The Metronome

[Gijsch]

Ok, Let's see if I can figure out a fitting aspect ratio. I will report back on this.

Some more questions, where can I find some theory behind these enclosures ?
As nice as it was to find a table with suggested enclosure dimensions, it would be even better if I understand what's going on inside these cabinets,or at least be able to try.
How forgiving are these cabinets with regards to variations in T/S parameters ?
The table on frugal-horn speaks about a design fo the AN 10" , not sure if this is the stamped basket or cast frame version.
Besides, I read about published AN T/S parameters being rather different from actually measured parameters.

At the moment I don't have the tools to measure T/S parameters by myself, neither do I have acces to the MJ Kings sheets. Are these really requirements to build these fullscale metronomes with any chance of succes, or can I rely on the tables for a safe starting point ?
Last set of speakers I built was a kit with an 10" coax in a more or less simple BR enclosure, this will be a bit more "experimental" , thus the need to learn more before I start building.

[planet10]

The Metronome can be modeled "close-enuff" with MJK's ML-TQWT sheets.

The one in the tables, is, i believe, the stamped basket.

dave

[AmadeusMozart]

Originally Posted by Gijsch

Ok, Let's see if I can figure out a fitting aspect ratio. I will report back on this.

Some more questions, where can I find some theory behind these enclosures ?
As nice as it was to find a table with suggested enclosure dimensions, it would be even better if I understand what's going on inside these cabinets,or at least be able to try.
How forgiving are these cabinets with regards to variations in T/S parameters ?
The table on frugal-horn speaks about a design fo the AN 10" , not sure if this is the stamped basket or cast frame version.
Besides, I read about published AN T/S parameters being rather different from actually measured parameters.

At the moment I don't have the tools to measure T/S parameters by myself, neither do I have acces to the MJ Kings sheets. Are these really requirements to build these fullscale metronomes with any chance of succes, or can I rely on the tables for a safe starting point ?
Last set of speakers I built was a kit with an 10" coax in a more or less simple BR enclosure, this will be a bit more "experimental" , thus the need to learn more before I start building.

The metronome is the most satisfying enclosure that I have build during my life. I am very fond of the FF105WK as stand alone metronome and the FF125WK combined with the FF105WK metronomes playing together are just amazing and the perfomance is something to be heard in order to be believed. Ofcourse with such small drivers absolute SPL levels are limited but for near field listening still very respectable enough, letting you feel the bass in your chest. Good enough for me.

The FF1xxWK take a long time to break in, reckon on several hundred hours.

The principle is similar to a Voigt pipe except tapered in two directions. If the front and back do not have the same size then the increase in size is not purely exponential (the Voigt is linear). Found them rather forgiving towards tuning and this showed up in modelling.

[AmadeusMozart]

Originally Posted by gafhenderson

Think Dave/planet10 has an onken box plan for those, which given the feedback on the other onken enclosures he has done, would probably be a pretty good bet.

Lowering will make a difference, how much needs to be simulated. Adding a suprabaffle seems to mke very little difference from my recent experiences especially when well chamfered.

I much prefer the driver lowered, YMMV. I have them sitting halfway the total length of the metronome top to floor.

[Gijsch]

I guess I got the message. Time to contact MJ King for a set of worksheets

[AmadeusMozart]

Originally Posted by Gijsch

I guess I got the message. Time to contact MJ King for a set of worksheets

IMHO these enclosures are not as critical as bass reflex.

In the case of the FF125WK I could change the length of the port from 1.25" to 5" with only minimal change in performance. Optimum was around the 2.5" - 2.75".

I've built the plain Voigt pipes in the past and found them very forgiving of parameters which makes for stable performance. What a lot of listeners do not realise is that when the voice coil heats up (playing at loud levels) the parameters change, sometimes considerably, and those can change enough to make a bass reflex work well outside its design specs.

You can spend a lot of time modelling however never forget that modelling is only an approximation of the final result. There are enclosures that model horribly yet sound very good and others that model perfect and sound horrible. Modelling is only a simulation of what to expect so in this case if you have some approximate design just go for it and then see if you can measure afterwards what changes will do. I used the Samson USB Go-mic and some freebee software to measure. (Holmimpulse)

[Gijsch]

So I got Martin's worksheets up and running, and start to understand how they are working, at least a little bit. Problem is I still don't really understand the principles behind them. What would be the optimal length of a metronome ? Why choose what taper ? Height of the driver ?
What's the influence of the Vas on the dimensions ?
I already took a good ride on the www searching for the knowledge behind a metrnome or a TQWT, managed to read the first 15 pages on this topic, but am still a little clueless.

In Martin's TQWT sheet I entered the driver parameters of the Audio Nirvana cast frame 10" drivers and enclosure dimensions as found on the frugal horn page for the stamped basket variations of the same drivers. Results seemed quite promising at first glance until I saw the predicted in-room graphs. Big hump between 50 and 100 hz, but a dip between 100 and 200 Hz.
How could I try to improve on this ?

Any help would be welcome :-)

Gijs

[faithintruth]

Anybody tried these with FE206eN? I have already built them with FE 126 and they are awesome.

[Jim Shearer]

Just wanted to report that I have tried Fostex FE103en in the Mets I built for FE108eSigma. (I had pulled the FE108eS to try out in the foam core board Cornucopya spiral horns.)

The cabinets aren’t optimal for the 103, but they are close enough to work pretty well. Also used the same BSC as w/ the 108: 1 mH and 4.5 ohms.

IMO the FE103en is an under appreciated driver in the USA. I can see why folks in Japan like it so well. With only 60 hrs on the drivers, they are sounding smooth & lovely. If anyone has been holding off on building a Met with the 108 due to its cost, consider going ahead with the 103. When I have some time, I think I will run some simulations to see how tweeking the dimensions of the box for the 108 can improve performance for the 103.

Cheers, Jim

[drewh1]

Well, I read through almost the entire Metronome thread, whew - alot of information. I just love the look of this speaker and have to build it. Will likely use hard wood front panels with plywood sides and back.

I am currently building a Bottlehead 2A3 SET and want to match it to the met. Shooting for a 96db sensitivity. I want to use an 8" driver and haven't decided on the driver yet, likely Fostex or Hemp (opinions on drivers are welcome)

My questions:

1. I will include an internal brace - do I need to increase the overall internal volume to compensate?
2. Some posts have said the Metronome is not so efficient, does that mean that the efficiency of the driver will be lowered due to the interaction with the cabinet? If so, what would I expect from a driver rated at 96db
3. Why don't you incorporate an oval baffle like the C&C Abby? Would that lower reflections?

Anyway - this is a great forum, I really appreciate the opportunity to interact with all you knowledgeable people.

Thanks in advance!