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Converting an Adam Audio T5V to sealed?

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ppataki

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I was wondering if anybody here has done anything like that or if it is considered a good or a bad idea....

Early next year (or even this December, will see) I consider getting my hands on a pair of Adam Audio T5V speakers. After seeing the measurements/reviews/comments I got intrigued by them and definitely want to give them a try.
I prefer sealed speakers to vented ones, with almost two dozens of DIY builds behind me I think I can safely say that
I could just plug the port on the T5Vs but I could also take it apart, totally remove the bass reflex tube, probably use some vibrodamping material on the walls, maybe even some felt and some melamine foam too. Then seal the port and perform before/after measurements + listen to how it sounds before/after
EDIT: forgot to mention that I would of course use EQ to compensate for the gentle bass roll-off when sealed and I would use Dirac Live before/after the mod too

Is this a mad idea? To be honest I might give it a try even if it is :)
Any comments would be welcome
Thank you
 
In my experience, if you take a speaker that was designed to be ported and seal the port, you will have a very bass light, thin sounding speaker. If you are going to be using a sub, then that is a different scenario and might be fine. As you probably know, ported speakers use a driver with a low Q and sealed speakers use a driver with a higher Q, which will determine the bass response in the finished product. Good luck!
 
ppataki said:
I was wondering if anybody here has done anything like that or if it is considered a good or a bad idea....

Early next year (or even this December, will see) I consider getting my hands on a pair of Adam Audio T5V speakers. After seeing the measurements/reviews/comments I got intrigued by them and definitely want to give them a try.
I prefer sealed speakers to vented ones, with almost two dozens of DIY builds behind me I think I can safely say that
I could just plug the port on the T5Vs but I could also take it apart, totally remove the bass reflex tube, probably use some vibrodamping material on the walls, maybe even some felt and some melamine foam too. Then seal the port and perform before/after measurements + listen to how it sounds before/after
EDIT: forgot to mention that I would of course use EQ to compensate for the gentle bass roll-off when sealed and I would use Dirac Live before/after the mod too

Is this a mad idea? To be honest I might give it a try even if it is :)
Any comments would be welcome
Thank you
Click to expand...
I think running them with the plugged port is an OK-to-moderately-bad idea and modifying the cabinet to remove the port is a challenging DIY project in search of a problem.

You will be straining the amp of the T5V if you EQ the bass back to where it was with the port, but I guess you can do it anyway.

Plugging the port should work as well as fully removing it, plus it's reversible if it doesn't work well, so start there.
 
Assuming the manufacturer knows what they are doing you'll make it worse!

Good speakers can be made either way. Generally the box is "tuned" (or "sized" if sealed) to work with the particular driver.

Voodooless posted this graph which shows the general relationship between sealed and ported cabinets.

The ported box can have a lower -3dB frequency cutoff but the curve is steeper so at some point the sealed box has more output. The ported box can be made to go even lower if you design-in a little (unnoticeable?) 1 or 2dB bump before the cutoff. A badly-designed ported speaker can have a big bump and a nasty sounding resonance. If you don't know what you're doing a sealed box is less risky.

A smallish sealed subwoofer can go super-low with EQ boost and enough amplifier power.

EQ doesn't work as well to extend the range of a ported box because of the steeper slope, plus below the tuning frequency there is no resistance to cone movement so the woofer "flops in-and-out" without making much sound.
 
ppataki said:
I was wondering if anybody here has done anything like that or if it is considered a good or a bad idea....
Click to expand...

It depends on implementation. All you're doing is raising the cutoff frequency, changing the shape of the knee & rate of rolloff. If you can make a higher sub cross work in your situation, you shouldn't have any problems.

Where it can be an issue, as mentioned, is if the mid-woof Q is too low, which in this case is doubtful. Most in that class are mid Q.
 
DVDdoug said:
A smallish sealed subwoofer can go super-low with EQ boost and enough amplifier power.
Click to expand...
Of course, with lots and lots of amplifier power being applied, the EQ-boosted small closed-box loudspeaker will have its voice-coil heat up relatively quickly. A lot of power is "wasted" getting the cone moving at lower frequencies against the restoring force of the low-compliance small enclosure.
DVDdoug said:
EQ doesn't work as well to extend the range of a ported box because of the steeper slope, plus below the tuning frequency there is no resistance to cone movement so the woofer "flops in-and-out" without making much sound.
Click to expand...
Early work by Thiele (1961), Loudspeakers in Vented Boxes, and Keele (1975), A New Set of Sixth-Order Vented-Box Loudspeaker System Alignments, has demonstrated that the use of filter-assisted vented-box low-frequency alignments produces results that address the problem of out-of-band driver excursion. These make use of a second-order auxiliary high-pass filter that also introduces some peak lift.

The example below demonstrates that filter-assisted vented-box low-frequency alignments work particularly well in extending the low-frequency range of a vented-box enclosure (solid curves) compared to the original unassisted design (dashed curves). Here the −3dB low-frequency cut-off frequency has been lowered from 46.9Hz to 36.2Hz. That's a 10.7Hz reduction, which is quite considerable. The action of the high-pass filter has been tuned so that it has also considerably reduced the out-of-band driver excursion, which is now slightly less than the in-band driver excursion. These results have been achieved using a moderate amount of peak boost of about 4.8dB at 41Hz. Note that the filter-assisted alignment utilized a lower box tuning frequency of Fb = 35.0Hz, while the QB3 unassisted alignment utilized a much higher box tuning frequency of Fb = 46.5Hz. The box volume stayed constant at Vb = 226 litres.

1731393382284.png
 
ppataki said:
Yes, good point, thank you for raising it. Forgot to mention that I will integrate it with this sub.
Click to expand...
In this case just plug the port to get rid of port resonances and other unwanted sounds it might emit. EQ is probably not needed at all.
 
ppataki said:
...I consider getting my hands on a pair of Adam Audio T5V speakers. After seeing the measurements/reviews/comments I got intrigued by them and definitely want to give them a try.
I prefer sealed speakers to vented ones, with almost two dozens of DIY builds behind me I think I can safely say that
I could just plug the port on the T5Vs but I could also take it apart, totally remove the bass reflex tube, probably use some vibrodamping material on the walls, maybe even some felt and some melamine foam too. Then seal the port and perform before/after measurements + listen to how it sounds before/after.
EDIT: forgot to mention that I would of course use EQ to compensate for the gentle bass roll-off when sealed and I would use Dirac Live before/after the mod too.
Click to expand...
The T5V speakers don't have a particularly extended bass response. They seem to be −3dB at about 60Hz or so, going by Adam Audio's published response curve. They claim to be −6dB at 45Hz, but that does not seem to be borne out by the measured frequency response curve. That's not entirely surprising, as the woofer is small, being only 5 inches in diameter.

Taking a guess that the woofer in the T5V loudspeaker could have similar Thiele–Small parameters to those of the Focal 5 N 411 L woofer, the QB3 tuning for that driver produces a result that's quite similar to that of the T5V.

1731400853659.png


If we now switch to a closed-box alignment, keeping the enclosure volume the same, we can expect the following response. The dash-dot cyan line represents the original vented-box alignment. Here it can be seen that, at a nominal 10W re 8Ω of input power, the sealed driver exceeds 5mm of excursion below 40Hz. It seems that there may not be much scope to EQ the closed-box alignment to improve its bass performance. That's the very real downside of small loudspeakers.

1731401161975.png
 
witwald said:
It seems that there may not be much scope to EQ the closed-box alignment to improve its bass performance.
Click to expand...
Since I will use a sub the goal is not to enhance the bass response of the T5Vs but rather to listen and measure the impact of converting them into a sealed design
I am expecting better transients (better impulse/step response) but we will see :)
I will document the experiment here; I plan to make it happen in December/January
 
ppataki said:
Since I will use a sub the goal is not to enhance the bass response of the T5Vs but rather to listen and measure the impact of converting them into a sealed design.
Click to expand...
@ppataki, I did a VituixCAD simulation of an estimated version of what a closed-box (blocked vent) version of the Adam Audio T5V loudspeaker might be.

The assumption was that the low-frequency alignment would have a Qtc=0.584 with a box resonance frequency of Fc=74.7Hz. The red curve in the plot shown below represents this.

Next, I added a subwoofer model. This consisted of a second-order Butterworth high-pass filter with a −3dB cut-off frequency of 25Hz. Next, I added a second-order Butterworth low-pass filter with a −3dB cut-off frequency of 55Hz. A gain stage was also included, and this was set to A=−0.9dB. The green curve in the plot shown below represents the resulting subwoofer frequency response curve.

With the subwoofer connected with inverted polarity, the closed-box T5V response and the subwoofer response sum together to produce a very flat response. The black curve in the plot below is the summed response. The crossover frequency is at about 66Hz, where the two responses are at –6dB relative to the level of the response in the passband. This indicates that the drivers are in-phase at the crossover frequency. In this simulation, the combined system has a −3dB low-frequency cut-off point of about 27Hz. Note that below about 20Hz, there is a small amount of phase cancellation occurring between the output of the subwoofer and the closed-box T5V (the green curve lies slightly above the black curve).

1731665021950.png


The low-pass filter applied to the subwoofer is of a low order. Hence, it will not introduce a lot of phase shift in the passband of the system. This should enhance the transient response of the system by minimizing any waveform distortion. Of course, it would likely be possible to successfully use a higher-order low-pass filter on the subwoofer. However, it is quite likely that that would necessitate adding a suitable high-pass filter to the closed-box T5V to achieve a reasonably flat summed response.

I'm looking forward to reading about the results of your experiment. Keep us posted...
 
Last edited:
witwald said:
@ppataki, I did a VituixCAD simulation of an estimated version of what a closed-box (blocked vent) version of the Adam Audio T5V loudspeaker might be.

The assumption was that the low-frequency alignment would have a Qtc=0.584 with a box resonance frequency of Fc=74.7Hz. The red curve in the plot shown below represents this.

Next, I added a subwoofer model. This consisted of a second-order Butterworth high-pass filter with a −3dB cut-off frequency of 25Hz. Next, I added a second-order Butterworth low-pass filter with a −3dB cut-off frequency of 55Hz. A gain stage was also included, and this was set to A=−0.9dB. The green curve in the plot shown below represents the resulting subwoofer frequency response curve.

With the subwoofer connected with inverted polarity, the closed-box T5V response and the subwoofer response sum together to produce a very flat response. The black curve in the plot below is the summed response. The crossover frequency is at about 66Hz, where the two responses are at –6dB. This indicates that the drivers are in-phase at the crossover frequency. In this simulation, the combined system has a −3dB low-frequency cut-off point of about 27Hz. Note that below about 20Hz, there is a small amount of phase cancellation occurring between the output of the subwoofer and the closed-box T5V (the green curve lies slightly above the black curve).

View attachment 406663

The low-pass filter applied to the subwoofer is of a low order. Hence, it will not introduce a lot of phase shift in the passband of the system. This should enhance the transient response of the system by minimizing any waveform distortion. Of course, it would likely be possible to successfully use a higher-order low-pass filter on the subwoofer. However, it is quite likely that that would necessitate adding a suitable high-pass filter to the closed-box T5V to achieve a reasonably flat summed response.

I'm looking forward to reading about the results of your experiment. Keep us posted...
Click to expand...

Thank you for the analysis @witwald
just FYI I will use a high pass filter of 24db/octave on the T5Vs and a low pass filter of 24dB/octave too on the sub, both at 80Hz and both linear phase
The port will be stuffed (not sure with what but I plan to use melamine foam to do that) and it will be also covered in an airtight fashion with self-adhesive vibrodamping sheets
I am also very interested in seeing the results :)
 
I've converted the VituixCAD model to use linear-phase 4th-order Butterworth low-pass and high-pass filters, set to 80Hz. The results are shown below.

1731678252794.png


The simulation using only the 2nd-order Butterworth low-pass filter on the subwoofer is shown below. This configuration has a slightly greater group delay below 30Hz or so.

1731677493327.png



A simulation using 4th-order Linkwitz–Riley low-pass and high-pass filters is shown below. The filters have been adjusted to produce an 80Hz crossover frequency between the subwoofer and the main speakers. In this instance, the subwoofer and main speakers are both connected with positive polarity.

1731677819983.png
 
witwald said:
1731678252794.png


The simulation using only the 2nd-order Butterworth low-pass filter on the subwoofer is shown below. This configuration has a slightly greater group delay below 30Hz or so.
Click to expand...

I am really happy to see the simulation - it justifies my idea pretty well!
Thank you
 
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