JBL 3677

[Stephan]

Thanks!

My idea to create the inner enclosure for the 3677 is quite simple but a bit difficult to explain, I shall try to do a drawing tomorrow.
If the height of the 3677 element is important to have at about 600mm above floorlevel, it might be possible, just by turning this concept upside down.
You would then have the bass unit on top... That could work.

To test different configurations: You might try to build separate enclosures that are rather wide and low so they can be adjusted up and down, perhaps it is possible to tune them separately and after that decide for a combined design.

There are a very large amount of parameters that can be adjusted and that might interact with each other. I think its important not to get lost. One should perhaps try focusing on the musically most important design considerations first and take care of less important after that.

[ThomasOK]

Hello!

I have followed this discussion closely. It would be very interesting trying to combine the 3677 and 4645C in to a common enclosure. I have made a simple outline combining the internal volume of both and placing the speaker elements close together.
Depth is 400mm (50mm less compared to Akubarik).
Combined gross volume approx.: 110+250= 360 litre
Front/back 25mm
Sides/top/bottom 19mm
Weight, approx: 110kg
I have added the Akubarik and 3677 for reference.
WAF will be zero but I think it would work in many ordinary livingrooms
This would be a really fun project!

Wow! A 360 liter cabinet! And I thought my 100 liter ATCs were big.

Interesting idea but with the separation of the tow bass drivers into their own sections of the cabinet and the extra bracing needed for such large panels it would have to be quite heavy too.

[tokenbrit]

I'm reminded of (the other) Linn speakers :)

[ThomasOK]

Good call. I should have thought of that.

[jlwdm]

I'm reminded of (the other) Linn speakers :)

I see those big Linn Audio speakers on Ebay continuously. I just googled him and see he worked many years ago at JBL - although as a sales rep. It all comes together.

Jeff

[Music Lover]

Based on previous discussions with a few experienced speaker designers (inkluding Linn staff), a combined enclosure (with sub) going to be a compromize.
For ultimate performance and flexibility, including adaptability to a specific room, they recommend separate sub speakers.

[Stephan]

At: Music Lover

You might be right, but at the same time Linns top speakers Isobarik, Keltik and Komri have succeeded, with this design.
Also it seems quite difficult to make a subwoofer integrate well and consistently with speakers.
If you have separate subs you can place them anywhere except in the same place as the main speakers, so where do subs mostly want to be? If you turn of the sub in a pair of Keltiks/Komri will they still want to be placed at the same position compared to only have the subs playing in the speakers? That would give an indication how large the compromise are in these speakers.

[Music Lover]

At: Music Lover

You might be right, but at the same time Linns top speakers Isobarik, Keltik and Komri have succeeded, with this design.

Agree. And these are great speakers! Owned all of them.
But it's easier to sell a a complete package.
In a design, you always have to make compromizes.

Also owned a 345sub and it ended up in a different position (with Komri and Akurate)
But I let Fredrik write about his experience, I have very little experience in sub integration.

Sadly, big speakers are a very hard sell on todays market. Even the 3677 going to be a challange for most wifes: big and very old looking.
Then imagine an even bigger speaker with 18" sub...

[Stephan]

Here are two pictures with the woofer on top and internal chamber for the 3677 element





Here is a proposal on how the distance between speaker element and ports can be adjusted
With rotating mdf-boards

[matthias]

I have to say that I do not want to tolerate a bigger speaker than a 3677 in my living room.
The 3677 with its 15 inch woofer should be able to produce enough low bass content with the right crossover.
IMHO, it is better to design a new crossover for the 3677 than to create some new huge speakers.

Matt

[Stephan]

At matthias

Yes, you are probably right.
That would make a better solution, reducing complexity as much as possible

[lejonklou]

Love your drawings, Stephan!

[Spannko]

Here are two pictures with the woofer on top and internal chamber for the 3677 element





Here is a proposal on how the distance between speaker element and ports can be adjusted
With rotating mdf-boards

I love the idea of rotating ports. I never even imagined that the driver to port distance may be relevant, never mind coming up with a solution.

How is the "midrange" (lol) ported?

[lejonklou]

I love the idea of rotating ports. I never even imagined that the driver to port distance may be relevant, never mind coming up with a solution.

How is the "midrange" (lol) ported?

I have not experimented with driver to port distance, that may have an impact as well. But I have played around with a ported design and found that bass unit to floor and wall distances are most important while port to floor and wall distances also matters.

We have found 3677 to perform best at 35 cm above the floor and I suspect the center of the bass unit to be what matters here. The bass reflex ports are two and positioned high up on the cabinet. My guess is that if we put 3677 on its side, the optimal distance between the center of the bass unit and the floor would be unchanged. Two ports at different heights is probably not good, but Stephan's idea with a rotating piece of baffle could probably be used to find the optimal position for the port. The only problem is that it will also move sideways...

Another idea is to make the baffle with, say, five pairs of ports, at different heights above the floor (now assuming that twin ports is optimal) and then block/stuff four out of five pairs. Then moving the blocks so that a different pair is free. An approximate height above the floor could quickly be determined. And then another baffle could be made to fine tune it.

[lejonklou]

By the way, I love how we're all able to toss around loudspeaker design ideas like this. With electronics it's just not possible. Too abstract and too much theory. Although in practice; what I do with the amps can sometimes resemble experiments such as this proposed search for optimal positions of ports and drive units. In an electrical domain instead of a physical one.

[Spannko]

Another idea is to make the baffle with, say, five pairs of ports, at different heights above the floor (now assuming that twin ports is optimal) and then block/stuff four out of five pairs. Then moving the blocks so that a different pair is free. An approximate height above the floor could quickly be determined. And then another baffle could be made to fine tune it.

Great idea!

[Stephan]

Ok, I missunderstood the purpose of moving the ports. I thought you wanted to tune port to speaker element distance.
Also I forgot to say that you may rotate the whole enclosure to get the ports horisontally aligned, during tuning.

There are many variables to play with...
Just looking at the ports
Should a ported design be used at all.
Diameter? Depth? Number of ports. Location, front, back, up, down? Should all ports be identical. Should they be close to each other? Everything will matter, more or less.

It is valuable to have the 3677 as a good base design to start from.

[Stephan]

Love your drawings, Stephan!

Thanks!
I use Autodesk Inventor, it can be downloaded and used for free if you have a child in swedish college (gymnasium), not allowed for commercial use though. Inventor is easy to learn and have built in tutorials.

[Spannko]

Here's a drawing of the remodelled 3677 with the bass unit moved up by about 60mm and the horn moved up by about 120mm. It's better looking, imho but it means that the distance between the lf and hf units is increased by about 60mm. I wonder how this will affect the performance?

[matthias]

It's better looking, imho but it means that the distance between the lf and hf units is increased by about 60mm. I wonder how this will affect the performance?

Yes, looking much better, but I could easily live with the proportions of the original 3677, if these are the better sounding ones.
I think, the higher priority on the to-do-list for the 3677 has the crossover. I found the wiring diagram here:
http://www.jblproservice.com/pdf/Theatr ... s/3677.pdf
It is a rather complex beast and should getting better with some reducing of complexity. The sensitivity of the woofer/compression driver is around 99dB/109dB. My suggestion would be running the woofer directly without crossover and connect the CD with a first order high-pass filter with one cap and two resistors.
What do the crossover experts of this forum think about?

Matt

[lejonklou]

My suggestion would be running the woofer directly without crossover and connect the CD with a first order high-pass filter with one cap and two resistors.
What do the crossover experts of this forum think about?

We are making experiments with the filter right now!

One conclusion is that the bass unit definitely needs low pass filtering, as when it plays high frequencies they sound distorted. (And in my opinion bass units that perform better without a low pass filter are extremely rare).

My guess is that the CD (high frequency compression driver) will not do well with such a flat filter.

We're currently trying to replace the fuses with a resistor, tuning the level of the CD and the level of the notch filter.

My impression so far is that the original JBL filter is very good and it's not easy to improve it. Certainly not necessary to enjoy this fabulous speaker!

[matthias]

I started making speaker stands over 25 years ago and have tested several different design ideas and now have a base design that I'm happy with. I'm now in the process of developing this base design and trying to perfect it for the 3677. So there is more to come from this speaker in almost all areas. Get on board, the doors are not closing, mind the gap to all other speakers...

Linnofil,
what is the price for a pair of your superb looking 3677 stands?

Thanks

Matt

[matthias]

My impression so far is that the original JBL filter is very good and it's not easy to improve it. Certainly not necessary to enjoy this fabulous speaker!

Fredrik,
as the 3677 are designed to work with a subwoofer, is there a high-pass filter in the woofer circuit?

Matt

[lejonklou]

Fredrik,
as the 3677 are designed to work with a subwoofer, is there a high-pass filter in the woofer circuit?

No, just a third order low pass. So the rolloff is determined by bass unit, enclosure volume and ports.

[matthias]

We're currently trying to replace the fuses with a resistor, tuning the level of the CD and the level of the notch filter.

Thanks for your report, Fredrik.
We are curious about the results.

Matt