xmax of mid woofer

[SentinelAeon]

I am having some problems with dayton audio TCP115-4 and high filter. The reason i noticed it only now is simple: i saw many builds using this daytons, even profesionaly built and sold and i never heard anything about high filter on the TCP115-4. Here is 1 example: it only mentions low pass on the woofer and high pass on tweeter:

https://www.audioholics.com/bookshel...d-mk442-review

I built a similar speaker and i am happy with it, i have been using it for a year in bluetooth speaker, driving it to the max everytime i use it, playing normal music on it. Only now i looked at xmax graph in winISD and my blood frooze. I attached an image of xmax graph without high pass .. and 1 with a high pass, second order butterworth at 75Hz, that is the only way i am able to limit its xmax to safe values. As you see, -3dB seriously suffers.

So my questions are 2:

1) How was my bluetooth speaker able to survive all this, judging by the graph, it should be long dead.
2) Is there any better way around this ? The high pass like this moves F3 about 13Hz higher.

[rpb]

Your BT amp might have a high-pass already. Check the specs.

Try a 4th order high-pass at about 40hz. A 4th order does not start rolling off as soon.

[Millstonemike]

Just some thoughts: 1) Xmax is different than Xlimit. 2) the Xmax model may not account for increased resistance to movement as the woofer extends towards it's excision limits. and 3) there's likely little content below 40 Hz in normal music - church organ and home theater being two obvious exceptions.

You say you've been playing it very load w/o issues. If it ain't broke, don't fix it

[wogg]

You've been using it without issues already, don't let a graph change that.

Xmech > Xmax, which avoids damage to the driver. Every woofer is different, but I suspect that little guy is hard to bottom out. Chances are you were going over Xmax when cranking, and just getting increased distortion and not bottoming out.

[wogg]

Nice Millstonemike, simultaneous reply saying pretty much the same thing ;)

[SentinelAeon]

Thank you for all the replies,

I have been using it no problem but this time i have to build it for a friend and that is different, that is why i worry. Again, it really surprised me that in that link i gave in my first post, in a professional system they are selling, they didnt include it. So maybe i worry to much.

Sadly i do not have any useful specs as its a cheap WUZHI 2x50W bluetooth amplifier. The reason i am still using it is that i am satisfied with it. One interesting thing i noticed on this amplifier is that even at maximum volume i barely get any distortion, there is some but it is still perfectly acceptable when used outside on a picnic. I did some measurments at low frequencies using killawatt and most i managed to get out of a single channel with this 4 ohm tcp115 i got was about 55W, some obviously is lost due to DC suply and other things.

Another thing that crossed my mind is, might it be that small diameter port is also restricting its xmax ? Its a 2.9 cm port and about 20cm length

I think this time around i will do it without a highpass filter and just keep a single dayton at home for reserve if this one breaks. In the future i will look at some of the more complex crossovers but that raises the costs of the system.

[Millstonemike]

T....

Sadly i do not have any useful specs as its a cheap WUZHI 2x50W bluetooth amplifier. The reason i am still using it is that i am satisfied with it. One interesting thing i noticed on this amplifier is that even at maximum volume i barely get any distortion, there is some but it is still perfectly acceptable when used outside on a picnic. I did some measurments at low frequencies using killawatt and most i managed to get out of a single channel with this 4 ohm tcp115 i got was about 55W, some obviously is lost due to DC suply and other things.

Post a Pic of the amp. I may have pertinent info on this issue.

On your power out ... The 2 x 50 W amp rating is simply the max heat dissipation the class D chip can handle, not the power out you get. Your rms power @ <0.5 THD per channel will be governed by this equation:

P_rms = ((V_ps - 1)² / 2) / IMP_{sp ... (}PS Volts - one, squared then divided by 2 then divided by speaker impedance). For example: a 24 V supply with a 4 ohm woofer will yield ~66 W rms per channel.

Most reputable amps use an rms power rating based on a sine wave signal. If you measured power out with music as a signal, you'll see less power than the calculation I provided. That's because music has much less power density than a sine wave.


Your in a good place. For most posts of builds with problems, the specs all line up but the system sounds like S$/t.

As before: Si no está roto, no lo arregles

[Chris Roemer]

The THERMAL limit of that little 4"er is 40w, not 45w. (Your screenshot shows you @ 45?)
Mine are in a .10 box tuned near 50 and they'll play a STRONG 40Hz.
My amp is only 20rms/ch. (Lepai)
No problems.

[Millstonemike]

I wouldn't worry about modelling 50 or 60 W into a driver rated for 40 W. The driver thermal ratings assume a sine wave. My empirical observations show that music has about half the power density of a sine wave. So an amp rated for 60 W rms will deliver an average of ~ 30 W average over time. The larger issues are Xmax and port velocity a their respective peaks.

[tvrgeek]

Add a simple first order HP at some low frequency. 25Hz is common. A simple cap in the input of your amp will do. Often called a "subsonic filter"

[LOUT]

Roughly what size/value of cap is used for a ~25hz HP when it's at the amp input?

I imagine the cap value required changes pretty drastically depending on the amp's input impedance, or do most amplifiers stick toward a pretty common input imp enough that this shouldn't really be a concern?


Really cool either way...the input has really high and flat impedance (compared to the speakers) so a much smaller cap value can do the same job.

[wogg]

First order RC filter calculation: C = 1/(2*Pi*R*F) Resistance (R), frequency (F) and capacitance (C) can all be algebra'd back under the fraction on the right side or to the left to solve for. Given a 10k input impedance, about 0.64uF gives you a first order knee at 25Hz.

[SentinelAeon]

I would like to ask another question ... like i said in a 3.6L (0.127 cubic foot) enclosure i have this nice daytons. And i use a 3cm diameter port that is 14cm long (port diameter 1.17 inches, 5.5 inches long).

This enclosure is calculated. And i am getting a pretty nice graph in winISD with it. You can see the port velocity, SPL and frequency graphs in attachment. As you can see, i should be getting almost 100dB at 60Hz. Well, i did a little test using my dB meter, i was comparing JBL extreme 1 vs my speaker and here is what i got:

JBL extreme 1:
- music - 97dB (prodigy song, max recorded value)
- 130Hz - /
- 120Hz - 90dB
- 100Hz - 91dB
- 80Hz - 78dB
- 60Hz - 75dB
- 50Hz - 80dB
- 40Hz - 52dB
- 30Hz - /
- 20Hz - /
- 15Hz - /
- 10Hz - /

3.6L TCP115 4 ohm 45W + cheap chinese 8W tweeter capped at 4K:
- music - 103dB (prodigy song, max recorded value)
- 130Hz - 84dB
- 120Hz - 87dB
- 100Hz - 90dB
- 80Hz - 81dB
- 60Hz - 79dB
- 50Hz - 70dB
- 40Hz - 65dB
- 30Hz - 75dB
- 20Hz - 70dB
- 15Hz - 70dB
- 10Hz - 60dB

This is really strange, not at all like the graph winISD gave me. This box was calculated quite precisely. And while dB meter isnt the most accurate thing in the world, me and my friend agreed that the sound we perceived was indeed similar to how the numbers scaled. For instance when going from 40Hz to 30Hz on my speaker, u can clearly see a big boost in volume.

So two questions:

1) where is this low frequency boost coming on my speaker. I am guessing its the chuffing of the port, not the actualy bass ?
2) everything from 50Hz and up is supposed to be much louder as much as winISD SPL graph shows, at least 10dB if not more. Where am i losing the SPL ? Could it be that port is to small of a diameter and its blocking it ?




And here is crazy low tuning of the box which shows that strange "boost at 30Hz" ... but no way i tuned it like that ... for that i would need port length about 5 times longer than i have.

[Millstonemike]

.... Well, i did a little test using my dB meter, i was comparing JBL extreme 1 vs my speaker a.

First, I suggest eliminating some variables. You say you tested with a song. How about using a sine wave feed. I have this PC app, "SineGen", that allows you to use a Windows PC to generate a signal at a chosen audio frequency. It doesn't "install" on Windows. Just download the app and double click it's icon, and ignore the security warning. I've used it for years w/o issues (no malware, ads, etc.) and others here have used it as well.

You can type in a start frequency (e.g., 130 Hz, upper left box), measure then move the freq. down 10 Hz and measure again until you've covered the range. If you have a DVM, even a cheap one, you can also measure the AC voltage going into the speaker and graph that. That would illuminate/eliminate any signal variations. You can download the app from my Google drive Here.

[devnull]

LOUT commented "I imagine the cap value required changes pretty drastically depending on the amp's input impedance, or do most amplifiers stick toward a pretty common input imp enough that this shouldn't really be a concern?"

Yup, they vary all over the place, enough to cause problems. I've got amps that have 6K, 10K, 47K and 50K unbalanced input impedances. The spec sheet should tell you and if it doesn't a quick look at the schematic or service manual will.

[LOUT]

Thanks. I recently found the service manuals for a couple of older amps I'm using, so I'll give those a look.

[wavefunction]

Cheap amps are known for not meeting their specs . And power specs are often given at 1 kHz. Below 40 Hz, your amp could easily be 2x25W or less. And that is without any high pass filtering. Just skimping on power supply capacitance.