Members frosty55 Posted December 26, 2012 Members Share Posted December 26, 2012 I built my self a 2X12 guitar cab, modelled pretty much on the Marshall 1936 cab. When I play through my Marshall JMP, it sounds like theres a continental quilt covering the speakers, its so dull !! Any ideas please? Thanks Link to comment Share on other sites More sharing options...
Members Wayne2 Posted December 26, 2012 Members Share Posted December 26, 2012 Double-check the speaker impedences (ohms) and that the wiring is doing what it is supposed to (i.e. series or parallel). Link to comment Share on other sites More sharing options...
Members Wayne2 Posted December 26, 2012 Members Share Posted December 26, 2012 Double-check the speaker impedences (ohms) and that the wiring is doing what it is supposed to (i.e. series or parallel). Link to comment Share on other sites More sharing options...
Members WRGKMC Posted December 26, 2012 Members Share Posted December 26, 2012 Question is, what kind of speakers are you using. If the tone is bad, it might be the speakers frequency responce. If the levels are low (and the impedance is matched as Wyane mentioned) Then the speakers may have a low SPL. The only other item I can think of besides faulty wiring where contacts are shorting is the speaker baskets are not mounted on a flat surface and the baskets are twisted. This can cause the speaker coil to rub and not move freely. My First guess is you're using non guitar speakers and you have a big frequency/volume loss Bass guitar or HiF speakers will do this. They are designed to push lows in an acousticaly designed cab. Guitar speakers push midrange and will sould good in just about any cab, open backed or enclosed. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted December 26, 2012 Members Share Posted December 26, 2012 Question is, what kind of speakers are you using. If the tone is bad, it might be the speakers frequency responce. If the levels are low (and the impedance is matched as Wyane mentioned) Then the speakers may have a low SPL. The only other item I can think of besides faulty wiring where contacts are shorting is the speaker baskets are not mounted on a flat surface and the baskets are twisted. This can cause the speaker coil to rub and not move freely. My First guess is you're using non guitar speakers and you have a big frequency/volume loss Bass guitar or HiF speakers will do this. They are designed to push lows in an acousticaly designed cab. Guitar speakers push midrange and will sould good in just about any cab, open backed or enclosed. Link to comment Share on other sites More sharing options...
Members frosty55 Posted December 26, 2012 Author Members Share Posted December 26, 2012 I wired the cab to be 16 Ohms, in series. The drivers are Celestion G12T-75. Its a closed back cabinet and trying to rectify the dullness I cut a two and a half inch port near the bottom of the cab. The drivers are flat against the front as theyre supposed to be. I have made several guitar cabinets over the years and would like to think I construct a well made cab. Link to comment Share on other sites More sharing options...
Members frosty55 Posted December 26, 2012 Author Members Share Posted December 26, 2012 I wired the cab to be 16 Ohms, in series. The drivers are Celestion G12T-75. Its a closed back cabinet and trying to rectify the dullness I cut a two and a half inch port near the bottom of the cab. The drivers are flat against the front as theyre supposed to be. I have made several guitar cabinets over the years and would like to think I construct a well made cab. Link to comment Share on other sites More sharing options...
Moderators isaac42 Posted December 27, 2012 Moderators Share Posted December 27, 2012 What kind of grill/grill cloth are you using? Link to comment Share on other sites More sharing options...
Moderators isaac42 Posted December 27, 2012 Moderators Share Posted December 27, 2012 What kind of grill/grill cloth are you using? Link to comment Share on other sites More sharing options...
Members WRGKMC Posted December 27, 2012 Members Share Posted December 27, 2012 The 75's should be plenty loud. Unless you're playing bass, the cab should not be ported and when it is ported, the port needs to be tuned so the back wave is in tune with the front wave. You likely have phase cancellation occuring due of the port. Try closing it up or you have to tune the port with the proper tube length so the resonant frequency of the bass signal is in phase with the front of the speaker. There are several ways of doing this. You can google up the details if you dont know how already. One is to use a multimeter, punp the resonant frequency into the cab while monitoring the signal, and adjust the tube length till the meter gives you maximum voltage. The other would method which is better is to use two mics, one on the port and one on the speaker. Run both mics into either a dual scope or dual channel audio analyzer and visually match the two waveforms as you pan through the audio frequencies. You would then tune the tube length so the two waves go positive and negative at the same time. If the port length is too long of short, the waves will be shifted and cancel eachother out. How well this will work depends on whether the cab has the right air volume to begin with for the speakers resonant frequency. Since this is a critical factor in ported cabinet building/tuning, you may or may not be able to tune the cab for optimal frequency response. If the cab is too small, even with the port in phase, you can wind up having too much upper lows making the speakers sound muddy for guitar. If the cab is too big the speakers wind up sounding farty and lifeless. This is why I suggest closing the port first. Sealed cabs do have to have the right air volume too but you wont have to deal with te phase cancellation issue. The air inside a sealed cab does act as a shock absorber for the speaker piston and it will bounce back quickly if the air is right. This gives the guitar strings a snappy responce. You can however pack the cab with additional insulation to reduce the air volume if the cab is larger and sounds too bassy. A cab size of 15"H x 28"W X 14"D is just about perfect for a 2X12" cab and should get you the proper bass response. If its smaller/shallower than 14" then your lower guitar strings wont have as much thump on the low notes. You'll have to use the amps EQ to boost the frequencies it lacks. If its bigger simply pack the cab tightly with additional fiberglass insulation against the sides to reduce the air volume which reduces the bass response. The ideal amount of insulation lets you run the amps bass EQ setting at 12:00 If you have the cabs interior dimensions I can calculate what you're getting now by plugging the dimensions and speaker specs into an online calculator that calculates the proper cab resonance. For guitar its isnt a hyper critical calculation. Guitar is a midrange instrument and unless you are into playing Jazz Guitar you want most fundamental frequencies of the guitar strings that go as low as 80hz to be tapered off at below 150hz. to be Its mainly when you port a cab and want to achieve maximum bass volume in HiFi, Bass guitar A normal electric guitar range is between 150~6Khz. Everything below is rolled off by both the amp head and speakers. What you hear as a nice thump from the strings is actually the strings first harmonic which is an octave above the strings fundamental tone which begins at about 165Hz. Having a port, even when its tuned, produces too much fundamental frequencies, which overpowers the speakers abilities to produce the secondary harmonics. This makes the strings sound like muffeled crap. Reduce the fundamental bass responce and more direct midrange from the speakers will be heard and those speakers will clean right up and come alive. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted December 27, 2012 Members Share Posted December 27, 2012 The 75's should be plenty loud. Unless you're playing bass, the cab should not be ported and when it is ported, the port needs to be tuned so the back wave is in tune with the front wave. You likely have phase cancellation occuring due of the port. Try closing it up or you have to tune the port with the proper tube length so the resonant frequency of the bass signal is in phase with the front of the speaker. There are several ways of doing this. You can google up the details if you dont know how already. One is to use a multimeter, punp the resonant frequency into the cab while monitoring the signal, and adjust the tube length till the meter gives you maximum voltage. The other would method which is better is to use two mics, one on the port and one on the speaker. Run both mics into either a dual scope or dual channel audio analyzer and visually match the two waveforms as you pan through the audio frequencies. You would then tune the tube length so the two waves go positive and negative at the same time. If the port length is too long of short, the waves will be shifted and cancel eachother out. How well this will work depends on whether the cab has the right air volume to begin with for the speakers resonant frequency. Since this is a critical factor in ported cabinet building/tuning, you may or may not be able to tune the cab for optimal frequency response. If the cab is too small, even with the port in phase, you can wind up having too much upper lows making the speakers sound muddy for guitar. If the cab is too big the speakers wind up sounding farty and lifeless. This is why I suggest closing the port first. Sealed cabs do have to have the right air volume too but you wont have to deal with te phase cancellation issue. The air inside a sealed cab does act as a shock absorber for the speaker piston and it will bounce back quickly if the air is right. This gives the guitar strings a snappy responce. You can however pack the cab with additional insulation to reduce the air volume if the cab is larger and sounds too bassy. A cab size of 15"H x 28"W X 14"D is just about perfect for a 2X12" cab and should get you the proper bass response. If its smaller/shallower than 14" then your lower guitar strings wont have as much thump on the low notes. You'll have to use the amps EQ to boost the frequencies it lacks. If its bigger simply pack the cab tightly with additional fiberglass insulation against the sides to reduce the air volume which reduces the bass response. The ideal amount of insulation lets you run the amps bass EQ setting at 12:00 If you have the cabs interior dimensions I can calculate what you're getting now by plugging the dimensions and speaker specs into an online calculator that calculates the proper cab resonance. For guitar its isnt a hyper critical calculation. Guitar is a midrange instrument and unless you are into playing Jazz Guitar you want most fundamental frequencies of the guitar strings that go as low as 80hz to be tapered off at below 150hz. to be Its mainly when you port a cab and want to achieve maximum bass volume in HiFi, Bass guitar A normal electric guitar range is between 150~6Khz. Everything below is rolled off by both the amp head and speakers. What you hear as a nice thump from the strings is actually the strings first harmonic which is an octave above the strings fundamental tone which begins at about 165Hz. Having a port, even when its tuned, produces too much fundamental frequencies, which overpowers the speakers abilities to produce the secondary harmonics. This makes the strings sound like muffeled crap. Reduce the fundamental bass responce and more direct midrange from the speakers will be heard and those speakers will clean right up and come alive. Link to comment Share on other sites More sharing options...
Members Kazinator Posted December 30, 2012 Members Share Posted December 30, 2012 The info that is missing in this thread is: sounds blanketed compared to what. What speakers have you been playing through (and hence adjusted your hearing toward)? Did the same speakers sound bright in another cab, or are you comparing to different speakers? There can be a big difference between how much high end different guitar speakers deliver, when all else is equal (similar cabinet, same amp, etc). This is one reason for the presence control on the amp. You need to dial in more for some cabinets, less for others. But the bottom line is that it is perfectly possible to plug into a different cab with different speakers and feel like it is covered in wool, without there being anything wrong with the speakers or cab. Are the speaker cones doped? Are they smooth, or do they have concentric ribbing? All else being the same, a ribbed speaker cone will more easily show higher modes of vibration (2D version of string harmonics) than a flat one. Likewise, an undoped speaker cone will also break up more easily than a doped one, which is stiffer and forced to move as a unit, emphasizing its fundamental resonant frequency. Link to comment Share on other sites More sharing options...
Members Kazinator Posted December 30, 2012 Members Share Posted December 30, 2012 The info that is missing in this thread is: sounds blanketed compared to what. What speakers have you been playing through (and hence adjusted your hearing toward)? Did the same speakers sound bright in another cab, or are you comparing to different speakers? There can be a big difference between how much high end different guitar speakers deliver, when all else is equal (similar cabinet, same amp, etc). This is one reason for the presence control on the amp. You need to dial in more for some cabinets, less for others. But the bottom line is that it is perfectly possible to plug into a different cab with different speakers and feel like it is covered in wool, without there being anything wrong with the speakers or cab. Are the speaker cones doped? Are they smooth, or do they have concentric ribbing? All else being the same, a ribbed speaker cone will more easily show higher modes of vibration (2D version of string harmonics) than a flat one. Likewise, an undoped speaker cone will also break up more easily than a doped one, which is stiffer and forced to move as a unit, emphasizing its fundamental resonant frequency. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted December 31, 2012 Members Share Posted December 31, 2012 Originally Posted by Kazinator Are the speaker cones doped? Are they smooth, or do they have concentric ribbing? All else being the same, a ribbed speaker cone will more easily show higher modes of vibration (2D version of string harmonics) than a flat one. Likewise, an undoped speaker cone will also break up more easily than a doped one, which is stiffer and forced to move as a unit, emphasizing its fundamental resonant frequency. He says they are Celestion G12T-75 speakers that should sound pretty good with a Marshall head. I use 4 of them in my Marshall 1960 cab with my Marshall head and they kick butt. Surely dont lack for highs. He'd have to re-EQ his head for the different cab size of course. My bet is on the back wave being out of phasewith the front wave because of the port. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted December 31, 2012 Members Share Posted December 31, 2012 Originally Posted by Kazinator Are the speaker cones doped? Are they smooth, or do they have concentric ribbing? All else being the same, a ribbed speaker cone will more easily show higher modes of vibration (2D version of string harmonics) than a flat one. Likewise, an undoped speaker cone will also break up more easily than a doped one, which is stiffer and forced to move as a unit, emphasizing its fundamental resonant frequency. He says they are Celestion G12T-75 speakers that should sound pretty good with a Marshall head. I use 4 of them in my Marshall 1960 cab with my Marshall head and they kick butt. Surely dont lack for highs. He'd have to re-EQ his head for the different cab size of course. My bet is on the back wave being out of phasewith the front wave because of the port. Link to comment Share on other sites More sharing options...
Members Wayne2 Posted December 31, 2012 Members Share Posted December 31, 2012 I think he might have decided it was the amp's fault?http://acapella.harmony-central.com/...g-Marshall-amp. Link to comment Share on other sites More sharing options...
Members Wayne2 Posted December 31, 2012 Members Share Posted December 31, 2012 I think he might have decided it was the amp's fault?http://acapella.harmony-central.com/...g-Marshall-amp. Link to comment Share on other sites More sharing options...
Moderators isaac42 Posted December 31, 2012 Moderators Share Posted December 31, 2012 Originally Posted by WRGKMC He says they are Celestion G12T-75 speakers that should sound pretty good with a Marshall head. I use 4 of them in my Marshall 1960 cab with my Marshall head and they kick butt. Surely dont lack for highs. He'd have to re-EQ his head for the different cab size of course. My bet is on the back wave being out of phasewith the front wave because of the port. That would affect the lows, but not the highs. Seems much more likely to be the amp to me. Link to comment Share on other sites More sharing options...
Moderators isaac42 Posted December 31, 2012 Moderators Share Posted December 31, 2012 Originally Posted by WRGKMC He says they are Celestion G12T-75 speakers that should sound pretty good with a Marshall head. I use 4 of them in my Marshall 1960 cab with my Marshall head and they kick butt. Surely dont lack for highs. He'd have to re-EQ his head for the different cab size of course. My bet is on the back wave being out of phasewith the front wave because of the port. That would affect the lows, but not the highs. Seems much more likely to be the amp to me. Link to comment Share on other sites More sharing options...
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