[matevana]

John K did some research on a damped (stuffed) U frame vs open U Frame: http://www.musicanddesign.com/u_frame.html

[Bumpy]

John K did some research on a damped (stuffed) U frame vs open U Frame: http://www.musicanddesign.com/u_frame.html

Thanks Matevana, some good reading there together with the link to Nao.

I did a VERY crude experiment yesterday evening using fluffy pillows to stuff the structure behind the bass driver. I didn't notice a great deal of improvement in the bass and the lovely imaging in the lower frequencies was compromised, so not a lot of encouragement there

If I was asked why, I would guess that the bass is affected less if you are listening near field and that with a bass crossover of 650 Hz the stuffing would be impacting on the lower midranges.

I will still keep the idea in mind.

[matevana]

I agree with you. I haven't been successful in properly damping a U/H frame enclosure. John is a smart guy and I don't doubt his hard work. I just haven't been able to achieve positive results in my attempts.

[Bendingwave]

I stick (frost king) foam directly on to the (driver) magnet.

[Bumpy]

Is that just to stop reflections from the magnet, or is there more to it?

[Bumpy]

Just thinking aloud.

I keep asking myself why I don't speed up the break-in process for my new SEAS Exotic W8 drivers, by playing them face to face out of phase at high volume etc. The reality is, the cones have a linear travel range of 6mm and a max travel range of 22mm and I have never actually seen the cones move at all in their suspension. So, the break-in process is going to take a few hundred hours (similar to Lowthers).

I have decided that for me personally its like having the most beautiful woman in the World doing a strip tease in your room. It's much more fun watching the whole performance evolve rather than leaving the room and closing the door.

I guess this You Tube video (that I have posted before) is the opposite philosophy.

https://www.youtube.com/watch?v=orC1QXULd5w

[Bumpy]

Yesterday I disconnected the bass drivers and ran the SEAS Exotic W8 full range in the bass. This confirmed

1. That the SEAS drivers are really wonderful and quite capable of running much lower than the Saba Greencones they replaced.
2. The Altec 416B alnico bass drivers are crossed over way too high for the SEAS drivers and are trampling on some of the magic.

Current crossover I believe is about 650Hz and SEAS recommend a crossover for their driver of 100Hz, hence the clash.

My first task this evening is to reconnect, then reverse the polarity of the bass driver to see what effect that has.



As I understand it, the low pass filter on the Altec is a 2nd order Butterworth. My inductors are Jantzen C Cores and capacitors are Audionote Kaiseis so a bit too expensive to be experimenting by substitution

Can anyone recommend an on line calculator so I can select values for this Butterworth crossover or alternative components I can use to experiment. I am warming to the idea of a calibrated measuring microphone.

[matevana]

Most use the same mathematical formulas for a given type/order, so it's really a question of who's interface you prefer to work with. I tend to like the ERSE site: http://www.erseaudio.com/CrossoverCalculators

[Bumpy]

Thanks Matevana, you wont believe how long I searched for such a calculator

In my low pass filter my actual inductors are 3.9mH and caps are 100uF.

The calculator suggests that to get a crossover value of 500 Hz one should use inductors of 3.6mH and caps of 28uF. As the caps are three times the value of those recommended would you know if this pushes up or lowers the crossover point.

Also could could you recommend 'cheapish' inductors and capacitors that I could experiment with before switching to expensive ones to finalise the low pass.

Thanks for your continued help.

PS reversing the polarity of the bass drivers made no significant difference.

[matevana]

A higher value capacitor in a 2nd order low pass filter, will increase the rate of attenuation of any high frequencies above the cut off point (roughly 500 Hz in this case). The crossover point is largely determined by the inductor in this circuit; the way in which it rolls-off is influenced by the cap.

[Bumpy]

A higher value capacitor in a 2nd order low pass filter, will increase the rate of attenuation of any high frequencies above the cut off point (roughly 500 Hz in this case). The crossover point is largely determined by the inductor in this circuit; the way in which it rolls-off is influenced by the cap.

Thanks Matevana, spot on reply.

[Bumpy]

My midrange and tweeters are working brilliantly. The big challenge that remains is to seamlessly integrate the bass drivers using low pass filters.

I hope to leave myself plenty of flexibility and would like to be able to adjust not only the crossover point, but also the order of slope. Quality components for experiments are VERY expensive and I appreciate that the more complex the crossover the more it is likely to lower sensitivity of that driver which is not good.

This is leading me to think about powering the bass drivers separately with DSP amplifer such as the MiniDSP PWR ICE125. Has anyone gone down that route?


Although not open baffles, I am drawing inspiration from the Salk Exotica 3 speakers which also use the SEAS Exotic midrange and supplement it with servo woofers. This is what they say

SERVO WOOFERS
In order to maintain high sensitivity and provide bass response down to 20Hz, we've incorporated a servo-controlled woofer section into the equation. So your amplifier only supplies power to the midrange and tweeter section of this speaker.

Those speakers of theirs retail about $13000 and have an excellent reputation.

http://www.salksound.com/model.php?model=Exotica+3

[WC]

http://www.rythmikaudio.com/F8.html

Essentially this is the low end of the speakers. You can also buy the drivers and the amp to put in your own enclosure if you would like. There are also open baffle versions available.

[Bumpy]

Just a bit of an update.

I have the 15" bass unit disconnected for now until I work out a low pass filter.

The tweeter has its existing capacitor to protect it and the SEAS Exotic W8 is running full range (both top and bottom) - no capacitors, no inductors, just silver wire to connect it. This is by far the best it has sounded.

Essentially this is now a two way open baffle and the best it has ever been. I could live with it for a few months if I have to. The vintage Tweeter and Exotic W8 work beautifully together so looks like I fluked that.

The next job is to integrate the open baffle bass driver into the system, just like one would a subwoofer.  As there is no high pass filter imposing a defined slope on the midrange driver (eg Butterworth 12dB), integration is that bit more difficult and continues to insist I buy a calibrated microphone and do some measurements.

Maximum flexibility seems to be the order of the day so a DSP amp is attractive, but it needs a high level input as the system volume will be controlled by the 211 triode integrated. This is very common for subwoofers, but not DSP 

Here is a spec for what I am looking for.

1. High level inputs from speaker terminals of main amp (therefore no impact whatsoever on the existing two way drivers)
2. DSP for maximum flexibility.
3. Amplification should be best SQ but probably can cope with 50 W/channel minimum. (Class A/B or D Class?).
4. No thump at turn on.

Will try and post a YouTube video later though I dont yet have a good microphone.

[Bumpy]

I am firming up on the way to go now. I will parallel up the signal to the speakers. Part will go normally to the OB mid and tweeter and part will go to a 'speaker to line level' converter to give a signal that will be fed to a Minidsp 2x4 for setting up and optimising the low pass filter. Hence to a highly modified Rotel amp and on to the bass drivers.

I have just bought the Rotel that has been modified and it is coupled with a cheap Marantz CD player that I saved from a skip. This combination is being used to run in the SEAS drivers (currently 140 hrs).

I was so impressed with the SQ that I took a video.   Remember no bass drivers and just the cheap combo feeding the OBs. Shame about my camera which seems to add a bit of an echo, but then I'm buying the MiniDSP UMIK-1 which I'm hoping will do a better job.

https://youtu.be/At48Yh4EnHI

And another with same conditions.

https://youtu.be/gVeZeEeRBzM

[matevana]

Here is a spec for what I am looking for.

1. High level inputs from speaker terminals of main amp (therefore no impact whatsoever on the existing two way drivers)
2. DSP for maximum flexibility.
3. Amplification should be best SQ but probably can cope with 50 W/channel minimum. (Class A/B or D Class?).
4. No thump at turn on.

It would be nice to find both high level inputs and DSP in the same unit, but that may prove difficult. I've had decent results with the Yung plate amps. Most have both speaker level and line level inputs, but the lowpass uses an analog signal processor and they obviously don't do biquads, pre/post eq, etc. They are dead quiet when they turn on, but oddly there is a bit of a thump when they power-off, about 20 minutes after the last signal.

[mcgsxr]

I wonder if the Dayton DSP-408 could work?

It is not an amp, but will do all the other things you're looking for.  You could use a pro amp for the woofers.

[Bumpy]

I wonder if the Dayton DSP-408 could work?

Thanks for the recommendation . I will have a look at it. My experience on the MiniDSP site forum is not good - its typical of many HI Fi forum and may threaten my buying from them.

[Bumpy]

A friend leant me a signal generator this evening.

The SEAS Exotic has worthwhile output down to 100hz and thankfully is where I planned to cross it over.

The 15” Altecs with the existing low pass filters have worthwhile output up to 3.5khz. This is far too much overlap and the reason I will employ DSP with separate amp for the bass.

Just thinking out loud really, but the Altecs were supposed to be crossing at 6-700 hz. Useful output at 3.5khz seems rather odd. What do you think?

For completeness it’s low pass filter is currently a 3.9mH inductor in series and a 100uF capacitor in series.

[Bumpy]

A friend leant me a signal generator this evening.

The SEAS Exotic has worthwhile output down to 100hz and thankfully is where I planned to cross it over.

The 15” Altecs with the existing low pass filters have worthwhile output up to 3.5khz. This is far too much overlap and the reason I will employ DSP with separate amp for the bass.

Just thinking out loud really, but the Altecs were supposed to be crossing at 6-700 hz. Useful output at 3.5khz seems rather odd. What do you think?

For completeness it’s low pass filter is currently a 3.9mH inductor in series and a 100uF capacitor in series.

I sometimes feel I am talking to myself, but at least it keeps a record here

I have slept on it and this is my theory for the high frequencies heard from the bass driver.

The bass driver in OB has a severe roll off at low frequencies due to cancellations around the baffle. For this reason to get a balanced output, the bass driver (in my OBs) is more sensitive than the mid range driver (its about 98-100dB) and delivers a higher volume than one can hear at the seating position. But as one gets towards 1Khz the roll off effect from the baffle is severely reduced so the high frequency output from the bass driver has a higher 'volume' and can be heard.