With wave guide the smaller T25B tweeter schould be perfect to combine with the MW19TX. Where do you plan to cross over?
It's probably bad to hear - but the T34A is pretty bad to put in a waveguide. It's membrane geometry is built for wide dispersion and very bulging - causes problems at high frequencies.
If you want a WG - get T25B ot T34B. If you want to use the T34A - get a low crossover and enjoy the incredible wide dispersion of that tweeter
AKABAK, I asked Stanislav of Bliesma nicely and he gave me the info that I needed. More mesh resolution would clean up the over 10K wobbles seen in the previous graph.
Getting the details from the manufacturer if they are willing is the best way, there are cheap small 3D scanners now to go with the cheap small 3D printers.
A soft profile gauge and a couple of cardboard templates would probably work too.
A gentle waveguide works but the tall dome and wide dispersion does make it tricky, real life measurements of something very similar to the simulation I ran.
https://www.diy-hifi-forum.eu/forum/showthread.php?17431-Die-AB-Wave&p=247807&viewfull=1#post247807
That is good advice and the German project linked above does just that. The Beryllium drivers are much more flexible for waveguide applications.If you want a WG - get T25B ot T34B. If you want to use the T34A - get a low crossover and enjoy the incredible wide dispersion of that tweeter
With wave guide the smaller T25B tweeter schould be perfect to combine with the MW19TX. Where do you plan to cross over?
It's probably bad to hear - but the T34A is pretty bad to put in a waveguide. It's membrane geometry is built for wide dispersion and very bulging - causes problems at high frequencies.
If you want a WG - get T25B ot T34B. If you want to use the T34A - get a low crossover and enjoy the incredible wide dispersion of that tweeter
Thanks @fluid and @IamJF for your replies and insight!
By using a waveguide for the T34A my goals were to
1) reduce diffraction. My earlier prototype of the 2-way showed huge diffraction. I expect the extreme wide dispersion of the T34A made diffraction even more intense than usual.
2) slightly improve the directivity match with MW19TX around the crossover point of 1300 hz (with LR4).
3) slightly reduce reflections. My living room is quite reflective, mainly via floor and ceiling. A waveguide might reduce the high frequency scattering a bit.
But, back to the drawing board, and see if I can achieve my goals without a waveguide with
1) large trapezoidal cabinet chamfers
2) center to center distance of 1.2x between woofer and tweeter
3) careful chosen baffle dimensions and driver positioning
The small waveguide would still assist in this, I don't have anything ready made like Brandon but I can knock something up that you could print and test if you want.
This is going to be hard without something deeper and comes with other issues.
Small waveguides like these don't do a great deal to fix this
The chamfers will help a lot. 1.2 x wavelength at 1300Hz is gonna look pretty weird
When the crossover is that low 1/2 wavelength is 13cm so if you squeeze the drivers together and get the CTC under 0.5 WL there is no reason to push them out to 1.2WL.
Vituix and simple piston simulations can give you a good idea of baffle diffraction, and generally by avoiding bad decisions like making multiple diffraction sources the same distance a lo of the bad stuff can be mitigated.
This my vision of something similar, the small waveguide can still fit inside the T34A's mounting diameter.
That would be great @fluid !
If it could fit inside the default ~10.5cm mounting diameter, that would be perfect because then I can easily switch and compare measurements.
The MW19TX diameter is already 18.7cm, the T34A is 10.4cm. So minimum distance c-t-c is at least 14.6cm (15.6 with 1cm spacing). That is approx 2cm above 1/2 wavelength. Is that still close enough?
1) I use 25mm roundings on all corners - that helps. Huge and expensive router but it pays off. And do a position simulation, off center position ist most of the time preferable.
2) Get them as close as possible! It sounds more as "one driver" if the acoustic centers come close together. I very often modify frontplates but with Bliesma you have to be VERY careful.
3) Get the reflections at least linear and sound good. An absorbing cloud will also help ... ;-)
I don't know exactly but you can reach out to Stanislav - he was always super supportive for me!
But I know that they where not able to do the shape of the aluminium version with Beryllium cause the material is to hard/not easy to handle.
Btw membrane resonance of the T25B is way higher as ScanSpeaks and the others - they are leading in this regard. Sensitivity is also higher but they can handle less power, so over all sound pressure level is about the same.
^^Hi,
we can go further with the tips. While any edge roundover and offset helps diffraction ripple best performance comes when the system approximates a sphere, start the rounding right at the transducer edge and make as big roundovers as fit
Also driver spacing, thing is its not possible to get drivers (tweeter) close enough to actually make point source acoustically, without going to third dimension (multiple entry horn). Usually the close spacing ends up being about worst possible, worst power response and nulls towards early reflections. So the next best option is to expand the driver spacing, introduce side lobes and try smoothen response towards early reflections, smoothen power response. The main lobe is usually still wide enough to not introduce problems in main listening position. With good direct sound and smooth power response, early reflections, the sound should be more "one driver" than with close driver spacing. Of course consider case by case. And the looks is a bit weird. Another way to make it would be have the drivers closer together and just use higher xo frequency.
we can go further with the tips. While any edge roundover and offset helps diffraction ripple best performance comes when the system approximates a sphere, start the rounding right at the transducer edge and make as big roundovers as fit
Also driver spacing, thing is its not possible to get drivers (tweeter) close enough to actually make point source acoustically, without going to third dimension (multiple entry horn). Usually the close spacing ends up being about worst possible, worst power response and nulls towards early reflections. So the next best option is to expand the driver spacing, introduce side lobes and try smoothen response towards early reflections, smoothen power response. The main lobe is usually still wide enough to not introduce problems in main listening position. With good direct sound and smooth power response, early reflections, the sound should be more "one driver" than with close driver spacing. Of course consider case by case. And the looks is a bit weird. Another way to make it would be have the drivers closer together and just use higher xo frequency.
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OK let me see what I can do
That's about 0.58 WL which is heading into the messy zone. I suppose it would depend on what a practical alternative would be. Simulating similar sized pistons in Vituix and varying the XO frequency and CTC distance will give you an idea of which you like best. You can always fudge the phase a bit or have the slopes a little asymmetrical to get the in room and power response smoothed out.
That's why I use dome mid drivers when I want as broad as possible radiation - centers are at 8cm distance with my actual design. That's 0.42 WL for the low crossover configuration.
In my hearing trials I compare to KEF LS50 and Neumann KH120 - both solid performers with very good radiation off axis. And I always tend to prefer the closest distance between HF and MF. I even prefered a TM configuration over a MTM cause the signal source was more "pointy", MTM had some vertical "dimension" to it. (Sorry, no native speaker
) What was surprising cause I WANTED to like the MTM ;-)But my room is very controlled and listening distances are small - so that's kind of an extreme situation.
To the project - you can remove about 1cm of the T34A front plate which gets you to 0,51 WL. Or change the tweeter (T25B?) and go with a waveguide.
I even prefered a TM configuration over a MTM cause the signal source was more "pointy", MTM had some vertical "dimension" to it. (Sorry, no native speaker
I've had opposite experiences, where (good) MTMs had a more focused sound that seemed to project to the listener more than a TM using the same drivers. I always assumed the it was the lower vertical reflection energy of the MTM that was the cause. Now there were other tradeoffs with MTM, but in this regard it seemed better than TM. And it has always struck me that as "bad" as MTM are, there are many that have been very well reviewed many times. Olson's Ariel for example. Another is the Salk SongTower that has won shootouts at get-togethers over much more impressive speakers, JBL M2 comes to mind. Now this was purely sound quality at casual listening levels. At concert levels, or probably even club levels, the M2 pulled ahead.
Do you have any (simulated) measurement spin-data from what you think is a good MTM-speaker? Most of the ones I have seen have a pretty "bad" lobing in the vertical window.
I don't. Just pointing out the weird incongruity between the measurements and subjective impressions. I wonder though, even though a speaker might have much rougher off-axis response, does it matter if that response is also 6 dB lower than something like a TM? I think that is where the benefit from some of the better MTMs may be coming from. Yes it's worse off-axis but there is also less energy getting reflected to combine with the summed response at the listening position. Another consideration may be where this lower energy is in the spectrum. If it's lower in the 1-3khz area, perhaps this helps subjective performance because humans really dislike energy that is almost the same as the on-axis, reflecting off the ceiling and to the listening position? Or maybe some of the experiences I've had are exactly due to the common 8' drywall ceiling. If it was a taller ceiling, a treated ceiling, or outside, the superior-measuring TM would pull ahead subjectively. So a lot of this might be conditional, but if it is the most common condition than certain tradeoffs might swing one way versus the other in different conditions.
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BTW guys, what is the less expensive in your countries, please ? CNC 5 axes or 3D print ?
Seems to me the CNC should be very cheap due to the rapidity of the process VS 3D print. Ocupation rate of the CNC machine is short and the energy consummed too between 10 minutes and several hours !
Any experience about cost effective CNC ?
Seems to me the CNC should be very cheap due to the rapidity of the process VS 3D print. Ocupation rate of the CNC machine is short and the energy consummed too between 10 minutes and several hours !
Any experience about cost effective CNC ?
Alright yeah. No speaker is perfect ofcourse, every design has it's benefits and compromises. It makes me wonder if at the end of the day it comes down to preferences, with the high directivity vs low directivity designs.
Personally I haven't heard coaxial speakers yet, but those seem to me a jack off all trades. Can't go wrong if the acoustic spectrum is linear to all sides..?
I also always liked MTMs. But I never had the chance for a direct 1:1 comparison until I made one - with my main monitors you see here. I need the mtm configuratoin cause it's also used as measurement speaker. Made 2 setups with the Hypex module and a switch to quickly switch.
But I had the same experience with a free standing version (with 2" midrange drivers and ScanSpeak tweeter) - the sound source had more vertical "dimension" as with a point source. It doesn't sound particularly bad - it's just less correct and I like the point source sound and room it makes.
But these are speaker with very close acoustical centers - not the typical 6"/1" wedon'tcareaboutoffaxissound bookshelf speakers. And the room is very controlled.
So with bigger distances between the drivers and reverbant rooms ... you would need to do a proper listening comparison by yourself
(cause I try to use directional speakers in reverberant rooms )(btw - at the moment only the upper midrange driver is active. Hypex module with digital input, Bliesma Beryllium tweeter, ScanSpeak 20cm drivers in closed volume and a heavily dampened room - it's precise as a headphone)
Close listening distances tends to favour coaxial or similar designs, and if you spend enough time listening like that it can skew your preference. There is nothing wrong with that either, listening conditions are a key part of understanding others subjective opinions.
CNC is usually more expensive when comparing production from basic materials, the CNC has to be "operated" so you are paying the wages of the operator, a 3D printer is usually left alone to do it's thing. Some objects are easier to print, a 5 axis CNC is a very expensive thing to buy and operate, for woodwork, good planning and using a 3 axis CNC on both sides of the material is what is done in general.