I have a pair of T25B. It won't match as is but with a pair of augerpro waveguide should be a possibility. I don't plan to get the M74A for now.
That's a really good question! Firstly apologies as I am still new with this so I might be making some wrong assumptions.
Room size is 400 sq ft / 37 m^2 . It is slightly big for a pair of PTT8 but should be sufficient. I tried a pair of PTT6.5, it did ok in this room with a little bit of strain. I am hoping the PTT8 will handle it better. I am free to place it anywhere in the room. To back wall distance is flexible.
As for Vb, f3. Again please correct me if I am wrong. Firstly I am pretty flexible. Obviously the lower the better given the compromise on either sealed or ported alignments. I'd like to have it sealed but f3 modeled around 49Hz which I can probably live with but ported goes down to 29Hz. I listen to mostly classical so a sense of scale for orchestral pieces are important to me.
And the final Vb is flexible.
Also, I started doing a lot of active XO but this one I want to have it passive.
At a higher level goal, this is all for learning purposes. I am even ok to try different alignments but I hope each iteration will give a decent result and at the same time I get to learn something.
The great thing about Purifi is that you can avoid HP filters and hereby get a smoother transition to subwoofers, and then get a much better sub 150Hz response in any room. I cross two 8" woofers at 60Hz with first order HP filters, to avoid excessive in the very low end and at the same time get a smooth blend with my subwoofers, which play up to around 90-110Hz. That overlap, gives a much smoother overall response in the entire room, in my experience.
My understanding from Geddes' work is, that you'd need a main speaker capable of at least 40-50Hz to blend well with subwoofers, because a HP filter to protect smaller woofers, would introduce phase issues, making the integration in the modal range worse. Which is also why I prefer closed boxes all over, to simply get rid of potential phase issues. You gain a lot of SPL with ports and PR... But I believe the price is phase issues. When not using subwoofers and long FIR filters, then closed boxes are for me the easiest.
The overlap between subwoofers and mains, blend them well, even out the response very smoothly and uses the mains as extra bass sources... Smoothing out the overall response even more. The trick is no or low order filters on the mains and then experiment with the subs. All compromises taken into account, I found the best balance with low order on the mains and 48dB LR on the subs. The overall smooth bass response, is in my view WAY more important, than the way you get it.
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Currently the way I see it is this:
The PTT8.0X is too good a mid-bass to NOT use it as a mid-bass.
A) By that I mean it's phenomenal from 40Hz to 2KHz, and using it just as woofer up to 300 to 600Hz, for example, is a bit of a wasted opportunity IMHO.
Because there are plenty of other woofers that have been available for the past decades that can play fine from 40Hz to 600Hz.
Larger (?future) Purifi woofers will also do this range as well, with even more authority and potentially lower distortion!
But to go from 40Hz to 2KHz... none are as smooth and flat up to 2Khz.
Like all 8" drivers it starts to beam at 1K, so you'll need to cross over somewhere between 1-2Khz.
Since most modern tweeter are comfortable down to only about 2KHz, this mean you'll need a mighty robust tweeter, or a tweeter with a waveguide. So you'll need to think about that too.
B) Cabinet volume. In a sealed box anything from 20-30L litres works ok.
With sealed 30L, F3/F6/10 is 58/42/30Hz. That's ok for smaller rooms or certain musical styles.
If you want deeper bass, I would install some passive radiators.
But a quick fix would be a pair of 2" ports, 14"-16" long. With ports this long, they'll have to go along the length of the cabinet, hence down-firing is the obvious choice.
With this BR of 30L and Fb of 30Hz, the F3/F6/F10 is 38/30/25Hz.
If you're not sure which way to go, I would build the BR cabinet, then block the ports with some thick socks and this turns it into a sealed box.
Then you can listen to both and see how you like it.
Spoiler alert- Most people like more bass, and the group delay is still fairly low at 100/50Hz (1ms/6ms), so you'll probably prefer the BR. But really under 200Hz it really depends on your room, how far away from the wall you place your speakers, and your program material.
I like sealed with a F3 of 40Hz, but that's my room.
B) Baffle dimensions- A wider baffle like 350mm wide allows a buttery smooth response all the way out to 2KHz.
eg:
In a narrower baffle it looks something like this eg. 24cm wide:
Here's an overlay of the difference:
The narrower baffle results in a loss of about 1dB under about 600Hz, but a bump centred around 1.3Khz.
If you're doing a passive crossover; for the narrower cabinet that means
i) 1 dB sensitivity loss (passive crossovers are subtractive)
ii) having to deal with that 1dB bump around 1.3Khz with your crossover (more components)
At this point you might be wondering... really? does 1dB really make a difference?
But actually sometimes that's all the difference there is between something that i can't get it to sound quite right.
to "Ah, just right!"
Best of luck and have fun!
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How did you calculate that beaming starts at 1k?
Speed of sound/diameter of cone equals 1988 hz
Or am I wrong?
Speed of sound/diameter of cone equals 1988 hz
Or am I wrong?
Dutch & Dutch C8 cross their 8" at 1150 Hz... So maybe something else is in play too 🤔
If you look at all the 8" drivers on hificompass.com and examine the normalized off-axis response, you can see this beaming. In nearly every 8 inch woofer, the 30-45-60 degree responses follow the 0-axis responce up to about 1k. They start to diverge from the 0-axis response somewhere between 1k and 1.2k. By 2k, the 45 degree response is 4-6 dB lower than the 0-axis response.
This is a typical 8" driver normalized off-axis response. 15, 30, 45, 60 degrees.
... more thoughts... There is a guideline from the "pre-simulation era" that says that a driver starts to beam when Ka = 2.
For a driver with an Sd of 220 cm^2 (typical of an 8" woofer), Ka=2 corresponds to 1300 Hz.
So all of this broadly agrees with @tktran303 's statement about starting to beam at 1k.
For a driver with an Sd of 220 cm^2 (typical of an 8" woofer), Ka=2 corresponds to 1300 Hz.
So all of this broadly agrees with @tktran303 's statement about starting to beam at 1k.
@tktran303 Thanks for all the wonderful suggestions.
Some thoughts and responses.
350mm baffle makes a lot of sense. The drivers outer dimensions are 221mm and that leave around 65mm each side, which won't look out of place.
As for Vb. I played around with VCad before and arrived at closer to 40L for BR. Are there tradeoff to smaller box other than higher F3?
As for going from 40Hz to 1-2kHz. I totally agree. Right now in my mind, I am thinking one of: T25B+augerpro, JBL 2451+STX825, or TW29BNWG. All of which are comfortable to 1.5kHz if not lower.
Some thoughts and responses.
350mm baffle makes a lot of sense. The drivers outer dimensions are 221mm and that leave around 65mm each side, which won't look out of place.
As for Vb. I played around with VCad before and arrived at closer to 40L for BR. Are there tradeoff to smaller box other than higher F3?
As for going from 40Hz to 1-2kHz. I totally agree. Right now in my mind, I am thinking one of: T25B+augerpro, JBL 2451+STX825, or TW29BNWG. All of which are comfortable to 1.5kHz if not lower.
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My biggest waveguide for the T25B is 6.5", and that has pretty much last pattern control at that point. So I wouldn't expect the distortion to look any different than the factory tweeter at 1.5khz. OTOH, they tweeter naturally rolls off pretty fast that low, so I'm not sure how possible it is to cross that low. That's why I never made a larger waveguide for it.
Do it! Waveguiding a good tweeter ( suitable for the job ), is some of the best thing I ever did for my home audio experience 👍
The SB26ADC i use, is a great tweeter on its own. But a WG like Augerpro's, helps the basic great tweeter construction/design, sound its best, with the improved/controlled acoustic output, which a normal flush mounted tweeter won't have.
It's been two years since I purchased a set of PTTs. Only now have I finally fired one up and I'm doing a lil celebration. To get just the one driver going I spliced it into a BW cabinet I had lying around. The upper chamber is about 12L sealed but the tweeter hole is acting as a vent. To approximate the recommended crossover I had to roll a nasty air coil from some 12awg magnet wire and at some point I gave up on counting turns and went for big.
It's running on straight battery power through an M2. The BWs are bi-wire so I am running the PTT and the BW tweeter together. It's pure Frankenstein but I'm loving it already. Just the cobbled together hardware is giving a serious glimpse into the potential of this stuff and I can tell it's gonna be excellent in final form.
Seeing the PTT in the narrow BW cabinet has me leaning towards a narrow version of the aluminum baffle. The original baffle I made for it is 8" but that almost seems too bulky now. Can't wait to get all this gear into a final package!
It's running on straight battery power through an M2. The BWs are bi-wire so I am running the PTT and the BW tweeter together. It's pure Frankenstein but I'm loving it already. Just the cobbled together hardware is giving a serious glimpse into the potential of this stuff and I can tell it's gonna be excellent in final form.
Seeing the PTT in the narrow BW cabinet has me leaning towards a narrow version of the aluminum baffle. The original baffle I made for it is 8" but that almost seems too bulky now. Can't wait to get all this gear into a final package!
Where are all the compact sealed multiple driver purifi diy speaker builds? 🙂
Looking at the success of Kii, D&D, Buchardt I would have thought purifi tech would attract more innovative/modern (?) designs. Not judging anything I’ve seen here as old/inferior however. I’m inspired by everything.
Looking at the success of Kii, D&D, Buchardt I would have thought purifi tech would attract more innovative/modern (?) designs. Not judging anything I’ve seen here as old/inferior however. I’m inspired by everything.
The restriction is access to good, cheap DSP technology. Everything you're using as an example is active and uses principals that aren't very well understood by the public like delay, phase, cancellations and actually getting a decent enough recording of the equipment to do any of it correctly. D&D started on this forum. The thread is still up.