My "tweaked" Alto-G: I made the box too big -> boomy bass. What to do?

[mr_push_pull]

Hi everybody

Finally, after moths spent waiting for the drivers to arrive I had a chance to listen to my "tweaked" Alto-G enclusures (Alto-II with a G20SC tweeter). Here "tweaked" means that I increased the volume from 28l to 40l, following someone's suggestion (I won't disclose the name since it is a public character into the DIY world and I don't want to offend him). The simulations were OK, but the audible result is that I have a boomy bass.
Now, the questions is: what to do? Rebuilding the enclosures is out of the question, I don't have the time to do that. Cutting the bottom means re-cutting the hole for the port, making another botton, etc. I don't like that.

Two options remain: putting a board in the upper part can reduce some 6.5 liters. Another box glued at the middle of the enclosures could make for the remaining 5.5 liters.

Second option, which I'm not sure about: reducing the length of the port seems to have the same result as the reduction of the box volume, at least in theory, I'm not too sure about this.

Another thing I'm thinking about is breaking in of the woofer. Breaking in lowers Fs and increases Vas, and maybe the woofer will "fit" better in the box. Just a thought.

Please advise me what to do.


Calin

[larry]

hi,
just put some brick-stones or some bags of sand in the enclosure to reduce the volume.
greetings,
larry

[Frankynstone]

Hi mr_push_pull!

Another option was to change the length of the port. A longer port makes it sound more like a colsed box but the low frequency response is extended still. Don't wait for a wonder, but some fine tuning is possible.

One possible Problem is, that the port is near the bottom of the enclosure. If it was directly below the woofer the danger of rumbling might be lesser. But i can't really immagine, that you want do do many experiments, do you?

Get on well with it!

Frank

[mr_push_pull]

Of course I'll experiment a bit. I only have 7.4 centimeters until I reach the back lid with the port. I presume that getting near the walls of the enclosures with the port is a problem. Is it so? How much space should I reserve?

[Frankynstone]

I've got some tiny bass reflex cubes from RFT, the port dia is about 4 cm and it ends in a corner one cm apart each wall. So the lenght of the port seems to be complemented by that. Appears to be no prob since the bass is free from noise, quite deep (gentle peak at 50 Hz) and loud enough. The simply made the port as long as possible.

If youn don't want to hear strange effects, maybe half the dia is a possible minimum for the distance between back lid and end of the port. Otherwise air-flow noises could appear at high volume.

[mr_push_pull]

Original geschrieben von Frankynstone
If youn don't want to hear strange effects, maybe half the dia is a possible minimum for the distance between back lid and end of the port. Otherwise air-flow noises could appear at high volume.

Im my case (BR 15.34 port), this means that I'll be able to extend about 4 cm. I hope it will be anough. I'll experiment with a cardboard tube since BR 15.34 has only 14.7 cm.

[ichse1]

If you use the full length of BR15.34 , the box is already tuned lower than the "original". So a further increase of length will probably make it worse.

Try a shorter port, bricks or anything else in the box and try to move the boxes in the room. Or close the port (socks!) and tell us your experiences.

[4real]

Well, adding volume to the box with the same BR length lowers the tuning frequency. As does extending the BR tunnel. A shorter BR will give you a bump, leading to an even more boomy sound. I think extending is the best method of un-booming your box. Also try to put some stuffing in the box to make it more "dead" (but let the air go from speaker to BR tunnel).

You also might try closingthe BR tunnel.

Also try to simulate what you habe right now, and check the group delay. If it is a bit high, you can end up with a boomy sound.

Another thing is placement: Put them a small distance from the walls and not agains them!

[mr_push_pull]

Original geschrieben von ichse1
If you use the full length of BR15.34 , the box is already tuned lower than the "original".

Do you imply that the Alto-G has the port shorter than 14.7 cm, the full lenght of the BR15.34? Or do you mean that the higher volume lowers the tuning frequency for the same port length?

What I did last night was measure the woofers. I've been told that the W170S has a history with deviations from the published specs. I did find some deviations, for instance a Qts of 0.53 instead of 0.41. Well, I haven't broken-in the drivers before measuring, but could these deviations have a part of responsibility for my problems?

[ichse1]

Or do you mean that the higher volume lowers the tuning frequency for the same port length?

Exactly!

[mr_push_pull]

Original geschrieben von ichse1
Exactly!

Anyway, a shorter port will worsen everything I think, especially transient response

[VISATON]

I don't think that the problem mainly is caused by the tuning of the enclosure. The Alto II has a very strong low frequency performance, even with the volume of 28 l. 40 l is definitely too much, but I suppose the room resonances are the real reason for the "booming bass". Please test it with closed tubes (simply put in a cloth) at various positions in the room.

[mr_push_pull]

Original geschrieben von VISATON
I don't think that the problem mainly is caused by the tuning of the enclosure. The Alto II has a very strong low frequency performance, even with the volume of 28 l. 40 l is definitely too much, but I suppose the room resonances are the real reason for the "booming bass". Please test it with closed tubes (simply put in a cloth) at various positions in the room.

Boomines disappears with choked port, but I'll have to experiment some more to reach a verdict. And I also think that room response is part of the problem. I'll probably put an obstructing board in the upper part to take approx 6.5 liters and some extra bracing in the middle to take the remaining 5.5 liters.