The Metronome - mass loaded TL speaker - Make in India

[Hari Iyer]

@Hari, your subjective listening opinion please.

Hi Jousha,
The reason I did not add much of subjective opinions was it's very perspective and means different things for different people and does not make much sense in general.
Since you asked I will be using the below adjectives to describe them in my opinion,
Tight bass, detailed and open midrange, airy but a little bit grainy highs, excellent transient response and attack, uncompressed dynamic response, warm sound signature. Images like crazy and imaging is everywhere and not in center alone, wide sound stage.
For removing the little bit grainy highs, I am planning to use planet10 phase plugs later.

 

[Hari Iyer]

For tackling the grainy highs at high SPL and the tendency to shout in the upper midrange, I have added a unique phase plug. This is made out of a disposable paper cup and fitted on the whizzer cone. There was lot of risk in doing this modification as it would have permanently damaged a brand new driver which is used for less than 10 hours. But this is what DIY is all about - taking risk and benefiting out of that.

Now the shout above 6KHz and the grain has completelydisappered and the SPL indicates a gentle roll-off above 10KHz which is in line with the lows and mids.

The SPL is reasonably flat from 70Hz to 10KHz beyond which there is a gently roll-off.


The impulse response is spot on with the rising and falling pulse of the same amplitude indicating perfect linearity.

The step response shows tight integration and a decay associated with some interaction with cabinet walls but no major resonance issues in the enclosure.

 

[Hari Iyer]

This is the impulse and step response without the phase plugs. You can see a huge difference in the integration of the lows, mids and highs.

 

[Sumanta]

For tackling the grainy highs at high SPL and the tendency to shout in the upper midrange, I have added a unique phase plug. This is made out of a disposable paper cup and fitted on the whizzer cone. There was lot of risk in doing this modification as it would have permanently damaged a brand new driver which is used for less than 10 hours. But this is what DIY is all about - taking risk and benefiting out of that.

Now the shout above 6KHz and the grain has completelydisappered and the SPL indicates a gentle roll-off above 10KHz which is in line with the lows and mids.

Interesting thinking. You have actually "stopped vibration of the whizzer cone and that reduced the shout", is this statement correct for what you did?

 

[Hari Iyer]

IMO the whizzer cone acts as a waveguide at mid- high and high frequencies there by increasing its SPL at thoae frequencies. Also the whizzer cone cause cavity resonance and interacts with low, mid bass and mid frequency by masking them.

The paper cup with some fiber stuffing blocks the cavity resonance and reduces the SPL at the frequencies above 10Khz ( this is evident by the SPL response). Also the impulse response and step response show that the rising and falling pulse are well integrated and show coherent behaviour which was not without the phase plug. The total measured weight of the cup and stuffing is just 0.7 grams. If the weight of the cup+ stuffing is high it will alter TS parameters which can inturn affect the tuning freq.

I have not yet measured the system impedance with the phase plug as I had to give the box for veneering/ polishing. I am expecting a reduction of tuning frequency by few Hz due to the added mass. Hope they don't indicate any new resonance issue.

 

[Hari Iyer]

How effective is my whizzer cone treatment method using the disposable cup method + polyfill stuffing method. Here are some impedance measurements for review,

1. Free air impedance and phase of the raw driver
This shows some resonance at around 1.2KHz, 2.8KHz, 3.8KHz, 5.9KHz and other high frequency. Low to mid bass frequency resonance is clean without any wrapped impedance or phase


2. Unstuffed impedance and phase of the driver in the Metronome box with the modified whizzer cone + polyfill stuffing.

This shows the odd harmonic resonance at 260Hz, 500Hz, 750Hz. The mid and high frequency whizzer cone resonance has completely disappeared. This is evident from the cleaner impedance and phase plot above 1KHz without any sacrifice of the high frequency energy.

3. Stuffed impedance and phase of the driver in the Metronome box

This again displays some energy in the lower mid bass region and a small resonance in the 3.9KHz region which needs to be damped. Other than this the mid and high freq region where the whizzer cone operates is clean with this implementation.

The cup + stuffing method not only damps the whizzer cone vibration, but also helps in eliminating the resonance associated with it. The stuffed impedance response does not indicate any new resonance or tuning related issue too. If you have read my earlier post, i had designed the box for a tuning freq of exactly 60Hz and the measured result also indicate the same in the Unstuffed impedance curve.

 

[Hari Iyer]

Did two more mods on the driver today morning,
- Added two small foam piece behind the whizzer cone and the main cone to damp any unwanted vibration of the whizzer cone.
- Added some felt to the driver basket behind the driver and also covered the magnet with the felt to prevent any early reflection coming from the rare of the driver and escaping from the cone.

Subjective listening after this is very encouraging with smooth mid-range and airy highs without the presence of any grain in the sound stage. Earlier i was a bit reluctant to hit the volume knob due to some listening fatigue at high SPLs, now after this simple mods that's history.

I have not yet measured the impedance, SPL or step response but am expecting a better measured impedance and step response after the mods.

Thanks for looking,

Cheers,

 

[magma]

HARI
you are getting dangerously close to designing your own driver

milind's route ?

wish you well

 

[Hari Iyer]

HARI
you are getting dangerously close to designing your own driver

milind's route ?

wish you well

I am very very far away from it imo. Also not inclined to that route as it requires a different passion though i have some simulator software to desire the required parameters. Unless thee are large orders making the drivers to specific specifications is not practical and hence doing any work in that area is not of much use.

Here are the measured impedance after the mods applied today morning,

 

[Hari Iyer]

Further subjective listening for 2 weeks of the Metronome gave me an indication that having a pure resistive load and flat impedance increased the mid-range gain and shout. Also my 300Bs are more prominent have more presence in the mid-range.

I re-designed the compensation network for the driver and amplifier anamoly to make the load a bit inductive below 3KHz and capacitive above 3KHz. This increased the impedance at 3KHz by 50% more than the linear region. This not only removed the mid-range masking the lows and highs, but also increased the airiness and mid-bass. Also the details are more clear, no clutter in the mid-range and a more resolved sound-stage. I think now i have done with the version 1 of the tweaks with the metronome and I will now leave them for cone breakin to set-in before i think of any further mods (if any).

Below is the designed and measured impedance / phase of the metronome:

I have adjusted stuffing with varing density in the upper and lower half. The acoustic choke now has a lower stuffing density compared to the terminus end which is indicated in the impedance measurements.

I have yet to measure the SPL, Impulse, Step response of the metronome.

 

[Hari Iyer]

This is how they finally look and measure

 

[Hari Iyer]

I started this project some-where near July last year and now can say that its completed with all my tweaks in place. Now the Metronome is not a single full-range speaker but has a Audiopur Ribbon Tweeter to compliment the highs. I have crossed the tweeter at 3KHz as the Fostex has reasonable response till 6Khz. I have listened to them and found it quite satisfying comparing to other high-end speakers in the market. Pending work is the Grill and flush mounting of the tweeter with the baffle.

Some measurement to feast your eyes:

The parallel notch on the Fostex was required to tame its response which was a bit higher between 300Hz to 1.2KHz. Also the RT has a increasing response after 3KHz which was as high as 10dB not getting controlled by an L-pad. Hence went for an un-conventional design of using an inductor to tame its response with encouraging results both in the simulation and measurement. Other components are used for phase control and crossovers at 3KHz.

This speakers sounds much better than it actually measures compared to a conventional woofer + tweeter design. I have given more importance to subjective listening than actual measurements for this speaker.

Any FM keen to listen are welcome after a PM on weekends.

Thanks for looking.

 

[Hari Iyer]

Was a bit uncomfortable about the dip at 6KHz and the rising SPL with frequency which tempted me for a mod of the crossover. Here are the new measurements after the mods,

 

[Sumanta]

Congratulations Hari!

 

[heliumflight]

Congo Hari Sir!

 

[tuff]

Maybe i can come and give it a listen this time.Good stuff.

 

[Hari Iyer]

Maybe i can come and give it a listen this time.Good stuff.

You are welcome on any weekend afternoons after a PM.

Cheers,

 

[Hari Iyer]

After measuring my speakers in the room and doing objective listening, i realized that further flat response was not possible using passive components and this will require some active equalization needs to be done to flatten the response to nullify the effects of the room in which they are playing.

I used REW to measure the speakers - one at a time and calculated the EQ required to be applied to them. Then i downloaded the Peace parametric equalizer and updated the EQ values to the parametric equalizer and routed the VLC player through the parametric equalizer. Now the sound is much balanced with no chesty bass on the vocals.

Here is the response of my un-EQed and EQed speaker for your view. I am now convinced about the ARC method of EQing the final loudspeaker to suit your room without the need for costly room treatment.

 

[Hari Iyer]

I finally did not implement the EQ after two weeks of listening. i rather went with an optimum room placement placing the two speakers in a non-parallel wall. This removed all the room modes and the dip at 180Hz caused by the rear wall boom. I have measured the response with this new setup and the boom just vanished.

BTW, this is how they look with the grills on.

I have mounted the ribbon tweeter from the inside panel to give an physical offset with the Fostex. This was for aligning the driver in time and possible further improvement in the overall step response. I have not yet measured the step and will do so later. The sound stage now is very convincing, with good imaging and width the usual mellow response.

 

[HormusPeston]

Nice build.