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The Metronome - mass loaded TL speaker - Make in India

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Hari Iyer

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FM who have been following my Fostex MLTL thread would know by now that this is a continuation of that thread below.

http://www.hifivision.com/speakers/63965-my-dream-project-planning-tl-fostex-full-range-driver.html

So why start a new thread.

Reason:
- The Metronome is such a highly DIYed speaker globally that it deserves a separate thread.
- The original Metronome thread in diyaudio.com is over a decade old and had several iterations to the original design. This design is even today discussed in the forum and is very active since 10 years. Probably this design would be the highest DIYed speaker till date.
- One of the major advantage of the Metronome is its extremely high WAF approval. In my case the moment i showed the images to my wife, i got a nod from her. Also the footprint is not wide on the floor but a little tallish towards the ceiling which should be okay for many. I was not sure if someone had build a Metronome in India (atleast not known to me).
- As i was working on various simulations with my box geometry was not able to conclude on what to finally design. Hence took help of TL gurus in other forums for a suggestion. Almost all of them told me to built a BLH design as the FE166en was more suitable for this geometry. The BLH was ruled out due to its largish size of enclosure which would have not been suitable for my smallish living room. Some pointed me towards a TABAQ and others towards a frugal horn lite designs.
- When i was exploring various designs landed upon the Metronome design in the frugal horn website. There are many published designs there but none for the FE166en. Also i noted that these designs when simulated in the LA were not very perfect designs considering theory and logic. Hence they would require considerable tweaking and cannot be blindly followed.
- It took me over 3 months to fine tune and tweak my design before the design was finalized and the final wood was cut. I am still tweaking for the right amount of stuffing. This part could not be finalized without the suggestion and inputs from our FM Kapvin and am still seeking suggestions from him.
- I will be receving the work in processs box today for my initial testing and measurements. Will post images of that as soon as its delivered today evening.
- I am planning to use my harmonic balance compensator with this design as i will be keeping the box atleast 5 feet away from my rear wall. Will post some images of the objective simulations.
 

Hari Iyer

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Posting some images from my simulator for the technically minded. Hope to get the same response in my objective measurements too. For subjective listening keeping my fingers crossed as of now.









 

prem

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The Metronome should sound good. It's loosely based on Cain&Cain Abby speakers which I had heard long back and had sounded good
 

Hari Iyer

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Thanks Prem for the information. Ironically the Cain Cain Abby uses the same FE166e driver in its version of Metronome. Its tuned a bit lower than what i have tuned. Its a whopping 70" tall while mine version is 56" tall tuned at around 58Hz.

I completed yesterday night the assembly and after subjective listening found the bass to be tight, but the sound stage had a mid-range shout masking the clear reproduction of highs and also somewhat masking the mid-bass. After an hour of listening went ahead and measured the impedance of the speaker system. I found that there was a huge impedance peak in the 8KHz region. I had used the published TS parameter to enter the inductance of the voice coil to design my network and that approach was totally wrong.

I reverse calculated the inductance value from the REW measurement and substitute the measured inductance value for the compensator. I again then retweaked it for an accurate component value for the compensator. I also completed my 'Right' speaker with this value and measured the impedance again in the REW. Now it looks accurate and the way i intended it to be. I have yet to fine tune and tweak the values for a smoother curve and it was getting late at night and couple of power outages in my location. Hence balance work will be completed today. Yet to complete my subjective listening.



The impedance curve above clearly indicates wrong consideration of voice coil inductance value from the published parameter which i think caused the mid-range harshness and shout.



The new corrected value for the compensator now indicates a flat impedance curve and a pure resistive load for the amplifier. From this curve you can notice that there are some resonance issues in the 280Hz and 1.1KHz area which needs to be addressed by careful stuffing of the enclosure. The enclosure tuning is exactly around 55Hz as indicated by the measurement which is exactly the goemetric mean of the peaks at 34Hz and 87Hz. So all in all a well measured speaker vis-a-vis the design values.

BTW, I have now removed some stuffing from the previous measurement to check the bottom end extension available which is evident from the impedance peaks.
 
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M

mpw

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There was an earlier build with some very nice pics by FM jaybe...have u looked at it ? Maybe it would help you.
 

Hari Iyer

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Thanks for the link, ironically I too have posted on that link. But thlis design looks like a straight line ML TL and not a metronome.

The metronome is a Quadratic TQWT speaker - similar to a vigot pipe. It's more of a oscillating horn speaker after the 3rd harmonic frequency and a TL below that frequency. So I will call it a hybrid horn.
I have now completed all my tweaks on my speaker and measured the impedance it's ruler flat impedance and phase. Also removed some stuffing to increase the bottom end and now have tuned the box with equal impedance peaks for the driver and the box. Will post images of the semi finished box shortly
Thanks.
 

manniraj

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Yes I think he evaluated all the designs including Metronome and dropped it because of the size 56" tall and went with the Bob Brines which is a MLTL with a helper tweeter of FT17H. My visit to his place is still pending and need to hear his setup which as per some of the members who have heard is very nice and simple :clapping:
 
M

mpw

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thats a unique look - atleast for me.

Congratulations ! Your effort and persistence are to be appreciated :clapping:

I am sure it will look good with lights - just like Eiffel Tower does.

As to the sound - i want to come and hear this :)

PS : On a jocular note - if it doesnt sound good .. offer it to the Chinese for their next space mission :D

regards
 

venki7744

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Wow!! that was super fast :). I have been thinking about building a small Metronome ever since I got those Tympany drivers from LinuxGuru. However unlike you, nothing materialized its still sitting as a jpg in my laptop. Here is what I designed a while back.

Freq Response with Filling.jpg

Schematic with Filling.jpg

Do let us know how it sounds.

Cheers,
Venki
 

Hari Iyer

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thats a unique look - atleast for me.

Congratulations ! Your effort and persistence are to be appreciated :clapping:

I am sure it will look good with lights - just like Eiffel Tower does.

As to the sound - i want to come and hear this :)

PS : On a jocular note - if it doesnt sound good .. offer it to the Chinese for their next space mission :D

regards

Thanks mpw, i am currently tweaking the speakers and its very tricky as the stuffing in this enclosure is so very crucial. Even 20 to 30 grams makes a lot of difference in both the bottom end and mids. To get the accurate stuffing is going to take time. Also this driver will require minimum of 50hrs to 100 hrs of breakin. I am doing this breakin by feeding low freq (35Hz) at moderate volume level. So this should be done within this week.

Also i have yet to test without my compensator network which is going to make or break this design. My initial simulations are not very accurate considering the measured data. Hence some challenges there too. Yesterday did some modifications and am pleased with the measured results. As for subjective listening test they do sound very open, resolved and intimate, but for me only subjective does not matter if objective is not in place. Hence tryig to balance out subjective and objective.

I may be giving this enclousre for veneering / polishing today or tomorrow and would get them back probably this weekend. Will keep if you informed. Hope to complete my tweaks by today.

Cheers,

This is the proposed simulated changes i will be working on the compensator network to get everything in sync. Hope they also measure the same.



Below is the respective simulated square wave response.

 
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Sumanta

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Great going Hari.

I was not sure if someone had build a Metronome in India (atleast not known to me).

I know one Mr. Saran in Kolkata made it at least two years back. I heard them in his house when I was there to listen to his OBs.

He is a member in this forum too, but I forgot his handle here.
 

jmascreen

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which software is it?

Wow!! that was super fast :). I have been thinking about building a small Metronome ever since I got those Tympany drivers from LinuxGuru. However unlike you, nothing materialized its still sitting as a jpg in my laptop. Here is what I designed a while back.

View attachment 21825

View attachment 21826

Do let us know how it sounds.

Cheers,
Venki
 

Hari Iyer

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Below is the final simulated and measured results which i am planning to finally settle down for some time atleast. Will change only after feedback and views from others subjective listening and my further objective measurements,



 

Hari Iyer

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Performed a quick REW SPL measurement today as below. This response is not 'Gated'

 
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