[gkannan]

Car: Tata Indica V2

DIY Audio setup:
4-way quasi active with ALLO Class D low profile amps.

Source: Eclipse CD7200 MKII single din 3-way active head unit

Amplifier: DIY 7-channel amplifier built with three ALLO Volt+ amp TPA3116D2 stereo boards and one mono TPA3116D2 board.

Speakers:
Pair of Dayton Audio miniAMT tweeters
Pair of Dayton Audio 4 inch Reference 100-4 wideband
Pair of Dayton Audio 7-inch Reference RS180-4 midbass
Pair of Dayton Audio 7-inch Reference RS180-4 for subwoofer duty in isobaric configuration.

Kenwood KOS-300 for USB playback

Accessories: MX high grade banana plugs and n-tech 16awg speaker cables.
Quaden basic interconnects
4 laptop adapters. to power the four amplifier boards
12 volt to 220 volt (350 watt) converter to provide power to laptop adapters
Power and Ground wiring: Finolex 320 wires
Relay used for amplifier remote turn on from head unit

Design:
Tweeter and wideband fabricated in custom fiber glass enclosure in the dashboard
Carpet on entire dashboard to absorb sound waves and minimize reflection off windscreen.
Midbass fabricated into the front doors with fiberglass with two additional spacers for depth. Both doors properly damped with thick tarfelt sheets
No speakers in the rear except subwoofer in the boot.
Isobaric subwoofer with both driver cones facing each other and the outer one wired out of phase for a push pull configuration.

Interconnect wiring:
High out from head unit split to provide inputs to the amplifier boards powering the widebands and tweeters.
Mid out from head unit connected to amplifier board powering the midbass drivers
Sub Out connected to mono board to power the subwoofer

Crossover Points:
Tweeters passively high passed at 10 khz with capacitor
Wideband actively high passed at 315hz / 12db slope in the head unit
Midbass actively band passed between 315hz/12db and 63hz/18db on the head unit
Subwoofer actively low passed at 63hz / 18db slope on the head unit

All drivers time aligned and gain matched.
Entire tuning done by ears.

A sample of the sound quality recorded over phone mic

https://youtu.be/YiuAMQdgjes

Some pictures of the setup:
In order: Dashboard view, boot view, the Eclipse head unit, ALLO 7-channel amplifier build, Dayton midrange and tweeters, Dayton midbass, Dayton subwoofer, subwoofer design

[sandeepmohan]

Originally Posted by gkannan

Isobaric subwoofer with both driver cones facing each other and the outer one wired out of phase for a push pull configuration.

I've seen sub woofers faced back to back, inside the cabinet, not with one outside the cabinet, facing another driver.

How do you stand to gain the benefits of the external sub woofer facing another internal sub woofer in terms of moving air withing the cabinet?

Looks like a lot of work needed to sort out the acoustics for an Indica.

[gkannan]

Originally Posted by sandeepmohan

How do you stand to gain the benefits of the external sub woofer facing another internal sub woofer in terms of moving air withing the cabinet?
Looks like a lot of work needed to sort out the acoustics for an Indica.

The benefits of this design are
50% reduction in enclosure volume with higher power handling, lower distortion, lower group delay as compared to a single driver vented design.

To keep the drivers in phase in this design, they are wired in reverse with respect to each other. It results in halving the average impedance, in my case the impedance drops to 2 ohms (each driver being 4 ohms).
So I also get more power at half the enclosure volume.

These ALLO amps are quite low in power, but highly efficient Class D designs in a palm size board. They average at 15 watts RMS at 20 volts (output from laptop adapter) with peak power of 50 watts.
The mono board can do 30 watts nominal and around 70 watts peak at 2 ohms load.
These mono boards easily handle 2 ohm loads so the isobaric design perfectly suited my requirement.

The ALLO stereo boards cost Rs. 2300 each and the mono Rs. 1000. In effect I spent under 10k in building the 7-channel amp.

The entire setup was designed with efficiency and power handling in mind. The total load on the alternator is just around 15 amps.

Every car has acoustic challenges, the problem with Indica is limited door depth which can badly affect the performance of a midbass driver. But another advantage is cabin space, so I could fabricate the door design to compensate.
There is no space in A Panel for mounting bigger drivers, so I had to go for a dedicated enclosure in the dashboard which offers reasonable depth.
I have also played with the angle of the speakers in the dashboard to minimize reflections and improve directivity resulting in butter smooth highs even though the drivers are in an on-axis position.

[sandeepmohan]

Originally Posted by gkannan

The benefits of this design are
50% reduction in enclosure volume with higher power handling, lower distortion, lower group delay as compared to a single driver vented design.

Thanks for that detailed reply. I did read that the external sub woofer was wired in reverse phase. That is all good.

My question is more around how much additional bass or bottom are you gaining with this configuration versus just a single driver? Are you able to measure frequency response (I know this is a car)? I ask as the subwoofer is placed externally, facing another driver.

Higher power handling is the result of two drivers. This is understood. Quite obviously, two sub woofers mean they do not need to work (including the amplifier) as hard and that results in lower distortion.

I have seen a single sub woofer placed this way, with the magnet sticking out but not directly facing another driver. Trying to under the acoustical benefits of such a setup. If it leads to more quality bass, then all good.

[gkannan]

Originally Posted by sandeepmohan

Thanks for that detailed reply. I did read that the external sub woofer was wired in reverse phase. That is all good.

My question is more around how much additional bass or bottom are you gaining with this configuration versus just a single driver? Are you able to measure frequency response (I know this is a car)? I ask as the subwoofer is placed externally, facing another driver.

This design only reduces VAS by half and not the f/s, so the woofers cannot play lower i.e extend down the frequency response than as a single driver with the same port design.
What it however does is substantially improve the power handling in half the enclosure size, so the sub does not bottom out when it peaks with such low profile amplifier boards. This substantially improves the integration with the midbass, especially since the sub is in the boot.
For similar performance with a single driver I would have needed a more powerful amplifier.

By the way I at one time had the Morel Ultimo 12 inch subwoofer powered by a 1000 watt RMS monoblock in the same car, and later a Infinity Kappa 10 inch powered in bridged mode from a Pioneer 944 amplifier.

[navin]

Originally Posted by gkannan;4382364
Amplifier: DIY [B

7-channel[/b] amplifier built with three ALLO Volt+ amp TPA3116D2 stereo boards and one mono TPA3116D2 board.

Speakers:
Pair of Dayton Audio miniAMT tweeters
Pair of Dayton Audio 4 inch Reference 100-4 wideband
Pair of Dayton Audio 7-inch Reference RS180-4 midbass
Pair of Dayton Audio 7-inch Reference RS180-4 for subwoofer duty in isobaric configuration.

Interconnect wiring:
High out from head unit split to provide inputs to the amplifier boards powering the widebands and tweeters.
Mid out from head unit connected to amplifier board powering the midbass drivers
Sub Out connected to mono board to power the subwoofer

Crossover Points:
Tweeters passively high passed at 10 khz with capacitor
Wideband actively high passed at 315hz / 12db slope in the head unit
Midbass actively band passed between 315hz/12db and 63hz/18db on the head unit
Subwoofer actively low passed at 63hz / 18db slope on the head unit

Some pictures of the setup:
In order: Dashboard view, boot view, the Eclipse head unit, ALLO 7-channel amplifier build, Dayton midrange and tweeters, Dayton midbass, Dayton subwoofer, subwoofer design

Insane work.

Technically this is 4 way active even if you have used a passive crossover for the tweeter. I assume that you used a Passive Line Level (PLLXO) crossover for the tweeters. Did you roll off the wideranges electrically or did you just let them roll of naturally?

Any reason for you preference for Dayton over other brands like Vifa, SB Acoustics, SEAS, etc?

Any reason why you opted for the RS180 over the 225 (I understand that the 270 would have been too big)?

Also given that you were going active you could have used the RS75T as it has a more compact frame so the tweeter and fullrange could have been closer and you would have needed a smaller baffle.

We need more guys with this degree of passion. Reminds me of my younger days.

Originally Posted by sandeepmohan

My question is more around how much additional bass or bottom are you gaining with this configuration versus just a single driver?


I have seen a single sub woofer placed this way, with the magnet sticking out but not directly facing another driver. Trying to under the acoustical benefits of such a setup. If it leads to more quality bass, then all good.

Isobarik is not new. I first saw this in the early 70s when KEF had a speaker using 2x B139 (12x8" woofers) in an isobaric (equal pressure) configuration. The biggest reason for using this is to reduce the box volume thereby giving the system a lower Qtc.

There is only one disadvantage to isobaric. You do not gain (3db vs 6db) as much as you would have if you had put 2 woofers in a box but 2 woofers in a box would take double the volume (for the same Qtc and F3) not half. There is no free lunch.

[gkannan]

Originally Posted by navin

Insane work.

Technically this is 4 way active even if you have used a passive crossover for the tweeter. I assume that you used a Passive Line Level (PLLXO) crossover for the tweeters. Did you roll off the wideranges electrically or did you just let them roll of naturally?

Any reason for you preference for Dayton over other brands like Vifa, SB Acoustics, SEAS, etc?

Any reason why you opted for the RS180 over the 225 (I understand that the 270 would have been too big)?

Also given that you were going active you could have used the RS75T as it has a more compact frame so the tweeter and fullrange could have been closer and you would have needed a smaller baffle.

We need more guys with this degree of passion. Reminds me of my younger days.

Thanks Navin. Am I still young when looking at the other side of 50

To start with, I was running the setup with the same drivers in active mode except for the sub which was an Infinity Kappa with two Pioneer GM-X944 amps. My car which just completed 15 years, was no more able to take the load of the amps, so I had to do away with them and look for an power optimized solution when i chanced upon the ALLOs and this was the end result.

1. Eclipse CD7200 mkii: This head unit is the heart and soul of the setup. 3-way active, wide crossover options, individual gain controls, time alignment, clean high volt preamp output and a great DAC are some of its strong points.

2. Regarding the xo on the tweeters, it is just a nice little good quality capacitor. The attenuation is done on the ALLO board to gain match with the wideband. The Dayton miniAMT (air motion) has a high f/s of 5 khz, so it does not intrude much down the frequency band. I have crossed it at 11khz (6db), the crossover point was chosen based on the roll off of the Dayton RS100 wideband.
So the tweeter is literally quiet from 9 khz and down. It primarily gives airiness to the setup.

3. I find the Daytons good VFM for money. Superb build and more importantly, the drivers in the same reference series which share the same cone material, design and specs are very easy to work with.

The reasoning behind the choice of drivers: The Dayton RS180-4, RS100-4 go very well with each other. The RS180 is almost the perfect size for a car door.
The RS180 is a tough beast to tame in a 2-way when blending with a tweeter at LPF, but is composed as a 3-way where the LPF can be set low. Its low end performance is top class. At around 50 watt RMS and a decent spl, I found it is a good candidate for low profile Class D amps.

The RS100-4 is an absolute revelation. Given the right enclosure, its performance is aplomb. In my setup it is playing 80% of the octaves and blends brilliantly with the RS180 which falls in the same series. I have high passed it 315 hz (12db slope), so it playing somewhere from 200hz to around 14khz...the roll off starts from around 10 though, from where the tweeters take off.
Another big plus with the RS100 is its on axis performance. Detailed, good layering and separation without the high end fatigue. Its metal cone is another advantage in handling lows and at around 3 inches there is hardly any beaming. The phase plug design also helps in a big way.
Both the RS100 and the tweeters are placed close to one another and in a horizontal plane (I could not align vertically due to space constrain in Indica).

Since I could not go for mono block amps, I chose the half-palm sized TPA3116D2 mono board which pumps out around 70 watts at 2 ohms, 0.1% THD.
I had a pair of RS180 in hand, so studied how it could be used. Then I read on the various subwoofer designs and hit upon the Isobaric design. The RS180 specs were just too tempting not to try out. With two of them in parallel, I could get better power handling at 2 ohms from the TPA3116 board. The isobaric design also saved me space and it worked surprisingly well.

Regarding the RS75, the RS100 though needing a bigger enclosure, has a much superior performance at the low end without much compromise in the highs.

Overall it was money spent well, and I could increase the life of my car by another 5 years saving a few lakhs in buying a new one
So much so for a fund restricted audio maniac.

Note: You can just check the T/S parameters of the above drivers and their response curves and see that they match quite well. (It is available on Dayton Audio website).

Anyhow thanks for your kind words. At 53, it offers encouragement to the creaking bones.

Originally Posted by navin

There is only one disadvantage to isobaric. You do not gain (3db vs 6db) as much as you would have if you had put 2 woofers in a box but 2 woofers in a box would take double the volume (for the same Qtc and F3) not half. There is no free lunch.

There is no loss in gain when wired in parallel, and no addition either. VAS is halved. Power handling improvement is what I looked for as my amp was stable at 2 ohms.
I was restricted to size and choice of drivers due to the limited power in hand, so took this route.

[Prodigy07]

Kannan sir - Hats off for successfully executing such a complicated build

I'm still skeptical in going 4 way active with my Pioneer 80PRS!

OT - Is that song from a dedicated album of Rajesh Vaidhya's Instrumental? If yes, could you please provide more details?

[gkannan]

Originally Posted by Prodigy07

OT - Is that song from a dedicated album of Rajesh Vaidhya's Instrumental? If yes, could you please provide more details?

yes it is from Rajesh Vaidya's dedicated instrumental album. I purchased it from the kiosk in Giri Trading, Mylapore.

[navin]

Originally Posted by gkannan

There is no loss in gain when wired in parallel, and no addition either.

True. Forgot that 'No' is halved so next result is 0db.

Originally Posted by gkannan

The Dayton miniAMT (air motion) has a high f/s of 5 khz, so it does not intrude much down the frequency band. I have crossed it at 11khz (6db), the crossover point was chosen based on the roll off of the Dayton RS100 wideband.

Fc should be about 2x Fs so with a Fs of 5k a FC of 10k is about right.

Originally Posted by gkannan

The reasoning behind the choice of drivers: The Dayton RS180-4, RS100-4 go very well with each other. The RS180 is almost the perfect size for a car door.
The RS180 is a tough beast to tame in a 2-way when blending with a tweeter at LPF, but is composed as a 3-way where the LPF can be set low.

I understand using the RS180 for the midbass, the woofer could have been the RS225 to give you a little more headroom. And yes, like many 6-7" midwoofers, the RS180 does require some taming if used in a 2 way. The doped paper woofers like Vifa's PL series were better behaved above 2kHz.

Originally Posted by gkannan

The RS100-4 is an absolute revelation. Given the right enclosure, its performance is aplomb. In my setup it is playing 80% of the octaves and blends brilliantly with the RS180 which falls in the same series...Regarding the RS75, the RS100 though needing a bigger enclosure, has a much superior performance at the low end without much compromise in the highs.

Now I understand why you used the RS100. At first glance your crossovers are 63Hz, 315hz, and 10k. With the RS100 operating above 300Hz about half (50%) your music spectrum would be handled by the RS180 and excursion limitations would not be a significant factor. But if you are sending 80% of the music to the RS100 then you need a bigger driver.

[mashmash]

That is some build, even the youtube video recorded on a mobile sounds impressive.

I guess the setup you had when I heard was different, right? Even that was absolutely out of this world. The way each and every instrument comes alive, is like sitting in an open air auditorium and listening to the music being played Live. Absolutely Fantastic.

Looking forward to your next visit.

MaSh