Building powered subwoofer for Christmas, recommendations?

[MrPirate2882]

As you might guess, I always tend to over think things.

I hate to do this to you since it isn't your sub, but if you were going to choose, would you do the ported 12" quatro or the sealed 15" quatro?

I doubt that the majority of the sub systems I have heard were all that well engineered, so I really have very little "hearing" experience between the two.

Decisions, Decisions...

 

[TLS Guy]

As you might guess, I always tend to over think things.

I hate to do this to you since it isn't your sub, but if you were going to choose, would you do the ported 12" quatro or the sealed 15" quatro?

I doubt that the majority of the sub systems I have heard were all that well engineered, so I really have very little "hearing" experience between the two.

Decisions, Decisions...

I know nothing about your musical preferences. But since you ask I will give you my opinion, and that's all it is. You have to understand you are talking to an old guy who has disliked the pop culture since early childhood. My dislike continues to increase. After centuries of wonderful tasteful art, and yes there are huge quantities, we moved into the twentieth century, "The Age of Ugliness." At least that is what I call it. I suspect this was a reaction to the upheaval of two world wars, especially the first. The first World War changed European society, dramatically and for ever. This only intensified after the second, were it also had a huge impact in North America also. What I'm getting at is the fact that there is more beautiful music composed over the centuries than any one individual can get to know in a lifetime. So obviously my choice would be the sub that would be the least intrusive, and give the performance back as much of it's natural balance as possible.

Now your biases will likely be very different. I would pick the closed box, but you might not. All I can do is tell you the technical details.

Now between 40 and 120 Hz both subs will generate a sound pressure level of 113 db and that's loud. Now at 30 Hz the closed box sub is about 6db down. However at 18 Hz they are both 18 db down. That is because the closed box is second order roll off and the vented fourth.

Now you can EQ the closed box. Now it happens that the bass boost of this plate amp is perfect to Eq for the closed box sub all the way to 20Hz.

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=300-805

There is no free lunch, because it will take more power from the amp, and above 99 db you will exceed the mechanical limits of the driver. So with Eq the closed box sub will generate a sound pressure level of around 99db.

If you use bass boost on the vented box, it will just cause distortion and may damage the driver.

If you do build the closed box, I would make it about 2.3 cu.ft. to allow for the volume of the driver, and braces etc.

So you will have to make your mind up about what sort sound you want from your sub.

 

[jinjuku]

Also, you may want to call Parts Express and see if they will sell the 12" DVC subwoofer for the same price as the Quattro.

I built a dual 12" Quattro based sub (vented) and a month and a half later they have a sale with the 12" DVC for $86 instead of $109. AHHHH! tear my hair out sometimes.

 

[MrPirate2882]

So you will have to make your mind up about what sort sound you want from your sub.

Interesting post. Musically, This sub will mostly be asked to play 70's style rock, as this is the era my dad came out of, sometimes 80's rock.

However, it won't generally be used for much music, only action movies.

 

[TLS Guy]

What favor do you like and DVC?

Then you have to decide what flavor you like like your bass. The tuned ported enclosure will come in a fuller more resonant flavor. The sealed will come in a tighter flavor, like a drum with a tight skin.

The 70s rock is interesting. I was heavily involved in audio back then, and designed some speakers for recording studios in Western Canada, among other things. I do remember the rock enthusiasts of that period tended to favor the sound of sealed woofers. The Altec Lansing 411 8A in a sealed enclosure being well favored. So I think that was likely the kind of sound they were after.

Jinjuku has made a comment about DVC drivers. For your application there is absolutely no advantage. The reason being the drivers are 4 Ohm and that is the optimal load for the amp you have selected. It seems there are a number of people following this thread, and some private messages, so I will go a little into the indications for the use of DVC drivers.

1). It gives you a choice of impedances. Say you have two voice coils of nominal 4 ohm impedance. You can use one VC and the impedance will be 4 ohm. You can parallel the coils and the impedance will be 2 ohm. The sensitivity will be up by 3db, but it will suck more amp power. You can put the voice coils in series and the impedance will be 8 Ohm and the sensitivity will be down 3db.

2). You can use the second voice coil for active or passive Eq of the step and diffraction losses of smaller bass/mid drivers in narrow fronted enclosures. This becomes a two and a half way crossover with one bass mid driver rather than two. So impedance is halved as the fill coil cuts in. There should be more of these dual voice coil bass/mid drivers around than there are.

3). If you make an integrated speaker, that can reach into the depths, and use a DVC woofer you have an interesting possibility. You can use one voice coil for the standard speaker, and your setting for the main left right speaker setting to large. You can connect the LFE channel to another amp and connect that to the other voice coil. Gary Gallo does this. For this reason I would like to see more DVC woofers around than there are.

You have to remember the hand off from subs to mains, is a crossover, with all the problems that that entails. Even with a lot of care, the chances of getting a perfect splice between sub and the other speakers is remote. Therefore I believe for best results the speakers should have a uniform +/- 3db response from at least 30 Hz to 20 KHz. They should offer a means of integrating the LFE channel. The center speaker should also be designed to splice correctly with the woofer. My speakers achieve this. Gary Gallo's are the only commercial speakers that I'm aware of that do this. There may be others but I'm not aware of them.

 

[MrPirate2882]

If it was going to be used for mostly music, then I think I would go for the sealed, as I prefer tight bass.

The ported will most likely do a better job with filling in the larger gap between the lowest lows and where his mediocre satellites cut off.

As for the fill, since it is to be minimal on the ported woofer, would it be better to use the egg crate type padding instead of polyfill? It would be easier to attach to the sides (with staples), but I don't know if it would have negative effects.

 

[TLS Guy]

If it was going to be used for mostly music, then I think I would go for the sealed, as I prefer tight bass.

The ported will most likely do a better job with filling in the larger gap between the lowest lows and where his mediocre satellites cut off.

As for the fill, since it is to be minimal on the ported woofer, would it be better to use the egg crate type padding instead of polyfill? It would be easier to attach to the sides (with staples), but I don't know if it would have negative effects.

I would use the Polyfill. Put in on with a little glue, but don't use too much, or it will soak into the fill and make it go hard.

I think you are all set now. Please let us all know how the project goes.
A very happy Christmas to you and your family.

 

[annunaki]

Dual voice coil woofers should ALWAYS be used with both coils receiving the same signal. You can use seperate amplifiers to do this but it gets pretty complicated. Manufacturers often state in the manuals for DVC drivers that both coils must be used at the same time.

 

[annunaki]

Use of polyfill in a ported enclosure has little to no benefit if the enclosure is properly designed for the driver. Lining the walls with it will not do much other than to perhaps lower any vent or mechanical noises from the driver. If the enclosure is braced properly there should be no resonances to try and damp given the bandwidth the driver is playing and the enclosure size.

 

[TLS Guy]

Dvc

It is absolutely not true that the voice coils have to receive the same signal. Garry Gallo does not do it in his highly touted reference speakers. I won the stereophile audiophile sound off some years ago with a pair of speakers using Focal dual voice coil drivers. There were two DVC drivers in both speakers. One coil in each driver carried the bass mid signal and the other coils in each driver the fill signal. There are lots of other instances also. Dual voice coil drivers open up interesting possibilities.

 

[annunaki]

My question is why would you want to do something so ridiculous as that? Wiring the coils in series or parallel and sending it the mid and bass signal achieves the EXACT same thing and there is less chance of issues developing from sending two different voltages into the speaker potentially counteracting each other.

 

[annunaki]

Dual voice coil drivers open up interesting possibilities.

They do in terms of wiring configuration either to a single amplifier, a stereo amplifer to one driver, or multiple drivers to a single amplifer, as was the original intent of the design.

Sending different signals to each coil that could be achieved by sending the combined signal to the speaker with the coils wired in parallel or series makes absolutely no sense. It does the exact same thing with 10x less hassle.

 

[TLS Guy]

My question is why would you want to do something so ridiculous as that? Wiring the coils in series or parallel and sending it the mid and bass signal achieves the EXACT same thing and there is less chance of issues developing from sending two different voltages into the speaker potentially counteracting each other.

Using the second voice coil for the passive fill circuit is a well established technique. There is only one amp. The bass/mid coil hand over to the tweeter, and is a normal two way crossover. The second coil is fed from a first order filter, typically one inductor and a zobel network. The turnover frequency is usually between 200 and 400 Hz. It works out very well indeed.

As far as using a coils for the LFE channel, I have never done that. The Gallo ref.3 speakers do. I can't see anything terrible about it from an engineering standpoint.

Here is the link, and I have copied the relevant passage about using the woofers second voice coil for the LFE.

http://www.roundsound.com/reference-3-speakers.htm

Combine Your Reference 3.1 Stereo Speakers with our Reference 3 S.A. Subwoofer Amplifier for the Ultimate
Stereo or Home Theater System

Reference 3.1 speakers are equally comfortable in either stereo or home theater configurations. The Reference 3 S.A. (subwoofer amplifier) is our 2 x 240 watt stereo amplifier which incorporates an active crossover/bass EQ option to extend the Nucleus Reference 3.1's bass response to a room-shaking 22Hz by driving the woofers' second voice coil directly. The combination of the Reference 3.1 stereo speaker and the S.A. subwoofer amplifier takes this home stereo system's unparalleled sound yet another step further, maximizing full-range performance with true stereo subwoofer bass extension from a small, unobtrusive package.

Gold-plated, all-metal binding posts ensure secure speaker wire connections, and the full-height removable grille cage with welded steel support members lends a more traditional appearance. In addition, each of your Reference 3.1 speakers undergo extensive computer quality control testing.

 

[annunaki]

I am not so sure that what is actually happening there. It looks to me like it is just a glorified bi-amping system for the subwoofer. I would like to see an actual wiring diagram on the speaker to verify what is being done.

If you are going to send one coil a signal from say 150hz-800hz and another coil 800hz-2,500hz why not send both coils a 150hz-2,500hz signal as it achieves EXACTLY the same thing. The use of all the extra crossover components is just a waste of money and audiophoolry.

 

[TLS Guy]

Still not understanding

It does not do the same thing.

Lets take the Eq circuit first.

Lets say coil one is fed a signal 20 Hz to 2500 Hz with second order crossover for instance.

Now lets feed coil 2 a signal 20 Hz to 250 Hz first order.

Lets do it all with a passive crossover, no biamping, then the second coil will start to augment the woofer output as the first order crossover shelves in. This is the same as a 2 1/2 way crossover with two drivers, but this does the same thing with on DVC driver.

In the Gallo ref 3, the first voice coil is fed the same signal as any 3 way design, and it is passive. Now lets take the LFE output and amplify it, and send it to the second voice coil. You now need no sub and have a properly integrated speaker. I can quite see why Mr. Gallo did that.

If you still don't understand, please send me a private message with your Email, and I will send circuits. I can't seem to copy circuits to these postings.

 

[annunaki]

Actually all you are doing is rolling off the response on the driver first order at 250hz and then steepening it up to a 3rd order at 2500hz. This can easily done by feeding both coils the same signal from a properly designed crossover. It is not a 2-1/2 way design because you are still using the same woofer cone with both coils attached to it. All it will do is create a dip in frequency response 1st order from 250hz on up to 2500hz (where the response will already be -18db because of the first order rolloff. However because you are sending the driver two different signals (fighting each other) it may only be down by 12db or so at 2500hz. Again, this can be achieved quite easily by sending both coils the same signal. It is useless more or less. Who wants the response rolled off that much through the lower midrange?

The other question is why is a 2-1/2 way crossover even necessary on a two way design with a woofer and a tweeter??? The only reason a 2-1/2 way was used is to lower the output level through the midrange when two mid/bass drivers are used with a tweeter in the same cabinet. It also helps cure lobing issues in MTM designs. Again this can be done easily by designing the right crossover and feeding both coils the same signal.

As for the Gallo design, that makes more sense, though I am sure the woofer is designed to operate that way and/or there may be a switch involved on the speaker to cut off power from the mid-high range amplifier still taking advantge of the internal crossover. Nearly all currently available DVC woofers are not designed to operate in this fashion.

 

[TLS Guy]

Incorrect again.

What you have written is absolute nonsense.

Small mid woofers in narrow fronted cabinets, suffer from diffraction loss at frequencies blow 500 Hz. This is a first order roll off. It depends to some extent on the step response of the driver, with some drivers being more prone than others. However the major determinant is the width of the cabinet. This determines the roll off frequency of the start of the diffraction loss. As an aside, Ted Jordan maintains that speakers should not have narrow fronts but wide ones. He has been right about an awful lot of things, and designed some of the finest moving coil drivers, including the Jordan Watts module back in the sixties. Diffraction loss is masked to a degree by reflections from room boundaries, especially in small rooms.

http://www.ejjordan.co.uk/

Anyhow, a common way of compensating for this is to use a second driver, with a first order filter, whose slope is the inverse of the diffraction loss. This results in a properly balanced lower midrange. There are numerous speakers on the market that employ this technique. As I have stated previously all narrow fronted speakers should be diffraction compensated.

Using the same circuit that would normally feed the second driver to feed the second voice coil of a single woofer amounts to the same thing, except that two woofers will reinforce the low bass better. However the method of diffraction compensation is basically equivalent whether it is done with two drivers or one with dual voice coil. I am certainly not alone in having used this technique. Focal of France used this in a line of speakers, and very successfully too.
I would bet there are others, but a lot of manufacturers who don't put their drivers on the OEM market, play their cards close to their chests.

In no way does this technique lead to any 18db dips in response, that is completely erroneous and has no basis in fact.

 

[annunaki]

What you are explaining is a diffraction compensation circuit. That is entirely different than what you describe in the previous posts. What you describe in your previous post is dual low pass crossovers at different frequencies and differing slopes. A diffraction compensation circuit acts similar to a passive, fixed frequency eq. I understand its uses and benefits. They do make a difference. AGAIN this can EASILY be achieved with a properly designed crossover and BOTH coils on the same signal. There is no need nor advantage to running a differing signal to each coil. As both coils are on the same former attached to the same cone. If both coils do not act in unison, they will counteract each other causing cancellation.

For all intents and purposes there is NO advantage to running both coils with different signals. There is nothing to be gained by doing it that can't be done with a properly and competently designed crossover system.

An inverse slope of diffraction loss is an eq as it boosts the signal, rather than rolling of the response. The way you explained it previously suggests a lowpass slope. If you were referring to a diffraction compensation circuit, I apologize. As stated above though, this can be done by sending both coils the same signal with a properly designed crossover.

 

[TLS Guy]

DVC and diffraction compensation

I stated in my first post about this topic under item 2 that this was for diffraction compensation! Here it is.

2). You can use the second voice coil for active or passive Eq of the step and diffraction losses of smaller bass/mid drivers in narrow fronted enclosures. This becomes a two and a half way crossover with one bass mid driver rather than two. So impedance is halved as the fill coil cuts in. There should be more of these dual voice coil bass/mid drivers around than there are.

The voice coils will not fight each other, unless they are wired out of phase, any more than two drivers will.

I realize sometimes you can achieve diffraction compensation in two way crossovers. However you are lucky when all th stars line up. You have to be able to start the woofer crossover very low down and still achieve good performance at crossover, especially smooth frequency response. SPL is better with two drivers or the dual voice coil technique. Admittedly the impedance drops and more power is demanded from the amp with either two driver or DVC solution.

Because of the problems of achieving diffraction compensation in most small two way speakers, very few are in fact diffraction compensated.

I can assure you the DVC solution to this problem works very well, if you have a DVC driver that is in other ways suitable. It is also a very simple solution, requiring at the most three components.

 

[annunaki]

I stated in my first post about this topic under item 2 that this was for diffraction compensation! Here it is.

2). You can use the second voice coil for active or passive Eq of the step and diffraction losses of smaller bass/mid drivers in narrow fronted enclosures. This becomes a two and a half way crossover with one bass mid driver rather than two. So impedance is halved as the fill coil cuts in. There should be more of these dual voice coil bass/mid drivers around than there are.

I apologize for missing the note of diffraction compensation.

The voice coils will not fight each other, unless they are wired out of phase, any more than two drivers will.

I realize sometimes you can achieve diffraction compensation in two way crossovers. However you are lucky when all th stars line up. You have to be able to start the woofer crossover very low down and still achieve good performance at crossover, especially smooth frequency response. SPL is better with two drivers or the dual voice coil technique. Admittedly the impedance drops and more power is demanded from the amp with either two driver or DVC solution.

Because of the problems of achieving diffraction compensation in most small two way speakers, very few are in fact diffraction compensated.

I can assure you the DVC solution to this problem works very well, if you have a DVC driver that is in other ways suitable. It is also a very simple solution, requiring at the most three components.

What do you mean when the stars line up? A diffraction circuit will either work or it will not. The amount of coils on the driver has nothing to do with that. Running the diffraction compensation circuit through one coil alone does not make much logical sense either. If you want to take full advantege of diffraction compensation it would make more logical sense to have it affect the driver through both coils utilizing the same signal.

Most small inexpensive two way speakers don't use dcc's because it costs more. For each pair, yes the cost is relatively low, but if you are building 300-400 pairs of them it gets pricey from a manufacturer's point of view. Others take enclosure design into account to help alleviate the need for their use. In a standard cabinet they can have much benefit.