GM - If you would be so kind..........

[GM]

Greets!

No, I didn't do any measurements, I did the initial design and simmed what effect the changes he wanted done to satisfy what I assume were WAF related issues might have. That said, I don't know for sure what dims he used, but there's no mention of a 54" height unless this includes his stands since the inside cab height dim is supposed to be 42.5". Note too that the original design was much bigger at ~17.64 ft^3/29.5 Hz Fb, but he chose a ~10.38 ft^3 compromise since they would be near a wall, so be forewarned if you plan on placing well away from any boundaries.

45"?! Wow! How tall are you? I prefer the driver slightly above listening height, so my standard 38" puts the driver above all but the tallest folks I've measured when seated in a typical sofa, etc..

Raising the driver will load the vent more, lowering Fb for a given vent size and potentially causing a bit of 'ringing'. This can be ameliorated either by raising the cab off the floor more or reducing vent length or adding a little more damping. That said, you'd probably have to compare it side by side with Jay's to notice any subtle differences, so assuming that's not going to happen I would keep the design the same and raise the driver up as required and in a worst case scenario you'll have to shorten the vent as required to fine tune it in-room. This is often required anyway since down low the room's modes dominate and I seriously doubt yours is the same as Jay's. Indeed, it wouldn't surprise me if you needed a longer vent (tuned lower) or at least some damping at the bottom to reduce vent loading.

Then there's the effect of passive EQ on its performance, such as the amp's output impedance combined with the wire gauge chosen on the driver's specs.

This is what has made MLTLs my fave cab for decades, plenty of tuning flexibility if you make them big/tuned low enough.

GM

[apblossom]

GM,
I have a pair of A7-500's with 902's and 416As'. I have listened to them for a while and have two desires. I'd like more bass, and I'd like the 511b nearer ear level. So I've been contemplating building a new woofer box to accomplish same. I've considered Onken and bass reflex. I noted above you like the MLTL, but I believe your system at home has two 515's per side in a BR enclosure. I'm not particualrly constrained in the volume of the box. What would you suggest?
Paul

[GM]

Greets!

Yes it does and its aspect ratio makes it a MLTL. Anyway, a simple one fold MLTL can be made to allow you to continue to mount the horn on top.

GM

[Seadweller]

Greetings!

My cabinet maker is beginning to draw up the detailed constuction plans for my 604 enclosure, which is being modeled after the well regarded MLTL design by Jay Fisher. Rather than making a box, and putting it on a stand, I am integrating a stand into the design of my cabinet. Jay indicated that you conducted some measurements on this cabinet, therefore I would greatly appreciate your input.

My problem is this: If I design the cabinet so that the bottom-firing port is 10" from the floor, given the critical placement of the driver from the top of the cabinet, I end up with the center of the driver being only ~34" from the floor, which seems awfully low. I measured the height of my ear from the floor in my favorite listening chair, and it's ~45".

I'm not sure if this is acceptable, or if I should somehow address the issue in the design. The cabinet is already spec'd to be 54" tall, which is quite large. I hesitate to bring the bottom of the cabinet higher from the floor to raise the driver height, because to bring the driver to my ear level would require a 20" space from the port to the floor, and result in a cabinet nearly 64" tall! I'm also afraid I might lose the necessary boundary effect for smooth bass response.

What kind of leeway do I have with the MLTL alignment so it doesn't throw everything out of kelter? Can I raise the driver higher in the cabinet without ill effect, or is the position super critical to maintain the MLTL alignment?

I thought of perhaps raking back the cabinet to bring the vertial plane of the driver higher at the listening position, or perhaps I could even use adjustable spikes.

Any input/advice would be GREATLY appreciated!

[Seadweller]

Again, many, many thanks!!!!!

I am maintaining the exact 42.5" internal cabinet height, however I have slightly changed the width and depth while maintaining the same CSA. I don't want to do anything to disturb the performance of the design.

Jay has his cabinets on stands, and I'm not sure exactly how tall his system is, but I can guess based on the overall cabinet height, and stands which I believe are around 10" tall.

I've integrated the stand into my design, and in keeping with the required internal cabinet height and recommended port distance from the floor, I end up with a total cabinet height of 54".

I'm going to assume that raising the port off the floor another 2" will be much less disruptive to the end result than raising the driver in the cabinet. I know nothing about acoustics, but would surmise that the small change in the "boundary effect" caused by raising the port distance from the floor, will be less noticable than changing the driver position in the cabinet, which disrupts the alignment. I'm already at 54", so what's another 2"-3"?

Now I just have to decide if I want to make a squared off monolith, or spend twice the money and radius the edges, etc. I guess if I'm doing it once, I might as well go all the way!!!

[GM]

Greets!

You're welcome!

Hmm, width, depth are fairly critical in such a large cab to keep internal standing waves from summing, so a golden or acoustic ratio is desirable. If this occurs then more damping is required, which can overdamp the driver's upper BW too much.

I don't either, all he sent me was a picture of the completed speaker with it's Buck Rogers style stanchions.

WRT this 10" recommended port height, I'm assuming here that JF did some experimentation since the calc'd minimum dim I gave him was considerably less, so again, it may sound best to you at a different height in your room. Anyway, at 10" it's already high enough that raising it shouldn't make any audible difference other than how the speaker interacts with the room.

GM

[Seadweller]

I greatly appreciate the input.......

Regarding width and depth, am I OK changing these dimensions slightly if I maintain the same CSA, or should I stick with the original dimensions? I'm trying to narrow it slightly, but it's already the size of a 1969 Impala, so I can go back to the original dimensions if my changes will impact the performance/design of the MLTL alignment....

[GM]

Greets!

Don't know what dims he used, I would normally recommend (i.d.)~26.125" W x 16.187" D.

GM

[Seadweller]

The original spec. of these cabinets was (I.D.) 42 1/2" H x 24 1/8" W x 17 11/16 D....

Does a change in the W an D change the "tuning" of the pipe, even if the CSA remains the same?

[GM]

Greets!

Depends. As I said, it potentially affects how much damping is required to smooth the woofer's box response, with golden or acoustic ratios requiring the least. As it increases, it also begins damping vent action, rolling off its output, lowering Fb. This is not necessarily a bad thing as additional damping is a tuning tweak for when the room is very 'live'. A worst case scenario is you have to shorten the vent to regain its bottom octave 'presence'.

Still, it's best to design for max adjustment. Obviously, there can be size, location, WAF, etc., constraints, so you make do as best you can.

GM