Discussion in 'Speakers' started by Cakecake, Apr 23, 2018.
How does baffle size affect imaging? I noticed imaging isn't as sharp.
I'm not sure, but why not stick to the "normal" baffle size that PAP and others have used? Considering that the baffle size could affect optimal Xover values, I would think that having a baffle that's too wide or narrow could shift everything a little. I'm sure some of the other guys could explain this better.
Yes. The baffle size does affect the baffle loss as the FR measurement in my previous measurement with 54cm (PAP dimension) vs a 6 feet wide baffle shows.
the crossover cutoff, as you indicated, is tailored to boost the woofer response (or conversely, suppress the full range driver response) to compensate for this loss.
the wider the baffle, the lower the cutoff, but also the larger the crossover component value. right now, with 54cm baffle, the crossover point is around 250-300Hz.
I am trying to understand the decision process made in the design. I believe some of the decision is due to the aesthetic of the PAP design. Which looks really nice with the driver arrangement.
A narrower baffle will allow higher crossover, which means we can potentially use cheaper components for the crossover and/or a higher order crossover. but will ultimately ruin the good look. for me that's not the most important factor (still some factor..) as long as it sounds good/better.
I did build the PAP size baffle. I am treating it as the starting point of a lot of experimentation as it is tried and tested. I want to understand if it can be improved. The OB15Neo are well capable of going higher than 300Hz. what if I narrow the baffle so the cutoff is higher and will that gets me better imaging?
More experimentation needed?
here is what I have built so far. I should receive the other 2 OB15Neo tomorrow to complete it. the top 15" is the Lii Audio F15. Which is a pretty impressive 15" full range but the OB15Neo beats it in bass pretty handily.
PS. Please correct me if i am wrong. This is my first foray into building speakers and I am learning and tweaking as I go.
I am puzzled. As I have the impression that a point source should give very good imaging. But I am not getting good imaging with my current setup. I tried:
- disconnecting the woofers
- disconnecting the woofers + removing the high pass
neither of which give better results.
the question is. how do i narrow down the issue? i have suspected the baffle width could be the problem. can the dipole be an issue?
I can :
- mount the driver standalone with any baffle, still dipole
- mount the driver into a cabinet. I have one that might take a little bit of work to coerce the C-10 into.
Hang a thicc blanket over the back of the baffle, it might make it image more to your liking and also cuts down brightness/glare a bit.
Wide baffle gives wider stage and less back-forth projection. That is just the way it is with OB that does bass.
Unless, you go with some heroic effort and hang the widebander on open space and DSP/EQ the low midrange response back.
I presume you have these >3ft from reflecting surfaces.
Some diagnosis questions: Does it image but not sharply, or is there virtually no stereo image? Does the imaging get sharper if you stand further back, or is it always diffuse, or locked to the individual speakers?
If there’s any DSP in the chain, I suggest turning it off for diagnosis.
Take a picture or pictures of your entire listening space and post more specifics as to how you have it set up.
Troels mentions some trade-offs between wide and narrow baffles
It's not entirely clear, but from what I gather you have less reflecting surfaces from narrow baffles which improves imaging.
I think the idea of narrow baffles is (1) to push the baffle-step out of the response range of the driver and (2) to smooth the frequency response by eliminating destructive interface that comes from baffle edges.
With respect to (1), a large baffle has better efficiency above the step frequency, but the trade off is the step itself and a linear distortion above it: every any non-infinite baffle will exhibit constructive and destructive regions in the frequency response above the step frequency at wavelengths where the principal baffle dimensions equal n*(λ/2). That’s why round baffles (which have exactly one principal dimension) are the worst and rectangular baffles are pretty good.
With respect to (2), baffle edges/corners act as radiators and lead to comb filtering (and in principle somewhat more diffuse imaging, but I doubt thats your problem). Separating the baffles for each driver with a gap (which you didn’t do so much) helps prevent energy from one driver from exciting IMD modes on the adjacent driver—but at the cost of more baffle edges acting as radiators. Using chamfers, rounded baffle edges, curved boxes, and/or felt on the baffles, can reduce the energy radiated from sharp edges.
I'm looking at the picture of your implementation, and I'm a bit puzzled. Are your results based of the original PAP, or do they reflect your own implementation with the Lii Audio F15?
I don't feel confortable with having another full range separated that far. There might be some constructive and destructive interference when using those two full range that far appart at the frequencies responsible for imaging.
Furthermore, that is a completely different driver. Did you change the crossovers? I don't feel confortable just replacing drivers on a design w/o crossover and alignment considerations.
I agree with @ultrabike
Also there's a reason to have a WTW arrangement. You don't get lobing since it's symmetrical, which is the same as time alignment. Switching out the top woofer would screw that up and probably affects imaging too.
Exactly. The PAP is not just some random design based. The reason the two woofers can be separated that much is because the low woofer only assists the top woofer below around 150 Hz for bass and impact. Then it has to be rolled off so that it does not screw up the midrange (i.e. a 2.5 design).
Turn off the top woofer and a 10 dB (or more) suck up will likely develop from 150 Hz to 1 kHz. Not to mention the system becomes bright and weird as it no longer has the contribution from the top woofer below 150 Hz.
Maybe these are all just theories. But the point is, all of these modifications will (in theory) screw up imaging, and then some.
EDIT: This post is not meant to critizise or put down anybody. But to help figure out what could be happening with the system, and why it may behave like it does.
Lots of replies!
Some clarification first. I will respond to specific replies in more posts.
I will take some pics of my setup and post it here. There is plenty of space behind the speakers, around 6 feet so there are lots of room for the rear waves.
I originally ordered the Lii Audio C10. they gave the pair of F15 for free so I was testing them out. Later on I order a quad of the PAP OB15Neo. But PAP made a mistake and sent me just 2. I had the baffle made already so I mounted the F15 to try out. However, early this week I received the OB15Neo and mounted those instead. The PAP OB15Neo is better than the F15 in bass, but the F15 beat the PAP OB15Neo above 1kHz.
My concern with imaging is with 4x PAP OB15Neo + Lii Audio C10. I will update the picture to minimize confusion in the future.
Please update the picture and attach measurements for the setup represented by the picture. Otherwise it's hard to say what is going on.
That's the case only for the AMT version of the PAP Trio15. The other designs have both woofers wired in parallel. The cutoff is around 250-300Hz which means they have to use a full range for the mid/top. They cannot do that for the AMT as the AMT only goes down to 800Hz so they separated out the woofers, one handling bass+mid and the other one fill in the roll off bass.
will do that this weekend!
So you are saying that the Vostavix design is really a 2-way with a cutoff at 250-300 Hz? That may work, though one may get a bit too warm of a response. I may run some sims about it to night.
All that said. I don't think you should put 2 full range speakers that far appart. And I think adding the full range up top may have implications on your crossover approach. Not doing so may be the cause of the issues you have with imaging.
Furthermore, the PAP specific driver does have good low frequency extension relative to many other 15" Pro woofers. The coaxial you are using up top likely does not go down that low and may indeed be responsible for the lack of quality bass you are experiencing relative to the PAP woofer.
I have removed the full range at the top. now there are 4 PAP 15". let me post a photo this evening.
Listened to the PAP Trio 15 voxative at AXPONA this morning, outstanding on the music they were playing. Female vocals with bass and percussion, essentially, didn't have a chance to listen to mid-range stuff. I may be picking up a show special on these.
What was the rest of the chain? And how do they sound with Slayer?
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