Nearfield Monitor: FE103E bass reflex

[gmilitano]

Hi Gio. You are quite correct in that I measured them right out of the box. They definitely have more than 300 hours of playing time by now though. I'll recheck their parameters this weekend by running them through fuzzmeasure again to see how much they've changed. Hopefully I'll have enough energy after work on Saturday to build a small box to measure their Vas as well.

Brian,

It would be nice to see the measured results of the broken in driver to compare them with the out of box numbers.

Let us know how you make out.

Regards,
Gio.

 

[sreten]

Using TGs filter seems to me to be a very good idea.

Hmmm.....

with limited amplifier power perhaps not.

You could however easily build a line level version of the
filter where you could also make the resistor adjustable.

/sreten.

 

[BWRX]

Hi sreten. Now that I skipped out of work before they could ask me to stay I have some time to reply Thanks for all your replies so far!

I think eveyone who has posted has said or implied adding a tweeter
is not a good idea, it turns a good full range driver into a poor bass/mid driver.

You will lose the transient and phase coherency which is the
main advantage of using a full range driver.

I agree that there are more suitable drivers that could be used for the bass/midrange but the 103 will allow me to crossover at a much higher frequency than a conventional 2 way. That will have the advantage of retaining the coherency all the way up to through the critical midrange and upper midrange while hopefully losing the congested sound caused by the 103 trying to reproduce the full spectrum. Furthermore, the active 24dB/octave Linkwitz-Riley crossover is phase coherent. And the shallow depth of the 103 coupled with the flush mounting of the tweeter will minimize phase difference by decreasing the horizontal distance between the center of the two voice coils. Angling back the enclosure slightly will effectively line them up nicely when it comes time to listen.

It would be fairly disheartening to build your box with a cutout
for the tweeter and then realise you'd rather have not done that.

I won't be upset if I end up not liking the tweeters. They're only $36 per matched pair, which is the cost of just one of the 103s!

Using TGs filter seems to me to be a very good idea.

I don't really see a need to use it. But like you said it could be implemented actively as well, which is a better option.

AFAIK the basic t-amps have a fairly high bass roll-off, ~ 70Hz,
in this context this is a very good thing. What is does mean
though is your bass alignment is 5th order. (And much better
as its active than the original Wharfdale Diamond, which used
a series capacitor for a small reflex box.)

The stock SI has bass rolloff because of the input coupling cap. I have amp3s with larger coupling caps which lowers the cutoff frequency down to below 10Hz. I also won't be using just the amp3 but a different 10W class d amp as well. They're not quite built yet though.

You should be able to make the box even bigger and extend
the bass a little more with a 5th order alignment. Certainly the
power handling below port frequency will be much improved.

That's a very interesting point! I hadn't even thought about using the input high pass characteristic to protect the 103... Definitely something to look into!

 

[sreten]

Hi,

for a LR4 the drivers are phase coherent relative to each other,
but overall phase coherency disappears. Or another way of
putting it you add group delay at the c/o frequency which is
worse with LR4 than LR2.

One point of TG's filter (which is probably optimised for farfield)
is than it also effectively extends the real treble response.

I just feel a nice home for the driver is as a full range speaker.

The c/o and tweeter cause more problems than they probably fix.

/sreten.

 

[BWRX]

But isn't having the drivers phase coherent relative to each other at the crossover point more important than overall phase coherence? The 24dB/octave slopes also sum to be flat if you match the low and high pass sections.

There won't be any need for TGs filter to extend the real treble response if I use a real tweeter

A 2 way speaker certainly has its advantages and disadvantages compared to a single driver speaker. Complexity and cost is a disadvantage for the 2 way but on and off axis frequency response and overall sound quality should be better. Plus biamping with an active crossover allows the amps to directly control the drivers.

Two speakers filling out a front baffle looks nicer too, but that's just a pleasant bonus.

I've got the panels for the test boxes cut out. I just have to cut the mounting holes in the baffles and drill and screw them together.

 

[BWRX]

I finally built a solid 7"x7"x7" (external) test box out of 3/4" MDF. The baffle is removable with a seal so I can use baffles with different size cutouts for different size speakers up to 6.5".

Anyway, I have a pair of RS1197s that were sitting around so I decided to measure them with FuzzMeasure. Here are the numbers it came up with.

Free Air: Fs 131.759995, Qms 5.366343, Qes 0.712545, Qts 0.629023, Re=7.1ohms
2.853L Sealed Box: Fs 166.929993, Qms 6.645197, Qes 0.943037, Qts 0.825840, Re=7.1ohms

Vas=Vb((Fb/Fs)^2-1)=1.726L

So the T/S parameters for one of my 1197s are:
Fs=131.759995
Qms=5.366343
Qes=0.712545
Qts=0.629023
Re=7.1ohms
Vas=1.726L

Attached is the frequency response showing the free air and sealed box response.
Note the peak around 1200Hz - that's due to the standing wave mode caused by the square box. A quick calculation shows that this is in fact the case. The internal dimensions are 5.5"x5.5"x5.5" (5"=0.1397m). The wavelength of the standing wave will be twice the dimension of the box because at the sides of the box the velocity will be zero and the pressure will be at a maximum. So the frequency of the standing wave should be around (343m/s)/(2*0.1397m)=1228Hz.

 

[BWRX]

Here are the numbers FuzzMeasure came up with for one of the FE103E's.

Free Air: Fs 110.759995, Qms 3.789947, Qes 0.561386, Qts 0.488959, Re 7.5ohms
2.853L Sealed Box: Fs 153.020004, Qms 5.636709, Qes 0.819863, Qts 0.715756, Re 7.5ohms

Vas=2.592L

T/S parameters for FE103E:
Fs=110.759995
Qms=3.789947
Qes=0.561386
Qts=0.488959
Re=7.5ohms
Vas=2.592L

The numbers I got when I measured them right out of the box are very similar except Fs actually increased (same with the RS1197). Not sure how that works, but I measured them in almost the exact same manner and with the same calibration.

 

[sreten]

But isn't having the drivers phase coherent relative to each other at the crossover point more important than overall phase coherence? The 24dB/octave slopes also sum to be flat if you match the low and high pass sections.

There won't be any need for TGs filter to extend the real treble response if I use a real tweeter

A 2 way speaker certainly has its advantages and disadvantages compared to a single driver speaker. Complexity and cost is a disadvantage for the 2 way but on and off axis frequency response and overall sound quality should be better. Plus biamping with an active crossover allows the amps to directly control the drivers.

Two speakers filling out a front baffle looks nicer too, but that's just a pleasant bonus.

Hi,

I just don't like uniformed design.

The "phase coherency" of LR4 is an illusory concept.

Overall phase coherence is a major feature of full range drivers.

You are trying to shoehorn an entirely unsuitable driver into a design methodology.

If you want a "nice" home for the 103's you should put them in a design that suits them.

the 103 will allow me to crossover at a much higher frequency than a conventional 2 way.

Once you do this driver spacing nulls become a large issue.
Also bi-amping becomes fairly pointless as dynamic gains will be minimal.

You should use them full range, adding a supertweeter with a simple
series capacitor to improve top end extension and dispersion.

This would be suitable :

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=275-030

If you want an active LR4 2-way (incidently the final acoustic response
should be LR4, not the electrical response of the active c/o) you should
use a different bass/mid with the creek tweeter.

If your next post says you are going to plough on regardless I will leave you to it.

/sreten.

 

[BWRX]

You are trying to shoehorn an entirely unsuitable driver into a design methodology.
Once you do this driver spacing nulls become a large issue.
Also bi-amping becomes fairly pointless as dynamic gains will be minimal.

I wouldn't say enitrely unsuitable, although you have made some good points as to why this is the case. Sure there are other drivers out there that could be better for this application. However, I already have these on hand so that's what I have to work with Same with the amps and most of the parts needed to make an active crossover. Making the enclosure will be that hard part!

You should use them full range, adding a supertweeter with a simple series capacitor to improve top end extension and dispersion.
This would be suitable :
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=275-030

That does look like a pretty nice (and cheap too!) tweeter to use with this sort of design.

If you want an active LR4 2-way (incidently the final acoustic response should be LR4, not the electrical response of the active c/o) you should
use a different bass/mid with the creek tweeter.

That's one advantage of using the 103 and this tweeter - the extended frequency response of the 103 and the low end capability of the D25 means that the final acoustic response in the crossover region will be just the electrical response.

If your next post says you are going to plough on regardless I will leave you to it.

You're making me second guess myself a little here But thanks for discussing as you've given me a couple more things to research before going ahead with this.