Yes, the final slope rate with determined the " sound" of the system, it doesn't matter if you get there by alignment or EQ. What I was mainly getting at is that you could use 1 woofer in a smaller box and add EQ to the system to get the desired LF response. I suppose you could also EQ a LF hump out of a system but let me think about that one. The Qtc is just a number that reflects how damped the woofers is in a box, I don't think speed is the exact way to describe it but I totally understand what you are referring to. I personally like sealed systems with a QTC of around .85 or so , tends to be a bit more punchy which to me sounds like " speed" don't be so locked into the numbers, do what sounds good to you, and again, you can get to a desired QTC by box size and / or EQ, do remember that excursion goes way up with EQ in a small box . Sorry, I'm kind all over the place here but as always in design, there are trade offs, keep an eye on F3 and excursion....... Or go ported..... One more option just to make this post more confusing, have you ever listened to a passive radiator? Best of both worlds, much lower f3 than a sealed system but still retains the punch or speed of a sealer woofer, no port chuffing, but....... The moving mass has to be larger than the active driver hence a larger diameter cone...... But..... You can put it on the side or rear..... Food for thought .
Since audio isn't a modulated signal I don't think there is any group delay. There is simply time in msec or phase in degrees. There isn't any degrees per second. Honestly I dunno, Prove me wrong. I have to think about this.
Regarding rear of box 'things', if you want to get adventurous, there is a way to get substantially greater sub-output than a simple rear port >
This is to use a 'semi driven' 12 or 15" driver rear mounted. The amazing thing about this is that the most suitable drivers for this are rather cheap
Auto Subwoofers that have very high Xmax & very low Fs. The 'trick to semi drive them' is to connect them via a high value inductor with HIGH DCR.
An inductor in the range of 10 to 12mH would normally be very expensive, however, with a desired DCR of 6 to 10ohms, it is not expensive at all.
This scenario creates what could be called: 'An actively assisted passive radiator', and can create quite amazing results with a touch of room EQ.
PS.
The high DCR of the 'drive inductor' pulls-up the LF impedance way above the 4ohms of the Auto Subwoofer.
The +/- phase wiring is always obvious when you get it right 🙂 [ the rear 'Sub' and its inductor connect directly to the amplifier ]
Sounds interesting but adding that amount of resistance to the woofers will greatly increase it's Qes and Qts making it way under damped / boomy but if that is the goal then it should work
I'm sorry but I don't know the math well enough to give you "proof" but GD is a part of any filter system where slope rate or phase changes. Low frequencies systems roll off because of the enclosure / drivers mass combo and creates attenuation and phase changes, there is always GD when there is phase change, GD is not a a different type of delay, it's just another way to look at delay and phase change. Also, the amount of delay varies with frequency it's not linear . And the term " linear phase speakers" is all marketing..... Although they can't be made these days via DSP.
My other point is that you can easily measure the equivalent amount of delay in feet, if I placed my subwoofer around 25 feet behind my system, it would have around 20 ms of delay ( depending on where you live because the speed of sounds changes a little) Now from purely a intuitive standpoint, you would most likely conclude ( with all output levels adjusted for) that having your speaker 25 feet away would probably do something weird to the sound quality and yes it does.
I posted a great article showing that even 20 ms of GD at low frequencies is audible, in this test, it changed the sound of percussive instruments.
Because different bass alignments have different LF roll off they also have different amount of delay and I am confident that this is audible, people love the natural sound of sealed systems, vented systems typically offer lower bass but many find them unnatural, dipoles have only a 6dB roll of and to my ears sound the best but with many trade offs.
I just tried chat gpt, it gives lots of info on this topic and some crazy math formulas that are above my pay grade
There is more , Group delay is pretty much ignored at least in home audio and the other thing that is ignored is absolute phase, yes you system will sound different if you flip the red and black wires on your speakers ( at the same time) ... But this is for another thread.
I've tried the absolute phase experiment, it is absolutely true in my experience. Thanks for the info on GD, I'll study it further.
In my experience, absolute phase is heard best when you have a system with a great 3D sound stage and playing vocals that were recorder with minimal micing, when switched, the vocals will come forward or go back into the stage, I cant tell you which polarity is correct, I suppose the one that sounds better to me. I did a demo to a DSP engineer in an anechoic chamber, the DAC had a phase switch. He stayed in the chamber alone for 20 min and came out telling that the switch must do something else besides reversing phase and wanted to measure the data stream because this was impossible. I guess one should never believe their lying ears.
I don't! Haha. These are beyond my skills. But I learned an interesting method - thanks 🙂
What I described was a form of passive radiator to replace the use of a port. Ports & passive radiators don't have any direct link to electrical damping.
The small amount of drive to the 'Car Sub' / passive radiator creates a 'synergy effect' with the very low frequency pressure within the box.
The achieved result is not actually an increase of "BOOM", but rather an increase of very low frequency 'THUNDER' = sub output.
Of coarse, the main front-firing woofer still provides regular bass, and is separately wired WRT the rear device.
The key to success lies in the selection of a VERY LOW Fs 'Car Driver' that roughly matches your desired tuning frequency. EG. 20Hz .
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It's quite an interesting subject & debate.
You would think that if a Kick Drum had an initial forward moving pressure wave, then your speakers should follow that accordingly.
Significant phase-shifts found with numerous speakers would seem to 'throw a spanner into the works'.
PS.
Did you know that there was a point in time where JBL drivers and Tannoy drivers had different cone direction upon battery connection of
+ to + and - to - ? I'm not sure what the situation is now 😕
Even before reaching a speaker, there are many chances of polarity reversals and phase shifts in every recording.
A kick drum with a hole in the front head is a Helmholtz resonator, AKA a bass reflex cabinet, AKA a phase inversion cabinet.
The output from the port hole will vary in phase from the original beater head movement and will be 180 degrees out at the tuning frequency, in one specific place. Small movements of the mic around that “place” will yield rather different results.
Kick drums with no port hole are often recorded from the beater side, opposite polarity from the other side.
The microphone's XLR connector “+" voltage pin may be pin two or three depending on the vintage and manufacture of the microphone.
The current standard is positive pressure on the microphone diaphragm should produce a positive-going voltage on pin two. Older mics are often pin three "+".
Personally, I preferred pin three as "+" from a wiring standard, but it didn't win, though millions of microphones and amplifiers XLR inputs were wired that way.
The phase/impulse response of a condenser and dynamic mic are quite different, a moving-coil (dynamic) microphone's electrical waveform lags by 90 degrees and distorts the amplitude of the initial transient.
There are many consoles and outboard gear that invert polarity from input to output.
Many recording consoles have polarity switches on each input.
Most inputs are high passed with filters imparting anywhere from 90 to 360 degrees of phase change, and EQ/Tone controls may be used that can have similar phase changes through out the entire audio bandwidth.
The polarity (and phase response) of each recorded input before mixing is nearly random, and the polarity of the recording may be switched when mastered.
A/B tests have generally proven we are immune to detecting "absolute polarity" so the answer to whether cone movement direction matches a recording is a moot point, even if absolute polarity happened to make it through the recording process.
JBL's old convention of positive voltage to the red terminal causing the low frequency cone to move inward is the opposite of most speaker manufacturers.
Other than on some of their legacy woofers still in production, JBL has changed to the standard of positive signal at the red or + terminal will cause the low frequency cone to move outward.
Most of JBL's high frequency compression drivers are still wired opposite to that standard.
https://jblpro.com/de/site_elements/tech-note-polarity-conventions
I totally agree with everything you mentioned, as I stated, phase reversal is best heard when listening to a system that gives a 3 dimensional sound stage, and simple recordings of vocals are played, the differences heard are not in the frequency domain, they manifest as difference's in the sound stage , the performer might move forward or back, usually one direction sounds subjectively better but who knows if it is actually " phase correct". The changes in stage are subtle but it is very interesting that any changes can be heard.
Here is another tweak with no exact explanation, series Crossovers sound very different than parallel crossovers and again, the differences are heard in the sound stage presentation. I have built identical crossovers both parallel and series, parallel tend to produce a strong center lock in the sound stage while series give you much more width and depth but not that center lock . Not sure why, any guesses? It may have to do with back EMF that the amp sees or possible loading on the amp .
Here is another tweak with no exact explanation, series Crossovers sound very different than parallel crossovers and again, the differences are heard in the sound stage presentation. I have built identical crossovers both parallel and series, parallel tend to produce a strong center lock in the sound stage while series give you much more width and depth but not that center lock . Not sure why, any guesses? It may have to do with back EMF that the amp sees or possible loading on the amp .
Add to all that the phase tricks used in Beatles, Hendrix, and Pink Floyd and over production of albums from the 80's, and the overly compressed trash ever since. I'm not sure you can find absolute phase in any 'pop' recording, and in very few classical recordings.
I have a huge problem trying to get the phase right with my T-lines and subwoofers, I can't imagine what a sound engineer goes through.
I have a huge problem trying to get the phase right with my T-lines and subwoofers, I can't imagine what a sound engineer goes through.
Well said and excellent post 🙂
There is such a myriad of stages where things can get phase altered or even inverted. Great that you mentioned microphones and XLR wiring.
I worked at an importing/distributer company of professional recording equipment where I was instructed 'from above' to continue wiring
XLR as Pin3 hot > even after the industry had adopted Pin2 as hot. Even that phase inversion switch at the front-end of famous mixing consoles
really says it all.