Recently I made a subwoofer enclosure for a 10" 250W RMS driver. The port that I have made is based on the calculation that WinISD made (6x36x90cm tuned on 31Hz) and at the first try sounds decent.
After I tried using the sub with the amplifier outside the cabinet for make some inspections. To my surprise the sub sounds a lot higher on volume and I can't still figure out why. I temporary made a hole in the back of the sub (with also the port open on the front) but the higher sound seems to be heard only in the back, not watching the front.
So I tried to make another hole in the front (covering the back one) but all returns to the original low volume sound.
I'm tiring to understand why the front port and the back hole produced so much volume in order to try to replicate it.
After I tried using the sub with the amplifier outside the cabinet for make some inspections. To my surprise the sub sounds a lot higher on volume and I can't still figure out why. I temporary made a hole in the back of the sub (with also the port open on the front) but the higher sound seems to be heard only in the back, not watching the front.
So I tried to make another hole in the front (covering the back one) but all returns to the original low volume sound.
I'm tiring to understand why the front port and the back hole produced so much volume in order to try to replicate it.
?? So you're saying that the box's internal net volume (Vb) is larger without the amp inside and there's now a vent in the rear + the original one in front?
slightly larger yes. The volume inside is around 1.5 ft3 and the volume of the amplifier inside is 26*28*5cm (considering the transformer and the board the volume is not 26*28*3cm but a a lot less).
But the fact is that with the amplifier in or out the cabinet the sub sounded louder only with the back hole and the front vent, and I don't understand why.
Assuming this, I don't think that the amplifier is the cause of this "problem"
But the fact is that with the amplifier in or out the cabinet the sub sounded louder only with the back hole and the front vent, and I don't understand why.
Assuming this, I don't think that the amplifier is the cause of this "problem"
Not per se, just adding some more SPL potential when outboard.
OK, your wording implied otherwise, i.e. more net Vb = higher SPL around tuning for a given vent design. Add another vent and now tuning will be higher in frequency and SPL (especially if just a hole Vs the other being a tuned pipe) + summing spreads it over a wider bandwidth (BW).
IOW if I'm following and without all the details, specs used, the simple hole in the back appears to be dominating tuning to the point where the original vent is acting as an aperiodic vent at best (lossy sealed).
OK, your wording implied otherwise, i.e. more net Vb = higher SPL around tuning for a given vent design. Add another vent and now tuning will be higher in frequency and SPL (especially if just a hole Vs the other being a tuned pipe) + summing spreads it over a wider bandwidth (BW).
IOW if I'm following and without all the details, specs used, the simple hole in the back appears to be dominating tuning to the point where the original vent is acting as an aperiodic vent at best (lossy sealed).
Do you have any acoustical measuring capabilities? Some near-field measurements at the port exits and at the driver for the different configurations might help show what's going on.
Adding a 1 and/or 2 meter measurement may also help. Optimally this would be done outdoors away from any structures. But in room with the microphone and speaker in exactly the same locations may be sufficient.
Improperly tuned enclosures can have significant peaks in response. They often come with degraded transients as well, so are typically avoided in modern designs. Your extra hole may be doing something like that.
A dipole configuration typically has peaks in response as well. From your description, it seems like the amp hole is big enough that this is possible. Response is determined by the path length from the front to the back of the cone, so moving the extra hole from the back to the front of your enclosure would change that. If you only hear the loudness difference when close to the subwoofer or in a particular orientation, a dipole effect seems more likely. A dipole rolls off lower frequencies though, so you would typically lose very low frequency output even if you gained some midbass.
Someone fluent in Hornresp or another complex simulator may come along and model the effect for you if you provide the driver data and current enclosure dimensions.
Adding a 1 and/or 2 meter measurement may also help. Optimally this would be done outdoors away from any structures. But in room with the microphone and speaker in exactly the same locations may be sufficient.
Improperly tuned enclosures can have significant peaks in response. They often come with degraded transients as well, so are typically avoided in modern designs. Your extra hole may be doing something like that.
A dipole configuration typically has peaks in response as well. From your description, it seems like the amp hole is big enough that this is possible. Response is determined by the path length from the front to the back of the cone, so moving the extra hole from the back to the front of your enclosure would change that. If you only hear the loudness difference when close to the subwoofer or in a particular orientation, a dipole effect seems more likely. A dipole rolls off lower frequencies though, so you would typically lose very low frequency output even if you gained some midbass.
Someone fluent in Hornresp or another complex simulator may come along and model the effect for you if you provide the driver data and current enclosure dimensions.
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Hi guys... unfortunately again. I made another box and it was build virtually perfect. The port was round on the front (sub on the front) and tuned for something below 30 hz i don't remember. Amplifier on the rear.
I removed the amplifier aaaaand AGAIN the volume is higher. WHYYY????
I removed the amplifier aaaaand AGAIN the volume is higher. WHYYY????
Basically a repeat of the explanation for the higher volume GM gave in #4:
The amplifier hole is a port, it's port frequency (Fb) combined with the other port is raised from "something below 30 Hz" to a much higher frequency, the higher Fb sounds louder in volume not only because it is, but also because your hearing is more sensitive to upper bass than lower bass.
The amplifier hole is a port, it's port frequency (Fb) combined with the other port is raised from "something below 30 Hz" to a much higher frequency, the higher Fb sounds louder in volume not only because it is, but also because your hearing is more sensitive to upper bass than lower bass.
