Proper bass tuning for the Seas L18

[LNeilB2]

I have spent the last year with the Seas L18 in a .5 cu ft enclosure from Parts Express as depicted by John Krutke on his website. He later mentioned that if he had to do it again he would increase interior volume.

That said, what would your recommendations be for internal volume/tuning? I'm going to have custom floorstanding cabinets made, and I'd like to get it right.

TIA,

Neil

[sreten]

Hi,

I cannot see him saying that as 0.75 cuft is about the maximum you
can get away with without overdamping bass too much, 14(0.5cuft)
/16 litres is about right. In 21(0.75cuft) litres port tuning becomes
quite critical and needs to be to the nearest Hz.

/sreten.

[LNeilB2]

Thanks so much for the quick reply. Am I to understand (based on your uploaded response graphs) that 12.5 liters is a better call?

Which choice provides better power handling?

Thanks so much!

[sreten]

Hi,

No 12.5 litres is not a better call.

I've said it many times before, but what some simple box modeling program says is optimum, is usually not.

Rebuilding the boxes is not really worth doing IMO,
it is certainly not worth doing because 14L is "too small".

Add a subwoofer......

/sreten.

[Zaph]

Hello,

I do recall making a statement like that.

I wouldn't go so far as to say the .5 cu ft enclosure is too small, but I will say that the tuning frequency I used in that PE box was chosen by ear in my listening room, and is a compromise with enclosure size. I suspect if you went a little bigger you might be able to get a little more depth in-room at the expense of power handling. Don't rely too much on models, your ears are the best when it comes to selecting a tuning that works with your room.

If you do want to have a better understanding of what tuning/enclosure really works in a design, you'd need a model that includes the series inductor, and an actual room response curve. I got my "room response curve" by having a speaker measured anechoic first then measured in room, then subtracting one from the other to see exactly my room is doing. I wouldn't expect people building my designs to do all that though, so experimenting is the key.

.75 cu ft definitely is too large (I've tried it) but I think .65 cu ft would be about right. From there I'd recommend experimenting with the tuning in your room to see what sounds the best to you.

Is it worth rebuilding? I'd say no, unless your goal is a different and/or better looking box design - in that case it's certainly worth it. Too bad PE boxes don't come in exotic burls or waterfall bubinga.

[LNeilB2]

Thanks to all for the input. I'm happy to see you weigh in as well John, thanks for that.

My reasons for rebuilding are twofold - I prefer the appearance of a floor stander. Just looks better to me. I would also like to have a separate crossover chamber, and perhaps some room for mass loading with sand.

Considering that I'm using large air core inductors, big 600v caps and the impedance correction circuit, I'm sure I've stolen a bit of internal volume from spec. Perhaps I'll make the volume .55 and split the difference. I do not want to compromise power handling, so it sounds as though going much larger will not be a good idea.

Kudos to all for the help...

[Mor den Siur]

What about tuning with Seas P18 passive radiator??

[sreten]

Originally posted by Zaph

I do recall making a statement like that.

Apologies if I misrepresented your position. From my perspective
any box volume over the "classical" alignment is not "too small".
As you say it is best to understand all that is going on rather
than blindly following a simulation tool.

Originally posted by LNeilB2

Perhaps I'll make the volume .55 and split the difference. I do
not want to compromise power handling, so it sounds as
though going much larger will not be a good idea.

Power handling is a moot point. Vented boxes quickly overload
below port tuning so low tuning is good, but then you do not
get the extra power handling further up in frequency with the
higher port tunings.

In this particular case there is not a great range of freedom.
I'd follow Zaph's suggestion of what is about right 0.65cuft/
18litres which is the lilac curve already shown, there with a
port tuning of 36 Hz.

For perspective 41Hz is the bottom E of an electric bass. Generally
speaking a box vented to 41Hz will struggle with the lower B / 31Hz
of a 5 string bass / bottom end of a keyboard / piano and in a lot of
cases not capture kick drum fundamantals.

For this case the of sensible tunings is narrow, but I will note that by
definition the lower port tunings have superior transient response.
The thing to avoid IMO is an obvious "knee" in the response.
IMO ~ 36Hz is about right for a nominal 18L box.
But some prefer the "more" bass of higher tunings, especially
on sustained bass notes with less transient character.

Note that the -6dB point slowly extends with the lower tunings
but not by much, its the response above that should match to the
room which you expect to have bass gain, therefore the flattest
response is not what is best, ideally droop and gain match.

Originally posted by Mor den Siur
What about tuning with Seas P18 passive radiator??

A PR is usually only needed in small boxes requiring low port tunings
and high output, i.e. the required port is too large for the box. In the
case the required port is not particularly large, and minimising box
volume not a concern (can be increased to accommodate a large
airflow port) there is little benefit in using a passive radiator.


/sreten.

[Zaph]

Apologies if I misrepresented your position. From my perspective any box volume over the "classical" alignment is not "too small". As you say it is best to understand all that is going on rather
than blindly following a simulation tool.

No problem, we're all on the same page here, your advice is good. I will almost never tune to anechoic flat/lowest F3 myself - it just doesn't work well in most rooms, not to mention the power handling issues.

[sreten]

Hi,

I suppose I should finally add that if you routinely like driving speakers to there limits
then in terms of power handling in the bass there is no substitute to a subsonic filter.

For an 18L box tuned to 36Hz maximum power dips to a minimum ~ 50W at 55Hz.
Below port tuning it is ~ :
50W at 31Hz, 25W at 29Hz, 12.5W at 25Hz, 6W at 20Hz, 3W at 10Hz.

The exact actual numbers do not matter much, its the principle that counts.

/sreten.