NEW PURIFI 8'' MWoofer [PTT8.0X04]

[ernestcarl]

My apologies, but I don't understand what you're asking for or even referring to, so maybe you can explain it differently?

I think I explained very well, why a fullrange system doesn't fit "perfectly" in a mutlisub setup, don't see what is not constructive about it?

Hmmmn... one would need to create a global EQ (based on measurements from the different seating areas) to create a more blanced bass distribution for each full-range channel when combined to the equalized multi-sub response.

 

[abdo123]

My apologies, but I don't understand what you're asking for or even referring to, so maybe you can explain it differently?

I think I explained very well, why a fullrange system doesn't fit "perfectly" in a mutlisub setup, I don't see how that is not constructive?

Okay the most utmost priority in any bass managed system is that all sources arrive in phase at the listening position so no output (excursion) is wasted.

Lets say we're listening in mono, this means that if we have 3 sources (one of them is full range) we only need to adjust the delay on two of these to actually get them all in phase.

lets push it a step further to stereo, in a stereo setup you want both left and right to be equally distanced from the listening position, so we still only need two of the four sources to have adjustable delay.

So full range speakers can be without a doubt integrated into multiple subwoofers setup as long as the subwoofers have adjustable delay.

Adjusting delay (or gain for that matter) of individual sources to optimize for flattest response instead of assuring that all sources arrive in phase compromises maximum output and should be avoided.

 

[OWC]

Okay the most utmost priority in any bass managed system is that all sources arrive in phase at the listening position so no output (excursion) is wasted.

Lets say we're listening in mono, this means that if we have 3 sources (one of them is full range) we only need to adjust the delay on two of these to actually get them all in phase.

lets push it a step further to stereo, in a stereo setup you want both left and right to be equally distanced from the listening position, so we still only need two of the four sources to have adjustable delay.

So full range speakers can be without a doubt integrated into multiple subwoofers setup as long as the subwoofers have adjustable delay.

Adjusting delay (or gain for that matter) of individual sources to optimize for flattest response instead of assuring that all sources arrive in phase compromises maximum output and should be avoided.

No that's in fact not the concept of getting rid of room modes this way at all.
One does not have multiple subwoofers to maximize total output.
A multiple subwoofer system setup is there to level out the peaks as well as dips at one or multiple listening positions.

I would highly recommend diving into the concept of room modes and Floyd Toole's book Sound Reproduction.
It's beyond the scope of this topic and far to much information to explain, besides the fact that it's a very well written book te begin with.
(so it will me basically copy-pasting everything in my own words, which is rather silly)
As well as checking out the references I just mentioned.

Full range systems can still have benefits in combination with additional subwoofers, I never said that they didn't.
I only said that the amount of freedom of getting the optimal result out of everything is less.

Speaking of which, adding subwoofers with lowpass filters to a full-range system is also not a very good idea in general, since you will get phasing issues around that (subwoofer) crossover frequency.

 

[OWC]

Hmmmn... one would need to create a global EQ (based on measurements from the different seating areas) to create a more blanced bass distribution for each full-range channel when combined to the equalized multi-sub response.

That's one way yes. Although a multi-sub system is more than just an EQ.

Practically speaking it just limits you a little more in sense of freedom of placement, technical setup as well as aesthetics
Is it a workable setup? Sure, why not.

 

[abdo123]

A multiple subwoofer system setup is there to level out the peaks as well as dips at one or multiple listening positions.

I would highly recommend diving into the concept of room modes and Floyd Toole's book Sound Reproduction.
It's beyond the scope of this topic and far to much information to explain, besides the fact that it's a very well written book te begin with.
(so it will me basically copy-pasting everything in my own words, which is rather silly)

Full range systems can still have benefits in combination with additional subwoofers, I never said that they didn't.
I only said that the amount of freedom of getting the optimal result out of everything is less.

Speaking of which, adding subwoofers with lowpass filters to a full-range system is also not a very good idea in general, since you will get phasing issues around that (subwoofer) crossover frequency.

How about instead you read these articles by Dr. Earl Geddes, who has done his PhD in reproduction of sub-frequencies in small rooms, on the use of multiple subwoofers?

Two Great Articles on Multiple Subwoofers by Dr. Earl Geddes

I have written before on the absolute necessity of multiple subwoofers for high-fidelity reproduction of modal region frequencies in a hom...

seriousaudioblog.blogspot.com

you will notice that he never applies high-pass filters on his (full-range) speakers to further reduce spatial variation within the room.

A multiple subwoofer system setup is there to level out the peaks as well as dips at one or multiple listening positions.

Absolutely incorrect. Multiple subwoofers never 'remove' a mode, it only reduces spatial variation / seat to seat variation within that frequency. you will still need EQ to reduce a peak or boost a dip.

Speaking of which, adding subwoofers with lowpass filters to a full-range system is also not a very good idea in general, since you will get phasing issues around that (subwoofer) crossover frequency.

You're still not making any effort to comprehend what i'm trying to say, i never said adjustable delay on subwoofers is optional, only on speakers.

 

[OWC]

How about instead you read these articles by Dr. Earl Geddes, who has done his PhD in reproduction of sub-frequencies in small rooms, on the use of multiple subwoofers?

Two Great Articles on Multiple Subwoofers by Dr. Earl Geddes

I have written before on the absolute necessity of multiple subwoofers for high-fidelity reproduction of modal region frequencies in a hom...

seriousaudioblog.blogspot.com

you will notice that he never applies high-pass filters on his (full-range) speakers to further reduce spatial variation within the room.


Absolutely incorrect. Multiple subwoofers never 'remove' a mode, it only reduces spatial variation / seat to seat variation within that frequency. you will still need EQ to reduce a peak or boost a dip.


You're still not making any effort to comprehend what i'm trying to say, i never said adjustable delay on subwoofers is optional, only on speakers.

I never make any effort in comprehend what I'm saying?
It's quite literally written right there?
I have no idea how to even respond to those things and how those kind of comments have any positive and/or constructive contribution to a discussion?
(and the nice positive vibe/attitude in general)

It feels more like having an argument just for the sake of having an argument at this point, instead of having an healthy critical view on the matter.
Besides, if we are going to talk on this kind of level I also expect a certain level of knowledge as well as having just an open and positive mind on the subject.
"Just" referring to some articles without understanding and having the insight what it means in the bigger of things, is not discussing.
I find it borderline disrespectful to be very honest, with the default idea that everyone here is just a total noob or something?
(and even if so)

Yes, I am extremely familiar with Earl Geddes his work, have read it multiple times when they just came out, and later as well.
Also discussed it with many many people before. Some of them producing one of the best active monitors one can buy atm. (objectively spinorama speaking)
If you checked those other references you will see his work is right there as well.
You don't have to tell me what all those guys do, what their background is and what their findings are, they are VERY well known to me.
I also deeply admire and respect them for all the work and effort they did.
In fact, those are must have standards for any engineer in the field in my opinion.

it only reduces spatial variation / seat to seat variation within that frequency

That is exactly when we are looking for.

Fact is, I am just not exactly agreeing with his approach in general. (and I am not the only one for that matter)
For one, extra loading your full-range speaker with lower frequencies is never a good idea.
Excursion wise (distortion) as well as IMD
Yes, it will give you a little bit better spatial variation, but another subwoofer or two will do the same thing without having those downsides.
With the benefits of being able to get mid-woofers that can just focus on frequencies above 100-300Hz or so.
Which practically also means you can make the cabinet a lot smaller, moving internal standing waves up meaning damping material will work a lot more efficient

As in the given example, this will be a major issue in a 40-50 liter cabinet.

I am also not so sure about the whole idea of not being able to remove a mode.
To give a simplified example, when the listener is very close to the wall and the source is on the opposite wall, the output will be maximum, so a huge peak will occur (at the frequency of the distance between the walls minus some losses and shifting because of end-correction)
When I place another source close by the listener that is the opposite phase of the other previous source, the level at that position will and must be lower.

By definition any wave in space has a polarity relative to another wave.
Which would suggest that a standing wave also a some kind of phase.
If I add two sources in the same plane (2 dimensional) on the opposite site with reversed polarity, the result will be zero.
(and it actually is, just measure it in a plane wave tube)
Which brings us to Geddes his point of not being able to interact with the room modes.
His work is solid on this, I have no doubt about that, but somehow it seems in conflict with some other fundamentals at the same time.

Besides is the practical story from this.
I basically doubt if some people ever played with delays in their room with multiple subwoofers?
I have (in fact, it's part of my job) and there are plenty of cases were a delay most certainly helped with room modes.
No NOT by removing them, but by leveling out the whole response.

Anyway, I am more than happy to discuss that thought, but only if that can be done on a constructive way.
Which can be a nice topic, however totally offtopic to my earlier comment about a multi-sub system and even much more offtopic to Purifi speakers.

 

[Mario Sanchez]

Any comments on the response taking off in the mid kHz region?

It's probably just the aluminum cone doing the stiff cone thing -- dramatic breakups.

 

[D!sco]

You will be surprised to find out that for many famous 188” drivers it’s the opposite. It is not easy to move a large piston without breaking up.

I feel like I've destroyed at least one of these in my youth. Crazy xmax, high moving mass and low rigidity are a recipe for disaster

 

[changster]

I can't wait to try these as midbass drivers in a car.

 

[ROOSKIE]

Any comments on the response taking off in the mid kHz region?

Speaking of which, adding subwoofers with lowpass filters to a full-range system is also not a very good idea in general, since you will get phasing issues around that (subwoofer) crossover frequency.

I overlap 1/2-1 octave all the time on purpose to help fill in nulls.
48db slope on the subs means zero issues with phase cancellation in the over covered regions.

 

[witwald]

The breakup modes at 5.2 kHz and 6.8 kHz seem to be very bad and relatively uncontrolled. They are certainly far from being well damped, at almost 15 dB above the flat part of this driver's response.

 

[jhaider]

If we are talking about a non-compromise approach anything else than a 2-way monitor plus a multi-sub setup is a to much of a compromise in my books.

I think that depends on your dispersion target. If you’re targeting wide a 3-way with a tiny mid (2”-4”) makes a lot of sense. This woofer would be really nice in that kind of 3-way.

Imagine that stiff paper surround when the cone is moving a total of 4cm, almost 2” without tearing itself apart…

There aren’t many manufacturers one can count on making that work, but B&C is in the “yes they can” club. The iPAL drivers have been around a while and are well proven at this point.

 

[jhaider]

Dr. Earl Geddes…never applies high-pass filters on his (full-range) speakers to further reduce spatial variation within the room.

Well…technically no. But model the B&C woofers he uses in the closed boxes he uses. They start to roll off fairly high on their own, to the extend that he basically uses a 2nd order high pass on them. They’re monsters so strain isn’t an issue.

 

[Adi777]

I think that depends on your dispersion target.

Is it about the width of the sound stage, the field of fire?

 

[fluid]

The breakup modes at 5.2 kHz and 6.8 kHz seem to be very bad and relatively uncontrolled. They are certainly far from being well damped, at almost 15 dB above the flat part of this driver's response.

Purifi have an app note that shows how to use a passive notch filter to tame the aluminium drivers breakup

https://purifi-audio.com/wp-content/uploads/2022/03/220211_R05-Notchfilter.pdf

 

[Puddingbuks]

8C utilizes Wavecore 8.5 inch drivers as subwoofers and they are among the best I've seen in term of low distortion.

SW223BD02_03

I meant the front woofer.

 

[SDC]

Can't wait to try these beasts in 2 way unity horn. Perfect size and amazing lows, I've been waiting for so long.

 

[witwald]

Purifi have an app note that shows how to use a passive notch filter to tame the aluminium drivers breakup

https://purifi-audio.com/wp-content/uploads/2022/03/220211_R05-Notchfilter.pdf

Thanks for the link; the document made for interesting reading. The passive notch filters do seem to do quite a good job at bringing down the peaks to follow the desired acoustic roll-off.

 

[hardisj]

Purifi Audio PTT8.0X04-NAB-02 8 Inch Woofer Review

Purifi Audio PTT8.0X04-NAB-02 8 Inch Woofer Review

www.erinsaudiocorner.com

 

[changster]

Purifi Audio PTT8.0X04-NAB-02 8 Inch Woofer Review

Purifi Audio PTT8.0X04-NAB-02 8 Inch Woofer Review

www.erinsaudiocorner.com

Nice! Thanks for this. Will you be writing a Thoughts / Conclusion subjective section?