Dual Voice Coil Subwoofer Question

[Kurt 3,222]

I have a question about a Dual Voice Coil subwoofer driver.  I came across a sub driver that a friend had tried to build into his son's car... (he failed, mainly due to lack of motivation :)).  It's a Dayton Audio 10" sub driver with Dual Voice Coils. I looked up the p/n... they go for $225, and have good reviews.  So, I'm tempted to play with it.  But, I have never dealt with a DVC driver.  What's the advantage of having two voice coils?  I know that you can change the impedance of the driver by wiring the coils in series vs. parallel.  Other than that... is there any other potential advantage?  If I had an amp that was stereo output only, could I feed left side output into one coil and right side into the other (or, would I even want to do that?).  Or would it be better to feed the sub mono and wire the voice coils together (in series or parallel).  Thanks for your thoughts.

[Nahash5150 10,984]

DVCs simply allow for multiple wiring configurations to adjust impedance. If you parallel the VC's together - you'll get half the total impedance of the coils so if they are both 8 ohm, you'll make it into a 4 ohm driver. You can wire in series to double the coil impedance - so 16 ohm with two 8 ohm coils.

 

You can also wire each channel from a stereo amp to each coil. Hopefully, you run a mono signal into the channels so you don't get weirdness.

 

They don't 'sound better' than SVC drivers or have any other real advantages other than wiring configuration flexibility.

[Will Meyer 2,422]

The dual VC subs worked like a mixer. You'd feed the Left speaker lead into one coil, the Right into the other coil, and your output becomes mono - a homogenization of both channels.  Obviously polarity is important so the signals don't cancel each other.  Many of the home passive subs use this methodology. 

[Kurt 3,222]

Thanks, guys.  That's helpful.  Much appreciated.

 

[straylight 395]

 

One possible advantage of DVC subwoofers is the ability to drive the subwoofer with more power and spread the drive wattage across two voice coils instead of just one. Will this make a difference in bass dynamics or perceived quality of sound output?  That would likely depend on your particular subwoofer design. Its easy to find out though...just drive it with one channel (L) of a stereo amp and listen....then change over to driving it with two channels (L+R with mono input) to hear the difference and let us know what you hear.

 

Some SW models might perform better with two channels driving them but others may not. The back EMF of two channels may do a better job of controlling the SW driver movement. However the damping factor of the amplifier may play a bigger role in the SW sound than the number of channels you drive it with.

 

Edited June 17, 2023 by straylight

[Nahash5150 10,984]

Sorry - amplifier DF plays very little role in the response of a mechanical driver. The method of calculating DF (driver impedance/amp output impedance) has been debunked many times as a reliable statistic in determining the effectiveness of an amplifier to 'control cone movement'. There is almost no difference between a DF of 20 up to Infinity as far as the entire system is concerned (cable resistance, internal impedance, variable frequency impedance, imaginary resistance, etc).

 

http://linea-research.co.uk/wp-content/uploads/LR Download Assets/Tech Docs/Damping factor debunked -01a.pdf

 

https://en.wikipedia.org/wiki/Damping_factor

 

It's also easy to 'fudge' an amp's rated damping factor with negative feedback, which can make the output impedance look vanishingly small, but in real world applications can cause significant distortions and non-linearities.

 

Furthermore, it's typically desirable to drive a loudspeaker with a system that looks more like a current source (high output impedance) since the motor driver of a loudspeaker is an inductor, which responds well to current, not voltage - ergo 'the tube sound'.

 

 

All this should help indicate how complex the relationship between amplifier and speaker really is. There just isn't any specs that will break it down so you know what amps should drive certain speakers. There's a general idea, but in no way can one simply rely on such things as 'high DF' to determine if a certain amplifier can effectively drive a certain configuration, or that by adjusting the DF somehow you can you expect a better response.

 

 

[straylight 395]

On 6/18/2023 at 9:29 AM, Nahash5150 said:

amplifier DF plays very little role in the response of a mechanical driver...the effectiveness of an amplifier to 'control cone movement'

 

On 6/18/2023 at 9:29 AM, Nahash5150 said:

All this should help indicate how complex the relationship between amplifier and speaker really is. There just isn't any specs that will break it down so you know what amps should drive certain speakers. There's a general idea, but in no way can one simply rely on such things as 'high DF' to determine if a certain amplifier can effectively drive a certain configuration, or that by adjusting the DF somehow you can you expect a better response.

 

Sorry for not replying sooner but I have been away.  Judging by the links you have provided and your well referenced reply we can probably both agree that the topic of amplifier-loudspeaker interaction is very complicated and perhaps one of the least understood areas of audio. So its a great topic to debate on the forum. After reviewing your first reference which takes a position to debunk the connection between DF and controlling cone movement I may have a tendency to agree with you on that particular point. However that does not mean DF is unimportant to the perceived sound of a loudspeaker or subwoofer.

 

The following is taken from the Wikipedia link you provided on DAMPING FACTOR:

 

"John Atkinson and Stereophile have recognized the importance of amplifier damping factor, and have made the use of the simulated loudspeaker load a routine part of their measurements of amplifiers. It is clear from the various amplifier frequency response curves that low damping factor values result in significant changes in the frequency response of the amplifier in a number of frequency bands. This will result in broad levels of sound coloration that are highly likely to be audible.

 

 "the amplifier with the low damping factor is acting more like a graphic equalizer than is the amplifier with the moderate damping factor."

 

"Some amplifier designers, such as Nelson Pass, (of Threshold) claim that loudspeakers can sound better with lower electrical damping, although this may be attributed to listener preference rather than technical merit."

 

The fact that both Atkinson and Pass take up opposite positions on the DF issue seems to indicate that despite their differences they at least each believe it is very important to the sound produced by the amp-speaker combination.  I too have heard the bass related difference they talk about between low damping factor and high damping factor amps. Tube and transistor amps have widely different DF characteristics (yes, among many other differing characteristics) . Although this may have nothing to do with the effectiveness of an amplifier to tightly control cone movement the DF related EQ coloration is nonetheless still present in the amplified signal and therefore audible to the listener. 

 

One might even  go as far as to say that perhaps the 'graphic equalizer effects' or 'tone alteration' produced by low damping amps might tend to make the listener hear or perceive a less tight bass response than a high damping factor amp due to addition bass coloration peaks that are artificial and an artifact added to the original bass output in the low DF amp.  

 

Unless you have something else to add I'll respectfully stay with my original statement to Kurt ..." However, the damping factor of the amplifier may play a bigger role in the SW sound than the number of channels you drive it with."

 

Edited July 17, 2023 by straylight

[Nahash5150 10,984]

There's nothing to debate. You just compared opinions to actual science, and that's apples and oranges.

 

Audio myths die hard, and DF as a basis for quality is one of the most prevalent myths there is.

[Kurt 3,222]

Thanks, guys... this is all very interesting.  I'm learning from everyone's comments.  I was able to put the driver in a cabinet and test it out.  I tried running it as you would with a conventional one amp/2 speaker setup- left and right channel from amp feeding separate voice coils.  And, I tried running the voice coils in series with a mono input and lastly I tried the running the voice coils in parallel with a mono input.  I used the same amp (M1.0t mkII Opt 2) for each setup.   Honestly, there was very little difference in sound quality.  If I had to pick one setup over the other, I'd pick the conventional setup for a 2 channel amp feeding the separate voice coils.    So, I think that's how I will setup the final configuration.   I'll post pictures of my project once I get to finishing the cabinet....... that may be a while down the road.  I've got lots of projects starting to back up on me, lol!  Thanks again for all the help.

[straylight 395]

On 7/17/2023 at 8:10 AM, Kurt said:

I'd pick the conventional setup for a 2 channel amp feeding the separate voice coils.

 

This has also been my experience with dual voice coil woofers and somehow using those two channels seems to make it a bit more dynamic than when driving with one channel only.

 

I have owned Bob's Sunfire True Subwoofer EQ...with its built in EQ, passive radiator and 2700 watt amp for many years now...its a killer unit. There is nothing else that can rumble the walls for movie soundtracks or stereo listening. Just got it back after recent repair at Deltronics. 

 

[straylight 395]

On 7/17/2023 at 6:36 AM, Nahash5150 said:

You just compared opinions to actual science, and that's apples and oranges.

 

DF related changes in bass EQ response reported by Atkinson were measureable as several db over a broad range of bass frequencies (especially at or near the system resonant frequency)...therefore audible...not just opinion or myth. 

[Nahash5150 10,984]

On 7/20/2023 at 4:46 PM, straylight said:

 

DF related changes in bass EQ response reported by Atkinson were measureable as several db over a broad range of bass frequencies (especially at or near the system resonant frequency)...therefore audible...not just opinion or myth. 

 

Link to this article please.

[straylight 395]

https://en.wikipedia.org/wiki/Damping_factor

[straylight 395]

Look at 'In practice' section of link above. 

[Yamacarver 853]

The Carver challenge and damping Factor. I have a question. When Bob nulled his amp against the tube amp, did they wind up with the same damping Factor?

Remember the null test was successful when the speaker didn't move and therefore cone control was not a factor.

And another question, has anyone made a hybrid amp, ie solid state with output transformers or a tube amp with power transistors?

[straylight 395]

On 8/10/2023 at 10:02 PM, Yamacarver said:

The Carver challenge and damping Factor. I have a question. When Bob nulled his amp against the tube amp, did they wind up with the same damping Factor?

Remember the null test was successful when the speaker didn't move and therefore cone control was not a factor.

 

And another question, has anyone made a hybrid amp, ie solid state with output transformers or a tube amp with power transistors?

 

All very good questions.

 

The McIntosh amp you see below is a MC352 stereo amp designed by Gordon Gow (one of the founders of the McIntosh company ) that has both solid state transistor outputs and also output transformers (look for them on the right and left in photo right behind the faceplate). They are bifilar wound transformers. Amp has 4 separate amplifier circuits in it. Each amp section handles 1/2 of the musical wave (top vs. bottom) and the trannies are some of the finest sounding transformers in production today.  In fact there are lots of McIntosh amps and perhaps other brands that have the same configuration, so yes it has been done. Its an incredible sounding amp and although it does not sound like a tube amp it is very smooth and clean when you listen to it even at ear blistering levels. Listening fatigue is very low even after hours of listening.  I believe this is attributed to the quality of the trannies and their bifilar nature. It is the most expensive type of transformer to manufacture. 

 

 

Regarding the 'cone movement' and 'Carver Challenge' Bob told me that before he even entered into the challenge he had already duplicated the null matching in his own lab.  But he was also using an oscilloscope and perhaps other tools to monitor the difference signal between his amp and the challenge amp. So he probably achieved the 'least' difference in speaker movement (or oscilloscope trace difference) because getting 100% null is probably near impossible. The trick is to get it just below the level of human perception of the difference. So this does not not necessarily mean the amps had the same damping factor at all.  In fact it would be highly unlikely that they had exactly the same damping factor but the null process may have assisted in reducing the overall difference between them somewhat. Remember the 'cone control' for the null test is less about cone control and more about nulling the difference signal between amps....you are using cone movement (or oscilloscope trace) to detect the amount of difference...and you might just have to ask Bob for a definitive answer on that point. It would be a very interesting result if the entire null process made the damping factors equal...so I'm not ruling that out because it would be very interesting to consider but I suspect there is much more at play here between amps than just damping factor (like significant distortion products, transient response characteristics and phase related anomalies in the two amp signals).

 

Regarding your last question tube amps have been designed WITHOUT output transformers but the tubes are a special type and only work in circuit designed to accept them. I have been told that these amps have a 'live' and 'zippy' sound, not at all like the smoothness of tubes.  But they can operate completely devoid of matching output transformers.

 

A good example is the Futterman OTL Amp:

https://jacmusic.com/techcorner/ARTICLES/English/Harvey-Rosenberg/futterman.htm

 

BTW - I don't think you can build a tube amp with power transistors - its a mismatch from the start since circuit-wise they each have very different operational requirements. However you CAN build transistor amps with MOSFET transistors which sound more like tubes than transistors because their distortion and clipping characteristics sound more tube-like.

 

 

Edited August 12, 2023 by straylight