Having listened to a bass/mid drive unit playing in free air (baffleless) and then listening to the same unit after being mounted in a sealed enclosure, I’m struck by the difference in sound. Obviously, I expected to hear more bass, but I didn’t expect the midrange to become more confused/distorted. I’ve tried with and without sound insulation, but the improvement with stuffing was relatively minor.
So, my question is: what is it that causes a deterioration in the “intrinsic quality” of the drive unit. Some ideas I’ve come up with are:
So, my question is: what is it that causes a deterioration in the “intrinsic quality” of the drive unit. Some ideas I’ve come up with are:
- the compliance of the air in the enclosure generating non-linearities in the cone movement ?
- the rear sound waves from the cone bouncing around within the enclosure and eventually emerging out through the cone, which by then would essentially just be noise?
- incorrect enclosure stuffing technique!
- the enclosure walls vibrating due to mechanical transfer from the drive unit and the varying air pressure within the enclosure?
- incorrect enclosure design and construction!
All of the above except maybe to say that the spring of the air is more linear than that of the cone suspension.
Yes, and others.. and it would take measurements to work out which.
It's worth mentioning that it can be done right.
It's worth mentioning that it can be done right.
2 and 4 are something I believe happens. I did one experiment where I mounted the whole driver on a compliant suspension to isolate it mechanically from the box. The SPL put inside it by the speaker radiated from the cheap MDF enclosure walls regardless. Whether that's something you'd hear, maybe. It told me consumer level cabinet constructions - what those manufacturers can afford - are not optimal.
I've never taken a speaker in a cabinet and put sound into the enclosure via a second speaker in a sealed box, to see how much of that flys through the 1st speakers cone with whatever attenuation and over frequency. That would be an interesting experiment on the acoustic transparency of speaker cones.
These days I'm pretty enamored with OB, as it uses the speakers rear wave to enhance the stereo illusion via effects of the rear-radiation. "Enhance" is subjective - its a trade off to eliminate the rear-firing energy from finding its way back through the speaker cone - so soon anyway. You lose the mechanical stiffness of the box and the OB panel resonates and rings with nothing to tie down the edges to. So there's material and structural stuff that needs attention in the same way as for a ordinary cabinet - you dont just get away with paying mind to that part by going OB.
I've never taken a speaker in a cabinet and put sound into the enclosure via a second speaker in a sealed box, to see how much of that flys through the 1st speakers cone with whatever attenuation and over frequency. That would be an interesting experiment on the acoustic transparency of speaker cones.
These days I'm pretty enamored with OB, as it uses the speakers rear wave to enhance the stereo illusion via effects of the rear-radiation. "Enhance" is subjective - its a trade off to eliminate the rear-firing energy from finding its way back through the speaker cone - so soon anyway. You lose the mechanical stiffness of the box and the OB panel resonates and rings with nothing to tie down the edges to. So there's material and structural stuff that needs attention in the same way as for a ordinary cabinet - you dont just get away with paying mind to that part by going OB.
It may also be an impression of clarity, destroying bass and low mids can make high mids and highs stand out better, our brain finds that signal easier to decode: "clarity"
There is one famous example in the Musical Instrument world: VOX AC30 amplifiers, of Beatles/Rolling Stones/Queen fame (and hundred others) are famous for their "Chimey tone", also called "jangly sound", which will be mentioned in all discussions or mentions about them.
Obviously I was very curious about what frequencies they were boosting.
When I got the schematic copy I read it all ways possible, could find ZERO treble boosting circuit, BUT at last noticed the "wrong", ludicrously small Volume pot bypass cap: 500pF for a 500k pot, murdering everything below 636 Hz, go figure.
There is one famous example in the Musical Instrument world: VOX AC30 amplifiers, of Beatles/Rolling Stones/Queen fame (and hundred others) are famous for their "Chimey tone", also called "jangly sound", which will be mentioned in all discussions or mentions about them.
Obviously I was very curious about what frequencies they were boosting.
When I got the schematic copy I read it all ways possible, could find ZERO treble boosting circuit, BUT at last noticed the "wrong", ludicrously small Volume pot bypass cap: 500pF for a 500k pot, murdering everything below 636 Hz, go figure.
IME, much of the problem is driver mounting/isolation and judging by how the pioneers did their early bass systems that I learned from they took it very seriously until the 'bean counters' took over production control, forcing a near century's worth of time honored bolting the driver to a baffle/box, though at first they didn't use a gasket, but a raised third rim that bit into the plywood baffle with the outer two as torque limiters to keep the installers from cracking the cast frames of the day, and at most, some of us recommend/add some cab loading via tie bracing to mass load/damp it as a mostly acceptable compromise.
Thanks everyone, that’s quite reassuring. This is my first attempt at building a speaker and I’m on a very steep learning curve! The enclosure is constructed out of 25mm mdf, and it sounds like I probably need to focus firstly on sound absorption and possibly bracing and drive unit mounting. No surprises there then!
You're talking about effects above resonance (i.e. midrange), so any effects on compliance are irrelevant, as the cone is mass-controlled above resonance.
Stuffing the enclosure will have little effect on internal sound reflections per se, but may well be useful for damping standing waves. A useful by-product is the increase in effective enclosure volume, as compression/rarefaction of the air within will follow approximately isothermal behaviour (as opposed to adiabatic). Much more useful is lining the internal walls with thick absorbent material (e.g. felt).
Enclosure wall effects are the reason for many discussions regarding rigidity, bracing, constrained-layer damping etc etc.
Enclosure shape and the effect of internal baffles is underestimated, in my view, and leads on to the elephant in the room - your 2nd point "the rear sound waves from the cone bouncing around within the enclosure and eventually emerging out through the cone, which by then would essentially just be noise".
One good reason to go open-baffle...
I find the direction of this whole discussion very strange. Open baffle? I tried that in 1970.
One of the first lessons I learned about speaker drivers was the importance of an enclosure. I bought an amplifier, the same brand as the college was using on headphones in the library listening rooms. I hooked up a spare 6"x9" car radio driver to it and set it on the dresser. The sound was awful. Tinny, gutless, soft. The same driver pointed up through a hole in the metal dashboard of a car reflecting to a glass windshield 45 deg from my head sounded good.
So I cut a 5"x8" hole in a cardboard box, installed the driver behind it. It was a Quam. I taped the top of the box shut. Set that on the dresser. Voila! much better. I cut a 1" square hole in the back of the box, even better.
A year and 52 paychecks later, I did some listening in the hifi store to improve my experience. I liked AR3 and KLH5 but $700 the pair was 9 months pay. I hated all the bookshelf speakers, as Simon & Garfunkle tracks were low on my list ofproper source material. LWE III for $240 the pair did an okay approximation of real sound. 10" woofer + 3" tweeter, sealed plywood box with no finish, feedback to the amp to boost the bass.
What are all you OB fans smoking? I've never seen an OB speaker in any hifi store, in the 30 years that hifi stores even existed. Now speakers are sold in warehouses (Best Buy) with no electricity, amplifer, source tracks or salesmen within 30 meters. You're supposed to look at the speaker on the shelf and develop an affection for it, without ever hearing it. Maybe those words in the reviews mean something to some people. I never found any association between heaps of words in a magazine, and accurate sound. Maybe I'm too difficult to hypnotize to be a proper consumer. I bought my current speaker after first noticing they looked like the Bell Labs experiments in theaters. Followed by the Voice of the Theater speaker installed in my local cinema 1966. Audition at a musician's supply confirmed my suspicions although the 10" woofer model was gutless in the bass notes of a piano, the 15" woofer model was adequate. Two way 15" woofer + 1.4"CD horn was it. Bliss, until the burglar carried them off to the musician's exchange. Too much pawn shop value. Back to unfinished plywood box & burlap grill for the next iteration.
One of the first lessons I learned about speaker drivers was the importance of an enclosure. I bought an amplifier, the same brand as the college was using on headphones in the library listening rooms. I hooked up a spare 6"x9" car radio driver to it and set it on the dresser. The sound was awful. Tinny, gutless, soft. The same driver pointed up through a hole in the metal dashboard of a car reflecting to a glass windshield 45 deg from my head sounded good.
So I cut a 5"x8" hole in a cardboard box, installed the driver behind it. It was a Quam. I taped the top of the box shut. Set that on the dresser. Voila! much better. I cut a 1" square hole in the back of the box, even better.
A year and 52 paychecks later, I did some listening in the hifi store to improve my experience. I liked AR3 and KLH5 but $700 the pair was 9 months pay. I hated all the bookshelf speakers, as Simon & Garfunkle tracks were low on my list ofproper source material. LWE III for $240 the pair did an okay approximation of real sound. 10" woofer + 3" tweeter, sealed plywood box with no finish, feedback to the amp to boost the bass.
What are all you OB fans smoking? I've never seen an OB speaker in any hifi store, in the 30 years that hifi stores even existed. Now speakers are sold in warehouses (Best Buy) with no electricity, amplifer, source tracks or salesmen within 30 meters. You're supposed to look at the speaker on the shelf and develop an affection for it, without ever hearing it. Maybe those words in the reviews mean something to some people. I never found any association between heaps of words in a magazine, and accurate sound. Maybe I'm too difficult to hypnotize to be a proper consumer. I bought my current speaker after first noticing they looked like the Bell Labs experiments in theaters. Followed by the Voice of the Theater speaker installed in my local cinema 1966. Audition at a musician's supply confirmed my suspicions although the 10" woofer model was gutless in the bass notes of a piano, the 15" woofer model was adequate. Two way 15" woofer + 1.4"CD horn was it. Bliss, until the burglar carried them off to the musician's exchange. Too much pawn shop value. Back to unfinished plywood box & burlap grill for the next iteration.
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^ 😀
yeah drivers sound very different boxed or not. If one wants to compare then they should be EQ:d for same response for starters as this is easily audible difference, low frequencies cancel out without a box. Another thing is where one listens at, if in room polar patterns of both boxed and naked drivers are very different so listen outside for example to take out sound in room which again is very audible. Perhaps not so big difference anymore listened alone but who listens drivers alone, they are usually part of a system (assuming, we are on a multiway forum🙂) and there is many differences between boxed and open back systems.
While any driver will sound different to any other when listened naked or in a box or what ever, I'm not sure how much information it gives if the driver response is then filtered for real application. One could have just tossed away the better sounding one, which sounded worse outside the actual application. Perhaps someone with lots of experience, or some strict ideology, could judge drivers this way and do right decision but to me it seems more logical to compare drivers in application.
yeah drivers sound very different boxed or not. If one wants to compare then they should be EQ:d for same response for starters as this is easily audible difference, low frequencies cancel out without a box. Another thing is where one listens at, if in room polar patterns of both boxed and naked drivers are very different so listen outside for example to take out sound in room which again is very audible. Perhaps not so big difference anymore listened alone but who listens drivers alone, they are usually part of a system (assuming, we are on a multiway forum🙂) and there is many differences between boxed and open back systems.
While any driver will sound different to any other when listened naked or in a box or what ever, I'm not sure how much information it gives if the driver response is then filtered for real application. One could have just tossed away the better sounding one, which sounded worse outside the actual application. Perhaps someone with lots of experience, or some strict ideology, could judge drivers this way and do right decision but to me it seems more logical to compare drivers in application.
Open-baffle does of course need (simple) EQ. There's plenty written on the subject, for anyone interested...
I can't stand the sound of closed box speakers. I can tolerate sub in closed box for low quality system, but in the main system I need to have open baffle sub too. Otherwise its 4way all open baffle.
I always hear midrange boxiness and it bothers me. Place the woofer in the closed box, fine, but please for goodness sake, place your mid on open baffle and listen. Be open minded.
Cheers!
I always hear midrange boxiness and it bothers me. Place the woofer in the closed box, fine, but please for goodness sake, place your mid on open baffle and listen. Be open minded.
Cheers!
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I have, many times. Jamo, Quad, Magnepan, some others. Also at large Hi-Fi shows.
Open Baffle isn't as easy to get right as box speakers, but it can be done well when you know how. I've heard them and built them. I've also heard and built some pretty awful ones. 😀
