cheap project in the UK

[consort_ee_um]

mmm, might be able to make a pair of decent computer monitor LS from these. It would be worth trying a sixth order alignment with a filter as in this thread:

http://www.diyaudio.com/forums/showthread.php?threadid=68368

Need to make the peak higher in frequency though and have an overdamped box alignment.
This would give extended bass without exceeding Xmax
I imagine the transformer fitted is rather small so the amplifier drive capability will be limited anyway.

 

[pinkmouse]

So what rails do you have on the traffo guys? Just thinking about powering active EQ...

 

[richie00boy]

Tweeter cutout: 74mm OD x 50mm ID
Woofer cutout: 115mm OD x 94mm ID

Thanks Vikash.

TM025F1 cutout: 70mm OD x 50mm ID, holes 62mm PCD
AP100Z0 cutout: 117mm OD x 90mm ID, holes 107.5mm PCD

So the AP won't fit and the TM would have a bare bit, but it looks like the standard drivers are OK anyway.

 

[Vikash]

I take back my original 'pants' comment. I took some more pics of the amp section, and had another listen but this time I put the tone controls in the middle instead of right down and they actually sound quite good (remembering they're £12.50 each!). The short comings of running the woofer fullrange and a single cap on the tweeter is very evident, but I certainly see potential now.

The tranny is marked as 12.5v x 2.

The port is 30mm dia. x 67mm which I calculate as ~73Hz tuning.

I'm giving them a bit of a run in now, and then I'll measure the FR and impedance plots.

 

[sreten]

I take back my original 'pants' comment. I took some more pics of the amp section, and had another listen but this time I put the tone controls in the middle instead of right down and they actually sound quite good (remembering they're £12.50 each!). The short comings of running the woofer fullrange and a single cap on the tweeter is very evident, but I certainly see potential now.

Pants ? from what I remember with both tones set at minimum
they sound absolutely hideous, all your left with is probably the
worst area of their performance - the mid treble integration.

I'm glad you do see some potential in the effort to modify them,

/sreten.

 

[sreten]

mmm, might be able to make a pair of decent computer monitor LS from these. It would be worth trying a sixth order alignment with a filter as in this thread:

Hi,

throw an inductor into the line level passive tone controls and
a sixth order bass alignment is fairly straightforward. The only
caveat here is getting sufficient damping into the 4th order
alignment - based on my listening tests this is going to be
difficult - I'm of the opinion the Q is borderline for reflexing.

/sreten.

 

[sreten]

Hi,

just some further notes regarding stuffing :

Moving the foam insert I added to the back of the box and then
lightly stuffing the rest of the box with BAF did tame the bass
somewhat though it was still a bit strong around 100Hz.

/sreten.

 

[sreten]

detuning the port detail

/sreten.

 

[sreten]

Is the electronics in one speaker only, or are they proper twins?

Hi,

realised last night the ambitious could buy two sets and then
end up with one passive pair and rewire the right speakers to
fully active (one amplifier per driver) for the full active experience.

There may be compelling reasons to do this. For example if the
4 ohm midbass units midrange is relatively flat but much higher
output level than the mean level of the 8ohm tweeter.
My listening tests suggest the midrange is higher than the tweeter
level, but if these are a number of peaks they will have to go.

/sreten.

 

[Vikash]

Re: detuning the port detail

detuning the port detail /sreten.

What's the aim of this?

 

[sreten]

Re: Re: detuning the port detail

What's the aim of this?

Hi,

a simple way of varying the port tuning if you so choose.

I've found I prefer the resultant overdamped bass in nearly all
reflex speakers I've tried it on, its not as drastic as closing the
ports - which loses too much bass in some cases.

My recommended "room gain" friendly reflex alignment is :

From the reflex response suggested by most software detune
the port frequency by root2 (half an octave down) and increase
the box size a little (usually 10% to 20%).

/sreten.

 

[Vikash]

Measured woofer T/S:

Fs	VAS	Qms	Qes	Qts	Re	Sd
92	2.09	2.5	1.19	0.8	3.4	52
87	2.56	2.4	1.14	0.8	3.4	52

Attached is a model of the current enclosure and port tuning.

 

[consort_ee_um]

The magnet looked as if it would give a better Qts ie smaller than 0.8
A negative resistance output amplifier will lower the Q. See this thread and scroll down to mo-amps posting.

http://www.diyaudio.com/forums/showthread.php?threadid=19114

With a lower Q we could get the desired overdamped response without resorting to port constriction.
I still have the artworks for that board..... might have to get some more made!

 

[Vikash]

Merged woofer and port frequency response:

 

[Vikash]

Tweer FR:

 

[Vikash]

Tweeter without cap:

 

[Vikash]

Woofer impedence:

 

[Vikash]

Tweeter Impedence:

 

[Vikash]

Ok, I hope this is enough info to be useful sreten. I can email the Speaker Workshop file over with the measurements if you like.

 

[richie00boy]

Nice work Vikash. Qts looks too high though for a vented box.

A negative resistance output amplifier will lower the Q. See this thread and scroll down to mo-amps posting.

http://www.diyaudio.com/forums/showthread.php?threadid=19114

With a lower Q we could get the desired overdamped response without resorting to port constriction.
I still have the artworks for that board..... might have to get some more made!

I can't see any posts by moamps on that thread, nor talk about any boards. Can you explain further?