As an experiment for a 2 way, I tried fixing a tweeter in front of a full range, so both speakers are concentric. The speakers are:
It sounds pretty good to my ears, as a point source with good frequency response. This speaker handles 100 Hz and above, with a 6dB crossover at 2200 Hz .
I use it as a nearfield, augmented by a subwoofer.
Thoughts?
- Peerless India LR10DT, 1 inch dome tweeter
- Philips 9710 clone 8 inch full range
- Cabinet 21 L
It sounds pretty good to my ears, as a point source with good frequency response. This speaker handles 100 Hz and above, with a 6dB crossover at 2200 Hz .
I use it as a nearfield, augmented by a subwoofer.
Thoughts?
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I've often wondered why this hasn't been resurrected before now (I remember an EMI 13"x9" speaker from the '60s, which had 2 tweeters mounted in front of the main driver). Maybe it has?
Anyway, do you think there are any negative effects in mounting something as obstructive as a "normal" sized tweeter in front of an 8* driver? Compared with a "proper" coaxial? It's quite possible that there actually are benefits...
By the way, I'd watch that 1st-order crossover - remember that the tweeter excursion will still be doubling each octave below the crossover frequency (until its fundamental resonance - which hopefully is well damped).
Anyway, do you think there are any negative effects in mounting something as obstructive as a "normal" sized tweeter in front of an 8* driver? Compared with a "proper" coaxial? It's quite possible that there actually are benefits...
By the way, I'd watch that 1st-order crossover - remember that the tweeter excursion will still be doubling each octave below the crossover frequency (until its fundamental resonance - which hopefully is well damped).
I did not include any passive delay compensation,not sure if that's a thing even. I can only adjust the gap between the FR and the tweeter.
If there is excessive diffraction, or comb effects, won't I be able to discern by ear? I don't have any measuring instruments.
The tweeter Fs is listed as 1200 Hz, so I opted for a crossover of 2200 Hz. I don't play loud, so I think I should be OK?
Considering the tweeter geometry, is there an optimal gap between the FR and the tweeter?
It sounds good, when compared to other similar speaker drivers in conventional cabinets and on Open Baffles.
If there is excessive diffraction, or comb effects, won't I be able to discern by ear? I don't have any measuring instruments.
The tweeter Fs is listed as 1200 Hz, so I opted for a crossover of 2200 Hz. I don't play loud, so I think I should be OK?
Considering the tweeter geometry, is there an optimal gap between the FR and the tweeter?
It sounds good, when compared to other similar speaker drivers in conventional cabinets and on Open Baffles.
Long time ago i had vintage lafayette speakers, pseudo coax, like thread starter did, where tweeter was even on small baffle. I thought it would be detrimental, but they measured and sounded ok.
Btw, there was real coax recently, perhaps b&c?, where front of the cone was completely covered by the horn.
Btw, there was real coax recently, perhaps b&c?, where front of the cone was completely covered by the horn.
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I guess car speaker drivers had such arrangements for a while.
I forgot to mention, the imaging is mind blowing now.
I forgot to mention, the imaging is mind blowing now.
There was a DIY kit for this concept. Measured / reviewed here, with diffraction effects discussed.
https://www.enjoythemusic.com/magazine/equipment/0600/super12.htm
I have some early KEF "Q" bookshelf speakers with tweets integrated in the woofers. They sound very good, but if anything goes wrong I don't think there are any spare parts. I see they still sell similar speakers.
This kind of solutions, tweeter on front of a woofer, inevitably suffer some from the fact that the two need to play at same frequencies around some crossover frequency. The other will affect the others output being there as "non ideal" construction / obstruction. The tweeter will cause diffraction and reflections to the woofer output at frequencies where it is acoustically big. And the tweeter, even if low diffraction structure for itself, will radiate backwards to the woofer cone and reflect from there making interference. Either of these will happen or both, unless the tweeter structure was bigger than the woofer, or woofer smaller than the tweeter if you will. This sounds silly but can be made with big waveguide for the tweeter, like the B&C linked above but bigger, bigger than the woofer. Add some holes to the waveguide profile for the woofer to breath through, good roundovers for the waveguide to reduce diffraction. This kind of construct would also have an effect for response of both but perhaps less so or at some high frequency where it is not so audible perhaps. See Danley Sound Labs studio monitors for example.
Whether any of this matters too much is up to the particular construct and what the listener expects for the sound. Perhaps little diffraction doesn't matter too much when it is at very short distance mostly affecting past some kHz.
The interference for each others output could be minimized also by using small dome tweeter (without flange) as close to the woofer as possible, now we have the traditional HIFI coaxial construct like KEF's. Here the moving woofer cone acts as waveguide and will affect some to the tweeter response with increasing SPL as excursion increases.
Between these two extreme constructs there is the flanged tweeter hovering in front of a woofer that op posted and this has most ill effect, while tweeter behind the woofer cone with or without separate waveguide would have less.
After all of this, remember to chamfer / roundover the box edges, it too causes diffraction no matter if the tweeter is coaxial or not. And its just a fact we have to live with that we cant have two different objects occupying same physical space, so its always some kind of a compromise, pick your poison 🙂
Whether any of this matters too much is up to the particular construct and what the listener expects for the sound. Perhaps little diffraction doesn't matter too much when it is at very short distance mostly affecting past some kHz.
The interference for each others output could be minimized also by using small dome tweeter (without flange) as close to the woofer as possible, now we have the traditional HIFI coaxial construct like KEF's. Here the moving woofer cone acts as waveguide and will affect some to the tweeter response with increasing SPL as excursion increases.
Between these two extreme constructs there is the flanged tweeter hovering in front of a woofer that op posted and this has most ill effect, while tweeter behind the woofer cone with or without separate waveguide would have less.
After all of this, remember to chamfer / roundover the box edges, it too causes diffraction no matter if the tweeter is coaxial or not. And its just a fact we have to live with that we cant have two different objects occupying same physical space, so its always some kind of a compromise, pick your poison 🙂
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Thanks for the link, I need to read it some more.
I have attached the cross over schematic and the simulation response.
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You may be better off avoiding circular diffraction because it can sum and cancel strongly on axis. MEG has been producing a range of studio speakers for decades using a fairly similar approach.
If you look at the measurements in Audio Express, they're not great.
Coaxial compression drivers have a ton of issues, and I personally think a Unity horn is a superior solution.
In the most general terms, your scheme might be a decent coaxial speaker. I can think of two "objections" that purists might make. The first, already mentioned is the possibility of diffraction in the tweeter and/or its mount. If the tweeter is 1 inch diameter, it would be acoustically non-existent to your mid's wavelengths below ~ 3 to 4' = ~ 3-4 KHz. I'd guess with x-over well below, it shouldn't be a big issue.
A second issue will likely be the widely different dispersion. The mid will beam more as frequency rises. At the x-over it seems unlikely the dispersion will be compatible with the tweeter.
Even so, the two above limitations may not be a problem in practice. Good luck with your project.
Wild Idea: my speakers are modified Unity (Yorkville U15) with the "towel mod" and foam inserts a la Geddes. Has anyone ever considered that these HOM and/or diffraction reducing mods might be applicable to more conventional drivers? Not with a horn or waveguide, but might it be possible to "stuff" the mid (or at least mount foam ahead of the driver? Depending upon the mounting, a tweeter might be mounted directly upon the foam. Seems this would address a lot of diffraction or reflection issues, if mechanically damping the mid was not an issue. There's a project for Bateman: a Gedlee waveguide without the waveguide!
In fact, allow me to brain storm this a bit more. What we have is a "normal" (say) mid-woofer in a sealed enclosure. On its own it typically won't have diffraction issues, as those are generally a tweeter malady. Rather than a traditional 2-way with the tweeter on the same vertical plane, what happens if we now have a thick piece of acoustic foam to the front of the woofer (but not touching it, which would damp its motion?) Now mount the tweeter of your choice directly ahead of the woofer completely supported by the firm foam. It can even be recessed slightly, which will further reduce its diffraction risk. The tweeter will likely be acoustically invisible to frequecies within the woofer's bandwidth. The foam will serve to reduce unwanted diffraction or reflection of sound from either driver. Other than looking very odd, what have I overlooked? A time aligned crossover would be a challenge, but easy with digital.
A second issue will likely be the widely different dispersion. The mid will beam more as frequency rises. At the x-over it seems unlikely the dispersion will be compatible with the tweeter.
Even so, the two above limitations may not be a problem in practice. Good luck with your project.
Wild Idea: my speakers are modified Unity (Yorkville U15) with the "towel mod" and foam inserts a la Geddes. Has anyone ever considered that these HOM and/or diffraction reducing mods might be applicable to more conventional drivers? Not with a horn or waveguide, but might it be possible to "stuff" the mid (or at least mount foam ahead of the driver? Depending upon the mounting, a tweeter might be mounted directly upon the foam. Seems this would address a lot of diffraction or reflection issues, if mechanically damping the mid was not an issue. There's a project for Bateman: a Gedlee waveguide without the waveguide!
In fact, allow me to brain storm this a bit more. What we have is a "normal" (say) mid-woofer in a sealed enclosure. On its own it typically won't have diffraction issues, as those are generally a tweeter malady. Rather than a traditional 2-way with the tweeter on the same vertical plane, what happens if we now have a thick piece of acoustic foam to the front of the woofer (but not touching it, which would damp its motion?) Now mount the tweeter of your choice directly ahead of the woofer completely supported by the firm foam. It can even be recessed slightly, which will further reduce its diffraction risk. The tweeter will likely be acoustically invisible to frequecies within the woofer's bandwidth. The foam will serve to reduce unwanted diffraction or reflection of sound from either driver. Other than looking very odd, what have I overlooked? A time aligned crossover would be a challenge, but easy with digital.
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Sorry, i forgot about this thread, since there is nothing new here.
When it comes to your question, no, definitely no. Planars are mostly dipolar, with sound radiating back and front.
Whats the point having sound from planar bouncing back to mid? Some kind of sound effect?
Btw, the link points to amt tweeter, not planar...