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Thank you @mijostyn. Can anyone tell me if REM is the software that would help me? Or is there another app I should look into? And this is what I am undecided over: a ported closure to extend response from 38 down to 25, or if an infinite baffle will take it to 25 anyway without a port? (I guess I need the cabinet simulator app as @eric_squires noted.)
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@hsbrock , That is what ported closers are all about. It is not the kind of driver I am use to dealing with. A BL of 31 is a very potent motor. It sounds like more of a driver for infinite baffle designs.
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@erik_squires I looked at DIYaudio, and I'll look again, but I didn't see content as well-directed as this thread. Is REM a cabinet simulator app? Are there any free apps that are adequate? I am wondering if my first question is even possible - to lower effective response with the cabinet? and if the stiffness will help or hinder in that regard?
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@hsbrock Really you need a cabinet simulator and to spend more time at DIYaudio. :)
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@mijostyn +2 @mahgister +1 @erik_squires This has been a fascinating read and I am impressed with all the sharing of knowledge. I just joined because (to me) I have an odd question and don't know how to start a new thread, and also because it ties into this thread. I have an 18" driver (normally I don't go beyond 15", but this has a BL 31, so I figured I had adequate cone control), and maintains a SPL of 96+dB between 100Hz and its Fs 38, which is my relevant range for this sub. The curious thing is that its free-air response is flat enough that it stays above 93dB beyond its Fs and down to 25Hz, and I would like to build a cabinet that takes advantage of this, a cabinet that can extend its response from 38 to 25. Its Vas calls for a 4.13 cu.ft. cabinet, and its compliance is fairly stiff with a Cms of 0.05mm/N. With its Qts right at 0.40 I'm torn between a ported and a sealed. It moves a lot of air with a Vd at 1286 cc, and of course, that's without much excursion. So, my question is two fold: how can I build a cabinet to drive the response down to 25Hz? And if so, does the cone stiffness hinder or help, and how can I take advantage of the driver's properties? Any help would be appreciated!
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@unreceivedogma
Sorry, I must have misread. I thought you said you had the Velodyne crossed at 2k!
All the best.
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@unreceivedogma , That is exactly the point. You want as little baffle showing as possible. I just finished building new subwoofers, They are 30 inch long, 15" in diameter with a 12" driver stuck in both ends. The construct is easy. I did it for different reasons as subwoofers do not image.
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I forgot to mention this but honestly DIYaudio is a much better place for speaker building questions than Audiogon. Lots of builders with first hand experience into all sorts of designs.
Best of luck,
Erik
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@curiousjim
— I am not aware that I have any control over the Velodyne crossover setting. It comes at 85HZ. I don't know where you get over 100. The Velodyne frequency response is 18-85hz. The resonant frequency is <4hz
— Yes they are great! This is a fun conversation.
@mijostyn @erik_squires
— Altec's 620 cabinet is 18" x 26" x 40", for 9 cubic ft. Mine is 18 x 26 x 38, with a 2" base
— The diameter of the driver frame is 15.2", so 18" leaves little room. Otherwise, I am trying to visualize your cabinet design. I guess I would have to draw it out first, but it seems quite ambitious: not easy to execute.
— My latest thinking is to start at the beginning. I've had the 604Cs for 40 years, the D for 25 years. They haven't been re-coned in almost 10 years. They are all over 60 years old. It might be wise to send them to Great Plains to get them re-magnetized and refurbished. Then fool with the cabinet.
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@unreceivedogma
I have no dog in this, but I am curious why you have the Velodyne set up so high? I have never had a subwoofer set past 100hz with like a 12db roll in.
Oh and BTW, you have three of the smartest and nicest people helping you here.
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@unreceivedogma
Actually, I would modify that design to make the baffle 18 X 18" decreasing the size of the face. A tube would be perfect. You can buy aluminum pipe in that diameter. This assumes a cutoff at 100 Hz. It would be like the driver suspended in space. No enclosure effects. An appropriate stand could hold that at ear level no problem.
I suspect the crossover is second order. They are shelving it to keep higher frequencies from dominating the bass, a high shelf filter. This is probably due to baffle step, a problem my design above will not have.
You would close the port and epoxy the panel in place to keep it from resonating, only if you are dedicated to subwoofers.
My goal would not be to maintain a period presentation, but to take the driver to its maximum performance in term of sound quality and image. It is the very rare system that can cast the best possible image. Images of all instruments and voices should be well delineated in space with blackness between. They are hung in space as if standing there. In most cases, particularly high frequency instruments like cymbals, items are bloated and run into each other. Close your eyes and listen. The analogy would be with light. Shine a naked lightbulb is a room with white walls (reflective) and the whole room and everything in it will light up. Shine the same light in a flat black room and only the the objects within will light up. Theoretically you could get the same effect in a darkened white room with individual lights focused exactly on the objects only. Hard to do for sure, same for sound. It is very difficult to get the sound focused on the individual instruments. This is why the speakers and room have to be considered as one transducer. All this assumes the best recording and mastering. The other problem is that the recording and mastering are being done by people who are listening to their own problems. In any case you would be surprised how good a system/room can image. Line source dipoles are so good at this because if you absorb the sound coming from the rear they are "shining light" only on the instruments and not the room. The problem with omnidirectional speakers is they are the naked light bulb in the white room.
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Good morning @mijostyn
- plywood
- the “port” is just a rectangular hole about 2.5” or 3” x 12” cut into the baffle in front, below the driver. A wooden block is affixed inside the cabinet that I slide up and down to open or close the port, or place in between.
- the Altec crossover is 1600
- The Mastering Lab crossover that I use is 2000. It’s shelved (I’m not sure what the term means, but I know what they are for, 😆) at 8000 also.
- the novel cabinet shape that you use sounds like an interesting approach but it begs the question: all that weight being supported so high off the floor must be supported by something that will have its own resonance issues. ? Might be a bridge too far for me 😬
- I would send pictures but this forum does not seem to allow for attachments.
- I have noticed that some cabinets have a piece of wood at an angle inside the cabinet. This does not. ?
@timlub thanks for that link. I see that this topic has a history here!
As always, thanks again. I’m really learning something here.
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@unreceivedogma
Great. I'll bet they are plywood. The older manufacturers used plywood. MDF did not become available until the late 60s. Plywood is stiffer than MDF and will resonate at a higher frequency. It is also lighter and not as well damped. It is also way more expensive. Look at the back of the cabinet. If the rear panel is held on by screws it is for certain plywood. J Frum is correct in what he says from a modeling perspective but the equations assume an infinitely stiff structure in an anechoic chamber. They can not tell you what any given speaker is going to sound like in a real environment.
If I had those drivers I would build 10 cubic foot sealed enclosures 20" X 20" X 40". I would mount the driver in the 20" X 20" face and create a stand that held that face at ear level. I would cross them to subwoofers a 80-120 Hz and control the whole show with a digital preamp. Making it look good would be a challenge
In your case I would block the ports from the rear with plywood and cross to TWO 15" or FOUR 12" subwoofers using an active 2 way crossover. If you really wanted to get the absolute best out of the system and be able to tune it exactly to your taste get a digital preamp like the new DEQX Pre 4, Trinnov Amethyst or Anthem STR.
If you are asking why the strange shape (my enclosure), mounting a driver like that increases the stiffness of the baffle and places the mass of the enclosure in line with the driver minimizing the effect of Newtonian forces created by the driver. The small face minimizes enclosure effect which should improve the imaging.
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@mijostyn
"....In order for me to get a handle on your enclosures I need the interior dimensions and the material they are made of such as 3/4" plywood or 1" MDF."
I am certain that they are plywood but I can tell you tomorrow. Altec specs from their brochure below: I will check to see if mine in actuality do match exactly.
SPECIFICATIONS
Type: Bass reflex enclosure
Dimensions: 40" (1 01 .6 em) H 26" (66.0 em) W 18" (45.7 em) D
Pressure Sensitivity: 100 dB SPL at 4' with ALTEC 604-8G loudspeaker when measured on axis with 1 watt input of band-limited pink noise from 100 to 10,000 Hz and calculated to 4' equivalent (Ref.: 0 dB == 0.0002 dyne/cm2)
Speaker Accommodations: 15", front-mounted
Internal Volume 9.0 cubic ft
Weight: 104 pounds (47.2 kg), enclosure only
Finish: Hand-rubbed oil on rift-cut oak, charcoal brown grille cloth
Recommended ALTEC Speaker: 604-8G Duplex Loudspeaker
ARCHITECT'S AND ENGINEER'S SPECIFICATIONS
The speaker cabinet shall be the bass reflex type, and shall provide front mounting for 15" speakers only. The cabinet shall meet the following criteria. Grille assembly,snap-on. Grille cloth, charcoal brown. Internal volume, 9.0 fe. Dimensions, 40" H x 26"W x 18"0. Weight, 104 pounds. Finish, hand-rubbed oil on rift-cut oak.
The speaker cabinet shall be the ALTEC Model 620A.
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@unreceivedogma
I could not afford them either. Just happened to be at the right place and time.
I read an Altec spec sheet on the Duplex and the 3dB down point was 60 hz which would be about right for a woofer of that type of construction.
T-S parameters (Thiele/Small) are a set of parameters that define a driver's electromechanical behavior. From them you can calculate the volume of the enclosure you need to obtain a given type of performance. They help getting you in the ballpark when designing a loudspeaker. https://en.wikipedia.org/wiki/Thiele/Small_parameters
In order for me to get a handle on your enclosures I need the interior dimensions and the material they are made of such as 3/4" plywood or 1" MDF. The type of enclosure, sealed or ported and the dimensions of the port or ports. In today's world of loudspeakers, with the advent of DSP you can get away with murder. I design and build my own subwoofers and rely on digital signal processing to get them under 20 hz at + 6 dB. I am about to shoot the finish on my new ones and will publish pictures of the entire process on Imgur when I am finished. The best way to handle subwoofers is with digital bass management which is antithetical to the type of system you have or rather the type of attitude you have. It certainly is more of a challenge and I understand the attraction. You can push the envelope a lot further. You can high pass your Duplexes by putting the right value capacitor in series with the input of your amps. You have to know the input impedance to calculate the value. Then low pass the sub with the filter it has, the highest it will go without calling attention to itself. With two subs I would definitely plug the ports but I have to warn you that I really dislike ported speakers. I would rather push the speaker down with digital bass management and use subwoofers designed specifically to make low bass. What you have in the Duplex woofer is really a very large midrange driver. Middle C is 254 Hz. In it's day it was a very fine driver and still is. Back then subwoofers were nonexistent.
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@mijostyn
- there will be three Moroccan rugs. 🙂
- I use Doug Sax’s Mastering Lab crossovers. http://www.rintelen.ch/download/604xover_SP.pdf I had Jon Specter replace all the caps with Jensen audio grade caps
- as for the current enclosures, they ARE custom DIY enclosures, built to Altec specs of the 1960s. https://www.hifiengine.com/manual_library/altec-lansing/620a.shtml I think there is room for improvement, but I don’t (yet) know the first thing about it, engineering-wise.
- Altec claims that the 604C and D go down to 30HZ
- As for the Velodyne UHL15, it seems to crossover at 85HZ, see https://www.stereophile.com/content/velodyne-uld-18-amp-uld-15-subwoofers-specifications and https://www.manualslib.com/manual/533050/Velodyne-Uld-15.html?page=10#manual I don’t know that it can be adjusted to 100.
- T-S parameters?
- I had Lafayette speakers to go with the Dyna. I couldn’t afford AR speakers.
see what J Frum says here:
https://hifihaven.org/index.php?threads/embiggening-the-altec-620-thoughts-experiences-with-9-cu-ft-cabs-for-altec-604-8g.7649/
Y’all need to get religion with regard to enclosure simulation. With T/S parameters, modeling a basic bass-reflex cabinet is easy and accurate. It’s a brave new world.
You’ll learn all about the delicate balancing act between the driver’s electromechanical properties, enclosure volume, and tuning. It’s a lot more complicated than “bigger = better”, and you’ll see the effect changes have on frequency response, power handling, and group delay.
I’ve modeled the 604-8G every which-way, and I can’t come up with anything that’s better overall than a 9 cu. ft. cabinet tuned to about 40 Hz. - essentially, a 620.
I’ve said it before, and I’ll say it again: It’s almost like those Altec engineers knew what they were doing.
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@unreceivedogma , AHH the Duplex. I was thinking Voice of the Theater. Nice trick with the burlap. Yes, I think a rug would be in order. I beat you by one year. I built my ST 70 and PAS 3X when I was 13. A friends father gave me a pair of AR 2ax's which he used at a party and wanted to get rid of. He owned an electronics firm in Boston.
Your woofer crosses to the horn at 2 kHz and cuts off at 60 Hz. I can not find the T-S parameters for the 604a,b or c. I would treat it like a Bozac woofer with a large sealed enclosure on the order of 8 cubic feet. They are crying for custom enclosures. IMHO you need two subwoofers one next to each main speaker crossing as high as possible to get the low bass out of the Duplexes. It will make the Duplexes so much cleaner. I have never heard the Futtermans but I use triode OTLs and I bet they are a great match for the Duplexes. They are another reason though to take the low bass somewhere else. Are you high passing the Duplexes now? You mentioned custom crossovers.
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@mijostyn @erik_squires
Thank you both, bunches. I’m learning a lot already.
Eric, the room is semi-anechoic, not anechoic. The floor would have to be treated as well, which it most certainly is not.
In my last home, I did the room this way and it worked very well. The room doubled as a library, and as I added books to the walls, the room became brighter: the books were the way to control room acoustics.
I started out building my own Dyna 70 and Dyna PAS when I was 14 years old, but since then I’ve otherwise never given too much technical thought to how to design a better system other than to substitute new components.
I’ve had the components I have now for 30 years on average, and with the new home (the wife and I leave this home feet first only: I came close 8 weeks ago, I got double bypass surgery after the discovery of a completely blocked Widowmaker, 😂. The surgeon says that after I complete recovery, I will be better than new! 🙂) and new listening room, and with my amp engineer who has worked on many home audio systems saying that he has heard only one other system that sounds as good as this one, I’m not gonna change the components, my thoughts have turned to how to get more out of what I have, so that means returning to thinking more about the science of these things. The weakness of the Altecs and of the Futtermans are convincing extension at the bottom. They are really good right now, don’t get me wrong but something does nag at me in this area. The cabinets are solid for their day, but there is some resonance there. They do allow for port size adjustments, but it’s just unscrewing a block of wood and sliding it up or down! Maybe painting the interior with a material that will stiffen the walls? I don’t know, and then it has to be reversible because what if it doesn’t work. A friend built beautiful new cabs for his Tannoys but he is top shelf carpenter, works for Broadway, I can’t afford him.
Maybe I need to change the subwoofer. But I don’t want to spend a lot of money either. The current sub crosses at 70. And maybe I just never found the right spot for that sub. In the new room, there will be lots of room to fool with placement.
configuration is
Cartridge: Koetsu Onyx
Tonearm: Sumiko MMT
Table: VPI HW MK IV with SAM
Step-Up Transformer: SHURE A86A
Preamp: Beard P505
Phase Alignment: BBE282ri sonic maximizer
Subwoofer: Velodyne ULD-15
Amps: Julius Futterman OTL3s, converted to triode by Jon Specter
Crossovers: Mastering Lab
Speakers: Altec Lansing 604C coaxial studio monitors
Semi-anechoic room design and treatment: by architect C.B. Wayne
cables: whatever
https://www.theaudioatticvinylsundays.com/about
Oh, and as for rock wool, it is used in a lot of commercial and audio acoustic panels. I use it to insulate my home because
- it’s the best thermal barrier
- it’s far and away the most fire resistant. Fiberglass, fire-resistant cellulose, etc burns by the time you hit 375 degrees This stuff doesn’t melt until you hit 2,000 degrees. An important consideration in historic buildings, of which all the buildings we have restored to date are
- it has excellent sound absorbing properties
My architect had done a few recording studios. He said that in my audio room, don’t sheet rock the walls Just cover the rock wool with burlap and then I will have the equivalent of a high quality recording studio for 1/20 of the cost, for the amount I was spending to make the thermal barrier anyway. Safe health wise also.
I don’t like using headphones
Thank you again.
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@mijostyn
There’s no argument about wide vs. limited dispersion in my writing, so I’m not really sure if you are replying to anything I wrote, except obliquely. That paragraph was in response to the idea of an anechoic room being ideal.
Acoustics and room treatments do go hand in hand though. The more controllable the dispersion the less room treatments are needed, but I know of no case outside of a measurement lab where a truly anechoic experience is a good thing.
I used to be a rep for Roger Sander’s speakers, and so I know the head-in-vise experience of a flat ESL very well. My statements as I made them, not as interpreted, stand.
While tight dispersion may give you the feeling of having your ear right up against the speaker they also do a poor job of communicating the illusion of space behind and to the sides of speakers, but a good solution when you have zero control over the room. OTOH, if this is your ideal maybe headphones are a better solution for you. Far cheaper and requiring less fuss.
A room with controlled bass modes, a good mix of dispersion and absorption (including the ceiling) will outperform any attempt of recreating even the old Live-End, Dead-End experience, let alone anything approaching fully anechoic.
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@erik_squires I agree entirely up until the last comment. This argument between wide dispersion and limited dispersion has been going on since I was knee high to a grasshopper.
Obviously, wide dispersion bounces sound all over the room creating more and louder reflections. Very limited dispersion, like a flat panel ESL is very annoying but sounds terrific if you lock your head in a vice. Controlled dispersion on the order of 45 degrees like you might get from a horn system or curves panel ESLs is best in terms of image and comfort. Dipole line sources are even better because of strong attenuation to the sides, floor and ceiling.
I think it helps to think of sound like light. If you shine a flashlight at an object only things in line with the object will light up but switch on a naked bulb and the entire room lights up. Omnidirectional speakers "light up the entire room." This usually makes a system very bright which some people like especially at low volumes. You may note that cymbals are poorly localized and there is a tendency towards sibilance with female voices and violins. A system with controlled dispersion usually sounds dull at first and people will think there is no high end. if you pay attention you will note that the cymbals are well defined and the high frequencies are there but now they are coming from the cymbal and not the entire room. Such a system is smooth and effortless without any sibilance. With loads of sound deadening you can make an omnidirectional system sound more like a controlled dispersion one at some expense and nail holes.
@unreceivedogma , What is rock wool? I have not heard that term. Sounds like you have a nicely dampened room which is great because Altecs have a tendency to get shouty.
I think you are overthinking things. Use the pair of drivers you think are best constructed and listen to the results. Stiffening the front baffle of the cabinets makes sense but doing it right would mean removing the old one or using screws every 6 inches. You can not place clamps over such a large structure. My approach to the problem would be to make entirely new enclosures. I would remove the ports, decrease the volume depending on the math and cross to subwoofers at 80 to 100 Hz. That would be killer!
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I think you are really getting confused about how the resonant frequency of a speaker driver (a good thing) works and mixing it up with how cabinet panels resonate (which is completely undesirable). The resonant frequency of a driver is used to model the bass performance in a cabinet in terms of the -3dB point as well as the slope and optimal flatness (Q) of the low end. It has nothing to do with distortion introduced due to imperfect cabinet materials. Along with Qts, and equivalent air mass and other parameters the resonant frequency is something you plug into your cabinet design software.
Driver resonance frequency has zero to do with the materials used or bracing methods used to construct the cabinet itself. The driver resonant frequency also has zero to do with driver value or quality but it is an indicator of the type of driver you have on your hands. A driver with a resonant frequency of 300 Hz is probably not going to go lower than a midrange for instance.
Also, you want diffusion between and directly to the sides and often behind the speakers and listening area. Anything truly anechoic is going to sound too dead, and lack imaging and space.
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@erik_squires
thank you Eric.
I am working on finishing the room.
All the walls are 5” rock wool.
The gable ceiling is 12” rock wool.
All covered with fire resistant burlap instead of sheet rock.
The floor is hard wood.
Essentially, a semi-anechoic room. Very dead: the difference in sound quality is immediately perceptible as you climb the stairs into the room.
I was told by the guy who built my Futterman OTL3s that stiffening lowers the resonant frequency, but he was also quick to offer that speaker cabinet design is not his area of expertise. What you said about stiffening the baffle only makes good sense, as I would like to decrease the energy flowing through the cabinet walls.
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I was right about you ... 😊
Your answer make sense for me and help me thanks... I hope it will helpful fot the OP...
Hah, thanks @mahgister - the free air resonance is not, by itself, the most important thing in determining the use of a ported enclosure or not, and certainly nearly useless in determining in-room performance.
The questions of whether this is best as a ported or sealed cabinet is a different question than "what would work well in my room."
I’m thinking that a speaker with lower resonant frequency will sound better than the one with a higher resonant frequency.
I think this is not the right way to think about it. The question is driver to cabinet matching and then matching the total speaker (driver in a specific cabinet) to the room. There’s no best answer based on resonant frequency alone.
These questions are best asked in DIYaudio but you can also read the last paragraph here:
https://eminence.com/blogs/blog/sealed-vs-ported-enclosures
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@unreceivedogma , Boy are you making like complicated.
The free air resonance of a driver is determined mostly by the mass of the construct (cone, suspension, voice coil and former) and the stiffness of the entire suspension. I doubt you will hear any difference between the drivers. Try them both.
As for the enclosures, each surface has a resonance frequency. Every enclosure is a symphony of resonances. If you stiffen the walls by doubling up on the plywood you will raise the frequency of those resonances. There is no way to know if that will be better or worse than what you have now. Certainly a very stiff, heavy baffle (the surface to which the woofer is attached) is beneficial. It will limit the transfer of energy to the rest of the enclosure. I think I would leave everything else alone.
If you really want to make them sing get another subwoofer and a two way crossover. Cross at 100 Hz or even higher. The woofers in that speaker carry a significant portion of the midrange which is being Doppler distorted by bass below 100 Hz. Taking those frequencies away from the Altecs will clean them up noticeably, very noticeably at higher volumes.
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Hah, thanks @mahgister - the free air resonance is not, by itself, the most important thing in determining the use of a ported enclosure or not, and certainly nearly useless in determining in-room performance.
The questions of whether this is best as a ported or sealed cabinet is a different question than "what would work well in my room."
I’m thinking that a speaker with lower resonant frequency will sound better than the one with a higher resonant frequency.
I think this is not the right way to think about it. The question is driver to cabinet matching and then matching the total speaker (driver in a specific cabinet) to the room. There’s no best answer based on resonant frequency alone.
These questions are best asked in DIYaudio but you can also read the last paragraph here:
https://eminence.com/blogs/blog/sealed-vs-ported-enclosures
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Ask erik_squires he is very helpful...
He know basic acoustic ...
He know a lot about speakers design, he created some, and i know nothing useful for you for this complex problem solution ...
Thank you @mijostyn @mahgister
This is not about a subwoofer.
The reason I ask is that I have a pair of Altec Lansing 604Cs and I now, as of last night, was able to get a 604D to match the 604D that I already have.
I am currently using the 604Cs. The D was a backup in case one blew. Now that I have two D’s, should I switch?
As far as I can tell, however, the ONLY difference in the specs is the free air resonance.
I will be putting the cabinets on rubber feet designed to isolate them from the wood plank floor so that the building doesn’t become a de-facto loudspeaker. I’d like to close the port so as to make the midrange more detailed. This entails losing some bass, but …
I use a Velodyne ULD15, with an active crossover at 60hz for the bottom.
I’m thinking that a speaker with lower resonant frequency will sound better than the one with a higher resonant frequency.
But is the difference too small to even matter, or are the numbers a logarithmic progression instead of arithmetic and thus the difference bigger than one might think? And, does having an active sub crossover at 60hz make this question moot?
one other question: the cabinets are DIY, made of 3/4 ply with a veneer, geometry and materials to Altec specs standard in the day (1950s/60s). Would the bass benefit by stiffening them with another 3/4 layer of ply or solid wood on the interior? If so, do I stiffen all 6 sides, or would just the 4 perimeter sides (not front and back) suffice?
Also, someone told me that one mechanical difference between the two is that the stock C used a paper surround and the stock D used an accordion surround. As Cs are today almost always reconed with the accordion surround (mine are), and as the materials of the cone help determine the free air resonance, simply reconing the C allegedly makes it a D.
And yes, while I did once have a high math aptitude I’m these days inclined to look for layman’s answers to these questions, or as simple as possible.
Thoughts?
Thank you again.
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Thank you @mijostyn @mahgister
This is not about a subwoofer.
The reason I ask is that I have a pair of Altec Lansing 604Cs and I now, as of last night, was able to get a 604D to match the 604D that I already have.
I am currently using the 604Cs. The D was a backup in case one blew. Now that I have two D’s, should I switch?
As far as I can tell, however, the ONLY difference in the specs is the free air resonance.
I will be putting the cabinets on rubber feet designed to isolate them from the wood plank floor so that the building doesn’t become a de-facto loudspeaker. I’d like to close the port so as to make the midrange more detailed. This entails losing some bass, but …
I use a Velodyne ULD15, with an active crossover at 60hz for the bottom.
I’m thinking that a speaker with lower resonant frequency will sound better than the one with a higher resonant frequency.
But is the difference too small to even matter, or are the numbers a logarithmic progression instead of arithmetic and thus the difference bigger than one might think? And, does having an active sub crossover at 60hz make this question moot?
one other question: the cabinets are DIY, made of 3/4 ply with a veneer, geometry and materials to Altec specs standard in the day (1950s/60s). Would the bass benefit by stiffening them with another 3/4 layer of ply or solid wood on the interior? If so, do I stiffen all 6 sides, or would just the 4 perimeter sides (not front and back) suffice?
Also, someone told me that one mechanical difference between the two is that the stock C used a paper surround and the stock D used an accordion surround. As Cs are today almost always reconed with the accordion surround (mine are), and as the materials of the cone help determine the free air resonance, simply reconing the C allegedly makes it a D.
And yes, while I did once have a high math aptitude I’m these days inclined to look for layman’s answers to these questions, or as simple as possible.
Thoughts?
Thank you again.
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Thanks mijostyn.
I never think about that because i never need a sub or i did not want to bother me with one...
But bass frequencies are necessary...For sure... My headphone deep bass is enough for me now...
@unreceivedogma , 1+ @mahgister Subwoofer drivers have a long list of characteristics that defines the size and type of enclosure. Both of your drivers might be usable in sealed enclosures and ported enclosures or only in one or the other. Read this https://en.wikipedia.org/wiki/Thiele/Small_parameters.
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@unreceivedogma , 1+ @mahgister Subwoofer drivers have a long list of characteristics that defines the size and type of enclosure. Both of your drivers might be usable in sealed enclosures and ported enclosures or only in one or the other. Read this https://en.wikipedia.org/wiki/Thiele/Small_parameters.
Having said all this and just having finished the construction of a new set of subwoofers, you can pick a driver suited to small sealed enclosures with as low an Fs as possible and with a lot of power and digital signal processing make it do whatever you want. A large B X L product ( above 25 T.m) helps a lot. You can push a sealed enclosure lower than a ported one. The ported one will go lower before rolling off but then drops off like a cliff. The sealed sub will start rolling off earlier but will continue to have useful output down lower. This is a very cursory explanation of a complicated design process. I hate math.
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