I’m going round in circles so looking for some direct advice.
I’ve built 160L sealed cabinets for 15” Tannoy Monitor Golds. Initially they have simply been lined with butyl rubber sound deadening and open cell acoustic foam, but the measured bass response is a little all over the place, some of which is caused by the room but some I feel may be caused by the lack of stuffing.
My understanding is that the MG 15” isn’t particularly well suited to sealed cabs so I may have to port them at some point but I’m looking for advice regards further cabinet stuffing to see if I can improve the response in a sealed cab.
As I understand it, the MG 15” has a low Q (0.2), which is not greatly improved by the sealed cabinet. My concern is that further stuffing the cabs will only serve to lower the Q again.
How far should I go with stuffing and where is best to place it?
Alternatively, should I bite the bullit and port the cabs now before wasting any further energy stuffing them?
All advice and opinions gratefully received.
Thanks.
I’ve built 160L sealed cabinets for 15” Tannoy Monitor Golds. Initially they have simply been lined with butyl rubber sound deadening and open cell acoustic foam, but the measured bass response is a little all over the place, some of which is caused by the room but some I feel may be caused by the lack of stuffing.
My understanding is that the MG 15” isn’t particularly well suited to sealed cabs so I may have to port them at some point but I’m looking for advice regards further cabinet stuffing to see if I can improve the response in a sealed cab.
As I understand it, the MG 15” has a low Q (0.2), which is not greatly improved by the sealed cabinet. My concern is that further stuffing the cabs will only serve to lower the Q again.
How far should I go with stuffing and where is best to place it?
Alternatively, should I bite the bullit and port the cabs now before wasting any further energy stuffing them?
All advice and opinions gratefully received.
Thanks.
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160 liter is a big cabinet, so even with the foam lining the walls, there is a lot of empty air in there... you could definitely have some acoustic resonances (standing wave).
Rock wool is a low cost but very effective damping material. Shredded denim is another very good material. I would fill the cabinet 50% with either rock wool or shredded denim, and see if things improve. A 50% fill should not affect the bass response (Qtc), but it should significantly reduce any standing wave resonances, assuming that is an issue for you. If you notice no change, then standing wave resonances were not the cause of your bass response problems. If you notice a nice improvement, you can experiment with more or less of the fill material.
j.
Rock wool is a low cost but very effective damping material. Shredded denim is another very good material. I would fill the cabinet 50% with either rock wool or shredded denim, and see if things improve. A 50% fill should not affect the bass response (Qtc), but it should significantly reduce any standing wave resonances, assuming that is an issue for you. If you notice no change, then standing wave resonances were not the cause of your bass response problems. If you notice a nice improvement, you can experiment with more or less of the fill material.
j.
1. Bass reflex with a lower “bass-shelf” tuning frequency,
2. Suspend the rock wool in the cabinet - not letting it near the walls or driver,
3. Make sure the rock wool is almost exactly an inch away from the port’s “entrance”,
4. Remove any material from the walls, and even consider waxing the walls to get a low air resistance result,
5. Wax the interior of the port to lower air resistance,
6. Make sure the cabinet is very well sealed, no air-gaps from cabinet edges or around the driver or around the port’s exit.
The rock wool should be at least 4” thick, spray glue together if needed.
2. Suspend the rock wool in the cabinet - not letting it near the walls or driver,
3. Make sure the rock wool is almost exactly an inch away from the port’s “entrance”,
4. Remove any material from the walls, and even consider waxing the walls to get a low air resistance result,
5. Wax the interior of the port to lower air resistance,
6. Make sure the cabinet is very well sealed, no air-gaps from cabinet edges or around the driver or around the port’s exit.
The rock wool should be at least 4” thick, spray glue together if needed.
Since this is a sealed cabinet (at this time), you can simply fill the lower half to start with. However, you could also put some behind the driver.
Is that tannoy driver a woofer, or is it a coax? what I am getting at is does that driver handle midrange frequencies? If yes, then I would definitely put a layer of rockwool behind the driver.
Is that tannoy driver a woofer, or is it a coax? what I am getting at is does that driver handle midrange frequencies? If yes, then I would definitely put a layer of rockwool behind the driver.
Yeah, is ~60 L too big for a max flat (0.707 Qtc) sealed based on the attached published specs unless driven with a high output impedance, so currently at a presumed over-damped ~0.457 Qtc based on this math, ergo ideally shrink net volume (Vb).
Regardless, either way, increasing damping is going in the wrong direction, instead you want to quell its eigenmodes, so historically heavily damped one side, top, back and only add more if it sounds 'hollow' and/or 'rings', which can be tested using the pioneer's simple 'click' test.
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clarification: about 2-3” away from walls/driver magnet/ port but filling the rest of the space except about 1” from port entrance and the area near the baffle/driver
Also, bass reflex/shelf and sealed around walls/driver/port will make the biggest difference.
well, yes, but that does not really start to happen until the cabinet is completely full of stuffing. On a sealed box, the stuffing must be compressed in order to start the process of increasing apparent volume.
With a typical 40 liter box, if you line the walls with 4 inch of insulation, you have effectively filled the enclosure to 50% capacity with stuffing. With the OP's 160 liter box, lining the walls with 4" is almost insignificant. That is why I suggested he fill to 50%.
He complained the measured bass was "all over the place", not that it was weak. Of course it is somewhat weak, anytime a woofer with Qts of 0.22 is put in a sealed box the bass is going to be weak. I assume he will EQ it to be more flat, or as he says, add a BR port later. But for now, he wants to address the bass which is "all over the place", which to me suggests he has a standing wave resonance issue.
So I stand by my advice. Fill the box with 50% fill of something affordable like rock wool. For $15 he can see if this helps his problem.
j.
OK, a 4" dia. x 6.62" vent tunes it to ~Fs based on just lined as I suggested and handles all 50 W rating at acceptable vent mach; don't know about with stuffing since never ported a basic BR, though cab looks to be at least 36" i.d. tall, so best to put the vent down low and maybe need to shorten it a bit.
Certainly not suggesting that damping is a bad idea. It’s very important. My point was that the first thing he needs to do is port the cabinet. Adding stuffing to a sealed cabinet that is too large is not the correct order to do things. They really need to be done together.
IOW, no need for a paint job until you rebuild the engine.
IOW, no need for a paint job until you rebuild the engine.
Looks like that box was designed to be close to back wall or even corner placement.
If it stays closed 50% damping will help standing waves.
If ported at least some damping fixed behind the magnet of the driver helps killing standing wave. It's not the question of how much damping but the right position damping the wave is the trick. You can clearly hear it if done right.
If it stays closed 50% damping will help standing waves.
If ported at least some damping fixed behind the magnet of the driver helps killing standing wave. It's not the question of how much damping but the right position damping the wave is the trick. You can clearly hear it if done right.
Thank you all for the feedback and suggestions.
The Tannoy driver is dual concentric so it deals with the full frequency range with a crossover frequency of 1000Hz. I have been advised a number of times to port the speakers but just wanted to try it as a sealed enclosure first. One issue I’m also trying to avoid is exacerbating a few low level room modes at around 33hz and 95hz respectively.
With regards to a port, if / when I do it, I was looking to install a rectangular or slot port low down on the front baffle, is there any reason not go this route?
👍🏻
The Tannoy driver is dual concentric so it deals with the full frequency range with a crossover frequency of 1000Hz. I have been advised a number of times to port the speakers but just wanted to try it as a sealed enclosure first. One issue I’m also trying to avoid is exacerbating a few low level room modes at around 33hz and 95hz respectively.
With regards to a port, if / when I do it, I was looking to install a rectangular or slot port low down on the front baffle, is there any reason not go this route?
👍🏻
Let's start from the beginning.
Does low frequency response lack? What do you not like?
Don't be afraid of a very flat tuning (low Q) - when it fits the room, why not? It just wastes space but as you already have the cabinet ...
You for sure NEED dampening in the cabinet. A closed volume makes it way easier cause you can just stuff it with e.g. sheep wool or similar material. Important is to get material in the middle of the volume to get rid of the main reosnance! (and that's one of the problems of ported - when you do that you loose your efficiency. So some resonances are left)
To really nail this you need to measure nearfield response of the woofer and/or impedance. You see cabinet resonances there, dampen until they are gone.
When bass response is to flat/low but over all SPL level is more than enough - you need to change the crossover or use some active EQ to simply add low frequencies. In a closed volume you can do that without hesitation - closed subwoofers for Homecinema are based on the fact you correct and adapt the frequency response to the room.
Does low frequency response lack? What do you not like?
Don't be afraid of a very flat tuning (low Q) - when it fits the room, why not? It just wastes space but as you already have the cabinet ...
You for sure NEED dampening in the cabinet. A closed volume makes it way easier cause you can just stuff it with e.g. sheep wool or similar material. Important is to get material in the middle of the volume to get rid of the main reosnance! (and that's one of the problems of ported - when you do that you loose your efficiency. So some resonances are left)
To really nail this you need to measure nearfield response of the woofer and/or impedance. You see cabinet resonances there, dampen until they are gone.
When bass response is to flat/low but over all SPL level is more than enough - you need to change the crossover or use some active EQ to simply add low frequencies. In a closed volume you can do that without hesitation - closed subwoofers for Homecinema are based on the fact you correct and adapt the frequency response to the room.
I would not port it, it’s a 2-way and you’d have to deal with the port resonances too. You need measuring capabilities for that. Instead fill it to at least 50% with (mineral or denim) wool. Even a full fill could be beneficial or necessary to bring enclosure cavity resonances back to an acceptable level.
The bass being all over the place is most likely caused by the setup and the room acoustics. 2x15” serves you quite well to evoke all those eigentones…
The bass being all over the place is most likely caused by the setup and the room acoustics. 2x15” serves you quite well to evoke all those eigentones…
Ok, I just did some playing around and stuffed 1 cabinet and measured at 1m using REW:
Green is un-stuffed.
Red is stuffed like this:
You can clearly see the room modes up to 200hz, I may add a little more behind the driver and go again.
Ps. I use Dirac to deal with the room modes, not much else I can do about those in my domestic setup.
Green is un-stuffed.
Red is stuffed like this:
You can clearly see the room modes up to 200hz, I may add a little more behind the driver and go again.
Ps. I use Dirac to deal with the room modes, not much else I can do about those in my domestic setup.