Anyone running with separate amp and active crossover for their bass drivers

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Openly Baffled

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Hi Bumpy,

I am hugely encouraged by the runaway success of my midrange, so I press on.

Great that you have achieved Open Baffle Nirvana in the midrange. It's certainly a sound that once heard, can never be unheard - so no going back.

Deep bass is always a challenge. Mine can be flat to 20Hz with active equalization and bi-amping - hence my interest in this thread. This is using a 15" and 12" woofer combo.

Below is an REW plot of my speakers - in room - from the discussion with Giles above.


Kyron Audio's Gaia achieve 25Hz with no baffles and active equalization... at a price ;)
http://kyronaudio.com.au/gaia.html
I would love to hear these in action.

Distance from the wall is important. I find 5-6ft is a good trade-off between sound and practicality. In a hall with 15ft behind them they sound quite different.

Don't be too concerned about bass-mid centre distance. The phase error only appears in sounds reflecting off the floor or ceiling. I think the advantage of raising the mid away from the floor should counter any other negatives.

gils

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Hello,

no correction  ;)




best regards Gilles

Bumpy

  • Jr. Member
  • Posts: 199
Hello,

no correction  ;)




best regards Gilles

Thats great Gilles. Do you have a reference to your system?

Bumpy

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I have been reflecting on my 15" bass drivers which are vintage alnico Altec 416B.

They are what is know as VOTT, meaning 'Voice of the Theatre', and spent their formative years in a theatre or cinema so I guess they are well able to pump out the low frequencies  :wink:

Up till now, running in unison with the mid range and tweeter fed by a single amp, they deliver an acceptable level of bass for me, but interestingly I have never really seen the cones move even on heavy bass notes. I am therefore guessing with a separate amp and DSP I may be able to release the genie from the bottle.


Bumpy

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Simple question I thought I would slip in here.  :)

The picture shows my simple high pass filter on the tweeter. I believe twinning up capacitors like this is done to 'neutralise' magnetic fields, but what is the configuration called. I did know but have forgotten  :duh:




gils

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Thats great Gilles. Do you have a reference to your system?

this is speaker infraflex  36"  :)



best regards Gilles

gils

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  • Posts: 72
I have been reflecting on my 15" bass drivers which are vintage alnico Altec 416B.

They are what is know as VOTT, meaning 'Voice of the Theatre', and spent their formative years in a theatre or cinema so I guess they are well able to pump out the low frequencies  :wink:

Up till now, running in unison with the mid range and tweeter fed by a single amp, they deliver an acceptable level of bass for me, but interestingly I have never really seen the cones move even on heavy bass notes. I am therefore guessing with a separate amp and DSP I may be able to release the genie from the bottle.



Hello Bumpy,

very good job but the Altec 416 is made for horn speakers, his QTS too low does not allow him to produce bass in open cabinet, he find you a speaker 15 "or 18" low blow (50 €) with a small engine, much like the 15A eminence at high QTS.

best regards Gilles

Bumpy

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Its always an interesting debate around Qts. Many of us, including me, learnt most of what we know from the Lampizator.

Here is how he describes the bass driver with a recommendation for the Altec in the P17 on which mine are based  - 

Max Fs 37Hz, optimum 25Hz
Min sensitivity 97dB
Max Qts 1 optimum 0.35

The other advantage of the Altecs in my baffles is the voicing marries up beautifully with vintage alnico magnet, paper cones of the mid and tweeter.

I have an open mind on this and if not successful with the Altecs I'm quite prepared to try others.

Tyson

I use active servo bass drivers in my setup (GR Research Super 7s).  It's nice because it goes to 20hz with tons of power, but is also extremely fast, tight and tuneful.  They'll play up to 200hz and thus will mate with just about any "top portion" you care to run.  It's nice because it solves the whole bass issue in one elegant package. 

Servo drivers in an OB config really is a game changer.

Bumpy

  • Jr. Member
  • Posts: 199
I use active servo bass drivers in my setup (GR Research Super 7s).  It's nice because it goes to 20hz with tons of power, but is also extremely fast, tight and tuneful.  They'll play up to 200hz and thus will mate with just about any "top portion" you care to run.  It's nice because it solves the whole bass issue in one elegant package. 

Servo drivers in an OB config really is a game changer.

Interesting alternative. Do you have a website reference?

Tyson

Interesting alternative. Do you have a website reference?

The kits are on the GR Research website here - http://gr-research.com/diysubwooferkits.aspx

And they also have a forum here on AC.  The thread that's probably most relevant to check out is the one discussing the H-Frame flat packs, here - https://www.audiocircle.com/index.php?topic=139480.0

Bumpy

  • Jr. Member
  • Posts: 199
The kits are on the GR Research website here - http://gr-research.com/diysubwooferkits.aspx

And they also have a forum here on AC.  The thread that's probably most relevant to check out is the one discussing the H-Frame flat packs, here - https://www.audiocircle.com/index.php?topic=139480.0

Thanks, a good read.

gils

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 :D

U-Frame  40 cm  for 18" and U-Frame 20 cm for 10" :)





https://drive.google.com/file/d/1KPzI9mvwnelNzvyA72NHTrWvbKpsAgf5/view?usp=sharing

best regards Gilles

Bumpy

  • Jr. Member
  • Posts: 199
Its always an interesting debate around Qts. Many of us, including me, learnt most of what we know from the Lampizator.

Here is how he describes the bass driver with a recommendation for the Altec in the P17 on which mine are based  - 

Max Fs 37Hz, optimum 25Hz
Min sensitivity 97dB
Max Qts 1 optimum 0.35

The other advantage of the Altecs in my baffles is the voicing marries up beautifully with vintage alnico magnet, paper cones of the mid and tweeter.

I have an open mind on this and if not successful with the Altecs I'm quite prepared to try others.

I have Googled and read quite a lot of stuff on the relative merits of high and low Qts.

This is my easiest to understand definition.

Qts: The Qts is the total damping which is the combination of mechanical and electromechanical damping. The higher the number = the drivers inability to come to rest after the electrical signal has ceased.

So in the context of our bass drivers, high Qts means the driver is more 'springy' and able to respond better to the signal hence better (easier) low bass, but that comes at the expense of poorer control which must impact on SQ.

Low Qts can be selected for more control of the driver hence improved SQ. But the driver is more damped and low bass is more difficult to achieve easily. I would welcome your response.

Openly Baffled

  • Jr. Member
  • Posts: 13
I would welcome your response.

I agree with your observations and definition.

The "Q" of a second order system is a simple measure of resonant damping. Q < 0.7 is overdamped and less resonant, Q > 0.7 is underdamped and more resonant.

High Qts driver are used in open baffle to increase bass near the drivers Fs. I believe this comes at the cost of ringing and poor impulse response.

My obs and listening tests lead me to the conclusion that high Qts is undesirable unless the system needs to be passive.

Active systems can tolerate low Qts drivers and give better performance but require more power and more EQ.

I personally went for a Qts just under 0.7 in an attempt to get good impulse response with minimal EQ. The result seems to be tight, deep and "effortless" bass. The majority of GR Research's excellent servo subs also have Qts near 0.7 with one notable exception.


gils

  • Jr. Member
  • Posts: 72
hello,

impulse reponse bad ?  :nono:

look   :D



best regards Gilles

MJK

  • Full Member
  • Posts: 462
    • Quarter Wavelength Loudspeaker Design
I agree with your observations and definition.

The "Q" of a second order system is a simple measure of resonant damping. Q < 0.7 is overdamped and less resonant, Q > 0.7 is underdamped and more resonant.

High Qts driver are used in open baffle to increase bass near the drivers Fs. I believe this comes at the cost of ringing and poor impulse response.

My obs and listening tests lead me to the conclusion that high Qts is undesirable unless the system needs to be passive.

Active systems can tolerate low Qts drivers and give better performance but require more power and more EQ.

I personally went for a Qts just under 0.7 in an attempt to get good impulse response with minimal EQ. The result seems to be tight, deep and "effortless" bass. The majority of GR Research's excellent servo subs also have Qts near 0.7 with one notable exception.

You can't just look at a drivers Qts and conclude how it will perform in an OB system,

While a high Qts (1.0 to 1.5) woofer will ring in a box when placed in an OB the low end will be rolled off and the resulting combined SPL response will be flat and then roll off to eventually become an 18 dB/octave slope. You can adjust the depth and shape of the bass response by changing the size of the baffle and the position of the woofer.

If you place a lower Qts (< 0.5) woofer in an OB speaker the low end will be very weak until you add some low frequency boost/EQ to raise the low frequency output producing a flat SPL response that will also eventually roll off at 18 dB/octave.

If the low and high Qts OB speaker systems exhibit similar low frequency responses then the woofer cone's are behaving in a similar manner. The low Qts woofer with EQ added will produce the same infinite baffle response shape as the high Qts woofer, both may ring.

Assuming the goal for OB bass is the same the performance should also be reasonably close if you get their with a low Qts or high Qts woofer. A simple, inexpensive, and passive option is only achieved with a high Qts woofer without any sonic problems if the designer knows what they are doing. A low Qts woofer traditionally used in a box speaker will probably be more expensive due to the bigger/stronger motor, require EQ which means an active set up, which means a second amp adding more cost and complexity. Both approaches can work well, pick your trade-offs.

Openly Baffled

  • Jr. Member
  • Posts: 13
While a high Qts (1.0 to 1.5) woofer will ring in a box when placed in an OB the low end will be rolled off and the resulting combined SPL response will be flat and then roll off to eventually become an 18 dB/octave slope. You can adjust the depth and shape of the bass response by changing the size of the baffle and the position of the woofer.

I agree in part. My understanding is…

Qts is derived from Qms which is a measurement of mechanical damping at resonance in an infinite baffle configuration. This is very similar to the mechanical behavior exhibited in an open baffle speaker which is related to infinite baffle when the woofer is mounted on a solid board..

The reason that most systems using high Qts drivers don’t exhibit a rise in their bass response, is because Fs is below the baffle cut-off frequency and therefore the “bump” at Fs is subject to a -6db/oct baffle slope.

However, the resonance at Fs is still occurring and results in the desired bass boost that some Open Baffle designers are after. BUT, the boost is only a result of resonance and this can be heard as a bass artifact and impacts the impulse response due to ringing.

From a basic physics point of view there is no free lunch. The bass boost is only a result of resonance and the ringing in the time domain is convolved to product a response gain a in the frequency domain.

It's not altogether a bad thing - getting bass where otherwise there would be very little is certainly a plus for a passive speaker.

MJK

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    • Quarter Wavelength Loudspeaker Design
Quote
However, the resonance at Fs is still occurring and results in the desired bass boost that some Open Baffle designers are after. BUT, the boost is only a result of resonance and this can be heard as a bass artifact and impacts the impulse response due to ringing.

I don't agree with that at all. There is no ringing in a well designed OB with a high Qts woofer.

So you don't think that a low Qts woofer with EQ applied, to selectively boost the lowest frequencies and counteract the 6 dB/octave roll-off due to the baffle, does not exhibit the same resonant behavior as a high Qts woofer if you tune the systems to produce the same low frequency SPL response.

gils

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Hello

Listen to the difference between the original and my copy with the cabinet open baffle, there is a problem mainly in the low medium "ringring" there is other but less important.
the bass 18 "is low 30Hz to 80Hz and the medium 10" 80Hz to 2KHz, the compression over the spectrum up to 18Khz.
the Altec 416 of very good quality could be tuned from 80 Hz to 2 Khz and use a loudspeaker for bass with high QTS to reproduce the bass.
I will try to find a good quality speaker in 10 " whatever his QTS, there I think will be the right solution, the pickups when taking his sound were 2 m from the speaker.

https://drive.google.com/file/d/1dGagEpdXyg491T1y_84s49_mi5BkWcqD/view?usp=sharing

original version

https://youtu.be/_agnoIXNc3w

best regards