moderate SPLs(and some that can remain linear at very high SPL but these are expensive). However, most of these modern drivers tend to have relativel low overall Q and VAS parameters, therefor the enclosures that you have would be too large unless you blocked off part of the internal volume. Since you have push-pull setup, I would probably use Peerless XLS drivers(very good drivers(relatively linear motors for very good price)) along with passive radiators and block off part of the internal volume in order to achieve the optimal internal volume. This is a cost-effective solution that would yeild high-quality results. If you do not already have a parmetric E.Q., I would suggest adding one so that you can increase the in-room response quality by reducint the amplitude of standing-wave resonances at the listening position. This would be the single largest improvement in sound quality for the bass response. You can aquire a fine unit for only $130 USD such as a Behringer Feedback Destroyer series digital parmetric. The E.Q. on that Richter xover is 1/2 octave resolution. INsufficient precision.

-Chris

blownrx7 said:
I have a pair of ACI Saturn subwoofers that I purchased/assembled in 1990. I initially used them with a pair of Dahlquist DQ-10's and a Audio Control Richter Scale Series III crossover/equalizer. Each sub has 2-12" drivers arranged in a push-pull arrangement at the bottom of a tall (~4 ft) column . They were great for music but recently got a little out of sorts when I pressed them into service for the HT stuff. Lo and behold I discovered that the woofer surrounds were laying at the bottom - disintegrated. :eek:
Right now, I am going the cheapest route possible and refoaming the surrounds. But, longer term, I was wondering if I could reuse the cabinets and replace the drivers or even make them active subs....
The cabinets are approximately 15x15x ~4 ft tall! They are extremely well-built so I feel "re-using" them is a viable option.
I was hoping some of you knowledgeable types might make a suggestion for my next step?
Stay with the refoamed woofers?
Put in new drivers? What are the popular/desired/best for low freq etc?
Stay with the push/pull configuration or go with std single driver?
Go active? Of course that opens up a whole buch of options.
My budget? Hmmm. I guess about $1000 to redo both units.
Thanks in advance for your help!
 
gregz

gregz

Full Audioholic
I second WmAx's sentiment of ditching the push/pull configuration in favor of a simpler (and more efficient) alignment using a quality driver.

As for your box volume, there are several aligments that can make use of all that volume and then some. Your enclosures are anywhere from 3 to 4 cubic feet in volume depending if the dimensions you gave are interior or exterior measurements. With a single 12" subwoofer in each box, you could go with:

a) Sealed box with Q=.707 (low, TIGHT bass, slow low frequency rolloff)
b) 4th order Butterworth ported enclosure (EXTREMELY low bass response)

Out of the two alignments above, for any given speaker the sealed box will be smaller than the 4th order Butterworth ported. Many, many 12" drivers will need between 3 to 4 cubic feet for one of these alignments (rarely both).

What's more, with the sealed box, you can usually change the volume by +/- 20% and still get results close to your goal.

One more link to add to Swerd's links is:

http://www.carstereo.com/help2/Articles.cfm?Car_Audio=Subwoofer Box Volume Calculator
 
blownrx7

blownrx7

Audioholic
Repair/Refurb passive sub

Thanks for all the info. I am now trying to do my homework. BTW, I went and measured rather than guesstimate ( a bad thing to do...) and the dimensions are 13.5 x 14.5 x 35 with 1" thich walls. That gives me appx 2.7 cu ft of internal volume.

I did post on other lists to get input and I got a number of suggestions (see below):
I also contacted ACI and they recommended use the current ACI Titan sub with their active amp - no need for the push-pull configuration anymore, I guess. Only problem is that they are asking more than my budget - they are offering to supply Titan drivers, Titan amps, proper amount of fill along with calculating the correct volume.
So now, I have a bit of a dilemna. Do I:
1.Go with the quasi-factory recommendation (Titan driver and amp) OR
2.Keep the push-pull configuration and passive set-up using Titan drivers (W-1238) (a number of people (including ACI say push-pull is no longer needed) OR
3.Use one Titan driver and keep it passive OR
4.Use the Adire DPL-12 - is that a better alternative than the W-1238 sub?
5. Use the Adire DPL-12 and cut a hole to install a passive radiator as well

What about amplification? I am currently using 2 channels of my 250w/ch@8ohms amp(Parasound A51) to drive the subs and utilizing the HT processor (Parasound C1 - I got such a deal btw...:) for crossover duties. Is that acceptable or should I go with a subwoofer "plate" amp?
 
blownrx7

blownrx7

Audioholic
Repair/Refurb Passive sub

I downloaded the WinISD program - very nice. Thanks for the tip!
Truth be told, I am at a loss for the meaning of many of the terms.
But the frequency response plots say volumes.
I do have another question about the function of a passive radiator. What does it do? The WinISD doesn't seem to have it as a potential variable.
Is it really a vairiation on the vented design :confused:

I am beginning to lean toward a single driver replacing the "isobaric" setup (I did learn something from WinISD - what I called push-pull is called isobaric in speaker-ease). For now it looks like keeping my external amp to keep my costs down.
 
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WmAx

WmAx

Audioholic Samurai
blownrx7 said:
I downloaded the WinISD program - very nice. Thanks for the tip!
Truth be told, I am at a loss for the meaning of many of the terms.
But the frequency response plots say volumes.
I do have another question about the fuction of a passive radiator. What does it do? The WinISD doesn't seem to have it as a potential variable.
Is it really a vairiation on the venterd design :confused:
PR design is very similar to a vented enclosure. I suggested PR because I thought you had two speaker holes in each cabinet......

I am beginning to lean toward a single driver replacing the "isobaric" setup (I did learn something from WinISD - what I called push-pull is called isobaric in speaker-ease) and keeping my external amp to keep my costs down.
This is logical -- no reason to add a PR if you only have on opening. The advantage of PR is lack of port noise as compared to a vented design(but a well iplemented port will not have any audible problems in music playback) and a PR is a logical choice when one desires a ported alignment that requires a port length that is too long to execute.

-Chris
 
T

Transducergeek

Enthusiast
RE-foam, it's cheap, it's fun! I have extra surrounds, I will sell super cheap..

Hello, I am an experienced Re-foamer... have done 30 plus now.. I have some spare 12" foam surrounds from a bulk buy. I will sell them to a forum member at discount at $11/pair. This is around 1/2 the price of other suppliers and are the same thing they sell.. except I dont ship glue, that you can easily obtain locally. Or I can do the work for you, but the shipping is a cost to consider. I will do them for forum guys for $20 per speaker. I have done JBL AR Infinity Bose Advent EV even my old Dahlquist DQ-10's! Let me know what you want to do..RE Transducergeet
 
T

Transducergeek

Enthusiast
I also have a pair of unused 12" woofers in the box if you want to just drop them in.

I have a set of never used 12" Pyle brand model PLG 12 chinese made "car audio" type woofers. I don't know if these interest you. But would be cheap, I will sell both for $60. Around 1/2 price. Plus whatever shipping is.. I never did finish that project, I tested them and they work fine, then re-boxed them, I am in LA.
 
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D

dan_wilkinson

Audiophyte
Optimal subwoofer enclosure volume?

gregz said:
What's more, with the sealed box, you can usually change the volume by +/- 20% and still get results close to your goal.

One more link to add to Swerd's links is:

http://www.carstereo.com/help2/Articles.cfm?Car_Audio=Subwoofer Box Volume Calculator
Gregz, i assume you find the box size calculator on the quoted website to be reliable? I find it interesting that they do not state this "golden ratio" which they use (although i guess you could calculate it).

My situation is that i have an active sub (a cheap one), and i am considering building a box which would be suitable dimensions for the boot of a car, and fitting it with the woofer from my active sub (wired to some terminals on the side/back). still undecided on sealed/ported and curious at to whether this changes optimal box volume.

Also, i would like to know more about PR designs... as in what material are they made of, what shape/dimensions? i have no idea about them and i think the only place i might have come across something like a PR enclosure was the "Woox" system on some cheapo Phillips "mini hi-fi".

Your knowledge greatly appreciated,
Dan
 
WmAx

WmAx

Audioholic Samurai
Gregz, i assume you find the box size calculator on the quoted website to be reliable? I find it interesting that they do not state this "golden ratio" which they use (although i guess you could calculate it).
The golden ratio is irrelevant in this case of low frequency application(s) unless the structure is relatively huge. The golden ratio is a method used to evenly distribute standing wave modes(resonances caused by 1/2 wavelentgh equivalnency of a dimension) within an enclosure. Considering the relative wave lenghths in air at frequencies <100Hz, it is just not an issue under normal circumstances. Besides, the internal standing wave resonances due to parrallel wall distance even in a full range system are secondary consideration -- the main issue here is the type and amount of acoustical dampening material used. The only time this is really troublesome is when dealing with a midbass/full range in a ported or passive radiator alignement. These alignements depend on maximum efficiency of the box tuning frequency(Qb). As you increase the internal dampening materials the coupling efficiency is lowered considerably, resulting in lowered amplitude resonse of the port or PR. In these cases, a design optimised to distribute the standing wave modes that would color the midrange is required in conjunction with a stragetically chosen level/placment of dampening materials.

-Chris
 
HowY

HowY

Audioholic Intern
Woooaaahhhhh.....

First things first.. it's an ISOBARIC SUB this is perfectly
fine and is PASSIVE because the natural driver roll off
and the out of phase wiring in concert with the trapped
volume of air work WITHOUT any passive crossover.

ANY passive (non amplified) sub can become an active
one just by adding a plate amp and removing to old electronics.

It's unlikely you'll EVER know the specs of the original drivers
unless you can properly test them and knowing the OHMS at
the crossover point and the q's of the driver would be critical
for building the box or verifing it's parameters to the drivers.

Get the repair kit from PE. I just did 2 15" drivers and the
kit is like 25 bucks... glue shims caps etc expect a few
hours a driver for the first time.... clean clean clean!

I've converted several passive (non amplified) subs to active
ones (with plate amp) no biggie - no brainer...

however in an iso configuration the drivers are out of phase
which might make for a wrinkle or two with wiring them up
correctly...

FWIW
 

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