Cab mod advice

[challxyz]

I'm toying with the idea of modifying my mesa 1x15 8ohm cab, I want it be a 4ohm cab, now this might sound like a really dumb question but is it just a case of swapping the 8ohm for a 4ohm and that's that? does the tweeter make any difference to the impedance and if so would I need to change that too?

any advice greatly appreciated :-)

Cheers

[Musky]

You can just swap the 8 ohm speaker for a 4 ohm one - AFAIK the tweeter can be disregarded as far as the overall impedance of the cab is concerned.

If you're doing this to get an increase in volume by unleashing the extra wattage you're likely to be disappointed though. You'll probably see slightly under 2dB increase in volume, which is all but inaudible in the real world.

Adding a second 8 ohm cab would be an entirely different kettle of fish though.

Edit: I'm assuming you'd be swapping the speaker like-for like. Obviously using a far more efficient speaker would provide a greater increase in volume, though depending on the specs may change the sound of the cab.

Edited February 26, 2011 by Musky

[chris_b]

A lot of expense for very little gain, and you might make it sound worse. 2 are always better than 1, so I'd go for the second cab idea.

PS. Just reread the OP. An 8 ohm Mesa Boogie 115 cab will sound great on it's own (I had one) and if you add a second cab (I had the 210) you will have one of the best sounds around. I used my 115 with an SVT3 PRO and 300 watts was loud enough for all of my bands. An extra 210 or 115 will give you such a good sound; I really wouldn't mess with the 115.

Edited February 26, 2011 by chris_b

[challxyz]

[quote name='Musky' post='1142165' date='Feb 26 2011, 10:50 AM']You can just swap the 8 ohm speaker for a 4 ohm one - AFAIK the tweeter can be disregarded as far as the overall impedance of the cab is concerned.

If you're doing this to get an increase in volume by unleashing the extra wattage you're likely to be disappointed though. You'll probably see slightly under 2dB increase in volume, which is all but inaudible in the real world.

Adding a second 8 ohm cab would be an entirely different kettle of fish though.

Edit: I'm assuming you'd be swapping the speaker like-for like. Obviously using a far more efficient speaker would provide a greater increase in volume, though depending on the specs may change the sound of the cab.[/quote]

Thanks for the reply, not doing this for the volume, more to do with working with my current rig, I want to pair the 1x15 up with a 4ohm 4x10 and so run them together at 2ohms powered by an Ampeg SVTII, this would also give me the option of using the 15 on it's own with the SVT running at 4ohms for smaller gigs.
As for a replacement I'll ask my local music shop to price me a new replacement driver, they deal with mesa stuff, so hopefully they can get me a like for like speaker.

cheers dude :-)

[alexclaber]

[quote name='Musky' post='1142165' date='Feb 26 2011, 10:50 AM']You can just swap the 8 ohm speaker for a 4 ohm one - AFAIK the tweeter can be disregarded as far as the overall impedance of the cab is concerned.

If you're doing this to get an increase in volume by unleashing the extra wattage you're likely to be disappointed though. You'll probably see slightly under 2dB increase in volume, which is all but inaudible in the real world.

Adding a second 8 ohm cab would be an entirely different kettle of fish though.

Edit: I'm assuming you'd be swapping the speaker like-for like. Obviously using a far more efficient speaker would provide a greater increase in volume, though depending on the specs may change the sound of the cab.[/quote]

That's essentially it. Unless your amp is very low on power your output will be being limited by your speaker's excursion limited power handling so you won't even get 2dB more, you might get nothing. Changing to a more efficient speaker won't really make any difference either because low frequency efficiency is dependent on the enclosure size and LF cutoff and changing the speaker won't change them.

Adding a second similar cab will make a big difference but not due to the 4 ohm load, due to the doubling of rig size, cone area and excursion limited power handling.

[alexclaber]

You'll get a better result running the 8 ohm 15" and 4 ohm 4x10" on the SVT's 4 ohm tap than you will running a 4 ohm 15" and 4 ohm 4x10" on the 2 ohm tap. The reasons are complicated but centre around both varieties of power handling and the realities of actual impedance curves.

[challxyz]

[quote name='chris_b' post='1142178' date='Feb 26 2011, 11:10 AM']A lot of expense for very little gain, and you might make it sound worse. 2 are always better than 1, so I'd go for the second cab idea.

PS. Just reread the OP. An 8 ohm Mesa Boogie 115 cab will sound great on it's own (I had one) and if you add a second cab (I had the 210) you will have one of the best sounds around. I used my 115 with an SVT3 PRO and 300 watts was loud enough for all of my bands. An extra 210 or 115 will give you such a good sound; I really wouldn't mess with the 115.[/quote]

Thanks Chris, I've been running the 2x10 with the 1x15 for a few years now with an Mpulse 600, you're right it is a brilliant combination, trouble is I also like my 410HLF which I've been using with an SVTII which will only run on 4 or 2 ohms, i'd like to use the 1x15 and the 410 but impedances are not matched, having said that the SVTII sounds great through the mesa 2x10 / 1x15 combination too....decisions, decisions

[challxyz]

[quote name='alexclaber' post='1142193' date='Feb 26 2011, 11:27 AM']You'll get a better result running the 8 ohm 15" and 4 ohm 4x10" on the SVT's 4 ohm tap than you will running a 4 ohm 15" and 4 ohm 4x10" on the 2 ohm tap. The reasons are complicated but centre around both varieties of power handling and the realities of actual impedance curves.[/quote]

hi Alex, so running these different impedance cabs together wouldn't wouldn't damage my amp, I thought all tube amps were a bit sensitive to this type of tinkering? :-)

[chris_b]

[quote name='challxyz' post='1142186' date='Feb 26 2011, 11:20 AM']....Thanks for the reply, not doing this for the volume, more to do with working with my current rig, I want to pair the 1x15 up with a 4ohm 4x10 and so run them together at 2ohms powered by an Ampeg SVTII, this would also give me the option of using the 15 on it's own with the SVT running at 4ohms for smaller gigs.
As for a replacement I'll ask my local music shop to price me a new replacement driver, they deal with mesa stuff, so hopefully they can get me a like for like speaker....[/quote]
OK, but if you run the 8 ohm 115 with a 4 ohm 410 your amp will see 2.7 ohm and your 410 will get double the watts that will go to the 115. So you won't over power the 115 at louder volumes. 300 watts into the 115 will still be loud.

My 115 had the EV speaker and a reconed unit was about £120 last time I looked. A replacement will be very expensive for what you are getting.

[alexclaber]

It'll be fine. Impedances aren't what the specs imply - have a look at this post from Bill Fitzmaurice which shows three different impedance curves: [url="http://www.talkbass.com/forum/f15/2-65-ohms-tube-amp-204691/index2.html#post10430002"]http://www.talkbass.com/forum/f15/2-65-ohm...ml#post10430002[/url]

What tap would you use for them?! All cabs are like this though!

[Bill Fitzmaurice]

[quote name='challxyz' post='1142194' date='Feb 26 2011, 06:28 AM']i'd like to use the 1x15 and the 410 but impedances are not matched,[/quote]
In most cases you don't want them matched. The average 1x15 does not have either the thermal or the displacement limited capacity of the average 4x10, so if both are 4 ohm receiving the same power the 1x15 is the weak link in the chain. That's especially the case with a 410HLF

Your positive experience with a 2x10/1x15 should be telling you something: it takes two fifteens to make a good match with four tens.
The exception to this would be a high excursion 15, such as the Eminence 3015LF.

[challxyz]

[quote name='Bill Fitzmaurice' post='1142397' date='Feb 26 2011, 03:03 PM']In most cases you don't want them matched. The average 1x15 does not have either the thermal or the displacement limited capacity of the average 4x10, so if both are 4 ohm receiving the same power the 1x15 is the weak link in the chain. That's especially the case with a 410HLF

Your positive experience with a 2x10/1x15 should be telling you something: it takes two fifteens to make a good match with four tens.
The exception to this would be a high excursion 15, such as the Eminence 3015LF.[/quote]

That's an interesting point, not thought of it like that before, thank you Bill

[challxyz]

Btw I tried the svt with the Mesa 1x15 and 410hlf today and it sounded awesome! However it's a very heavy rig, in discussions with Alex @ Barefaced

[chris_b]

[quote name='challxyz' post='1142481' date='Feb 26 2011, 04:41 PM']....Btw I tried the svt with the Mesa 1x15 and 410hlf today and it sounded awesome! However it's a very heavy rig, in discussions with Alex @ Barefaced....[/quote]
Ha, ha.... that's why I sold mine! I think the BFB should be an interesting move.

[Phil Starr]

[quote name='challxyz' post='1142135' date='Feb 26 2011, 10:22 AM']I'm toying with the idea of modifying my mesa 1x15 8ohm cab, I want it be a 4ohm cab, now this might sound like a really dumb question but is it just a case of swapping the 8ohm for a 4ohm and that's that? does the tweeter make any difference to the impedance and if so would I need to change that too?

any advice greatly appreciated :-)

Cheers[/quote]
I guess you've decided not to do it but there is one more reason not to. Making a 4ohm speaker is often done by just changing the voice coil and this changes all the T/S parameters meaning you need to change the cab. The most common change is to simply use a shorter voice coil and this reduces the excursion limit and hence your bass at power. Both Celestion and Eminence do just this. There's no reason why you can't engineer a 4 but it is rarely anything other than a bodged 8.

Edited February 26, 2011 by Phil Starr

[challxyz]

[quote name='Phil Starr' post='1142822' date='Feb 26 2011, 09:11 PM']I guess you've decided not to do it but there is one more reason not to. Making a 4ohm speaker is often done by just changing the voice coil and this changes all the T/S parameters meaning you need to change the cab. The most common change is to simply use a shorter voice coil and this reduces the excursion limit and hence your bass at power. Both Celestion and Eminence do just this. There's no reason why you can't engineer a 4 but it is rarely anything other than a bodged 8.[/quote]

yes gonna give it a miss Phil, now I know I can run an 8 with a 4ohm cab it's not an issue, must say I'm amazed at how much you can learn from posting 1 little question on BC, it's a brilliant community, thanks for all the advice guys!